Study of PocoFoam (TM) as a heat exchanger element in cryogenic applications

Abstract

Superconductors present great potential for weight reduction and increased power delivery when compared to traditional copper power delivery systems, but current systems require cryogenic cooling systems. Traditional superconductor cooling systems consist of helium cooled by helical heat exchangers made of Oxygen Free High thermal Conductivity (OFHC) copper tube. The helium is cooled by bulky heat exchangers consisting of OFHC copper coils wrapped around a cryogenic cooler heat sink for heat transfer into the working fluid. Metal foams have recently been studied in a variety of heat transfer applications, and could greatly reduce the weight of heat exchanger modules in superconductor cooling systems while simultaneously providing increased heat transfer effectiveness. Aluminum and Copper foams have been available for several years, but more recently, graphite foams, such as PocoFoam™, have been developed which have particularly good heat transfer characteristics. Using Computational Fluid Dynamics (CFD) to model a cryogenic heat exchanger application, this study examines the effectiveness and pressure drop of several metal foam heat exchangers, and compares their performance with the traditional helical coil design for superconductor cooling applications. The CFD simulation results show that a heat exchanger with the same heat sink contact area as existing helical heat exchangers weighs up to 95 percent less and can be up to 25 percent more effective, depending on system conditions such as pressure, cryogenic cooler temperature and helium inlet temperature. Aluminum and copper foam heat exchangers had comparable weight to the PocoFoam heat exchanger, but were significantly less effective than the helical or PocoFoam heat exchanger models.