[{"data":1,"prerenderedAt":73},["ShallowReactive",2],{"q-fire-109-1-fire-science-014":3},{"subject":4,"subjectSlug":5,"subjectKicker":6,"subjectShort":7,"question":8,"related":27,"sameNumber":52,"hasEssay":26},"火災學概要","fire-science","火災學 · Fire Science","火災學",{"id":9,"webId":10,"year":11,"session":12,"subject":4,"number":13,"stem":14,"options":15,"answer":20,"answerNote":21,"images":22,"imagesPending":23,"lawTimestamp":11,"explanation":24,"explanationDeep":25,"freq":12,"indexable":26},"fire-109-1-火災學概要-014","fire-109-1-fire-science-014",109,1,14,"火場溫度隨燃燒時間而逐漸升高，其空氣亦漸膨脹，空氣由外界流入該起火房間，同時熱煙霧也會從該起火房間流出。若忽略燃燒分解過程而產生之質量流率，建築物內部空氣溫度為 25℃，起火房間溫度為 800℃，流入起火房間之空氣體積流量為 1 m3\u002Fs，則流出起火房間之熱煙霧體積流量約為若干？",{"A":16,"B":17,"C":18,"D":19},"1.6 m3\u002Fs","2.6 m3\u002Fs","3.6 m3\u002Fs","4.6 m3\u002Fs","C",null,[],false,"本題考點：質量守恆與理想氣體熱膨脹，由溫度變化推算流出熱煙的體積流量。\n【正解理由】忽略燃燒分解產生的質量後，流入起火房間的空氣質量流率等於流出熱煙的質量流率，即 ρ₁×V̇₁＝ρ₂×V̇₂。依理想氣體定律，同一壓力下氣體密度與絕對溫度成反比，故 V̇₂＝V̇₁×T₂\u002FT₁,溫度必須換成絕對溫度。以 25℃＝298 K、800℃＝1,073 K 代入，得流出體積流量約 3.6 m³\u002Fs,故選 C。\n【逐項排除】\n(A) 1.6 m³\u002Fs 對應的煙層溫度僅 1.6×298≈477 K(約 204℃),遠低於題給的 800℃。\n(B) 2.6 m³\u002Fs 對應約 775 K(約 502℃),同樣不到 800℃,膨脹倍率明顯不足。\n(C) 1 m³\u002Fs×1,073 K÷298 K≈3.60 m³\u002Fs,與選項相符，為應選項。\n(D) 4.6 m³\u002Fs 對應約 1,371 K(約 1,098℃),溫度被高估近 300℃;若誤用攝氏比值 800÷25＝32 倍，更會得到 32 m³\u002Fs。\n【演算步驟】T₁＝25℃＋273＝298 K;T₂＝800℃＋273＝1,073 K;質量守恆 ρ₁V̇₁＝ρ₂V̇₂,且同壓下 ρ∝1\u002FT,故 V̇₂＝V̇₁×T₂\u002FT₁＝1 m³\u002Fs×1,073 K÷298 K≈3.60 m³\u002Fs。\n【記憶點】溫度先換成絕對溫標再相除，體積流量隨絕對溫度等比放大。","本題的物理核心是理想氣體狀態方程 PV＝nRT 的密度形式 ρ＝PM\u002FRT。火場與外界相通，壓力差僅數帕，可視為等壓過程，因此密度只隨絕對溫度變化，溫度升為原來的幾倍，同質量氣體的體積就膨脹為幾倍。25℃ 的空氣密度約 1.18 kg\u002Fm³,800℃ 時降到約 0.33 kg\u002Fm³,恰為 1,073\u002F298≈3.6 倍的倒數，兩種算法結果一致。\n「忽略燃燒分解過程產生之質量流率」這句假設不是敷衍：實際火災中，可燃物的質量燃燒速率通常只有每秒數十至數百公克，而流入房間的空氣量以每秒公斤計，兩者相差一至二個數量級，故省略燃料質量對結果影響有限，這也是煙控計算常用的簡化。\n這條關係在排煙工程上有直接意義。