Heat transfer correlations for liquid film in the evaporator of enclosed, gravity-assisted thermosyphons

Heat transfer correlations were developed for the liquid film region in the evaporator section of closed, two-phase, gravity-assisted thermosyphons in the following regimes. (a) laminar convection, at low heat fluxes, (b) combined convection, at intermediate heat fluxes, and (c) nucleate boiling, at high heat fluxes. These correlations were based on a data set consisting of a total of 305 points for ethanol, acetone, R-11, and R-113 working fluids, wall heat fluxes of 0.99-52.62 kW/m(2), working fluid filling ratios of 0.01-0.62, inner diameters of 6-37 mm, evaporator section lengths of 50-609.6 mm, and vapor temperatures of 261-352 K. The combined convection data were correlated by superimposing the correlations of laminar convection and nucleate boiling using a power law approach, to ensure smooth transition among the three heat transfer regimes. The three heat transfer correlations developed in this work are within +/-15 percent of experimental data.