Thermosiphons

Thermosiphons and Loop ThermosiphonsMRI machine, cryogenic magnet

Single phase and two phase loop thermosiphons (LTS) are used across multiple industries such as solar thermal hot water heating, electronics cooling, gas-fired heaters, and nuclear reactor cooling, and cryogenic magnet cooling. Since the operation of thermosiphons and loop thermosiphons is based on the natural circulation due to changes in fluid density in a gravity environment (buoyancy), the modeling of such systems can be challenging, especially in the presence of two-phase evaporation and condensation. With two-phase thermosiphons not only are density and gravity a factor, but you must also capture pool boiling and the falling water droplets as the fluid condenses.

A simple thermosiphon is a vertical pipe where liquid pools at the bottom and when heated, vapor rises in the middle of the pipe while liquid condenses near the top and fall down along the pipe walls. A higher-performing design is a loop thermosiphon (LTS), which separates the down-flowing liquid from up-flowing vapor (or two-phase) streams. Subcooling and superheating can occur more readily in such a loop. In some designs, liquid flows downward and two-phase fluid flows upward. In others, a two-phase mixture flows downward and vapor flows upward. As long as one line has a higher time-averaged density than the other, circulation will occur. An LTS self-determines both the pressure and the flow rate, and the flow rate is often unstable: intense, short time-scale oscillations and even temporary flow reversals are common.

Fortunately SINDA/FLUINT and FloCADĀ® provide the necessary tools required to capture all of these phenomena for both steady state and transient simulations. There are multiple approaches to modeling a thermosiphon depending on the design of the system and what data you need from the analysis.

To aid in demonstrating these options, CRTech has created the following sample models:

Unique features relevant for analyzing LTSsPostprocessed model of solar thermal collector panel with thermosyphons

  • Complete thermodynamics: phases appear and disappear as conditions warrant
  • 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
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.