Study On Flow And Heat Transfer Of Stirling Engine With Carbon Dioxide Working Medium

Renewable energy development is an important way for China to promote energy transition.more and more attention is paid to the field of CSP.The Stirling engine is the core equipment of the dish solar thermal power generation system,and its efficiency and power will determine the power generation capacity of the entire system.CO₂ as a Stirling engine circulating medium can improve the safety of the machine,reduce costs,extend the machine’s operating time,and reduce the frequency of gas replenishment.Therefore,the oscillating flow characteristics of CO₂ in a Stirling engine are studied.First,the FVM（Finite Volume Method）was used to model the metal mesh with different pores and diameters,and then Fluent software was used to simulate gas flow（air and CO₂）in the wound woven wire under different inflation pressures,operating frequencies,hot end temperatures.Finally,the correlations of flow resistance coefficient and Nusselt number of CO₂ are obtained by calculation.It was found that the flow resistance correlation of CO₂ in the cold blowing and hot blowing processes was significantly different.In addition,the flow resistance coefficient of CO₂ is greater than the flow resistance coefficient of air with 144<Re<3587.When the Reynolds number is low（Re<1733）,the difference is greater than 10%,under the high Reynolds number（1733<Re<3587）,the difference is less than 10%.The cyclic average flow resistance coefficient formula isf=320.9/Re+7.331/Re^{0.1 96}.Compared with air,the Nusselt number of CO₂ is larger when the Reynolds number is low.As the Reynolds number increases,the Nusselt number of air gradually exceeds that of CO₂,and the difference is more obvious especially at high Reynolds numbers.The final correlation is:Nu=-1.7575+5.79668×Re^0.30901.Subsequently,experimental and simulation studies were also performed on the hysteresis characteristics and cycle rate of carbon dioxide.The error of pressure and pressure drop of test sections between the experimental and simulation results were both less than 10%.Then the model was applied to higher pressure and frequency conditions and it was found that different inflation pressures and gas types had less influence on speed-pressure hysteresis and cycle rate,while the operating frequency and mesh size had a greater effect on both.Therefore,both the hysteresis angle and the circulation rate at the inlet of the regenerator are fitted into the functions of working frequency and the mesh size.This can be used in design procedures to develop more efficient regenerators.Finally,a CO₂module is added to the improved Simple model to evaluate the performance of Stirling engine.With the CO₂ calculation module enabled,the error ranges of power and efficiency between experimental and simulation results are:3.9%¹6.7%、10.2%¹6.5%.What’s more,the output power accuracy of the model is improved by14.3%²8.5%,the output power and the efficiency error range have been reduced:55.9%,72.7%,so theoretical support for the development of CO₂ Stirling engines is provided and the applicability of the improved Simple model to different gas working fluids is improved.