CFD Analysis For Finding Axial Thermal Conduction Effect In Cryogenic 2 - Stream Counter Flow Plate Fin Heat Exchanger

Abstract

Thermal effectiveness of heat exchangers, used in the process cycle, is one of the important parameters which decide the efficiency of helium refrigerator/liquefier (HRL). To achieve high effectiveness, it is necessary to use plate-fin heat exchangers, which provides very high heat transfer surface area per unit volume of heat exchanger. Such heat exchangers also have benefit of low pressure drop of fluid flowing through it. These cryogenic heat exchangers will be placed within a vacuum chamber having vacuum of about 10-5 mbar and hence compact heat exchangers are preferred to reduce the size and cost of the vacuum chamber. Due to the compactness in size, there is axial heat conduction through aluminium metal medium from higher to lower temperature. As per the chosen thermodynamic configuration of indigenous HRL, it will have 8 cryogenic vacuum-brazed aluminium plate-fin heat exchangers. This HRL can produce liquid helium at 4.5 K and can operate as refrigerator-cum-liquefier with equivalent cooling capacity of about 1 kW at 4.5 K. This project work is for the analysis using CFD (Computational Fluid Dynamics) software for the heat exchanger which will operate in the temperature zone 300 to ~90 K. In this temperature zone, minor property variations in the helium fluid will be there, which will be accounted in this CFD analysis. It has 2 streams (He/He) in counter flow configuration. These 2 streams of helium _ow are at 2 different pressure: high pressure (HP) helium gas stream of ~ 14 bar coming from the compressor system and the low pressure (LP) helium stream of ~1 bar going back to the compressor suction from the liquid helium (LHe) Dewar. The tentative flow rates of LP and HP streams are same and ~65g/s, for nominal operation. This project will involve understanding the design done by analytical and empirical correlations and finding the axial conduction by analysis in CFD taking into account of actual complex fin configurations used in the design.