Author Topic: Energy required to heat milk  (Read 332 times)

Online Alpkäserei

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Energy required to heat milk
« on: April 30, 2014, 10:16:11 PM »
I am designing my vat heating system.

Here is my scenario:

I will have a free-hanging copper vat that is suspended over a heat source.
I need to determine how much energy this heat source must put out (BTU's, for example) in order to easily achieve the proper heating curve associated with my recipes.

So that said, I need to know what the energy required to raise a gallon of milk 1 degree in temperature is,
I need to figure how to transfer that into the output of a heat source
I also am not sure how to figure the output of a heat source

I may simply use a gas burner,
But I would like to use a fluid heat transfer system.

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Offline Sailor Con Queso

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Re: Energy required to heat milk
« Reply #1 on: May 01, 2014, 08:43:05 AM »
I use a 70 gallon poly stock tank heated with hot water heating elements as my water bath. I use a 142 quart stainless stockpot with batches of 30 gallons of milk. I initially fill the tank up manually with hot water say 100F and the milk will be around 40F.

So, thinking out loud, if I fill the tank up to the 65 gallon level after the milk pot is in place. That would be 30 gallons of displacement for the milk and 35 gallons of actual hot water. So the average fluid (water & milk) temperature would be (35/65)x100 + (30/65)x40 = 72.3F. Let's say 72F. I am trying to decide on the size and number of heating elements. The 110 v 1500W elements are easier to deal with for controllers but do not heat fast enough.

It takes one BTU of energy to raise one pound of water, one degree F. Assuming water & milk are both 8.5 lb/gal So 65 gallons x 8.5 = 553 pounds. It will take 553 BTUs to increase 65 gallons by one degree.

For an electric heating element 1 kw/hr = 3413 BTUs. Obviously, this assumes 100% of the energy goes to heating the water and none of it is lost.

A 1.5kw produces 5119 BTUs/hr. So 5119/553 = 9.25 degree rise per hour
From 72F to 90F = 18 degree rise or about 2 hours to heat to rippening temp. Too long

Two 1500w would give 18.5 degrees per hour. One hour for “make ready”, but probably too slow for heating to 125F for thermophilics.

A 4500w would give 27.75 degrees per hour or about 39 minutes to “make ready”.
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Online Alpkäserei

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Re: Energy required to heat milk
« Reply #2 on: May 01, 2014, 10:08:42 AM »
Milk has a range of weights, we usually figure 8.63 pounds per gallon. It varies based on solids content. Butterfat is less dense than water, protein is more dense, minerals are more dense. Grass fed milk can push above 8.7

When figuring for a heat source without direct contact, our heat loss is going to be high. So I figure I need a heat source 2 to 3 times larger, at least, than what would be used if we had a direct transfer.

What I am looking at doing is to build a boiler that instead of water heats a heat transfer fluid that remains liquid at a very high temperature, such as motor oil which boils at nearly 600 F. This fluid is run through a coil located directly under the vat, with a reflector mounted under the coil, so the vat is then heated by means of convection and radiation (replicating having an open flame under it) Obviously the closer the heat source, the less of the heat is lost through radiation. Having a copper vat will also be a great help due to its high conductivity.

So really what I am after is how hot I will need to run this liquid, and how big of a coil I will need to construct, and also the proper positioning of the coil relative to the vat. 
I can always experiment with fluid temperatures later.

Plan B is just to use a gas burner.




« Last Edit: May 01, 2014, 10:52:15 AM by Alpkäserei »
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Offline jwalker

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Re: Energy required to heat milk
« Reply #3 on: May 01, 2014, 11:01:20 AM »
That's a very interesting and ambitious plan A , could be very costly as well.

Every time you convert energy from one form to another , or exchange heat from one medium to another , there is going to be a loss that will be costly and have to be accounted for , not sure what the advantages to a system like that would be.

You would also have to take into account the ammount of oil in the system (reservoir) , the diameter and thickness of the coils , the heat loss during circulation of the oil , and the GPM's needed to circulate the oil , I would think a circulation pump would be necessary as well.

I would personally think that the Plan B would be more efficient as well as cheaper , calculating the size of a gas burner needed would be very simple , just go bigger than needed on the burner and adjust gas as necessary , until you find what works.

But if you go thru with the first one , be sure to post it here , it would be interesting.
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Offline Sailor Con Queso

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Re: Energy required to heat milk
« Reply #4 on: May 01, 2014, 11:31:51 AM »
Go with the gas burner and build a methane generator to use waste from your herd.
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Online Alpkäserei

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Re: Energy required to heat milk
« Reply #5 on: May 01, 2014, 11:36:47 AM »
The advantage of plan A is

I can use wood for heat

wood is free

I live in a woods

I'm also a timber frame and log carpenter

Wood is free. I have lots of wood.

I want to design a system that allows me to use wood, but satisfies state legal code for cheese make rooms -which means I can't use direct wood heat.
I also want to use the free-hanging vat rather than a jacketed steam or hot water vat. This is because I plan to have an exhibition cheese operation where people can look at it, and I am really trying to replicate the Alp methods. Also I learned how to work in such a vat, I know the tricks and get get precise results in such. I want to work with what I know.
And then there is the romance of the idea of using the old style of vat.

So I am willing to sink some money into a system that will allow me to make use of my free heat source and let me use my hanging vat.

