Muluken GETIT : Numerical modeling and optimization of a regenerative Stirling refrigerating machine for moderate cooling applications

Abstract : The Stirling cycle machine has many successful applications as a prime mover and cooling machine. The Stirling cycle heat engine has a good potential for use in the future because of some advantages like external combustion, and fuel flexibility. The Stirling machine is used in cryogenics but applications for domestic cooling are still underdeveloped. The main goal of this study is to develop a precise thermodynamic numerical model that could predict the performances and provide means for further optimization. Hence, this dissertation presents the numerical modeling, simulation, experimental validation, and parametric optimization of an air-filled Beta type Stirling refrigerator for domestic application.

The research shows that a non-ideal second-order numerical model called the modified simple model has been developed. The model incorporates effects of shuttle heat loss and mass leakage loss to the buffer space directly to the differential equations of pressure change, rate of change of mass of gas in compression and expansion spaces, and mass flow rates across these working spaces. Moreover, other power losses and heat losses are included as independent losses to evaluate the cooling production and associated COP. The model is simulated using MATLAB code for Beta configuration FEMTO-60 Stirling engine operating as a refrigerator. The model is validated both with an experiment conducted in the FEMTO-ST laboratory in refrigerating mode and by reversing the model to work producing engine, so that the validation could be made with different theoretical models developed by other scholars so far. The validation results confirm that the proposed numerical model could be used to design a Stirling cycle refrigerating machine with reasonable accuracy. The contribution of this study also includes investigation of the effect of different working fluids (air, nitrogen, hydrogen and helium), effects of losses (shuttle heat and mass leakage) that have a direct effect on the operating condition of the cooling machine and parametric optimization. Air and nitrogen showed better cooling performance than helium and hydrogen mainly due to the higher mass flow rate. The effects of incorporating shuttle heat loss in the differential equations on the temperature and pressure of working gas and the overall performance of the Stirling refrigerator are analyzed. Parametric optimization includes the effect of operating (rotational speed, charging pressure, and temperature) and geometrical (phase angle, regenerator length, porosity, displacer height, displacer gap, piston-cylinder clearance gap, swept volume ratio, and piston diameter to stroke ratio) parameters on the cooling performance as well as on share of different power and heat losses. Finally, we propose a set of parameters to optimize a refrigerating Stirling machine achieving a COP of 129\% for a cooling power of 625 W at a temperature of -4°C.

It will be presented in English as the research has been conducted in English. Due to the current sanitary restriction, it will be podcasted online.

You could follow with the following link:

: https://teams.microsoft.com/l/meetup-join/19:xtxveZLw6XqHPaUCBvrGzxxbQm4Hhv5aFjQRER-zQxE1@thread.tacv2/1624463002883?context=%7B%22Tid%22:%22ca5a017f-00e6-423c-a8c6-0a1b459f6827%22,%22Oid%22:%2242db5d95-3ca2-4ed8-b53e-e8ecc4e99e24%22%7D

Localization : Energy Department- Parc Technologique - Belfort