Effect of surface efficiency on the thermal design of plate-fin heat exchangers with passages stack arrangement

To better apply the correlations established from passages single stack format to evaluate the performance of plate-fin heat exchanger with double stack arrangement, a new calculation method of surface efficiency is proposed in the paper. The variations of local Colburn factor and local pressure drop are studied. Besides, the distribution of dimensionless temperature and local fin efficiency are investigated. Comparison of Colburn factor between single stack and double stack modes is discussed. Seven different fin geometries with 38 sets of simulation data are used to verify the effectiveness of the proposed new method. The results show that the deviations of the surface efficiency between simulated results and formula values are the smallest for the proposed new method. Using usual, Li & Shen, Kraus and proposed new methods to calculate the surface efficiency of the double stack format, the mean absolute deviation of Colburn factor between single stack and double stack modes is 3.7% with air as the medium, while it is 28.1%, 16.6%, 12.9% and 3.2%, respectively for water as the medium. Therefore, regardless of medium used, the proposed new method could give the data of the single stack and double stack modes in a uniform format for guiding the thermal design of plate-fin heat exchanger with serrated fin.