Calculating Entrance Lengths in Hydrodynamics

  • Thread starter Thread starter pauleck
  • Start date Start date
  • Tags Tags
    Hydrodynamics
AI Thread Summary
The dimensionless hydrodynamic entrance length is calculated using the formula z+=zh/(Re*Dh), where zh is the hydrodynamic entrance length, Re is the Reynolds number, and Dh is the hydraulic diameter. If the hydrodynamic entrance length zh exceeds the total channel length L, it is not necessary to assume zh equals L for calculating z+. Instead, it indicates that the flow has not fully developed by the end of the channel. Therefore, zh can be longer than the actual channel length without any adjustments needed for z+. Understanding this concept is crucial for accurate hydrodynamic analysis.
pauleck
Messages
1
Reaction score
0
Hi everybody,
first of all, sorry for any grammatical mistakes, I am a non-native English speaker.
So here is my concern,

the dimensionless (hydrodynamic) entrance length is defined as:

z+=zh/(Re*Dh)

,where zh is the hydrodynamic entrance length, Re is the Reynolds number, and dh is the hydraulic diameter of the duct.

If zh exceeds the total channel length L, do I have to assume zh=L for calculating z+??

Thank you very much
 
Engineering news on Phys.org
pauleck said:
If zh exceeds the total channel length L, do I have to assume zh=L for calculating z+??

No. The entrance length is longer than the channel length, and the dimensionless entrance length is longer than the dimensionless channel length. zh is not limited to the actual channel length. If zh>L it just means that at the end of the channel the flow hasn't fully developed yet.
 
  • Like
Likes Chestermiller

Thread 'Race car suspension Class'

Posted June 2024 - 15 years after starting this class. I have learned a whole lot. To get to the short course on making your stock car, late model, hobby stock E-mod handle, look at the index below. Read all posts on Roll Center, Jacking effect and Why does car drive straight to the wall when I gas it? Also read You really have two race cars. This will cover 90% of problems you have. Simply put, the car pushes going in and is loose coming out. You do not have enuff downforce on the right...
View full post »

Thread 'Cantilever help'

I'm trying to decide what size and type of galvanized steel I need for 2 cantilever extensions. The cantilever is 5 ft. The space between the two cantilever arms is a 17 ft Gap the center 7 ft of the 17 ft Gap we'll need to Bear approximately 17,000 lb spread evenly from the front of the cantilever to the back of the cantilever over 5 ft. I will put support beams across these cantilever arms to support the load evenly
View full post »
Thread 'Physics of Stretch: What pressure does a band apply on a cylinder?'

Thread 'Physics of Stretch: What pressure does a band apply on a cylinder?'

Scenario 1 (figure 1) A continuous loop of elastic material is stretched around two metal bars. The top bar is attached to a load cell that reads force. The lower bar can be moved downwards to stretch the elastic material. The lower bar is moved downwards until the two bars are 1190mm apart, stretching the elastic material. The bars are 5mm thick, so the total internal loop length is 1200mm (1190mm + 5mm + 5mm). At this level of stretch, the load cell reads 45N tensile force. Key numbers...
View full post »

Similar threads

Advanced Hydrodynamic Problem - University level
Replies
49
Views
4K
Hydrodynamic entrance length: independent of Re?
Replies
1
Views
4K
Predicting flow rates of a pressure driven system
Replies
8
Views
2K
Solve Drying Room Issue: Calculate Air Flow Speed & Mass Flow Rate
Replies
3
Views
2K
Flow through Interconnected Tubes
Replies
1
Views
1K
Surface roughness in 2D sinusoidal corrugation
Replies
1
Views
4K
Condenser calculations - uncertainty
Replies
10
Views
3K
Problem when calculating the center of mass of a triangle
Replies
5
Views
2K
Estimating the heat transfer coefiicent
Replies
12
Views
2K
Fluid Dynamics in Pipe Lines Problem
Replies
1
Views
1K

Hot Threads

Recent Insights

Back
Top