Overall Heat Transfer Coefficient In Pasteurizer/Heat-Exchanger

For a project like this, I would approach a few heat exchanger mfrs, who are likely to have software and expertise for close calculation of such coefficients. (And who can offer guarantees of performance.)

Can you really chill milk to -2ºC without freezing it?

I think there are enough solutes in milk to cover that, as long as the decimal is moved one place to the left:

degrees C Horvet standard (undiluted) milk

The general herd bulk tank standard is -0.505 °C (-0.525 °Horvet)

Milk that freezes at -0.2 °C has officially been declared as diluted milk product.

I suspect that if cooling to -2.0 °C, the intention is to produce ice cream.

For pasteurization and cooling refer to the link below, I am surprised if you did not already find substantial information on the internet about this topic.

heat transfer calculations

you are right at that border, When I was on the farm, if we had problems with the bulk milk cooler where the temperature dropped below 32 F, it depends on the component content I mentioned earlier. But keep in mind the milk fat, freezing the fat globules rupture the cell walls, giving it an off texture as well as taste..

Yuck!

that is a disappointment...

going off topic slightly, the biggest issue we had when we upgraded our milking equipment was getting air in the milk. Not many can notice it, but for me it tasted somewhat rancid, but it wasn't.

(2) ways to advert it,

• inspect to see what the cause is.
• or put in a deaerator, the diary receiving plant usually does this with the deaeration.

We found that the problem was, it was when we purged the lines after we were done milking at that shift, someone (my brother) was too aggressive when that happens, (transfer lines were under about 15 hg/in vacuum) and we reduced that and changed the procedure.

of course in a dairy plant, the milk would have went through an homogenizer first, but still.

Approaching manufacturers of heat exchangers for sterile use directly would be a better use of time than waiting for <...CR4 members...> who are <...masters in milk dairy industry...> to respond. Better than that, these manufacturers have telephone numbers that one can use to get immediate, industry-specific information, whereas <...CR4 members...> don't.

The manufacturers will need to know details of the heat transfer fluid(s) involved and the approximate pipe sizes, which details have been withheld from the forum.

This is an iterative process.

Start making the calls!

that is not really required to know for designing pasteurization, You send the information to the people you are getting the HX plates from to do the calculations. Because you have to do that anyways... I have the thermal properties of milk somewhere, but I'd have to do some really deep digging.

I do not know the sanitary standards you are using. I have used the standards set forth from USDA-3A regulations.

Its based on time and temperature and basically is...

• Lower Temperature >>> Longer time
• Higher Temperature >>> Shorter Time (HTST) this is what we normally use, I'm not going to get into Flash pasteurization.
• Now pasteurizers are based on lb's/hour so basically volume. such as 10,000lb/hour to over 100,000 lbs/hour
• What it is, you heat the milk up to 160 degree F (Minimum, you may have to heat this a little higher to make up for the losses., also milk is heat sensitive, and the sugars will start changing state as it nears 180ºF, even before then )
• and pass it through a holding tube that since you have the milk metered with a mass flow recorder, you have a RTD recording the temperature on the inlet and outlet of the holding tube. 165ºF inlet, you know with the flow the of the milk it will take 15 seconds to flow through the holding tube and then you have a RTD on the outlet to record the temperature of which it has to be at least 160ºF for it to continue on as pasteurized milk. if it's less 160ºF it get diverted back to the balance tank to run through the system again.

Also regeneration of heat of your pasteurized milk is another thing to save on utilities. but that's another topic.

I have this for about 25 years... pretty interesting for a basic knowledge.

one more thing with your requirements of;

should not go above 90 Deg.C and chilling is to -2 Deg.C

You have to keep in mind that if this is raw milk,... the butterfat content will affect thes temperature. the high the butterfat test, the more heat sensitive it is, and 90 Deg C is high for this on a high test BF batch.

For the last 30 years, dairy processing plants have been trying to standardize the milk, Which is very difficult due to during a cows lactation. In the early lactation the milk output in volume is high, the BF is lower as opposed to the cows nearing the end of their lactation period.

as far as -2 Degrees C., Why? Where did this come from.

http://www.eng-tips.com/viewthread.cfm?qid=173817

seems to have the properties you need to design a heat exchanger/piping system for what you need to do. There are several other sites if you google Thermodynamic Properties of Milk.