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Abstract

This paper presents the experimental test results for two 2nd generation Micro-Electro-Mechanical Systems (MEMS) heat exchangers that are a composite of silicon plates with micromachined flow passages interleaved with glass spacers. The MEMS heat exchangers were designed for use as the recuperative heat exchanger within a Joule-Thomson (JT) cycle used to energize a cryosurgical probe. The heat exchangers were tested using two different methods. The first method utilized a cryocooler to provide the cooling at the cold end of the heat exchanger. This method allows a large temperature difference to be applied to the heat exchanger with a minimal pressure difference between the streams, and therefore allows accurate testing with little risk of failure. The second test method installs the heat exchanger in a JT cycle using either a micro-valve or orifice to create the isenthalpic pressure drop. A numerical model that includes estimated heat leaks was used to predict heat exchanger performance. The results of the numerical model are compared with experimental test results over a range of conditions. The second MEMS heat exchanger was fabricated with integrated platinum resistance thermometers (PRTs). Therefore, test results include spatially resolved internal temperature distributions, allowing detailed comparisons with the numerical model.