以STAR-CD軟體作陶瓷板式熱交換器與梯間加壓性能模擬

Abstract

摘要

本文應用 STAR-CD 套裝軟體分別模擬兩個案例。第一個案例為模擬兩50KW陶瓷板式熱交換器（材料分別為碳化矽以及堇青石）之溫度場及壓力場．並利用此數據作接下來之熱應力之分析。裝設的環境，其廢熱側進口溫度為1000℃，預熱側進口溫度為27℃。因為計算格點將近兩百二十萬個，為了提高計算的效能，本案例使用STAR-CD平行計算軟體來處理。模擬出來的結果顯示碳化矽及堇青石兩熱交換器其總熱傳量分別為56.74 KW和56.72KW。和傳統經驗公式比較的誤差為2~4%，由此可見模擬結果相當的準確。此案例模擬出來的速度場和壓力場可提供作為陶瓷板式熱交換器的熱應力計算，這是傳統經驗所無法辦到的。 第二個案例為高層建築梯間加壓系統性能評估。模擬的對象為20層的高樓(四層在地下室)，裝設在頂樓的加壓風機其流量為19000CMH。為了知道不同的梯間設計對梯間防煙效能的影響，分別建立了三種不同的模型，分別為梯間無模擬樓梯、梯間含前室、梯間模擬剪刀樓樓梯間。並再針對門縫有無氣密設計，防火門有無打開以及可壓縮流和不可壓縮流等三種設計參數對梯間加壓性能的影響。其模擬結果顯示梯間裝設氣密條有助於加壓，不過防火門打開與否影響壓力分布更鉅。此外樓梯模擬有無對模擬結果有巨大的影響，不可壓縮流無法忠實模擬大樓頂端因風機高速進氣導致密度提升的情形。最後STAR-CD模擬結果顯示利用傳統經驗公式計算梯間加壓所需的風機風量，有壓力不足的風險。

ABSTRACT

This thesis utilizes a commercial code, STAR-CD, to simulate two projects. The first part is to predict the thermal and pressure flow field inside two 50W ceramic compact heat exchangers to provide the input data for the following thermal stress analysis. The ceramic materials used in the heat exchanger are SiC and MAS, respectively. In the operation condition, the highest temperature in exhaust gases is 1000□C, whereas the lowest one in preheated air is 27□C. In order to calculate efficiently, a parallel computing algorithm is used to handle the large number of grids, 2,200,000 approximately. The predicted total heat transfer rates of the SiC and MAS recuperators are about 56.74 and 56.72kW. The difference between the predicted heat transfer rate using STAR-CD and the analytic one is only about 2~4%, indicating that the predicted heat transfer rate is quite accurate. The predicted temperature and pressure profiles from the present study are used to compute the thermal stress analysis of Ceramic Plate Recuperator, whereas the analytic ones can not provide such information. The second part is to evaluate the stairshaft pressurization system in a high-rise building. The story number of the stairshaft is 21 and 4 of which are underground. The supply air fan with a capacity of 19000 CMH is set on the roof. In order to understand the different effects on the performance of smoke prevention, three models of stairshaft configuration, the stairshaft without stairs, the stairshaft connecting with lobbies, and the stairshaft with scissors-typed stairs are established respectively. The varying parameters are the door with or without weather strip (leakage effect), the fire door opening conditions, closed or opened, and the use of compressible or incompressible flow assumptions. The simulation results show the installation of door weather strip is found beneficial to pressurization, however, the conditions of opened or closed fire door affect the pressure distributions in stairshaft more effectively. Besides, the stairshaft with or without stair has decisive influence on the predict results. The flow with incompressible flow assumption can not show the density which becomes higher due to compression in the top levels. Finally, the predict results by STAR-CD show the capacity of supply fan using analytic method may have the risk of insufficient pressure.