Effect of pipe surface roughness on frictional pressure drop in gas-liquid two phase flows

Abstract

The main objective of this experimental work is to investigate the effect of pipe surface roughness on frictional component of gas-liquid two phase pressure drop. The pressure drop measurements are carried out with air-water two phase flow in two different flow loops. First flow loop consists of 12.7 mm I.D. (smooth pipe), 12.5 mm (rough pipe) while second flow loop consists of both smooth and rough pipes of 27.8 mm I.D. The smooth and rough pipes are made up of polycarbonate and stainless steel material, respectively. Thus, all experiments are carried out for four different combinations of relative roughness. The gas and liquid flow rates are varied systematically so as to generate all key flow patterns observed in two phase flow. Experimental results show that the increase in the relative roughness increases the frictional pressure drop as a function of both gas and liquid flow rates. This effect is substantial for inertia driven flows (annular flow) compared to bubbly and slug flow patterns. It is also seen that the effect of increase in relative roughness on the frictional pressure drop increases with decrease in the pipe diameter. Moreover, the measurements carried out in 12.7 mm and 12.5 mm I.D. pipes at upward and downward inclinations show that the effect of relative roughness on frictional pressure drop is independent of the pipe inclination. The general trends of frictional pressure drop for different relative roughness are found to be in agreement with the experimental observations reported in literature. Evaluation of the existing two phase flow models developed for smooth pipes show that these correlations under predict the frictional pressure drop in rough pipes.