Wort Chilling Thermodynamics Question

[mwheeler]

The summer in Mobile, Alabama is hot. The tap water can be north of 70 degrees, which makes it impossible to chill my wort down to a reasonable pitching temp in a reasonable amount of time without some method of chilling my cold liquor.

I brew 10 gallon batches and cool the wort via gravity feed thru a plate heat exchanger. I prechill my garden hose cooling water in with a copper coil immersion chiller in a salted ice water bath.

My immersion chiller is (2) 20' lengths of 1/4" ID copper tubing ran in parallel (with a T at the input and output). I have had little success adequately pre-chilling my cold liquor with this chiller.

My question is, would i be better off coupling the two lengths of copper to make (1) 40' coil? By the books, I would assume that it would be a wash as the flow rate would double and the cold liquor would spend the same amount of time in the ice water bath either way.

hope my question makes since.
thanks

 

[ASantiago]

I'm not going to answer your specific question, but offer something else instead.

Could you just chill the wort using your regular method and then immerse the fermenter in cold water to finish the job?

Also, since you are doing 10 gals, I'm assuming you have a fermentation chamber of some sort to do temp controlled fermentations. If this correct, how about cooling the beer using your usual method and then finishing by putting the fermenter in the FC?

I live in FL and use the regular garden hose water for chilling (either immersion or plate). I finish the cool down by putting the fermenter in my FC for a while, usually overnight. I've been doing this for a couple of years.

 

[kombat]

I recirculate my wort back into my boil kettle during chilling. I use hose water until the wort temperature drops to around 80° F. I then switch the chilling circuit over to a second pump that circulates water from an ice water bath in a camping cooler to get me down the remaining 15-20° F.

 

[mwheeler]

i'm fairly new to this game and do not yet have a ferm chamber set up. i am fermenting in two 5 gallon buckets set inside 2 plastic totes full of water. not a perfect set up, but it works for now.

i believe finishing it off with an ice bath is the simplest solution. are there any issues with pitching a few hours after the boil for the wort to reach proper pitching temp?

I have tried recirculating the wort the old fashion way (picking up the fermenter and dumping it back in the kettle) but i still have trouble getting it below 85F after that.

 

[ASantiago]

i believe finishing it off with an ice bath is the simplest solution. are there any issues with pitching a few hours after the boil for the wort to reach proper pitching temp?

I finish cooling wort overnight, sometimes up to 24 hours, regularly (as in: every single batch). I have not had any issues. However, I keep very good sanitation and pitch a healthy amount of yeast from a starter that takes over the wort within 12 hours. If you do both of those (or pitch rehydrated dry yeast in the right amounts), you too will not have any issues with the delay before pitching.

 

[schockstrap]

Running the 2 coils in series through the ice bath should make a big difference in the temperature of the water entering your plate chiller. The design parameters for a heat exchanger are temperature difference and surface area. Running the 2 20ft coils in parallel gives you a higher flow rate (less resistance) and half the surface area (since a given molecule can only pass through one coil). Running a single 40ft coil will give you double the surface area and a slower flow rate, which should mean colder water flowing into your plate chiller (fixed surface area, but bigger temperature difference).

 

[mwheeler]

Running the 2 20ft coils in parallel gives you a higher flow rate (less resistance) and half the surface area (since a given molecule can only pass through one coil). Running a single 40ft coil will give you double the surface area and a slower flow rate

seems logical.. I will be putting this to the test. i had set them up running in parallel when using the immersion chiller for the more typical use (immersing in the wort). My thoughts were that running (2) 20 foot lengths would provide a higher average delta T between the cooling liquid and the wort than (1) 40.

I'm sure I could figure all of this out with equations, but it would be more fun and require much less math to just experiment.

 

[ruger988]

Sounds like your set-up isn't far from what I do, and I seem to have the same issues getting down the last 15-20*. Next brew day I plan to pump the ice water through the chiller rather than use it to "pre-chill" the hose water (set a pump in the cooler of ice water and route that through the chiller that is in the wort) and hope that gives me better results.

 

[wilserbrewer]

Or just run the two chillers I'm parallel at a lower flow rate.

Might take a long time. Either way you only have X temp coolant and Y surface area of chilling coil...

If your not cooling enough, you are running to quickly through the cooler regardless parallel or series.

Ok edit since feeding the cooler via gravity it will be slower flow in series, and have more time to chill.

Or just pinch pack the wort flow tubing to slow it down the way you have it rigged.


Wilserbrewer
Http://biabbags.webs.com/

 

[Pkrd]

Put one immersion chiller in the wort to cool it down to tap water temperature. Then finish it with the chilled plate heat exchanger.

 

[ReformedBrewer]

I live in Florida so I have this same exact problem. I employ two methods:
1. Cool to 80F with my immersion chiller using ground water and then put in fermentation cooler overnight, pitch in the morning. I should mention this also helps settle the trub below my screen and makes racking a piece of cake.
2. Use a submersible pond pump in a cooler full of ice water and hook that up to my immersion chiller! This method takes me about 20 extra minutes to drop from 80F down to 65F with constant stirring to keep wort moving over the coils.

 

[mwheeler]

after spending too much time internally debating series vs parallel with the immersion chiller, i've thought up the obvious solution: fill up my mash tun with ice water and gravity flow the ice water through my plate chiller.

i think my immersion chiller conundrum has been a red herring. just need to cut out the middle man all together. I'm sure the 35-40F water will be able to handle the job just fine.

what's more, I could use dry ice to cool the water in the mash tun and feel like a mad scientist.

 

[retheisen]

How about running your plate chiller at full bore with regular temp tap water ... then run the semi-cooled wort from the plate chiller output to the inside of the two immersion chillers in series in the saltwater ice bath, then out to your fermenter.

