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# Inlet Velocity with Turbulent or Laminar Flow

## Inlet Velocity with Turbulent or Laminar Flow

(OP)
Hi,

When it comes to determine the suitable inlet velocity most designers / engineers has their own general rule of thumb per say for vapor flow somewhere around 10 m/s to 20 m/s and liquid flow somewhere around 3 m/s to 5 m/s.

My question is does type of flow can be a 'rule' for determining the appropriate inlet velocity and this is where I think the logic comes in mind that the appropriate inlet velocity shall be limit to laminar flow instead of turbulent flow but again this is my take on determining the inlet velocity.

Does anyone think the same as this logic? Also kindly share your general rule of thumb for determining the appropriate inlet velocity.

### RE: Inlet Velocity with Turbulent or Laminar Flow

Inlet into what?

Laminar flow is very low for most "normal" fluids unless you're got really viscous fluids.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

### RE: Inlet Velocity with Turbulent or Laminar Flow

No, most companies can't afford the big pipe and equipment to maintain laminar flows, especially for non-viscous fluids. Turbulent flows cut capital costs a lot.

Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

### RE: Inlet Velocity with Turbulent or Laminar Flow

Context is everything. When I have water for medical injection systems, I have to keep the entire system in turbulent flow to prevent a microfilm buildup so laminar flow is not always the best basis. For my situation, I have to minimize pressure drop while still maintaining turbulent flow and any other constraints. I have had this very question and when I searched through this site, the consistent idea I saw was that the allowable pressure drop criterion should be the starting point for specifying velocity.

### RE: Inlet Velocity with Turbulent or Laminar Flow

(OP)
LittleInch,

Inlet velocity through a heat exchanger.

### RE: Inlet Velocity with Turbulent or Laminar Flow

(OP)
Thank you gentlemen for your respond. Yes I nearly forgot about the pressure loss criteria because for plate and shell heat excahnger we mostly get the pressure drop coming entirely from the plate side. So I guess the optimum velocity would be the one that doesn't contribute so much on the entrance and exit nozzles.

The reason I was thinking of having laminar flow perhaps that turbulent flow 'may' contribute to uneven flow distribution between the plates.

### RE: Inlet Velocity with Turbulent or Laminar Flow

No. Too slow and the plates may overheat.

"He's declaring war on the planet itself."- Vicente Fox

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