Heat Transfer and Combustion Homework

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In summary, the "Heat Transfer and Combustion Homework" covers key concepts related to the mechanisms of heat transfer, including conduction, convection, and radiation, as well as the principles of combustion. The assignments challenge students to apply theoretical knowledge to practical problems, analyzing heat transfer processes in various scenarios and understanding the chemical reactions involved in combustion. The homework aims to enhance problem-solving skills and deepen comprehension of thermal dynamics and energy transfer in engineering contexts.
  • #1
MaisieMitchell
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Homework Statement
The outer surface of the insulation on a horizontal steam pipe has a radius of 50mm and is at a temperature of 90Deg C. The atmospheric air surrounding the pipe is at a temperature of 14 Deg C, and has the property values listed in part (c) above. Estimate the rate of heat loss by natural convection to the atmosphere by each metre length of pipe.

Only require help with part (D).
Relevant Equations
Nu = 0.53Gr^0.25Pr^0.25
Q3.png
Q3.1.png


Does this working out look okay? Thanks in advance.
 

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  • #2
I'm not going to check your arithmetic. I assume you used consistent units so that the dimensionless groups actually came out dimensionless..

I don't see any part D here. I assume part D requires you to calculate the heat transfer rate per meter of pipe, given the heat transfer coefficient, the pipe diameter, and the temperature difference. Let's see your equations for doing this.
 
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  • #3
Correct part D is the question sorry - Estimate the rate of heat loss by natural convection to the atmosphere by each metre length of pipe.

The equation for doing this is

Q=hA(DeltaT)

therefore..

Q=h(2Pi*rL)(DeltaT)

Q=1.34*(90-14/0.1)^0.25 *0.1*Pi * 1 * (90-14)

Q = 167.9855 w/m
 
  • #4
MaisieMitchell said:
Correct part D is the question sorry - Estimate the rate of heat loss by natural convection to the atmosphere by each metre length of pipe.

The equation for doing this is

Q=hA(DeltaT)

therefore..

Q=h(2Pi*rL)(DeltaT)

Q=1.34*(90-14/0.1)^0.25 *0.1*Pi * 1 * (90-14)

Q = 167.9855 w/m
Based on the heat transfer coefficient you calculated in part C, I get about the same result.
 
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Thanks, when you say about the same result - is there something that I have missed?
 
  • #6
MaisieMitchell said:
Thanks, when you say about the same result - is there something that I have missed?
I don't think so (other than roundoff). I get 167.1
 
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  • #7
Thanks again!
 
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FAQ: Heat Transfer and Combustion Homework

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 (liquid or gas) due to the fluid's movement, and radiation is the transfer of heat in the form of electromagnetic waves.

How do you calculate the heat transfer rate in conduction?

The heat transfer rate in conduction can be calculated using Fourier's Law of Heat Conduction, which is given by the equation: Q = -kA(dT/dx), where Q is the heat transfer rate, k is the thermal conductivity of the material, A is the cross-sectional area through which heat is being transferred, and dT/dx is the temperature gradient.

What is the difference between laminar and turbulent flow in convection?

In laminar flow, the fluid flows in parallel layers with minimal mixing, resulting in a smooth and orderly motion. In turbulent flow, the fluid experiences chaotic changes in pressure and velocity, leading to increased mixing and eddies. Turbulent flow generally enhances heat transfer compared to laminar flow.

What factors affect the rate of combustion in a chemical reaction?

The rate of combustion in a chemical reaction is affected by factors such as the concentration of reactants, temperature, presence of a catalyst, surface area of the reactants, and the nature of the reactants. Higher temperatures and concentrations generally increase the rate of combustion.

How do you determine the efficiency of a heat engine?

The efficiency of a heat engine can be determined using the formula: Efficiency (η) = (Work output / Heat input) * 100%. Alternatively, for an ideal Carnot engine, the efficiency can be calculated using the temperatures of the heat reservoirs: η = 1 - (T_cold / T_hot), where T_cold and T_hot are the absolute temperatures of the cold and hot reservoirs, respectively.

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