Heat transfer coefficient in elliptical tube at the constant heat flux

Abstract

Cross-flow heat exchangers with elliptical tubes are often used in industrial application. In comparison with round tubes, the elliptical tubes have a better aero-dynamic shape, which results in a lower pressure drop of working fluid flowing through the inter-tubular space of heat exchanger. Also, a higher heat flux is transferred from gas to the wall of such a tube due to the more intense heat exchange process. To prove this thesis, the values of the heat transfer coefficient from the wall of the elliptical pipe to the water flowing inside were determined, using the data from the conducted measurements. This study presents also research stand with a vertically positioned tube. In order to obtain a constant heat flux through the wall of elliptical tube, a resistance wire is used, evenly wound on the external surface of tube measuring section. The use of thermal insulation minimized heat loss to the environment to a negligible value. Installed K-type thermocouples allowed one to obtain, for various measurement conditions, the temperature distribution within the elliptical tube wall (for a given cross-section) and the water flowing inside it (in a given cross-section, at different depths, for both axes of the ellipse). The design of the stand allows such measurements in several locations along the length of the measurement section. The measurement results were used to verify numerical calculations. The relative error of the heat transfer coefficient value determined on the basis of CFD calculations using the SST-TR turbulence model in relation to the one determined on the basis of the measurement data is about 11%.