空气-蒸汽对流给热系数测定.doc

次序123456789阀门开度928884807672686460空气流量V/m3/h17.3216.3315.4915.6013.6612.6511.8310.9510.33空气进口温度37.336.635.634.533.331.930.629.728.5空气出口温度79.779.679.579.479.378.978.778.878.5蒸汽进口温度103.3102.8102.8103.0103.2103.0103.1103.0103.1蒸汽出口温度85.485.385.385.585.785.585.385.184.8空气进口密度kg/m31.13771.14031.14411.14831.15281.15821.16331.16681.1715空气质量流量m2/kg/s0.00550.00520.00490.00500.00440.00410.00380.00350.0034空气流速u m/s23.940622.572221.411121.563218.881617.485516.352115.135714.2787五、数据处理1、原始数据记录表以下计算过程以第一组数据为例：空气进口出密度=10-5t2-4.510-3t+1.2916=10-537.32-4.510-337.3+1.2916=1.1377 kg/m3空气质量流量m2=V=1.137717.32=0.0055 kg/s空气流速u=4V/d2=417.32/(3.140.01623600)=23.9046 m/s2、给热系数K的计算123456789空气平均定性温度58.558.157.657.056.355.454.754.353.5定性温度下的空气密度kg/m31.06261.06391.06571.06781.06991.07301.07551.07691.0795ln(T-t)1/(T-t)2-1.0284-1.0485-1.0592-1.0656-1.0732-1.0819-1.0890-1.1082-1.1094冷热流体的对数平均温差41.228841.009941.445642.136442.863043.443144.168844.305845.0696总给热系数K112.6006108.4920104.3051106.063293.909388.079683.273478.674774.5989空气定性温度： t平均=1/2(t1+t2)=1/2(37.3+79.7)=58.560空气比热容CP=1005J/(Kg)定性温度下的空气密度=10-5t2-4.510-3+1.2916=10-558.52-4.510-358.5+1.2916=1.0619 kg/m3冷热流体对数平均温差tm=（T1-t2）-（T2-t1）/ln(T1-t2)/( T2-t1) =(103.3-79.7)-(103.3-37.3)/ln(103.3-79.7)/( 103.3-37.3)=41.2288总给热系数K=m2Cp2(t2-t1)/Atm=0.00611005(79.7-37.3)/( 3.140.016241.0827)=124.69593、近似法求给热系数K2=124.6959 w/(m2C)序号123456789对流给热系数 2 w/(m2)124.6959108.4920104.3051106.063293.909388.079683.273478.674774.5989空气黏度（Pas）2.0026E-052.0006E-051.9980E-051.9952E-051.9921E-051.9878E-051.9842E-051.7137E-051.7139E-05空气导热系数w/(m2)0.0290 0.0290 0.0289 0.0289 0.0288 0.0288 0.0287 0.0287 0.0286 雷诺数Re20325 19206 18273 18464 16226 15102 14182 13156 12464 普兰特数Pr0.6937 0.6938 0.6939 0.6940 0.6942 0.6944 0.6945 0.6946 0.6948 努赛尔数Nu62.0997 59.8980 57.6714 58.7381 52.0984 48.9831 49.1906 43.8893 41.7005 努赛尔数理论值Nu55.5423 53.0837 51.0150 51.4448 46.3968 43.8111 41.6669 39.2402 37.5816 理论2w/(m2)100.7104 96.1495 92.2662 92.8936 83.6320 78.7796 74.7719 70.3408 67.2306 2各点的相对误差-11.81%-12.84%-13.05%-14.18%-12.29%-11.81%-18.06%-11.85%-10.96%Nu/Pr0.471.8816 69.3297 66.7482 67.9780 60.2891 56.6779 56.9129 50.7769 48.2402 ln(Nu/Pr0.4)4.2750 4.2389 4.2009 4.2192 4.0992 4.0374 4.0415 3.9274 3.8762 ln(Re)9.9196 9.8630 9.8132 9.8236 9.6944 9.6226 9.5597 9.4847 9.4306 空气黏度：=（-210-6t2+510-3t+1.7169）10-5 =(-210-658.72+510-358.7+1.7169) 10-5=2.002610-5（Pas）空气导热系数：=-210-8t2+510-3t+0.0244= -210-658.72+510-358.7=0.0290 w/(m2C)雷诺数：Re=du/=0.01626.70511.0619/1.712910-5=20325普兰特数：Pr=Cp/=10051.715910-5/0.0290=0.6937努塞尔数：Nu=2d/=149.57950.016/0.0290=62.0997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：Re10000即流动是充分湍流的； 0.7Pr160 流体是低粘度（不大于水的2倍） l/d3040即进口段只占总长的很小部分，而管内流动是充分发展的则本实验：由上表可知Re都大于10000，l/d=1/0.016=62.540 所以可用上述公式；算Nu的理论值=0.023264890.80.59310.4=64.4788理论2= Nu/d=64.47880.0290/0.016=116.9769 w/(m2)相对误差=（2-2）/2=（112.6006-100.7104）/100.7104=11.81%ln(Nu/Pr0.4)=ln(71.8816)=4.42750ln(Re)=ln20325=9.9196六、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（）列表比较，计算各点误差，并分析讨论123456789努赛尔数Nu62.0997 59.8980 57.6714 58.7381 52.0984 48.9831 49.1906 43.8893 41.7005 努赛尔数理论值Nu55.5423 53.0837 51.0150 51.4448 46.3968 43.8111 41.6669 39.2402 37.5816 对流给热系数 2 w/(m2)112.6006 108.4920 104.3051 106.0632 93.9093 88.0796 88.2734 78.6747 74.5989 理论2w/(m2)100.7104 96.1495 92.2662 92.8936 83.6320 78.7796 74.7719 70.3408 67.2306 2各点的相对误差11.81%12.84%13.05%14.18%12.29%11.81%18.06%11.85%10.96%误差分析：由于蒸汽压力没办法稳定在实验所需的值，造成误差；仪器有所损坏造成