The Influence of Pulsation on Heat Transfer in a Heat Exchanger for Parallel and Counter Water Flows

In this study, in order to increase the heat transfer rate in concentric double-pipe heat exchangers by an active method, a rotating ball valve was mounted downstream of the outer pipe end and used as a pulse generator. In the experimental set-up, hot water (40-70 °C) was passed through the inner pipe with fixed mass flow rate (Reynolds number ≈ 10,200) while cold water was passed through the annulus with Reynolds number ranging from 2,000 to 10,200 and exposed to pulsation. The investigation is performed for pulsation frequency ranged from zero to 40 Hz while the amplitude was kept constant by fixing the ball valve at heat exchanger outlet. The influences of pulsation frequency, Reynolds number, and inlet hot water temperature on heat transfer enhancement were reported for both parallel and counter flows. The experimental results indicate that the tube with the ball valve inserting downstream provides considerable improvement of the heat transfer rate. The maximum enhancement in Nusselt number for the parallel flow was about 20% while it was about 90% for counter one. Correlations for relative average Nusselt number, for different pulsation frequencies and Reynolds numbers are provided with maximum standard error of 12%. [A.E. Zohir. The Influence of Pulsation on Heat Transfer in a Heat Exchanger for Parallel and Counter Water Flows. New York Science Journal 2011;4(6):61-71]. (ISSN: 1554-0200). http://www.sciencepub.net/newyork.