應用於中高溫熱泵殼管式冷凝器設計之數學模型發展與驗證

中高溫熱泵熱水系統出水溫度可提高至80℃以上，但為了達到高出水溫度，需相對提高冷凝溫度，造成壓縮機耗電加大，性能係數降低。而在高冷凝溫度的情形下，冷媒在冷凝器內冷凝過程中的過熱段焓差比大幅增加，因此，在滿足出水溫度80℃以上的要求下，冷凝器之設計必須要能夠有效回收冷媒側高過熱段之熱能來降低冷凝溫度，以兼顧系統的能源效率。而在冷凝器的設計過程中，須考慮包含：流體的熱力性質、流體的進出口溫度、熱傳面積等參數，通常需藉由實驗量測來了解冷凝器的性能，但藉由實驗量測需耗費較多的成本與時間，因此若能夠建立可供用於中高溫熱泵系統所使用之冷凝器的數學模型以發展設計程式，可大幅減少實驗量測所耗費的成本與時間。有鑑於此，本研究的主要目的在於：以一台中高溫熱泵系統所使用之殼管式冷凝器，進行實驗量測，並建立熱力關係式和數學模型後，進行冷凝器熱傳率和設計問題(尺寸設計、性能估算和壓降)之計算，其結果與實驗量測數據進行驗證。研究結果發現：以所發展之數學模型在尺寸設計(管長計算)的計算上整體差異值為3.85%，在性能估算(熱水質量流率、熱水出水溫度、冷凝溫度和冷媒出口溫度)的計算上所有的差異值均在0.6~5.6%以內，在壓降計算上整體的差異值為5.48%。

關鍵字

中高溫熱泵；殼管式冷凝器； UA-LMTD-F法； ε-NTU法

並列摘要

Water outlet temperature of moderately high-temperature heat pump systems may rise up to 80℃. However for the purpose of this, it must rise condensing temperature, and also cause the power output of compressor increase, coefficient of performance decrease. In high condensing temperature, the enthalpy difference ratio of superheated vapor in condensing process of condenser is also rise. Therefore, the designing of the condenser must recover the heat of superheated vapor so that reduce the condensing temperature. During the designing of a condenser, it should be consider many parameters, such as fluid thermal properties, fluid inlet and outlet temperature, heat transfer areas of condenser and so on, it usually need experimental measurements to know the heat capacity of the condenser, but it will cost a lot of money and time. So if we can develop the mathematical model of the condenser in moderately high-temperature heat pump to write program may reduce a lot of money and time in experimental measurements. The purpose of this study was to develop the mathematical model of a shell-and-tube condenser in a moderately high-temperature heat pump system, calculated heat transfer rate and design problems (sizing, rating and pressure) of the condenser, the calculations of the mathematical model were valid by experimental data. The modeled results showed that the deviations of sizing were 3.85%, 0.6~5.6% of rating, and 5.48% of pressure drop.

並列關鍵字

Moderately high-temperature heat pump ； Shell-and-Tube condenser ； UA-LMTD-F method ； ε-NTU method

參考文獻

[1] A. Kahraman and A. Celebi, "Investigation of the performance of a heat pump using waste water as a heat source," Energies, vol. 2, 2009, pp. 697-713.

[4] Y.A. Kara and O. Guraras, "A computer program for designing of shell-and-tube heat exchangers," Applied Thermal Engineering, vol. 24, 2004, pp. 1797-1805.

[5] R.D. Moita, C. Fernandes, H.A. Matos and C.P. Nunes, "A cost-based strategy to design multiple shell and tube heat exchangers," Journal of Heat Transfer, vol.126, 2004, pp. 119-130.

[6] T. Karlsson and L. Vamling, "Flow fields in shell-and-tube condensers:comparison of a pure refrigerant and a binary mixture," International Journal of Refrigeration, vol. 28, 2005, pp. 706-713.

[7] R. Selbas, O. Kızılkan and M. Reppich, "A new design approach for shell-and-tube heat exchangers using genetic algorithms from economic point of view," Chemical Engineering and Processing, vol. 45, 2006, pp. 268-275.

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應用於中高溫熱泵殼管式冷凝器設計之數學模型發展與驗證

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