Forum Admin.Equations for Heat Transfer Problems

In summary, the conversation is about a student seeking help with their upcoming heat transfer exam. They are looking for the relevant equations to solve questions on a tutorial sheet and have not been able to find them through their notes or online. The tutorial sheet includes questions on heat transfer through insulation, radiation exchange, and composite walls. The post also mentions that the original post is five years old and the thread is now closed.
  • #1
guppygould
20
0

Homework Statement


Hey all! So I have an exam coming up soon for my heat transfer module at uni and I'm fairly confident with the material, but in one of the tutorial sheets I have there are some questions which I don't know how to solve. I'm not really asking for a solution to these questions, I'd just like to know the relevant equations that I'd need to use to solve them. I've looked through my notes and used google but no such luck as of yet. Here is a copy of the tutorial sheet:

"Tutorial Sheet No. 2

Q1 The inside surface of an insulating layer is maintained at 290˚C, and the outside surface dissipates heat by convection to air at 20˚C. The insulation layer is 5cm thick and has a thermal conductivity of 1.25W/mK. Determine the minimum value of the heat transfer coefficient at the outer surface if the outside surface temperature should not exceed 75˚C.

Q2 A large wall of thickness 5cm and thermal conductivity k = 0.65W/mK has a front surface with an emissivity of 0.8. At this surface there is radiation exchange with the surroundings and convection heat transfer to the air. The air and surroundings are at 22˚C, and the convection heat transfer coefficient is 20W/m2K. If the front surface temperature of the wall is 152˚C what is the rear surface temperature?

Q3 A small, thin metal plate is insulated on one side and exposed to the sun on the other side. The plate absorbs solar energy at a rate of 600W/m2 and dissipates it by convection into the ambient air at 300K with a convection heat transfer coefficient 22W/m2K, and by radiation into the surrounding area which may be assumed to be a blackbody at Tsurr = 270K. The emissivity of the surface ε is 0.9. Determine the equilibrium surface temperature of the plate.

Q4 A cold room has walls constructed of 0.25m brick on the outside, 0.1m foam insulation material in the middle and 1.5cm wood on the inside. The air temperature on the outside is constant at 20˚C and the room is to be maintained at a temperature of -5˚C. The convection heat transfer coefficient for air to brick is 15W/m2K and for wood to air is 30 W/m2K. The thermal conductivities of wood, foam and brick are 0.15, 0.025 and 1 W/mK, respectively. Determine:

(a)the overall heat transfer coefficient
(b)the heat transfer rate per unit area of the wall surface
(c)the outside and inside surface temperatures of the composite wall
(d)the amount of energy to be removed by refrigeration in a 24 hour period if the total wall area is 75m2"



Homework Equations


This is what I need to know, it'll be the same equation for all of them or at least similar ones.


The Attempt at a Solution


I need the relevant equations to attempts the question.

Thanks in advance,

-Leo
 
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  • #2
Hey,
Do you have the solutions?
 
  • #3
pinkgirl said:
Hey,
Do you have the solutions?
The OP is almost five years old. So, no; I don't think he has the answers you seek.
 
  • #4
SteamKing said:
The OP is almost five years old. So, no; I don't think he has the answers you seek.
Yes. This thread is hereby (mercifully) closed.

Chet
 

Related to Forum Admin.Equations for Heat Transfer Problems

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

Heat transfer is the movement of thermal energy from one object or medium to another. It is important because it affects many aspects of our daily lives, from cooking food to regulating the temperature in our homes and buildings. Understanding heat transfer is crucial for engineers and scientists in developing efficient technologies and processes.

2. What are the different modes of heat transfer?

The three main modes of heat transfer are conduction, convection, and radiation. Conduction is the transfer of heat through direct contact between two objects or substances. Convection is the transfer of heat through the movement of fluids, such as air or water. Radiation is the transfer of heat through electromagnetic waves, such as from the sun.

3. What factors affect heat transfer?

The rate of heat transfer is influenced by several factors, including the temperature difference between the objects, the thermal conductivity of the materials, the surface area and distance between the objects, and the presence of insulating materials.

4. How can heat transfer problems be solved?

Heat transfer problems can be solved through various analytical and numerical methods, such as using mathematical equations and computer simulations. It is important to accurately determine the boundary conditions and properties of the materials involved in the heat transfer process.

5. What are some real-world applications of heat transfer?

Heat transfer has numerous applications in our daily lives, such as in heating and cooling systems, refrigeration, cooking, and industrial processes. It is also crucial in fields like aerospace engineering, where heat transfer plays a significant role in the design of aircraft and spacecraft.

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