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.

Publication: TFAWS2021-CT-01.pdf

Source: TFAWS 2021

Author: Erin M. Tesny, Daniel M. Hauser, Jason W. Hartwig

Year: 2021

Content Tags: two-phase, twinned tanks, chilldown, solid finite elements, finite elements, finite element, parametric analysis, parametric, material properties

This study explores JWST thermal and structural testing issues and possible solutions, as presented to NASA in June 2004

Publication: bell_telescope.pps

Source: Aerospace Thermal Control Workshop 2005

Author: William Bell, Frank Kudirka, & Paul-W. Young

Year: 2005

Content Tags: chilldown, refrigeration cycle, convection heat transfer, insulation, radiation, flow regime mapping, radiation analysis groups

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.

Publication: TFAWS07-1008.pdf

Source: TFAWS

Author: Dmitry Khrustalev

Year: 2007

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

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.

Publication: TFAWS07-1012.pdf

Source: TFAWS

Author: Xiao-Yen J. Wang and James R.Yuko

Year: 2007

Content Tags: nozzles, expansion, CFD, mli, multi-layer insulation, convection heat transfer, steady state, heat flux

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

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 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:

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

Over the past 15 years, the industry standard tool for thermal analysis, SINDA, has been expanded to include advanced thermodynamic and hydrodynamic solutions (“FLUINT”). With the recent culmination of the unique modeling tools, SINDA/ FLUINT has arguably become the most complete general-purpose thermohydraulic network analyzer that is available.

Traditional network elements for fluid circuit analyzers include control volumes and flow passages. During the development of modeling tools capable of handling phasic nonequilibrium within SINDA/ FLUINT, several new network elements were created as by-products. This paper describes one of them: control volume interfaces or “ifaces” for short.

Ifaces are used to describe how one control volume abuts another. While originally developed to model liquid-vapor interfaces within two-phase control volumes, they can also be used to describe pistons, spring bellows, liquid slugs, and curved interfaces such as those between bubbles and liquid as well as those within capillary structures (e.g., sintered wicks). More importantly, they can be used as an imaginary film to subdivide quasi-stagnant control volumes, extending the reach of a 1D network into certain 2D and 3D problems.

Despite their abstract nature, ifaces have been well received by analysts for a variety of modeling tasks.

Publication: ifaces.pdf

Source: AIAA

Author: Brent A. Cullimore, David A. Johnson

Year: 2000

Content Tags: iface, network elements, liquid surface, bellows, piston, two-phase, capillary systems, wicks, solver, variables, registers, parametric, user logic, finite element, finite difference, submodels, boundary conditions, steady state, transient, two-phase flow, nonequilibrium, twinned tanks

A cryogenic capillary pumped loop (CPL) has been developed, designed, fabricated and successfully demonstrated by test. Using no moving parts, the novel device is able to start from a supercritical state and cool a remote dissipation source to 80-90K. Design studies were conducted for integration requirements and component design optimization and prototype units were designed, fabricated and successfully tested with excellent results. The development included the miniaturization of CPL technology to allow heat acquisition from sources with a small footprint and direct integration to a cryocooler cold finger. Applications include the cooling of cryogenic electronics, sensors, and fuels. The technology possesses many advantages over cryogenic heat pipes including ground testability and mechanical isolation. Because of the CPLs ability to transport loads over a distance, cryocoolers can be located remotely from the detector (up to a meter away or across a gimbaled joint). In addition, it passively seeks the coldest rejection environment, allowing a single cryogenic CPL to enable switching between multiple passive cryogenic radiators. This work was performed under funding from NASA Goddard Space Flight Center.

Publication: IECEC98.pdf

Source: IECEC

Author: Jane Baumann, Brent Cullimore

Year: 1998

Content Tags: capillary pumped loop, CPL, CCPL, cryogenic, cooling loop, supercritical, start-up, design optimization, two-phase, heat loads, working fluids, evaporator, condenser, robust design, capillary systems, wicks, heat pipe, heatpipe

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

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.

