Learning Forum

[al al]

Hi!

I have a student license and i work with workbench 2024 R1 

I want to cheak the temperature in a conteiner from the basic matiriel here (steel) and the influance of a ventilator on the temperature inside.

The conteiner is big box made of floor and the other body conect but in seperate.

First I use steady state, I enterd preety simple boundry condition of 25 [c] from the floor and the anther walls get radiation while the envairomate is 35[c]. I put emisivity of 0.9. 

for some reason the temprature in the highest temp in the conteiner is 35[c] (like the boundru condition of the radieition) while in the reality the temperture will be much higher, I dont know where is my mistake...
more over I try to add the flow from the ventilator so I did hole in the conteiner and planed to put there condition of mass flow but this option is blocked to me, its because the student licence or I need to define something else?

I add photo of the radiation condition I made


Thanks for any help!

[peteroznewman]

Please insert an image of your model in your reply and label any surfaces with applied boundary conditions. It is difficult to understand the model from your description alone.  If there is ventilation, I was expecting the model to have surfaces that have convection and the ambient air could be 35 C. You can also have  radiation heat transfer, but that may be a smaller effect that the convection. 

 

[al al]

first of all thanks on the commet

in the first pic I put a temprature constraint because the floor is on the ground where the temp is prety still, now when i think about it maybe I should change it to condaction

the second pic is for the all other 5 walss in the cube (exept the floor) where I pot the radiation (its in a hot place with direct sinlight) and naglectic wind

in the third pic I add a convection in the ventilator (the ventilator rpresnt as the hole I created), when I add this I get error like in this pic

1.

2.

3.

[peteroznewman]

Convection doesn't work the way you think it does. You added a hole to provide "ventilation" and applied a convection boundary condition thinking that would blow cool air into the box. It doesn't work that way in a Steady State Thermal analysis. The way convection works is that heat can be carried away from any surface that touches a large and free flowing body of cooler 25 C air. Therefore, all the external surfaces of the box except for the surface on the floor would get the convection boundary condition. I suggest you take the free course on Convection Heat Transfer.

Radiation doesn't work the way you think it does either. If the box was in a room and the temperature of the walls of the room was 35 C and there was no direct sunlight, then what you have in the model is correct, but that represents a tiny amount of heat transfer.  Also, how is it possible that the walls of the room are at 35 C when the air is at 25 C?  That doesn't make sense.  But you said the box is in direct sunlight. That can be modelled using Radiation.  I suggest you take the free course on Radiation Heat Transfer.

[al al]

Thanks I will see those videos hopeful its he;p me
one more question: so you think I should  treet to the temperature from the floor as conduction? so should i see this tutorial too?

 

[peteroznewman]

Conduction automatically happens throughout the material, you don’t need to do anything to make that happen. A temperature boundary condition on the floor creates a surface for heat to enter or leave the body to balance the heat flow in the rest of the structure. 

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[al al]

ok, thanks for all the help I hope I made it, I will appriciate if you can give me a feedback on my work

so here a picture of the conteiner and a object (for example engine) that prouduce heat flux (section view)

so as we can see in the left side, the boundry condition i make are:

1. fixed temperutre - of 25[c] of the earth the contiener seat on (like in the video you send me of the fire)
2.  convection - on the all wales (not enclud the floor) with value of film coefficent = 50W/m^2C while temp is 35[c] this from the wind
3. Heat flux - I didnt saw the option of radiation from the sun so I saw a viedo that says that the approximate heat flux that can replace the radiation is 1000 W/m^2 so i put it on the top of the conteiner (I decided that the sun is in the middle of the sky)
4. Heat flux 2 - an approximate heat flux from the object (engine or what else) of 400 W/m^2
5. convection 2 - the holes (rectungular holes) in the walls are not forced convention so I put 35[c] and film coefficent = 10W/m^2C the convection is on the wall of the engine like in the pic
6. convection 3 - the 1 hole in the walls are forced convention (ventilator) so I put 35[c] and film coefficent = 50W/m^2C the convection is on the wall of the engine like in the pic             here image without no section view    

tThanks very much