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3D CFD simulation of a Vuilleumier heat pump

2019; Elsevier BV; Volume: 153; Linguagem: Inglês

10.1016/j.applthermaleng.2019.03.053

1873-5606

George Dogkas, E.D. Rogdakis, Panagiotis Bitsikas,

Thermodynamic and Exergetic Analyses of Power and Cooling Systems

A 3D CFD simulation has been conducted in order to investigate the thermodynamic and flow characteristics of a Vuilleumier heat pump. Vuilleumier heat pumps are machines with few components which need a heat source of high temperature to operate and in some cases additionally some work input. The simulated machine comprises of one cylinder inside which two displacers reciprocate. The design of the machine resembles two opposing GPU-3 Stirling engines which is an existing engine and it was based on calculations conducted with the use of a 1D analytical mathematical model. The CFD simulation run for several cycles until convergence was established and yielded the spatial and temporal distribution of the temperature, pressure and velocity inside the several spaces of the heat pump. The pressure drop along the components of the heat pump was calculated and also the flow reversal time instances at the interfaces where adjacent components coincide. Other mathematical models used in the past couldn't provide information neither about the flow direction everywhere inside the machine nor about the opposing flow streams inside the common compression space. Moreover, the CFD model provided the heat quantities entering or exiting the heat pump. The two heat exchangers that are placed in order to absorb heat, resulted to reject heat for a small time period during the cycle from a section of their body. Furthermore, the heat flow did not follow strictly the temperature difference between the bulk gas and the solid wall. It was driven by the temperature difference between the gas near the wall and wall. This discrepancy indicates a counter flow inside the tubes of the heat exchangers. Finally, it was expected that the CFD machine would require an amount of work to operate, because it was designed based on an analytical model without losses. So, the CFD simulation, which includes pressure drop losses, resulted to require additional external work, which can be minimized designing a thick cold displacer rod.