空气纵掠平板时局部换热系数的测定

空气纵掠平板时局部换热系数的测定5、 实验记录及数据处理 U/v1.68I/A17.08板宽b0.065总长l0.66x离前缘距离温差t-tf局部换热系数hx227.224.59070341452923.064383892830.621.85840303513.532.920.330307992137.517.8364568763040.216.6384858924142.815.6277367495445.214.7979454177052.912.643991178953.612.47886441911055.712.00838658613552.912.6439911716452.612.71610518819950.813.16667584423450.113.35064137527547.114.201000698由以上的数据用excel软件画出折线图如下从图中可以看出距离平板前缘越远，局部换热系数越小，接着经过一段系数不变的距离后，局部换热系数又有上升的趋势。这是因为在平板的起始段，很薄。随着x的增加，由于壁面粘滞力的影响逐渐向液体内部传递，边界层逐渐增厚，但在，某一距离xc以前会一直保持层流的性质。这时的边界层称为层流边界层。而层流边界层主要通过热传导导热，则，将冷却公式联立，得到以下关系式：由上式可知当平板温度和液体温度一定时，y越大，即 越大，局部换热系数h越小。 故距离平板前缘越远的，很厚，h局部换热系数h越小。但自距前缀xc处起，流动朝着湍流过渡，最终过渡为旺盛湍流，此时湍流产生不规则脉动，强化了对流传热，使局部换热系数h升高。6、 误差分析及问题讨论本实验误差来源1、 金属片纵向导热2、 电热功率并不是均布在整个表面3、 片面外界辐射散热的影响4、 各种仪器本身的误差，如热电偶的灵敏度问题1、 由于测得的数据点少，故很难从实验数据得知流体从层流变为湍流的距离xc。2、 由于本实验没有考虑片面外界辐射散热的影响，故可能给实验带来一定的不确定度。试材名称 : 水泥珍珠岩测量时间(s) : 1000试样厚度(mm) : 15.0试样重量(g) : 40.0试样容重(kg/m3) : 加热器电压(V) : 5.4012加热器电流(A) : 0.0855总采样次数 : 201时间冷面温度热面温度冷面与热面温度025250524.9250.110252501525250202525025252503025.125.103525.125.104025.125.104525.225.205025.125.105525.225.206025.225.206525.225.207025.225.207525.225.208025.225.208525.225.30.19025.325.309525.325.3010025.325.3010525.325.3011025.425.4011525.425.4012025.425.4012525.425.4013025.425.50.113525.425.50.114025.425.4014525.525.5015025.525.5015525.525.5016025.525.60.116525.525.5017025.525.5017525.525.5018025.525.5018525.525.60.119025.625.6019525.525.60.120025.625.6020525.625.6021025.625.6021525.625.6022025.725.7022525.725.7023025.625.6023525.625.70.124025.625.70.124525.725.7025025.725.7025525.725.7026025.725.7026525.725.7027025.725.7027525.725.7028025.725.80.128525.725.80.129025.725.80.129525.725.80.130025.725.80.130525.725.7031025.725.80.131525.725.80.132025.825.8032525.725.80.133025.725.80.133525.725.80.134025.825.8034525.725.90.235025.825.8035525.825.8036025.825.90.136525.825.90.137025.725.90.237525.725.90.238025.825.8038525.825.90.139025.825.90.139525.725.80.140025.825.90.140525.8260.241025.8260.241525.8260.242025.8260.242525.8260.243025.826.10.343525.826.10.344025.826.10.344525.826.10.345025.826.10.345525.826.10.346025.826.10.346525.826.20.447025.826.20.447525.826.20.448025.826.30.548525.826.20.449025.826.20.449525.826.30.550025.826.20.450525.926.30.451025.826.30.551525.826.40.652025.826.30.552525.826.40.653025.826.30.553525.826.40.654025.826.40.654525.826.40.655025.826.40.655525.826.40.656025.826.40.656525.826.40.657025.826.40.657525.826.40.658025.826.40.658525.926.40.559025.826.40.659525.826.40.660025.926.40.560525.826.50.761025.826.40.661525.926.40.562025.926.50.662525.826.50.763025.826.50.763525.826.50.764025.926.50.664525.826.50.765025.926.50.665525.826.50.766025.926.60.766525.926.50.667025.926.50.667525.826.50.768025.926.50.668525.826.50.769025.826.50.769525.926.60.770025.926.50.670525.926.60.771025.926.50.671525.926.60.772025.926.60.772525.926.60.773025.926.60.773525.926.60.774025.826.60.874525.926.60.775025.926.60.775525.926.60.776025.926.60.776525.926.60.777025.926.60.777525.926.60.778025.926.60.778525.926.70.87902626.70.779525.926.70.880025.926.70.88052626.70.781025.926.70.88152626.70.78202626.80.882525.926.70.88302626.80.883526.126.70.68402626.80.884526.126.70.68502626.80.88552626.80.88602626.80.88652626.80.887026.126.80.787526.126.80.788026.126.90.888526.126.90.889026.126.80.789526.126.90.890026.126.90.890526.226.90.791026.226.90.791526.126.90.892026.226.90.792526.226.90.793026.1270.993526.2270.8940