化工原理传热实验

一、实验名称

冷空气-蒸汽的对流传热实验

二、实验目的

(1)测定冷空气-蒸汽在套管换热器中的总传热系数K。

⑵测定冷空气在光滑套管内的给热系数。

⑶测定冷空气在螺旋套管内的给热系数。

⑷比较冷空气在光滑套管内和螺旋套管内的传热性能，绘制N〃与Re之间的关系加

线。

(5)熟悉温度、流量等化工测试仪表的使用。

三、实验原理

(1)冷空气-蒸汽的传热速率方程：

Q=KA/

A/1—A/2

In

\t2

Q=q3p&f)

实验测得冷空气流量心、冷空气进出换热器的温度小&；蒸汽在换热器内温度7,可得K。

(2)总热阻为

11bd14

1丁初十顺

冷空气走管程，由于蒸汽为较大，k较大,可忽略后两项，即4*K。

(3)流体在圆形直管中强制对流时，

Nu=CRePr"

KJh】ddup_cN

其中=Rc=——,Pr=o

k、"k}

对冷空气而言，在较大温度范围内Pr基本不变，取0.7；流体加热，〃=0.4,可简化为M/=CRe"'，

改变流量，Re、N“改变，双对数坐标下作Re和N〃关系是一条直线，拟合此直线方程，即为

Re和的准数方程。

四、实验装置图及主要设备(包括名称、型号、规格)

(1)实验装置示意图如下图所示(冷空气走管程):

ZT\9/TX12

19

图1对流传热实验装置示意图

1-涡轮流量计；2,3,7,10-球阀；4,5,8,9,lh12,14,15,18,19-温度传感器；6-冷凝水收集

杯；13-蒸汽发生器；16-闸阀：17-消音器：20-风机：1#,2#-换热器

(2)设备及仪表。

设备:风机、蒸汽发生器、普通套管换热器、螺旋套管换热器、消音器。

仪表:气体涡轮流量计、差压变送器、温度变送器、温度控制器、无纸记录仪、液位计。

五、实验步骤

(D熟悉传热实验装置及仪表使用，检查设备，做好实验操作准备。

⑵启动总电源和仪表电源。

(3)检查蒸汽发生器内的液位是是否到指定液位。高于指定液位时，才能启动其电源加

热，使蒸汽发生器内的水沸腾汽化产生蒸汽。全开冷空气支路调节阀(闸阀16),选择1#

换热器，全开此换热器的切换阀(球阀3)。

(4)观察控制柜上蒸汽发生器的温度控制仪表，当蒸汽发生器内温度显示升到100C。后,

启动风机。

(5)稳定10-15min,记录冷空气流量，蒸汽温度和冷空气进、出口温度。

⑹调节空气支路调节阀(逐渐关团闸阀16),改变冷空气流量，稳定10T5min后，记

录冷空气流量，进、出口温度和蒸汽温度。

⑺重复操作实验步骤(6),8T0次，流量从大到小，均匀分布，完成1#换热器的测定。

(8)全开冷空气支路调节阀(闸阀16),选择另一个2#换热器，全开此换热器切换阀(球

阀2),关闭已做完实验的1#换热器的切换阀(球阀3)。

⑼重复操作实验步骤(5)(6)(7),完成2*换热器的测定。

(10)实验数据采集完毕后，全开球阀2、3和闸阀16,然后依次关闭风机、蒸汽发生器、

仪表和总电源。

六、实验原始数据记录列表

表1上管传热实验原始数据记录表

进口端温度出口端温度流量蒸汽温度1蒸汽温度2蒸汽温度3蒸汽平均温度

序号

(C)(C)(/3/h)(°C)(C)(C)(℃)

