Water flow in wort chiller

[alecrippa]

Hi,
How can I compute the optimal flow rate for my immersion chiller?

Too much flow and water is too fast to steal energy from the wort, too little and it will take forever..

Or, more formally:
Given a volume of wort of 19 liters (5 gallons) at boiling temperature, and a steel chiller 8m (26 feet) long and 10mm (~1/2") thick where water ar 5deg Celsius (40deg F) flows, what is the maximum flow (in L/s) that produces maximum heating of the water? (I.e. steals energy from the wort at the fastest rate)

Thanks

 

[RPh_Guy]

Running the water at full speed will minimize chilling time. There is no speed that's "too fast" to transfer heat.

That makes things easy

 

[Pkrd]

Yes, faster the better, but probably not much point going too high.

The big gains are in getting the heat from the wort to the chiller, not from the chiller to the water.

 

[Vale71]

Given a volume of wort of 19 liters (5 gallons) at boiling temperature, and a steel chiller 8m (26 feet) long and 10mm (~1/2") thick where water ar 5deg Celsius (40deg F) flows, what is the maximum flow (in L/s) that produces maximum heating of the water? (I.e. steals energy from the wort at the fastest rate)

The answer is easy: infinite flow rate. While the actual rate of cooling is limited by the size, shape and material characteristics of the chiller, you'll only reach its full potential if the water mantains the same temperature (in your case 5°C) throughout its entire length and you can only achieve that (theoretically) with infinite flow. Mathematically if you where to graph the relationship between flow rate and heat transfer rate the curve would be asymptotical to the design value or if you prefer, the limit for the transfer rate equals the design value for infinite flow.
The real question you want to ask is what is the rate that will give me the best compromise between speed and total water usage but there's no definitive answer for that, it really depends on how much water you're willing to waste (if you're not reusing it that is).

 

[Pkrd]

The answer is easy: infinite flow rate.

Somewhere between 10l/minute and infinity won't you get non laminar flow?

 

[HopSing]

I would also assume it depends on the efficiency of the chiller. This could be measured by the difference in temperature from in-flow and out-flow of the chiller. The closer those become, the less efficient the chiller is at removing heat from the wort. Variables include heat conductivity of chiller (copper vs. stainless), length of chiller coil, difference of temp between wort and water, etc.

For example, if the length of the chiller coil was very short and the temperature difference between the water flowing through the coil and the wort was small, the likelihood of having a small temperature change between in-flow and out-flow would be much greater. In this case putting a higher volume of water through the chiller may not make a difference in a practical sense.

On the other hand, using a highly efficient chiller, such as the JaDeD Hydra, my guess is you'll see an in-flow and out-flow temperature change until wort and water become very close in temp. As @Vale71 mentioned, it's likely there is a compromise between heat exchange and water usage. This means a high volume of water in the beginning of the chilling process when there is a huge difference between in-flow and out-flow temp, but reducing flow rate as those two temperatures get closer.

Personally I run full pressure through my 50' stainless chiller until I get the wort to about 110F, then I switch over to a cooler with blocks of ice and a pond pump for the in-flow source. While using tap water, the out-flow is going into my washing machine so I'm wasting very little water.

As a side note, I hear there is a stainless version of the Hydra chiller coming out. Could be the best of both worlds.

~HopSing.

 

[Vale71]

Somewhere between 10l/minute and infinity won't you get non laminar flow?

Isn't non-laminar flow what you actually want to have to maximize heat transfer to the cooling water? Laminar flow is what would actually cause the system to become inefficient.

 

[f.pelosa]

The answer is easy: infinite flow rate. While the actual rate of cooling is limited by the size, shape and material characteristics of the chiller, you'll only reach its full potential if the water mantains the same temperature (in your case 5°C) throughout its entire length and you can only achieve that (theoretically) with infinite flow. Mathematically if you where to graph the relationship between flow rate and heat transfer rate the curve would be asymptotical to the design value or if you prefer, the limit for the transfer rate equals the design value for infinite flow.
The real question you want to ask is what is the rate that will give me the best compromise between speed and total water usage but there's no definitive answer for that, it really depends on how much water you're willing to waste (if you're not reusing it that is).

Do I need this correctly if I summarize this discussion in:

• No chance you can get a flow that is faster than the speed at which heat is transferred
• This especially holds for high DT between tap water temperature and wort temperature.
• As the DT gets smaller, slower flow rate could be preferred as the pipe conductive properties may slow heat transfer down

 

[alecrippa]

The answer is easy: infinite flow rate. While the actual rate of cooling is limited by the size, shape and material characteristics of the chiller, you'll only reach its full potential if the water mantains the same temperature (in your case 5°C) throughout its entire length and you can only achieve that (theoretically) with infinite flow. Mathematically if you where to graph the relationship between flow rate and heat transfer rate the curve would be asymptotical to the design value or if you prefer, the limit for the transfer rate equals the design value for infinite flow.
The real question you want to ask is what is the rate that will give me the best compromise between speed and total water usage but there's no definitive answer for that, it really depends on how much water you're willing to waste (if you're not reusing it that is).

Do I need this correctly if I summarize this discussion in:
No chance you can get a flow that is faster than the speed at which heat is transferred
This especially holds for high DT between tap water temperature and wort temperature.
As the DT gets smaller, slower flow rate could be preferred as the pipe conductive properties may slow heat transfer down

 

[kh54s10]

What is more important than water flow rate is to keep the wort moving around the coils of the chiller. If the wort is stagnant, it will cool the wort in contact with the chiller and take a long time to cool the rest.

 

[hjblwme]

Here is a highly technical explanation that most of us will probably not understand. The last is probably the best. But all will have technical answers.


https://www.engineeringtoolbox.com/conductive-heat-transfer-d_428.html


https://www.engineeringtoolbox.com/...conductivity-temperature-pressure-d_2012.html


https://www.engineeringtoolbox.com/arithmetic-logarithmic-mean-temperature-d_436.html

https://www.engineeringtoolbox.com/heat-load-steam-pipes-water-d_287.html


Just run the water so that it comes out the end and if your worried about wasting it then bottle and use to bathe, flush, drink, or brew.

 

[Robert65]

Just run the water so that it comes out the end

Once in a while you get on the forum and see a reply that resolves everything into perfect clarity... *angels singing*

 

[hjblwme]

Once in a while you get on the forum and see a reply that resolves everything into perfect clarity... *angels singing*

I hated to be the wise guy but couldn’t resist. It’s like someone else said earlier. Our chemistry experiments are not sensitive enough nor efficient enough to be concerned with the maximization of thermodynamics of our chillers and their efficiency.

 

[rburrelli]

RDWHAHB. Why do we even bother concerning ourselves with such technicalities?

 

[burntchef]

I wound my own copper emersion chiller. I toasted myself for noodling that the water should enter at the top, and exit from the bottom. Beyond that, cold flow good, hot flow bad.
Eric

 

[bracconiere]

unless your tap water is really expensive, and your asking how much heat CAN you get out of least amount of water....i agree with everyone else more better....

if i was a rich man and had a pump and counterflow, i'd probably just max the water flow, and dial the pump for wort to pitching temp into fermenter....

 

[odie]

I run it pretty slow so that the water coming out is plenty hot. I don’t like to waste water. It drops pretty fast for me. Stirring helps a lot. The idea is for the cold water to absorb the heat. A slow to moderate flow works fine for me