What is the required thickness of insulation for a furnace roof equipment?

In summary, the conversation is about setting up an excel spreadsheet to calculate the thickness of insulation needed for a furnace wall or the resultant outside wall temperature, using various formulas found online. The specific application involves adding a piece of equipment to a furnace roof, consisting of two stainless steel cylinders with insulation in between to achieve a temperature within the internal cylinder of +/- 60 Deg C. More information is needed about the composition, temperature, and flow of fluids inside and outside the cylinders, as well as constraints and type of insulation, to accurately calculate the required insulation thickness.
  • #1
PWoolfall
1
0
I would be grateful for your help with a small project I am involved in at work. I would like to set up an excel spread sheet to calculate either the thickness of insulation required to reduce the temperature of say a furnace wall from the inside to the outside, or calculate the resultant outside wall temperature, knowing the insulation details and inside temperature. I have come across several different formulas on the net, which unfortunately have left me a little confussed.
An application I am currently looking at involves adding a piece of equipment to a furnace roof. This equipment consists of an outer stainless steel cylinder having an outside diameter of 750 mm, a wall thickness of 3 mm, and externally subjected to a temperature of 650 deg C. Inside the cylinder is another cylinder again constructed with stainless steel with a wall thickness of 5 mm. I need to sandwich a sufficient thickness of insulation between the cylinders, to achieve a temperature within the internal cylinder of +/- 60 Deg C.

Any help would be much appreciated.
 
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  • #2
Hello PWoolfall,

If I understand correctly:

  • you want to build a system made of two coaxial cylinders
  • the gap in between the cylinders would be filled by some insulation
  • the external cylinder would be in contact with hot air at 650°C
  • you want to keep the internal cylinder below 60°C
Obviously, if there is no cold air flowing inside the inner cylinder, then you will never be able to keep it below 60°C. Regardless of the amount and quality of the insulation, after some time, the inner cylinder will reach 650°C.

If there is cool air flowing in the inner cylinder, then the design is possible but needs more information:

  • composition of the fluid inside the inner pipe
  • temperature of the fluid flowing in the inner pipe
  • flowrate inside the inner pipe
  • similar information regarding the outer pipe:
    is it in contact with some hot fluid?
    what is the composition of this fluid?
    is this fluid moving?
    where does the heat come from?
    some combustion?
    ...
  • which kind of insulation material are you considering?
  • what are you geometrical constraints?

If you chose a insulation material with heat conductivity of 0.04 W/K.m,
if you use an insulation thickness of 0.1 m,
then the cold air inside the inner tube should take out an amount of heat of at least q=236 W/m²:

since q = 0.04/0.1 * (650-60) W/m²

if you pipe is 1 meter long, its surface would be 4.7 m², and this would imply a cooling power of

Q = q*4.7 = 1100 W = 1.1 kW

This would only be possible if the cooling fluid is cold enough and has a sufficient velocity.

Before further calculations, please check these comments.
 
Last edited:

1. What is heat transfer and why is it important?

Heat transfer is the movement of thermal energy from one object or substance to another. It is important in many fields including engineering, physics, and chemistry as it helps us understand how heat moves and impacts various systems and processes.

2. What are the three modes of heat transfer?

The three modes of heat transfer are conduction, convection, and radiation. Conduction is the transfer of heat through a solid material, convection is the transfer of heat through a fluid or gas, and radiation is the transfer of heat through electromagnetic waves.

3. How do I calculate heat transfer?

The formula for calculating heat transfer is Q = mcΔT, where Q is the amount of heat transferred, m is the mass of the substance, c is the specific heat capacity, and ΔT is the change in temperature.

4. What factors affect heat transfer?

The rate of heat transfer is influenced by factors such as the temperature difference between the two substances, the type of material the heat is passing through, and the surface area available for heat transfer. Other factors include the distance between the two objects, the thermal conductivity of the materials, and the presence of any insulating materials.

5. How is heat transfer used in real-world applications?

Heat transfer calculations are used in a variety of real-world applications, such as designing heating and cooling systems for buildings, calculating the efficiency of engines and power plants, and determining the temperature distribution of materials in manufacturing processes. It is also important in assessing the impact of heat on the environment and developing strategies for energy conservation.

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