## Orifice Pressure Drop with Viscosity Change

## Orifice Pressure Drop with Viscosity Change

(OP)

I was working on designing an orifice in a system the other day when I noticed an anomaly that I wanted some insight on. I searched around as best I could to try to find why the system behaved this way but could not find anything so I figured I would try here.

In essence what I am seeing is as I increase viscosity for a fixed pressure drop through an orifice the flow increase along a range (10-1300 cP) then after an inflection point it begins decreasing in flow. My gut feel on viscosity changes is that as viscosity increase the relative pressure drop will increase, thus decreasing flow since the pressure difference across the orifice is fixed. I attached an excel file that shows the data sets I have from 2 different orifice sizes and they both have roughly the same trend.

If anyone could shed some light on this phenomenon I would be greatly appreciative. The only idea I have is at the low ranges the viscosity changes decrease Reynolds number at a faster rate than the higher viscosity increases pressure drop. Then at some point the viscosity outweighs the effect on the Reynolds number and starts to decrease flow.

Thanks in advance.

In essence what I am seeing is as I increase viscosity for a fixed pressure drop through an orifice the flow increase along a range (10-1300 cP) then after an inflection point it begins decreasing in flow. My gut feel on viscosity changes is that as viscosity increase the relative pressure drop will increase, thus decreasing flow since the pressure difference across the orifice is fixed. I attached an excel file that shows the data sets I have from 2 different orifice sizes and they both have roughly the same trend.

If anyone could shed some light on this phenomenon I would be greatly appreciative. The only idea I have is at the low ranges the viscosity changes decrease Reynolds number at a faster rate than the higher viscosity increases pressure drop. Then at some point the viscosity outweighs the effect on the Reynolds number and starts to decrease flow.

Thanks in advance.

## RE: Orifice Pressure Drop with Viscosity Change

David Simpson, PE

MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual.Galileo Galilei, Italian Physicist## RE: Orifice Pressure Drop with Viscosity Change

Good luck,

Latexman

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

## RE: Orifice Pressure Drop with Viscosity Change

orifice bore in the first set is 0.68 in second set is 1.36 in

pipe diameter is 3 in

x axis is viscosity in cP

y axis is flow in lb/hr

This is assuming all other physical properties stay constant. It is used in a variable process and we were trying to hold everything else constant over the varying viscosity.

## RE: Orifice Pressure Drop with Viscosity Change

Good luck,

Latexman

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

## RE: Orifice Pressure Drop with Viscosity Change

The equations are all laid out in the Wikipedia article at https://en.wikipedia.org/wiki/Orifice_plate

However, it is difficult to visualize the behavior from such complicated equations and I have attached the graph of the discharge coefficient against the Beta ratio and Reynolds Number from Coulson & Richardsons "Chemical Engineering" Vol 1. The maximum for the coefficient of discharge occurs at lower Re for small Beta ratios, and this agrees with the results in your graph.

Katmar Software - AioFlo Pipe Hydraulics

http://katmarsoftware.com

"An undefined problem has an infinite number of solutions"