# Heat transfer through AL shield by radiation & convection

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1. Apr 18, 2016

### RekhaP87

Hi all,

I am new here, and want to thank you for help in advance! I am working on a project and need some help - I need to figure out surface temp on an object at some distance from the heat source:

I need some help getting started.

Is it going to be: Heat transfer (radiation) + Heat transfer (conduction fiberglass) + Heat transfer conduction (Al + Heat transfer (radiation)

How do take into account convection to find surface temp at reflective surface and surface temp at green surface?

I am assuming I know the following: h(convection) air, k (fiberglass), k (Al).

Thanks,
Rp

2. Apr 19, 2016

### Mech_Engineer

This is a relatively complicated problem to solve, have you taken a course in Heat Transfer? What have you done so far to try and solve the problem?

This would be solved analytically using the thermal-resistive circuit method, calculating the "thermal resistance" for each part of the problem and then solving for temperature drops across each resistor. Are you familiar with this method?

3. Apr 19, 2016

### RekhaP87

Hi, thank you for your response! I have taken few heat transfer classes, and am familiar with the thermal-resistive circuit method. I know basic radiation, conduction, and convection equations has well.

25mph air is throwing me off in how to add the convection contribution + radiation from the heat source to the reflective material.

4. Apr 20, 2016

### Mech_Engineer

To calculate the contribution of of multiple heat transfer methods, you only need to calculate each method's thermal resistance and then add them as if they were parallel resistors. See attached diagram. When calculating the thermal resistance for convection, you need to calculate the convective coefficient $h$, which uses the speed of the flow as an input.

The equations you'll need to use are:
• Thermal Resistance, Conduction: $R = \frac{L}{k A}$
• Thermal Resistance, Convection: $R = \frac{1}{h A}$
• Thermal Resistance, Radiation: $R = \frac{1}{h_r A}$
Make sure and take view factors into account when you're calculating your radiation transfer coefficients.

#### Attached Files:

• ###### Resistor Network.JPG
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5. Apr 20, 2016

### CWatters

I think you will need to know more about the thermal properties of the surface who's temperature you are trying to calculate. For example the thermal resistance between it an some point that you consider to be at a fixed temperature.

6. Apr 22, 2016

### Nidum

There is not enough information in the initial description of the problem to allow of any meaningful calculations .

Post a sketch showing the actual configuration in 3D and tell us more about that heat source .