Experimental study on thermo‐hydraulic performance of metal foam twisted tape in a double pipe heat exchanger

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AbstractA recent study compared experimentally the hydraulic and thermal activity of twisted tape inserts for two types, metal foam twisted tape (MFTT) and traditional twisted tape (TTT), in a double pipe heat exchanger. The investigation goal of the innovatively designed MFTT is to enhance the heat transfer process, which provides a higher thermal enhancement factor over those of TTT under the same conditions. Heat transfer activity in terms of Nusselt number (Nu) and Nusselt number ratio (Nu/Nuo) as the heat exchanger equipped with the proposed MFTT and TTT inserts with various tape‐twist ratios (y/W = 3.6, 5.2, and 6.8) are considered over various values of Reynolds numbers (16,300 < Re < 32,500). The results reveal an improvement in heat transfer rate with both MFTT and TTT and this improvement is proportional inversely to the twisted ratio, but the MFTT showed the highest value of heat transfer compared to TTT and clear tube. Also, the Nu of MFTT augments averaged about 175%–230% compared to the TTT depending on the twist ratio and about 275% and 500% over that of the clear tube. At a twist ratio of 3.6, the heat transfer coefficient is recorded at 37% and 45% for MFTT and TTT models, respectively, with an increase in Re. However, friction factor (f) increases about 35% for MFTT with decreasing in twist ratio (from 6.8 to 3.6). The effectiveness of the proposed MFTT in the range of Re used is found to be about 12%, 15%, and 18% higher than those induced by TTT at twisted tape ratio (y/w = 3.6, 5.2, and 6.8), respectively.