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Non-Grey and Temperature Dependent Radiation Analysis Methods
Most radiation analysis tools in use in the aerospace industry assume that grey conditions hold. That is, over the range of temperatures considered, optical properties are assumed to have a constant value with respect to wavelength. This reasonable approximation for systems that are near room temperature may show significant error at temperature extremes, particulary for conductive materials at cryogenic temperatures. Other areas where non-grey analysis may be appropriate is in furnace and lamp design, and in systems with specialized optical filters such as thermalphotovoltaics.
This short course reviews the definitions of optical properties and discusses the conditions for which greyness holds. A number of approaches to modeling non-grey radiation are discussed, and the approach used by Thermal Desktop is described. Non-grey analysis with materials that have temperature dependent properties at a given wavelength is also discussed. The new methodology is reviewed, in particular its dynamic integration with the thermal analyzer. Example cases are presented to highlight appropriate areas for non-grey radiation analysis.
Source: TFAWS Short Course 2005
Author: Tim Panczak
Highlights in thermal engineering at Carlo Gavazzi Space
Nonlinear Programming Applied to Thermal and Fluid Design Optimization
Historically, thermal/fluid modeling began as a means of validating and sometimes correcting passively cooled designs that had been proposed by nonspecialists in heat transfer and fluid flow. As dissipation fluxes have risen, and as air cooling reaches the limits of its usefulness, involvement of thermal engineers is required earlier in the design process. Thermal engineers are now commonly responsible for sizing and selecting active cooling components such as fans and heat sinks, and increasingly single and two-phase coolant loops.
Meanwhile, heat transfer and fluid flow design analysis software has matured, growing both in ease of use and in phenomenological modeling prowess. Unfortunately, most software retains a focus on point-design simulations and needs to do a better job of helping thermal engineers not only evaluate designs, but also investigate alternatives and even automate the search for optimal designs.
This paper shows how readily available nonlinear programming (NLP) techniques can be successfully applied to automating design synthesis activities, allowing the thermal engineer to approach the problem from a higher level of automation. This paper briefly introduces NLP concepts, and then demonstrates their application both to a simplified fin (extended surface) as well as a more realistic case: a finned heat sink.
Author: Brent A. Cullimore
Parametric Thermal Analysis and Optimization Using Thermal Desktop
Thermal analysis is typically performed using a point design approach, where a single model is analyzed one analysis case at a time. Changes to the system design are analyzed by updating the thermal radiation and conduction models by hand, which can become a bottleneck when attempting to adopt a concurrent engineering approach. This paper presents the parametric modeling features that have been added to Thermal DesktopTM to support concurrent engineering. The thermal model may now be characterized by a set of design variables that are easily modified to reflect system level design changes. Geometric features, optical and material properties, and orbital elements may all be specified using user-defined variables and expressions. Furthermore, these variables may be automatically modified by Thermal Desktop’s optimization capabilities in order to satisfy user-defined design goals, or for correlating thermal models to test data. By sharing the set of design variables among analysis models spanning multiple disciplines, further integrated analysis and design may be accomplished. The framework into which Thermal Desktop is embedded in order to support an integrated Thermal/Structural/Optical design, analysis, and optimization system is also presented.
Author: Timothy D. Panczak, Brent A. Cullimore
Content Tags: concurrent engineering, parametric, parameterize, register, registers, dynamic mode, dynamic SINDA, symbol manager, expression editor, expressions, design optimization, orbital heating, model correlation, solver, optical properties, heat pipes, symbol, variables, case set manager, properties, structural
Automating Thermal Analysis with Thermal Desktop
Thermal analysis is typically executed with multiple tools in a series of separate steps for performing radiation analysis, generating conduction and capacitance data, and for solving temperatures. This multitude of programs often leads to many user files that become unmanageable with their multitude, and the user often looses track as to which files go with which cases. In addition to combining the output from multiple programs, current processes often involve the user inputting various hand calculations into the math model to account for MLI/Insulation and contact conductance between entities. These calculations are not only tedious to make, but users often forget to update them when the geometry is changed.
Several new features of Thermal Desktop are designed to automate some of the tedious tasks that thermal engineers now practice. To start with, Thermal Desktop is a single program that does radiation analysis, generates conduction/capacitance data and automates the building of a SINDA/FLUINT model to solve for temperatures. Some of these new features of Thermal Desktop are Radiation Analysis Groups, Property Aliases, MLI/Insulation Objects, Contact Conductance Objects, Model Browser, and the Case Set Manager.
This paper describes the application and benefits of Thermal Desktop along with other unique features used to automate the thermal analysis process.
Author: Mark J. Welch, Tim Panczak
Integrating Thermal And Structural Analysis with Thermal Desktop
Structural and thermal engineers currently work independently of each other using unrelated tools, models, and methods. Without the ability to rapidly exchange design data and predicted performance, the achievement of the ideals of concurrent engineering is not possible.
Thermal codes have been unable to exploit the geometric information in structural models and the CAD design database, and do not facilitate transfer of temperature data to other discipline’s analysis models. This paper discusses the key features in Thermal Desktop for supporting integrated thermal/structural analysis. Approaches to thermal modeling in an integrated analysis environment are discussed along with Thermal Desktop's data mapping algorithm for exporting temperature data on to structural model grid points.
Author: Tim Panczak, Mark J. Welch
Content Tags: structural, finite elements, finite difference, structural mesh, temperature mapping, temperature map, concurrent engineering, concurrent design, radiation calculations, CAD geometry, postprocessing, orbit, orbital heating, radiation analysis groups, Monte Carlo, ray tracing, data mapper, solver
The Finite Element Method and Thermal Desktop
Despite recent advances in computer aided design (CAD) based tools, spacecraft thermal analysis remains outside the realm of finite element method (FEM) based analysis. The primary complaints against FEM often cited are:
- FEM is not based on physical principles.
- FEM codes do not provide procedural modeling for heaters, heat pipes, or other abstract thermal control components.
- Inadequate radiation analysis capabilities.
- FEM codes generate inappropriately large thermal models.
However, a failure on the part of existing FEM based codes does not invalidate the advantages of the Finite Element Method. Properly implemented, FEM based systems can have significant advantages.
A simple first law interpretation of FEM is presented, and shows that finite difference (FD) and FEM meshes may co-exist in the same thermal model, and solved using traditional analyzers such as SINDA/FLUINT.
A description of an integrated FD/FEM based system that efficiently satisfies all areas of spacecraft thermal analysis, including thermal radiation, is also presented.
Source: CRTech White Paper
Author: Tim Panczak
Upper Stage Tank Thermodynamic Modeling Using SINDA/FLUINT (Presentation)
Source: TFAWS Short Course
Author: Paul Schallhorn, D. Michael Campbell, Sukhdeep Chase, Jorge Piquero, Cindy Fortenberry, Xiaoyi Li, Lisa Grob
Modeling Two-Phase Loops with Several Capillary Evaporators
Two-phase loops with several capillary evaporators are being developed for a variety of existing and future space applications. While modeling of loop heat pipes with one or two conventional evaporators is relatively straightforward and can be done, for example, using Excel VBA, modeling of loops with several three-port or four-port evaporators requires more specialized software such as Thermal Desktop™.
This paper presents steady state Thermal Desktop™ (Sinda/Fluint) models for systems with three main and one secondary capillary evaporator. The main evaporators have four ports and are interconnected with multiple fluid lines with bends, valves, and connectors. The system components also includes a temperature-controlled two-phase reservoir, condenser, back-pressure regulator, local heat exchangers, etc.
