Publications

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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.

Publication: TFAWS07-1013.pdf

Source: TFAWS

Author: Eric T. Malroy

Year: 2007

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

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.

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.

Publication: sfpaper.pdf

Source: IECEC

Author: Brent A. Cullimore

Year: 1998

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, 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.

Publication: sf981574.pdf

Source: ICES 1998

Author: Brent A. Cullimore

Year: 1998

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

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.

Publication: sfpaper.pdf

Source: IECEC 1998

Author: Brent A. Cullimore

Year: 1998

Content Tags:

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.

Publication: releng1.pdf

Source: CRTech White Paper

Author: Brent A. Cullimore

Year: 2000

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

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.

Publication: COMAPI-ICES.pdf

Source: ICES

Author: B. Cullimore, S. G. Ring, J. Baumann

Year: 2004

Content Tags: parametric, parameterize, dynamic mode, dynamic SINDA, third-party software

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.

Publication: 1999-01-.pdf

Source: ICES

Author: Jane Baumann, Brent Cullimore, Boris Yendler, Eva Buchan

Year: 1999

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

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.

Publication: AIAA2000-2285.PDF

Source: AIAA Thermophysics

Author: Jane Baumann, Brent Cullimore, Jay Ambrose, Eva Buchan, Brois Yendler

Year: 2000

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

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.

Publication: AIAA2001-3078.pdf

Source: AIAA

Author: Jane Baumann, Suraj Rawal

Year: 2001

Content Tags: radiator, LHP, Loop Heat Pipe, capillary pumped loop, CPL, noncondensable gas, evaporator, evaporators, condenser, condensers, working fluids, pressure drops

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.

Publication: LHPmodelGuide.pps

Source: Aerospace Thermal Control Workshop

Author: Jane Baumann

Year: 2003

Content Tags: LHP, Loop Heat Pipe, compensation chamber, evaporator, evaporators, condenser, condensers, iface, capillary systems

FDM/FEM System-level Analysis of Heat Pipes and LHPs in Modern CAD Environments

Publication: aerospace2005heatpipes.pps

Source: Aerospace Thermal Control Workshop

Author: Brent Cullimore, Jane Baumann

Year: 2005

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

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.

Publication: 99es-40.pdf

Source: ICES

Author: Tim Panczak, Mark J. Welch

Year: 1999

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

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.

Publication: tDesktop99.pdf

Source: ICES

Author: Mark J. Welch, Tim Panczak

Year: 1999

Content Tags: radiation analysis groups, property, alias, multi-layer insulation, mli, insulation, contact conductance, model browser, case set manager

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.

Publication: 00ICES-266.pdf

Source: ICES

Author: Timothy D. Panczak, Brent A. Cullimore

Year: 2000

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