Publication: lhp.pdf

Source: ICES

Author: Brent Cullimore, Jane Baumann

Year: 2000

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

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

The NASA standard tool for thermohydraulic analysis, SINDA/FLUINT, includes thermodynamic and hydrodynamic solutions specifically targeted at the growing demand for design and analysis of liquid propulsion systems. Applications in this field have included:

• Helium pressurization system design
• Cryogenic line chill-down transients
• Regenerative nozzle cooling
• Cryogenic turbomachinery chill-down transients
• Hydrazine line filling
• Feedline transients, including pogo suppression
• Feedline anti-geyser design
• Cryogenic tank pressurization and discharge, including thermal stratification, dissolved pressurant, and capillary liquid acquisition devices

Many organizations have previously used separate in-house tools specialized for each of the above applications. However, these organizations typically do not have the resources nor infrastructure to maintain these codes when cognizant engineers are lost, nor to modify and validate them for new vehicles or applications, nor to train new engineers on their use.

The use of a single general-purpose tool to encompass all such analyses offers not only solutions to the above problems, but also enables integrated analyses and the ability to communicate with vendors and customers.

Publication: propulse.pdf

Source: CRTech White Paper

Author: Brent A. Cullimore, Cynthia M. Beer, David A. Johnson

Year: 2000

Content Tags: chilldown, cryogenics, turbomachinery, register, registers, oxidizer tank, two-phase flow, cryogenic storage, nonequilibrium, valves, parametric, model correlation, solver, supercritical, mixtures, pressurant gas, orifices, compressors, user logic, choking, choked, nozzles, slip flow, liquid surface, interface, capillary systems, thermal stratification, stratified tanks, stratification

This paper describes the application of the general purpose SINDA/FLUINT thermohydraulic analyzer to the modeling of vapor compression (VC) cycles such as those commonly used in automotive climate control and building HVAC systems. The software is able to simulate transient operation of vapor compression cycles, predicting pressures, coefficients of performance, and condenser/evaporator liquid positions in a closed two-phase system with a fixed fluid charge. The program can also be used to size components, to estimate the impact of tolerances and other variations, and to help estimate uncertainties given limited test data.

SINDA/FLUINT has a user base numbering in the thousands. It has several graphical user interfaces, preprocessors, and 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, widespread application to vapor compression cycles is comparatively recent (Ref 2), and is largely due to an increased demand for transient modeling of air conditioning systems. Toward this requirement, SINDA/FLUINT’s unique abilities to analyze transient two-phase phenomena have been recognized as being critical to achieving accurate performance predictions.

Publication: vc.pdf

Source: ICES

Author: Brent A. Cullimore

Year: 2000

Content Tags: condensers, evaporator, registers, evaporators, slip flow, orifices, valves, capillary tubes, parameterizing, parametric analysis, reliability engineering, robust design, model correlation, vapor compression, compressor, parametric, parameterize, solver, transient

This paper describes a new means of analyzing the thermal response of air-cooled and liquid-cooled electronics that overcomes limitations in available tools and current design methods. It also shows how these new tools and methods can extend the reach of such thermal/fluid analyses by helping to size and locate components as well as dealing with both pre-test uncertainties and post-deployment variations in manufacturing, environment, and usage.

As the time lag from design to market diminishes, the pressure to abandon “build and test” approaches to electronics thermal cooling has created a wide variety of design analysis methods ranging from simple hand calculations of energy balances to detailed three-dimensional CFD (Computational Fluid Dynamics) approaches. Surprisingly few options are available between these two extremes, leaving most designers feeling that they face an “all or nothing” choice. Hand calculations and other simple software approaches, while contributing to an engineer’s intuition, cannot be relied upon for the entire design cycle, especially with the reduced emphasis on hardware prototyping that is necessary to speed up product development time. Fluid network modeling (FNM) approaches offer more analytic power but lack strong connectivity to geometric thermal models, and are therefore cumbersome to use. CFD approaches include limited geometric thermal modeling, but are relatively inflexible because they focus on detailed point design evaluations, and therefore contribute little to design knowledge.

This paper will describe a new approach using multidimensional heat transfer modeling in combination with ducted or quasi-multidimensional flow solutions for fast and easily modifiable models of electronics packaging that lends itself to high-level operations such as sizing and reliability estimation.

