Optimization of the orifice shape of cooling fan units for high flow rate and low-level noise in outdoor air conditioning units

Abstract

Demand for air conditioners is steadily increasing due to global warming and improved living standards. The noise, as well as the performance of air conditioners, are recognized as one of the crucial factors that determine the air conditioners' values. The performance and noise of the air conditioner are mostly determined by those of its outdoor unit, which in turn depend on those of the cooling fan unit. Therefore, a cooling fan unit of high-performance and low noise is essential for air-conditioner manufacturers and developers. In this paper, the flow performance and flow noise of the entire outdoor unit with an axial cooling fan in a split-type air-conditioner were investigated. First, a virtual fan tester constructed by using about 18 million grids is developed for highly resolved flow simulation. The unsteady Reynolds-Averaged Navier-Stokes equations are numerically solved by using finite-volume computational fluid dynamics techniques. To verify the validity of the numerical analysis, the predicted P-Q curve of the cooling fan in a full outdoor unit is compared with the measured one. There was an excellent agreement between the two curves. The further detailed analysis identifies the coherent vortex structures between the fan blade tip and fan orifice, which adversely affect the flow performance and causes flow noise. Based on this analysis, the optimization of fan orifice was carried out using the response surface method with three geometric parameters: inlet radius, neck length, and outlet angel of the orifice. The optimum layout for the high flow rate is proposed under the understanding that the increased flow rate can be converted to noise reduction. The additional computation using the proposed optimum orifice shows that the flow rate is increased by 4.6% at the operating point. Finally, the engineering sample was manufactured by using the optimum design, and the measured data confirmed that the flow rate were increased by 2.1%, the noise reduction was made by 2.8 dBA, and the power consumption is reduced by 4.0% at the operating rotational speed.