Thermal calculations of plate–fin–and-tube heat exchangers with different heat transfer coefficients on each tube row

Abstract

In finned tube heat exchangers, the first rows of tubes are most effective when the air velocity in front of the exchanger is less than about 3.5 m/s. The heat transfer coefficient (HTC) decreases with each subsequent row and stabilizes only from the fifth row onwards. The paper examines a two-pass double-row plate-fin and tube heat exchanger (PFTHE) made of circular or oval pipes. A method for determining the air side Nusselt number on individual pipe row was developed, using the results of CFD (Computational Fluid Dynamics) modelling of the heat exchanger. Also, a heat transfer correlation was found for the mean HTC for the whole PFTHE using CFD modelling. The correlations based on the results of CFD modelling match very well the empirical correlations based on experimental tests of two car radiators. The analysis shows that the first rows of PFTHE are the most effective in terms of thermal effectiveness. By building a heat exchanger with two rows of pipes, it is possible to reduce investment expenditures at the same thermal output significantly. Heating systems with PFTHE air heaters with fewer rows of pipes are characterized by lower fuel consumption due to their higher efficiency. The investment costs for automotive radiators can also be reduced. The introduction of PFTHE heat exchangers with fewer pipe rows has a positive impact on the environment. Both material expenditures on the construction of PFTHE, energy consumption by the air fan, and fuel consumption for heating purposes are reduced.