127.968.055.397.299.0100.698.9

230.169.952.598.899.7101.5100.0

330.570.350.498.799.5100.999.7

429.970.247.297.599.3101.299.3

529.270.144.698.499.4101.199.6

628.469.942.598.899.4100.899.7

727.769.840.498.799.4101.599.9

826.969.638.599.399.2101.099.8

926.169.336.499.299.4101.299.9

1025.268.834.499.399.4101.099.9

1124.668.732.5100.099.5101.5100.3

1224.068.430.0100.099.2101.5100.2

1323.668.228.0100.499.3101.5100.4

1423.268.125.2100.399.2101.4100.3

1522.867.923.3100.799.5101.4100.5

1622.567.721.1100.599.1101.0100.2

P=96.OkPa换热器5#

表2下管传热实验原始数据记录表

进口端温度出口端温度流量蒸汽温度1蒸汽温度2蒸汽温度3蒸汽平均温度

序号

(℃)(C)(nT3/h)(C)(C)(℃)(℃)

129.566.057.595.098.2107.3100.2

230.367.253.498.398.5108.0101.6

330.167.748.298.998.6108.1101.9

429.768.046.299.598.7108.2102.1

529.368.144.498.698.9108.3101.9

628.867.942.996.098.8108.1101.0

728.167.941.099.398.5108.0101.9

827.367.838.599.298.5107.9101.9

926.867.836.5100.298.5107.8102.2

1026.067.834.998.998.7108.0101.9

1125.367.832.698.698.7108.0101.8

1224.967.930.2100.598.6107.8102.3

1324.468.028.499.598.7108.0102.1

1423.968.126.1100.498.5107.7102.2

1523.668.423.299.898.6107.9102.1

1623.368.721.598.598.7108.0101.7

P=96.OkPa换热器5#

七、实验数据处理(以一组实验数据为例进行计算)

1.判断管的类型，以上管第一组数据为例

温差Ar=68.0-27.9=40.1C°

上管流量上管温差下管流量下管温差

(m'3/h)(℃)(nT3/h)(℃)

55.340.157.536.5

52.539.853.436.9

50.439.848.237.6

47.240.346.238.3

44.640.944.438.8

42.541.542.939.1

40.442.141.039.8

38.542.738.540.5

36.443.236.541.0

34.443.634.941.8

32.544.132.642.5

30.044.430.243.0

28.044.628.443.6

25.244.926.144.2

23.345.123.244.8

21.145.221.545.4

当流量较高时，流量相近时上管温差要高于下管温差，故上管为螺旋套管，下管为光滑

套管。

2.G上管第一行数据为例，

由于当地大气压为96.OkPa,查表可知蒸汽温度T=98.32℃。

对数平均温差"二牛泮,98.5-27.9=4759°C

In-LIn----LIn-----------

Ar2T-t298.32-68.0

冷空气定性温度1=上且=279+68.0=47.951;

22

根据定性温度，运用内插法求得冷空气密度，冷空气比热、冷空气黏度、冷空气导热系

数。由于定性温度在40-53℃之间，

空气密度夕=凡℃-出管冷°*。-40),即

.(1.128-1,093)

P=1.1Zo--------------------------x(47.95-40)=1.100依/加

10

冷空气比热7=冬会+(°小〃研)*«_40),即

^,=(1.013+0.004/10*(47.95-40))*1000=1016.18J/kg.℃

冷空气黏度〃=〃40c+(以。)*«-40),即

4=(1.91+0.005*(47.95-4()))xl(r5=1.950xl(r5Pa-s；

4

冷空气导热系数我二440c+化°U"屈*(l40)

10

k=(2.756+(2.826-2.756)/10*(47.95-40))x10-2=2.812x102W/(m*K)；

根据换热器5#的参数，管程：025*2.5长度L=1.3m

螺纹管的传热面积A=1.反力，即4=1.1x3.14x(25-2x2.5)4-1000x1.3=0.090疗.

光滑管的传热面积A?=7rdl,BPA=3.14x(25-2x2.5)-1000x1.3=0.082〃/.

