空氣縱掠平板時局部換熱系數(shù)的測定

1、空氣縱掠平板時局部換熱系數(shù)的測定5、 實(shí)驗記錄及數(shù)據(jù)處理 U/v1.68I/A17.08板寬b0.065總長l0.66x離前緣距離溫差t-tf局部換熱系數(shù)hx227.224.59070341452923.064383892830.621.85840303513.532.920.330307992137.517.8364568763040.216.6384858924142.815.6277367495445.214.7979454177052.912.643991178953.612.47886441911055.712.00838658613552.912.6439911716452.612

2、.71610518819950.813.16667584423450.113.35064137527547.114.201000698由以上的數(shù)據(jù)用excel軟件畫出折線圖如下從圖中可以看出距離平板前緣越遠(yuǎn)，局部換熱系數(shù)越小，接著經(jīng)過一段系數(shù)不變的距離后，局部換熱系數(shù)又有上升的趨勢。這是因為在平板的起始段，很薄。隨著x的增加，由于壁面粘滯力的影響逐漸向液體內(nèi)部傳遞，邊界層逐漸增厚，但在，某一距離xc以前會一直保持層流的性質(zhì)。這時的邊界層稱為層流邊界層。而層流邊界層主要通過熱傳導(dǎo)導(dǎo)熱，則，將冷卻公式聯(lián)立，得到以下關(guān)系式：由上式可知當(dāng)平板溫度和液體溫度一定時，y越大，即 越大，局部換熱系數(shù)h越小。

3、 故距離平板前緣越遠(yuǎn)的，很厚，h局部換熱系數(shù)h越小。但自距前綴xc處起，流動朝著湍流過渡，最終過渡為旺盛湍流，此時湍流產(chǎn)生不規(guī)則脈動，強(qiáng)化了對流傳熱，使局部換熱系數(shù)h升高。6、 誤差分析及問題討論本實(shí)驗誤差來源1、 金屬片縱向?qū)?、 電熱功率并不是均布在整個表面3、 片面外界輻射散熱的影響4、 各種儀器本身的誤差，如熱電偶的靈敏度問題1、 由于測得的數(shù)據(jù)點(diǎn)少，故很難從實(shí)驗數(shù)據(jù)得知流體從層流變?yōu)橥牧鞯木嚯xxc。2、 由于本實(shí)驗沒有考慮片面外界輻射散熱的影響，故可能給實(shí)驗帶來一定的不確定度。試材名稱 : 水泥珍珠巖測量時間(s) : 1000試樣厚度(mm) : 15.0試樣重量(g) : 40

4、.0試樣容重(kg/m3) : 加熱器電壓(V) : 5.4012加熱器電流(A) : 0.0855總采樣次數(shù) : 201時間冷面溫度熱面溫度冷面與熱面溫度025250524.9250.110252501525250202525025252503025.125.103525.125.104025.125.104525.225.205025.125.105525.225.206025.225.206525.225.207025.225.207525.225.208025.225.208525.225.30.19025.325.309525.325.3010025.325.3010525.325.

5、3011025.425.4011525.425.4012025.425.4012525.425.4013025.425.50.113525.425.50.114025.425.4014525.525.5015025.525.5015525.525.5016025.525.60.116525.525.5017025.525.5017525.525.5018025.525.5018525.525.60.119025.625.6019525.525.60.120025.625.6020525.625.6021025.625.6021525.625.6022025.725.7022525.725.70

6、23025.625.6023525.625.70.124025.625.70.124525.725.7025025.725.7025525.725.7026025.725.7026525.725.7027025.725.7027525.725.7028025.725.80.128525.725.80.129025.725.80.129525.725.80.130025.725.80.130525.725.7031025.725.80.131525.725.80.132025.825.8032525.725.80.133025.725.80.133525.725.80.134025.825.80

7、34525.725.90.235025.825.8035525.825.8036025.825.90.136525.825.90.137025.725.90.237525.725.90.238025.825.8038525.825.90.139025.825.90.139525.725.80.140025.825.90.140525.8260.241025.8260.241525.8260.242025.8260.242525.8260.243025.826.10.343525.826.10.344025.826.10.344525.826.10.345025.826.10.345525.82

8、6.10.346025.826.10.346525.826.20.447025.826.20.447525.826.20.448025.826.30.548525.826.20.449025.826.20.449525.826.30.550025.826.20.450525.926.30.451025.826.30.551525.826.40.652025.826.30.552525.826.40.653025.826.30.553525.826.40.654025.826.40.654525.826.40.655025.826.40.655525.826.40.656025.826.40.6

9、56525.826.40.657025.826.40.657525.826.40.658025.826.40.658525.926.40.559025.826.40.659525.826.40.660025.926.40.560525.826.50.761025.826.40.661525.926.40.562025.926.50.662525.826.50.763025.826.50.763525.826.50.764025.926.50.664525.826.50.765025.926.50.665525.826.50.766025.926.60.766525.926.50.667025.

10、926.50.667525.826.50.768025.926.50.668525.826.50.769025.826.50.769525.926.60.770025.926.50.670525.926.60.771025.926.50.671525.926.60.772025.926.60.772525.926.60.773025.926.60.773525.926.60.774025.826.60.874525.926.60.775025.926.60.775525.926.60.776025.926.60.776525.926.60.777025.926.60.777525.926.60

11、.778025.926.60.778525.926.70.87902626.70.779525.926.70.880025.926.70.88052626.70.781025.926.70.88152626.70.78202626.80.882525.926.70.88302626.80.883526.126.70.68402626.80.884526.126.70.68502626.80.88552626.80.88602626.80.88652626.80.887026.126.80.787526.126.80.788026.126.90.888526.126.90.889026.126.80.789526.126.90.890026.126.90.890526.226.90.791026.226.90.791526.126.90.892026.226.90.792526.226.90.793026.1270.993526.2270.8940