有一φ60×3.5mm的钢管,其外包有两层绝热材料,里层为40mm厚的氧化镁粉,平均热导率λ=0.07W/ (m·℃);外层为20mm厚的石棉层,其平均热导率λ=0.15 W/(m·℃)。若管内壁温度为500℃,最外层温度为80℃,管壁的热导率λ=45W/(m·℃),试求每米管长的热损失及两保温层界面的温度。
正确答案:
(1)每米管长的热损失:本题为三层圆筒壁导热。
已知r1=0.053/2=0.0265m,r2=0.06/2=0.03m,
R.sub>3=0.03+0.04=0.07m,r4=0.07+0.02=0.09m;
T.sub>w1=500℃,tw4=80 ℃,λ1=45 W/(m·℃),
λ2=0.07W/(m·℃),λ3=0.15W/(m·℃)
![](https://img.274949.com/Images/2020-04/04/y7ylskxu.jpg)
(2)保温层界面温度tw3。可用双层圆筒壁导热计算,
![](https://img.274949.com/Images/2020-04/04/h16q49o8.jpg)
已知r1=0.053/2=0.0265m,r2=0.06/2=0.03m,
R.sub>3=0.03+0.04=0.07m,r4=0.07+0.02=0.09m;
T.sub>w1=500℃,tw4=80 ℃,λ1=45 W/(m·℃),
λ2=0.07W/(m·℃),λ3=0.15W/(m·℃)
![](https://img.274949.com/Images/2020-04/04/y7ylskxu.jpg)
(2)保温层界面温度tw3。可用双层圆筒壁导热计算,
![](https://img.274949.com/Images/2020-04/04/h16q49o8.jpg)
![](https://img.274949.com/Images/2020-04/04/es0a6s9i.jpg)
答案解析:有
![](/editor/images/201705/qrcode_for_gh_573e2a458573_258.jpg)
微信扫一扫手机做题