Heat Transfer through multiple walls

In summary: No, the top and bottom of the air-gap will not be open. The goal is to reduce the heat or temperature leaving the Plastic wall at 60C.
  • #1
Joey Dela Cruz
2
0
Hi guys,

I am newbie on thread and currently working on a project
I need some help on the Heat flow on multiple walls.

Here is the setup (see figure below)
The first wall is a Steel material which has a 350C temperature(1kwatts) and the an Air Gap is present then followed by a Plastic wall which is required to have around 60C (30watts)

350C(1kwatts)--> |(Steel)|--- |Air Gap| ----|(Plastic)|--->60C(30watts)

The goal for me is to know or get thickness/distance of the Air gap between the Steel and Plastic so to reduce the Heat or Temperature leaving the Plastic wall at 60C
I was trying to use and figure out the solution using the formula
dQ/dT = AΔT/(L1/k1+L2/k2+L3/k3) but was stuck
Any advise here?
 
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  • #2
I would advise you to try setting up a "thermal-resistive circuit" analysis for this problem. Similar to the classic V=I*R electrical circuits equation, there is a heat transfer analysis method which uses a "T=q*Rt" equation, where T (temperature, K) is equivalent to voltage, q (heat flow, W) is equivalent to current, and Rt (thermal resistance, K/W) is equivalent to resistance. You can find equations for thermal resistance for each of your wall's layers, and then analyze just as you would any other electrical circuit (series thermal resistances are added, parallel thermal resistances use the inverse relationship).

MIT has an online summary of the analysis method I'm describing, you can find it here: http://web.mit.edu/16.unified/www/FALL/thermodynamics/notes/node118.html
 
  • #3
Mech_Engineer said:
I would advise you to try setting up a "thermal-resistive circuit" analysis for this problem. Similar to the classic V=I*R electrical circuits equation, there is a heat transfer analysis method which uses a "T=q*Rt" equation, where T (temperature, K) is equivalent to voltage, q (heat flow, W) is equivalent to current, and Rt (thermal resistance, K/W) is equivalent to resistance. You can find equations for thermal resistance for each of your wall's layers, and then analyze just as you would any other electrical circuit (series thermal resistances are added, parallel thermal resistances use the inverse relationship).

MIT has an online summary of the analysis method I'm describing, you can find it here: http://web.mit.edu/16.unified/www/FALL/thermodynamics/notes/node118.html
Thanks Dude...will start from here!
 
  • #4
@ Joey Dela Cruz.
Will you keep the top and bottom of the air-gap open, so air can rise in the gap and continuously cool the walls by convection ?
 

1. How does heat transfer through multiple walls?

Heat transfer through multiple walls is a process where heat energy moves from one side of a wall to the other. This can occur through three main methods: conduction, convection, and radiation. Conduction is the transfer of heat through direct contact between two surfaces, convection is the transfer of heat through the movement of fluids or gases, and radiation is the transfer of heat through electromagnetic waves.

2. What factors affect heat transfer through multiple walls?

Several factors can influence heat transfer through multiple walls, including the thickness and material of the walls, the temperature difference between the two sides of the wall, and the presence of any insulating materials. Additionally, the surface area and orientation of the walls can also affect heat transfer.

3. How can multiple walls be designed for efficient heat transfer?

To design multiple walls for efficient heat transfer, it is important to consider the material and thickness of the walls. Materials with high thermal conductivity, such as metals, are more efficient at transferring heat. Additionally, adding insulation, such as foam or fiberglass, can reduce heat loss through the walls.

4. How does heat transfer through multiple walls impact energy efficiency?

Heat transfer through multiple walls can have a significant impact on the energy efficiency of a building. If heat is able to easily transfer through the walls, it can result in higher energy consumption for heating or cooling. Designing walls with proper insulation and materials can help improve energy efficiency and reduce heating and cooling costs.

5. How can heat transfer through multiple walls be measured?

Heat transfer through multiple walls can be measured using devices such as thermometers, thermal imaging cameras, or heat flux sensors. These devices can provide information on the temperature difference between the two sides of the wall and the rate of heat transfer. Additionally, computer simulations can also be used to model and measure heat transfer through multiple walls.

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