噴射器漸擴段長度的最佳化設計與分析

Optimal Design Of The Diffuser Length For An Ejector

鍾崴宇(Wei-Yi Chung)

指導教授 ： 顏瑞和

國立臺灣大學/工學院/機械工程學研究所/碩士(2012年)

https://doi.org/10.6342/NTU.2012.02527

摘要

由於太陽能噴射式製冷系統技術日益成熟，無論是量產化地裝設在各家各戶，或是巨大尺寸的設計，成本的負擔絕對不容小覷；因此，本研究特地針對噴射器中最顯著的長度-等截面漸擴段長度進行研究，在不影響性能的前提下，節省最多的噴射器長度，以符合成本與性能的最佳平衡。
本研究使用商用計算流體力學(CFD)軟體Fluent，針對噴射器漸擴段幾何形狀對內流場影響進行研究，並結合噴射器等截面段長度，探討等截面段與漸擴段長度如何影響噴射器性能，研究發現，在設計漸擴段時，理論上噴射器擁有越大的出口截面積，出口流速就越慢，會有越高的臨界溫度，但漸擴角度太大會產生邊界層分離現象，導致出口截面積的大小會受制於漸擴角度，無法持續增大來提高臨界溫度，因此出口截面積設計上是存在最佳的尺寸範圍，才能使噴射器擁有最佳的性能，由此可知，縮短噴射器等截面漸擴段長度前，須先找出噴射器出口截面積與漸擴角度能適用的範圍，在為噴射器等截面漸擴段設計最佳的長度。
噴射器等截面漸擴段長度在特定的範圍內並不會影響噴射器性能，而最短的長度就為最佳化等截面漸擴段長度。本實驗結合太陽能輔助製冷供熱技術，替可調式噴嘴噴射器的操作溫度範圍Tg=90~110℃、Te=8~15℃以及Tc=35~40℃設計最佳化的等截面漸擴段長度，以往設計等截面漸擴段的總長度都固定為215mm，雖可使噴射器正常運作，但長度卻設計太長，浪費製作噴射器的原料，其實最佳化等截面漸擴段的總長度只需設計160mm就可使噴射器操作在最佳的性能上，相較於原始長度215mm能縮短25.6％以上，由此可知，研究噴射器等截面漸擴段長度可以有效的減少噴射器製作成本。

關鍵字

噴射器

並列摘要

The ejector is the most essential component in an ejector cooling system affecting its performance. Thus, designing the best ejector has long been the objective of research by many scholars. Since the early application of one-dimensional theory could not be used to analyze the length of the component, this study instead used computational fluid dynamics (CFD) to investigate the impact of the process of shortening and elongating the length of the diffuser section of the ejector on the injector flow field. This study further analyzed methods for minimizing the length of the diffuser section without affecting the performance of the ejector under various operating temperatures and changes to the throat area of the primary nozzle, so as to meet the criteria of cost and maximum benefit to performance. The following conclusion can be drawn.
The larger cross-sectional area of the diffuser exit, yielding the slower exit velocity, makes the critical temperature higher. And if the diffuser angle is too large, the boundary layer separation in the diffuser may occur, that limits the size of cross-sectional area to increase the critical temperature. Therefore, the cross-sectional area of the diffuser exit has the optimal size range. The constant cross section area length and diffuser length have a specific size range that does not affect the performance of the ejector. The case study of a variable throat nozzle ejector for operating with the range of the generator temperature, Tg, from 90℃ to 110℃, evaporator temperature, Te, from 8 to 15℃ and condenser temperature, temperature, Tc, from 35 to 40℃, the constant cross section area length and diffuser length can be 25.6% shorter than that of the original design.

並列關鍵字

Ejector

參考文獻

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