传热速率。=/夕］,加，B|J2=55.34-36()0x1.1()0x1016.18x40.1=688.71V；

总传热系数K=-^-,即长=—竺引一=161.1VV/(m2.℃)；

A\tnt0.090x47.59

由于KB九，即给热系数约为总传热系数。

雷诺准数Re=等=翳,即Re=需蓝零詈遥2=552。85；

努塞尔准数M,二也二型，BPM/=1611X0°^=114.6O

k、k}2.812x10-2

八、实验结果与分析(含数据结果列表和作图)

表3螺旋套管传热实验数据结果记录表

HAAI

温差定性蹒空气密度空气雌tfig*10A5传热面积对数平均温差倒腿率总传热系数导热碘*1042

(mA3/sNuRe

(X)(℃)(kg/mA3)(J/kg*X)(Pa*s)(mA2)(X)(W)(W/(mA2*X))(W/(m*K))

)

40.147.951.1001016.181.9500.01540.09047.59688.7161.1114.655208.52.812

39.850.001.0931017.001.9600.01460.09045.45645.2158.1111.951799.02.826

39.850.401.0921017.161.9620.01400.09045.03618.7153.0108.249612.72.829

40.350.051.0931017.021.9600.01310.09045.32587.3144.3102.146556.42.826

40.949.651.0941016.861.9580.01240.09045.66563.8137.597.444093.22.824

41.549.151.0961016.661.9560.01180.09046.10545.9131.993.542138.02.820

42.148.751.0971016.501.9540.01120.09046.43527.0126.489.740148.12.817

42.748.251.0991016.301.9510.01070.09046.87510.1121.286.138370.12.814

43.247.701.1011016.081.9490.01010.09047.38488.7114.881.736392.02.810

43.647.001.1041015.801.9450.00960.09048.07467.0108.277.134531.02.805

44.146.651.1051015.661.9430.00900.09048.36446.7102.873.432689.42.803

44.446.201.1061015.481.9410.00830.09048.80415.794.967.830252.92.799

44.645.901.1071015.361.9400.00780.09049.09390.088.563.328284.72.797

44.945.651.1081015.261.9380.00700.09049.31353.679.957.125492.72.796

45.145.351.1091015.141.9370.00650.09049.60328.773.852.823611.32.793

45.245.101.1101015.041.9360.00590.09049.85298.566.747.821412.62.792

表4光滑套管传热实验数据结果记录表

温差定性盟空气密度的比热蟠*10"5流员釉面积对数平均温差总传热系数空幅热系数

NuRe

(X)(℃)(kg/mA3(J/kg*X)(Pa*s)(mA3/s)(mA2)(X)(W)(W/(mA2**10A2(W/(m*K

36.547.751.1011016.101.9490.01600.08248.29652.1165.4117.757470.82.810

36.948.751.0971016.501.9540.01480.08247.19610.6158.5112.553067.12.817

37.648.901.0971016.561.9550.01340.08246.94561.3146.5104.047858.22.818

38.348.851.0971016.541.9540.01280.08246.89548.1143.2101.645885.62.818

38.848.701.0981016.481.9540.01230.08246.98533.9139.298.844135.92.817

39.148.351.0991016.341.9520.01190.08247.31520.3134.795.742730.12.814

39.848.001.1001016.201.9500.01140.08247.58506.7130.492.840920.42.812

40.547.551.1021016.021.9480.01070.08247.95484.8123.888.238524.72.809

41.047.301.1021015.921.9470.01010.08248.14465.6118.584.436575.92.807

41.846.901.1041015.761.9450.00970.08248.45454.4114.981.935053.02.804

42.546.551.1051015.621.9430.00910.08248.72431.9108.677.532808.82.802

43.046.401.1061015.561.9420.00840.08248.80405.0101.772.630419.62.801

43.646.201.1061015.481.9410.00790.08248.92386.496.769.128639.42.799

44.246.001.1071015.401.9400.00730.08249.04360.290.064.326350.22.798

44.846.001.1071015.401.9400.00640.08248.95324.581.258.023422.42.798

45.446.001.1071015.401.9400.00600.08248.85304.8