Experimental study of thermal performance in a tubular heat exchanger using inclined perforated vortex rings

Abstract

This paper presents an experimental investigation on thermal and friction characteristics in turbulent airflow through a tubular heat exchanger inserted with 45° inclined perforated vortex rings (P-VRs). For the present work, the P-VR elements employed to create the streamwise vortices were mounted on the tube wall using two small straight wires to link the P-VR elements together. Influences of three relative ring-height or blockage ratios (e/D = BR = 0.20, 0.15 and 0.10) and three relative ring-pitches or pitch ratios (P/D = PR =2.0, 1.0 and 0.5) for a fixed angle of attack of 45° on the Nusselt number (Nu), friction factor (f) and thermal enhancement factor (TEF) for turbulent tube flows, Reynolds number (Re) ranging from 4200 to 26,000 were explored. The measured result has shown that the rate of heat transfer and friction loss rise considerably with increasing BR but declining PR. The highest values of Nu and f around 3.37–4.38 and 14.07–39.42 times above the smooth tube, respectively are at BR = 0.2 and PR = 0.5. The highest TEF is seen to be about 1.55 at PR = 1.0, BR = 0.10. Further, the Nu and f correlations were established by fitting the experimental data having the deviations from the measured data by ±7% each.