積液式熱交換器(LOF-AHX)應用於冷凍系統之研究

Abstract

積 液 式 熱 交 換 器 (LOF-AHX) 應 用 於 冷 凍 系 統 之 研 究 學生：宋炳彥 指導教授：盧定昶 國立交通大學機械工程研究所 摘 要 本實驗採用的冷凍系統是以氣冷式進行熱交換，及使用環境控制室來控制外界環境溫度變化，以進行實際性能分析。冷凍庫容積為250公升，工作流體為R-404a，壓縮機為1/3馬力，搭配積液式熱交換器(Liquid Over Feeding-Accumulator Heat Exchanger；LOF-AHX)裝置在冷凝器出口與蒸發器出口之間的迴路，以進行熱交換使毛細管入口端增加過冷度及壓縮機入口端獲得飽和汽態或接近飽和汽態之過熱汽，並兼具液汽分離器的功效以保護壓縮機免於液壓縮。先測試冷凍系統之base line(基準)狀態，再經由控制閥開關調整為LOF(積液式)狀態，並進行兩者的性能測試比較。測試結果顯示，本實驗系統於base line狀態時，適合毛細管長度為1.6 m，及適合冷媒充填量為600 g；於增置LOF-AHX時，搭配適當的過度冷媒充填量後之總充填量為800 g，及搭配適宜的增長毛細管長度後之總長度為2.0 m 。實驗顯示增置LOF-AHX，同時可降低壓縮機吐出溫度及獲得較低的壓縮壓力比，進而增加冷媒質量流率，以提升系統冷凍能力，使得系統冷凍性能係數獲得改善。如冷凍庫內溫度維持在-15℃時，當外界環境溫度為20℃，則過冷度可增加約14℃、過熱度可降低約11℃，COP值可提升約13﹪；而當外界環境溫度為32℃時，COP值可提升約10 ﹪。

Experimental Study of A Liquid Over Feeding－ Accumulator Heat Exchanger Refrigerating System Student：Ping-Yen Sung Advisor：Ding-Chong Lu Institute of Mechanical Engineering National Chaio Tung University ABSTRACT In the present study, a refrigerating system was built with air-cooling heat-exchangers and tested with adjusted room temperature in the environment control room in order to analyze the functional performance of the refrigerating system. The volume of the cooling space is 250 liter, driven by a 1/3 HP compressor with working fluid R-404a. The refrigerator is equipped with an LOF-AHX (Liquid Over Feeding-Accumulator Heat Exchanger) in which a piping circuit is assembled in both the outlet of the condenser and the outlet of the evaporator so as to attain subcooling of capillary inlet point and saturated or low superheated vapor of compressor inlet point of the working fluid. The LOF-AHX is also used as the liquid-vapor separator to protect the compressor from liquid compression. We tested the base line state without LOF, and change to LOF loop for the comparison of the test results. The test results showed that the appropriate capillary length is 1.6 m and refrigerant charge is 600 g for base line state of system，and that the appropriate capillary length is 2.0m and refrigerant charge is 800 g for LOF state of system. The test results indicated that improvement of the system with the LOF-AHX has a lower compressor discharge temperature, a lower compressor high-low pressure ratio, higher refrigerant mass flow rate, higher cooling capacity and better COP. For example, for a cooling space at -15℃, and ambient temperature at 20℃, the LOF system can raise the subcooling to 14℃, and can reduce the superheat to 11℃, as well as improve the COP by 13﹪in comparison with the base line.