Performance of shell-and-dimpled-tube heat exchangers for waste heat recovery

Abstract

This paper presents an experimental study of waste heat recovery shell-and-tube heat exchangers. The exchanger heat duty, overall heat transfer coefficient, effectiveness and tubeside friction factor are investigated as functions of the tube surface geometry (plain or dimpled), the flow type (counter or parallel), the tube Reynolds number and the shellside heat capacity rate. Water and the exhaust gases of a Diesel engine are passed inside the tube and the shell, respectively. The heat transfer characteristics increase with an increase in tube Reynolds number and the shellside heat capacity rate, for all the flow types and the surface geometries examined. The counter-flow, shell-and-dimpled-tube heat exchanger, compared with that exchanger having a plain tube, increases the heat duty and the overall heat transfer coefficient by 80%, and the heat exchanger -effectiveness increases by 35%. For the parallel-flow, shell-and-dimpled-tube heat exchanger, the heat duty, the overall heat transfer coefficient and the effectiveness increase by 30, 55, and 25%, respectively. At the same time the dimpled tube increases the tubeside friction factor by 600% over that of the plain tube. The rate of waste heat recovered from the exhaust gases of the Diesel engine by the counter-flow, shell-and-dimpled-tube heat exchanger is equal to 10% of the maximum brake power of the engine running at 1500 rpm, and the tube Reynolds number equal to 8875.