Analysis and improvement of full field falling film and heat transfer characteristics in the evaporators

Addressing the current issues of unclear falling film heat transfer characteristics and unsatisfactory heat transfer performance in evaporator, this study investigates the falling film heat transfer characteristics under both uniform and non-uniform flow conditions and explores the improvement of heat transfer performance across the entire evaporator. Firstly, this study investigates the R134a flow field and the heat transfer coefficient distributions under two distinct flow conditions using a two-dimensional two-phase flow transient model of the falling film evaporator. Secondly, four improvement strategies are proposed based on the aforementioned characteristics. Finally, the effects of improved structures on R134a distribution, fluid velocity, and the overall heat transfer coefficient are investigated. The results demonstrate that under uniform and non-uniform flow conditions, the falling film region forms counterclockwise and clockwise rotational flow fields, respectively. The lateral flow of R134a within this region leads to restricted evaporator performance. Improved structures with different numbers of vertical baffles are designed. These structures effectively suppress low velocity transverse flow, increase high velocity longitudinal flow, promote uniformity of liquid R134a distribution, and enhance heat transfer performance in the falling film region. The improved structure shows significant enhancement in the overall heat transfer coefficient, with improvements of 12.38% and 69.22% over the original structure under the two operating conditions, respectively.