Heat Transfer and Exergy Analysis of a Spiral Heat Exchanger

Abstract

The heat transfer effectiveness of a countercurrent spiral heat exchanger is expressed as a function of number of transfer units, ratio of flow capacity rates, number of spiral turns, and dimensionless start-point angle of spiral (dimensionless angular angle of the start point of a spiral curve constituting the solid wall of the heat exchanger). The heat transfer effectiveness is weakly dependent on the dimensionless start-point angle of spiral, but moderately increases with the number of spiral turns. As the number of spiral turns is larger than 20, the heat transfer effectiveness of the spiral heat exchanger approaches that of a counterflow heat exchanger. The heat transfer effectiveness of the spiral heat exchanger has a maximum. The optimum number of transfer units at the maximum heat transfer effectiveness increases with the number of spiral turns, whereas it increases with a decrease of the ratio of flow capacity rates. In the second-law analysis, an optimum hot flow-to-cold flow capacity-rate ratio is found. For obtaining a large net recovered exergy rate, the spiral heat exchanger needs to possess a large number of transfer units (greater than 2.0) and operate at a near balanced-flow condition. In addition, a small consumed mechanical power is demanded.

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Notes on contributors

Duc-Khuyen Nguyen

Duc-Khuyen Nguyen is a Ph.D. student in the Mechanical Engineering Department of National Chung Hsing University, Taiwan. He received the B.S. degree in mechanical engineering from Nong Lam University, Vietnam, and the M.S. degree in heat transfer from National Chung Hsing University, Taiwan. His research interests include heat transfer enhancement, drying technology, and postharvest technology.

Jung-Yang San

Jung-Yang San is a professor in the Mechanical Engineering Department of National Chung Hsing University, Taiwan. He received his master's degree from Stanford University and Ph.D. degree from the Illinois Institute of Technology. His research interests include waste heat recovery, adsorption heat pump, heat transfer enhancement, and jet impingement cooling.