Wort Chiller Just Ain't Chillin

[Dave70]

So, in conclusion..

 

[TheWiggman]

There are two pretty conflicting viewpoints here. Here's the science/engineering for those interested. What we're concerned about the the convection coefficient of the liquid inside the tube (water), of the tube itself, and outside the tube (wort)

For laminar flow, the formula for the heat transfer convection coefficient, W/(m2•K), of the fluid inside a circular pipe is -

hbar = mdot * cp x (Tout - Tin)
pi * D * L T diff

mdot is the mass flow rate. Therefore if the flow is increased, the convection coefficient becomes higher and more heat energy is able to be transferred.
HIGHER FLOW = better

For turbulent, the general approach can be applied -

q = h * A * (T diff)

For h, the Nusselt number is needed. One approximation is the Dittus-Boelter equation for Re > 10000 (more info below)

Nu = 0.023 * Re ^4/5 * Pr^n

Higher flow will increase the Reynold's number, which increases the Nusselt number, which increases h. This in turn results in a higher energy transfer in J/s (q).
HIGHER FLOW = better

For 10l/min through a 1/2" stainles tube the Reylond's number is ~36000, which is well turbulent (>4000 is considered turbulent). The only reason I included the first equation is that even if you did get your water flow down to laminar, the result is still the same - more flow is better.

If you want to cool the wort down faster, increase the flow of your water.

Just as important is flow in your wort. If you don't have a recirc pump on it, move the coil around in your kettle to get a nice whirlpool going. Otherwise yes it will take a long time.

PS: if you slow the water flow down the temp of the water coming out will be higher. This isn't relevent for what we're trying to do - we don't want hot water coming out, we want as much energy transferred as possible.

 

[Ducatiboy stu]

A chiller is quicker than no-chill.

 

[JaseH]

I haven't bothered reading all the shit fight about cooling physics, but if your goal is to chill quickly with minimal water wastage - piss the coil chiller off and get a plate chiller.

27L of 100C wort into the fermenter in under 5min at ~2C above tap water temp. If cooling speed/efficiency isn't the goal then the all this discussion seams a pointless?

 

[TheWiggman]

OP owns the chiller and isn't getting performance out of it. He wants aid getting better performance out of it (or clarification it's no good)

Maintain high water flow
Keep the wort and/or chiller moving

I'm guessing he wasn't doing the latter.

 

[Ollieb]

Whoa fellas what about how out of control this thread became overnight....!

All I wanted to do was start a chat about chilling some beer... I think some of us could take 5, go chill and have a beer.. (even if it is only 11:45 am).

I appreciate everyone's help and opinions but let's keep it pleasant between each other. This is not a measuring contest huh...

With so much info here and lots of good stuff for me to test and trial with my chiller I think we can leave this one for now.

I will be sure to let everyone know what worked once I brew on Sunday. Slower rate of flow or faster rate of flow.

Thanks again for everyone's contributions.

Ollie

 

[Ducatiboy stu]

Whatever you do.....dont start a yeast if you think this thread is getting epic.....

 

[Dave70]

If you want to cool the wort down faster, increase the flow of your water.

This seem to run counter to the bush mechanic practice of knocking a couple of teeth of a cars water pump in order to prevent overheating. Bush mechanics being a highly specialized field.


I'd agree the must be an optimum 'range' of flow, but the law of diminishing returns must kick in at some point.

That sad, I'm pretty fuked at maffs.

 

[TheWiggman]

You're absolutely right, there is a point of diminishing returns. Efficiency will reduce, but efficiency and performance are different. Industrial heat exchangers come with an efficiency curve for this reason.

Eg. in a car if you want to go faster, open the throttle more. There will be a point at which your l/100km will increase and lots of extra fuel gives minimal gain, but the more you put your foot down the faster the car will go.
That's an example of efficiency, not necessarily analogous to this problem.

 

[Goose]

Yep all good stuff, however it seems to me that the eloquent prose from some here may have confused the thinking between the property of temperature and definition of heat.

Its not that hard. Theory and science are all very well. But you have know how to apply it.

When cooling your wort with an immersion coil you want the exit cooling water to be as hot as possible.

This is where the confusion begins, because it is not necessarily correct. Your objective is to have the wort as cool as possible in as short a period of time as possible. There are many variables involved, the main ones being total surface area, conductivity of the metal, entry temperature of coolant and what seems to be contentious here because it is well within our control which is the water flow rate.

This means that the water is extracting the heat in the wort to the maximum potential of your cooling system (ie. whatever type of coil you use; whatever mains water pressure you have; whether or you jiggle the coil or not, etc, etc, etc).

Maximum temperature of cooling water outlet does not necessarily mean maximum heat rate of removal.

