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Second Thermal and Fluids Engineering  Conference

ISSN: 2379-1748
ISBN: 978-1-56700-430-4

EXPERIMENTAL INVESTIGATION OF THE HEAT TRANSFER IN A HORIZONTAL MINI-TUBE WITH THREE DIFFERENT INLET CONFIGURATIONS

Hou Kuan Tam
Department of Electromechanical Engineering, Faculty of Science and Technology, University of Macau, Taipa, Macau, China

Lap Mou Tam
Department of Electromechanical Engineering, Faculty of Science and Technology, University of Macau, Taipa, Macau, China; Institute for the Development and Quality, Macau SAR, China

Afshin J. Ghajar
School of Mechanical and Aerospace Engineering, Oklahoma State University, Stillwater, OK 74078, USA

Qian Wang
Department of Electromechanical Engineering, Faculty of Science and Technology, University of Macau, Macau SAR, China

Abstract

In the traditional heat exchanger, the inlet configuration entering the straight tube include the sharp-edged contraction, re-entrant inlet, bell-shape nozzle, and different angle bends. For the macro-tube, the effect of different inlet configurations on heat transfer in the laminar, transition, and turbulent regime can be found in the open literature. However, those information has not been well studied in the smaller diameter tubes such as the mini-tube and micro-tube. Therefore, an experimental setup was built for this study to measure the mini-tube heat transfer under the uniform wall heat flux boundary condition.

In this study, heat transfer was measured in a test section fitted with a horizontal mini-tube of 2 mm inner diameter. Three inlet configurations (straight tube length, 90° bend, and 180° bend) were used in this study. The entire experiment covered the Reynolds number range between 900 and 3000. From the heat transfer results, the heat transfer characteristics from the laminar to upper transition regions was observed. Regardless of the inlet type, the influence of buoyancy on laminar heat transfer was present in the minitubes. However, the start of transition was inlet-dependent. From the entrance to fully developed region, the laminar heat transfer of the 90° and 180° bends was observed to be higher than that of straight tube length. Moreover, the 180° bend had a slightly higher laminar heat transfer than the 90° bend in the fully developed region.

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