新冷媒R-134a在平板式熱交換器冷凝熱傳及壓降之實驗研究

Abstract

本篇論文係藉由實驗研究，探討新冷媒R-134a在一垂直平板式 熱交換器中的冷凝熱傳數及壓降。熱交換器內的三塊板子形成兩個 流路，向下流的R-134a將熱傳給向上流的冷水。影響本冷凝實驗的 參數有：冷媒質通量，熱通量，系統壓力及冷媒乾度。 實驗結果指出熱傳及壓降在高乾度時比低乾度高很多。當質通量 增加時，熱傳也隨之增加，壓降增加幅度較熱傳多。另外，熱傳和壓 降也隨著熱通量增加而有微的上昇，在較高壓力時熱傳增加較大。 而較大的系統壓力會導致熱傳些許減少，但對壓降沒影響。最後得到 對熱傳係數及壓降的關係式。

An experimental refrigerant loop has been established in the present study to measure the condensation heat transfer coefficient h and pressure drop ΔP of R-134a in a vertical plate exchanger. Two vertical counter flow channels were formed int he exchanger by three plates of comercialized geometry with a corrugated sin shape of a chevron angle of 60°. Downflow of the condensing R-134a in one channel releases heat to the cold upflow of water in the other channel. the effects of the refrigerant mass flux, imposed heat flux, system pressure (saturated temperature) and vapor quality of R-134a on the measured data were explored. The results indicate that at a higher vapor quality the condensation heat transfer and pressure drop are significantly higher. The increase in the pressure drop with the quality is much larger. While a rise in the refrigerant mass flux only causes a mild increase in the h values for most cases. The corresponding rise in the Δp is slightly larger. Furthermore, it was noted that the condensation heat transfer is only slightly better for a higher imposed heat flux. But the associated ΔP is larger. However, at a higher system pressure the rise in h with the heat flux can be significant. finally, at a higher system pressure the h value was fond to be slightly lower. But the effects of the system pressure on ΔP is small. Correlations were also developed for the measured heat transfer coefficients and pressure drops in terms of the Nusselt number and friction coefficient.