Joule-Thomson (JT) Cooling

Joule-Thomson Design and Analysis

CRTech tools are used to model the complexities of Joule-Thomson or JT cooling systems, as either blow-down systems or closed cycles (e.g, Linde-Hampson). Because they provide compact and vibration-free cold heads, such coolers are popular for cooling of sensors and electronics including cryogenic and MEMS (microcooling) applications.

The combination of SINDA/FLUINT plus FloCAD® (an optional Thermal Desktop® module) can be used for detailed modeling, system-level modeling, and sizing and sensitivity analyses of cold heads and other heat exchangers.

Key features relevant for analyzing JT cooling systems include:

  • Real-gas and saturation dome properties readily available for the most commonly used fluids including hydrogen, helium, nitrogen, argon, CO2, methane, and propane. Additional and custom fluids (e.g., mixed gas coolers) descriptions can be created by CRTech or the user.
  • System-level heat exchangers (e.g., NTU, UAtot, effectiveness) for sizing (e.g., set an outlet temperature) and for high-level simulations
  • Complex heat exchangers in cold heads and in multi-stage coolers (regenerators, recuperators, intercoolers)
  • Transient analyses including tank blow-down and structural cool down
  • Expansion into the dome including two-phase heat exchange. See also Two-phase Flow Analysis.
  • Arbitrarily complex control systems (PID etc.) applied to valves, compressors, etc.
  • Access to parametric modeling and Advanced Design Modules (optimization and sizing, automated model calibration to test data, reliability and statistical design, etc.)

Sample Model of a JT Cold Finger

A sample model is available to illustrate the application of SINDA/FLUINT and Thermal Desktop/FloCAD to the modeling of the Joule-Thomson cycle. These examples demonstrate:

  • JT cryostat analysis
  • Design optimization and dynamic blow-down (chilldown) analysis
  • Modeling of labyrinth seals (even though they purposely leak in this application)
  • Modeling of heat exchangers, at both the system and detailed levels
    • Including application of compact heat exchanger (CHX) methodology
  • Use of FloCAD for both sketch-pad modeling and for geometric modeling

The models with documentation are available for download.

Click here to fetch the JT Modeling Example from our User Forum

 

dispersed vs. coalesced front

Tuesday, June 26, 2018, 1-2pm PT, 4-5pm ET

This webinar describes flat-front modeling, including where it is useful and how it works. A flat-front assumption is a specialized two-phase flow method that is particularly useful in the priming (filling or re-filling with liquid) of gas-filled or evacuated lines. It also finds use in simulating the gas purging of liquid-filled lines, and in modeling vertical large-diameter piping.

Prerequisites: It is helpful to have a background in two-phase flow, and to have some previous experience with FloCAD Pipes.

Register here for this webinar

FloCAD model of a loop heat pipe

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 is designed to be attended in the order they were presented. 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.