Modeling and simulation of a falling film evaporator for a water vapor heat pump system

With the advantages of excellent heat transfer performance and less refrigerant charge, falling film evaporator has been widely used in seawater desalination and other industries. However, due to the practical problems of liquid level control and dry patches interactions, the structure design of falling film evaporator should be optimized for refrigeration applications. To resolve those problems, a simulation model for water-to-water falling film evaporator used in a water vapor heat pump system was conducted in this paper. Through the finite element method, the temperature distribution along the working tubes and the heat exchanger has been obtained. The distribution of heat transfer coefficient along the tube is also investigated to find out the best liquid level control solutions. For an available falling film evaporator with 4 pass working tubes under boiling temperature of 80 degrees C and spraying mass of 0.4 kg.s(-1), it is suggested that 2 pass working tubes should be in falling film region in order to achieve the largest heating capacity. Most important of all, it is proposed that there is an optimal boundary line between full liquid and falling film region. It may provide some suggestions for future design of falling film evaporators.