Study on impinging flow field characteristics dispensed from water spray ejectors in an evaporator

Horizontal tube falling film evaporators have shown their advantages of high heat transfer coefficient and low refrigerant charge over those with flooded tube bundles in applications of different refrigeration systems. The falling film evaporators primarily consist of a bundle of horizontal tubes connected by headers at each end, as in the conventional shell and tube heat exchangers. The shell side liquid is introduced via water spray ejectors to the top of bundles and subsequently drains to lower tube banks where liquid films flow and evaporate on the exterior tube surfaces. Although there are many experimental and modeling studies on the falling film dispersion and evaporation of refrigerants, the majority of those studies mainly explore the processes of the fluid entering the top of evaporators and flowing down the heat transfer tubes as a liquid film from which refrigerator is evaporated. Relatively limited efforts were attempted to explore the impinging flow and spreading development of working fluids occurred inside an evaporator, whereas the impingement flow field can significantly affect the performance of a falling film evaporator. The objective of this research is to perform CFD simulations for investigating the liquid jet impingement and spreading behavior issued from water spray ejectors in an evaporator. The volume-of-fluid (VOF) method was utilized to simulate the liquid water-air interfacial flow motions for the water spray flow development. The predicted time sequences of the liquid jet dispersion were compared with the photographed images in terms of the contours and time histories of computed and visualized spreading shapes to validate the present numerical model. To better understand the ejector design, numerical computations were extended to examine the influences including mass flow rate, dispense angle and diameter of hole on the distribution efficiency.