Pressure drop calculations 1

[davedaneshi]

Hi,
In our shampoo/conditioners plant, we use diaphragm pumps for transferring products from tanks to fillers. Products are in the range of 5000 to 10000 CP viscosity.(depending on temperature)We use 2" food grade pressure hose/pipe for pumping. I guess we are dealing with Newtonian fluids only but pump flow rates are not consistent for different temperatures and viscosities.
Can somebody please give me links to an online pump pressure calculator for Newtonian and Non-Newtonian fluids.
Thanks,

 

[Latexman]

Try this one:

Link

Good luck,
Latexman

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

 

[LittleInch]

If you're using a diaphragm pump, surely flow rate is not affected, other than issues in flowing this material into the pump in the first place??

diaphragm pumps are in the positive displacement category so shouldn't be that concerned with non Newtonian or not.

Can you explain a bit more with some figures / data?

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

 

[BigInch]

Non-Newtonian etc pressure drops are not any different than Newtonian. They just change with velocity within the pipeline. If you do your pressure calculations at the highest viscosity (generally at the lowest velocity, your results will be conservative, although temperatures along the pipe may have significant influence, if the fluid's viscosity is temperature sensitive and you have no or little insulation. Note that operating at low velocities can make startup and shutdown very difficult at times. You will need to think about how much pump power and pressure is required for those temporary conditions, vs line size, over the full range of flow rates that the system will see.
High pumping pressures are needed when starting up. Once past startup you will probably have to either reduce pump discharge pressure to 1/2 or less, or otherwise deal with increasing flow rates.

 

[davedaneshi]

Hi Latexman,
The link is taking me to Google search. Is there any particular website you were referring me to?
Please send me links to calculation pages.

Thanks,

 

[LittleInch]

BI - he's using a diaphragm pump - the pump doesn't really care what the discharge pressure is so long as it is less than its maximum surely?

Sure you need to calculate your max pressure to make sure your pump can supply this, but after that there's no purpose to the calculation - the pump supplies a fixed volume on every stroke providing it gets that amount in on the inlet stroke

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

 

[BigInch]

The pump doesn't care? Well it should be capable of supplying whatever pressure is needed without breaking... as always. And he should care if he's buying the pump, so he knows how much maximum working pressure to specify. The pipe obviously has some interest in withstanding the maximum pressure and the highest ultimate flow rate will eventually occur at whatever discharge pressure the pump outputs as soon as velocities are constant at all points along the pipe.

As far as controlling the system, pressure obviously affects flow rate, so the key to designing non-Newtonian flowing systems is to realize that the highest pressures will be needed at lowest flow rates (during startup) and you will need a lot less power and pressure as the system approaches design flow rate. Rather than designing only for design flow rate, with non-Newtonian flow it is equally, if not more important, to look at lower flow rates. If you want to try to hold a constant flow rate, these systems can usually benefit from variable speed pumps.

 

[davedaneshi]

LittleInch and BigInch,

Thanks for your responses, here are more details:
- Shampoo is to be pumped from 10,000 lit tank- h=3m. (6000 CP at 25 deg C and 9500 at 22)
- 2" pressure hose of 25 ft transfers product to pump. Air at pomp is in the range of 90-100 psi
- Another 2" hose+solid SS pipe+4*90 turns take product to a tank on filler machine (L tot=78 ft)
- This surge tank is kept at 15-25 psi (by air pressure)
- Although pipes go 12 ft high, pump and discharge points are at same elevations
- I cannot get even 7 GPM from this pump.(pump curve is attached)

We have maxed out pressure because available air is not above 110 psi. I'm thinking to put a Pressure 2:1 diaphragm pump and have discharge head double the air pressure, but I'm concerned about hoses and piping.
Should I upsize pipes and hoses? But as I mentioned before some days we get 10 GPM with the same conditions and some days we struggle with even 7 GPM. so, I thought maybe Newtonain, Non-newtonian characteristics cause this.
I appreciate your helps.

 

[BigInch]

Its possible. It can get very tricky. I don't know a lot about shampoo. I only use a little bit from the bottle, and that's tricky enough for me.

At 7GPM pressures will probably be higher than needed then when at 10GPM. After a while, pressure will drop as velocity picks up. Then flow rates will increase while pressure continues to drop. What you see may depend heavily on when you look.

Some fluids are also dependent on how they have been handled previous entering the pipe and pump system. Some fluids may have a different pressure loss after running through a pump operating at 7GPM and 10GPM because of different shearing characteristics of the pump.
Best to design a system that can handle a multitude of conditions effectively.

