[{"data":1,"prerenderedAt":73},["ShallowReactive",2],{"q-fire-108-1-fire-science-006":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-108-1-火災學概要-006","fire-108-1-fire-science-006",108,1,6,"當受熱平面與熱輻射線方向垂直時，其輻射角為 0 度；兩者平行時，輻射角為 90 度。假設輻射源強度不變，當受熱平面由垂直逐漸傾斜，致使輻射角由 0 度增加至 60 度時，該平面所受的輻射熱通量變為原來的若干倍？",{"A":16,"B":17,"C":18,"D":19},"1\u002F3","30.5\u002F2","1\u002F2","1\u002F20.5","C",null,[],false,"本題考點：輻射熱傳的餘弦法則——受熱面傾斜時，其接收到的輻射熱通量隨輻射角的餘弦值遞減。\n【正解理由】依輻射熱傳的餘弦法則，受熱平面接收的熱通量 q\" = q₀\" × cos θ，θ 即題目定義的輻射角（輻射線方向與受熱面法線的夾角）。物理意義是：面板傾斜後，同一束輻射能量被攤在較大的投影面積上，單位面積接收量因而下降。輻射角 0 度時 cos 0° = 1，接收量最大；增加到 60 度時 cos 60° = 0.5，熱通量降為原來的 1\u002F2，故選 C。\n【逐項排除】\n(A) 1\u002F3 不對應任何常見角度的餘弦值，係把角度比 60 ÷ 180 誤當成熱通量衰減比，混淆了角度線性與餘弦非線性。\n(B) 選項所示 √3 ÷ 2 ≒ 0.866 是 cos 30°，對應只傾斜 30 度的情形，錯在把題目的 60 度取成其互餘角 30 度。\n(C) 正確。cos 60° = 0.5，輻射熱通量由 q₀\" 降為 0.5 q₀\"，恰為原來的一半，與題目所問倍數相符。\n(D) 選項所示 1 ÷ √2 ≒ 0.707 是 cos 45°，對應傾斜 45 度；且輻射衰減依餘弦而非依平方根關係，角度與函數都取錯。\n【記憶點】輻射熱通量隨 cos θ 遞減：0 度全收、60 度剩一半、90 度平行時歸零。","輻射熱通量的餘弦法則源自朗伯（Lambert）餘弦定律：對一個漫射輻射面而言，某方向的輻射強度與該方向和法線夾角的餘弦成正比；反過來看受熱面，同一束輻射打在傾斜面上時，有效受照面積放大為原本的 1 ÷ cos θ 倍，單位面積的熱通量因而縮為 cos θ 倍。幾個關鍵角度值務必背熟：cos 0° = 1、cos 30° ≒ 0.866、cos 45° ≒ 0.707、cos 60° = 0.5、cos 90° = 0，也就是受熱面與輻射線平行時完全收不到輻射。\n完整的輻射熱傳計算還要加上兩層：一是輻射源本身的強度，依史蒂芬-波茲曼定律 E = εσT⁴，σ 為 5.67 × 10⁻⁸ W\u002Fm²·K⁴，火焰溫度只要上升，輻射能量即以四次方倍率暴增；二是幾何關係，工程上以視角因數（configuration factor）綜合表達距離、面積與角度的影響，簡化的點源模型則寫成 q\" = χ_r Q ÷（4πr²）× cos θ，χ_r 為輻射分率（一般可燃物約 0.2 至 0.4），可見熱通量同時受距離平方反比與角度餘弦兩項壓低。\n這些數字在火災學裡有明確的門檻意義：人體皮膚感到疼痛的輻射熱通量約 2.5 kW\u002Fm²，木材類可燃物在無引火源下的臨界引燃熱通量約 10 至 12.5 kW\u002Fm²，因此建築物間隔距離、開口面積與外牆耐火性能的規範思維，本質上就是把鄰棟受照面的熱通量壓在臨界值以下。相關考點包括由火焰高度與距離估算延燒風險、視角因數的定性比較，以及輻射、傳導、對流三種熱傳在不同火災階段的主導性排序。",true,[28,32,36,40,44,48],{"webId":29,"stem":30,"number":31,"year":11,"session":12},"fire-108-1-fire-science-005","可燃性液體的閃火點（flash point），是指當其表面蒸氣與空氣混合達燃燒下限時的：",5,{"webId":33,"stem":34,"number":35,"year":11,"session":12},"fire-108-1-fire-science-007","下列有關蒸氣爆炸的敘述何者錯誤？",7,{"webId":37,"stem":38,"number":39,"year":11,"session":12},"fire-108-1-fire-science-004","今有 A、B 兩種可燃性氣體以 1：1 之體積混合，已知 A、B 之燃燒下限分別為 3.0%、7.0%，若兩者間互不催化亦不反應，則理論上此混合氣體之燃燒下限為若干%？",4,{"webId":41,"stem":42,"number":43,"year":11,"session":12},"fire-108-1-fire-science-008","若乙烷的燃燒熱為 350 kcal\u002Fmole，依據 Burgess-Wheeler 法則，下列何者最為接近乙烷的燃燒下限？",8,{"webId":45,"stem":46,"number":47,"year":11,"session":12},"fire-108-1-fire-science-003","不同材質與厚度的牆壁或隔熱板，顯示不同的熱傳導效果；此可藉由下列何者估算？",3,{"webId":49,"stem":50,"number":51,"year":11,"session":12},"fire-108-1-fire-science-009","就同一種可燃性粉塵而言，下列何種措施有助於降低發生粉塵爆炸的危險性？",9,[53,57,61,65,69],{"webId":54,"year":55,"stem":56,"number":13},"fire-114-1-fire-science-006",114,"依據我國公共危險物品之分類，下列有關可燃液體與易燃液體之敘述，何者正確？",{"webId":58,"year":59,"stem":60,"number":13},"fire-113-1-fire-science-006",113,"有關防止靜電災害的方法，下列敘述何者正確？",{"webId":62,"year":63,"stem":64,"number":13},"fire-112-1-fire-science-006",112,"在標準狀態下，下列氣體中何者之爆炸範圍最廣？",{"webId":66,"year":67,"stem":68,"number":13},"fire-111-1-fire-science-006",111,"火災成長歷程中，下列何者非閃燃之現象？",{"webId":70,"year":71,"stem":72,"number":13},"fire-110-1-fire-science-006",110,"阿里山發生森林火災，已知火災當天的相對濕度為 60.0%，前一天相對濕度為 50.0%，再前一天相對濕度為 40.0%，試求火災當天的實效濕度？",1785129967478]