Abstract:

With ultrasonic transducers stuck on the side walls (4mm-thick) of a generator, the effects of ultrasonic waves (28kHz) on the performance of an absorption refrigerator (10kW) were experimentally investigated under two height levels of LiBr solution in the generator. The mechanism of boiling heat and mass transfer enhanced by ultrasonic waves in LiBr solution was also analyzed. For the case without ultrasonic waves, the flow rate of LiBr solution increases with the speed-motor frequency of solution pump increasing from 17Hz to 18Hz, the height level of the solution in the generator rises by 5cm and the refrigeration capacity increases by 16.8%, but the COP (coefficient of performance) decreases by 44.3%. The ultrasonic waves enhance the refrigerator performance and the effects are related to the solution height levels in the generator. The refrigeration capacity and COP are improved by 19.6% and 13.8%, respectively when the solution height level is 8—10cm higher than the center line of the ultrasonic transducers; when the solution height level is 3—5cm higher, the refrigeration capacity and COP are only improved by 4.7% and 5.4%, respectively. The experimental results provide guidelines for performance improvement of small LiBr absorption refrigerators by using ultrasonic waves.

Key words: absorption refrigeration, heat and mass transfer, solution pump, ultrasonic wave, frequency

摘要：

在10kW溴化锂吸收式制冷机发生器侧壁（厚度4mm）粘贴超声波振子，实验研究了频率为28kHz超声波在溴化锂溶液两种不同液位高度下对机组性能的影响，并对超声波强化溴化锂溶液沸腾传热传质机理进行了分析。实验结果表明：无超声波作用时，溶液泵转速控制电机运行频率从17Hz升高到18Hz，溶液泵流量升高，发生器中溴化锂溶液液位升高5cm，制冷量增加16.8%，但性能系数（COP）降低44.3%；而施加超声波作用可以强化溴化锂吸收式制冷机性能，且强化效果与溶液液位有关，当机组发生器内液位高于超声波换能器中心线8~10cm时，机组制冷量升高19.6%，COP提高13.8%；而当液位与换能器中心线相差3~5cm时，制冷量提升并不明显，仅为4.7%，COP提升5.4%。实验结果为超声波作用提升小型太阳能溴化锂吸收式制冷系统性能提供指导和依据。

关键词: 吸收式制冷, 传热传质, 溶液泵, 超声波, 频率