Publication: IPACK2001-15523.pdf

Source: InterPack

Author: David A. Johnson, Mark J. Welch, Brent A. Cullimore

Year: 2001

Content Tags: CFD, convection heat transfer, natural convection, parametric, finite elements, finite difference

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

This paper describes the need for dynamic (transient) simulation of automotive air conditioning systems, the reasons why such simulations are challenging, and the applicability of a general purpose off-the-shelf thermohydraulic analyzer to answer such challenges.

An overview of modeling methods for the basic components are presented, along with relevant approximations and their effect on speed and accuracy of the results.

Publication: vtms2001.pdf

Source: VTMS

Author: Brent A. Cullimore, Terry J. Hendricks

Year: 2001

Content Tags: compressor, evaporator, evaporators, condensers, slip flow, working fluids, registers, vapor compression, throttle, capillary tube, choked

Modeling lessons learned form Ford, Visteon, GM, Delpi, Danfoss, etc.

Publication: VCimaps.pps

Source: ITherm

Author: Brent Cullimore

Year: 2002

Content Tags: vapor compression, compressor, two-phase heat transfer, evaporator, condenser, parametric, slip flow, finite difference

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

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.

Publication: FloCAD3-ICES.pdf

Source: ICES

Author: B. Cullimore, D. A. Johnson

Year: 2003

Content Tags: finite difference, heat pipe, Loop Heat Pipe, finite element, structural mesh, duct, noncondensible gas, condenser, wall

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.

Publication: TED-AJ03-537.pdf

Source: ASME-JSME

Author: John D. Bernardin, Curtt Ammerman, Steve Hopkins

Year: 2003

Content Tags: expansion, contraction, pump, valve, heat exchangers, cooler, heat loads

The National Renewable Energy Laboratory (NREL) and U.S. Department of Energy (DOE) are interested in developing more efficient vehicle air conditioning (A/C) systems to reduce fuel consumption in advanced vehicle designs. Vehicle A/C systems utilizing electrically-driven compressors are one possible system design approach to increasing A/C system performance over various drive cycle conditions. NREL’s transient A/C system model was used to perform multivariable design optimization of electrically-driven compressor A/C systems, in which five to seven system design variables were simultaneously optimized to maximize A/C system performance. Design optimization results demonstrate that significant improvements in system COP are possible, particularly system COP > 3, in a properly optimized system design with dynamically-controlled operation. System optimization analyses investigated dynamic A/C system design strategies employing dual-compressor-speeds in electrically-driven systems to evaluate their effects on system performance. A system optimization methodology was developed which can systematically quantify impacts on A/C system design and performance resulting from varying degrees of design influence being given to widely different design objectives. The technique is based upon formulating optimization objective functions from linear combinations of critical design performance parameters that characterize independent design goals. It was demonstrated here by giving varying degrees of design influence to maximizing system COP and maximizing evaporator cooling capacity over SC03 and US06 drive cycles.

Publication: C599-061.pdf

Source: NREL

Author: T. Hendricks

Year: 2003

Content Tags: design optimization, compressor, condenser, evaporator, expansion, system-level modeling, design variables

This paper describes a vehicle-level simulation model for climate control and powertrain cooling developed and currently utilized at GM. The tool was developed in response to GM's need to speed vehicle development for HVAC and powertrain cooling to meet world-class program execution timing (18 to 24 month vehicle development cycles). At the same time the simulation tool had to complement GM's strategy to move additional engineering responsibility to its HVAC suppliers. This simulation tool called "e-Thermal" was quickly developed and currently is in widespread (global) use across GM. This paper describes GM's objectives and requirements for developing e-Thermal. The structure of the tool and the capabilities of the simulation tool modules (refrigeration, front end airflow, passenger compartment, engine, transmission, Interior air handling …) is introduced. Model data requirements and GM's strategy for acquiring component data are also described. The paper includes an example of a typical application of the tool with sample output from the simulation and some comparison to actual test data from a vehicle under the same test scenario.

