傳遞原理實(shí)驗(yàn)-傳熱實(shí)驗(yàn)數(shù)據(jù)處理舉例

五．原始數(shù)據(jù)記錄。錢盒號(hào)」3031.昏內(nèi)徑di=16mm. 6=1.5mm.&feL=l.3mHo.蒸汽壓力MT'a蒸汽溫度匸m3/h匸匸下壁溫上壁溫10.030105.0020.0031.0082.709E.40100.3020.030105.0015.0030.4083.8096.30100.2030.030105.0010.0030.1085.8096.80100.6040.030105.005.0030.1088.6097.50101.00歩盤號(hào)」3032.皆內(nèi)徑di=16mm.皆壁帛冠=1.5mm,&ftL=l.3mHo.蒸汽壓力MT'a蒸汽溫度1C空勺說屋m3/h空T進(jìn)口溫度■C空T出口溫度■C下壁溫匸上壁溫?Q10.034105.0020.0030.6081.0039.80100.6020.034105.0015.0023.6082.70100.30101.3030.034105.0010.0028.3085.00100.40101.4040.034105.005.0027.3087.5039.51：1100.60計(jì)算示例以裝置號(hào)3032第1組數(shù)據(jù)為例30.6+81.030.6+81.02=55.8°C,查得pc=1.076kg/m3,Cpc=0.24kcal/kgC,(T—t)—(T(T—t)—(T—t)2 LT—tIn2T—t1WpC(t—t)K= c——c pc2 1—1088AAtm3.14x0.0175x1.3x44.55=342kj/m2hCp=20.3pPa?s,入=0.02461w/mC1熱負(fù)荷計(jì)算Q=WpC(t2-t])=20x1.076x0.24x4.18x(81.0-30.6)=1088kj/hccpc212.傳熱系數(shù)K計(jì)算81.0—30.6 “=44.55C105—81.0In105—30.6KAAtm=WcpcCpc(t2-t1)3?給熱系數(shù)?計(jì)算cAtmct —t100.6—81.0lnm上 2lnt —t99.8—30.6m下 1(tm上—U—5下—Atmct —t100.6—81.0lnm上 2lnt —t99.8—30.6m下 1aAAtccmc=Wpc (t-t)aAAtccmcccpc2 1

10883.14x0.016x10883.14x0.016x1.3x39.32=424kj/m2h°C4?給熱系數(shù)ah計(jì)算pcAtmhaAAt(T-lnmh)-(T-t－t100.6－99.8T-lnT-pcAtmhaAAt(T-lnmh)-(T-t－t100.6－99.8T-lnT-ln105－99.8=4.79CT-T-105－100.6Wpcpc1088冗dlAt3.14x0.019x1.3x4.792929kj/m2hCmh5.雷諾數(shù)R譜朗特?cái)?shù)Pr的計(jì)算e20/3600=20/3600=27.65m/s0.785x0.0162Redup0.016Redup0.016x27.65x1.076=2.34x10420.3x10-6Cpp0.24x20.3x10-6Pr== =0.71九0.0246x3600ad424x0.016NUC=―c—= =65.97九0.0246x4.18六.過程運(yùn)算表3031號(hào)裝置過程運(yùn)算表Ho.m=/h熱呈X1戸Kj/h3TCKX10_EKj/n/h匸ahX10sKj/m.h'CacX10EKj/mEh'CReXlO-^Hu120.0011.0745.053.442.5724.432.3868.8215.008.6443.E92.771.A523.621.7856.1310.00b.0242.491.381.3822.bl1.1840.445.003.2240.771.100.7321.430.5A22.9回歸方程N(yùn)uzO.028Pr°R』円"相關(guān)系數(shù)EzO.999T.區(qū)大相對(duì)囁迫為1.43靄.區(qū)丈相對(duì)囁盪發(fā)生在第［組教據(jù)No.HuPrReX1hHue168.800.702.3869.7925b.130.701.7855.39340.410.701.1840.11422.980.700.5923.133032號(hào)裝置過程運(yùn)算表No.空氣說屋m=/h熱gxio-2Kj/h仝X：KX10EKj/mEhX2ahX103Kj/m.h匸acX10sKj/m.h匸ReX10^JTu120.001U.8844.553.422.9324.232.3765.6j215.008.5943.532.TE.2.6523.3T1.7852.2：310.00b.1U42.182.021.9322.481.1338.4445.003.2340.381.120.8421.430.5922.or回歸方程N(yùn)u^O.Q29P嚴(yán)詁剛相關(guān)系數(shù)班Q.9999.區(qū)丈相對(duì)囁迫再-Q.W4乩區(qū)丈相對(duì)囁直荒生在第？組數(shù)據(jù)No.HuPrReX1『4Hue165.bH0.702.37G5.72252.200.701.7352.43338.440.701.1338.14斗22.070.700.5922.14作圖法關(guān)聯(lián)曲線方程N(yùn)u/P0.4=aRb (17)re由下圖3031，用作圖法待定上式函數(shù)中的常數(shù)a和b，方法如下：以直線為斜邊，作直角三角形，讀得斜邊上二點(diǎn)A(10000，40.6)，B(20000，70.2)該三角形的高與該三角形底邊之比的值，即為此函數(shù)的指數(shù)b；然后在直線上讀得一點(diǎn)坐標(biāo)，將該坐標(biāo)待入式(17)，可求得常數(shù)a。In70.0-In40.6b= =0.786ln20000-ln10000將點(diǎn)(10000，40.6)待入得40.6=alOOOO0-786a=0.029.??N=0.029R0-786P0-4uer裝置號(hào)3031Nu/Pr0-4對(duì)Re關(guān)系圖

O103 2 3 4 5E78310^ 23 4 5E78310gReZ//z，■-/O103 2 3 4 5E78310^ 23 4 5E78310gReZ//z，■-/IIIIIIIIIIIIIIIIINu/Pr04對(duì)趾關(guān)系圖裝置號(hào)3032Nu/Pr0-4對(duì)Re關(guān)系圖3 4 5678910eoooooooO038765431-20487653Nu/Pr4對(duì)趾關(guān)系圖實(shí)驗(yàn)結(jié)果討論與分析從理論及經(jīng)驗(yàn)公式可知：Nu=0.023Ro.8Pro.4。而此公式適用的條件是：e⑴光滑管內(nèi)R>10000即流動(dòng)是充分湍流的，這一點(diǎn)是重要的；e(2)0.7VP<160；r⑶流體是低粘度的(不大于水粘度的2倍)；⑷l/d>30?40即進(jìn)口段只占總長(zhǎng)的很小一部分，而管內(nèi)流動(dòng)是充分發(fā)展的。本實(shí)驗(yàn)關(guān)聯(lián)的Nu=0.030Re0.778Pr0.4與理論公式作比較有偏差，可能有以下原因造成的。冷u er空氣進(jìn)口溫度隨冷空氣進(jìn)口流量的下降而不斷上升，這對(duì)傳熱的穩(wěn)定影響很大，因此，為了減少此影響因素，在設(shè)備設(shè)計(jì)時(shí)冷空氣進(jìn)入系統(tǒng)前，設(shè)置空氣冷卻裝置，以避免空氣溫度變化太大造成數(shù)據(jù)誤差厲害。冷空氣流量取20、15、10、5m3/h，其他變量若發(fā)生變化,熱平衡就被破壞，要建立熱平衡需要一定的時(shí)間，因此t2必須穩(wěn)定5min以上不變方可讀數(shù)取樣。入0.400.8u0.8整理a=0.023 U，由此式可知：物性參數(shù)中0對(duì)給熱系數(shù)影響最大，但對(duì)卩0.