Convection coefficient for an annular finned pipe

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Discussion Overview

The discussion revolves around the calculation of the heat convection transfer coefficient for an annular finned pipe. Participants explore various aspects of heat transfer, including conduction and convection, and seek guidance on how to approach the problem using specific parameters related to the pipe and fins.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant expresses uncertainty about how to proceed with the project and whether to incorporate conduction heat transfer in their calculations.
  • Another participant suggests that fins are typically used to enhance heat transfer on the side with the lowest heat transfer coefficient, indicating a focus on fin efficiency.
  • Several participants request additional information, such as diagrams and specific parameters (e.g., flow rate, fluid type) to better understand the system being analyzed.
  • A participant proposes a method to calculate the outer surface temperature of the pipe through heat conduction before determining the film temperature and heat flux.
  • There is mention of the Biot number and its relevance, though its application in this context is debated.
  • One participant questions the need for Bessel functions in the analysis, suggesting that a steady-state approach may simplify the problem.
  • Another participant seeks clarification on the difference between the heat transfer coefficient on the air side and the overall heat transfer coefficient.
  • Discussion includes the need for specific equations to calculate heat conduction, film temperature, and convection heat transfer.

Areas of Agreement / Disagreement

Participants express various viewpoints and uncertainties regarding the approach to calculating the heat transfer coefficients. There is no consensus on the best method or the necessity of certain mathematical tools, indicating that multiple competing views remain.

Contextual Notes

Participants note limitations in available resources, such as the lack of examples in textbooks for calculating overall conduction/heat transfer coefficients for finned tubes. There are also unresolved questions regarding specific parameters and the application of theoretical concepts.

Who May Find This Useful

This discussion may be useful for individuals working on heat transfer problems involving finned surfaces, particularly in engineering or physics contexts, as well as those seeking to understand the complexities of convection and conduction in thermal systems.

mech-eng
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Hi. I am stuck on a project on calculation of heat convection transfer coefficient for a annular finned pipe.

All parameters [Diameter of pipe, diameter of fins for each case, the distance between fins, fin thickness, pipe length and fin number] are determined. And I have two book Fundamentals of Heat and Mass Transfer by Incropera/Dewitt and Heat and Mass Transfer by Çengel. I cannot determine how I will proceed. Should I refer to the conduction heat transfer for this project as well?

Would you like to give some guidance please?

Thank you.
 
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Not really my expertise. Who knows @SteamKing is good at this too...
I do have Incropera at work, as well as Bird Stewart and Lightfoot; they might have some info too. Tomorrow at best.
 
I would like to learn what your job is? And do you refer to the books while you are working?

Thank you.
 
I'm a physicist and I make computer models of chemical processes, so now and then I dabble with heat transfer.
 
BvU said:
I'm a physicist and I make computer models of chemical processes, so now and then I dabble with heat transfer.

I would be very happy if I could cope with this project which bonds my hands and I know your helps are precious. So I will wiat for tomorrow.

Thank you.
 
Can you please provide a diagram. That would be very helpful. Apparently, a fluid is flowing through the annulus, but what is inside the inner pipe and what is happening outside the outer pipe? What is the flow rate and what is the fluid? What are the actual data?
 
pict.JPG
Chestermiller said:
Can you please provide a diagram. That would be very helpful. Apparently, a fluid is flowing through the annulus, but what is inside the inner pipe and what is happening outside the outer pipe? What is the flow rate and what is the fluid? What are the actual data?
. Inner and outer diameters of the pipe is 33 mm and 35 mm, respectively and inner temperature of the pipe is 60 celsius. Thickness of the fins 1 mm, length of the pipe is 15 cm, the distance between fins 5 mm. So in every 5 mm there is one fin so there are 30 fins. These were constants. And now is the cases.

The temperature of air is optional as well.

1) Diameter of the fin 40mm, radius 20 mm

2) Diameter of the fin 42.5 mm, radius 21.25 mm

3) Diameter of the fin 45 mm, radius 22.5 mm

The velocity of the flow is optional, i.e I would like to choose the easiest and the most untedious one, the kind of fluid is optional as well.

Is everything O.K now?

P.S Eventhough I have studied convetion for two days, I am still for the situation of how I will derive the h, the convention coefficient.

Thank you.
 
My idea is first to calculate the heat conduction to calculate temperature of outer surface of the pipe, then assuming an environmental temperature I can calculate the film temperature surrounding the pipe. With this film temperature and knowing the environmental temperature I can calculate heat flux. But

1) With what equation, I can calculate the heat conduction and outer temperature of the pipe with specified number of fins?

2) With knowing, outer temperature and environmental temperature, I can calculate the film temperature, by those temperatures.

3) With what equation, I can calculate the convection heat transfer from the pipe with fins, knowing and using that film temperature and environmental temperature?

Thank you.
 
Last edited:
Thanks for the description.
Looks a lot like what this guy works through. Pretty hefty with Bessel functions and such.
[obsolete: put together before I was interrupted]:

I agree with Chet (as always :smile:): the subject appears so broad that a little focusing is more than welcome.

What's the aim and the scope of you project ? Steady state or dynamic ? pipes with annular fins ?
Where is it that you get stuck ?

Generally fins are used to improve the heat transfer on the side with the lowest heat transfer coefficient, so design is considering the fin efficiency.

In very thorough books (in german :smile: ) I do find the Biot number popping up (you had a thread on that -- but a lot of the books don't use the name Biot).
 
