Radiation Heat Transfer and Environmental Heating

RadCAD® computes radiation exchange factors within the thermal model and with the environment using both solar and infrared spectra. It is a module available for use with Thermal Desktop® or even as a standalone product, and it operates in the same CAD environment.

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Overview

Fast and Accurate Thermal Radiation Solutions

An ultra-fast, oct-tree accelerated Monte-Carlo ray tracing algorithm is used by RadCAD to compute radiation exchange factors and view factors. Innovations by C&R Technologies to the ray tracing process have resulted in an extremely efficient radiation analyzer.

Using finite difference "conics" (simple geometric objects) or curved finite elements from TD Direct®, RadCAD can accurately model diffuse or specular reflections and transmissive surfaces regardless of node density. The needs of the thermal solution dictate the number of nodes, not the accuracy requirements of the radiation.

RadCAD makes use of user-defined databases of optical properties. Each surface coating defines absorptivity, transmissivity, and reflectivity along with specularity in both the solar and infrared wavelength regimes. These properties can be defined versus incident angle or even with wavelength dependence.

Articulated Geometry: Moving Parts

RadCAD is fully equipped to handle moving geometry. Fully user-definable Trackers allow part of the geometry to follow the sun, nadir, or any star. These Trackers can be nested to operate on multiple axes.

More generic movement can be accomplished using Assemblies, which allow any part of the geometry to rotate and/or translate in unlimited nested configurations. Because they are general purpose, Assemblies can be used to model anything from deploying a multi-jointed antenna to opening a door of a furnace.

Radiation Environments

The definition of the environment can be one of the most challenging parts of a thermal analysis, but RadCAD makes it easy. Because the sun plays such a critical part in most environments, even for stationary components on the Earth, the environments within RadCAD are called Orbits. These Orbits define the appropriate diffuse and direct solar, albedo, and ground IR heating for everything from objects located in a window to ships, aircraft, spacecraft, and even rovers on distant planets.

Feature Summary

Thermal Radiation Calculation Features

CAD drawing methods and high-level RadCAD surfaces including snap-on methods that use CAD drawings as "scaffolding"
Variable geometry through the use of articulators (assemblies and trackers)
Solve for form factors, radiation exchange factors, or absorbed fluxes
Choice of solution methods: accelerated Monte Carlo ray tracing (MCRT) or progressive radiosity
Proprietary advances in Oct Cell technology for amazingly fast computations
True curved geometric surfaces
Specular and Diffuse surfaces
Angular dependent surface properties
Full orbital plotting package with both basic and Keplerian input
Analysis groups offer significant speed savings
Optical Property Aliases help in database management
Refraction capabilities for transparent specular surfaces
Automatic Oct Cell optimization for determining best subdivision and surfaces per cell criteria
Vector List Orbit definition for modeling trajectory orbits
Arbitrary source input for modeling IR/Sol Lamps
Fast spinning surfaces
Symmetry/Mirror planes
Automatic restart determination
Free Molecular Heating (FMH) algorithms
Quick checks to allow for finding surfaces that overlap to aid in radiation model debugging
Postprocessing (view factors, RADKs, fluxes, SINDA temperatures, etc.)

Import and Export Capabilities

TRASYS import and export
Nevada import
STEP-TAS import and export
IDEAS FD import
TSS import and export

Publications

Non-Grey and Temperature Dependent Radiation Analysis Methods, T. Panczak (TFAWS Short Course 2005)

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non-grey_radiation_short_course.pdf

Highlights in thermal engineering at Carlo Gavazzi Space (17th Workshop on Thermal and ECLS Software-ESTEC 2003)

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17th_EWTES_MOLINA_FREQUENCYDOMAIN.pdf

Integrating Thermal And Structural Analysis using Thermal Desktop (ICES 1999)

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99es-40.pdf

A CAD-based Tool for FDM and FEM Radiation and Conduction Modeling (ICES 1998)

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ices-98es-51.pdf

Customizable Multidiscipline Environments for Heat Transfer and Fluid Flow Modeling (ICES 2004)

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COMAPI-ICES.pdf

Automated Determination of Worst-case Design Scenarios (ICES 2003)

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WorstCase-ICES.pdf

Ground Plane and Near-Surface Thermal Analysis for NASA’s Constellation Programs, Joseph F. Gasbarre, Ruth M. Amundsen, Salvatore Scola - NASA Langley Research Center, Frank B. Leahy and John R. Sharp - NASA Marshall Space Flight Center (TFAWS 2008)

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TFAWS-08-1017_presentation.pdf

Non-grey Radiation Modeling using Thermal Desktop/SINDAWORKS, Dr. Kevin R. Anderson, Dr. Chris Paine, Jet Propulsion Laboratory(TFAWS 2006)

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TFAWS06-1009_Paper_Anderson_Paine.pdf

Emittance & Absorptance for Cryo Testing, D. Green (2005)

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Green.pps

Training: All about Loop Heat Pipes

Since a significant portion of LHPs consists of simple tubing, they are more flexible and easier to integrate into thermal structures than their traditional linear cousins: constant conductance and variable conductance heat pipes (CCHPs, VCHPs). LHPs are also less constrained by orientation and able to transport more power. LHPs have been used successfully in many applications, and have become a proven tool for spacecraft thermal control systems.

