Heat Transfer through fins

In summary: I would say that installing the fins outside the pipe would be the better design because it would decrease the thermal resistivity between the pipe and the atmosphere, leading to higher heat transfer coefficient and better cooling.In summary, installing fins outside the pipe is the better design for cooling hot air in a tube exposed to atmospheric temperature. This is because it decreases the thermal resistivity between the pipe and the atmosphere, resulting in a higher heat transfer coefficient and better cooling. Other factors to consider include temperature differences, forced convection, and cleaning and manufacturing costs.
  • #1
Ali Durrani
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If hot air passing through a tube which is exposed to the atmospheric temperature is to be cooled at a certain temperature, fins are installed to increase the heat transfer from the hot air, which one is better design? to install the fins inside the pipe or outside the pipe ? and why?
 
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  • #2
The total thermal resisitivity is the sum of all single resisitivities in series. If one resisitivity is much higher than all the others it becomes the crucial one and a decrease of the other resistivities has almost no improving effect. Based on your problem, I'd say the thermal resistivity between the hot air and the inside of the tube is lower as their is there is higher relative speed due to the forced circulation (higher Re → higher Nu → higher heat transfer coefficient). So the decisive thermal resisitivity can be found at the heat transfer between the pipe and the atmosphere, therefore this one should be decreased by mounting fins. Of course this is only the interpretation of your question, there are many more factors which are influencing the problem, like the temperature differences and if there is a forced convection at the outside (e.g. if the pipe is part of a vehicle which is moving relative to the air surrounding it), etc.
 
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  • #3
Other considerations are cleaning, and cost/difficulty of manufacture. Imagine trying to clean the inside of a pipe containing fins. Imagine trying to weld fins on the inside of a pipe.

Chet
 
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1. How does heat transfer through fins work?

Heat transfer through fins occurs through a process called conduction. This means that heat is transferred from a hotter object to a cooler object through physical contact. The fins act as extended surfaces, increasing the surface area available for heat transfer and thus enhancing the overall heat transfer rate.

2. What factors affect heat transfer through fins?

The main factors that affect heat transfer through fins are the surface area of the fins, the thermal conductivity of the material, the temperature difference between the two objects, and the geometry of the fins (thickness, shape, arrangement). Other factors such as the presence of a fluid flow and the presence of insulation can also affect heat transfer through fins.

3. How can we calculate the heat transfer rate through fins?

The heat transfer rate through fins can be calculated using the fin equation, which takes into account the fin geometry, material properties, and temperature difference. There are also various empirical and numerical methods available for more complex fin configurations.

4. What are the different types of fins used for heat transfer applications?

There are various types of fins used for heat transfer applications, including straight fins, annular fins, pin fins, and plate fins. These different types of fins have varying geometries and are used in different applications depending on the heat transfer requirements.

5. How can we improve the heat transfer through fins?

There are several ways to improve heat transfer through fins, such as increasing the surface area of the fins, using materials with higher thermal conductivity, and optimizing the fin geometry. Additionally, enhancing fluid flow over the fins or using insulation can also improve heat transfer.

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