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# Heat Flow in a Room

## Heat Flow in a Room

(OP)

1. Goal
I am trying to find out what the temperature of a ships electronics room will be at the hottest time of year using ANSYS. There is a port facing wall and the other three are inside the ship. I have all of the U and R ratings of the walls and decks. There are three electronic racks in the room with different components in them drawing power and giving off heat, I have a rough estimate of the power draw and heat dissipated from the electronics.

The model looks like this, I have a port wall that is exposed to solar radiation and the ambient air temperature, I will ignore the radiation for now and just focus on the air temperature. I have the air temperature inside the ship which is also being blown into the room through a vent at a certain flow speed. The same temperature is being transmitted through the walls and deck.

The walls, decks, and vents all reduce heat in the space while the electronics create heat. What I want to model is the steady-state heat of the room when all of the heat takers are in balance with the producers.

2. Geometry and Mesh
I have the room modeled in ANSYS SpaceClaim, it is a trapezoid shell that is 8ft high. I cut out two slots for the inflow and outflow vents. There are three rectangular extrusions in the room that represent the different electronic racks that give off heat.

1) Is this cutout method appropriate for simulating airflow into and out of the system?

2) How should I model the mesh of the room, electronics, and vents so that they give an appropriate heat absorption/transfer response?

3) I simply extruded the dimensions of the electronics, does this mean that rectangular boxes have their own floor that is in contact with the deck below and that the heat will be transferred through contact? I just want to make sure the geometry of the boxes is separate from the room so that I can get the constraints/boundaries on them correctly, aka the heat they give off.

This is the results I get from auto generating the mesh, I cant remember how to do a cross sectional view to show the insides sadly:

3. Airflow
Should I use steady-state Thermal or Fluent, I’m leaning towards Fluent.

1) Where in either steady-state Thermal or Fluent do I simulate airflow into and out of an opening in the room?

2) Can I set the velocity and temperature of the air being blow in?

3) How should I attend to the outflow vent? Is there an option to leave it as natural outflow due to conservation of mass? Here I am expecting the outflow vent to be taking heated air out of the system and thus lower the temperature of the room.

4. Heat
I need to know how to model the walls with a thermal resistance or conductance so that I can simulate accurate heat flow out of the room.

1) In Fluent, how do I give the walls a thickness, or is there no point as long as I have the thermal conductance set at the wall boundary, where is this button to set this?

2) How do I model the electronics as giving off a certain amount of heat? What buttons do I press and what can I type in to set my parameters?

3) For the heat given off by the electronics, I heard that I need to simulate natural convection. Someone posted “If the air in the model does not include density as a function of temperature, then it won't expand when warmed and contract when cooled. This behavior is needed for natural convection to develop in a gravity field. How do I make this so, aka what buttons?

4) The major source of cooling will be the airflow into the room, with the walls and decks as doing the same but at a much smaller rate.

This seems pretty simple, I just want to make sure I make the best possible model for my given skill level and not make simple mistakes. Any advice or direction would be greatly appreciated.

### RE: Heat Flow in a Room

your images didn't post well ...

### RE: Heat Flow in a Room

(OP)
No its not schoolwork, I was just emailing an old proff whos the FEA guy.

I made some headway, but realized that I needed to be able to label the different parts inside. After doing this I had to remake my model and now only the electronic boxes are showing up in fluent, I get a error during meshing, its cant see the rooms walls and decks. Very weird and I dont know how to fix this. You can see from the image that all the parts in red cant be generated. I can generate a mesh but it doesn't translate into Fluent. It seems like solids can enter Mechanical, but not surfaces for some reason. Any idea why?

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