Numerical study of the cross-vapor stream effect on falling film heat transfer performance over a horizontal tube

Abstract

Vapor shearing can cause a falling film (FF) evaporator to exhibit various unusual phenomena. Under a cross-vapor stream, numerical simulations were conducted to examine the FF heat transfer performance outside a horizontal tube. The liquid film spreading, temperature fields, as well as time-averaged peripheral and axial, peripheral- and axial-averaged, and average heat transfer coefficients (HTCs) were presented, respectively. According to the results, we found that: (1) the cross-vapor stream produces deflections in liquid film spreading; (2) several zones of the tube surface have distinct distributions of HTCs, velocity vector fields, and liquid film thicknesses (LFT); (3) the cross-vapor causes apparent asymmetry for the axis-averaged peripheral HTC, especially at the higher vapor velocities; (4) the profiles of time-averaged peripheral and axial HTC on the upwind side are quite different from the one on the downwind side due to the cross-vapor; (5) within the current range of liquid flow rates, three trends of average HTCs can be observed with increasing vapor velocity; and (6) larger liquid flow rates can tolerate higher cross-vapor velocities to guarantee a better FF heat transfer performance.