# I Jet Spread Rate K Values- Momentum diffusement

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1. Oct 23, 2016

### Tom79Tom

The Problem Statement
I have a jet entering leaving a nozzle at ui into an ambient fluid with ue = 0
I am trying to equate the rate of momentum diffusement (or spread) to the shear forces caused by ue -ui

I understand that the rate momentum diffusement is are equated by empirical K- values (~0.1 for turbulent flow ~0.4 for laminar flow)

The Question

Is there any way to calculate the rate of momentum diffusement or spread directly from ui -ue
I am trying to understand what would happen as the flow develops from ui=0, ue = 0
Would the momentum diffusement always equal the rate of flow development or does K values < 1 indicate that a the momentum diffusement is inadequate to prevent a velocity gradient.

Attempt at a solution
I am thinking that it does as there is a length to the initial region where this occurs.
A K-value of 1 would indicate an immediate dispersal of any additional increase in ui
so no shear forces could ever develop.[/sub] and therefore no motive to cause a diffusement . A cyclical argument.
I think the K value must factor the viscosity of the fluid and its Reynolds number

Edit : sorry one other question, the initial region length is described as 5 diameters in length . Is that representative of a k value of 0.2
$$\frac{1D}{0.2}=5D$$

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Last edited: Oct 23, 2016
2. Oct 29, 2016