# Thread: ASTM D 6104 Query

1. ## ASTM D 6104 Query

I have been reading the ASTM D 6104 document and came across an interesting specification. In section 6.4 it states that, "The pipe diameter shall be selected such that it runs full and at a Reynolds number, based on the hydraulic diameter, in excess of 70 000 ". The pipe discussed here is used to mix the hydrocarbons with water.

What I do not understand is why the Reynolds number should be in excess of 70 000. This seems quite large for the application considered in this standard (Determining the Performance of Oil/Water Separators Subjected to Surface Run-Off).

Has anyone used this standard and know why this Reynolds number is so large or whether this is an error?

2. As I understand the Reynolds number when 2,000 or less the flow is laminar and if greater than 3,500 it is turbulent. Between 2,000 and 3,500 is known as the transitional flow range.

My guess is that one would want the flow to be very turbulent if 70,000 is a requirement..

https://www.engineersedge.com/fluid_...oody_chart.htm

3. Yes that is around the range for those conditions.
The ranges according to this text extract: https://www.kau.edu.sa/Files/0057863...hapter%208.pdf

The reason I was questioning this Reynolds number is that I have been using this criteria (section 6.4) to determine a suitable PVC pipe diameter for the mixer. To do this I have been applying an iterative method using the Colebrook equation. However, none of the Reynolds numbers calculated are that close to 70 000, despite being mostly turbulent. I guess it could be that this standard may be directed toward oil-water separators with very high water flow rates.
The highest water flow I have considered is 5000 L/hr, which produced the highest Reynolds number of around 50 000.