Heat transferred from an insulated enclosure

In summary: Kumar GauravIn summary, the conversation is about calculating the heat input required for a proposed enclosure made of stainless steel with insulation to maintain a temperature of 50 degrees inside. The enclosure has a surface area of 107,300 sq in. and the outside ambient air temperature is assumed to be -10 degrees F. The range of heat input required is calculated to be 3.7 kW to 6.6 kW, which may indicate that the 1.8 kW convection heater may be too small. The conversation also discusses creating a simple model to calculate the heat dissipation, taking into consideration factors like the type of steel and insulation, and convection coefficients for the inside and outside surfaces.
  • #1
steves1080
65
1
Thanks for checking out my post! I have a question for you heat transfer savvy folks.

I have a pretty large enclosure (SA = 107,300 sq in.) made of 1/4" thick stainless steel, and has a 1-inch thick layer of insulation lining the inside of the wall. The purpose of this proposed enclosure is to protect water pipes from freezing during the winter. I found a 1.8 kW convection heater that I'd like to use, so I took a cut at a calculation to figure out if that'd be enough heat input to maintain 50 degrees inside the enclosure. I am assuming a worst case outside ambient air temperature of -10 degrees F, so that's a difference of 60 degrees. I also assumed that the steel plays no impact as a thermal barrier (to be conservative), and that the air provides a light film layer of insulation on either side of the wall. The resources I've looked at said that the heat transfer coefficient for the air film layer should be somewhere in the range of 5 - 37 W/m2K, so I plugged in both of those and found a lower and upper limit for the heat input required. The range I am getting is 3.7 kW to 6.6 kW, which shows that the 1.8 kW might be too small. Does this seem reasonable? I know it's a large surface area and a big delta T, but I don't have much experience here. I attached my calculation below, so any help would be appreciated.

Thank you.

-Mike
 

Attachments

  • heattransferpanels.xlsx
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  • #2
Ignoring a bunch of factors, like internal and external convection, you can make a simple model on this one.

Total resistance = thickness of steel/(conductivity of steel*SA) + thickness of insulation/(conductivity of insulation*SA)
UA = 1/total resistance
heat dissipation = UA*(T_high-T_low)

What kind of steel is it and what kind of insulation is it? If you can specify what those are, I can probably find values of the conductivity for them (or maybe you already have in order to calculate those values?) Anyway, a good model with will include convection coefficients for the inside and outside surfaces.

convective resistance = 1/(convection coefficient * SA)

Then, just add them up like they're in series, invert it to get a value for UA, then calculate the heat transfer. Does that help any? This was a quick answer, not a thorough one. If anything needs clarification, let me know.
 
  • #3
jlefevre76 said:
Ignoring a bunch of factors, like internal and external convection, you can make a simple model on this one.

Total resistance = thickness of steel/(conductivity of steel*SA) + thickness of insulation/(conductivity of insulation*SA)
UA = 1/total resistance
heat dissipation = UA*(T_high-T_low)

What kind of steel is it and what kind of insulation is it? If you can specify what those are, I can probably find values of the conductivity for them (or maybe you already have in order to calculate those values?) Anyway, a good model with will include convection coefficients for the inside and outside surfaces.

convective resistance = 1/(convection coefficient * SA)

Then, just add them up like they're in series, invert it to get a value for UA, then calculate the heat transfer. Does that help any? This was a quick answer, not a thorough one. If anything needs clarification, let me know.
This looks like exactly what he did, except for neglecting the thermal resistance of the steel.

Chet
 

Related to Heat transferred from an insulated enclosure

1. What is "heat transfer"?

Heat transfer is the movement of thermal energy from one object or system to another due to a difference in temperature.

2. How does heat transfer occur in an insulated enclosure?

In an insulated enclosure, heat transfer occurs through three main mechanisms: conduction, convection, and radiation. Conduction is the transfer of heat through direct contact between materials, convection is the transfer of heat through the movement of fluids, and radiation is the transfer of heat through electromagnetic waves.

3. Why is heat transfer important in an insulated enclosure?

Heat transfer is important in an insulated enclosure because it affects the overall temperature and energy balance within the enclosure. If there is a significant amount of heat transfer, it can lead to temperature imbalances and potentially damage the contents of the enclosure.

4. How is heat transfer measured in an insulated enclosure?

The rate of heat transfer in an insulated enclosure is typically measured in units of watts (W) or British Thermal Units per hour (BTU/hr). This can be calculated using equations that take into account factors such as the temperature difference, thermal conductivity of materials, and surface area.

5. How can heat transfer be reduced in an insulated enclosure?

To reduce heat transfer in an insulated enclosure, insulation materials with low thermal conductivity can be used to reduce conduction. Additionally, creating air or gas pockets within the enclosure can limit convection, and reflective surfaces can help reduce radiation. Proper sealing of the enclosure can also prevent air leaks that can lead to heat transfer.

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