Experimental investigation and correlation development for two-phase pressure drop characteristics of flow boiling in offset strip fin channels

Abstract

The plate-fin heat exchangers with pressure-resistant offset strip fins are widely used in the C3MR and other liquid natural gas (LNG) systems, and the two-phase pressure drop characteristics of flow boiling in pressure-resistant offset strip fin channels is a crucial factor for designing and optimizing the compact heat exchangers. A cryogenic experimental rig was established to obtain two-phase pressure drop data in the present study and the fin thickness of 0.4 mm is selected based on an actual compact heat exchanger in the C3MR LNG liquefaction system. The tested fluid is R22, and the experimental conditions include mass fluxes of 64–128 kg/(m2·s), vapor qualities of 0.1–1.0, saturation pressures of 0.22–0.26 MPa, and heat fluxes of 0.7–5.5 kW/m2. The comparison between the obtained data for fin thickness of 0.4 mm and those for fin thickness of 0.1–0.4 mm in literatures show that, the friction factor f of gas flow in channels increases with the increasing fin thickness, and the increment is 306%–451% as the fin thickness increases from 0.1 mm to 0.4 mm. The research results of two-phase flow show that, as the vapor quality increases, the frictional pressure drops initially increase and then decrease, representing a maximum at vapor quality of 0.90. With the increment of heat fluxes, the average vapor quality increases, resulting in the increasing frictional pressure drops. The two-phase multiplier of two-phase pressure drop varies from 3 to 35 and increases with the decreasing fin thickness and hydraulic diameter. A new correlation of two-phase pressure drops in offset strip fins with different fin thicknesses was developed within a deviation of ±25%.