Analysis of Two-Stream (He/He) Cryogenic Plate-fin Heat Exchanger using CFD

Abstract

Effectiveness of heat exchangers is one of the important parameters which decide the efficiency of helium refrigerator/liquefier. 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. As per the chosen thermodynamic configuration of indigenous HRL, it will have 8 heat exchangers. It can produce liquid helium at ~4.5 K and can operate as refrigerator-cum-liquefier with equivalent cooling capacity of about 2 kW at 4.5 K. This project work is for the design and analysis using CFD (computational fluid dynamics) software for the heat exchanger which will operate at the lowest temperature zone between 7 to 4.5 K. In this temperature zone, there is large non-linear property variations in the helium fluid which will be accounted in this CFD analysis. It has 2 streams (He/He) in counter-flow configuration. These 2 streams of helium flow are at 2 different pressures: high pressure (HP) helium gas stream of ~4 bar coming out of the 3rd turbine after expansion from ~13 bar to ~4 bar and the low pressure (LP) helium vapor 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 ~90 g/s and ~100 g/s for nominal operation. This project will involve design and analysis taking into account of the manufacturing, assembly and maintenance aspects and different off-normal operational conditions. It will also involve the study of capabilities and deficiencies of Indian Industries to manufacture high performance heat exchangers and try to find ways to remove these deficiencies towards realizing such heat exchangers indigenously.