將室內空氣排出房間的過程稱為排空房間 (Emptying box) 問題, 利用室內空氣和環境空氣間的密度差形成之浮力排出室內空氣。 排空房間之問題有下列兩個特徵, 兩流體間之密度差遠小於環境流體的密度, 且兩流體為可
相互混合的。

本論文之目的為研究入流方向對於排空房間之流場型態的影響, 實驗工作以縮尺壓克力模型搭配鹽浴的方式進行模擬實驗。 鹽浴的方式進行模擬實驗則以密度流體及環境流體表示室內空氣及環境空氣。 根據不同的入流方向將實驗組別分為水平入流 (EM(H)) 及垂直入流 (EM(V)) 兩系列排空房間實驗, 其中 EM(H) 在入口處加入水平的壓克力檔板變更入流方向為水平方向,EM(V) 的入流方向則是垂直方向, 實驗條件為固定上開口面積為π cm2並變更上下開口面積比 (R) 為1, 0.5, 0.33, 等同於改變整體開口有效面積為1.92, 2.42, 2.57 cm2。

實驗結果發現入流為水平方向時, 其流場型態由密度層及環境流體層所組成, 密度層與環境流體層之間有顯著交界面。 當入流為垂直方向時, 實驗過程可分為排空密度層以及排空混合層兩個階段, 排空密度層之流場型態
為密度層, 混合層, 環境流體層三部分組成, 排空混合層之流場型態則由混合層, 次混合層, 環境流體層三部分組成。 結果顯示, 在固定初始交界面高度的條件下, 當整體開口有效面積增加或是初始縮減重力增加時, 水平入流及垂直入流的排空時間皆會呈現下降的趨勢; 在相同的實驗條件時, 垂直入流的密度層排空時間約為水平入流的密度層排空時間的50 ∼ 60 %左右, 垂直入流的完全排空時間較水平入流的完全排空時間長。 由於排空房間為一暫態之實驗, 雷諾數隨時間衰減, 因此流量係數不為定值, 造成理論估算與實驗結果有所落差。

The Emptying Box problem is the process of using the buoyancy force between the indoor air and the ambient air to empty the indoor air. The characteristics of Emptying Box are as follows: First,the density difference between indoor air and ambient air is small compared with the density of ambient air. Second, two fluids are miscible.

The purpose of this research is to study the Emptying Box problem with horizontal and vertical inflow directions. The salt-bath technique is used in simulation experiments by using an acrylic reduced-scale model. The salt-bath technique uses dense salty water and fresh water to simulate the density difference between indoor air and ambient air. Light-attenuation technique is used to analyze intensity data of the acrylic reduced-scale model. According to different inflow directions, experiments are categorized as two series, horizontal inflow type Emptying Box (EM(H)) and vertical inflow type Emptying Box (EM(V)). EM(H) uses a horizontal baffle board to change the inflow direction from vertical to horizontal, and the inflow direction of EM(V) without any baffle board is vertical. The opening area ratio of the inlet to the outlet is varied as 1, 0.5 and 0.33, i.e. the total effective opening area is 1.92, 2.42 and 2.57 cm2, when the inlet opening size is fixed.

The emptying process of EM(H) is only related to emptying the dense layer. The flow field of emptying the dense layer in EM(H) consists of the dense brine layer and the fresh water layer, and the interface between two layers is clear. The emptying processes of EM(V) consist of emptying the dense layer and emptying the mixed layer. The flow field of emptying the dense layer in EM(V) consists of
dense brine layer, mixed layer and fresh water layer, and the flow field of emptying the mixed layer consists of mixed layer, secondary mixed layer, and fresh water layer. The results show that the emptying time of either EM(H) or EM(V) decreases when either the total effective opening area increases or the initial reduced gravity increases.

The time of emptying the dense layer for EM(V) is about 50 ∼ 60 % of that for EM(H). The total emptying time of EM(V) is longer than that of EM(H) for the same total effective opening area and initial reduced gravity conditions.

There is a difference of interface height evolution between experimental results and theoretical results. This is caused by the Reynolds number decreasing with time during the experiment, hence the discharge coefficient is not constant.

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