The modeling provided better understanding of the critical fluid-flow mechanisms encountered in the experimental two-phase system. While there are several ways to interconnect the four-port evaporators together, modeling also helped to select more reliable configurations capable of operating with the main evaporators located on different elevation levels and with non-uniform heat load distribution.
Source: TFAWS Short Course
Author: D. Khrustalev, K. Wrenn, D. Wolf
Upper Stage Tank Thermodynamic Modeling Using SINDA/FLUINT
Modeling to predict the condition of cryogenic propellants in an upper stage of a launch vehicle is necessary for mission planning and successful execution. Traditionally, this effort was performed using custom, in-house proprietary codes, limiting accessibility and application. Phenomena responsible for influencing the thermodynamic state of the propellant have been characterized as distinct events whose sequence defines a mission. These events include thermal stratification, passive thermal control roll (rotation), slosh, and engine firing. This paper demonstrates the use of an off the shelf, commercially available, thermal/fluid-network code to predict the thermodynamic state of propellant during the coast phase between engine firings, i.e. the first three of the above identified events. Results of this effort will also be presented.
Author: P. Schallhorn, D. Michael Campbell, Sukhdeep Chase, Jorge Piquero, Cindy Fortenberry, Xiaoyi Li, Lisa Grob
Content Tags: Optimization, parametric, radiation, radiation analysis groups, conduction, evaporation, CFD, convergence, structural, heat flux, thermal stratification, register, two-phase, slosh, wall, splash
Analysis and Test Verification of Transitional Flow in a Dewar Vent
The pressure of the cryogen within a Dewar determines the operating temperature since the cryogen is typically in a saturated state. Thus, the operating temperature of a Dewar is directly related to the ambient pressure external to the Dewar and the flow losses associated with venting cryogen. Given the low vapor pressures of some cryogens, such as solid hydrogen, the vent flow from Dewars used in space can enter the transitional and molecular flow regimes. In order to accurately predict the operating temperature within such Dewars, the analysis tool used to model the cryostat must account for free molecular and mixed flow losses as well as those for continuum flow.
As part of our analysis of Dewar designs for the James Webb Space Telescope Mid-Infrared Instrument (MIRI), we modified the continuum flow modeling capability of SINDA/FLUINT to accurately predict the pressure drop due to transitional and molecular flow in the MIRI Dewar vent line. This paper describes the modifications made to the flow loss computations within the analyzer and the testing conducted to verify these modifications.
Source: Topsfield Engineering Service, Inc.
Author: Russell B. Schweickart and Gary Mills
FDM/FEM System-level Analysis of Heat Pipes and LHPs in Modern CAD Environments
Source: Aerospace Thermal Control Workshop
Author: Brent Cullimore, Jane Baumann
Content Tags: LHP, Loop Heat Pipe, radiation analysis groups, concurrent engineering, heat pipe, system-level modeling, noncondensable gas, VCHP, CCHP, wall, two-phase heat transfer, two-phase flow, condenser, condensers, evaporator, evaporators
The Design and Performance of a Water Cooling System for a Prototype Coupled Cavity linear Particle Accelerator for the Spallation Neutron Source
The Spallation Neutron Source (SNS) is a facility being designed for scientific and industrial research and development. The SNS will generate and employ neutrons as a research tool in a variety of disciplines including biology, material science, superconductivity, chemistry, etc. The neutrons will be produced by bombarding a heavy metal target with a high-energy beam of protons, generated and accelerated with a linear particle accelerator, or linac. The low energy end of the linac consists of, in part, a multi-cell copper structure termed a coupled cavity linac (CCL). The CCL is responsible for accelerating the protons from an energy of 87 MeV, to 185 MeV.
Acceleration of the charged protons is achieved by the use of large electrical field gradients established within specially designed contoured cavities of the CCL. While a large amount of the electrical energy is used to accelerate the protons, approximately 60-80% of this electrical energy is dissipated in the CCL’s copper structure. To maintain an acceptable operating temperature, as well as minimize thermal stresses and maintain desired contours of the accelerator cavities, the electrical waste heat must be removed from the CCL structure. This is done using specially designed water cooling passages within the linac’s copper structure. Cooling water is supplied to these cooling passages by a complex water cooling and temperature control system.
This paper discusses the design, analysis, and testing of a water cooling system for a prototype CCL. First, the design concept and method of water temperature control is discussed. Second, the layout of the prototype water cooling system, including the selection of plumbing components, instrumentation, as well as controller hardware and software is presented. Next, the development of a numerical network model used to size the pump, heat exchanger, and plumbing equipment, is discussed. Finally, empirical pressure, flow rate, and temperature data from the prototype CCL water cooling tests are used to assess water cooling system performance and numerical modeling accuracy.
Author: John D. Bernardin, Curtt Ammerman, Steve Hopkins
Adding Heat Pipes and Coolant Loop Models to Finite Element and/or Finite difference Thermal/Structural Models
Active cooling technologies such as heat pipes, loop heat pipes (LHPs), thermosyphons, loop thermosyphons (LTSs), and pumped single- or two-phase coolant loops require specialized modeling treatment. However, these 1D ducted systems are largely overlooked in 3D thermal modeling tools. The increasing popularity of CFD and FEM models and generation of analysis data from 3D CAD data are strong trends in the thermal analysis community, but most software answering such demands has not provided linear modeling elements appropriate for the simulation of heat pipes and coolant loops.
This paper describes techniques whereby CAD line-drawing methods can be used to quickly generate 1D fluid models of heat pipes and coolant loops within a 3D thermal model. These arcs and lines can be attached intimately or via linear contact or saddle resistances to plates and other surfaces, whether those surfaces are modeled using thermal finite difference methods (FDM), or finite element methods (FEM), or combinations of both. The fluid lines can also be manifolded and customized as needed to represent complex heat exchangers and plumbing arrangements. Furthermore, the assumption of 1D flow can be combined with 2D/3D models of walls, including advanced methods of extruding a complex 2D cross-section along a curved or mitered centerline.
To demonstrate these concepts, several distinct examples are developed and discussed.
Author: B. Cullimore, D. A. Johnson
Guidelines for Modeling Capillary Two Phase Loops At the System Level
LHPs and CPLs are increasingly accepted as thermal control solutions for spacecraft, and they are being investigated for various terrestrial applications as well. For a potential user of these technologies, modeling at the system level has been difficult, to say the least, and concurrent engineering methods were non-existent. New methods are now available to address these needs and concurrent CAD methods result in fast and accurate model generation. These same tools can be used for system level modeling of heat pipes, both fixed conductance with or without noncondensible gas or variable conductance.
Historically the thermal/hydraulic modeling of LHP has been approached with either oversimplified, design specific spreadsheets, or detailed thermal hydraulic models developed by the advanced user or LHP developer. To model these devices properly, and consequently gain confidence in the technology, the user needs to be able to model the LHP at the system level without becoming “caught up” in detail. This does not imply that the intricacies of two-phase flow and heat transfer within the evaporator core and secondary wicks of LHPs and CPLs aren’t important; but they should be left to the developers and the effects of these details can easily be enveloped through a series of steady state analyses. The potential user of the technology should focus on developing quasi-steady analyses to perform worst-case enveloping estimates, statistical treatment of the uncertainties, and post-test calibrations for use in extrapolation to untestable conditions. In a nutshell: if they are going to fly them, they’re first going to have to analyze them, integrated into their own vehicle model.
