先進噴射式製冷系統研發

Development of an Advanced Ejector Cooling System

胡勝雄(Sheng-Shiung Hu)

指導教授 ： 黃秉鈞

國立臺灣大學/工學院/機械工程學研究所/博士(2005年)

https://doi.org/10.6342/NTU.2005.02335

摘要

傳統噴射式製冷技術關鍵包括系統可靠度（唯一可動件－循環泵浦）、系統操作穩定性穩定性（噴射器背壓）與驅動源（太陽能或廢熱）等問題。
為了解決採循環泵浦可靠度問題，並考慮未來搭配太陽能與廢熱的應用，本研究開發一新型噴射式製冷系統，利用一多功產生器加熱及冷卻的交互切換來造成壓力差以將工作流體送回產生器，達到取代機械式循環泵浦的目的。本研究所製作的原型機連續運轉測試結果顯示冷媒採用R141b，噴射器A-G匹配，在產生溫度89℃、蒸發溫度8.5℃、及冷凝溫度37.0℃時，製冷量為0.75kW，系統COP為 0.225。
本研究並對替代R141b之冷媒－R365mfc於噴射式製冷系統應用作一系列的探討，包括物理特性、系統分析與實驗測試。研究結果顯示，在相同產生溫度、蒸發溫度與冷凝溫度的操作條件下，R365mfc需要較大面積比的噴射器。實驗結果顯示，在同樣的噴射器匹配下，R141b會有較高的製冷量與COP，然而R365mfc卻可以在較高的噴射器背壓下操作。採R365mfc的系統操作，噴射器A-G匹配，在產生溫度89.7℃、冷凝溫度36.7℃、蒸發溫度8.2℃下，製冷量為0.32 kW，系統COP為0.107。在相同噴射器A-G匹配下，本研究採R365mfc之系統COP雖然較採R141b低，但理論分析顯示，採R365mfc的噴射式製冷系統以大面積比的噴射器，便可將COP提升到與R141b相同。
為了應付因環境溫度過高的造成噴射器背壓之穩定性問題，本研究也開發新型水簾片式冷卻水塔。從水簾片單元之分析模式搭配實驗，推導出一水簾片單元經驗式，此經驗式在 誤差範圍內。以此經驗式設計之水簾片水塔，出水溫度誤差在 內。根據ASHRAE測試標準，在乾球溫度 oC，濕球溫度 oC下，水簾片水塔在測試後發現比一般水塔有較佳的表現（在高濕球溫度27℃下亦可達到同樣的要求），且相同散熱量與操作條件下與市售冷卻水塔相較，體積約減少一半。
本論文整合以上關鍵技術，包含解決循環泵浦可靠度，考慮未來搭配太陽能與廢熱的應用，替代冷媒的測試與噴射器背壓之穩定性問題，成功的針對噴射式製冷系統可靠度、穩定性、驅動性與前瞻性提出解決方案，對於噴射式製冷系統實際應用上將有顯著的貢獻。

關鍵字

噴射器 ； 製冷 ； 無動件 ； 熱能驅動

並列摘要

Some crucial problems hinder conventional ejector cooling system (ECS) from putting in use, like reliability of the mechanical circulating pump, stability of the back pressure of ejector, and heat recovery from solar energy or waste heat etc.
Taking reliability of the mechanical circulating pump and heat recovery problems into account, a new ECS is proposed. This new ECS utilizes a multi-function generator (MFG) to eliminate the mechanical circulating pump. The MFG is designed based on the pressure equilibration between high and low pressure through heating and cooling process. In this design, an ECS that contains no moving components and is entirely powered by heat can be achieved. A prototype using refrigerant R141b a working fluid was constructed and tested in the present study. The experimental results show that the system coefficient of performance (COP) is 0.225 and the cooling capacity is 0.75 kW at generating temperature (Tg) 89oC, condensing temperature (Tc) 37 oC and evaporating temperature (Te) 8.5 oC. It is shown that a continuous operation for the generation of cooling effect in an ECS with MFG can be achieved. This cooling machine can be very reliable since there is no moving part.
With the phasing-out of CFCs and HCFCs on the basis of the Montreal and subsequent international Protocols, an environment friendly refrigerant, R365mfc, for substituting R141b is studied. Comparisons of physical properties, theoretical performance of ECS and experiment tests with R141b and R365mfc are made. The results show R365mfc needs bigger geometric design parameter of the ejector A3/At at the same generating temperature, condensing temperature and evaporating temperature. In the same A3/At, R141b has higher cooling capacity and COP while R365mfc has higher critical condensing temperature. Experiment results show, the ECS with R365mfc and ejector A-G, the COP is 0.107 and the cooling capacity is 0.32 kW at Tg =89.7oC, Tc =36.7 oC and Te =8.2 oC. In the same ejector A-G, the COP with R365mfc is lower then R141b, but the COP with R365mfc can be improved by changing ejector into higher A3/At ratio.
A new cooling tower adopting cellulose pads as filling material to deal with the stability problem of the back pressure of ejector is also proposed. A correlation equation for a fundamental cellulose cell (0.3m 0.3m 0.15m) within ±5% is acquired and the prediction of the outlet temperature of the cooling tower using the correlation is also within ±5% error. According to ASHRAE test conditions, the dry-bulb temperature should be oC and the wet-bulb temperature should be oC, in our test, the new cooling tower with cellulose pad has better performance and smaller size than the same scale commercial cooling tower. For about 10kW heat-transfer rate, the size of the new cooling tower with cellulose pad is only half of the size of the commercial one.
This research successfully proposed (1) a new ECS with MFG to eliminate the mechanical circulating pump; (2) studies and tests of ECS with R365mfc for substituting R141b; (3) a new cooling tower adopting cellulose pads as filling material to deal with the stability of the back pressure of ejector. Hence, this research does significant contributions to the promotion of the ECS.

並列關鍵字

ejector ； cooling ； no moving part ； heat-driven

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