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Abstract: Visualization experiments were carried out for boiling of propane, isobutane and their mixtures on a smooth and four reentrant enhanced tubes. The results shown by the video pictures indicate a strong mixture effect on nucleation and evaporation processes on the enhanced surfaces. The fluid physical properties also influence the bubble behavior and consequently affect the heat transfer performance. The effects of reentrant enhanced surface geometries are complicated and closely related to mixture effects, fluid properties and working conditions. Based on the analysis of the available visualization results, the different heat transfer performance for different enhanced surfaces and especially the difference between pure fluids and mixtures, as shown in an accompanying paper [Chen et al., Int. J. Heat Mass Transfer, in press], are partially explained. [Copyright &y& Elsevier]

Abstract: Pool boiling heat transfer experiments were carried out on a conventional smooth tube and four enhanced tubes with reentrant surfaces using propane, isobutane and their mixtures as working fluids for six saturation temperatures. The heat transfer performance is very different for different surface–fluid combinations. Compared to the smooth tube, the mixture boiling heat transfer degradation is more significant for the enhanced tubes. The current data are compared with available literature data for the same fluids and also with data for R12 and R134a. Experimental results of boiling hysteresis and for twin-tube bundles are also provided. Further explanations for the different heat transfer performances is provided by means of visualization in an accompanying paper [Y. Chen, M. Groll, R. Mertz, R. Kulenovic, Visualization and mechanisms of pool boiling of propane, isobutane and their mixtures on enhanced tubes with reentrant channels, submitted to Int. J. Heat Mass Transfer (H/S 04016)]. [Copyright &y& Elsevier]