How fast to run water in wort chiller?

Howdy,

I have a stainless chiller. Should I: a.) run the water fast to keep the water in the chiller colder or b.) run slower to increase heat transfer time and save water?

Thanks

Strangelove said:

Howdy,

I have a stainless chiller. Should I: a.) run the water fast to keep the water in the chiller colder or b.) run slower to increase heat transfer time and save water?

Thanks

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I'd run the water fast, assuming I can dispose of the extra water easily or reuse it. You'd use less water with a copper chiller.

Okay...I'll spend 2 months worth of water bill money to switch to a copper one. Thanks.

nice and slow, you're just gonna waste water if you run it fast. where on earth did you get a stainless chiller???

Faster would increase the heat transfer rate. Rate of heat transfer = Massflow rate*specific heat capacity*difference in temp. Increasing mass flow fate would therefore increase rate of heat transfer. It will decrease your differential temp but the offset would be made up with total rate of heat transfer. Either way try a few batches and I bet you don't see more than a few minutes difference between start time and end time no matter how you do it. The major factor is the UA of the heat exchanger which you can not change.

Isn't the heat transfer coefficient of copper something like 10x-30x higher than that of stainless steel? I just remember the demo in my physics class back in college where the SS rod in a flame was still cool to the touch at the other end, about 12 inches away.

SilverZero said:

Isn't the heat transfer coefficient of copper something like 10x-30x higher than that of stainless steel? I just remember the demo in my physics class back in college where the SS rod in a flame was still cool to the touch at the other end, about 12 inches away.

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Doesn't matter what c is it is a constant as it is not changing in the equation. But yes copper has a much higher heat transfer coefficient than stainless.

If you want to save time (quickest cooling), run the water as fast as you can.
If you want to save water, run it slow.

DeafSmith said:

If you want to save time (quickest cooling), run the water as fast as you can.
If you want to save water, run it slow.

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Hit the nail on the head with that one. Strangelove your question kind of answered itself, it is your choice whether you want to save time or water

Sounds as though a few responders know the finer details of heat transfer. Can anyone comment on the effects of slowing the flow rate by dampening down the outflow side? I had some experience years ago with an electric instant hot water heater that continued to blow heating elements. I braised in a shutoff valve on the outflow side to build pressure around the element and never blew another element. I put a shutoff on my homemade chiller ad choke down the flow. I find the discharge water to be hotter and the cooling time shorter than just running water at full flow. Any one have any experience or knowledge about this??

JamesM said:

nice and slow, you're just gonna waste water if you run it fast. where on earth did you get a stainless chiller???

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http://www.midwestsupplies.com/stainless-steel-immersion-wort-chiller.html

Thanks for the answers. I guess I was looking for the break point at which water waste balanced with speed.

Strangelove said:

http://www.midwestsupplies.com/stainless-steel-immersion-wort-chiller.html

Thanks for the answers. I guess I was looking for the break point at which water waste balanced with speed.

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What size tube is that, 1/4"?
For what you are asking I would imaging that you would be going full force for the first few minutes and then backing off slowly untill the end. If you could mount a thermometer at the chiller outlet you could make sure that was only 5 or so degrees cooler than the wort temperature to try increase you water efficiency.

FastEddie212 said:

I find the discharge water to be hotter and the cooling time shorter than just running water at full flow. Any one have any experience or knowledge about this??

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The first part makes complete sense. You will have hotter water water coming out, because every molecule of water has more time in the chiller to be warmed up, so yes, it will be hotter.

However, it honestly doesn't make sense that the cooling time would be shorter. The faster you can run the water, the better off you should be. The thing to keep in mind is that the heat transfer is driven by differences in temp. The closer to the wort temp that the water through the tube gets, the less additional heat transfer you get.

As a though experiment, think about what happens if you reduce the flow rate to 1 gallon per week. Doesn't matter how hot that water gets (and it would come out quite hot!), you're not effectively chilling your wort. On the flip side, imagine you could put an infinite flow rate through your chiller. It would instantly chill your wort, because even if each molecule of water only increased in temp a fraction of a degree, that would pull out so much energy in total that the wort would be instantly chilled to the water temp.

discnjh said:

The first part makes complete sense. You will have hotter water water coming out, because every molecule of water has more time in the chiller to be warmed up, so yes, it will be hotter.

