碳氫混合冷媒應用於冷凍系統之性能與最佳化研究

Abstract

本研究針對R600a/R290混合冷媒進行小型R-134a冷凍系統換裝之性能研究。R-600a/R-290冷媒混合比例分別為35/65(HC1)、50/50(HC2)與100/0(HC3)，充填比例則是R-134a的冷媒充填量的30%、40%、50%與60%。各種HC冷媒在不更動毛細管長度的情況下以不同充填比例與環境溫度的進行冷凍系統性能實驗。本研究主要探討冷凍系統的性能係數、能源因數、庫內溫度、壓縮比、壓縮機外殼溫度與系統高、低壓壓力。由實驗結果分析各HC冷媒的最佳充填量並修正毛細管長度之後再依據CNS測試標準進行24小時的性能測試。 實驗結果顯示HC1、HC2與HC3的最佳充填量分別為40%、40%與40%。在最佳HC冷媒充填量之下大部分的實驗結果顯示HC冷凍系統的冷凍庫溫與消耗電力高於R134a冷凍系統。此外由低壓壓力可以發現所有HC冷凍系統的蒸發溫度均有過高的現象。這種現象代表毛細管所提供系統的高低壓力差不足。因此本研究以絕熱毛細管長計算公式搭配5℃過冷度的設定之下重新計算HC1、HC2與HC3冷媒的毛細管長度分別為5.0m、5.4m與5.6m。接著將冷凍系統換裝新的毛細管並根據CNS標準進行24hr的性能測試。實驗結果發現碳氫冷媒與R134a冷媒相比較最高能增加下拉溫度的斜率與能源因數分別為15%與12%；消耗電力方面最高可以節省22%。就整個研究結果而言，R134a冷凍系統要換裝碳氫冷媒必須重新設計毛細管。再者碳氫混合冷媒中的R600a所佔比例越高越能夠提升冷凍系統的EF與COP。此外HC冷媒的冷凍系統性能受到環境溫度上升的影響比R134a冷媒明顯，因此HC冷凍系統比較適合使用在環境溫度較低的場所。

This study adopted hydrocarbon mixtures (R600a/R290) in the small R-134a refrigeration system to evaluate the performance of refrigeration. The mixing ratio by mass of R-600a/R-290 refrigerant were 35/65 (HC1), 50/50 (HC2) and 100/0 (HC3), charged ratio were 30%, 40 %, 50% and 60% base on the charged amount of R-134a refrigerant. The HC refrigeration systems without changing the capillary tube lengths were carried out the performance test at different charged ratios and ambient temperatures. This study investigated the coefficient of performance (COP), energy factor, freezing temperature, compression ratio, compressor housing temperature, high side and low side pressure. To determine the optimal charged ratios of HC refrigerants and corrected capillary lengths, and then performed the 24-hour performance test according to CNS testing standards. The experimental results showed the optimal charged ratios of HC1, HC2 and HC3 were 40%, 50% and 40%, respectively. The most of the experimental results of HC refrigeration systems with the optimal charged ratios showed that freezer temperature and power consumption was higher than R134a refrigeration system. Moreover, all HC refrigeration systems had higher evaporation temperature phenomena that could be observed by the low pressure. This phenomenon demonstrated that the capillary tube could be not provided enough pressure difference between the high-pressure side and low-pressure side. Therefore, this study adopted the calculation of adiabatic capillary tube length with subcooling temperature of 5℃ to recalculate the capillary tube length of HC1, HC2 and HC3, and the capillary tube lengths of HC1, HC2 and HC3 were 5.0m, 5.3m and 5.6m, respectively. Next, the refrigeration systems with new capillary tube lengths to perform the 24-hour performance test according to CNS testing standards. Experimental results showed that the highest increased ratio of the slope of pull-down and the energy factor with HC refrigerants was 15% and 12%; electricity consumption can be saved up to 22% compared with R134a refrigerant. The results in terms of the whole, the R134a refrigeration system was retrofitted HC refrigerants must to redesign the capillary tube lengths. Furthermore, higher proportion of R600a in HC mixtures could enhance the EF and the COP of refrigeration system. Moreover, refrigeration system performance of HC refrigerant was affected by the ambient temperature raises significantly than R134a refrigerant, therefore, application of HC refrigeration system is more suitable in the place with lower ambient temperature.