## Cooling water pumps

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### Cooling water pumps

For those of you who use pumps to reclaim the water in your coil what type seem to work best? I bought a small fish pump and got very little water on the return side. Went to a larger pump and get about 1/4-1/3 gal per min overturn. What should I be shooting for as far as an overturn? Thanks for the help Chub
Chub

The flow you will require has alot to do with your still design - and the heat input. I have a straight jacketed condenser which requires lots of flow to work properly (probably min flow would be about what your pump is doing). my reflux coil needs only a tiny ammount of water to put the still into total reflux. Mine uses a 1500W element. An offset head design still or one with a jacketed coil condenser would need less flow. My pump is a circulator pump from a hot water heating system it is dead quiet and I can get about 8-10 L/min (2+ gal/min) through the still- way more than I need. These pumps are a bit expensive though ~\$80 Canadian new.
agl

Its an offset design It has about 25' of 1/4"copper for the coil I just wanted to make sure my flow is going to be ok. Right now I bench tested a small utility sub pump rated for 1000gph like I said I am getting about 1/4 to 1/3 gal per min I dont know if this restriction will burn the pump up? Chub
Guest

Hi, it sounds like you have heaps of surface area so the efficiency of you condenser should be good. I did a quick calculation to determine the rough volume required:

if no heat is lost i.e. it all goes into making steam which must give up it's heat to the condenser- and you want a distillate temperature of 40ºC, and the room temperature is 20ºC.
heat flow(watts)=massflow(grams/sec)* specific heat*(delta T of cooling water)
If we assumed that the distillate and output coolant would be the same temperature- (which they would be if you had the bare minimum flow)
then you end up with a figure of 12 grams / second / KW
so if you used a 1500W heater then the minimum flow would be~ 1L/minute or about 1/4 gal/min. You would want a big overhead beyond this calculation, since you want to be certain that everything is condensed even if your condenser is less effective than 100%. - (there are lots of important factors to consider for that fudge factor- steam velocity turbulence surface area,etc.).

As for the pump and it's ability to withstand that much throttling, if it is submersible it should be o.k. - as long as it is an impeller pump not positive displacement. Maybe run it for a while and see if it gets hot?
agl

Agl, don't forget the latent heat, energy to convert from vapor to liquid without a change in temp.

Chub, by 1000gph do you mean 1000gallons/hour or grams/hour?
Is your pump a submersable pump or a sump pump?

Too powerfull a pump on too small diamater tubing gets too much resistance,and the pump can cavatate and shake ,eventually burning out.
Hey guys!!! Watch this.... OUCH!

possum
Distiller

Posts: 1167
Joined: Thu Sep 08, 2005 9:33 am
Location: small copper potstill with limestone water

Thanks guys for your willingness to try to help me on this. It is a submersable pump rated at 1000gal per hour @ a 5 foot head which is about what it is. I had a fish pond pump which just trickeled out that was a magnetic drive 190 gal per hour. This coil was made for another purpose before I even got into this hobby, and on previous coils just like this one I was using a 12volt rv pump rated at 3.4 gal per min and it seemed to work very well ;however the reason I did not want to use this pump was the inconvenience of running an inverter. My coil is not blocked in any way so I guess I am a little shocked at how little is making it thru. I connot be the only person who has a coil that is 25'. Is it that hooking it to a tap in a house is just more common? I will check the pump unrestricted to see if it is working properly. It does not chatter seems to be running smoothly. Thanks guys I hope I was able to give you guys the info you needed. Chub
Chub

possum, the latent heat is the main trasport of heat in the system- the heater element has to overcome this to generate the steam, and the condeser has to remove the same ammout to convert the steam into liquid. I bypassed the whole mess with the simplified equation by assuming that all the heat you put in with the element must be taken out by the condenser- and neglecting the details.
agl

Chub,
The 1000gph - is at 5' head (2psi) so when you force through the 1/4 " tubing it must drop significantly more than 2psi. Different pumps are meant for different purposes and some with that high an output suffer more from a resriction than a low output one like an RV or aquarium pump for instance.
good luck!
agl

Now I see what you are saying agl, heat in = heat out
or, after stuff is up to temp, power in = power out.
Hey guys!!! Watch this.... OUCH!

possum
Distiller

Posts: 1167
Joined: Thu Sep 08, 2005 9:33 am
Location: small copper potstill with limestone water

Yep,
heat in = heat out,
crude, but you can figure if you're in the ballpark of correct flow rate.
Guest

agl

Chub, here is a thread that discusses a very similar situation to what you have described.
There are several suggestions for rigging a pump that may be too strong for the narrow 1/4 inch coil.

Hope that this eliminates some of your trouble .
You work with compressors and heat exchangers right ?
There are a few others on this board that do similar work.
At least 2 guys that do HVAC.(not me)
Hey guys!!! Watch this.... OUCH!

possum
Distiller

Posts: 1167
Joined: Thu Sep 08, 2005 9:33 am
Location: small copper potstill with limestone water

There is a formula somewhere that says for a certain size pipe @ x gal per min. add so much head per lineal foot. I can't find it right now. I'm sure it is on the web some where. I will look for all my notes later today. I know from experience that for 3/4in tubing @ 600-800gal per min you have to add like 3ft of head for every 10 lineal feet. I learned the hard way but that is an off topic disc.

Also, You can only fit so much water through that tube which I'm guessing is 1/4in O.D. At some point you will reach the maximum flow rate of the tubing.

My point is that 1/4in tubing is a hell of a lot more restrictive than 3/4(I know Duh stating the obvious) . If you think about it this way, you may be asking your pump to push more like 20' of head. Not to mention, through a little opening. Uphill both ways in the snow with no shoes on...
norcal
Novice

Posts: 66
Joined: Fri Jul 29, 2005 8:09 pm
Location: northern ca

The little pump might still be ok. How high up above the pump is the condensor? It might just be a matter of mounting the pump above the condensor to go with gravity instead of against it???
Guest

Th e entire system may need to be raised depending on the pump. Simply raising the pump may not work if the suction head for that pump is not correct.
Light travels faster than sound. That is why some people appear bright until you hear them speak.

Grayson_Stewart
Distiller

Posts: 1030
Joined: Sun Oct 24, 2004 10:56 am

I am using a boat bilge pump...unfortunately it is 12V but for the price (14\$CDN) you can't go wrong. but that said when i find an AC one for cheap I will make the upgrade
crackher