Evaluation of performance of heat exchanger tubings using a transient metho

An experimental method to determine the overall heat transfer coefficient in a concentric tube, parallel flow heat exchanger is presented. This method is based on transient analysis of such a heat exchanger subjected to an arbitrary temperature change at the inlet of one fluid stream. The transient method provides a speedy measurement in comparison to the traditional steady-state method. Numerical solution of the governing equations, together with the measurements obtained from the heat exchanger in transient state, provides a determination of the overall heat transfer coefficient. The method has been applied to study the performance of nine enhanced tubes using wire-coil inserts with three different wire diameters (0.813 mm, 1.016 mm, and 1.575 mm) and three different pitches (3.63 mm, 5.08 mm, and 8.47 mm).;Experimental measurements of thermal and hydraulic performance of smooth tube as well as enhanced tubes obtained by the transient method are presented in terms of Nusselt number (Nu) and friction factor ( f) in the range of Reynolds number of 15,000 to 45,000. The results agree well with those obtained with the steady-state method. The measurement for Nu and f are estimated to have maximum experimental uncertainty of +/-15% and +/-5%, respectively. A correlation was developed for enhanced Nusselt number that matches the experimental data within about +/-12%.