However, LHPs are not simple, neither in the details of their evaporator and compensation chamber (CC) structures nor in their surprising range of behaviors. Furthermore, there are uncertainties in their performance that must be treated with safety factors and bracketing methods for design verification.

Fortunately, some of the authors of CRTech fluid analysis tools also happened to have been involved in the early days of LHP technology development, so it is no accident that Thermal Desktop ("TD") and FloCAD have the unique capabilities necessary to model LHPs. Some features are useful at a system level analysis (including preliminary design), and others are necessary to achieve a detailed level of simulation (transients, off-design, condenser gradients).

CRTech is offering a four-part webinar series on LHPs and approaches to modeling them. Each webinar will last 60 minutes and are designed to be attended in the order they were presented. If you miss one in the series, please check out our video page for a recording, or contact us before the next webinar starts. While the first webinar presumes little knowledge of LHPs or their analysis, for the last three webinars you are presumed to have a basic knowledge TD/FloCAD two-phase modeling.

Part 1 provides an overview of LHP operation and unique characteristics
Part 2 introduces system-level modeling of LHPs using TD/FloCAD.
Part 3 covers an important aspect of getting the right answers: back-conduction and core state variability.
Part 4 covers detailed modeling of LHPs in TD/FloCAD such that transient operations such as start-up, gravity assist, and thermostatic control can be simulated.

Part 1: Introduction to LHP Modeling

May 31, 2018, 1-2pm (PT), 4-5pm (ET)

This webinar provides an overview of LHP design and operation, from a basic understand of components to a review of important performance considerations and limitations.

Many topics will be covered, from start-up issues to the purpose of the evaporator bayonet to capillary flow regulators to load balancing in parallel LHP units. However, we will cover these topics only in enough depth that you will be able to understand the reasons for various modeling approaches that will be covered in later webinars. In other words, this webinar will survey the various ways in which LHPs require a specialized approach to design analysis and simulation.

This webinar is one of a four-part webinar series on LHPs and approaches to modeling them. Each webinar will last 60 minutes and is designed to be attended in the order they were presented. If you miss one in the series, please check out our video page for a recording, or contact us before the next webinar starts.

Prerequisites: Basic understanding of two-phase thermodynamics and heat transfer.
Please register for Part 1 here

Part 2: Introduction to LHP Modeling

June 5, 2018, 8-9am (PT), 11am-noon (ET)

This webinar explains how the toolbox approach of Thermal Desktop and FloCAD can be used to design and simulate LHPs at a system level, where the focus is on predicting conductance of nominally operating LHP, including thermostatic control (variable conductance).

This webinar is one of a four-part webinar series on LHPs and approaches to modeling them. Each webinar will last 60 minutes and is designed to be attended in the order they were presented. If you miss one in the series, please check out our video page for a recording, or contact us before the next webinar starts.

Prerequisites: Basic understanding of Thermal Desktop and FloCAD operation as applied to two-phase systems. Basic familiarity with LHP components and operation (see Part 1).
Please register for Part 2 here

Part 3: Modeling Wick Back-conduction in LHPs

June 7, 2018, 8-9am (PT), 11am-noon (ET)

Modeling wick back-conduction in an LHP is critical to accurate prediction of the overall loop conductance and operating point. This prediction can't be separated from an understanding of what is happening in the wick core. This webinar presents time-honored methods of dealing with these complex topics in a relatively simple (if abstract) thermal/fluid network.Prerequisites:

This webinar is one of a four-part webinar series on LHPs and approaches to modeling them. Each webinar will last 60 minutes and is designed to be attended in the order they were presented. If you miss one in the series, please check out our video page for a recording, or contact us before the next webinar starts.

Basic understanding of Thermal Desktop and FloCAD operation as applied to LHP modeling (see Part 1 and Part 2).
Please register for Part 3 here

Part 4: Advanced LHP Modeling

June 12, 2018, 1-2pm (PT), 4-5pm (ET)

This webinar explains how Thermal Desktop and FloCAD can be applied to simulate complex and transient phenomena in LHPs, including condenser design, start-up, thermostatic control, and gravity assist (evaporator below condenser). The design of an actual LHP will be used to demonstrate concepts; the implications of attaching large masses to the evaporators (cooled electronics and support structures) will become clear as a result.

This webinar is one of a four-part webinar series on LHPs and approaches to modeling them. Each webinar will last 60 minutes and is designed to be attended in the order they were presented. If you miss one in the series, please check out our video page for a recording, or contact us before the next webinar starts.

Prerequisites: Familiarity with LHP modeling approaches in TD/FloCAD (see Part 1, Part 2 and Part 3).
Please register for Part 4 here

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RadCAD

Radiation Heat Transfer and Environmental Heating

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