Abstract
Despite of the large number of research dedicated to condensation heat transfer and pressure drop characteristics in pristine micro-fin tubes, experimental investigation on effects of tube expansion have not been reported in the open literature. The paper reports measured cross-sectional dimensions, condensation heat transfer and pressure drop data of R1234ze(E) in pristine (5.10 mm OD) and expanded (5.26 mm OD) micro-fin tubes with mass fluxes from 100 to 300 kg/(m2·s). Effects of mass flux, vapor quality and tube expansion on the heat transfer coefficients and friction pressure gradients were investigated in the study. When the mass flux is 100 kg/(m2·s), the heat transfer coefficient and pressure drop of R1234ze(E) decrease after tube expansion. However, when the mass fluxes are 200 and 300 kg/(m2·s), tube expansion effects on the heat transfer coefficient and pressure drop are not notable. In addition, the experimental results are analyzed based on the existing condensation heat transfer and pressure drop correlations.
Highlights
Since the invention of Fujie et al (1977), micro-fin tubes have been widely used in refrigeration and air-conditioning systems for high heat transfer and relatively low pressure drop performance
The results showed that the in-tube heat transfer performance of copper and aluminum tubes reduced by 9–36% after the tube expansion
In order to verify the reliability of the experimental system, single-phase heat transfer experiment of R1234ze(E) was conducted in 5.10 mm OD micro-fin tube
Summary
Since the invention of Fujie et al (1977), micro-fin tubes have been widely used in refrigeration and air-conditioning systems for high heat transfer and relatively low pressure drop performance. For finned tube heat exchangers, micro-fin tubes and the external fins must have a metal-to-metal interference fit to decrease the contact thermal resistance. Mechanical tube expansion process is used to expand the tube outside diameter which is forced against the external fin collar leading to an interference fit. The tube internal enhancements will be deformed or crushed to varying degrees for the mechanical expanding effect. The internal surface area of the micro-fin tube will be affected by tube expansion. Tube expansion may cause the negative effect on the thermal-hydraulic performance of finned tube heat exchangers
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