地熱發電用向心式渦輪機之最佳化設計與模擬分析

Abstract

地熱發電對位於環太平洋火山帶的台灣而言，是相當有潛力能發展的一項再生能源，故本論文根據宜蘭地區的地熱條件進行對向心式渦輪機之設計與模擬，其中假設渦輪機當中流體的質量流率與進出口熱力條件，並於文獻回顧後選擇R134a高密度流體為工作流體。為了建立渦輪機的尺寸和提高渦輪機效率，此篇論文運用mean-line approach design並透過engineering equation solver (EES)進行初步設計並配合基因演算法進行最佳化，接著使用商用軟體CFTurbo建立渦輪機的模型，最後使用商用軟體ANSYS CFX進行3D模擬分析並與初步設計結果進行比較。 本論文探討經由初步設計後得出的渦輪機尺寸，並且透過改變葉形結構和渦輪機參數觀察其對渦輪機性能的影響，因而發現在相同初步設計結果下隨著葉形結構的不同渦輪機所輸出的功率也有所不同；然而當葉片通道中有迴流產生時，改變葉形結構無法完全消除迴流狀況，而透過提升比速度(specific velocity)能改善葉片通道中的迴流情形，再加上最佳葉形結構的定義進而提升渦輪機的功率達3.5 %。

We present a numerical model of a turbine from a geothermal resource. According to the geographic condition in Yilan, the radial-inflow turbine is more suitable for our simulation. In order to know the performance of the radical-inflow turbine in refrigerant, we choose R134a, which is high density fluid and would have better efficiency of turbine in geothermal resources of low temperatures (below 100 oC). A method namely mean-line approach design is used to create the optimal geometry of the turbine by engineering equation solver (EES). Furthermore, we employ the commercial software (ANSYS CFX) to simulate the model and compare the result with the model from the mean-line approach. In present work, we create simulation model which was calculated by preliminary design, then we change the shape of rotor blade and turbine coefficients in order to understanding its effect. It would change the power of turbine by changing the shape of rotor blade. However when there is separation flow in the rotor passage, it seems no effect on changing the shape of rotor blade. When increasing specific velocity, it has great effect on making separation flow disappear. Therefore, it results in increasing 3.5 % power of turbine by defining the optimal specific velocity and optimal blade shape.