Fluid flow/heat transfer Area dilemma

In summary, there are two different calculations involved in fluid flow and heat transfer. For fluid flow, the area formula is A=(pi*D^2)/4, which is used to calculate the heat transfer coefficient based on fluid velocity. On the other hand, for heat transfer across a surface, the area formula is A=pi*D*L, which is used to determine the surface area of a tubular surface. It is important to know when to use each formula in order to accurately calculate the desired result.
  • #1
williamcarter
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4

Homework Statement


I have a confusion regarding areas.
Usually in fluid flow I am using the A=(pi*D^2)/4
However in heat transfer we usually use A=pi*D*L

Could you please explain this?I mean in first case(fluid flow) it is cross sectional area and in the 2nd case(heat transfer) is like the whole area.
Why is like that?

Could you please explain how to know when to use each formula of area?For example in this exercise regarding a pipe :
ImesfST.jpg

My question is which of the Area formulas we need to use in this problem?
We should use area A=pi*D*L right? Because it regards heat transfer.
However we do not know the Length L in the upper exercise.

Homework Equations


A=pi*D^2/4(fluid flow)
A=pi*D*L(heat transfer)

Where D=diameter
L=length

The Attempt at a Solution


I would like to be more confident in choosing the area formula , because I am confused.
Thank you in advance[/B]
 
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  • #2
There are two parts to the calculations. When you are looking at the fluid flow to calculate the heat transfer coefficient for the flow within the tube, you need to know the fluid velocity. To get this, divide the volumetric flow rate by the cross sectional area of the tube. When you are looking at the heat transfer across a surface, you need to determine that area of the surface. For a tubular surface, that's ##\pi DL##.
 
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Likes williamcarter
  • #3
Chestermiller said:
There are two parts to the calculations. When you are looking at the fluid flow to calculate the heat transfer coefficient for the flow within the tube, you need to know the fluid velocity. To get this, divide the volumetric flow rate by the cross sectional area of the tube. When you are looking at the heat transfer across a surface, you need to determine that area of the surface. For a tubular surface, that's ##\pi DL##.
Thank you, yes it makes sense.
 

1. What is the difference between fluid flow and heat transfer?

Fluid flow and heat transfer are two separate physical phenomena. Fluid flow refers to the movement of a fluid (liquid or gas) through a system or over a surface. Heat transfer, on the other hand, is the movement of thermal energy from one location to another. In many cases, fluid flow and heat transfer are interconnected, as the movement of a fluid can also involve the transfer of heat.

2. How does the area of a system affect fluid flow and heat transfer?

The area of a system can have a significant impact on both fluid flow and heat transfer. A larger area allows for more fluid to pass through, resulting in increased flow rate. Similarly, a larger area exposed to a heat source or sink can facilitate a higher rate of heat transfer. However, the specific effects on fluid flow and heat transfer will depend on the characteristics of the system, such as the geometry and material properties.

3. What is the dilemma between fluid flow and heat transfer when considering the area of a system?

The dilemma arises when trying to optimize the area of a system for both fluid flow and heat transfer. In some cases, increasing the area may improve one aspect, but negatively impact the other. For example, increasing the surface area of a heat exchanger may enhance heat transfer, but also increase pressure drop and hinder fluid flow.

4. How can the dilemma between fluid flow and heat transfer be resolved?

To resolve the dilemma, it is crucial to carefully consider the design and operating conditions of the system. This involves balancing the requirements for fluid flow and heat transfer and finding the optimal compromise for the specific application. Additionally, using advanced computational tools, such as numerical simulations, can aid in optimizing the area of a system for both fluid flow and heat transfer.

5. Are there any practical applications that demonstrate the importance of the fluid flow/heat transfer area dilemma?

Yes, there are numerous practical examples where the fluid flow/heat transfer area dilemma plays a crucial role. For instance, in the design of heat exchangers, where the goal is to maximize heat transfer while minimizing pressure drop. Additionally, in the design of cooling systems for electronics, where the area must be optimized to ensure efficient cooling without impeding the flow of air or liquid. The dilemma also arises in the design of industrial processes, such as chemical reactors, where the area must be optimized for efficient mixing and heat transfer.

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