Viscous Fluid (Fuel Oil/Diesel Fuel) Pipe Sizing
Viscous Fluid (Fuel Oil/Diesel Fuel) Pipe Sizing
(OP)
I am trying to set up a spreadsheet to obtain friction loss for fuel oil/diesel fuel fluids - or fluids with viscosities much in excess of water.
When I use D'Arcy, I find that there is a fairly narrow band between where the flow would be laminar Re<4,000 and where the velocities are getting a bit high.
A couple questions.
1. What are the recommended flow velocities I should be shooting for. I have seen information that says 3-12 feet per second. The fluids are going to be clean, for the most part, although they can start to degrade if they stay in the storage tank too long.
2. Is D'Arcy the equation I should use. I can iterate the friction factor so that is not an issue, but since these flows extend into both the laminar and turbulent regions, the friction factor calculation would be different in both. I have seen reference to Churchill as a means to perform this calculation, but have not used it much. Would this be a good application?
Thanks in advance for any help.
When I use D'Arcy, I find that there is a fairly narrow band between where the flow would be laminar Re<4,000 and where the velocities are getting a bit high.
A couple questions.
1. What are the recommended flow velocities I should be shooting for. I have seen information that says 3-12 feet per second. The fluids are going to be clean, for the most part, although they can start to degrade if they stay in the storage tank too long.
2. Is D'Arcy the equation I should use. I can iterate the friction factor so that is not an issue, but since these flows extend into both the laminar and turbulent regions, the friction factor calculation would be different in both. I have seen reference to Churchill as a means to perform this calculation, but have not used it much. Would this be a good application?
Thanks in advance for any help.





RE: Viscous Fluid (Fuel Oil/Diesel Fuel) Pipe Sizing
As long as you are confident that the fluids are Newtonian, D'Arcy is a good choice. If you have any concern about non-Newtonian behavior then you are pretty much on your own. None of the mainstream correlations come very close to matching measured data.
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: Viscous Fluid (Fuel Oil/Diesel Fuel) Pipe Sizing
RE: Viscous Fluid (Fuel Oil/Diesel Fuel) Pipe Sizing
RE: Viscous Fluid (Fuel Oil/Diesel Fuel) Pipe Sizing
That PowerPoint certainly was more cut and dried and confident than I've ever been. It felt like they were treating "rules of thumb" as "laws of nature". I don't mean to disparage rules of thumb, but they are just techniques that have worked in some number of cases and are generally a good place to start. That document reads like it is the only place to end. I'd be leery of guidance that was that cut and dried for all cases that ever were or ever would be.
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: Viscous Fluid (Fuel Oil/Diesel Fuel) Pipe Sizing
I have heard that exact presentation by Mr. Drow. His presentations typically are very knowledgeable, but I always like to see the engineering behind the rules of thumb so I can know when to not use them.
A problem I see as I am developing my spreadsheet, is that if I limit the flow to less than 7 gpm, most of the flows are going to be in the laminar, not turbulent with Re <3,000-4,000. In laminar flow, the friction factor will be 64/Re which is much different than what would be calculated by the iterative approach used for D'Arcy so my numbers are going to be much different. And in the "critical area" between laminar and turbulent, I have read that all bets are off.
However, I have also read on this site, that the use of Churchill's equation mitigates these disparities. And my spreadsheet calculations seem to bear that out. In the laminar area, Churchill gives me similar results as 64/Re and in the turbulent region, it gives me similar results to D'Arcy. In the middle regime, it appears to be about in the middle of the other two approaches.
These are all numbers to me - as I have no real experiential basis for either approach. I also understand the spreadsheet will be a tool and has to be used as such, as a guideline, not necessary something written in stone.
RE: Viscous Fluid (Fuel Oil/Diesel Fuel) Pipe Sizing
BTW, Churchill will also fit well.
RE: Viscous Fluid (Fuel Oil/Diesel Fuel) Pipe Sizing
RE: Viscous Fluid (Fuel Oil/Diesel Fuel) Pipe Sizing
Churchill uses the standard 64/Re to calculate the friction factor in the laminar regime so the results should be very similar to those you get using 64/Re directly. The main benefit of the Churchill equation is that it is able to combine separate equations for the laminar, critical and turbulent regime friction factors into one continuous equation. This makes it ideal for computer use where gaps and overlaps (as are often shown on Moody charts) would cause an automated computer solution to fail.