This presentation will identify important LHP and CPL design parameters and how they should be modeled in addition to outlining the criteria for developing a system level model using new concurrent CAD-based methods.
Source: Aerospace Thermal Control Workshop
Author: Jane Baumann
Viability of Loop Heat Pipes for Space Solar Power Applications
The primary thermal management issue associated with Space Solar Power (SSP) is the need to acquire, transport and reject waste heat loads, on the order of 3.8 GW, from the transmitter to remote radiator locations. Previous conceptual studies have focused on transporting these loads to large remote radiators. These concepts assumed the ability to transport the heat either passively or mechanical over large transport distances of 100 meters or more.
A recent study, Innovative Deployable Radiators (IDR) for Space Solar Power, focused directly on the thermal control issues. This study has produced new concepts which break the system into small clusters of radiators which have more reasonable transport lengths of 1-2 meters. This study considers a system based on the klystron conversion technologies with a system architecture based on cluster radiators located near the waste heat source. The study evaluated various fluids for use between 50 and 500°C to determine their viability for use in LHPs. The evaluation considered fluid properties in addition to material compatibility with traditional LHP wick and containment materials.
The results of this study have provided new insight regarding the feasibility and limitations of LHPs for Space Solar Power applications. New technology development areas have been identified for both traditional LHPs and liquid metal LHPs.
Author: Jane Baumann, Suraj Rawal
A Methodology for Enveloping Reliable Start-up of LHPs
The loop heat pipe (LHP) is known to have a lower limit on input power. Below this limit the system may not start properly creating the potential for critical payload components to overheat. The LHP becomes especially susceptible to these low power start-up failures following diode operation, intentional shut-down of the device, or very cold conditions. These limits are affected by the presence of adverse tilt, mass on the evaporator, and noncondensible gas in the working fluid. Based on analytical modeling correlated to startup test data, this paper will describe the key parameters driving this low power limit and provide an overview of the methodology for predicting a “safe start” design envelope for a given system and loop design. The amount of incipient superheat was found to be key to the enveloping procedure. Superheat levels have been observed to vary significantly based on evaporator design and even from unit to unit of identical designs. Statistical studies of superheat levels and active measures for limiting superheat should be addressed by both the hardware vendors and the system integrators.
Source: AIAA Thermophysics
Author: Jane Baumann, Brent Cullimore, Jay Ambrose, Eva Buchan, Brois Yendler
Content Tags: Loop Heat Pipe, LHP, noncondensable gas, start-up, evaporator, wicks, parametric, Phenomena, working fluid, model correlation, parameter, heat loads, compensation chamber, transient, capillary systems
Steady State and Transient Loop Heat Pipe Modeling
The NASA-standard thermohydraulic analyzer, SINDA/ FLUINT, has been used to model various aspects of loop heat pipe (LHP) operation for more than 12 years. Indeed, this code has many features that were specifically designed for just such specialized tasks, and is unique in this respect. Furthermore, SINDA is commonly used at the vehicle (integration) level, has a large user base both inside and outside the aerospace industry, has several graphical user interfaces, preprocessors, postprocessors, has strong links to CAD and structural tools, and has built-in optimization, data correlation, parametric analysis, reliability estimation, and robust design tools.
Nonetheless, the LHP community tends to ignore these capabilities, yearning instead for “simpler” methods. However, simple methods cannot meet the challenging needs of LHP modeling such as transient start-up and noncondensible gas (NCG) effects, are often hardware-specific or proprietary, or cannot be used in a vehicle-level analysis.
There are many reasons for this hesitancy to use SINDA/ FLUINT as it was intended. First, hardware developers tend to be less versed in analytic methods than the user community they serve. Second, there are political hurdles, such as the fact that ESA contractors are required to use ESA sponsored software. Third, the state-of-the-art in LHPs is not so advanced that the analysts can be ignorant of the complex two-phase thermohydraulic and thermodynamic processes and phenomena involved, and unfortunately most thermal analysts are accustomed only to “dry” thermal control (radiation, conduction, etc.).
Fourth, the general-purpose and complete nature of SINDA/FLUINT tends to make it intimidating, especially in light of the third reason listed above. SINDA/FLUINT is not designed strictly for LHPs or even for LHP-like systems; it has been used for everything from nuclear reactor cooling to dynamic models of human hearts and tracheae. The user’s manuals and standard training classes† rarely mention capillary phenomena because only a fraction of SINDA/FLUINT’s users are thus inclined. It is to address this fourth reason that this paper has been written, since the authors can do little to redress the first three problems.
This paper summarizes the available modeling capabilities applicable to various LHP design and simulation tasks. Knowledge of LHPs is assumed.
Author: Brent Cullimore, Jane Baumann
Content Tags: Loop Heat Pipe, LHP, noncondensible gas, condensers, evaporators, slip flow, phase suction, design optimization, reliability engineering, noncondensible gases, two-phase flow, two-phase, compensation chamber, network elements, nonequilibrium, wicks, capillary systems, liquid surface, interface, CAPPMP, iface, conduction
Noncondensible Gas, Mass, and Adverse Tilt Effects on the Start-up of Loop Heat Pipes
In recent years, loop heat pipe (LHP) technology has transitioned from a developmental technology to one that is flight ready. The LHP is considered to be more robust than capillary pumped loops (CPL) because the LHP does not require any preconditioning of the system prior to application of the heat load, nor does its performance become unstable in the presence of two-phase fluid in the core of the evaporator. However, both devices have a lower limit on input power: below a certain power, the system may not start properly. The LHP becomes especially susceptible to these low power start-ups following diode operation, intentional shut-down, or very cold conditions. These limits are affected by the presence of adverse tilt, mass on the evaporator, and noncondensible gas in the working fluid. Based on analytical modeling correlated to start-up test data, this paper will describe how the minimum power required to start the loop is increased due to the presence of mass, noncondensible gas, and adverse tilt. The end-product is a methodology for predicting a “safe start” design envelope for a given system and loop design.
Author: Jane Baumann, Brent Cullimore, Boris Yendler, Eva Buchan
Content Tags: Loop Heat Pipe, LHP, noncondensable gas, start-up, heat loads, compensation chamber, condenser, condensers, evaporator, evaporators, thermoelectrics, two-phase, two-phase flow, transient, bayonet, heat transfer coefficient, model correlation
Customizable Multidiscipline Environments for Heat Transfer and Fluid Flow Modeling
Thankfully, the age of stand-alone fixed-input simulation tools is fading away in favor of more flexible and integrated solutions. “Concurrent engineering” once meant automating data translations between monolithic codes, but sophisticated users have demanded more native integration and more automated tools for designing, and not just evaluating point designs. Improvements in both interprocess communications technology and numerical solutions have gone a long way towards meeting those demands.
This paper describes a small slice of a larger on-going effort to satisfy current and future demands for integrated multidisciplinary tools that can be highly customized by end-users or by third parties. Specifically, the ability to integrate fully featured thermal/fluid simulations into Microsoft’s Excel™ and other software is detailed. Users are now able not only to prepare custom user interfaces, they can use these codes as portals that allow integration activities at a larger scale. Previous enabling technologies are first described, then examples and repercussions of current capabilities are presented, and finally in-progress and future technologies are listed.
