Comprehensive analysis of single tube falling film heat transfer performance considering dynamic growth of fouling

Abstract

The heat transfer process in horizontal tube falling film flow generally involves gas-liquid phase change and dynamic growth of porous fouling layers. However, most studies neglect fouling effects. This paper uses the finite element method to conduct a coupled numerical simulation of falling film flow, phase change heat transfer, and fouling growth, and studies the variation trend of the heat transfer coefficient (HTC) and the average HTC as the fouling grows. Under constant temperature heating, the HTC of water and seawater during saturated evaporation decreases along the circumference, with a decrease of about 56 % in the top region (0°-20°) of the tube. The HTC of saturated evaporation increases with evaporation temperature and spray density. Especially in the range of θ < 20° and θ > 160°, the rise in spray density has a greater impact on HTC. Under the influence of seawater fouling, both h_i and h_w show a decreasing trend as the inlet liquid film temperature increases. Under constant heat flux, the HTC of saturated evaporation is independent of evaporation temperature and increases with spray density. With the accumulation of fouling, the h_ave-i and h_ave-w show a downward trend. The non-boiling HTC of water and seawater has a lower decline rate along the circumference. Due to the effect of fouling growth on the flow boundary layer, h_i and h_w first increase and subsequently decrease within 20° < θ < 160°. Under constant heat flux, h_ave-i and h_ave-w of non-boiling change from an increasing trend with increasing inlet temperature to a decreasing trend as fouling accumulates.