Regarding when to consider both laminar and turbulent flow

In summary, the conversation discusses the confusion of when to consider laminar and turbulent flow over a flat plate and how to calculate the local heat transfer coefficient for both conditions. It is determined that the Reynolds number plays a role in determining whether the flow is laminar, turbulent, or mixed. The value of the Reynolds number at L=2m is approximately 27*10^5 and most of the heat transfer is in the transition region. The conversation also mentions the speed and density of liquid propane and calculates a Reynolds number of 2.5x10^6 at L=200 cm, indicating that most of the plate is in the transition zone.
  • #1
FebinThomas
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TL;DR Summary
For flow over a flat plate when should i assume turbulent flow all over the plate and use the related equations(nusselt number) and when to use the laminar and turbulent equation(Nusslet number)
Hello,i am just a college student who has a little confusion on when to consider both laminar and turbulent flow -say over a flat plate,should i assume turbulent flow all over the plate and use the related equations(nusselt number) or use the laminar and turbulent equation(Nusslet number) but if so there i couldn't find an equation for finding local heat transfer coefficient(hx) for laminar and turbulent condition.

QUESTION
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Here should i consider laminar&turbelnt conditio or just assume turbulent all over.

I hope i have included the relevant information for understanding my question.
 
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  • #2
I believe whether or not its turbulent or laminar, or mixed is based on the Reynolds number?
 
  • #3
What is the value of the Re at L=2m in your example? Compare this with the transition from laminar to turbulent flow which occurs in the range Re=3x10^5 to Re=3x10^6.
 
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  • #4
erobz said:
I believe whether or not its turbulent or laminar, or mixed is based on the Reynolds number?
yes,but Re greater than (say for flat plate)5*10^5 is going to be turbulent right if it is mixed when its going to be turbulent.
 
  • #5
Chestermiller said:
What is the value of the Re at L=2m in your example? Compare this with the transition from laminar to turbulent flow which occurs in the range Re=3x10^5 to Re=3x10^6.
its about 27 *10^5 sir.
at x=2
 
  • #6
FebinThomas said:
its about 27 *10^5 sir.
at x=2
If th is calculated value is correct, then it sounds like most of the heat transfer is in the transition region. So there is going to be significant uncertainty in the values of the heat transfer coefficients.
 
  • #7
Wouldn’t 0.25 m/s be too slow for turbulence?
 
  • #8
At 300 K, the density of liquid propane is 0.493 gm/cc and the viscosity is 0.001 gm/cm-sec. So, under these conditions, I calculate a Re of about 2.5x10^6 at L = 200 cm, in agreement with your calculation. Most of the plate would be judged to be in the transition zone.
 
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1. What is laminar flow?

Laminar flow is a type of fluid flow in which the particles of the fluid move in an orderly, smooth manner, with little to no mixing or turbulence.

2. What is turbulent flow?

Turbulent flow is a type of fluid flow in which the particles of the fluid move in a chaotic, irregular manner, with mixing and turbulence present.

3. When is laminar flow typically observed?

Laminar flow is typically observed at low flow rates and/or in fluids with low viscosity, such as air and water.

4. When is turbulent flow typically observed?

Turbulent flow is typically observed at high flow rates and/or in fluids with high viscosity, such as oil and honey.

5. Why is it important to consider both laminar and turbulent flow?

It is important to consider both laminar and turbulent flow because they can have different effects on fluid behavior and can impact the design and efficiency of systems and processes that involve fluid flow. Additionally, the transition from laminar to turbulent flow can also have significant effects on the behavior of fluids.

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