Author: B. Cullimore, S. G. Ring, J. Baumann
Automated Determination of Worst-case Design Scenarios
This paper describes readily available techniques for automating the search for worst-case (e.g., “hot case”, “cold case”) design scenarios using only modest computational resources. These methods not only streamline a repetitive yet crucial task, they usually produce better results.
The problems with prior approaches are summarized, then the improvements are demonstrated via a simplified example that is analyzed using various approaches. Finally, areas for further automation are outlined, including attacking the entire design problem at a higher-level.
Author: B. Cullimore
Nonlinear Programming Applied to Calibrating Thermal and Fluid Models to Test Data (Semi-Therm 2002)
Nonlinear Programming Applied to Calibrating Thermal and Fluid Models to Test Data (Semi-Therm 2002)
Author: Jane Baumann, Brent Cullimore
Dealing with Uncertainties and Variations in Thermal Design
The major influence on the reliability of electronics is temperature, yet thermal/fluid modeling is plagued with uncertainties and unknowns. Nonetheless, if appropriate values of these unknown parameters are available for any specific electronics package, then its temperature response can be accurately predicted using modern thermal/fluid analysis tools.
Traditionally, uncertainties are dealt with by a combination of testing, safety factors or margins, and worst-case design scenarios. Analyses are performed iteratively in a repetitive “point design evaluation” mode. Computer-based design simulation tools have emphasized increasing detail and fidelity to physical phenomena, seemingly ignoring the fact that the inputs to these simulations are highly uncertain.
This paper describes both current and future methods of dealing with uncertainties in thermal engineering. It introduces advanced tools and alternative methodologies that can automate not only the quantification of reliability, but can also help synthesize designs on the basis of reliability. It advocates using rapid gains in computer speed not to increase the degree of detail in a model, but to help the engineer find a robust design by automating high-level design tasks.
Author: Brent A. Cullimore
Beyond Point Design Evaluation
Reliability Engineering and Robust Design: New Methods for Thermal/Fluid Engineering
Recent years have witnessed more improvement to the SINDA/FLUINT thermohydraulic analyzer than at any other time in its long history. These improvements have included not only expansions in analytic power, but also the additions of high-level modules that offer revolutions in thermal/ fluid engineering itself.
One such high-level module, “Reliability Engineering,” is described in this paper. Reliability Engineering means considering tolerances in design parameters, uncertainties in environments, uncertainties in application (e.g. usage scenarios), and variations in manufacturing as the stochastic phenomena that they are. Using this approach, the probability that a design will achieve its required performance (i.e., the reliability) is calculated, providing an assessment of risk or confidence in the design, and quantifying the amount of over- or under-design present.
The design to be evaluated for reliability will likely have been produced using traditional methods. Possibly, the design was generated using the Solver optimizer, another high-level module available in SINDA/FLUINT. Using design optimization, the user quantifies the goals that make one design better than another (mass, efficiency, etc.), and specifies the thresholds or requirements which render a given design viable or useless (exceeding a performance limit, etc.). SINDA/FLUINT then automatically searches for an optimal design.
Robust Design means factoring reliability into the development of the design itself: designing for a target reliability and thereby avoiding either costly over-design or dangerous under-design in the first place. Such an approach eliminates a deterministic stack-up of tolerances, worst-case scenarios, safety factors, and margins that have been the traditional approaches for treating uncertainties.
In any real system or product, heat transfer and fluid flow play a limited role: there are many other aspects to a successful design than the realm of thermal/fluids that is encompassed by SINDA/FLUINT. Therefore, this paper concludes with brief descriptions of methods for performing interdisciplinary design tasks.
Source: CRTech White Paper
Author: Brent A. Cullimore
Content Tags: design optimization, reliability engineering, robust design, constraints, boundary conditions, concurrent design, concurrent engineering, batteries, flow control, orifices, radiator, registers, two-phase flow, solver, model correlation, dynamic SINDA, dynamic mode, variables, Monte Carlo, material properties, third-party software, uncertainty analysis, uncertainty
Optimization and Automated Data Correlation
Optimization and Automated Data Correlation in the NASA Standard Thermal/Fluid System Analyzer
SINDA/FLUINT (Ref 1-7) is the NASA-standard heat transfer and fluid flow analyzer for thermal control systems. Because of its general formulation, it is also used in other aerospace specialties such as environmental control (ECLSS) and liquid propulsion, and in terrestrial industries such as electronics packaging, refrigeration, power generation, and transportation industries. SINDA/FLUINT is used to design and simulate thermal/fluid systems that can be represented in networks corresponding to finite difference, finite element, and/or lumped parameter equations. In addition to conduction, convection, and radiation heat transfer, the program can model steady or unsteady single- and two-phase flow networks. CRTech's SinapsPlus® is a complete graphical user interface (preand postprocessor) and interactive model debugging environment for SINDA/FLUINT (Ref 8, 9). SinapsPlus also supports the C language in addition to the traditional choice of Fortran for concurrently executed user logic. This paper describes revolutionary advances in SINDA/FLUINT, the NASA-standard heat transfer and fluid flow analyzer, changing it from a traditional point-design simulator into a tool that can help shape preliminary designs, rapidly perform parametrics and sensitivity studies, and even correlate modeling uncertainties using available test data. Innovations include the incorporation of a complete spreadsheet-like module that allows users to centralize and automate model changes, even while thermal/fluid solutions are in progress. This feature reduces training time by eliminating many archaic options, and encourages the performance of parametrics and other what-if analyses that help engineers develop an intuitive understanding of their designs and how they are modeled. The more revolutionary enhancement, though, is the complete integration of a nonlinear programming module that enables users to perform formal design optimization tasks such as weight minimization or performance maximization. The user can select any number of design variables and may apply any number of arbitrarily complex constraints to the optimization. This capability also can be used to find the best fit to available test data, automating a laborious but important task: the correlation of modeling uncertainties such as optical properties, contact conductances, as-built insulation performance, natural convection coefficients, etc. Finally, this paper presents an overview of related developments that, coupled with the optimization capabilities, further enhance the power of the whole package.
Source: IECEC 1998
Author: Brent A. Cullimore
Optimization, Data Correlation, and Parametric Analysis Features in SINDA/FLUINT Version 4.0
This paper describes revolutionary advances in SINDA/FLUINT, the NASA-standard heat transfer and fluid flow analyzer, changing it from a traditional point-design simulator into a tool that can help shape preliminary designs, rapidly perform parametrics and sensitivity studies, and even correlate modeling uncertainties using available test data.
Innovations include the incorporation of a complete spreadsheet-like module that allows users to centralize and automate model changes, even while thermal/fluid solutions are in progress. This feature reduces training time by eliminating many archaic options, and encourages the performance of parametrics and other what-if analyses that help engineers develop an intuitive understanding of their designs and how they are modeled.
The more revolutionary enhancement, though, is the complete integration of a nonlinear programming module that enables users to perform formal design optimization tasks such as weight minimization or performance maximization. The user can select any number of design variables and may apply any number of arbitrarily complex constraints to the optimization. This capability also can be used to find the best fit to available test data, automating a laborious but important task: the correlation of modeling uncertainties such as optical properties, contact conductances, as-built insulation performance, natural convection coefficients, etc.
Finally, this paper presents an overview of related developments that, coupled with the optimization capabilities, further enhance the power of the whole package.
