空气-蒸汽对流给热系数测定

《空气-蒸汽对流给热系数测定》由会员上传分享，免费在线阅读，更多相关内容在行业资料-天天文库。

1、空气－蒸汽对流给热系数测定紫铜管规格：直径φ21×2.5mm，长度L=1000mm外套玻璃管规格：直径φ100×5mm，长度L=1000mm1、原始数据记录如下表：序号12345678水蒸气压强P(MPa)0.030.030.030.030.030.030.030.03冷流体流量m3/h2220181512963冷流体进口温度t1℃47.846.045.645.144.443.641.640.4冷流体出口温度t2℃80.679.979.879.780.080.480.980.4蒸汽进口温度T1℃103.1102.8102.8103.0103.3103.2103.7103.5蒸汽出

2、口温度T2℃103.9103.5103.4103.7104.1103.6104.4104.02、根据将冷热流体的进出口温度换算成冷热流体间的对数平均温差,数据总结如下表.序号12345678冷流体流量m3/h2220181512963冷流体进口温度t1℃47.846.045.645.144.443.641.640.4冷流体出口温度t2℃80.679.979.879.780.080.480.980.4蒸汽进口温度T1℃103.1102.8102.8103.0103.3103.2103.7103.5蒸汽出口温度T2℃103.9103.5103.4103.7104.1103.6104.

3、4104.0Δtm36.776737.582237.764838.274638.687238.446339.479139.98893、在0～100℃之间，冷流体的物性与温度的关系有如下拟合公式。（1）空气的密度与温度的关系式：（2）空气的比热与温度的关系式：60℃以下＝J/(kg∙℃),70℃以上＝J/(kg∙℃)。（3）空气的导热系数与温度的关系式：（4）空气的黏度与温度的关系式：按以上公式，并以标准单位换算，得到如下数据结果表：序号12345678空气质量流率m(kg∕s)×1037.03376.41295.7754.8173.8582.8971.9380.971空气进口密度

4、ρ(Kg/m3)1.09931.10581.10721.10901.11151.11441.12171.126空气比热Cp(J/kg℃)10051005100510051005100510051005空气导热系数λ（W/m℃）×1022.94535672.93572.93372.93142.92992.92832.92252.9159空气粘度μ(PaS)×1052.032.0232.022.022.022.022.022.01对流传热系数α（W∕m℃）125.4877115.7145104.6247104.624771.011955.471338.585719.4242α2理论w

5、/(m2·℃)125.7769116.9923107.629693.124978.031762.110945.118225.9808误差0.23%1.09%2.79%6.47%9.00%10.69%14.48%25.24%4、对于流体在圆形直管内作强制湍流对流传热时，若符合如下范围内：Re=1.0×104～1.2×105,Pr＝0.7～120，管长与管内径之比l/d≥60,则传热准数经验式为，（4－9）式中：Nu－努塞尔数，，无因次；Re－雷诺数，，无因次；Pr－普兰特数，，无因次；当流体被加热时n＝0.4，流体被冷却时n＝0.3；按以上公式，并以标准单位换算，得如下数据结果表。

6、序号12345678雷诺数Re26353.8024168.3721792.5218202.7214602.1810985.337384.543714.26普兰特数Pr0.69250.69280.69290.69290.69290.69300.69310.6933努塞尔数Nu68.168463.066757.060147.541538.779630.308921.124810.6584Nu理论68.325463.763158.698950.8286742.6131833.9367924.7011514.25606ln(Nu理论/Pr0.4)4.37124.30194.21924.0

7、7523.89893.67123.35352.8037ln(Nu/Pr0.4)4.36894.29094.19094.00833.80463.55813.19712.5129lnRe10.179410.09289.98939.80939.58899.30438.90718.21995、由式，实验测定、、并查取下冷流体对应的、换热面积A，即可由上式计算得总给热系数K如下表。序号t2-t1(℃)换热面积A(m2)总给热系数K(W/m2℃)132.80.05024125.4877233