蒸汽壓縮式冰水機組之熱力最佳化分析

Thermodynamic Optimization of Vapor-Compression Liquid Chillers

傅彥鈞(Yen-Chun Fu)

指導教授 ： 李宗興

國立臺北科技大學/機電學院/冷凍空調工程系所/碩士(2005年)

https://doi.org/10.6841/NTUT.2005.00136

摘要

蒸汽壓縮式冰水機組為空調系統中最主要之耗用能源設備，故而致力於提升該製冷設備能源效率之相關研究一直是重要課題。現有冰水機組能源效率之衡量，皆採用源自於熱力學第一定律(能量守恆定律)之性能係數COP，然而該係數僅能表達冰水機組之整體能量平衡與能源轉換效率，並無法表達各元件可用能轉換之無效性或可用能毀滅程度。由於冰水機整體能源效率受到各元件可用能轉換之無效性的影響，因此將焦點集中於探討設計參數對元件可用能與其不可逆性之影響，將是研究如何提升冰水機組能源效率之最直接的途徑。此外，發展考量熱經濟觀念之冰水機組熱系統最佳化設計之研究，也是目前所迫切需求的。
因此本文之主要研究目的為：藉由熱力學第一、第二定律與可用能之觀念並配合實驗之驗證，發展可供具體分析與評估冰水機組各元件可用能毀滅比率之熱力分析模式，用以確定提昇冰水機組能源效率之改善方向。接著再經由設計參數分析探討冷凝與蒸發溫度對於機組各元件之不可逆性與元件彼此之間的影響，用以評估改善各元件對提升能源效率之潛力。最後，在考量熱經濟效益之前提下，發展熱力最佳化分析模式，藉以尋找熱交換器最佳熱導度(UA)之分配比例，達到在有限的成本下冰水機組系統性能最佳化之目的。
研究結果顯示：(1)影響冰水機組能源效率之元件可用能毀滅率，以壓縮機最大(約為37.4 - 46.6 %)，其次為冷凝器(約22.1 - 26.7 %)、蒸發器(約為16.7 - 24.2 %)、膨脹閥(約為8.6 - 10.3 %)，而連接管路之不可逆性對系統性能的影響可忽略。(2)降低冷凝溫度1℃， 之相對變化率為 -4.7％，COP相對變化率為 3.4％，而增加蒸發溫度1℃， 之相對變化率為 -4.6％，COP相對變化率為 3.9％。(3)在相同的熱交換器總熱導度 與冷凍能力之條件下，當冷凝器與蒸發器之總熱導度分配率為0.5時，可獲得冰水機組性能之熱力最佳化，此結果與Bejan [11]、Khan and Zubair [24] 所獲得的結論相同。

關鍵字

可用能 ； 不可逆性 ； 熱力最佳化 ； 蒸汽壓縮式

並列摘要

The vapor-compression liquid chiller is the main energy consuming equipment in the air-conditioner system, so studying on energy saving has been an important issue. The coefficient of performance (COP) used to express the whole energy efficiency for liquid chillers performance is based on the conservation of energy of thermodynamics, which is not able to indicate the exergy destruction or irreversibility of each component. Therefore, focusing on the irreversibilities of chiller components becomes the most direct way to improve energy efficiency of liquid chiller. In addition, the research on thermodynamic optimization as well as thermoeconomic of liquid chiller is urgent for equipment designer.
Therefore, the main research purposes of this study are: (1) developing an irreversibility analysis method for liquid chiller to indicate the direction of performance improvement; (2) parametric studing the influence of design parameters, such as condensing and evaporating temperature, on the component irreversibilities and the system performance, and to estimate the improvement potention of each component on the system energy efficiency; (3) developing a thermodynamic optimization method together with the consideration of thermoeconomic to study the optimium allocation proportion of thermal conductance of heat exchangers. Three experimental data are comparied with the prediction results obtained herein.
The results show that the compressor possesses the largest potential to improve energy efficiency with the ranges of 37.4 to 46.6%, followed in order by the condenser (about 22.1-26.7 %), and then the evaporator (about 16.7-24.2 %). Reducing 1℃of the condensation temperature will results the change of irreversibilities of - 4.7 % and the COP of 3.4 %. In addition, increasing 1℃of the evaporation temperature will results the change of irreversibility of -4.6% and the COP of 3.9%. Under the same total thermal conductance of heat exchanger and cooling capacity, the optimum allocation ratio of thermal conductance of the condenser and evaporator is 0.5.

並列關鍵字

exergy ； irreversibility ； thermodynamic optimization ； vapor compression

參考文獻

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[9] 李宗興、黃勝吉，「熱力學不可逆性應用於螺旋式冰水機組能源效率提昇之研究」，台北科技大學學報，36-2期，第63-71頁，2003。

[2] Bejan, A., Entropy Generation Minimization, Wiley, 1996.

[3] Bejan, A., Advanced Engineering Thermodynamics, Second Edition, Wiley, 1998.

[4] Bilgen, E. and Takahashi, H., Exergy analysis and experimental study of heat pump systems, Exergy, Vol.2, pp.259-265, 2002.