Heat Pipe Modeling and Two-phase
Loops
CRTech
tools are routinely used to model the complexities
of two-phase transport devices such as loop heat pipes
(LHP), capillary pumped loops (CPL), heat pipes, vapor
chamber fins, thermosyphons, and loop thermosyphons
(LTS). SINDA/FLUINT, unlike other thermal and fluid modeling software, has been enhanced over the years to specifically handle the modeling of these complex devices. The code has been used for
a variety of modeling tasks from capturing steady
state system level effects of two phase devices to
simulating detailed startup transients for component
design and sizing. SINDA/FLUINT is unique in its ability
to co-solve integrated thermal and fluid systems while
providing the complete thermodynamics of two-phase flow necessary to model
these devices accurately.
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Constant
Conductance
Heat Pipe |
Gas
Blocked Heat Pipe |
Loop
Heat Pipe |
How
to Model a Heat Pipe
Heat
pipe routines built into SINDA/FLUINT provide fast
system-level solutions to modeling heat pipes when
a full two-phase solution is not required. Both constant
conductance (CCHP, also called FCHP), with or without
noncondensible gas (NCG), and variable conductance
(VCHP) pipes can easily be simulated. Unlike other
non-CRTech heat pipe routines, this routine was written
specifically to co-solve wall temperatures and gas-front
locations, resulting in a more robust tool. The methods used in the built-in subrouintes are based on the following recommended modeling methods.
How
Not to Model a Heat Pipe
- A common "trick" is to model a heatpipe
as a bar of highly conductive material. However, that
method does not simulate a heat pipe's length-independent
resistance, cannot account for differences in film
coefficients between vaporization and condensation,
and cannot be extended to include NCG effects. Another
misconception is that heat pipes, being two-phase
capillary devices, require detailed two-phase thermohydraulic
solutions. While codes capable of such details exist,
such as CRTech's SINDA/FLUINT, such an approach would
represent computational overkill in almost all cases:
even heat pipe vendors use simpler calculations when
designing heat pipes.
FloCAD®, a Thermal
Desktop® module, provides
a unique tool for modeling heat pipes within a CAD
based environment. Complex geometries, such as serpentine
condensers or large networks of heat pipes, can easily
be generated.
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Flat
Heat Pipe for
Electronics Cooling
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Two
Phase Condenser |
HEATPIPE and HEATPIPE2
features:
- Constant
(fixed) conductance heat pipes (CCHP, FCHP) and
vapor chamber fins
- 1D
or 2D thermal model (axial, axial and circumferential,
rectangular)
- Distinct
vaporization and condensation coefficients for
grooved designs
- Prediction
of QLeff (power-length product)
- Optional
inclusion of noncondensible gas (NCG) degradation
- Fast
and easy geometric model generation using FloCAD,
including bonding or contact to thermal surfaces
and solids and even to other heat pipes
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| Intel
Xeon™ CPU Chip with Embedded Finned Heat
Pipes |
- Additional
features for variable conductance heat pipes (VCHP)
- Choose
working fluid from library or define a new fluid
- Perfect
gas or real gas descriptions for control gas
- Fast
and stable 1D (flat front) gas blocking algorithm
- Warnings
for erroneous designs, gas charges, environments
How
to Model a Loop Heat Pipe, Capillary Pumped Loop, or Loop Thermosyphon
The methods for modeling LHP, CPL, and LTS are very different than modeling heat pipes. Unlike a heat pipe, these devices require full thermohydraulic modeling of the fluid and containment system. SINDA/FLUINT has several features which make it uniquely capable of modeling two-phase capillary loops. The methods use for modeling CPLs and LHPs have been validated through correlation to test data.
Unique features relevant
for analyzing LHPs, CPLs, and LTSs include:
- Complete
thermodynamics: phases appear and disappear as conditions
warrant
- Capillary modeling tools for static or vaporizing
wicks
- Vapor trapping (up to the bubble point) in
capillary devices
- Capillary flow regulators (constant back-pressure
devices)
- From top-level steady-state evaporator-pump
modeling to
detailed tracking of unsteady liquid/vapor interfaces
within wicks
- Full phasic nonequilibrium two-fluid modeling
for unsteady hydrodynamics in heat pipes, LHP
compensation chambers, etc.
- Two-phase heat transfer correlations built-in
or user-defined
- Two-phase pressure drop correlations built-in
or user-defined
- Automatic flow regime mapping
- Homogeneous and slip flow modeling, including
countercurrent flow in the presence of gravity and
other accelerations
- Conservation of total charge mass for accurate
pressure predictions in transients or parametric
studies
- Complex liquid/gas mixtures including optional
dissolution of any gaseous solute into liquids
- Fast and easy geometric model generation of condensers
(serpentine, manifolded, etc.), including bonding
or contact to thermal surfaces and solids, using
FloCAD
LHP Sample Models - LHP sample models are available on request. Please contact C&R Technologies.
Sample
applications include:
Supporting
Resources
- A
free online training is available
Customization
and Consulting
CRTech
also provides consulting and custom software solutions
to specifically meet your needs. |