I am trying to work out the kinks right now, working on the concept of a high efficiency condensing boiler system (where the heating coil first passes through the exhaust flue to absorb waste heat)  with a ballast tank before the furnace -basically a vented reserve tank to regulate temperature and pressure.
My thought is to drop the oil temperature on the input side of the furnace, yes this will drop efficiency but again fuel is free. What this will do is create a greater heat imbalance throughout the liquid, which will increase the natural convection of the fluid. The higher the coefficient of difference, the greater the draw by convection will be. I'd like to optimize the whole system to eliminate the need for a pump. Also having a tank of cool liquid on one side of the system will help to ensure convection goes in the direction I want it to. Again, I have to create a system as out-of-balance as I can.
Some aspects are inefficient, like dropping the oil heat as much as I can before reheating. So I am trying to make up the difference by using a higher efficiency boiler system.

I would also place a bypass valve inline before the radiator coil, this would allow me to effectively shut the heat off on demand by sending the hot oil through another pipe, giving me more rapid control of the process. I feel this is safer than simply having a stop valve. There would also be a regulator valve allowing me to have some control of flow rate. I would install some kind of limiter on this valve so that it can never be completely shut. I want to prevent overheating my fluid, especially if it is something like oil.

The propane burner is simple and easy. But last winter LP got over $6 a gallon, and there was a shortage of supply around here (-20 degrees for 2 or 3 weeks, 30 mph winds...) This would be expensive over the long term but is a suitable temporary solution.

The methane generator is also a consideration. I will have a lot of input material for this and have explored the idea. I hope to build one in a few years to supply all my heating, cooking, and hot water needs. Also perhaps a limited amount of 12V power.
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Online ArnaudForestier

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Re: Energy required to heat milk
« Reply #6 on: May 01, 2014, 12:20:24 PM »
Alp, just checking in - you won't be using direct wood heat, but plan to use direct heat?  I ask, because our regulatory people will begrudgingly allow copper with a variance (because two industrial makers in our state use copper already, hard to turn me down), but are digging their heels in at direct fire - concerns of local leaching due to the concentrated heat.  I think I can win this fight, because there's actually nothing in the books as far as I can tell, dictating heating method (so, if it ain't covered, you can't deny it...though from my experience with other makers winning battles along these lines, winning the battle may invite more regulatory, er, zeal than one might wish, down the road). 

Have you run all this by your inspector?
- Paul

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Re: Energy required to heat milk
« Reply #7 on: May 01, 2014, 12:34:42 PM »
Yes I have been in constant contact with the State, working on the top end. So far they have been agreeable to what I have passed before them.

As for copper, they were satisfied it is safe since I could guarantee a neural (above 6) pH the entire time the cheese was in contact with copper.

I mentioned using a gas burner, they had no problems. Their only concern is with odor and that if a flame is naked, it be clean burning. -The same concept as applied to cooking ranges-

I can't use direct wood heat, because it is considered dirty and unsanitary. So plan A is indirect wood heat with a transfer fluid.

Note here: direct wood heat would involve an open flame under the vat, as per Alpine methods. Even though there is a loss of efficiency when transferring heat, the overall system would be more efficient, since and open fire is very inefficient. With a carefully designed boiler I will be able to extract more calories from the wood than I would be able to with a direct fire, since very little heat exits as exhaust.

I also have modified my design so that in line past the radiator coil is a second heat exchanger for heating water. I haven't decided whether to use a water tank, or an on-demand system.

Eventually, I may install a methane burner so that if I have a good system, I can keep my setup when I am running my digester.
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Online Alpkäserei

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Re: Energy required to heat milk
« Reply #8 on: May 01, 2014, 12:48:30 PM »


Here is a basic diagram of the system

I have drawn in a pump on the holding tank, if it is needed.
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Re: Energy required to heat milk
« Reply #9 on: May 01, 2014, 12:51:21 PM »
Cool, glad to hear it, Alp.  Getting them early is so much easier than getting them late, which I'm sure you know and sounds like you're doing.

BTW, had a long and very useful talk with Matthew Brichford.  For others who don't know, he's in dairy Tarentaise, an absolute rarity in the United States, as well as Abondance and Normande cows.  French folks went to his place, tried his Everton, and proclaimed, "why, this is Beaufort!" Sweeter approbation, I couldn't imagine.

French TV actually came to his place in Indiana, and did a nice spot on what they're doing.

Edit:  Awesome design!
« Last Edit: May 01, 2014, 12:59:37 PM by ArnaudForestier »
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Offline jwalker

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Re: Energy required to heat milk
« Reply #10 on: May 02, 2014, 07:28:43 AM »
Yes , free fuel is a big advantage. ;D

If you have lots of wood , check these out as well , http://www.tinytechindia.com/steampowerplan.htm , all you need to do is produce some steam.

They have complete systems up to 10 KVA , including boiler , steam driven engine and generator head , pretty affordable too , then one could use an electric burner under the Kettle , and wood to produce the electricity.

Just a thought , watch the videos as well , they're very interesting , in fact , you could run your entire operation on one of these , lights , electrical , etc. , talk about efficiency .

I was surprised at how affordable they are.
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Re: Energy required to heat milk
« Reply #11 on: May 02, 2014, 11:36:30 AM »
If I am going that direction, I might as well just build my digester
Which I might, I am just exploring different options
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