Publication: 2004-01-1510.pdf

Source: SAE Technical Paper Series

Author: Todd M. Tumas, Balaji Maniam, Milind Mahajan, Gaurav Anand, Nagendra Jain

Year: 2004

Content Tags: Components, heat exchangers, system-level modeling, third-party software, refrigeration cycles, model correlation

e-Thermal is a vehicle level thermal analysis tool developed by General Motors to simulate the transient performance of the entire vehicle HVAC and Powertrain cooling system. It is currently in widespread (global) use across GM. This paper discusses the details of the airconditioning module of e-Thermal. Most of the literature available on transient modeling of the air conditioning systems is based on finite difference approach that require large simulation times. This has been overcome by appropriately modeling the components using Sinda/Fluint. The basic components of automotive air conditioning system, evaporator, condenser, compressor and expansion valve, are parametrically modeled in Sinda/Fluint. For each component, physical characteristics and performance data is collected in form of component data standards. This performance data is used to curve fit parameters that then reproduce the component performance. These components are then integrated together to form various A/C system configurations including orifice tube systems, txv systems and dual evaporator systems. The A/C subsystem uses airflow rates, temperatures, humidity’s and compressor speed as inputs. The outputs include overall system energy balance, system COP, refrigerant flow rates and system pressures. The A/C simulation runs about three times faster to three times slower than real time. The modeling technique used is also capable of tracking the effect of system charge on the overall system performance. A database of automotive air conditioning components accompanies the simulation tool. This database is then integrated in e-Thermal to provide the component data for modeling. Validation results for component level models are demonstrated. They form the basis of system level models. System level validation is also demonstrated. The simulation times vary from 3 times faster than real time to 5 times slower than real time depending on the nature of the simulation.

Publication: 2004-01-1509.pdf

Source: SAE Technical Paper Series

Author: Gaurav Anand, Milind Mahajan, Nagendra Jain, Balaji Maniam, Todd M. Tumas

Year: 2004

Content Tags: parametric, two-phase flow, two-phase, Components, heat exchangers, compressor, condenser, evaporator, expansion, system-level modeling, third-party software, refrigeration cycles, model correlation

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

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.

Publication: Schweickart.pdf

Source: Topsfield Engineering Service, Inc.

Author: Russell B. Schweickart and Gary Mills

Year: 2005

Content Tags: pressure drop, capillary tube, nozzle, manifold, valve, slip flow

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.

Publication: AIAA-2006-50513.pdf

Source: AIAA

Author: P. Schallhorn, D. Michael Campbell, Sukhdeep Chase, Jorge Piquero, Cindy Fortenberry, Xiaoyi Li, Lisa Grob

Year: 2006

Content Tags: Optimization, parametric, radiation, radiation analysis groups, conduction, evaporation, CFD, convergence, structural, heat flux, thermal stratification, register, two-phase, slosh, wall, splash

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.

Publication: TFAWS06-1012_Paper_Khrustalev.pdf

Source: TFAWS Short Course

Author: D. Khrustalev, K. Wrenn, D. Wolf

Year: 2006

Content Tags: capillary systems, evaporator, evaporators, heat exchanger, wick, wicks, two-phase flow, two-phase, CAPPMP, condenser, condensers, flow regime mapping, sweep, pressure drops

Publication: TFAWS-08-1009_presentation.pdf

Source: TFAWS Short Course

Author: Paul Schallhorn, D. Michael Campbell, Sukhdeep Chase, Jorge Piquero, Cindy Fortenberry, Xiaoyi Li, Lisa Grob

Year: 2008

Content Tags: CFD, two-phase, slosh, thermal stratification, diffusion, boundary layer, twinned tanks, boiling

As air cooling of electronics reaches the limits of its applicability, the next generation of cooling technology is likely to involve heat pipes and single- or two-phase coolant loops (including perhaps loop thermosyphons, spray cooling, vapor compression refrigeration cycles, and loop heat pipes). These technologies are not suitable for analysis using 2D/3D computational fluid dynamics (CFD) software, and yet the geometric complexities of the thermal/structural models make network-style schematic modeling methods cumbersome.

This paper describes techniques whereby CAD linedrawing 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 lineal 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.

To demonstrate these concepts, two distinct examples are developed: a copper-water heat pipe, and an aluminumammonia loop heat pipe (LHP) with a serpentined condenser. A summary of the numerical requirements for system-level modeling of these devices is also provided.

Publication: cadloopmodelingrevised.pdf

Source: ICES

Author: David A. Johnson, Jane Baumann, Brent Cullimore

Year: 2002

Content Tags: CFD, LHP, Loop Heat Pipe, evaporator, evaporators, condensers, noncondensable gas, design optimization, parametric, two-phase flow, two-phase