Waste heat recovery is very important, because not only it reduces the expenditure of heat generation, but also it is of high priority in environmental consideration, such as reduction in greenhouse gases. One of the devices is used in waste heat recovery is heat pipe heat exchanger. An experimental research has been carried out to investigate the hydrodynamic and thermal performance of a gas- liquid thermosyphon heat exchanger in a pilot plant. The ε-NTU method has been used. The pressure drop has been calculated across tube bundle of the thermosyphon heat exchanger. Its module is composed of 6 and 15 copper pipes with aluminum plate fins with dimensions of 130 cm , 47 cm and 20 cm . The tubes have been filled by water with filling ratio of 30 %, 50 % and 70 %. The density and thickness of fins are 300 fin/m and 0.4 mm, respectively. The configuration of tubes is in-line with 30 mm pitch. The results show that as the ratio of Ce/Cc raises the amount of heat transfer increases. The effectiveness of heat pipe heat exchanger remains constant as the temperature of hot stream rises, but the amount of heat transfer increases. Filling ratio in normal region (30-70 %) has no effects on experimental results. A new correlation for thermosyphon heat exchanger with individual finned tubes and in-line geometry has been proposed for calculating pressure drop across tube bank of a . The error in pressure drop for 40 experimental points in the new correlation is less than 15 %. This indicates that the new correlation possesses an acceptable accuracy predicting pressure drop.

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