So put a thermometer in the outflow water (good idea to plumb a short-stick dial thermometer with a T-piece at the exit end of your coil). Increase the input water flow until the temp just starts to drop. This is the point at which the water flow is so high that the cooling water does not have enough time in the coil to heat up by absorbing as much heat as it can from the wort. Back off the water flow a tad.

This saves water, granted. But it does not mean more heat is removed.

But the situation does not remain the same.

Heat transfer from wort to water is not a constant. The greater the temp difference between the wort and the cooling water the greater is the rate of heat transfer between the two. So the maximum potential heat transfer occurs at the start of cooling process when the wort is just off the boil.

As the wort cools the temp difference between the wort and the water is reduced, so the rate of heat transfer diminishes.
This means you have to give the water more time in the coil to account for the poorer rate of heat transfer. So you have to progressively back off the water flow as the wort cools to give the water more time to absord the wort's heat. If you don't you are needlessly wasting water.

You use less water but also lower your heat removal rate.

Towards the end, when you're getting down towards pitching temp, the rate of heat transfer is appalling compared to the beginning. It will take the most time, but the least water, to knock off the last few degrees. If you have another coil to put in an ice bath (ie. a pre-chiller) this is the time to use it. You will increase the temperature difference between the water (which is now icy cold) and the now not-so-hot wort and thus increase the rate of heat transfer between the two. (Note that at the start of the cooling process its pretty pointless using a pre-chiller because the temperature differential is large anyway - you will get max use out of the ice in your pre-chiller bucket by using it towards the end of the wort cooling process).

Hope this dispels the idea that you can just pick one water flow rate for the whole process to run at best efficiency. Nature disagrees.

Nature disagrees and so do I. Efficiency can be defined in many ways. Time ? Economy ? Rate of heat transfer ? Our variables as homebrewers are mostly flowrate and cooling water starting temperature. If you are not worried about water usage and you want maximum heat transfer, that is to cool your wort as quickly as possible, then you need maximum possible flowrate and minimum possible coolant entry temperature.

Thankyou, and goodnight.

 

[Online Brewing Supplies]

I find it strange when out camping if I run past a campfire it doesnt warm me,
but if I walk past slowly I get hot.
Nev

 

[Goose]

I find it strange when out camping if I run past a campfire it doesnt warm me,
but if I walk past slowly I get hot.
Nev

LOL

yes nev mate, you do.

but if a thousand cold people ran past that campfire in the same time you stood there they'd all get a little bit warmer and the sum of the heat transferred to them in the same time would be more than the total transferred to you.

Thats because we all agree (at least) that the greater the temperature difference, the greater the rate of heat transfer. So each new bod that runs past the fire is the same cold temperature to start with.. whereas you standing there as you say you get hotter and hotter so you absorb less and less with each increment in time..

Make sense ?

 

[Ducatiboy stu]

So...does a given volume of water transfer a given amount of heat.

So more volume passed thru transfers more heat.

So the faster flow passes more volume which transfers more heat.

 

[The Judge]

I find it strange when out camping if I run past a campfire it doesnt warm me,
but if I walk past slowly I get hot.
Nev

Trolling statement of the thread!

 

[Online Brewing Supplies]

Well someone had to lighten up this thread. :lol:
Nev
ed sp

 

[Dave70]

OK, in the same vein, a question I don't think I've ever heard answered with any clarity.
What time frame actually constitutes chilling, and why does it even matter?

Just for the sake of the argument, say its pertinent for the reason of hop aroma / chill haze / hot break or whatever to have the wort temp reduced from 90 deg to 30 in X amount of time.
If truths exist about chilling at all, there must be a window in which optimum results are obtained, anything outside X must see desirable results taper off sharply.

It seems a given that we strive for the quickest chill possible, but is there really any justification in time / effort / expenditure of $$$ to shave 10 minutes off the time it took to drop down to pitching temp?

Would, given identical everything else, an ale that took 30 minutes to chill from 90 to 20 deg turn out demonstrably better than the same wort that took an hour to cool?

I'm interested because we obviously calculate bitterness and hop additions around chill / no chill, but what about slow chill? At what point does it cross the line?

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[Ducatiboy stu]

Dont be starting an argument Dave.......them engineers will get involved. And that will involve complex stuff like working out if your hose fitting is corect or if the time it takes is based on daylight savings time.

 

[TheWiggman]

"[SIZE=10pt]Arguing with an Engineer is a lot like wrestling in the mud with a pig: After a few hours, you realise the pig likes it.[/SIZE]"

 

[Not For Horses]

For Dave

http://aussiehomebrewer.com/topic/80799-time-frame-for-chilling-a-musing/

 

[Ducatiboy stu]

"Arguing with an Engineer is a lot like wrestling in the mud with a pig: After a few hours, you realise the pig likes it."

You can put lipstick on an engineer......