空氣-蒸汽對流給熱系數(shù)測定.doc

次序123456789閥門開度928884807672686460空氣流量V/m3/h17.3216.3315.4915.6013.6612.6511.8310.9510.33空氣進口溫度37.336.635.634.533.331.930.629.728.5空氣出口溫度79.779.679.579.479.378.978.778.878.5蒸汽進口溫度103.3102.8102.8103.0103.2103.0103.1103.0103.1蒸汽出口溫度85.485.385.385.585.785.585.385.184.8空氣進口密度kg/m31.13771.14031.14411.14831.15281.15821.16331.16681.1715空氣質(zhì)量流量m2/kg/s0.00550.00520.00490.00500.00440.00410.00380.00350.0034空氣流速u m/s23.940622.572221.411121.563218.881617.485516.352115.135714.2787五、數(shù)據(jù)處理1、原始數(shù)據(jù)記錄表以下計算過程以第一組數(shù)據(jù)為例：空氣進口出密度=10-5t2-4.510-3t+1.2916=10-537.32-4.510-337.3+1.2916=1.1377 kg/m3空氣質(zhì)量流量m2=V=1.137717.32=0.0055 kg/s空氣流速u=4V/d2=417.32/(3.140.01623600)=23.9046 m/s2、給熱系數(shù)K的計算123456789空氣平均定性溫度58.558.157.657.056.355.454.754.353.5定性溫度下的空氣密度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冷熱流體的對數(shù)平均溫差41.228841.009941.445642.136442.863043.443144.168844.305845.0696總給熱系數(shù)K112.6006108.4920104.3051106.063293.909388.079683.273478.674774.5989空氣定性溫度： t平均=1/2(t1+t2)=1/2(37.3+79.7)=58.560空氣比熱容CP=1005J/(Kg)定性溫度下的空氣密度=10-5t2-4.510-3+1.2916=10-558.52-4.510-358.5+1.2916=1.0619 kg/m3冷熱流體對數(shù)平均溫差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總給熱系數(shù)K=m2Cp2(t2-t1)/Atm=0.00611005(79.7-37.3)/( 3.140.016241.0827)=124.69593、近似法求給熱系數(shù)K2=124.6959 w/(m2C)序號123456789對流給熱系數(shù) 2 w/(m2)124.6959108.4920104.3051106.063293.909388.079683.273478.674774.5989空氣黏度（Pas）2.0026E-052.0006E-051.9980E-051.9952E-051.9921E-051.9878E-051.9842E-051.7137E-051.7139E-05空氣導(dǎo)熱系數(shù)w/(m2)0.0290 0.0290 0.0289 0.0289 0.0288 0.0288 0.0287 0.0287 0.0286 雷諾數(shù)Re20325 19206 18273 18464 16226 15102 14182 13156 12464 普蘭特數(shù)Pr0.6937 0.6938 0.6939 0.6940 0.6942 0.6944 0.6945 0.6946 0.6948 努賽爾數(shù)Nu62.0997 59.8980 57.6714 58.7381 52.0984 48.9831 49.1906 43.8893 41.7005 努賽爾數(shù)理論值Nu55.5423 53.0837 51.0150 51.4448 46.3968 43.8111 41.6669 39.2402 37.5816 理論2w/(m2)100.7104 96.1495 92.2662 92.8936 83.6320 78.7796 74.7719 70.3408 67.2306 2各點的相對誤差-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 空氣黏度：=（-210-6t2+510-3t+1.7169）10-5 =(-210-658.72+510-358.7+1.7169) 10-5=2.002610-5（Pas）空氣導(dǎo)熱系數(shù)：=-210-8t2+510-3t+0.0244= -210-658.72+510-358.7=0.0290 w/(m2C)雷諾數(shù)：Re=du/=0.01626.70511.0619/1.712910-5=20325普蘭特數(shù)：Pr=Cp/=10051.715910-5/0.0290=0.6937努塞爾數(shù)：Nu=2d/=149.57950.016/0.0290=62.0997對于流體在圓形只管內(nèi)做湍流時的對流傳熱系數(shù)若符合以下條件：Re10000即流動是充分湍流的； 0.7Pr160 流體是低粘度（不大于水的2倍） l/d3040即進口段只占總長的很小部分，而管內(nèi)流動是充分發(fā)展的則本實驗：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的理論值=0.023264890.80.59310.4=64.4788理論2= Nu/d=64.47880.0290/0.016=116.9769 w/(m2)相對誤差=（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、實驗結(jié)果與分析1、 冷流體給熱系數(shù)的實驗計算值與理論值（）列表比較，計算各點誤差，并分析討論123456789努賽爾數(shù)Nu62.0997 59.8980 57.6714 58.7381 52.0984 48.9831 49.1906 43.8893 41.7005 努賽爾數(shù)理論值Nu55.5423 53.0837 51.0150 51.4448 46.3968 43.8111 41.6669 39.2402 37.5816 對流給熱系數(shù) 2 w/(m2)112.6006 108.4920 104.3051 106.0632 93.9093 88.0796 88.2734 78.6747 74.5989 理論2w/(m2)100.7104 96.1495 92.2662 92.8936 83.6320 78.7796 74.7719 70.3408 67.2306 2各點的相對誤差11.81%12.84%13.05%14.18%12.29%11.81%18.06%11.85%10.96%誤差分析：由于蒸汽壓力沒辦法穩(wěn)定在實驗所需的值，造成誤差；儀器有所損壞造成