An Experimental Study of the Relative Effects of Transverse and Longitudinal Ribbing of the Heat Transfer Surface in Forced Convective Boiling

Abstract

This work describes an experimental investigation into the effects of surface geometry variations on heat transfer performance in forced flow boiling. Ribs of rectangular cross section were machined on flat stainless steel test specimens of 1.60 mm thickness. The height of the ribs was kept constant at 0.50 mm and a number of test specimens with rib width varying from 0.50 mm to 2.0 mm and rib spacing ranging from 0.50 mm to 3.5 mm were produced. In order to maintain a constant microsurface roughness of 0.7 μm over the entire test specimen, all test surfaces were subjected to vequa-blasting after machining. Precautions were taken to ensure that aging of the heat transfer surface had been established so that the data recorded were reproducible. Experimental data are reported for water at atmospheric pressure with flow velocities of 0.20 m/s to 1.40 m/s. Inlet subcoolings were varied from 5°C to 30°C. The results for the longitudinal ribbed surfaces (LRS) were compared with those for the transverse rectangular ribbed surfaces (TRS) and both sets of data were compared with the heat transfer performance of an optimum flat roughened surface.