空气横掠单管时平均换热系数的测定.doc

五、实验结果1给出所有原始数据记录于表1。2实验数据处理以1#管的第2种工况为例。试验管工作段ab间的发热量Q为：（W）故空气流对管外壁的平均换热系数h为：（W/(m2)）式中，A为电压测点ab间试验管的外表面积，且A为：(m2)以空气和壁面的平均温度查有关表格可知空气的导热系数=2.9210-2 W/(m)，空气运动粘度=19.3910-6 m/s，故得计算所有工况下的h、Nu和Re列于表2中。根据表2 做出lnNu-lnRe曲线图如图1所示。图1 lnNu-lnRe曲线图由图1可知lnNu=1.744lnRe+3.0107，即n=1.744，lnC=3.0107，C=20.3，故表1 原始数据记录表待测物理量1#管2#管3#管4#管外径D(mm)6.55.04.03.0长度L(m)0.0980.0980.0980.098面积A(m2)0.002000180.00153860.001230880.00092316工况1234123412341234来流速度u(m/s)20158.642016.29.7420.316.28.84.22014.28.94.2I参考值(A)25201612实测值(A)24.924.924.924.920.820.820.820.816.216.216.216.212.612.612.612.6U（V20.2）0.70.70.70.70.420.420.420.420.470.470.470.470.730.730.730.73温差电势(mV)2.523.565.127.341.451.82.6541.7422.994.132.343.044.045.6过余温度()61.284.5117.8163.636.144.564.294.14349.271.996.857.17394.9127.8Tw ()82.7106.2139.8186.258.166.386.2116.764.671.294.8119.277.894.5116.3149.7T ()21.521.72222.62221.82222.621.62222.922.420.721.521.421.9表2 各工况下的h、Nu和Re值1#管2#管3#管44#管1234123412341234h142.39 103.13 73.97 53.27 157.28 127.59 88.44 60.34 143.86 125.73 86.03 63.90 174.49 136.49 104.99 77.96 Nu32.5922.9615.7110.6928.4922.8715.4610.1920.7017.9611.918.6118.5014.1710.687.54Re7162.535028.372638.041102.165896.234665.902643.05999.504704.523677.641867.37834.163344.482272.001342.38580.91六、实验总结 通过本次实验我熟悉了空气流速及管壁