Modification on prediction method of heat transfer coefficient from a vertical-finite-length cylinder in saturated film boiling to discuss local heat transfer performance near the lower corner

Abstract

Saturated film boiling heat transfer around a vertical-finite-length cylinder has been investigated analytically to predict the local heat transfer coefficients at the bottom and lower vertical surfaces. Correlations of heat transfer for the vertical cylinder with top and bottom horizontal surface has been already analyzed by Momoki et al.(2007) and this correlations equations for heat transfer are in good agreement with the experimental data for the cylinders in saturated water. In the present study, this correlations are applied to estimate the local and average heat transfer rate through each surfaces of the cylinder. To predict the local heat transfer coefficient at the corner of the bottom surface and vertical lateral surface, Shigechi et al.(1999) analysis for film boiling heat transfer on horizontal bottom surface was modified in order to get finite vapor film thickness at the end of the bottom surface to predict finite value of local heat transfer coefficient at this end. In this modification, the vapor film thickness at the end of the bottom surface can be predicted and the prediction of the average heat transfer rate through all surfaces are in good agreement with the results of the Shigechi et al.'s method. Moreover, the local heat transfer coefficient at the end of the bottom surface can be predicted to discuss the local heat transfer characteristic of the bottom surface. The local heat transfer rate through the bottom surface and vertical lateral surface are described in terms of local Nusselt number with degree of superheat. The results on local heat transfer coefficient shows the highest value at the corner of the bottom surface and vertical lateral surface and it can be confirmed the experimental results of the vapor film collapse start from the corner of the bottom surface and vertical lateral surface of the cylinder in saturated film boiling.

Keywords

• film boiling
• film collapse
• heat transfer rate
• local heat transfer coefficient