二相流噴嘴應用於全流式發電系統之實驗性能分析研究

Abstract

本研究建立在全流式地熱發電機組中用以產生推力之噴嘴上，利用不同條件下之噴嘴型式使用單相流噴射或二相流流體進行噴射，偵測和記錄其在不同溫度點下產生之推力值和單位時間的質量變化量進而推算其速度和能量，並從繪製而成的圖表中分析並比較其中優劣，此外，亦沿用前人研究的方式，將實驗結果和理論數值之比值定義為推力係數，將此無因次數值在不同噴嘴條件、噴射方式和溫度點繪製成圖，並利用其在各條件下的最大值比對前人實驗成果得出結論和最佳化方案。 實驗結果顯示上述各項數據如推力值、質量流率、速度和能量，無論不同噴嘴條件下均隨溫度上升而增加，然而後兩者並未與喉部直徑呈現正相關，隨著喉部直徑的增加，將存在極限值使得速度呈現最大化，且從能量表現上看來，二相流噴射對比單相流噴射時，喉部直徑14mm的噴嘴將超過17mm的噴嘴，意味著二相流噴射下速度項對能量的影響將大於質量變化的影響。最後將實驗推力值和假設等熵過程下的理論推力值之比值視為推力係數，比較各噴嘴和不同噴射模式，係數均隨溫度上升而整體增加且以14mm表現最佳，且二相流噴射優於單相流。若總結所有最大推力係數並依據出口與喉部的截面積比繪製成圖，以此結果與前人研究比較可發現，不管擴散角度如何推力係數均會呈現中間極值的狀況，且隨角度增加將使得極值所在的截面積比增加，此外，若在本實驗以能呈現最大推力係數的方面進行考量並結合本次實驗的出口面積計算，喉部尺寸應設定為11.18mm上下能有更好的效果。

The purpose of the investigation is about the nozzle of total-flow geothermal power plant to generate thrust. Utilizing single phase or two-phase flow jet under different kinds of conditions, we detect and record the thrust and mass flow rate with specified temperature point, then calculate the velocity and energy, and analyzes the pros and cons from the chart. Besides, we adopt predecessors’ method and treat the ratio of experimental result to theoretical value as thrust coefficient, drawing diagrams of this dimensionless value under different nozzle conditions, jet type, and temperature point. It can produce conclusions and optimization by comparing the maximum under all conditions to predecessors’ result. The experimental results reveal that regardless of different nozzle conditions, all parameters above mentioned like thrust, mass flow rate, velocity and energy rise along with the increasing of temperature, but the latter two are not positive correlation with throat diameter. There exists the extremum maximizing velocity. Observing the energy chart and comparing two-phase jet to single phase jet, the nozzle of 14mm throat diameter is better than the nozzle of 17mm. It can show that with two-phase jet, the influence caused by velocity term are bigger than mass change term. Finally, treating the ratio of experimental thrust value to theoretical value supposed under isentropic process as thrust coefficient and comparing it under all nozzle and two types jet, the coefficient will rise along with temperature and the nozzle having 14mm throat diameter is the best. Furthermore, two-phase jet is better than single phase jet. If combining all maximum thrust coefficient and drawing diagrams with the cross-sectional area ratio of export to throat, compared to predecessors’ result, there can be observed that it would exist middle extremum regardless of different diverging angle, and the cross-sectional area ratio of the extremum also increases along with diverging angle. Moreover, if pursuing the nozzle which can produce maximum thrust coefficient, taking the fixed experiment export area into account, the throat diameter should be set 11.18mm making the performance better.