Loop Heat Pipes (LHP)

Modeling Loop Heat Pipes and other Capillary Devices

TadSat4 Loop Heat PipeThe methods for modeling LHPs and capillary pumped loops (CPLs) are very different from those used to model heat pipes. Unlike a heat pipe, self-pumping loops require full thermohydraulic modeling of the fluid and the thermal-structural environment. In addition to supporting the modeling of single-phase pumped loops, SINDA/FLUINT and FloCAD® have several features which make them uniquely capable of modeling two-phase pumped loops and capillary pumped pumps. Using SINDA/FLUINT and FloCAD, you can capture everything from the system-level effects of the LHP all the way down to detailed thermodynamic and hydrodynamic transient events such as LHP start-up, compensation chamber (reservoir) quenching, partially primed wicks, and pressure and flow oscillations.

When it comes to modeling two-phase loops, SINDA/FLUINT has the unique advantage over other fluid flow codes in that a portion of the software development team (engineers by training) were actively involved in the development of CPLs and LHPs during the late 1980s and 1990s, while they were also working on the development of SINDA/FLUINT. Consequently, when obstacles were encountered in the process of modeling these two-phase loops, new features were added to the software to overcome previous simulation limitations. Such features include interface elements ("IFACEs") for modeling compensation chamber and the liquid/vapor interface within the wick, a capillary evaporator pump, and a capillary device to model wicks, grooves, tubules, and so forth. During this time period, the ability to model lack of thermal equilibrium within the compensation chamber was also added to better estimate start-up responses.

Unique features relevant for analyzing LHPs and CPLs

  • 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 used in parallel condensers)
    • 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 LHP compensation chambers
  • 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 Thermal Desktop.

LHP with Serpentine Condenser Line, postprocessed FloCAD model shown on the right

Resources

Please visit our support forum for a sample of how to model an LHP, or for an advanced example.

An example of a CPL system, used to illustrate automated tools to calibrate models to test data, is available here.
 

Publications

Advanced Pipes in FloCAD
Thursday November 14, 9-10am MT (8-9am PT, 11am-noon ET)
This webinar introduces advanced features for FloCAD pipes in addition to working with complex geometry. Complex geometry includes interior fins and surfaces for heat transfer, flow around enclosed objects, annular flow, concentric pipes, and more. FK Locators and TEEs as modeling objects will also be introduced.
Custom Heat Transfer and Pressure Drops
Tuesday November 19, 2-3pm MT (1-2pm PT, 4-5pm ET)
Do you know what the default assumptions are in FloCAD, and whether or not they apply in your situation? Do you know how far you can go past that starting point? The answer: pretty far. There are numerous mechanisms in FloCAD for adjusting factors, scaling uncertainties, and applying different or supplemental correlations. This webinar summarizes the options available to you to customize your flow models to make sure that they apply to each new situation you encounter.
Heat Exchangers: Detailed and System-level
Thursday November 21, 2-3pm MT (1-2pm PT, 4-5pm ET)
This is two webinars in one. The first explains the use and assumptions behind the FloCAD HX system-level modeling object. The second webinar describes detailed-level modeling of complex heat exchanger passages, including application of Compact Heat Exchanger (CHX) methods.
Starting in 2020, we will begin offering Introduction to Thermal Desktop and Introduction to RadCAD as either in-person training or online training, alternating between online and in-person every three months. The training uses lectures and demonstrations to introduce you to basic Thermal Desktop and RadCAD usage. Hands-on tutorials provide practice building models and interpreting results (tutorials are completed by students outside of the online class time).
 
The next training class will be an online format in January 2020:
  • Introduction to Thermal Desktop (and SINDA) - A three-part series on January 14, 16, and 21 from 9am to 12pm, Mountain time
  • Introduction to RadCAD - January 23 from 9am to 12pm, Mountain time
For up-to-date schedules, fees, and policies, visit our Product Training page. To register for the class above, complete our registration form and select "Online" for the Training Format.
 
If you are interested in product training for your company based on your schedule, please contact us to obtain a quote for training between 8-12 attendees. We can come to your facility or the lectures can be presented online. Descriptions of the available classes can be found in our course catalog.
 
To keep up with our training opportunities, take a look at our new Events and Training Calendar.