In this study, the condensation heat transfer coefficient and pressure drop of steam are obtained in small rectangular tubes with different aspect ratios. The experiments were carried out on three rectangular tubes with aspect ratios of 1:2, 1:3 and 1:5, with mass flux between 25 and 45 kg/m2s, and vapor qualities between 0.1 and 0.8. The experimental data were analyzed to determine the effect of vapor quality, mass flux, and aspect ratio on the heat transfer coefficient and pressure drop. The results showed that the effect of aspect ratio on condensation heat transfer coefficient appears to be dependent on the flow pattern. For stratified flow, the condensation heat transfer coefficient increases as the mass flux increases. For annular flow, the condensation heat transfer coefficient hardly changed. The pressure drop always increases as the aspect ratio increases. Previous studies on round tube heat transfer and pressure drop correlations have not successfully predicted the small rectangular tube data; therefore, modified Shah correlation and Lockhart & Martinelli correlation are proposed, which predict the data with 20% and 23% RMS error, respectively.
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