Source: ICES 1998
Author: Brent A. Cullimore
Content Tags: design optimization, model correlation, parameterize, parametric, two-phase flow, two-phase, optical properties, submodels, registers, expression editor, user logic, concurrent engineering, concurrent design, dynamic mode, dynamic SINDA, specific heat, solver, constraint, slip flow, Phenomena, capillary systems, mixtures, working fluids, nonequilibrium, vapor compression, uncertainty, uncertainty analysis
Optimization and Automated Data Correlation in the NASA Standard Thermal/Fluid System Analyzer
SINDA/FLUINT (Ref 1-7) is the NASA-standard heat transfer and fluid flow analyzer for thermal control systems. Because of its general formulation, it is also used in other aerospace specialties such as environmental control (ECLSS) and liquid propulsion, and in terrestrial industries such as electronics packaging, refrigeration, power generation, and transportation industries.
SINDA/FLUINT is used to design and simulate thermal/fluid systems that can be represented in networks corresponding to finite difference, finite element, and/or lumped parameter equations. In addition to conduction, convection, and radiation heat transfer, the program can model steady or unsteady single- and two-phase flow networks.
C&R’s SinapsPlus® is a complete graphical user interface (preand postprocessor) and interactive model debugging environment for SINDA/FLUINT (Ref 8, 9). SinapsPlus also supports the C language in addition to the traditional choice of Fortran for concurrently executed user logic.
Author: Brent A. Cullimore
Thermo-electrochemical analysis of lithium ion batteries for space applications using Thermal Desktop
Lithium-ion batteries (LIBs) are replacing the Nickel–Hydrogen batteries used on the International Space Station (ISS). Knowing that LIB efficiency and survivability are greatly influenced by temperature, this study focuses on the thermo-electrochemical analysis of LIBs in space orbit. Current finite element modeling software allows for advanced simulation of the thermo-electrochemical processes; however the heat transfer simulation capabilities of said software suites do not allow for the extreme complexities of orbital-space environments like those experienced by the ISS. In this study, we have coupled the existing thermo-electrochemical models representing heat generation in LIBs during discharge cycles with specialized orbital-thermal software, Thermal Desktop (TD). Our model's parameters were obtained from a previous thermo-electrochemical model of a 185 Amp-Hour (Ah) LIB with 1–3 C (C) discharge cycles for both forced and natural convection environments at 300 K. Our TD model successfully simulates the temperature vs. depth-of-discharge (DOD) profiles and temperature ranges for all discharge and convection variations with minimal deviation through the programming of FORTRAN logic representing each variable as a function of relationship to DOD. Multiple parametrics were considered in a second and third set of cases whose results display vital data in advancing our understanding of accurate thermal modeling of LIBs.
Source: Science Direct (Journal of Power Sources)
Author: W. Walker, H. Ardebili
Thermal Modeling of Nanosat
Advances in computer technologies and manufacturing processes allow creation of highly sophisticated components in compact platform. For example, a small scale satellite, such as the CubeSat, can now be used for scientific research in space rather than big scale project like the International Space Station (ISS). Recently a team of undergraduate and graduate students at SJSU has the opportunity to collaborate on designing and building a miniature size CubeSat with the dimension of 10x10x10 cm. Although the integration of compact electronics allows sophisticated scientific experiments and missions to be carried out in space, the thermal control options for such small spacecraft are limited. For example, because of its small size there is no room for dedicated radiator or insulation panels. To minimize mass of the thermal control system while keeping the electronics at safe operating conditions, this thesis aims at studying the external orbital radiation heat flux the CubeSat is expected to expose to and the steady state heat conduction of the internal electronics. If the operating temperature from these heating conditions causes issue, appropriate thermal control solutions will be presented.
Source: San José State University
Author: Dai Q. Dinh
Analysis of Post-reentry Heating and Soak-back Affects in Unsealed Reentry Vehicles
Maintaining low temperature payloads through atmospheric reentry and ground recovery is becoming a larger focus in the space program as work in biology, cryogenic and other temperature dependent sciences becomes a higher goal on the International Space Station (ISS) and extraterrestrial surfaces. Paragon analyzes reentry system thermal control, particularly technology regarding small thermally controlled payloads anticipated for use in sample return from the International Space Station.
To minimize system mass and utilize the powerful insulative properties of a hard space vacuum the internal cavity of a small reentry vehicle can be left open. Thermally this causes concern during reentry, as even at very high altitudes there is enough pressure to cause a significant impact on insulation stratagems, such as MLI that rely on a high vacuum. At lower altitudes the vehicle is moving much slower, so the intense heat load of reentry is finished but soak-back from outer heated surfaces to the payload is a significant issue when air is present to facilitate heat transfer between layers. Initial assumptions that the cold temperatures of the upper atmosphere would cause a net cooling affect in the post-reentry times were overturned by a simple analysis set done in Thermal Desktop involving worst and best case scenarios as air starts to enter the vehicle. Additionally, CFD low pressure zones were shown to exist behind the vehicle where it is open to the atmosphere when the vehicle is travelling at extreme reentry speeds. These pressures are not so low however to prevent air from entering the vehicle. The impacts of this now apparent soak back, during the last phases of an atmospheric reentry were investigated leading to the conclusion that analyses of lower atmospheric portions of a reentry are critical to reentry studies and significantly changed the results.
An updated design is theorized using the knowledge gained from the preliminary studies called the Cryogenic Extended Duration and Reentry Thermal Control System (CEDR TCS) and the design is fully passive making it a low-complexity, zero-power system that does not necessitate the use of any consumables. The CEDR TCS uses a two-way pressure relief valve or “breather valve” that would allow the pressures inside and outside the vehicle to equilibrate once a great enough pressure differential is applied. This will allow air to leave while the unit is in space vacuum and prevent air from coming in until much later in the re-entry after much of the reentry heat has had a chance to convect to the upper atmosphere. Through further analysis CEDR is hoped to display a capability of near cryogenic temperatures through an atmospheric reentry and long durations on the ground.
Author: Erika T. Bannon, Jared Leidich, Alex Walker
Content Tags: mli, multi-layer insulation, heat loads, design optimization, CFD, transient, insulation, model correlation, phase change material, PCM, radiation, sink temperature, heat flux, radks, radiation analysis group, material properties
Improvements to a Response Surface Thermal Model for Orion
Adaptive Thermal Modeling Architecture for Small Satellite Applications
The United States Air Force and commercial aerospace industry recognize the importance of moving towards smaller, better, and cheaper spacecraft to support the nation’s increasing dependence on space-based technologies. Whether large or small, all spacecraft will require the same basic bus systems and environmental protection, simply scaled to fit the mission. The varying thermal environment in space is particularly important to spacecraft design and operation because of its affect on hardware performance and survivability. The Adaptive Thermal Modeling Architecture (ATMA) discussed in this thesis is meant to bridge the gap between the commercially available thermal modeling tools used for larger, more expensive satellites, and the low-fidelity algorithms and techniques used for simple first order analysis.
The ATMA consists of the MATLAB based Adaptive Thermal Modeling Tool (ATMT) and its user’s manual, as well as the process by which an inexperienced engineer can quickly and accurately perform on-orbit thermal trades studies for a range of space applications. The ATMA tools and techniques have been validated with an industry standard thermal modeling program (Thermal Desktop) and correlated to thermal test data taken from MIT’s CASTOR nanosatellite. The concepts derived and evaluated within ATMA can be extended to a variety of aerospace modeling applications. The ATMT program and modeling architecture are currently being utilized by members of MIT’s Space Engineering Academy (SEA) and undergraduate satellite team as well as the U.S. Air Force Academy’s FalconSAT-6 program.
