Influence of surface structure and tube material on the condensation heat transfer coefficient of n-pentane on horizontal single tubes and in tube bundles

Pure n -pentane was condensed on the outside of horizontal tubes with different geometries at a vapor temperature of 40 °C to investigate the influence of tube geometry on the condensation heat transfer coefficient α cond . The experimental matrix comprised a smooth copper tube, copper finned tubes with systematically varied fin density and fin height, a copper high-performance tube (HPT), and finned tubes made of a copper–nickel alloy. For each geometry, the condensation heat transfer coefficient α cond was evaluated as a function of the heat flux q ̇ . Additionally, the influence of the tube bundle effect on α cond was studied by controlled condensate irrigation. For the 0.9 mm low-finned Cu tubes, α cond increases with fin density up to 40 fpi and then reaches a plateau. At 30 fpi, the 0.9 mm tubes yield higher α cond than the corresponding 0.6 mm tubes for both Cu and CuNi, with a larger relative increase for Cu. For the HPT, enhancement factors of up to about eight relative to the smooth tube at identical wall subcooling are obtained. Compared with propane and n -butane, n -pentane attains similar or slightly higher α cond on smooth and low-fin-density tubes but falls below the shorter alkanes at high fin densities, which can be explained by larger condensate retention angles and partial flooding of fin channels. The experimental data from this work were employed to test three prediction models from the literature. The model of Al-Badri et al. (Int. J. Heat Mass Transf. 62 (2013) 463–472) reproduces α cond most consistently across all fin densities, fin heights, and tube materials. The Briggs and Rose model (Int. J. Heat Mass Transf. 37 (1994) 457–463) performs well at moderate fin densities but underpredicts at high fin densities, whereas the correlation by Reif et al. (Heat Mass Transf. 55 (2019) 3–16) shows large geometry-dependent deviations.