Numerical Modeling of a Micro-Scale Stirling Cooler

Design and Evaluation of a MEMS-Based Stirling Microcooler

“…Lee proposed a correlation of the Darcy drag d^/K and the Forchheimer coefficient F for a bank of the cylinders, given by [19] Table 1 Comparison of the regenerator effectiveness at different operating frequencies from an anaiyticai model (Eq. (21)) and COi\/ISOL multiphysics simulations [12]. Wiien the porosity is 0.798, 0.864, or 0.916, the maximum difference between the two predictions is less than 5%, giving confidence to the use of the much simpler anaiyticai model.…”

“…Predictions of the regenerator effectiveness ñ-om the NTU method and from COMSOL multiphysics simulations [12] for regenerator porosities of 0.798, 0.864, and 0.916 are presented in Table 1. In the present regenerator, the Knudsen number is less than 0.01.…”

“…Then, the actural cooling power for the system is q = hA(Tc -Tg,c) (16) In the hot chamber, the heat coming out of the hot chamber is (17) where Tf,,c and Tgjj are the gas temperature in the cold and hot chambers. The convection coefficient in the chamber is obtained from the COMSOL multiphysics simulation of the Stirling microcooler system [12]. The Nusselt number used for the calculation is Nu = O.SlóRe"'^'.…”

“…Here, we use q as the rate of the heat transfer. We start with the COP of the cooler, which is the ratio of the heat removal to the input work (12) The Camot coefficient of performance COP^, which represents the maximum theoretical efficiency possible between constant temperature heat source (Tc) and heat sink (T^), is [11] (13) COPr = - Eor r// = 313.15K and rc = 288.15K, COPç is 11.5. An estimate of the actual coefficient of performance requires knowledge of the real work input and the heat loss.…”

“…To predict the pressure drop in the regenerator (which is a microchannel containing a pillar matrix), a porous medium model is used in a COMSOL multiphysics simulation [12]. The relationship between the pressure drop and the gas velocity is then correlated by the permeability K and Forchheimer coefficient F [16][17][18].…”