[{"data":1,"prerenderedAt":73},["ShallowReactive",2],{"q-fire-112-1-fire-science-033":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-112-1-火災學概要-033","fire-112-1-fire-science-033",112,1,33,"當防火門兩側的壓力差加倍時，其透過門縫所流出的氣體體積流率有何變化？",{"A":16,"B":17,"C":18,"D":19},"大約倍增","大約減半","大約增為 4 倍","大約增為 1.4 倍","D",null,[],false,"本題考點：門縫等開口的流量與兩側壓力差關係，考白努利方程式導出的開口流量公式。\n【正解理由】依白努利方程式，壓力差全部轉為動能時流速 v＝√（2ΔP÷ρ），實際開口再乘上流量係數 C，體積流率 Q＝C×A×√（2ΔP÷ρ）。在開口面積 A 與氣體密度 ρ 不變的條件下，流率與壓力差的平方根成正比；壓力差加倍時，流率變為原來的根號二倍，即約 1.414 倍，四捨五入為大約 1.4 倍。故選 D。\n【逐項排除】\n(A) 流率要隨壓力差倍增，前提是兩者成線性關係，但門縫屬慣性主導的孔口流，關係是平方根而非線性，不正確。\n(B) 壓力差增加只會使流率上升，減半的方向與物理關係相反，不正確。\n(C) 由流率與壓力差平方根成正比反推，流率要增為四倍需壓力差變為十六倍，與題設的加倍不符，不正確。\n(D) 根號二約等於 1.414，壓力差加倍時流率約增為 1.4 倍，為正解。\n【記憶點】開口流量看的是「根號壓差」，壓差加倍流量只多四成，不是加倍。","門縫、破口、洩漏縫隙的氣流計算，在火災工程中一律套用孔口流公式。它由白努利方程式推得：忽略高程差與黏性損失時，兩側的壓力差轉換為動壓，得 ΔP＝ρv²÷2，移項即 v＝√（2ΔP÷ρ）；乘上開口面積得理論流率，再乘流量係數 C 修正縮流與黏性效應，得 Q＝C×A×√（2ΔP÷ρ）。建築縫隙常用的流量係數約在零點六至零點七之間，銳緣孔口偏低、圓滑入口偏高。\n這條公式的平方律關係是考點主軸：流率與壓力差的平方根成正比，因此壓差加倍流率增為根號二倍、壓差四倍流率才會加倍、壓差九倍流率增為三倍。反過來說，要讓漏氣量減半，壓差必須降到四分之一，或把縫隙面積減半，後者顯然有效得多，這也是為什麼防煙區劃的氣密性比加壓風量更關鍵。\n壓力差的來源在火災中主要有三項：熱膨脹造成的室內外壓差、熱浮力造成的煙囪效應，以及機械加壓送風。煙囪效應的壓差隨建築高度與室內外溫差增加而放大，冬季高層建築的中性帶上下常有可觀壓差；熱煙層的浮力壓差則與煙層溫度和厚度成正比。這些壓差都要透過同一條孔口流公式換算成通過門縫、電梯門、管道間的流量。\n易混淆的兩件事要分清：一是流量係數與流率不同，前者是無因次修正係數，後者是體積流量；二是質量流率與體積流率不同，兩者差一個密度，高溫煙氣密度小，同樣的體積流率所對應的質量流率遠低於常溫空氣。另可一併記住幾組換算關係：壓差為原來的二倍、四倍、九倍時，流率分別約為一點四一倍、二倍、三倍，反向則壓差降為四分之一時流率減半。本考點常延伸考中性帶位置的判斷、加壓防煙的門開啟力計算，以及煙控系統的排煙量估算。",true,[28,32,36,40,44,48],{"webId":29,"stem":30,"number":31,"year":11,"session":12},"fire-112-1-fire-science-032","將大塊的木頭切碎為小片的木屑時，下列敘述何者錯誤？",32,{"webId":33,"stem":34,"number":35,"year":11,"session":12},"fire-112-1-fire-science-034","對於具有分解爆炸性質的可燃性氣體，下列敘述何者錯誤？",34,{"webId":37,"stem":38,"number":39,"year":11,"session":12},"fire-112-1-fire-science-031","在長寬高為10×10×4 公尺的密閉空間中以高壓式二氧化碳作為滅火防護設備。若欲將空間中的氧氣濃度降至 15%以下以達到鈍化效果，至少應加入多少立方公尺的二氧化碳？",31,{"webId":41,"stem":42,"number":43,"year":11,"session":12},"fire-112-1-fire-science-035","相較於氣體爆炸，一般的粉塵爆炸具有下列那種性質？",35,{"webId":45,"stem":46,"number":47,"year":11,"session":12},"fire-112-1-fire-science-030","滅火藥劑的供給率關乎火災初期的滅火成敗、滅火時間與藥劑使用量，下列敘述何者錯誤？",30,{"webId":49,"stem":50,"number":51,"year":11,"session":12},"fire-112-1-fire-science-036","下列那一種措施有助於提高粉塵爆炸的防護作用以增加其安全性？",36,[53,57,61,65,69],{"webId":54,"year":55,"stem":56,"number":13},"fire-113-1-fire-science-033",113,"對於金屬鈉的敘述，下列何者錯誤？",{"webId":58,"year":59,"stem":60,"number":13},"fire-111-1-fire-science-033",111,"執行危害性化學品災害搶救指導原則（HAZMAT），下列有關區域管制（Zoning）敘述何者錯誤？",{"webId":62,"year":63,"stem":64,"number":13},"fire-110-1-fire-science-033",110,"當一小爆炸發生時，其壓力波將全廠之粉塵揚起，再被隨後而至之燃燒引爆所引起之全廠性爆炸，此現象為何？",{"webId":66,"year":67,"stem":68,"number":13},"fire-109-1-fire-science-033",109,"乙醇之燃燒化學反應式為下列何者？ 9 3",{"webId":70,"year":71,"stem":72,"number":13},"fire-108-1-fire-science-033",108,"電氣火災中，下列何者為積污導電現象？",1785129966617]