給熱系數(shù)的測定實(shí)驗(yàn)數(shù)據(jù)記錄與處理

1、實(shí)驗(yàn)數(shù)據(jù)記錄與處理1、實(shí)驗(yàn)原始數(shù)據(jù)記錄表次序 項(xiàng)目123456789水蒸氣壓強(qiáng)MPa0.020.020.020.020.020.020.020.020.02空氣進(jìn)口溫度t1°C32.730.328.024.622.121.420.82121.6空氣出口溫度t2七74.172.971.970.770.470.771.972.674空氣進(jìn)口處蒸汽溫度T1 °C103.2103.2103.2103.2103.2103.2103.2103.2103.2空氣出口處蒸汽溫度T2°C102.3102.3102.3102.3102.3102.3102.3102.3102.3空氣流

2、量V(m3/h)23.022.021.018.515.012.6108.57空氣進(jìn)口處密、3度 p (kg/m )1.15511.16441.17341.18691.19701.19981.20231.20151.1982空氣質(zhì)量流量 ms (kg/s)0.00740.00710.00680.00610.00500.00420.00340.00280.0023空氣流速U(m/s)31.791830.409629.027325.571720.733817.416413.822511.74929.6758計算公式:空氣進(jìn)口處密度:10 4;4.5 10 冷 1.2916空氣質(zhì)量流量:空氣流速：Um

3、is V4V2、給熱系數(shù)K的計算項(xiàng)目123456789空氣定性溫度t平均°C53.4051.6049.9547.6546.2546.0546.3546.8047.90定性溫度下的空氣密度，1.07981.08601.09181.09991.10481.10571.10451.10291.0989kg/m3冷、熱流體間的對數(shù)平均溫46.443548.179249.701451.857753.014553.071752.456451.885850.5873差 tm °C總給熱系數(shù)Kw/(m2-°C)151.704125.962120.948108.55990.9727

4、8.10065.13356.48248.132計算公式：1 空氣定性溫度：t平均J tt) (t 60) 空氣比熱:Cp 1005J/(kg ) 定性溫度下的空氣密度：=104平均4.5 10噸平均1.2916冷、熱流體間的對數(shù)平均溫差:tm傳熱面積：Ad2l 3.14 0.016 1 0.0502m2對流傳熱系數(shù):msCp(t2 tjKA tm3、近似法求給熱系數(shù)hh=K=103.1096w/(m2 -C)4、h理論值的計算計算公式: 空氣粘度：(2 10 %25 10 氣 1.7169) 10次序項(xiàng)目、123456789對流給熱系數(shù)h w/(m2°C)151.704125.962

5、120.948108.55990.97278.10065.13356.48248.132空氣黏度卩-5(10 Pa s)1.87821.86651.85531.83871.82641.82301.82001.82101.8249空氣導(dǎo)熱系數(shù)入 W/(m K)0.02700.02680.02660.02630.02620.02610.02610.02610.0261雷諾數(shù)Re29243283092732924474200681689913421113659332普蘭特數(shù)Pr0.69970.69990.70030.70110.70170.70180.70200.70190.7017努賽爾數(shù)Nu78

6、.063376.166572.684065.901355.644447.872339.997034.663029.4673努賽爾數(shù)理論值NlT74.643472.654670.659164.717255.232848.143840.041035.102229.9122理論IYW/(m 2 °C)125.767121.722117.577106.60590.30078.54365.20557.19748.859h各點(diǎn)的相對誤差-4.72-3.48-2.86-1.82-0.740.560.111.251.48logw Nu/Pr0-41.95461.93811.92331.88061.8

7、0701.71461.66351.60131.5309logioRe4.46604.4 5194.43664.38884.30254.22794.12784.05633.965 空氣導(dǎo)熱系數(shù):8 10 氣 0.0244雷諾數(shù)：Re duC普蘭特數(shù)：Pr努賽爾數(shù)：Nu巴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:Re 1.0 10< 1.2 10s Pr0.7: 120，管長與管內(nèi)徑之 60 廁 Nu O.O23Reo8Prndn=0.4 ° 所I 1本實(shí)驗(yàn)中，d0麗5 60,而Re P也基本在這個范圍內(nèi)，以可以用上述公式計算Nu的理論值：Nir O.O23Reo3

8、Prn理論給熱系數(shù)：d相對誤差：j 100%實(shí)驗(yàn)結(jié)果與分析1、冷流體給熱系數(shù)的實(shí)驗(yàn)計算值與理論值(Nu/Pr 04 o.O23 Re。®列表比較,計算各點(diǎn)誤差，并分析討論次序項(xiàng)目、123456789努賽爾數(shù)Nu78.063376.166572.684065.901355.644447.872339.997034.663029.4673努賽爾數(shù)理論值74.643472.654670.659164.717255.232848.143840.041035.102229.9122對流給熱系數(shù)h151.704125.962120.948108.55990.97278.10065.13356.4

9、8248.132w/(m 2-°C)理論h*W/(m2 °C)125.767121.722117.577106.60590.30078.54365.20557.19748.859h各點(diǎn)的相對誤差472-3.48-2.86-1.82-0.740.560.111.251.48誤差分析： 由于是接著上一組做實(shí)驗(yàn)，沒有等待儀器冷卻，導(dǎo)致實(shí)驗(yàn)數(shù)據(jù)存在誤差， 前幾組數(shù)據(jù)溫度過高。 迪圖斯貝爾特公式(NuO.O23ReoBPr)的條件Re 1.0 101.2 10而實(shí)驗(yàn)數(shù)據(jù)有一個沒有在此范圍之內(nèi)。所以用此公式算出的NiT和J存在 誤差o 實(shí)驗(yàn)過程中，流量存在波動時，沒有取平局值，導(dǎo)致實(shí)驗(yàn)誤差過大2、冷流體給熱系數(shù)的準(zhǔn)數(shù)式:Nu/Pr04 ARem 以In Nu/Pr0 4為縱坐標(biāo)'In Re為橫坐標(biāo)，將實(shí)驗(yàn)數(shù)據(jù)的結(jié)果標(biāo)繪在圖上，由實(shí)驗(yàn)數(shù)據(jù)作圖擬合曲線方程，確定式中常數(shù)A及m ；并與教材中的經(jīng)驗(yàn)式Nu/PK0.023Re-8 比較。I og (Re)1 og (Nu/Pr'O, 4)冷流體給熱系數(shù)的準(zhǔn)數(shù)式：Nu/PwYR®由圖表得擬合曲線方程：y=0.8478x-1.8377則