具積液式熱交換器之階層式混合冷媒之冷凍系統

Abstract

本研究目的為設計改良一自動階層式混合冷媒冷凍系統之冷凍能力。 實驗系統採用單壓縮機冷凍系統，工作流體R-32/R-134a的混合冷媒。系統中加入一個相分離器使混合冷媒濃度改變，其中使氣態與液態冷媒自動分離，氣態冷媒流經階層式熱交換器與膨脹後的低溫液態冷媒進行熱交換，然後較高濃度的高沸點冷媒流過蒸發器製冷，最後與較低濃度的低沸點成分冷媒匯流至壓縮機，完成單壓縮機的自動階層(Auto-Cascade)冷凍循環。另外在迴路中設計積液式熱交換器(Liquid Over Feeding Accumulator Heat Exchanger；LOF-AHX)，將其加裝在蒸發器出口與冷凝器出口之間的迴路，讓高壓循環的常溫液態冷媒與低壓循環的低溫氣態冷媒進行熱交換，可使進入壓縮機前的冷媒獲得過熱度，以保護壓縮機免於液壓縮；並可使進入膨脹閥前的液態冷媒獲得過冷度，提升冷凍效能增加冷媒質流率，並降低壓縮比與吐出溫度。 由於混合冷媒cascade loop有濃度偏移的效應，配合LOF更可大幅提昇其冷凍能力，故本實驗之最佳化COP達到2.126，最低溫度為-38.35oC，皆出現在混合冷媒搭配積液式熱交換器之cascade loop。

The objective of this research is to design and improve the efficiency of the cascade refrigeration system with zeotropic refrigerant mixtures. This system utilizes a single compressor with R-32/R-134a refrigerant mixtures. Phase separator is put in this system in order to change the concentration of refrigerant mixtures. The vapor phase flows through a cascade heat exchanger and exchanges latent heat with the low temperature liquid phase after expansion. Then, the higher-boiling-component mixture flows into the evaporator to create the low temperature cooling, and merges with the lower-boiling-component mixture, which leads finally back to the compressor and thus completes a cycle. Furthermore we design a Liquid Over Feeding Accumulator Heat Exchanger（LOF-AHX）between the outlet of the evaporator and condenser in order to make the high pressure liquid refrigerant exchange heat with the low pressure vapor refrigerant. This design enables the refrigerant: (1) to get super heat before sucking into compressor in order to protect compressor from liquid compression; (2) to get subcooling before entering expansion; (3) to increase the mass flow rate; (4) to raise the cooling capacity; (5) to reduce the pressure ratio and exit temperature. Due to the concentration shift effect of cascade loop of refrigerant mixtures, using LOF can raise cooling capacity substantially. Therefore, the optimal COP can reach 2.126, as well as the lowest temperature can reach –38.35oC. All of those results occur in cascade loop of refrigerant mixtures with LOF.