Help with calculations for counterflow chiller

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rustico_brewing

New Member
Hello everyone! Hope everything is going well. So i have been trying to design a counterflow chiller that can cool 15 gallons of boiling wort to yeast pitching temperatures (around 16 degrees celsius or 60.8F) in as little time as possible. What i am trying to figure out is how long the chiller has to be, and according to the calculations I´ve made using 10 degrees celsius (50F) water going at 5 gallons per minute and wort flowing at 1 gallon per minute. The chiller length ends up being around 5.39 meters or approximately 18 feet. What Im not sure is that is possible or makes any sense for the application that i am trying to design it for it, just seems too short. So what i´m trying to get help with is any resources that could help me get the calculations for the counterflow chiller or to somehow check if all my data is correct because i am pretty lost.
The heat transfer necessary for this process is approximately 16.69kW or 56948.6 BTUs.
I used these two websites for reference:
http://brewlikeapro.net/heatexchangers.htmlhttps://www.pdhonline.com/courses/m371/m371content.pdf
any input would be greatly appreciated! thank you very much in advance
cheers

For an objective of 'in as little time as possible', the answer is infinite length.

If your goal is maximum efficiency, a plate chiller is far more effective

Otherwise you need to account for the decreasing rate of heat transfer to the cold water as the wort cools down, and for the recovery time of your cold water supply, and for whether you will do a single pass or recirculate back into your kettle.

Simply wanting to chill as fast as possible is a noble goal, but you need to account for your actual needs and constraints. Why is time your driving factor? Is it really the only thing that matters?

LMTD (log mean temperature difference) is used to calculate counterflow exchangers.

LMTD = (greater temperature difference - lesser temperature difference) / ln(GTD/LTD)

Q = U *A * LMTD

Q = heat transfer rate
U = overall heat transfer coefficient (300 is a good starting assumption)
A = heat transfer area, pi * D * L
D = diameter of inner tube
L = length of inner tube

Also Q = W * C * delta T = w * c * delta t, if you need to find cooling water outlet temperature for LMTD
W, w = flow rate, lb/hr
C, c = heat capacity (1.0 is a good value to use)
T, t = temperature
Upper case = hot side, lower case= cold side

LMTD (log mean temperature difference) is used to calculate counterflow exchangers.

LMTD = (greater temperature difference - lesser temperature difference) / ln(GTD/LTD)

Q = U *A * LMTD

Q = heat transfer rate
U = overall heat transfer coefficient (300 is a good starting assumption)
A = heat transfer area, pi * D * L
D = diameter of inner tube
L = length of inner tube

Also Q = W * C * delta T = w * c * delta t, if you need to find cooling water outlet temperature for LMTD
W, w = flow rate, lb/hr
C, c = heat capacity (1.0 is a good value to use)
T, t = temperature
Upper case = hot side, lower case= cold side

In which unit is Q expressed as? Does the value for U = 300 apply for stainless steel tubing of any thickness? Again, which unit?

Thanks a lot for the equation, I'm trying to figure out if I can use a shotgun condenser as a wort chiller for small batches.

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