However, it honestly doesn't make sense that the cooling time would be shorter. The faster you can run the water, the better off you should be. The thing to keep in mind is that the heat transfer is driven by differences in temp. The closer to the wort temp that the water through the tube gets, the less additional heat transfer you get.

As a though experiment, think about what happens if you reduce the flow rate to 1 gallon per week. Doesn't matter how hot that water gets (and it would come out quite hot!), you're not effectively chilling your wort. On the flip side, imagine you could put an infinite flow rate through your chiller. It would instantly chill your wort, because even if each molecule of water only increased in temp a fraction of a degree, that would pull out so much energy in total that the wort would be instantly chilled to the water temp.

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The only thing I can think of to explain this is that maybe the flow rate at full flow is not fast enough to completely fill the chiller tubing, so the water flows in a channel down the tubing, leaving some of the chiller surface area without any cooling water. When he chokes it down some, the tubing fills and all the surface area is cooled.

DeafSmith said:

The only thing I can think of to explain this is that maybe the flow rate at full flow is not fast enough to completely fill the chiller tubing, so the water flows in a channel down the tubing, leaving some of the chiller surface area without any cooling water. When he chokes it down some, the tubing fills and all the surface area is cooled.

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I can't see that actually happening, the water from the hose will push all the air out. I would think it is a case of the impression that hotter water out of the chiller must equal more heat being removed.

I notice that if I agitate the wort gently but frequently while using my chiller, it works much faster. Keeps circulating the hotter water against chiller.

I spoke to an engineer friend after resolving the instant hot water heater element issue to see what might have changed to resolve the problem. He said that building higher pressures inside the lines could have the effect of increasing the surface contact of the water improving its heat transfer ability. I know that you cannot compress liquids but restricting the flow could certainly have the affect he suggested. In fact, it was pretty much proven with the heating elements. When I do choke down the outflow side, my pvc hoses connecting the garden hose to my wort chiller bulge due to the increased pressure. There has to be some similar affect on the inside of the copper tubing to whatever degree. Also, any temperature differential between the water and the wort will cause heat to be absorbed and removed. Granted, not as much heat can be removed when the temperatures grow closer but my outflow temp is 130-150F at the start when my wort is 70-90 degrees higher. I guess I'll just have to do some experiments with and without the line choked down to prove or disprove this objectively.

FastEddie,

It's possible that water loses some of it's heat transfer ability due to dissolved gasses coming out of solution.

There is dissolved nitrogen and oxygen gas in your cold water. When the water moves rapidly I think the pressure is reduced. The gas can form bubbles which could cling to the inside of the metal tubing - especially if that tubing is warmer than the water which will cause even more gas to come out of solution.

Those bubbles would be ruinous to heat transfer. Increasing the pressure in the tubing should aid in keeping the bubble from forming.

Stainless Steel has a lower conductivity than copper, but it can be compensated for by thinner walls and more feet of tubing in the coil. I don't know if that is what is done for this chiller - but my point is you can't assume that copper is always the most cost effective chiller material.

I doubt that restricting the outflow, will change anything dimensionally with the copper tubing. PVC, sure I could see that, but copper no. So I don't think slowing down the water flow (even with increased pressure) will improve the heat transfer ability of the chiller.

If you slow down the water flow from the faucet, the outlet water temp will increase because the volumetric flow of water is reduced. Longer time through the coils will increase the amount of heat picked up by the water per volume. I run mine at 60-75% in the beginning to save a little water, and to still be pretty efficient on heat removal.

Near the end, I turn the faucet fully on as the inlet and wort temperature approach each other. Heat transfer here is not nearly as efficient. I don't think you save much water by going slower as you are still targeting the same pitching temp with either faucet flow rate.

Also agree that the single best thing you can do to save water and increase speed is to GENTLY move the coils through the wort. Put your finger on the outlet to see this effect vs just letting it sit on the bottom.