Pulsation incitation and performance investigations for 3D Fin-and-Tube heat pipe heat exchanger by inserting dividing boards for various working fluids

Abstract

In our previous study, we have shown that a heat pipe heat exchanger system modified from a commercial air-to-air heat exchanger operates without pulsations for working fluids of dielectric HFE-7000 or R134a, or under low heat loads for water, due to the large internal tube diameter of 5.6 mm. To incite pulsation and enhance the thermal performance, a straight dividing copper board is inserted into the straight section of each of the tube to form two semicircular compartments with an effective hydraulic diameter of 3.4 mm. The heat transfer characteristics and thermal performance against the hot air inlet temperature for the novel boarded model and the non-boarded model are experimentally explored with three working fluids (water, HFE-7000 and R134a) under six filling ratios (35%, 38.5%, 50%, 55%, 65%, 71.5%). Because water already works in a PHP mode in the non-boarded model under high heat loads, the thermal performance in the boarded model improved mildly by 2.7%–10.6%. Whereas, for HFE-7000 and R134a, the heat transfer mode is successfully incited from thermosyphon in the non-boarded model into PHP in the boarded model. The most significant thermal performance improvement was observed for HFE-7000 by 8.3%–24.5%. The improvement can be attributed to the switch of heat transfer mode, the generated corners for condensate accumulation, and the additional heat conduction via the copper board.