Effect of condensate on air-side pressure drop in wavy fin-and-tube heat exchangers: Influence of airflow direction, humidity, velocity, and fin pitch

• Air flow direction affects the pressure drop under dehumidifying conditions. • A correlation for the mass of retained condensate is proposed. • A method to estimate pressure drop under dehumidifying conditions is proposed. • Heat transfer increases owing to dehumidification. An experimental investigation was conducted on wavy fin-and-tube heat exchangers with fin pitches of 4 mm and 5 mm to evaluate their thermal-hydraulic performance under dehumidifying conditions, considering both upward and downward airflow directions. As anticipated, condensation was found to enhance heat transfer. However, it also significantly influenced relative air-side pressure drop, with upward airflow resulting in higher relative pressure drops than downward airflow. At a face velocity of 3 m/s, reversing the airflow direction from downward to upward increased the relative air-side pressure drop by 79 %, indicating a strong dependence on flow orientation under dehumidifying conditions. An empirical correlation was developed to estimate the mass of retained condensate under downward airflow conditions, based on measurements for both fin pitches, with a coefficient of determination (R 2 ) of 0.895. Furthermore, an empirical method was proposed to characterize relative air-side pressure drop behavior as a function of retained condensate mass, face velocity, and fin pitch. The root-mean-square error (RMSE) of the prediction was 0.0593. Based on the experimental findings, upward airflow is not recommended under dehumidifying conditions, particularly at higher face velocities.