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The present study investigates the Joule-Thomson (JT) effect due to pressure drop on three-fluid heat exchangers (HXs) with three thermal communications. The increased miniaturization of cryogenic HXs has led to the introduction of the JT effect. The present study investigates JT effects on a three-fluid HX with three communications presenting different JT effects, which leads to a rise or drop in effectiveness values. The study is carried out using finite element analysis and MATLAB, considering seven nondimensional parameters of which one is JT pressure drop. The highest effectiveness is achieved for the positive JT effect at the hot stream. This improved effectiveness at hot fluid is achieved by maintaining the size (number of transfer units) of the HX more than 3.1, along with the ratio of the cold fluid heat capacity to the hot fluid heat capacity above 0.8 and the intermediate fluid temperature above 0.7.

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Purpose The purpose of this paper is to attain higher effectiveness with an introduction of Joule–Thomson effect on a three-fluid heat exchanger with two communications. It also gives a range of parameter values that have to be maintained for achieving effectiveness above 0.85. Attaining effectiveness above 0.85 is very important for the heat exchanger to perform the liquefaction of hot fluid. Design/methodology/approach The analysis is conducted using Galerkin’s method, a finite element approach. Findings This investigation determines crucial values for the cryogenic heat exchanger to achieve effectiveness above 0.85. The important findings are as follows: effectiveness above 0.85 is attained if the heat exchanger size is within the range of 8–10; ratio of heat flow resistance between intermediate and hot stream to heat flow resistance between cold and hot stream should be maintained between 1 and 10; the intermediate fluid temperature should be maintained between 0 and 0.2; the ratio of thermal capacity of the hot fluid relative to a cold fluid should be maintained between 1.25 and 1.42; and the ratio of thermal capacity of the hot fluid relative to an intermediate fluid should be maintained between 2 and 2.5. Research limitations/implications The investigation has presented a finding for improving the effectiveness of the cryogenic heat exchanger. Higher the Joule–Thomson pressure drop effect, more is the drop in temperature of the fluid resulting in additional cooling or lowering of the fluid temperature. The practical implementation is also explained, i.e. to achieve practically the Joule–Thomson pressure drop in a cryogenic heat exchanger. Originality/value To the best of the authors’ knowledge, no investigations were carried out previously on Joule–Thomson investigation on a three-fluid heat exchanger with two communications, for different values of Joule–Thomson pressure drop.