 

[passedpawn]

Parallel them for quickest chilling.

Heat will move much more quickly when the target is colder. Paralleling the coils will ensure the entire length of coil is cold. With one long coil, the last half of the cold will be warm as it's picked up a lot of heat already.

Additionally, by paralleling the coils, the resistance to the water's flow is halved. This means the flow through both paths will be greater than if it was one continuous coil. By increasing the flow rate of the chilling water, you will increase the cooling rate.

No brainer here.

 

[retheisen]

Back to the original question ... run a test. How far from the bath temperature are you after passing one gallon of tap water through a single length of immersion chiller? How far are you from bath temperature after running though both lengths? If you can drop one gallon of water from 75 to 55 with a single length of chiller in 20 seconds (3 gpm) then you have removed 167 BTU's from that gallon of water ... if you can keep that up for an hour then you are working at a rate of 30,000 btu's per hour.

If by running two chillers in parallel you can do one gallon from 75 to 55 in 15 seconds (4 gpm) then you are moving 40,000 btu's per hour.

if you run the two in series and can get from 75 to 45 in 20 seconds (3 gpm) then you are working at 45,000 btu's per hour.

Do you have sufficient ice in your bath to sustain that level of flow for the

212 - 65 = 147 degrees to remove from 10 gallons of liquid.

10 gallons times 8.33 pounds per gallon times 147 degrees = 12245 BTUs of heat in your ten gallons of boiling wort to be removed to get to 65 degree pitching temp.


if your plate chiller sees cooling liquid entering at 45 degrees at a rate of 3 gallons per minute (series chillers) and you need to get from 212 to 65 on the hot side ... then you should be able to run .4 gallons per minute of wort through the chiller and get an output of 65 degrees. 25 minutes to cool 10 gallons

if your plate chiller sees cooling liquid entering at 55 degrees at a rate of 4 gallons per minute (parallel chillers) and you need to get from 212 to 65 on the hot side ... then you should be able to run .27 gallons per minute of wort thourhg the chiller and get an output of 65 degrees. 37 minutes to cool 10 gallons

Can your ice bath hold up for 25 minutes? 37 minutes? with 75 degree tap water running through it at 3 or 4 gallons per minute? Do you chillers behave the way I described? You would need to do some testing.

http://www.advantageengineering.com/fyi/288/advantageFYI288.php fo an online btu/hour calculator.

 

[schockstrap]

Parallel them for quickest chilling.

Heat will move much more quickly when the target is colder. Paralleling the coils will ensure the entire length of coil is cold. With one long coil, the last half of the cold will be warm as it's picked up a lot of heat already.

Additionally, by paralleling the coils, the resistance to the water's flow is halved. This means the flow through both paths will be greater than if it was one continuous coil. By increasing the flow rate of the chilling water, you will increase the cooling rate.

No brainer here.

The problem is that this ignores the effect of surface area. For chilling hot wort you may be correct (though even there you'll have diminishing returns on temperature difference vs surface area). When passing cooling water through a pre-chiller coil you have a little different situation... The temperature of the ice bath is essentially constant because it's in a state of phase equilibrium -- is going to be at our very near the melting point of ice in local conditions. The temperature differential is going to be pretty small no matter what you do, so to maximize cooling of the water in the coil your only real option is increasing surface area of the coil. The longer coil will result in a cooler temperature of the water leaving the pre-chiller.

 

[fmr_army]

I'm not a thermodynamicist, nor even very smart. Therefore I will bypass the OP's question and look at the underlying question which, as I understand it, is "since I have not-cold tap water, how can I best cool my wort to a reasonable pitching temp?"

I like the previously mentioned method of cooling it somewhat and then leaving it un-inocculated in a cool place to finish the job, and then pitching the yeast. My problem is that I would almost certainly forget to pitch the yeast in a timely manner. (I blame gulf war syndrome for much of my forgetfulness, and the remainder on being married for 19 years and having two teenaged kids. I do what I'm told, when I'm told, how I'm told.)

My solution to a similar problem (although I'm in Northern Virginia, the summer water temps get pretty warm, and it's a pain for me to deal with 30+ gallons of warm water) was to ditch the immersion chiller and go to a counterflow chiller. I use a bunch of ice in a 5 gallon bucket with a Harborfreight submersible pump to push that cold water through the CFC, while the wort flows through. I have a deep freeze and make chunks of ice in between brewdays, but will probably get lazier and just buy 20# bags from the store. My system gets 10 gallons down to pitching temp in about 30 minutes, while transfering it from kettle to fermenter.

I made my CFC out of a 20ish foot piece of refrigerator copper, a crappy hose, some copper fittings and pipe and odds and ends. Works like a champ. Longer tube is better. I got the know-how from HBT. And if I could do it, anyone can. I did have (get?) to buy a soldering set though.

Total cost for my chilling setup was somewhere around $100, if memory serves.

...and now back to the smart kids discussing smart stuff...

 

[passedpawn]

The problem is that this ignores the effect of surface area. For chilling hot wort you may be correct (though even there you'll have diminishing returns on temperature difference vs surface area). When passing cooling water through a pre-chiller coil you have a little different situation... The temperature of the ice bath is essentially constant because it's in a state of phase equilibrium -- is going to be at our very near the melting point of ice in local conditions. The temperature differential is going to be pretty small no matter what you do, so to maximize cooling of the water in the coil your only real option is increasing surface area of the coil. The longer coil will result in a cooler temperature of the water leaving the pre-chiller.

Yea, maybe you're right. Guess it's not a no-brainer. I admit I didn't read the OP for comprehension, and I thought we were cooling wort here. Now my head hurts. I'll think on it later.