Experimental study on the flow and heat transfer of a horizontal falling film evaporator with spray compensation

Abstract

Falling film evaporators are widely used in the refrigeration and air conditioning industries. However, uneven liquid-film distribution and dry-out issues have long posed critical challenges and bottlenecks to their development. Therefore, this study proposed a spray compensation method that utilises an atomising nozzle to redistribute the unevaporated refrigerant on the surface effectively. In order to test the performance, a visual experimental setup was established to evaluate the flow and heat-transfer characteristics associated with this method. The results indicated that spray compensation effectively improved the working fluid velocity and enhanced the disturbance of the working fluid. Even during dry-out, spray compensation could fill the liquid film, maintaining a coverage rate of over 70 %. Moreover, it was demonstrated that spray compensation significantly enhanced the heat-transfer performance of the test tube, with the average heat-transfer coefficient increasing by a factor of 2.73 compared to the state without spray compensation. Notably, pronounced enhancement was observed in the circumferential position from 120° to 240°, where the local enhancement ratio at 180° was as high as 5.73. These findings suggest that spray compensation can effectively alleviate heat-transfer deterioration caused by dry-out, indicating considerable potential for practical applications in falling film evaporators.

Keywords

• Falling film evaporator
• Spray compensation
• Dry-out
• Falling film flow
• Heat transfer