Design of a stirrer 2

[ajxxx]

I would like to know the recommendations of which design amongst the attached would be the best for :

** Creating a VORTEX and highest downward thrust (for pushing the fluid down towards a drain plug) when used as a stirrer...

I would like to know if there are any better designs than the ones I have thought of for achieving my purpose. Thanks in advance

 

[ajxxx]

Sorry forgot to attach the design file

 

[ornerynorsk]

Look at boat propellor designs as a first thought. What fluid and viscosities are you working with, and does it contain any solids, particulates, etc?

 

[rb1957]

your design would produce minimal downward thrust ... a propeller is designed to produce thrust, so if this is your goal ... go with a propeller.

 

[ajxxx]

A single propeller though would not probably produce enough thrust needed I believe. The issue is the polymer is less denser than water (0.9) so to push it down is an issue. Multiple propellers maybe @ different heights on the shaft???

Would it be able to provide more homogenous mixing & probably thrust too???

 

[IRstuff]

Density should have little to do with it. Downward thrust is created by momentum transfer from the impeller.

Please also refrain from double posting: thread378-274808 as it tends to result in duplication of answers

TTFN

FAQ731-376

 

[rb1957]

it may well be buoyant, but a propeller will produce the maximum thrust, depending on the pitch angle of the blades and the power provided. multiple propellers won't help much, if at all ... they're used in aircraft to recover the swirl of the fwd propeller and to increase the power for a given diameter (given that tip speed is limited).

you may consider shaping the bottom of the container, which might help the flow circulate.

are you trying to mix the fluids ? maybe work it from both sides ... one propeller pushing the lighter fluid down, another pushing the heavier fluid up ??

 

[ajxxx]

thanks....gr8 info...actually there are not 2 fluids...1 is water and the other is polymer melt (insoluble in water)...I was thinking of ordering the regular mixing left hand propellers to push the melt down...now maybe the best bet would be as recommended to put a propeller to push melt down (probably @ the top of the shaft) & another propeller on the shaft bottom (put the other way or right handed) to push water up...

Am just worried though that the bottom propeller might push the melt upwards or a single propeller @ bottom might not be sufficient to create the thrust we need in a large chamber...

Shaping the bottom of the chamber might work out great....have to though probably consider re-designing the whole chamber which would be costly....

 

[btrueblood]

Why don't you skim from the surface, if that's where the polymer is?

 

[rb1957]

i think he trying to mix them, even thought they don't want to mix ...

it'd be easy to separate them.

random thought d'jour ... could you heat the mixture slightly ?? (to encourage them to get along with each other)

 

[ajxxx]

No No.....I believe i was not able to get my message across more clearly......aim is not to mix them.....Water is just used as a dispersing agent for heat dispersion.....

Skimming is not possible as the chamber is a pressure vessel which is closed....Mixture is heated till 150 C so that the polymer is melted...

Aim is to get the melt out of the chamber to room pressure via the valve @ the chamber bottom so that the polymer will expand due to pressure differential....Water is essential though so that the material is not overheated......

Due to density difference though water gushes out first from the valve rather than the polymer so we need to make sure it is being thrusted down and forced out...

 

[berkshire]

How about an Archimedes screw running in a downward direction towards your outlet?

B.E.

 

[ajxxx]

wont the archimedes screw pull up my material as well??? The issue is polymer is dispersed in water and I believe the screw will just pull everything up....I want the material to be pushed out(down) - water is secondary : If it comes out after the material = NO ISSUES...but if it sneaks out before it...my expanded material would collapse because of the chamber heat!

 

[berkshire]

ajxxx
Remember this screw is pushing your material down.
The screw will pull a column of polymer water mix towards your outlet, some of your material will escape the sides of the screw and recirculate in the tank. A sleeve around part of the screw at the bottom will minimise that. Remember this screw would have to be centered over your outlet to work
What stops your water from draining out and leaving your polymer high and dry? do you open a valve in the bottom of the tank and let the water flash to wet steam? are you re-filling as you drain?
Is this a continuous flow, or a batch production system ?
If this is a batch production system then a tapered bottom to the tank will give you a better discharge. However I feel that if the flow rate is too slow your polymer will agglomerate in your tank.
B.E.

 

[ajxxx]

Yes there is a valve @ the bottom of the tank... No re-filling is done while draining - point is to get an instant release to subject the polymer to a high pressure differential required for expansion.

This is batch production system. Polymer tends to agglomerate but we are using surfactants to prevent that issue. I am giving the propellers a shot today as other coveted members have recommended.

Would also try to get the archimedes screw and give it a try if needed - any recommended companies to buy/customize the archimedes screw?

I need to somehow add resistance to the water flow to slow it down because it escapes far more easily than the polymer melt.

Info that all of you have provided though has been a big help and am in a much more better position than before for sure. Big thanks and please continue to assist with your recommendations if possible.

 

[rb1957]

if you heat the mixture to 150C ... isn't the water converted into steam ? or do you have a really high pressure ?

 

[ajxxx]

pressure is 600 psi so water still remains in liquid form.

 

[ajxxx]

and pressure is in the form of CO2(carbon dioxide) @ 600 Psi - CO2 serves as the blowing agent for expansion of polymer.

 

[berkshire]

ajxxx
An archimedes screw is simply the working part of a screw conveyor, there are many companies that can make what you want. Here is a link to just one of them.

http://www.kwsmfg.com/products/made-to-order/index.htm

B.E.

 

[rb1957]

so you've got water (@150C and 600psi), CO2 (@ 600psi) and your polymer all being vented out of the tank, to atmosphere. i think there's an awful lot of thermodynamics happening all at once ! the water is superheated, i'd've thought it would flash to steam; and that everything would get horribly mixed up as it comes out the vent.

it sounds like you're using the water as a heat sink ... could you use something else ? maybe the water is also a transport agent ?

it sounds ike you want to do the opposite of mixing ... you want to separate the polymer from the water. is the polymer still fluid at say 90C and 1atm ? reduce the temp, reduce the pressure, get a more controlled release ??