Author: 2Lt. John Anger Richmond, USAF, Colonel John Keesee, USAF Retired
Collaborative design and analysis of Electro-Optical sensors
Complex products are best developed in a collaborative design environment where engineering data and CAD/CAE results can be shared across engineering discipline boundaries within a common software interface. A new software tool that allows Electro-Optical (EO) sensors to be developed in this manner has been used to conduct an integrated Structural/Thermal/Optical (STOP) analysis of a critical lens subassembly in a flight payload. This paper provides a description of the software environment and a summary of the technical results that were produced with it.
Source: The Aerospace Corporation
Author: Jason Geis, Jeff Lang, Leslie Peterson, Francisco Roybal, David Thomas
Content Tags: concurrent engineering, concurrent design, third-party software, mesh, finite element, mashing, parametric, material properties, optical properties, boundary conditions, conductance, structural, thermocouples, transient
Crew Exploration Vehicle Composite Pressure Vessel Thermal Assessment
The Crew Exploration Vehicle (CEV) is the next generation space vehicle to follow the Space Shuttle. A design with the inclusion of a Composite Pressure Vessel (CPV) has been assessed for its thermal response. The temperature distribution on the CPV that results from the heat produced by internal spacecraft systems and external space environments was calculated as part of a project-level assessment to understand thermomechanical stresses. A finite element translation of the crew module CPV was integrated into an existing CEV Thermal Math Model (TMM) based on the 605 baseline configuration and analyzed for four orbital cases. Steady state temperature profiles were generated based on orbit average heating. Preliminary thermal analysis results suggest that the CPV requires less make-up energy when compared to the baseline aluminum pressure vessel. It is emphasized that only local make-up energy was considered in the study. The make-up energy did not include the zoning configuration that occurs with heaters. This document presents the approach and assumptions used for this thermal assessment.
Author: Laurie Y. Carrillo, Ángel R. Álvarez-Hernández, Steven L. Rickman
Ground Plane and Near-Surface Thermal Analysis for NASA’s Constellation Programs
Thermal Model Development for Ares I-X
Author: Ruth M. Amundsen, Joe Del Corso
Content Tags: third-party software, thermal stress, material properties, optical properties, conduction, convection heat transfer, radiation, submodels, radiation analysis groups, expression editor, symbol, symbols, symbol manager, logic manager, logic, user logic, boundary conditions, CFD
ATROMOS Mars Polar Lander Thermal Model
Author: Elsie Hartman, Hingloi Leung, Freddy Ngo, Syed Shah, Nelson Fernandez, Kenny Boronowsky, Ramon Martinez, Nick Pham, Ed Iskander, Marcus Murbach, Erin Tegnerud, Dr. Periklis Papadopoulos
Free Molecular Heat Transfer Programs for Setup and Dynamic Updating the Conductors in Thermal Desktop
Thermal Desktop has the capability of modeling free molecular heat transfer (FMHT), but limitations are observed when working with large models during transient operation. To overcome this limitation, a MatLab program was developed that processes the Thermal Desktop free molecular conductors. It sets up the logic and arrays for the Thermal Desktop GUI used by SINDA/FLUINT. The theory of free molecular heating is presented along with the process required to setup the conductors, arrays, logic and Fortran subroutines for FMHT modeling in Thermal Desktop.
Author: Eric T. Malroy
Content Tags: transient, third-party software, user-defined Fortran array, radiation analysis groups, surface elements, radiation, radiation calculations, case set manager, user-defined Fortran arrays (UDFAs), submodels, radks
Thermal Analysis on Plume Heating of the Main Engine on the Crew Exploration Vehicle Service Module
The crew exploration vehicle (CEV) service module (SM) main engine plume heating is analyzed using multiple numerical tools. The chemical equilibrium compositions and applications (CEA) code is used to compute the flow field inside the engine nozzle. The plume expansion into ambient atmosphere is simulated using an axisymmetric space-time conservation element and solution element (CE/SE) Euler code, a computational fluid dynamics (CFD) software. The thermal analysis including both convection and radiation heat transfers from the hot gas inside the engine nozzle and gas radiation from the plume is performed using Thermal Desktop. Three SM configurations, Lockheed Martin (LM) designed 604, 605, and 606 configurations, are considered. Design of multilayer insulation (MLI) for the stowed solar arrays, which is subject to plume heating from the main engine, among the passive thermal control system (PTCS), are proposed and validated.
Author: Xiao-Yen J. Wang and James R.Yuko
Implementation of STEP-TAS Thermal Model Exchange Standard in Thermal Desktop
Author: Tim Panczak and Georg Siebes
Content Tags: robust design, meshing, parametric, material properties, orbit, articulation, tracker, trackers, concurrent engineering, concurrent design, third-party software, optical properties, model correlation, thermocouples
Modeling Transient Operation of Loop Heat Pipes using Thermal Desktop
Loop heat pipes (LHPs) are used in multiple terrestrial and space applications. Transient analysis of conventional and advanced loop heat pipes with complex radiators under varying conditions where the heat load and the effective sink temperature change in time can be best accomplished using Thermal Desktop™.
This paper presents a transient model of a LHP developed using Thermal Desktop™ (Sinda/Fluint). It includes the evaporator connected to the reservoir and condenser with fluid transport lines with bends, flow balancers, and connectors. The condenser is bonded to a honeycomb panel with two face-sheets spreading thermal energy across the radiating surfaces. The model was correlated to the thermal-vacuum test data.
The modeling provided better understanding of the critical transient fluid-flow mechanisms encountered in the LHP under transient operational conditions. Analysis of the numerical results shows that the secondary wick should be transporting liquid from the reservoir to the primary wick during transient operation where the sink temperature is decreasing or the evaporator heat load is being reduced.
Author: Dmitry Khrustalev
Content Tags: LHP, Loop Heat Pipe, sink temperature, transient, evaporator, condenser, model correlation, wicks, heat loads, conduction, wall, two-phase flow, convection heat transfer, radiation, phase change material, CAPPMP, iface, heat sink
WPI Nanosat-3 Final Report, PANSAT - Powder Metallurgy and Navigation Satellite
This document summarizes the activities of the WPI Nanosat-3 (N3) program proposed in response to a BAA by the AFOSR and AIAA (University Nanosat Program, AFOSR BAA 2003-02) . Specifically, we proposed to have WPI undergraduate and graduate student teams under the direct guidance of WPI faculty, develop a nanosat that would be used as a vehicle to investigate:
- A GPS based navigation and orientation determination system
- the use of a powder metallurgy (P/M) component design methods to develop the primary satellite bus structure
Program highlights include the successful development of; i) a high quality satellite tracking and communications system, ii) powder metallurgy components of the satellite bus structure, iii) the sensor and communications subsystem, iv) the triple modular redundant processor system, v) the GPS navigation and orientation system, vi) a very high reliability and efficiency solar cell power system using custom designed switching power supplies, and vii) the satellite navigation/stability system. Also completed in conjunction with this NS3 program was a detailed MATLAB/Simulink model of the orbital mission. Finally, completed in parallel with the NS3 program but not supported by it was a prototype Picosat that built upon technology developed as part of the NANOSAT 3 program.