Churchill does make recommendations for formulas to use in the critical and turbulent regimes, but you are not constrained to using his recommendations. For example, in the turbulent regime I use the Colebrook-White equation and then use the Churchill method to combine it with the other regimes into one continuous formula. I do not believe that Colebrook-White is particularly better than Churchills equation for the turbulent regime, but C-W is the yardstick that all others are measured against and the results will match results from the Moody chart (very slightly) better than Churchill's does.
You are already aware of the problems in the critical regime. One downside of Churchill's equation is that because it generates unique friction factors in this regime people start to believe that they are accurate. The problem in the critical regime is that flows are not stable and the friction factor will vary with time. No method can predict accurate friction factors in the critical regime because they simply do not exist. The benefit of Churchill is that it generates unique friction factors in this regime - making computer solutions more stable. The best bet is to stay away from designing for flows in the critical regime. Rather change the pipe size and force the flow into either the laminar or turbulent regime.
Katmar Software - AioFlo Pipe Hydraulics
http://katmarsoftware.com
"An undefined problem has an infinite number of solutions"
RE: Viscous Fluid (Fuel Oil/Diesel Fuel) Pipe Sizing
Excellent description of the friction factor discussion. What you see as a "feature" of Churchill, I see as a "bug", but that is perspective. I've always followed the advice to design as far away from the transition region as I can. Trying to assign friction factors in a rapidly changing flow regime leads to apparent answers that fail to match measured data and can even lead you to a decision that you later regret. This is similar to the results that we get from all of the multi-phase flow correlations--the answers look so pretty on a 4-color 3D graph, but fail to match field data.
The reason for wanting to know friction factors is to make design decisions or to conduct troubleshooting analysis. Both of these activities require some level of confidence in the tools being used. I have no confidence that I can predict an order-of-magnitude friction factor in the transition region.
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: Viscous Fluid (Fuel Oil/Diesel Fuel) Pipe Sizing
Katmar Software - AioFlo Pipe Hydraulics
http://katmarsoftware.com
"An undefined problem has an infinite number of solutions"
RE: Viscous Fluid (Fuel Oil/Diesel Fuel) Pipe Sizing
We are in agreement, the only difference is that I won't even calculate a number in the transition region since I too often see people use a number because they have it even if it is complete nonsense.
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: Viscous Fluid (Fuel Oil/Diesel Fuel) Pipe Sizing
RE: Viscous Fluid (Fuel Oil/Diesel Fuel) Pipe Sizing
You are correct. When I stated about the difficulties with D'Arcy, I actually meant I was having difficulties with the Colebrook formula (iterative) for determining the friction factor to put into D'Arcy. In my spreadsheet, I am using D'Arcy to determine pressure drop for the various pipe sizes and flows, using Churchill to determine the friction factor for all regions.
But I will also take the advice and stay away from the "critical zone" with the pipe sizing.
RE: Viscous Fluid (Fuel Oil/Diesel Fuel) Pipe Sizing
RE: Viscous Fluid (Fuel Oil/Diesel Fuel) Pipe Sizing
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: Viscous Fluid (Fuel Oil/Diesel Fuel) Pipe Sizing
RE: Viscous Fluid (Fuel Oil/Diesel Fuel) Pipe Sizing
I know it can become a "gel", i.e. not able to be pumped at lower temperatures, but is it becoming non-Newtonian as it approaches that temperature?
If so, how should I deal with it, other than specifying some type of heater in the tank, similar to a diesel vehicle?
RE: Viscous Fluid (Fuel Oil/Diesel Fuel) Pipe Sizing
Heating it brings it back.
Heating tanks, heat tracing pipe, keeping it circulating and using insulation will all help.
RE: Viscous Fluid (Fuel Oil/Diesel Fuel) Pipe Sizing
An anti-gel additive will keep the diesel fuel flowing well in colder temps and will keep the diesel stabilized.