You've got to know how your fluid works at all pressures, temperatures and velocities, (shear rates) and if prior handling variations can affect it as well.

 

[LittleInch]

Non Newtonian flow is getting out of my knowledge envelope, but from what I can find out a pressure drop at around 7 to 10 gpm is about 1 psi per foot for a pipe of your size., which is about right. You only have 60 psi from end to end with the pressure in your receiving tank so yes, looks like your pump is underpowered.

What are your hoses and pipe pressure rated to?

Your viscosity has a big change for only a few degrees so I'm not surprised you're getting a big change on some days and not others.

Making the pipes bigger will help, but how much by is difficult to tell

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

 

[BigInch]

Sometimes making pipes bigger isn't the best way to go for non-Newtonian flow. Keeping things moving faster is often the best solution. Larger diameter means slower velocity which translates to low shear rates and higher "effective viscosity". It can also mean more heat loss and lower viscosity because of lower temperatures, as does longer time in pipe and greater surface area of the pipe to conduct off the fluid's heat. All depends on the ratio of friction loss to "effective viscosity", calculated by fluid base viscosity while considering shear rate effects. If those effects are extreme, slowly moving cooler fluid near the pipe wall can be highly viscous and flows laminar, while a warmer, or a higher shear rate core moves faster and is in turbulent flow. In other words ... it can get very messy and at times counter-intuitive. First study your fluid very well.

 

[LittleInch]

Also find out the ID of your hoses - sometime it can be a lot smaller than you think....

Asuuming a 1/1/2 " ID, 10 GPm is only 0.55 m/sec.

BI is on the right lines - find out as much as you can about the stuff you're pumping before you know whether greater veleocity and shear is good for you or not.

Or make sure your hoses and tubes can stand it and pump at 200 psi...


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

 

[davedaneshi]

BI,
"Then flow rates will increase while pressure continues to drop" is it the case for non-newtonian fluids?
I'm trying to get more data for fluid, but it's not easy. How can I experiment that the fluid is newtonian or non-newtonian or even in some conditions it shows non-newtonian behavior.
I'll find out pressure rating for hose and pipes, most likely in the range of 150 to 200 psi.
Thanks,

 

[BigInch]

I've needed two pumps configured in series during low startup flows, then later reconfiguring to two pumps in parallel at the higher design flow rate, but that one worked out well.

 

[LittleInch]

You need to be careful trying that with diaphragm pumps - they might not like the inlet pressure and getting two PD pumps in series can be interesting.

Let us know when you have some more information

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

 

[micalbrch]

Little & Big Inch: Note that OP is using an air driven diaphragm which behaves completely different than an electric diaphragm pump. Flow decreases with increasing pressure. An AOD pump has a flow/head curve similar (not identical) to a centrifugal pump.

Electric diaphragm pumps are not affected that much by viscosity. The viscosity affects the filling efficiency and if the check valves are not spring loaded or the balls are not heavy, the valves will close a bit slowly with viscous media but all that is in a low percantage range.

 

[BigInch]

I don't care what pump he's using, I speak only of the flow in the system, to which flow is not entirely dependent only on the pump curve and the non-Newtonian flow in the pipe system is the result of the pressure applied over time (possibly what you refer to as "filling efficiency") which remains the same no matter what pump is used (all pumps supply some flow at some pressure). The operating point is always at the intersection of the system curve and the pump curve at any given time. I'm only saying that where that operating point is at the next time step may surprise you.

 

[LittleInch]

micalbrch,

I can see that from the OPS pump curve, but I will admit I'm not too familiar with these pumps so a good point to make. however he's at a point way to the left of the curve so it's pretty clear to get more flow the issue is not the pressure he's pumping at, but other things. Now it could be he needs more pressure to get the flow rate up and then the pressure will magically fall in which case the flow increases up to a better equilibrium. Or he just needs more pressure and a roughly linear plot will occur.

My only contact with the fluids he refers to is in the shower in the morning so I don't have much more to add....

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

 

[katmar]

Check that your shampoo is not thixotropic. The gel types can be. If you try to pump a thixotropic fluid with a piston or diaphragm pump you can get serious problems. I learnt this pumping defoamer solution. The defoamer was very free flowing, but the sudden shear increase that comes with a piston or diaphragm instantly turned the contents of the pump housing "solid". Of course when we opened the pump, the shear had gone to zero and the contents flowed out like water. The best way to pump this type of fluid is with a slowly rotating peristaltic pump.

Katmar Software - AioFlo Pipe Hydraulics

http://katmarsoftware.com

"An undefined problem has an infinite number of solutions"

 

[BigInch]

ie. First know your fluid well.... very well.