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26th National Symposium on Cryogenics & Superconductivity (NSCS - 26) PS2-35
Analysis of Porous Regenerator material of Stirling cryocooler using

numerical techniques
R. D. Pokale 1, K V Srinivasan2, S U Bokade 1, A Manimaran3, Arul Prakasajothi3
1
M. C. T. RAJIV GANDHI INSTITUTE OF TECHNOLOGY, Andheri, Mumbai - 400 053 rahulpokale7310@outlook.com
2 Low Temperature Facility, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai – 400005. kvsrini@tifr.res.in
3School of Mechanical Engineering, Veltech Dr RR & Dr SR Technical University, Avadi, Veltech Road, Chennai – 600062. mullaimaran@rediffmail.com
INTRODUCTION
The regenerator is the key element of Stirling cycle cryocooler and performance of the regenerator directly affects the cryocooler performance. Regenerator is a compact
periodic heat exchanger in which the fluid is in direct contact with the solid heat transfer area. Thus, it is essential to have an idea about regenerator geometry, parameters
and their effects on the system. Porous materials type regenerator of the existing Stirling cycle cryocooler is considered. Porosity is one of the parameter which determines
the thermal and flow characteristics of regenerator and thus its performance. Predicting the porosity by analyzing sintered regenerator is the aim of the project. Assuming
the mass flow rate through the regenerator as constant, energy equations for matrix and helium gas working fluid is studied. Using the energy balance and continuity
equation, matrix and fluid thermal equations are derived. CFD simulation has been carried out using ANSYS 16.0 and the porosity of the regenerator is predicted using the
REGEN 3.3 Numerical Analysis Software for Regenerators. The obtained results are compared with the results of open literature.
Regenerator
Cryogenic regenerator is the heart of a cryocooler, which is a very efficient compact heat exchanger that has the capability of quickly transferring and storing heat from a gas,
which passes through it. It plays a major role in obtaining lower expansion space temperature for cryo-coolers. Out of four processes of Stirling cryocooler, two processes take
place inside the regenerator. It is a storage type heat exchanger which is made from material having high specific heat even at low temperature. A regenerator is a
bidirectional storage type heat exchanger. The design of cryogenic regenerator is a challenging task. Temporary storage of heat or thermal energy of working fluid. Very
important component to materialize Stirling cycle in a real machine. A regenerator is very difficult to design. The ideal regenerator would be of very high thermal capacity,
have no internal volume yet infinite flow area, infinite surface area, high heat transfer area, low viscous pumping losses, low dead space etc. These inherent design conflicts
are one of many factors which limit the efficiency of practical Stirling engines.
OBJECTIVE OF THE PROJECT

The basic objective of this project is to predict the regenerator porosity of the existing porous type regenerator used in the
Stirling cryocooler at TIFR, Mumbai. Based on our extensive literature survey, many experiments were carried out on fibrous
& mesh type regenerator and almost no works done on the porous type regenerator material.
Approach:
To analyze the thermal and fluid characteristics of the regenerator by varying other operating parameters, and thus
predicting the porosity of the regenerator.
Tools:
• Developing a mathematical model and finding proper numerical technique for obtaining its solution.
• Finding the thermal and fluid characteristics of the regenerator using differential governing equations.
• Analyzing the regenerator model using CFD tool to study the variation of temperature inside the regenerator.
Regenerator optimization is the process of choosing regenerator design parameters that maximize system Preliminary Assumption:
performance. For cryogenics refrigerators, optimization generally refers to maximizing the available refrigeration by • The fluid is considered as incompressible and has constant properties.
systematically selecting regenerator parameters such as geometry, type of matrix design, and matrix material that • Flow is two dimensional, laminar and steady.
achieve this goal. The critical parameters affecting the thermal performance of regenerator are the number of heat
transfer units, the fluid heat capacity ratio, the matrix heat capacity ratio and the thermal losses such as the
• Analysis of regenerator only.
longitudinal conduction. • The fluid inlet temperatures are constant during heating and cooling periods.
• Mass flow rate is constant.
• The void volume in the regenerator is zero, and thus the fluid stored energy is zero
Methodology:
• Modelling and analyzing using ANSYS CFD tool for the thermal and fluid flow characteristic of regenerator.
• Analyzing the results for different mass flow rates and comparing with the results of models in literature using REGEN 3.3.
GOVERNING EQUATIONS
Temperature variation along Pressure variation along the

the Regenerator length Velocity variation along the Regenerator length
Regenerator length
CONCLUSION
Case study carried out on the existing Stirling Cryocooler at TIFR with the preliminary assumption on actual input parameters like working fluid, charging gas pressure, charged
mass flow, geometry, material, temperature and with the observed output parameters as Temperature after expansion & refrigeration quantity. With the various iterations
results using the software REGEN 3.3, the results were analyzed and the best matching Regenerator Porosity is found to be at 69.62%. Considering the available literature
survey and the experimental values for the similar regenerator porosity varies in the range of 69 –71 %, which is well matching with our results

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26th National Symposium on Cryogenics & Superconductivity (NSCS - 26) PS2-35

Analysis of Porous Regenerator material of Stirling cryocooler using

OBJECTIVE OF THE PROJECT

Temperature variation along Pressure variation along the

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