给热系数的测定试验数据记录及处理

实验数据记录与处理1、实验原始数据记录表次序项目、123456789水蒸气压强MPa0.020.020.020.020.020.020.020.020.02空气进口温度t1°C32.730.328.024.622.121.420.82121.6空气出口温度t2°C74.172.971.970.770.470.771.972.674空气进口处蒸汽温度T1°C103.2103.2103.2103.2103.2103.2103.2103.2103.2空气出口处蒸汽温度t2°c102.3102.3102.3102.3102.3102.3102.3102.3102.3空气流量V（m3/h）23.022.021.018.515.012.6108.57空气进口处密度p（kg/m3）1.15511.16441.17341.18691.19701.19981.20231.20151.1982空气质量流量ms（kg/s）0.00740.00710.00680.00610.00500.00420.00340.00280.0023空气流速u（m/s）31.791830.409629.027325.571720.733817.416413.822511.74929.6758计算公式:①空气进口处密度：p=10-512—4.5义10-311+1.2916空气质量流量：m=Vxp空气流速：u=比九d2

2、给热系数K的计算次序项目123456789空气定性温度t°C平均53.4051.6049.9547.6546.2546.0546.3546.8047.90定性温度下的空气密度P'kg/m31.07981.08601.09181.09991.10481.10571.10451.10291.0989冷、热流体间的对数平均温差At°Cm46..443548.179249.701451.857753.014553.071752.456451.885850.5873总给热系数Kw/(m2°C)151.704125.962120.948108.55990.97278.10065.13356.48248.132计算公式:①空气定性温度：t=1(t+1)(t<60)平均2 1 2空气比热：Cp=1005J/(kg・°C)'定性温度下的空气密度：P'=10-512-4.5X10-31 +1.2916平均 平均冷、热流体间的对数平均温差：At=71T2；-(T2―Jm T-tln^ 2-T-11传热面积：A=冗d21=3.14x0.016x1=0.0502m2对流传热系数：K=，心2-t1)AAtm、近似法求给热系数hh=K=103.1096w/(m2・°C)

4、h理论值的计算序项目、、123456789对流给热系数hw/(m2-°C)151.704125.962120.948108.55990.97278.10065.13356.48248.132空气黏度〃(x10-5Pa-s)1.87821.86651.85531.83871.82641.82301.82001.82101.8249空气导热系数2W/(m-K)0.02700.02680.02660.02630.02620.02610.02610.02610.0261雷诺数Re29243283092732924474200681689913421113659332普兰特数Pr0.69970.69990.70030.70110.70170.70180.70200.70190.7017努赛尔数Nu78.063376.166572.684065.901355.644447.872339.997034.663029.4673努赛尔数理论值Nu'74.643472.654670.659164.717255.232848.143840.041035.102229.9122理论h'W/(m2.°C)125.767121.722117.577106.60590.30078.54365.20557.19748.859h各点的相对误差％-4.72-3.48-2.86-1.82-0.740.560.111.251.4810g.tu/ProJ1.95461.93811.92331.88061.80701.71461.66351.60131.5309log10ge)4.46604.45194.43664.38884.30254.22794.12784.05633.96计算公式：①空气粘度：H=(-2X10-6112+5X10-3t1+1.7169)X10-5②空气导热系数：九=2X10-812+8X10-51+0.0244④普兰特数：Pr=§卢⑤努赛尔数：Nu二㈣九⑥对于流体在圆形只管内做湍流时的对流传热系数若符合以下条件：Re=1.0x10411.2x105，Pr=0.7g120，管长与管内径之->60,则Nu=0.023Re0.8Prnd本实验中，-二=62.5>60,而Re，Pr也基本在这个范围内，n=0.4。所d0.016以可以用上述公式计算Nu的理论值：Nu,=0.023Re0.8Prn⑦理论给热系数：h'二处d⑧相对误差:x⑧相对误差:x100%实验结果与分析1、冷流体给热系数的实验计算值与理论值(Nu/Pro.4=0.023Re0.8)列表比较，计算各点误差，并分析讨论次序项目123456789努赛尔数Nu78.063376.166572.684065.901355.644447.872339.997034.663029.4673努赛尔数理论值Nu'74.643472.654670.659164.717255.232848.143840.041035.102229,9122对流给热系数hw/(m2-°C)151.704125.962120.948108.55990.97278.10065.13356.48248.132理论h'W/(m2.°C)125.767121,722117.577106.60590.30078.54365.20557.19748.859h各点的相对误差％-4.72-3.48-2.86-1.82-0.740.560.111.251.48误差分析：①由于是接着上一组做实验，没有等待仪器冷却，导致实验数据存在误差，前几组数据温度过高。②迪图斯-贝尔特公式(Nu=0.023Reo.8Prn)的条件Re=1.0x104—1.2x105而实验数据有一个没有在此范围之内。所以用此公式算出的Nu'和a2'存在误差。③实验过程中，流量存在波动时，没有取平局值，导致实验误差过大2、冷流体给热系数的准数式：Nu/Pro.4=ARem，以lnNuPr0.4为纵坐标，lnGe)为横坐标，将实验数据的结果标绘在图上，由实验数据作图拟合曲线方程，确定式中常数A及m；并与教材中的经验式Nu/Pr。，=0.023Re0.8比较。29S76一-11-11-11-1QoCE/nsMQIIog(Re) 1og(Nu/Pr0.4))冷流体给热系数的准数式：Nu/Pro.4=丫Rem由图表得拟合曲线方程：y=0.8478x-1.8377贝Um=0.8478（理论值