第16页
vcr?RgTcrpcr?287?247.53?0.448m/kg 60.1584?10∴Acr?qmvcr4?0.448??5.68?10?3m2 cfcr315.3喉部直径d = 85 mm
7.2 题略
cf1>50 m/s,应考虑初速度。
2002则 T*?T1??773??793K
2cp2?1005?T*?p*?p1??T???1????1c2f1?793??1???773??1.40.4?1.093MPa
对于渐缩喷管,临界状态时流量最大,此时
p2?pcr??p*?0.528?1.093?0.577MPa
?p*?T2?Tcr?T*??p???cr????1??1.093??793???0.577???0.41.4?660.7K
cf2?ccr?2cp(T*?Tcr)?515.68m/s
7.3 通过测量节流前后水蒸汽的压力和节流后的温度可推得节流前水蒸汽的干度。现有压力p1=2 MPa的湿蒸汽被引入节流式干度计,节流后压力降到p2=0.1MPa,此时测得温度t2 =130℃,试确定节流前蒸汽的干度。
解:分析:由蒸汽节流后的压力p2=0.1MPa和温度t2 =130℃,查附表2,可得节流后水蒸汽的焓,利用节流前后焓相等的概念,即h2 = h1, 再利用求湿蒸汽焓的公式求得节流前水蒸汽的干度。
查附表2,得: h2?h120?h1402716.3?2756.2??2736.25kJ/kg 22??x1?(1?x1)h1??h2?2736h1?h1.25kJ/kg
x1??2736h2?h1.25?908.64??0.96698 ?2798h1???h1.66?908.64
第17页
8.1题略(循环图见P129. F.8.10)
解:已知初始状态:p1?100kPa;T1?273?27?300K;压缩比??14; 工质吸热量 q1?q2?3?q3?4?1000kJ/k;g ??1.4
?V1? 1~2. 定熵,则 T2?T1??V???2???1?300?140.4?86.21K
设 V2?V,则 V1?14V
2~3~4. 由q2?3?q3?4?cv(T3?T2)?cp(T4?T3)?500kJ/kg
/cv?T2? ?T3?500500?862.1?155.85K 0.718500T4?500/cp?T3??1558.5?2056.0K
1.005V3?V2?V;V4??V4 4~5. 定熵,T5?T4??V?5??????1T4V3?1.319V T3;V5?V1?14V
0.4?1.319? T5?2056.0???14???799.2K
q2?q5?1?cv(T5?T1)?0.718?(799.2?300)?358.4kJ/k g1). w0?q1?q2?641.6kJ/kg 2). ?t?1?8.4 题略
解:由题意知:p1?101.325kPa;T1?T2?273.15K;V1?150m;p2?5MPa
3q2?64.16% q1p1V1101.325?103?150 吸入的气体质量为 m???193.876kg
RgT10.287?103?273.15(可逆)等温压缩过程的放热量:
Q?W?Wt?T?S p15?103?mRgTln?193.876?0.287?273.15ln?59257.7kJp2101.325 第18页
8.5 题略(循环图见P130. F.8.12)
解:已知:p1?100kPa;T1?20?273?293K;
??4kg/ s p2?500kPa;T3?900?273?117K3;m ①:1~2.定熵过程
T2?T1???p2???p?1???1??500??293???100??0.41.4?464K
?(h2?h1)?m?cp(T2?T1)?704.8kW; wc?m②:3~4.定熵过程 T4?T3???p4???p?3???1??100??117?3??500??0.41.4?741K
?(h3?h4)?m?cp(T3?T4)?1781wtur?m.4kW;
③:wc/wtur?704.8/1781.4?1:2.53=39.53 %; ④:?t?1?8.7
题略
T1293?1??36.9%; T2464 解:已知:T4?30?273?303K;T1??20?273?253K; P?H2?H1?3.5kW
①:查氨的压焓图(查图值可能不完全相同,以下是参考值) h4?h5?450kJ/k;;h2?182k5J/k ggp2?1.1MPa p1?0.17MPa; ??h1?157k0J/k gp2?6.47; p1②:??h1?h41570?450??4.39;
h2?h11825?1570?(h1?h4)?0.0137?(1570?450)/3.86?3.98冷吨; ③:Q2?m??m?(h2?h4)?0.0137?(1825?450)?18.87kW; ④:放热量Q1 第19页
??⑤:m
P3.5??0.0137kg/s
h2?h11825?1570