Conjugate Heat Transfer Analysis in Cryogenic Microchannel Heat Exchanger

Abstract

Printed circuit heat exchanger (PCHE) is a highly integrated plate type compact heat exchanger and most important as well as a most critical component in the cryogenic application. Compact heat exchangers are characterized by area density (? = AHT / V) i.e. heat transfer area per unit volume of the heat exchanger. The area density of compact heat exchanger is =700m2/m3 where the area density of printed circuit heat exchanger is = 25000m2/m3. Printed circuit heat exchangers are highly compact compared to conventional heat exchangers. The hydraulic diameter is less than 1mm. Printed Circuit Heat Exchanger manufacturing process is followed by chemical etching and chemical bonding. Microchannel for fluid flow are constructed by chemical etching of the metal plates according to different configuration then plates are stacked alternately and assembled by diffusion bonding. Due to its compact size, high efficiency, large heat transfer area PCHE (microchannel heat exchanger) are used in cryogenic refrigeration and liquefaction systems. A counter flow rectangular microchannel (40 mm × 1.6 mm × 1.2 mm) printed circuit heat exchanger is designed and simulated using commercial ANSYS FLUENT. The performance is investigated numerically with helium at cryogenic temperature. The performance is affected by axial conduction at low Reynolds number (Re = 100). Because of length and viscous nature, the fluid flow through the channel is laminar and thermally fully developed. The Nussle number (Nu), flux, dimensionless fluid temperature and wall temperature, effectiveness are determined for different Reynolds number Reynolds number (Re = 100) with varying material i.e. wall to fluid thermal conductivity ratio (ksf = 141.58 - 5061.5). Axial conduction (?) is calculated by using Kroeger’s equation. Effectiveness is calculated to investigate the thermal performance of the microchannel heat exchanger.