流體機械習題2.1壓縮機設計昆明理工大學

./設計一臺往復式天然氣壓縮機,結構見圖2-114。已知數(shù)據(jù)：吸氣壓力0.3MPa<G>,排氣壓力25MPa<G>,行程95mm,轉速980r/min,排氣量1.5,并要求一級氣缸直徑175mm,活塞桿直徑d=35mm。一級進氣溫度為25℃,若用戶要求排氣壓力為31MPa<G>,則各級壓力如何變化？一、設計條件吸氣壓力：0.3MPa<G>=0.4MPa〔絕壓排氣壓力：25MPa<G>=25.1MPa〔絕壓要求排氣壓力：31MPa<G>=31.1MPa〔絕壓由題意知：.PS1=0.4MPaPd4=25.1MPa行程s=95mm=0.095m轉速n=980r/minD1=175mm=0.175md=35mm=0.035m天然氣：k=1.32.二、確定各級直徑總壓比按等壓比分配：級次ⅠⅡⅢⅣPs<MPa>0.41.12583.1685648.917924Pd<MPa>1.12583.1685648.91792425.1ε2.81462.81462.81462.8146假設此壓縮機冷卻完善,所以由圖2-114可得：有已知條件帶入〔1式得又有公式〔2-38所以容積系數(shù)計算：<1>壓力系數(shù)取<2>溫度系數(shù)取<3>泄露系數(shù)〔無油潤滑<4>膨脹指數(shù)〔由表2-1得級次ⅠⅡⅢⅣPs<MPa>0.41.12583.1685648.917924Ps<bar>411.25831.6856489.17924m1.2251.3081.41.4由公式則分別取、、確定各級氣缸直徑：<Ⅱ>級直徑聯(lián)立以上兩式可得：帶入數(shù)據(jù)可得：聯(lián)立以上三式得：即解之得=0.103m=103mm查表取氣缸直徑=105mm。則實際行程容積為：活塞有效面積：〔Ⅲ級直徑又帶入數(shù)據(jù)得解之得0.057m=57mm查表圓整取60mm則實際行程容積為：活塞有效面積：<Ⅳ>級直徑又帶入數(shù)據(jù)得解之得0.034m=34mm查表得36mm則實際行程容積為：活塞有效面積：由公式與計算出新的,結果如下表：級次ⅠⅡⅢⅣ氣缸實際直徑D〔m0.1750.1050.060.036有效實際面積Ap<m2>氣缸直徑D〔m0.1750.1030.0570.034有效面積Ap<m2>0.7972.3976.78218.487實際0.7972.2956.12116.4900.1530.1300.1350.145實際0.1530.1530.2080.238實際三、計算活塞力由課本P22圖2-14分別?。焊骷夁M、排氣壓力和實際壓力比級次公稱壓力壓力損失實際壓力/MPa實際壓力比εⅠ0.41.12580.0290.0580.38841.19113.067Ⅱ1.12583.168560.0210.0431.10223.30482.998Ⅲ3.168568.91790.0190.0273.10849.15872.946Ⅳ8.917925.10.0170.0148.766325.45142.903、由公式壓力比由計算得出,結果如上表。止點氣體力計算：列次內止點<kN>外止點<kN>Ⅰ-Ⅳ16.27-19.23Ⅱ-Ⅲ16.06-17.99Ⅰ-Ⅳ內止點氣體力：=16.27kN<拉應力>外止點氣體力：=-19.23kN〔壓應力Ⅱ-Ⅲ內止點氣體力：=16.06kN<拉應力>外止點氣體力：=-17.99kN<壓應力>四、確定各級排氣溫度因假設冷卻完善,故：級次ⅠⅡⅢⅣ<K>298.15298.15298.15298.15<K>391.21389.09387.44386.06上表由<n=1.32>計算得出各級排氣溫度。五、計算軸功率并選配電機各級指示功率為總的指示功率為計算結果如下表：14283W13498W13008W12447W53237W取機械效率,軸功率為：取電機功率余度10%,,則選擇電機功率為65kW。六、變工況熱力計算1、確定與容積有關的系數(shù)級次壓力系數(shù)溫度系數(shù)泄露系數(shù)Ⅰ0.970.950.950.8754Ⅱ0.990.960.960.9124Ⅲ0.990.970.970.9315Ⅳ1.000.980.980.96042、設想容積的計算級次Tsλ0λk設想容積Ⅰ298.150.87541Ⅱ298.150.91241Ⅲ298.150.93151Ⅳ298.150.960413、壓力比及容積系數(shù)級次/MPaⅠ0.41.1512.8780.790Ⅱ1.1513.0702.6660.829Ⅲ3.0708.2712.6940.786Ⅳ8.27131.13.7600.6254、各級壓力比復算次數(shù)級次1Ⅰ0.41.20803.010.7787.1%Ⅱ1.20803.05252.530.84Ⅲ3.05258.55302.800.77Ⅳ8.553031.13.640.822Ⅰ0.41.11282.780.8098.