排煙機以體積流量(m³\u002Fmin 或 m³\u002Fs)標示能力，但高溫煙氣體積比常溫大好幾倍，同樣質量的煙在 800℃ 時要吸走的體積是常溫的 3.6 倍，故排煙量估算與風機選型都須以實際煙層溫度校正，不能直接套用常溫值。同理，高溫煙氣密度低、浮力大，是煙囪效應與火羽流上升的驅動力。\n延伸考點：火場開口的流動由中性帶劃分，中性帶以上熱煙流出、以下冷空氣流入，流入與流出的體積流量不相等而質量流率相等，正是本題的觀念；火羽流在上升過程中會大量捲吸周圍空氣，使煙層的質量流率遠大於燃燒生成物的質量流率，這是煙量估算比直覺大得多的原因。常見變化題型包括：已知流出體積流量反求火場溫度、以密度形式計算質量流率，或加入捲吸空氣量後求煙層下降時間；不論怎麼變，第一步永遠是把攝氏換成絕對溫度。",true,[28,32,36,40,44,48],{"webId":29,"stem":30,"number":31,"year":11,"session":12},"fire-109-1-fire-science-013","下列的滅火設備，何者屬於窒息法滅火原理？",13,{"webId":33,"stem":34,"number":35,"year":11,"session":12},"fire-109-1-fire-science-015","下列海龍替代滅火藥劑，何者之化學組成為五氟乙烷？",15,{"webId":37,"stem":38,"number":39,"year":11,"session":12},"fire-109-1-fire-science-012","下列常見之乾粉滅火藥劑敘述何者正確？",12,{"webId":41,"stem":42,"number":43,"year":11,"session":12},"fire-109-1-fire-science-016","假設建築物外部風速為 10 m\u002Fs，風壓係數為 0.6，空氣密度為 1.0 kg\u002Fm3，其對迎風面建築物所產生的風壓約為？",16,{"webId":45,"stem":46,"number":47,"year":11,"session":12},"fire-109-1-fire-science-011","某一線徑 2.0 m\u002Fm 之電線 1 km 長之電阻值為 5.657 Ω，熱阻抗為 378。若周遭溫度為 20℃，當此 10 cm 長之電線通過 10 安培時，其芯線溫度（℃）約為多少？",11,{"webId":49,"stem":50,"number":51,"year":11,"session":12},"fire-109-1-fire-science-017","T.N.T.炸藥化學名稱為三硝基甲苯（Trinitrotolene，C7H5N3O6），俗稱黃色炸藥，試問其氧平衡（Oxygen Balance, O.B.）為多少？",17,[53,57,61,65,69],{"webId":54,"year":55,"stem":56,"number":13},"fire-113-1-fire-science-014",113,"下列何者屬水蒸氣爆炸？",{"webId":58,"year":59,"stem":60,"number":13},"fire-112-1-fire-science-014",112,"依史蒂芬-波茲曼（Stefan-Boltzmann）公式之定義，輻射熱量與輻射物體絕對溫度的幾次方成正比？",{"webId":62,"year":63,"stem":64,"number":13},"fire-111-1-fire-science-014",111,"普通木造建築物旁欲蓋 9 公尺高之建築物，其延燒係數為 3 級（係數為 0.15），其防火間隔應保持多少公尺？",{"webId":66,"year":67,"stem":68,"number":13},"fire-110-1-fire-science-014",110,"自然發火性物質中的原棉，主要是因為下列何種熱之蓄積而發火？",{"webId":70,"year":71,"stem":72,"number":13},"fire-108-1-fire-science-014",108,"依 Thomas 閃燃公式（Thomas Flashover Correlation），有關室內火災發生閃燃所需最小釋熱率，下列敘述何者錯誤？",1785129967268]