摘 要
　　結合有限時間熱力學理論與可用能分析觀念的可用能效率最佳化方法被應用到數個冷凍循環系統，包含不可逆卡諾冷凍循環系統、不可逆布累登冷凍循環系統、不可逆中間冷卻冷凍循環系統以及二級不可逆併合冷凍循環系統。在分析中考慮的多重不可逆性包含熱庫與循環工作流體間有限的熱傳遞率、循環工作流體的內部損耗和熱庫之間的熱漏。定義為可用能輸出率與可用能輸入率的比值的可用能效率被提出作為最佳化的目標函數。可用能效率最佳化即將此目標函數求取最大值。這些最大可用能效率皆以解析的方法獲得決定。在最大可用能效率情況下，系統的相關最佳參數值亦皆可隨之求出。這些系統的參數都可在評估這些冷凍循環系統性能時，當作為有效而重要的設計準則。而一些系統的設計參數對此最大可用能效率之影響亦在文中加以討論。文中亦說明使用可用能效率作為目標函數的合適性。此外，在不可逆卡諾冷凍循環系統和不可逆布累登冷凍循環系統的研究中，針對一個固定總熱導率於高、低溫側熱交換器的配置問題，亦以數值方法加以討論，並獲得最佳配置之結果。

Abstract
　Exergetic efficiency optimization that combines finite-time thermodynamics theory and exergy concept has been applied to an irreversible Carnot refrigeration system, an irreversible Brayton refrigeration system, an irreversible inter-cooled refrigeration system and a two-stage irreversible combined refrigeration system. Multi- irreversiblities considered in these systems include finite rate heat transfer, internal dissipation of the working fluid and heat leak between heat reservoirs. Exergetic efficiency defined as the ratio of rate of exergy output to rate of exergy input of the system is proposed as the objective function to be optimized. The goal of exergetic efficiency optimization is to maximize the objective function. These maximum values of the exergetic efficiency can be determined analytically. The corresponding optimum values of parameters of these systems are obtained simultaneously. These parameters of the system can be effective and important design criteria while evaluating the performance of these refrigeration systems. The influences of design parameters of the system on the maximum exergetic efficiency are discussed. The appropriation of using exergetic efficiency as objective function is discussed. Moreover, in the research of irreversible Carnot and Brayton refrigeration systems, the allocation of a fixed total thermal conductance between the two heat exchangers is discussed using numerical calculation. The results of optimum allocation are also obtained.

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