| 摘要: | 台灣隧道開通以來發生過多起火災事故,使得各界更注意長隧道 內的行車安全,在長隧道內如果發生火災時,其應變救災策略首要任 務應是掌控火場情況,讓用路人有更長的安全疏散時間。所以對不同 強度火源附近煙流行為的了解以及如何透過現有通風系統予以緊急 控制和後續的排煙策略是相當重要的事項。台灣除了有長隧道外更有 不少短隧道。對短隧道而言,風機數量少,火災時其為控制煙流的唯 一手段。因此難免非常靠近火源,且必須在高溫中運作。本研究擬透 過電腦輔助模擬技術,探討短隧道在虛擬火災情況的煙流行為與其風 機系統操控能耐。本文在數值計算上使用泛用型計算流體力學(CFD)軟體 ANSYS CFX,針對單一噴流風機對火災煙流控制性能進行研究。研究結果顯 示噴流風機轉速不因火災高溫而改變的前題下,隧道火災高溫將降低 空氣密度使得風機推力下降。此時即使火源下游因空氣密度下降,造 成風速升高,但其實質通風量(質量流率)卻是下降。文中亦探討風機 啟動反應時間對火災煙流情況的影響效應。研究顯示風機啟動時機須 考量火源強度大小。火源強度低時風機應盡速啟動並持續運作。在中 等強度火源時,噴流風機啟動一段時間後,當推力因高溫下降時,需 關閉噴流風機。火源強度高時,噴流風機不宜啟動,以避免高溫區域 擴大。但如用路人皆已逃出,則可啟動噴流風機幫助排出煙流。
The effect of high-temperature smoke on the performance of a jet fan operated in a tunnel is explored by using a Computational Fluid Dynamics method. Results show that the heat released from the fire will reduce air density and therefore the jet fan thrust. The mass flow through the tunnel is therefore reduced, although the volume rate in the downstream of the fire is increased due to the expansion of air. In short tunnels, jet fans inevitably would be close to the fire should it occur, and they would be the only means to control the smoke flow. Therefore, we suggest that this temperature effect on jet fan performance had better be taken into comidetion as calculating the ventilation capacity for short tunnels. Fire size, fire location, and fan activated time are influential to the temperature distribution in a tunnel. Their effects on the temperature in the evacuation zone of the tunnel are therefore investigated. Results show that that jet fan is especially effective on maintaining acceptable condition for people evacuation as fire size is small and as it occurs at the downstream of the jet fan. To maintain fan’s thrust, we had better to activate the fan before it is surrounded by backlayering smoke. Generally, the performance of the jet fan will be hindered as the fire occurs at the upstream, and even worse as the fire size is large. |
