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

FloCAD online training

Class times: May 2 & 4 from 10am to 2pm MT

Cost: $425

This online class will provide an introduction to fluid modeling components within FloCAD. The class will be held over a 2-day period, with daily sessions running approximately 4 hours each. The class uses a mixture of lecture, demonstrations, and self-paced tutorials to allow attendees to practice building fluid system models and interpreting results. The presentations will comprise 2 - 3 hours of each session, and the instructor will be available during the remainder of the time for questions during tutorials. Attendees must have basic working knowledge of SINDA and Thermal Desktop as these topics will not be covered but their usage is required for FloCAD.

Register here

Thermal Desktop, RadCAD, and TD Direct in-class training

Date: April 25-28, 2017, 8:00 a.m. to 5:00 p.m., daily
Location: Lakewood, CO

CRTech will be hosting introductory training for Thermal Desktop, RadCAD and TD Direct. Lecture and hands-on tutorials introduce attendees to basic Thermal Desktop and RadCAD usage and allow practice building models and interpreting results. The class will also introduce students to SpaceClaim direct modeling CAD interface and advanced meshing tools in TD Direct.

Daily Schedule

Day 1 and 2: Introduction to SINDA and Thermal Desktop
Day 3: Introduction to RadCAD
Day 4: Introduction to TD Direct

To learn more about this class and to register, visit our Training Page.

Anode and cathode of a flow battery

Using Sinaps? It is not too soon to get started with TD/FloCAD!

This webinar describes the process for converting from Sinaps to Thermal Desktop (TD) and FloCAD. This process includes using an exporter which works with Version 6.0 of the CRTech tool suite (expected to be released in May of 2017).

Come learn about the basics of TD/FloCAD, including many compelling features not available in Sinaps. The webinar will also cover how to manage the transition period, during which you may be using both programs simultaneously. This is also a chance to ask questions. 

If you missed this webinar, please contact us for the presentation material and recording.