Heat transfer characteristics of in-tube steam condensation process under stratified flow

For stratified flow condensation process, the heat transfer mechanisms in the film condensation zone above the vapour-liquid interface and the condensate zone below the interface shows significant differences. In the multi-effect evaporation device, due to the high sensitivity of the thermal performance to the variation of the heat transfer parameters, the heat transfer parameters distributions in the film condensation zone and in the condensate zone are worth exploring. In this paper, a validated distributed parameter model was established to simulate the heat transfer and flow process in a single tube of the falling film evaporator. The variation of the heat flux in the condensate zone was presented under various operating conditions. The concept of the effective tube length and the partition map of the in-tube condensation heat transfer process were proposed for the better understanding of the flow and heat transfer process. Results show that the heat transfer in the condensate zone to the total heat transfer can accounts for more than 10% of the total heat transfer, thus cannot be neglected. For the design of falling film evaporator, the condensation heat transfer process in the tube should be located in the high-efficiency heat transfer section. The steam mass flow rate, heat transfer temperature difference and the length of the heat transfer tube should matched to each other to guarantee the condensation heat transfer process be located in the high-efficiency heat transfer zone.