Study on the dynamic and thermal performances of a reversibly used cooling tower with upward spraying

• Fouling problems were solved by using upward spraying reversibly used cooling towers.
• A mathematical model was developed to predict the device's thermal performance.
• Droplet size has a significant impact on the thermal performance.
• Droplet temperature rise in the descent stage is larger than that in the ascent stage.

In subtropical areas, the RUCT (reversibly used cooling tower) can be used in a heat pump system. This study proposed an upward spraying RUCT, in which the aqueous solution is sprayed upward from the bottom, to reduce the drag resistance and enhance the efficiency of conventional RUCTs. A mathematical model considering rising and falling droplets simultaneously was developed based on conversation laws of mass, energy and momentum. The validity of the model was examined against the operating data measured in real conditions. Based on the validated model, the influences of different air velocities (2, 2.5, 3 m/s), droplet diameters (0.8, 1.0, 1.2 mm) and initial droplet velocities (6, 8, 10 m/s) on the displacement, velocity and temperature distributions of the sprayed droplet were discussed in detail. The results showed that, when the ratio of initial droplet velocity to air velocity closes to 1, smaller droplets will rise higher than the larger droplets, while for large ratio, the opposite is true. Droplet diameter had a large impact on the thermal performance and the droplet temperature rise in the descent stage was 1.5–2.4 times larger than that in the ascent stage. This study provides a theoretical foundation for optimization designing of the upward spraying RUCT.