Source: Electrical and Computer Engineering, Worcester Polytechnic Institute
Author: Fred J Looft
Modeling and Sizing a Thermoelectric Cooler Within a Thermal Analyzer
Thermoelectric couples are solid-state devices capable of generating electrical power from a temperature gradient (known as the Seebeck effect) or converting electrical energy into a temperature gradient (known as the Peltier effect). Thermoelectric coolers, being solid state devices, have no moving parts which makes them inherently reliable and ideal for cooling components in a system sensitive to mechanical vibration. The ability to use TECs to heat as well as cool makes them suitable for applications requiring temperature stabilization of a device over a specified temperature range. Although these devices have been around for years, they are gaining popularity in the aerospace industry for providing temperature control within optical systems and for loop heat pipes.
Historically, modeling and sizing of thermoelectric coolers was left to the analyst to work off-line from the modeling task. The analyst would then need to create his own logic in SINDA for simulating the cooler. This presenation will demonstrate how thermoelectric coolers are now easily modeled using off-the-shelf simulation routines and 3D user interfaces. The analytical demonstration includes sizing of a cooler for a specific application based on area, temperature requirements and heat load through a series of parametric analyses. Cooler performance will also be characterized at the device and system level.
Source: Aerospace Thermal Control Workshop
Author: Jane Baumann
Content Tags: cooler, TEC, thermoelectrics, thermoelectric, LHP, Loop Heat Pipe, optical, user logic, parametric, thermostatic, convection heat transfer, expression editor, parameterize, steady state, transient, proportional, design opimization, system-level modeling
Non-grey Radiation Modeling using Thermal Desktop/SINDAWORKS
This paper provides an overview of the non-grey radiation modeling capabilities of Cullimore and Ring’s Thermal Desktop® Version 4.8 SindaWorks software. The non-grey radiation analysis theory implemented by Sindaworks and the methodology used by the software are outlined. Representative results from a parametric trade study of a radiation shield comprised of a series of v-grooved shaped deployable panels is used to illustrate the capabilities of the SindaWorks non-grey radiation thermal analysis software using emissivities with temperature and wavelength dependency modeled via a Hagen-Rubens relationship.
Source: TFAWS Short Course
Author: Dr. Kevin R. Anderson, Dr. Chris Paine
Analysis and Design of the Mechanical Systems Onboard a Microsatellite in Low-Earth Orbit: an Assessment Study
A study of the mechanical systems contributing to the design and performance of a picosatellite’s mission in low-Earth orbit (LEO) was performed through design and analysis. The unique architecture of this satellite stems from a form factor established by the internationally recognized CubeSat Program. This CubeSat-Plus architecture limits the satellite’s size to be no larger than a 10 x 10 x 15 cm cube with an overall mass not exceeding 2 kg. This satellite would then be launch into LEO and conduct on-orbit GPS measurements while remaining tethered to the second stage booster of a Boeing Delta II Launch Vehicle (LV). To ensure the structural integrity of the satellite, Finite Element Analysis (FEA) was conducted on all primary, secondary, and tertiary structural constituents to determine the maximum stresses experienced by the satellite during launch, deployment, and while in orbit around Earth. All space deliverable platforms must be designed in strength to satisfy a predetermined standard as set forth by the LV provider. Theoretical characterization of the dynamic environment coupled with the equation of motion, and static failure modes were the primary constituents of this assessment study. Consequential data sets piloted the assessment criterion and a means of implementing conclusive remarks. The design of this satellite will reveal evidence of system level design philosophies that were required given the extremely small form factor. The satellite’s on-orbit thermal environment was quantified and characterized using finite difference techniques and solar simulation software. The extremely dynamic behavior of a LEO satellite required a fundamental understanding of both long wave and shortwave thermal radiation along with creative strategies to ensure on-orbit thermal stability for the satellite’s electrical components. Thermal Desktop was employed to develop an accurate thermal model by which to assess incident radiation, conductive and radiative heat management, and temperature-dependent mechanical responses of the satellite’s structure and working systems. Conclusions from both the design efforts and model analyses show that this picosatellite is both sufficiently strong to survive the expected launch loads, and provides a thermally stable environment for the components housed within its interior.
Publication: SolomonD0506 (3).pdf
Source: TFAWS Short Course
Author: Dylan Raymond Solomon
JWST Testing Issues – Thermal & Structural
This study explores JWST thermal and structural testing issues and possible solutions, as presented to NASA in June 2004
Source: Aerospace Thermal Control Workshop 2005
Author: William Bell, Frank Kudirka, & Paul-W. Young
Thermoelastic Analysis in Design
This study explores the capability of Thermal Desktop to map temperatures from a thermal model to a Nastran model to evalautate thermal stress and distortion
Source: Aerospace Thermal Control Workshop
Author: William Bell & Paul-W. Young
Content Tags: chilldown, thermal stress, third-party software, convection heat transfer, walls, heat flux, convergence, temperature map, temperature mapping, finite element, finite elements, material properties, heat pipe, heatpipe, pipes
Parametric Models and Optimization for Rapid Thermal Design
Traditionally, the preliminary thermal design is behind the mechanical and electrical spacecraft design. Many factors contribute to this including a lack of detailed physical characteristics of the spacecraft and knowledge of the distribution of the thermal loads within the spacecraft. Therefore, the thermal design typically reacts to the mechanical and electrical designs. The thermal analyst gets a configuration and then tries to wrap an acceptable solution around it. The analyst relies on years of experience and trial and error to determine the appropriate design cases and create a thermal design. Depending on the experience level of the engineer, several iterations may be necessary to determine the worst-case design points and an acceptable thermal design.
Suppose analysis tools were available that would allow the thermal engineer to rapidly produce preliminary designs and weave the thermal design requirements such as thermal radiator size, preferred radiator location and heat load location into the overall spacecraft design. The result would be a more integrated spacecraft thermal design completed in less time using less of the spacecraft resources.
Advances in thermal analysis software provide the tools for the thermal engineer to perform preliminary analyses more quickly and accurately than ever before. The result is that the thermal engineer can have a greater influence on the spacecraft design process.
Source: SAE Technical Paper Series
Author: D. Martin
Margin Determination in the Design and Development of a Thermal Control System
A method for determining margins in conceptual-level design via probabilistic methods is described. The goal of this research is to develop a rigorous foundation for determining design margins in complex multidisciplinary systems. As an example application, the investigated method is applied to conceptual-level design of the Mars Exploration Rover (MER) cruise stage thermal control system. The method begins with identifying a set oftradable system-level parameters. Models that determine each of these tradable parameters are then created. The variables of the design are classified and assigned appropriate probability density functions. To characterize the resulting system, a Monte Carlo simulation is used. Probabilistic methods can then be used to represent uncertainties in the relevant models. Lastly, results of this simulation are combined with the risk tolerance of thermal engineers to guide in the determination of margin levels. The method is repeated until the thermal engineers are satisfied with the balance of system-level parameter values. For the thermal control example presented, margins for maximum component temperatures, dry mass, power required, schedule, and cost form the set of tradable system-level parameters. Use of this approach for the example presented yielded significant differences between the calculated design margins and the values assumed in the conceptual design of the MER cruise stage thermal control system.
Author: D. Thunnissen, G. Tsuyuki
Automated Multidisciplinary Optimization of a Space-based Telescope
Automated design space exploration was implemented and demonstrated in the form of the multidisciplinary optimization of the design of a space-based telescope.
