Refrigeration systems, called air-cooled chillers, are often used to cool buildings or industrial processes where water quality or supply is an issue. Water mist spray systems can be used on the condenser coils of air-cooled chillers to make them work more effectively and be more efficient. These systems spray a fine mist of water on the coils, which helps the heat move from the coils to the air around them. The mist on the coil surface takes heat from the air as it evaporates. This cools the coils and the refrigerant inside them. This process drops the temperatures of the condensing fluid and the amount of energy the compressor needs to run. As the title suggests, this project is conducted to validate the paper entitled “Enhancing COP of an air-cooled chiller with integrating a water mist system to its condenser: Investigating the effect of spray nozzle orientation [1]” published in the International Journal of Thermal Sciences. Accordingly, a spray nozzle was placed in a condenser to spray water mist and increase the system’s COP (Figure 1).

• Reference [1]: Heidarinejad, Ghassem, Mohammad Reza As’ adi Moghaddam, and Hadi Pasdarshahri. “Enhancing COP of an air-cooled chiller with integrating a water mist system to its condenser: Investigating the effect of spray nozzle orientation.” International Journal of Thermal Sciences137 (2019): 508-525.

Figure 1- Conical Spray nozzle after injection

Simulation Process

This study uses a 20-ton Trane Company air-cooled chiller to test the COP of a water mist system. A square-section channel with a cross-section of 0.7 m by 0.7 m (near the fan) is designed using Design Modeler software. The spray nozzle should be placed at a distance of 0.7 m from the inlet, just as shown in Figure 2. The simplicity of the computational domain leads us to use a Structured grid over it. On balance, 686000 hexagonal cells are generated in ANSYS Meshing software. The unsteady spraying process allows us to track the droplets in transient mode while the continuous phase is solved steadily. To model water mist spray regarding the evaporation of the droplets, 2-way Discrete Phase Model (DPM) along with Spieces Transport module is utilized. In other words, the Eulerian-Lagrangian approach is employed to simulate the process of water droplets’ evaporation. Bear in mind that it is a paper validation study, so all the essential parameters are taken from the reference paper.

Figure 2– Water mist system in condenser equipped with spray nozzle

Post-processing

The computational analysis of the water mist spray system reveals complex evaporative cooling patterns in the condenser area. The mass fraction contours of H2O vapor illustrate the spatial development of the evaporation process, with maximum concentrations detected around the spray nozzle injection point. The conical spray pattern produces a uniformly distributed mist cloud, wherein individual droplets experience phase transformation, absorbing latent heat and efficiently lowering the local air temperature. The DPM simulation illustrates the unidirectional interaction between discrete water droplets and the continuous air phase, revealing peak evaporation rates near the entrance region where temperature gradients are most evident.

Figure 3- a) mass fraction of water vapor b) evaporation takes place after the injection

More importantly, in order to check the simulation results with the reference paper, COP is reported. Based on the given equation, COP should be calculated regarding the outlet temperature:

The validation metrics focus on the system’s Coefficient of Performance (COP), which exhibits strong agreement with the reference data. The simulation predicts an outlet temperature of 37.92°C at an input air velocity of 15 m/s, yielding a COP of 3.05, in contrast to the observed value of 2.99 (T_out = 38.87°C). This minimal 2% variation supports the numerical methodology, especially the application of the Species Transport model and 2-way coupling inside the DPM framework. The significantly reduced outlet temperature in the simulation indicates a slightly improved heat transfer calculation, potentially attributable to idealized evaporation assumptions inside the numerical model. These findings validate the dependability of the computational framework for forecasting evaporative cooling efficacy in air-cooled chiller applications.