Experiments and Analysis on Film Boiling Heat Transfer Around a Finite-Length Vertical Cylinder With a Convex Surface Swelling Downward

Abstract

A method of predicting the overall heat transfer coefficient and the temperature at the lower limit of film boiling for a finite-length cylinder with flat top and bottom surfaces has been researched and proposed in a previous paper. This paper presents and compares an analysis in the case of a cylinder with a hemispherical bottom. The film boiling heat transfer around a vertical silver cylinder with a convex hemispherical bottom surface is investigated both experimentally and analytically in the present study. The obtained results are also compared and discussed with the authors’ previous results for a finite-length cylinder with flat top and bottom surfaces. Quenching experiments were performed using silver cylinders in saturated water. The diameter and length of the test cylinders are 32mm and 48mm, respectively. The test cylinder was heated up to about 600°C in an electric furnace and then cooled down in saturated quiescent water at atmospheric pressure. The resultant cooling and boiling curves and photographs of the film boiling phenomena are presented and discussed. The average heat transfer performance of the hemispherically bottomed cylinder is about 20% higher than that of the flat bottomed cylinder. The degree of wall superheating at the lower limit of film boiling is about 133K. The saturated film boiling heat transfer around the vertical finite-length cylinder with a convex hemispherical bottom was analyzed by taking into account the convective heat transfers from the bottom, side and top surfaces of the cylinder. The resulting analytical data correlated closely with the experimental data in the present study.