Off-the-shelf software representing the industry standards for thermal, structural, and optical analysis were employed. The integrated thermal/structural/optical models were collected and tasked with finding an optimum design using yet another off-the-shelf program. Using this integrated tool, the minimum mass thermal/structural design was found that directly satisfied optical performance requirements without relying on derived requirements such as isothermality and mechanical stability. Overdesign was therefore avoided, and engineering productivity was greatly improved.
This ambitious project was intended to be a pathfinder for integrated design activities. Therefore, difficulties and lessons learned are presented, along with recommendations for future investigations.
Author: B. Cullimore, T. Panczak, J. Baumann
Integrated Analysis of Thermal/Structural/Optical Systems
Productivity bottlenecks for integrated thermal, structural, and optical design activities were identified and systematically eliminated, making possible automated exchange of design information between different engineering specialties.
The problems with prior approaches are summarized, then the implementation of the corresponding solutions is documented. Although the goal of this project was the automated evaluation of coupled thermal/optical/structural designs, significant process improvements were achieved for subset activities such as stand-alone thermal, thermal/ structural, and structural/optical design analysis.
Author: B. Cullimore, T. Panczak, J. Baumann, Dr. Victor Genberg, Mark Kahan
Content Tags: finite element, finite elements, finite difference, parametric, conductance, contact conductance, design optimization, robust design, optical, registers, radiation, dynamic SINDA, dynamic mode
A CAD-based Tool for FDM and FEM Radiation and Conduction Modeling
Thermal engineering has long been left out of the concurrent engineering environment dominated by CAD (computer aided design) and FEM (finite element method) software. Current tools attempt to force the thermal design process into an environment primarily created to support structural analysis, which results in inappropriate thermal models. As a result, many thermal engineers either build models “by hand” or use geometric user interfaces that are separate from and have little useful connection, if any, to CAD and FEM systems.
This paper describes the development of a new thermal design environment called the Thermal Desktop. This system, while fully integrated into a neutral, low-cost CAD system, and which utilizes both FEM and FD methods, does not compromise the needs of the thermal engineer. Rather, the features needed for concurrent thermal analysis are specifically addressed by combining traditional parametric surface-based radiation and FD based conduction modeling with CAD and FEM methods. The use of flexible and familiar temperature solvers such as SINDA/FLUINT is retained.
Author: Tim Panczak, Steve Ring, Mark Welch
Content Tags: finite element, finite difference, concurrent engineering, heater, heatpipe, heat pipe, radiation analysis groups, optical properties, Phenomena, refraction, scaffolding, CAD geometry, layers, expression editor, solver, mesh, mesher, structural mesh, ray tracing, boundary conditions, thermal stress, radiator, conductance, batteries, orbital heating, mli, multi-layer insulation, radks, articulation, articulating
Assessment of the Mars Helicopter Thermal Design Sensitivities Using the Veritrek Software
The Mars Helicopter will be a technology demonstration conducted during the Mars 2020 mission. The primary mission objective is to achieve several 90-second flights and capture visible light images via forward and nadir mounted cameras. These flights could possibly provide reconnaissance data for sampling site selection for other Mars surface missions. The helicopter is powered by a solar array, which stores energy in secondary batteries for flight operations, imaging, communications, and survival heating. The helicopter thermal design is driven by minimizing survival heater energy while maintaining compliance with allowable flight temperatures in a variable thermal environment. Due to the small size of the helicopter and its complex geometries, along with the fact that it operates with very low power and small margins, additional care had to be paid while planning thermal tests and designing the thermal system. A Thermal Desktop® model has been developed to predict the thermal system’s performance. A reduced-order model (ROM) created with the Veritrek software has been utilized to explore the sensitivities of the thermal system’s drivers, such as electronics dissipations, gas gaps, heat transfer coefficients, etc., as well as to assess and verify the final thermal design. This paper presents the performance of the Veritrek software products and the details of the ROM creation process. The results produced by Veritrek were utilized to study the effect of the major thermal design drivers and Mars environment on the Mars Helicopter in as little as 10 days, an effort that would have taken over 4 months using traditional thermal analysis techniques.
Source: TFAWS 2018
Author: Stefano Cappucci, Michael T. Pauken, Jacob A. Moulton, Derek W. Hengeveld
Content Tags: third-party software, heater, emissivity, absortivity, conduction, heat loads, convection heat transfer, sweep, design space scanning, output, robust engineering, validation, design optimization
Tank Sizing Analysis for Reduced Gravity Cryogenic Transfer Receiver Tank
Understanding fluid behavior in microgravity is essential to further development of cryogenic storage in space environments. The Reduced Gravity Cryogenic Transfer project is designed to investigate tank chilldown in a microgravity environment onboard a parabolic flight. This work focused on examining the feasibility of chilling down different tank sizes using liquid nitrogen within the time constraints of the flight. Thermal models of four different tank geometries were made using Thermal Desktop and SINDA/FLUINT. The tank wall was modeled as a series of solid finite elements while the fluid inside the tank was represented by twinned liquid and vapor lumps. Fluid was injected into the bottom of the tank to simulate a dip tube and vented out of the top of the tank. The tank wall temperature as well as the state of the fluid inside the tank was tracked throughout the simulation. Several different cases were run with different chilldown operations for each tank model using a combination of charge, hold, and vent cycles. The average wall temperature, propellant mass savings and thermal efficiency of each of the four tanks were compared under seven different chilldown operations. A recommendation was made for the receiver tank size based on these parameters.
Source: TFAWS 2021
Author: Erin M. Tesny, Daniel M. Hauser, Jason W. Hartwig
Passive Thermal Control Design Methods, Analysis, Comparison, and Evaluation for Micro and Nanosatellites Carrying Infrared Imager
Advancements in satellite technologies are increasing the power density of electronics and payloads. When the power consumption increases within a limited volume, waste heat generation also increases and this necessitates a proper and efficient thermal management system. Mostly, micro and nanosatellites use passive thermal control methods because of the low cost, no additional power requirement, ease of implementation, and better thermal performance. Passive methods lack the ability to meet certain thermal requirements on larger and smaller satellite platforms. This work numerically studies the performance of some of the passive thermal control techniques such as thermal straps, surface coatings, multi-layer insulation (MLI), and radiators for a 6U small satellite configuration carrying a mid-wave infrared (MWIR) payload whose temperature needs to be cooled down to 100K. Infrared (IR) imagers require low temperature, and the level of cooling is entirely dependent on the infrared wavelengths. These instruments are used for various applications including Earth observations, defence, and imaging at IR wavelengths. To achieve these low temperatures on such instruments, a micro-cryocooler is considered in this study. Most of the higher heat dissipating elements in the satellite are mounted to a heat exchanger plate, which is thermally coupled to an external radiator using thermal straps and heat pipes. The effects of the radiator size, orbital inclinations, space environments, satellite attitude with respect to the sun, and surface coatings are discussed elaborately for a 6U satellite configuration.
Source: Applied Sciences, 2022, 12(6), 2858
Author: Shanmugasundaram Selvadurai, Amal Chandran, David Valentini, and Bret Lamprecht
Content Tags: mli, multi-layer insulation, surface elements, surface coating a mesh, radiator, phase change material, thermocouples, finite element, finite elements, convergence, material properties, properties, CCHP