[{"data":1,"prerenderedAt":73},["ShallowReactive",2],{"q-fire-108-1-fire-science-018":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-018","fire-108-1-fire-science-018",108,1,18,"當氣體進行「壓縮比=2」的斷熱壓縮時，下列對該氣體的敘述何者正確？",{"A":16,"B":17,"C":18,"D":19},"其體積減半","其壓力倍增","其絕對溫度倍增","其壓力與體積的乘積維持恆定","A",null,[],false,"本題考點：壓縮比的定義,以及斷熱壓縮下 PV^γ 為定值所導出的壓力與溫度變化。\n【正解理由】壓縮比依定義是壓縮前後的體積比 V1\u002FV2,壓縮比等於 2 即表示氣體體積被壓成原來的一半,這項結論不依賴過程是否斷熱。至於壓力與溫度,斷熱過程遵守 PV^γ = 定值(空氣等雙原子氣體 γ ≈ 1.4),壓力增為 2^1.4 ≈ 2.6 倍、絕對溫度增為 2^0.4 ≈ 1.3 倍,均非單純倍增。四者中僅體積減半的敘述成立,故選 A。\n【逐項排除】\n(A) 敘述正確,為本題應選者。壓縮比就是體積比,壓縮比 2 對應體積由 V 變為 V\u002F2,與過程性質無關。\n(B) 敘述錯誤。斷熱時 P2\u002FP1 =(V1\u002FV2)^γ = 2^1.4 ≈ 2.64 倍,壓力上升幅度大於 2 倍,並非剛好倍增。\n(C) 敘述錯誤。斷熱時 T2\u002FT1 =(V1\u002FV2)^(γ−1) = 2^0.4 ≈ 1.32 倍,絕對溫度確實上升,但遠不到 2 倍。\n(D) 敘述錯誤。PV 維持定值是等溫過程的波以耳定律;斷熱壓縮溫度升高,由理想氣體方程式 PV = nRT 可知 PV 乘積隨溫度上升而增大。\n【記憶點】壓縮比只講體積;壓力 2 的 1.4 次方、溫度 2 的 0.4 次方,只有體積剛好減半。","斷熱過程指系統與外界沒有熱交換,壓縮所做的功全部轉為氣體內能,因此溫度必然上升。三條關係式由 PV^γ = 定值與理想氣體方程式聯立導出:P1V1^γ = P2V2^γ、T1V1^(γ−1) = T2V2^(γ−1)、以及 T2\u002FT1 =(P2\u002FP1)^((γ−1)\u002Fγ)。γ 為比熱比 Cp\u002FCv,單原子氣體約 1.67、雙原子氣體(氮、氧、空氣)約 1.40、多原子氣體約 1.33,考試若未特別指定,空氣一律取 1.4。\n數值驗算:2^1.4 = e^(1.4×ln2)= e^0.9704 ≈ 2.64;2^0.4 = e^(0.4×0.6931)= e^0.2772 ≈ 1.32。若氣體初溫為 300 K,壓縮比 2 的斷熱壓縮後約為 396 K,約 123℃;若壓縮比提高到 20(柴油引擎的量級),T2 = 300×20^0.4 ≈ 300×3.31 ≈ 994 K,超過柴油的自燃溫度,這正是壓縮著火引擎不需火星塞的原理。\n這組觀念在火災學裡有幾個實際對應:高壓氣體急速充填時,容器內氣體被斷熱壓縮而升溫,若容器內殘留油脂即可能發火;液壓或油壓管路破裂時,油被高壓噴出霧化並遇熱源著火;柴油機故障時的失控自燃亦屬同類。反向的斷熱膨脹則使溫度下降,液化石油氣鋼瓶洩漏時瓶身結霜、管口出現白霧,就是氣體膨脹吸熱與水氣凝結的結果。\n易混淆對照:等溫壓縮(PV = 定值)過程中熱量被移走、溫度不變,壓力與體積成反比;斷熱壓縮則因溫度上升,同樣的體積縮減會得到更高的壓力,故斷熱線在 P-V 圖上比等溫線陡。相關考點還包括絕熱火焰溫度、氣體混合的道爾頓分壓定律,以及可燃性氣體因壓縮升溫而落入燃燒範圍的情形。",true,[28,32,36,40,44,48],{"webId":29,"stem":30,"number":31,"year":11,"session":12},"fire-108-1-fire-science-017","危害物質可能因混合儲存或載運而衍生危險，則下列那兩類公共危險物品於混合載運時的危險性最低？",17,{"webId":33,"stem":34,"number":35,"year":11,"session":12},"fire-108-1-fire-science-019","下列何種滅火劑使用於金屬火災時，沒有「與金屬產生化學反應而衍生危害物質」的可能？",19,{"webId":37,"stem":38,"number":39,"year":11,"session":12},"fire-108-1-fire-science-016","某發生火警的大樓，室內外溫度分別為 800℃與 20℃，中性帶位於 4 樓；6 樓的內外壓差為 60 Pa，若不考慮外部風等其他因素，則 8 樓的內外壓差約為若干 Pa？",16,{"webId":41,"stem":42,"number":43,"year":11,"session":12},"fire-108-1-fire-science-020","下列何種滅火劑所含成分之一，於放射後有刺激呼吸之作用，可有效降低場內人員的窒息危害？",20,{"webId":45,"stem":46,"number":47,"year":11,"session":12},"fire-108-1-fire-science-015","下列何種現象對於局部電阻所產生的效應恰與其他三者相反？",15,{"webId":49,"stem":50,"number":51,"year":11,"session":12},"fire-108-1-fire-science-021","依據建築物火災 t2 成長理論，在一定義為快速成長的火災中，釋熱率達到 1MW 的時間應為多少秒？",21,[53,57,61,65,69],{"webId":54,"year":55,"stem":56,"number":13},"fire-111-1-fire-science-018",111,"下列何者非電線走火之原因？",{"webId":58,"year":59,"stem":60,"number":13},"fire-110-1-fire-science-018",110,"根據「危害物質災害現場搶救標準作業程序」之規定，其首要工作為何？",{"webId":62,"year":63,"stem":64,"number":13},"fire-109-1-fire-science-018",109,"化學災害搶救程序 HAZMAT 之說明，下列何者正確？",{"webId":66,"year":67,"stem":68,"number":13},"fire-107-1-fire-science-018",107,"已知木造倉庫高 6 公尺，如延燒係數為 0.15，依木造建築物火災溫度標準曲線，其鄰棟建築物之理論安全距離應在多少公尺以上？",{"webId":70,"year":71,"stem":72,"number":13},"fire-106-1-fire-science-018",106,"有關煙囪效應之敘述，下列何者錯誤？",1785123163211]