Regenerator and Regenerator-Displacer Modeling

In Stirling cycle and Gifford-McMahon (GM) cycle engines, the displacer is the piston on the cold (heat input end) of the device. GM cycles also use regenerators, as do many Stirling cycles … at least those designs intent on achieving the highest possible thermodynamic efficiency. Regenerators are also key features in pulse-tube cryocoolers, a derivative of a Stirling cycle that lacks a displacer.

Regenerators are porous bodies, usually cylindrical in shape, through which fluid passes back and forth in a cyclic motion. They are often made either of packed (but not sintered) beads, or screens stacked perpendicular to the flow direction. Regenerators are hot on one end, and cold on the other. An ideal regenerator maintains that temperature gradient: heating fluid as it enters one direction, and cooling it when it flows in the opposite direction.

The following graphic from NIST illustrates both the regenerator and the displacer, as applied in a GM cycle:

Illustration of the regenerator and the displacer, as applied in a GM cycle

To quote Wikipedia:

“A regenerator is difficult to design. The ideal regenerator would be: a perfect insulator in one direction, a perfect conductor in another, have no internal volume yet infinite flow area and infinite surface area. As with the hot and cold exchangers, achieving a successful regenerator is a delicate balancing act between high heat transfer with low viscous pumping losses and low dead space. These inherent design conflicts are one of many factors which limit the efficiency of practical Stirling engines.”

Modeling a Single Stage Helium GM Cycle

In one variation of the GM cycle, the displacer is also the regenerator: the “regenerator-displacer” is a cylinder containing a porous material. This regenerator-displacer is driven back and forth between the cold end (say of a cryocooler, perhaps used in a vacuum pump or sensor cooling application) and the hot end where heat is rejected (by exhausting out the low pressure port).

In a paper by Kimo M. Welch, the action of a single-stage R-D is nicely summarized in the figure below:

The action of a single-stage R-D

A SINDA/FLUINT (Thermal Desktop® and FloCAD®) model has been developed corresponding to the above system.

The purpose of this model is two-fold:

  • Provide guidelines for regenerator modeling (the lessons learned being applicable to stationary regenerators as well)
  • Provide a template or starting point for modeling similar designs

Chart of Valve Flow Area versus Crank Angle

Chart of Temperature versus Crank Angle

Click here to fetch the Regenerator-Displacer Example from our User Forum


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.