Heat Transfer Enhancement of Condenser coil by Evaporating Droplets from Water Spray at the Upstream

Condenser coils are widely used in HVAC and industrial applications because they can effectively transfer heat between gas and liquid. However, when comparing to cooling towers which use evaporating water to reject heat into the ambient, the heat dissipation ability of a dry condenser coil is limited by the low air-side heat convection and high ambient dry bulb temperature. To solve this problem, a mist cooling technology which hybrids dry condenser coil and wet cooling tower by spraying water droplets at the upstream of the condenser coil was introduced and studied in this paper. The cooling performance of the condenser coil was significantly enhanced by the evaporation of water droplets while they were passing through the condenser coil. Numerical simulation of a typical finned tube condenser coil was conducted using a commercial CFD software, ANSYS Fluent to assess the performance of mist cooling technology. To describe the details in the mini-channels of the condenser coil, CFD models which only capture the smallest repeating computational domain with symmetry and periodic boundaries were introduced. After the dry condition cases were solved using Eulerian model, mist evaporation was introduced as discrete phase and solved using Lagrangian model. Then, under the same airflow velocity and absolute humidity, different spray characteristics were investigated including 2 different water spray rate with 5 different droplet sizes for 5 different distances between nozzles and coil under 5 different ambient temperatures. Higher spray rate, smaller droplet size, longer distance and hotter weather were found to be profitable to the performance with an improvement in heat transfer by up to 124.6%. Limitations and drawbacks in changing the studied parameters were also studied and discussed. The mist cooling technology can significantly enhance the air side heat transfer of a condenser coil and the results from this research can be useful in enhancing the efficiency of an air conditioning system.