New correlations for predicting convective heat transfer of single and multi-row heat exchangers employing staggered drop-shaped tubes

Abstract

In this paper, for the first time, air-side correlations were developed and introduced to describe the average Nusselt number Nu¯, friction factor f, and thermal−hydraulic performance ε of compact heat exchanger employing drop-shaped tubes considering the number of tube rows (NR). Drop-shaped tubes were arranged in a staggered formation and placed in 1 to 20 consecutive rows in the flow direction, each consisting of 7 tubes in the transverse direction. The Reynolds number (Re) varied from 1.78 × 103 to 18.72 × 103. The calculations were carried out using Ansys Fluent software package. Tube row and Reynolds number effects on the thermal and hydrodynamic characteristics of the studied heat exchangers were analyzed. The simulation results were in a good agreement with the available literature. The results showed that Nu¯ and ε increase, while f decreases as Re increases. Moreover, an increase in NR leads to an increase of f and a decrease of ε. The maximum values of Nu¯ were obtained for NR = 2, which were higher by 3.95–6.69% and 19.91–24.62% than those for NR= 1, and NR= 20, respectively. Heat transfer was stabilized only from the 19-row onwards. In addition, a 1-row heat exchanger had better thermal−hydraulic performance compared to that with a larger NR (ε for NR = 1 was about 22.32–27.24 times higher than those for NR = 20). The maximum deviation between the numerical results and the obtained correlations developed from them was ±8.87%, which provides a useful reference for future studies and designs of heat exchangers with different row numbers of drop-shaped tubes.