自然工质两级喷射器组合中间压力分配

Intermediate pressure allocation in two-stage ejector cascade with natural working fluids

建立了两级喷射制冷系统和两级喷射器组合的性能分析模型。以水、氨、R290、R600a为工质,研究了两级喷射器组合中间压力分配比与喷射系数的关系,当第一级和第二级喷射器的喷射系数相近时出现使总喷射系数最大的中间压力最佳分配比。探讨了不同工况下最佳分配比与总压缩比和膨胀比之间的关系。膨胀比一定时,最佳分配比随总压缩比的增大先增大,然后减小,最后又逐渐增大;膨胀比对最佳分配比也有一定影响,但与总压缩比的取值区间相关联。绝热指数是影响最佳分配比的重要因素,对处于相同最佳分配比工况的不同工质,绝热指数越大则所需的总压缩比也越大。提出了两级喷射器组合中各级喷射器结构选择方法。

The performance analysis models established for a two-stage ejection refrigeration system and therein two-stage ejectors cascade. Employing water, ammonia, R290 and R600a as the working fluids, respectively, the research is conducted on the relationship between intermediate pressure allocation ratios and entrainment ratios for the two-stage ejectors cascade. There is an optimal allocation ratio corresponding to the maximum total entrainment ratio when the first and the second stage entrainment ratios of the two-stage ejectors cascade are approximate. Further, the investigation is carried out on the relationship between optimal allocation ratio and overall compression ratio and expansion ratio at different working conditions. At a constant expansion ratio, the optimal allocation ratio first increases and then decreases, finally increases again with the increase of overall compression ratio. The expansion ratio also influences the optimal allocation ratio on the condition that coupling different range of overall compression ratio. The adiabatic exponent is a key factor to affect the optimal allocation ratio. As for different working fluids under the working conditions with the same optimal allocation ratios, the higher adiabatic exponent of a working fluid the higher overall compression ratio needed. The method to select the two kinds of ejector structure in two-stage cascade is proposed.