  • #10
You have a single finned tube with air blowing over it, correct? If you knew the heat transfer coefficient on the air side, would you be able to determine the overall heat transfer coefficient for a single fin? What have you learned so far about heat transfer to finned tubes?
 
  • #11
BvU said:
Thanks for the description.
Looks a lot like what this guy works through. Pretty hefty with Bessel functions and such.
[obsolete: put together before I was interrupted]:

I agree with Chet (as always :smile:): the subject appears so broad that a little focusing is more than welcome.

What's the aim and the scope of you project ? Steady state or dynamic ? pipes with annular fins ?
Where is it that you get stuck ?
.

First of all I think there is no need for Bessel functions and it's strange that I have never seen them in heat transfer. It should be steady state, making everything much easier, and pipes with annular i.e circular fins. I stuck at the beginning. I have never seen such an example. I have looked at the example questions in the mentioned sourced but I cannot see such a thing. As I said before I try to find the equation or derive the h. To do so, I have thought some steps that I write in #8.

Thank you.
 
  • #12
I can help you through this if you are willing to answer my questions in post #10. If not, have a nice day.:smile:
 
  • #13
Sory for late.

Chestermiller said:
You have a single finned tube with air blowing over it, correct?

Yes, I have a single pipe/tube airblowing over it, but it has 30 fins on surrounding it.

Chestermiller said:
If you knew the heat transfer coefficient on the air side, would you be able to determine the overall heat transfer coefficient for a single fin?

I don't know exactly answer of this question because I do not get the difference between the heat transfer coefficient on the air side and the overall heat transfer coefficient. Would you like the explain this difference so that I could take more steps.

Chestermiller said:
What have you learned so far about heat transfer to finned tubes?

I have two heat transfer books one is by Çengel and one is by Incropera/Dewitt. I have looked finned surfaces in these books but there isn't any example on calculation of overall conduction/heat transfer coefficient. The books focused just on increase of heat transfer due to fins. They have no information on calculation over all conduction heat transfer coefficient. I have speak to an instructor and said that it was a special case and I could just find them in the internet, not in the essential/fundamental heat transfer books. So, now I am searching for those studies.

Thank you.
 
Last edited:
  • #14
The overall heat transfer coefficient U is based on the overall heat flow Q, the inside area of the pipe ##A=\pi D_iL##, and the total temperature driving force between the inside surface of the pipe and the air, namely 40 C: $$Q=UA(40)$$.

If you knew the temperature at the base of an annular fin and the heat transfer coefficient between the fin and the surrounding air ##h_a##, would you be able to determine the radial temperature profile within the fin and the rate of heat loss from the fin to the air?
 
  • #15
Chestermiller said:
If you knew the temperature at the base of an annular fin and the heat transfer coefficient between the fin and the surrounding air ##h_a##, would you be able to determine the radial temperature profile within the fin and the rate of heat loss from the fin to the air?

I try to understand this post. I cannot understand the base of fin, and what is happening there? Please would you like to provide some information for the base of the fin.

Thank you.
 
  • #16
mech-eng said:
I try to understand this post. I cannot understand the base of fin, and what is happening there? Please would you like to provide some information for the base of the fin.

Thank you.

The base of the fin is where it is attached to the pipe. Suppose you somehow knew the temperature at this location.
 
  • #17
Chestermiller said:
If you knew the temperature at the base of an annular fin and the heat transfer coefficient between the fin and the surrounding air ##h_a##, would you be able to determine the radial temperature profile within the fin and the rate of heat loss from the fin to the air?

I think I should assume the base of the fin and inner surface of the pipe at the same temperature, i.e 60 celsius.

As I already know them, I still cannot determine the temperature profile within the fin and rate of heat loss from the fin to the air. I am not such skillful but I can conduct a study for them. Can I find them in the book of Çengel or in the book of Incropera/Dewitt? Or would like to give an instructive link for it? I have started to search it just now.

Thank you.
 
  • #18
mech-eng said:
I think I should assume the base of the fin and inner surface of the pipe at the same temperature, i.e 60 celsius.

There is no need to assume anything right now. Just do it algebraically, and call the temperature ##T_b##.
As I already know them, I still cannot determine the temperature profile within the fin and rate of heat loss from the fin to the air. I am not such skillful but I can conduct a study for them. Can I find them in the book of Çengel or in the book of Incropera/Dewitt? Or would like to give an instructive link for it? I have started to search it just now.
I am not familiar with these books. Do you understand the heat conduction equation? Have you ever seen an analysis of cooling fin heat transfer? I have no idea what level of understanding your are starting from. Have you studied differential equations?
 
  • #19
Chestermiller said:
There is no need to assume anything right now. Just do it algebraically, and call the temperature ##T_b##.

I am not familiar with these books. Do you understand the heat conduction equation? Have you ever seen an analysis of cooling fin heat transfer? I have no idea what level of understanding your are starting from. Have you studied differential equations?

I understand heat conduction equation. It is a simple algebraic equation and I can apply boundary conditions to the differential equations. I can solve linear differential equations and separable differential equations.

I try to study analysis of cooling fin right now.

Thank you.
 
  • #20
mech-eng said:
I understand heat conduction equation. It is a simple algebraic equation and I can apply boundary conditions to the differential equations. I can solve linear differential equations and separable differential equations.

I try to study analysis of cooling fin right now.

Thank you.
Excellent!
 

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