Two-tube heat exchanger with variable groove angle on the inner pipe surface: Experimental study

Abstract

Flow patterns in fluids affected by a grooved surface tube are different from a smooth pipe. The importance of a compact and optimal design of heat exchangers has led to extensive studies in the past focused on geometry (circular, square, etc.), depth, and distance between grooves. In terms of novelty, the present work studies the influence of the groove angle of the inner tube surface on fluid flow and thermal performance. The study method was experimental, and Wilson plots were used to determine the heat transfer coefficient. Three test sections, including smooth pipe and helical grooves, were made. Experiments were performed for the base case (smooth pipe) within the Reynolds number range of 9000–18000 and a constant inlet temperature of 20 °C for cold water. The hot water was kept constant in the Reynolds number range of 2700, and the inlet temperature was 50 °C. Heat transfer, friction factor, effectiveness, and the number of thermal units were evaluated as significant features in heat exchanger performance analysis. The results were presented in two arrangements of parallel and counter fluid flow for helical groove tubes, in comparison, with a smooth pipe. In low Reynolds, geometry and groove angle affect heat transfer more than flow rate. Heat transfer enhances as the groove angle becomes more vertical to the flow. Per 30° change in the slope of the spiral groove from parallel to perpendicular to the fluid flow, the Nusselt number and the friction factor increase by 25–32% and 8–9%, respectively.