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

 

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.