Design Calculation of Compact Plate and Fin Type of Heat Exchanger for Helium Liquefaction System

Abstract

Heat Exchanger Play a very important role in the field of Cryogenic application (specially in the Liquefaction of Gas Industry). For liquefaction of the gases, heat exchanger must have effectiveness greater than 0.95. No liquid yield if the effectiveness is less than 0.95 there. Therefore, best choice is to use Plate Fin Heat Exchanger for liquefaction. Plate Fin Heat Exchanger (PFHE) is very Famous in the field of cryogenic because of their high compactness (Surface area to volume ratio is very high nearly 1000), low weight and high effectiveness. It consists of stack of alternate flat plates called parting sheets and fins, both being brazed joint together as a block. Hot fluid and cold fluid exchange heat by flowing along the passages made by the fins between the parting sheets. Separating plates act as the primary heat transfer surfaces and the fins act as the secondary heat transfer surfaces intimately bonded to the primary surface. Aluminium is the best material for compact Plate Fin Heat Exchanger. In the present study plate fin heat exchanger with three fluids is used where first fluid is high pressure helium gas, second fluid is low pressure helium gas and the third fluid is liquid nitrogen. The experiment is conducted with different mass flow rates. Effectiveness, Heat transfer coefficient, Number of Transfer Unit (NTU) and Overall heat transfer coefficient of the plate fin heat exchanger have been calculated using different correlations obtained from the literature and the experimental data (related to temperature, mass flow rate and pressure drop) collected from the present experiments. Good effectiveness is found, when Liquid Nitrogen is used, because of better heat transfer due to high temperature difference. The calculation is done with or without axial heat conduction, with or without longitudinal heat conduction. It is observed that effectiveness decreases (by a percentage of .908%) when axial heat conduction is considered.