Enhancing COP of an air-cooled chiller with integrating a water mist system to its condenser: Investigating the effect of spray nozzle orientation

Abstract

Air-cooled chillers are widely used for providing cooling in buildings in hot and humid climates. Using a water mist system in connection with the chiller condenser can enhance the chiller COP. This paper studies the effect of a water mist system on chiller COP in various orientations of the spray nozzle. Besides, a sensitivity analysis is performed for some parameters of the ambient air including air temperature, air humidity ratio, and air velocity. Simulations are performed by the commercial ANSYS Fluent 16.0 software based on the Eulerian-Lagrangian approach. The nozzle orientation angle is introduced as the angle between the spray nozzle axis and the entering air stream direction. The simulations are done for five values of the orientation angle, including 0°, 22.5°, 45°, 67.5°, and 90°. The results suggest that increasing the orientation angle is usually beneficial to the system performance such that the orientation angle of 90° yields the maximum percent increase of COP of 10.6. This event is justified by the reduced horizontal momentum of droplets and consequently the high residence time of them and also the extended cooling area in elevated orientation angles. However, with the orientation angle of 22.5°, the system faces a performance breakdown leading to only 5.9% increase of COP. The deteriorated performance of the system in the 22.5° orientation angle is perceived to be mainly due to the small cooling area coverage and the low residence time of the water droplets because the droplets are constrained to move in a high momentum plume region of a small cross-sectional area in the orientation angle of 22.5°. The sensitivity analysis suggests that the investigated parameters highly affect the extent of the chiller COP enhancement.