Hi everyone,
I'm a beginner in Comsol and I have a very simple problem I can't find a solution for.
Basically my model is in 2D and is very easy: I have an horizontal plate from which is flowing a heat flow of 1 kW, then there is a layer of air (which is still at the beginning), another horizontal plate in alluminium (with such a thickness which makes impossible to model it as a shell), and finally a channel, where there is fresh water flowing through.
I want to model the heat exchange between all these layers. So I know there is natural convection between the lower plate and the lower surface of the upper plate, then conduction inside the upper plate made of alluminium, and finally forced convection in the channel. And this seems to be very easy.
My question is: how can I set the heat boundary condition for the lower surface of the upper plate? I know there is natural convection in the layer of air below. However, if I select "Convective heat flux" and choose natural convection, and then downside horizontal plate, I am required to provide the value of the external temperature in order to compute the convective heat transfer coefficient. But I do not know this value, because on the lower plate I only know the heat which is flowing through but not its temperature.
(Actually, the same issue applies also for the upper surface of the alluminium plate. Indeed, I do not know the temperature of the water after there has been an heat exchange).
Can anyone help me? I know it's a silly question, but I have just started using Comsol and can't solve it.
Thanks a lot!
- Davide
I'm a beginner in Comsol and I have a very simple problem I can't find a solution for.
Basically my model is in 2D and is very easy: I have an horizontal plate from which is flowing a heat flow of 1 kW, then there is a layer of air (which is still at the beginning), another horizontal plate in alluminium (with such a thickness which makes impossible to model it as a shell), and finally a channel, where there is fresh water flowing through.
I want to model the heat exchange between all these layers. So I know there is natural convection between the lower plate and the lower surface of the upper plate, then conduction inside the upper plate made of alluminium, and finally forced convection in the channel. And this seems to be very easy.
My question is: how can I set the heat boundary condition for the lower surface of the upper plate? I know there is natural convection in the layer of air below. However, if I select "Convective heat flux" and choose natural convection, and then downside horizontal plate, I am required to provide the value of the external temperature in order to compute the convective heat transfer coefficient. But I do not know this value, because on the lower plate I only know the heat which is flowing through but not its temperature.
(Actually, the same issue applies also for the upper surface of the alluminium plate. Indeed, I do not know the temperature of the water after there has been an heat exchange).
Can anyone help me? I know it's a silly question, but I have just started using Comsol and can't solve it.
Thanks a lot!
- Davide