This paper presents an ultrasonic mist generator used as an evaporative pre-cooler for air-cooled condensers in air conditioning applications. Ultrasonic mist generators eliminate pressure loss at the inlet air stream to the condenser and allow controlling the characteristics of the water atomized droplets. A water mist generation unit has been designed, built, and tested to assess its thermal performance and its water mist production capacity in terms of the mass flow rate of atomized water and size distribution of the droplets generated. To evaluate the performance and cooling capacity of the water mist produced by the ultrasonic mist generator, a set of tests has been conducted on a test bench consisting mainly of a subsonic wind tunnel equipped with instrumentation and control devices to modify the operating conditions. A Sauter mean diameter $D_{3,2}=13.2$ $\mathrm{\mu }\mathrm{m}$ has been determined using a photographic technique for the size distribution of the generated droplets and the range of water mist flow rates that the system can produce is between $0.11\times 10^{-3}$ and $0.52\times 10^{-3}\mathrm{kg∕s}$. It has been found that, under many operating conditions, the evaporative cooling process is not homogeneous throughout the air flow, so a novel performance indicator called ${\epsilon }_{\text{LCP}}$ (local cooling performance) has been defined to specifically evaluate this phenomenon. A maximum direct evaporative cooling efficiency ${\epsilon }_{\text{DEC}}=83.7\text{\%}$ is obtained for a water-to-air ratio $r_w=0.35\times 10^{-3}$ and air flow rate 630 m${}^3$/h. The maximum values of average evaporative cooling efficiency ${\epsilon }_{\text{AEC}}=65\text{\%}$ and average temperature decrease $T_{\text{drop}}$=4.3 °C are obtained for $r_w=2.41\times 10^{-3}$ and air flow rate 630 m${}^3$/h.

本文介绍了一种超声波薄雾发生器，用作空调应用中的风冷冷凝器的蒸发式预冷器。超声波雾发生器消除了进入冷凝器的进气流中的压力损失，并允许控制水雾化液滴的特性。已经设计，建造和测试了水雾产生单元，以根据雾化水的质量流量和所产生的液滴的尺寸分布来评估其热性能和水雾产生能力。为了评估由超声波雾发生器产生的水雾的性能和冷却能力，在主要由亚音速风洞组成的试验台上进行了一系列测试，该亚音速风洞配备了仪表和控制装置以改变操作条件。苏特平均直径$d_{3，2}=13。2$ $\mathrm{\mu }\mathrm{米}$ 已经使用照相技术确定了产生的液滴的大小分布，并且系统可以产生的水雾流速范围介于 $0。11\times \mathrm{1个}{0}^{-3}$ 和 $0。52\times \mathrm{1个}{0}^{-3}\mathrm{千克·秒}$。已经发现，在许多操作条件下，蒸发冷却过程在整个空气流中并不是均匀的，因此一种新颖的性能指标称为${\epsilon }_{\text{LCP}}$（局部冷却性能）已定义为专门评估此现象。最大直接蒸发冷却效率${\epsilon }_{\text{DEC}}=83。7\text{％}$ 获得水/空气比 ${\mathrm{[R}}_w=0。35\times \mathrm{1个}{0}^{-3}$ 风量630 m${}^3$/H。平均蒸发冷却效率的最大值${\epsilon }_{\text{AEC}}=\mathrm{65岁}\text{％}$ 和平均温度下降 ${Ť}_{\text{下降}}$获得的温度为= 4.3°C ${\mathrm{[R}}_w=2。41\times \mathrm{1个}{0}^{-3}$ 风量630 m${}^3$/H。