为什么模拟出来的温度有-99°C呢？

mochu

本分析有两个body，一个是制品，一个是外面的模具，定义载荷如下：

温度1：制品在刚放进去的0-0.1秒是850度
温度2：模具的在0-0.1秒是50度
对流传热1：全体body和空气的自然对流
对流传热2：冷却水管的强制水对流，15000w/m2·K


模具温度计算出来结果如下：

mochu

为什么都没有人来解答啊

mochu

呼唤版主啊

tonnyw

A couple of things about transient problem.
1. Make sure the units of specific heat, density, heat conductivity coefficients, film coefficients are correct.
2. Make sure your ambient temperature is correct.
3. Make sure your initial condition is correct.

对流传热1：全体body和空气的自然对流  <----------what is the value of film coefficients you chose?
对流传热2：冷却水管的强制水对流，15000w/m2·K <------------Where is the cool pipe located? Could you provide some kind of picture? The film coefficient in this case has to be determined by Prandtl number of Nusselt number. I forgot exactly which one. You have to find out yourself.

mochu

居然有人回复了，感动ing……

对流传热1：与空气的自然对流换热，22 W/m^2*k

对流传热2：冷却水管的强制水对流换热，由于不知道怎么算，查了一下常用值，有人推荐用15000 W/m^2*K.我想知道怎么求这个值。冷管与制品的距离是18mm，直径为10mm，长度为100mm，导热系数为0.643 W/m*k，请高人继续指导

A couple of things about transient problem.
1. Make sure the units of specific heat, density, heat conductivity coefficients, film coefficients are correct.
2. Make sure your ambient temperature is  ...
tonnyw 发表于 2010-3-22 11:32

tonnyw

5# mochu

I didn't see the figure.

mochu

现在能看见了么？我修改了一下



6# tonnyw

tonnyw

7# mochu

For this problem, I think the key thing is to determined the film coefficient (heat transfer coefficient) due to the forced convection from the cooling pipe. I think there should be a handbook about the determination of the film coefficient in this case.

mochu

关于你说的这一点我也想过，后来将冷却水管的传热系数改为了4500W/m^2*K，但是仍然会模拟出-331度，超越了绝对零度，是不可能的吧，截图如下



8# tonnyw

iomega

please upload the source so we can take a look.

rainerun

以前别的课题也碰过这样的问题，把网格加密就行了。迭代问题吧