Blast cooler

[Bob45]

Hi,

I need help on this one.

I'm putting in a blast tunnel to cool down some body cream from 70°C to 20°C in 30 minutes. The cream is in jars of 5" diameter by 1.75" high.

My concern is how can I determine the temperature that I should keep the tunnel at. Should I keep it at 10°C or lower

Thanks for your help

[US Iceman]

Hi Bob45,

The easiest method that comes to mind is to use a scraped surface heat exchanger to cool the cream before it is put into the jars.

Here is a link you can review for how these work.

http://www.spxprocessequipment.com/s...otsshe_wcb.pdf

If the cream is cooled down to 20C, then injected into the jars the process might be easier to accomplish.

If the jars are filled and then cooled, the lower temperature you are using to cool the jar could conceivably cause the jars to form condensation on the outside. This might present a problem for the labeling wrapped onto the jars.

If the jars once filled are to be cooled down to 20C then the problem becomes one of how do cool this. The heat transfer is a transient conduction heat load as far as the jars are concerned. Initially the jars will reject a lot of heat due to the high temperatures (70C).

As the outside surface of the jar starts to cool, the heat rejection from the jars begins to slow down.

How fast does the customer want the jars cooled down to 20C?

[Bob45]

Hi iceman,

First thing, the customer told me cream has to go into the jar hot. So that I have to live with.

Then I have 40 minutes to cool down the cream. Which is very short. By what I have found on the web the only solution would be to do some test.

Customer is short on time, production is suppose to start in about 2 weeks.

Does anybody has listings of blast cooler or freezer specifing for different kind of product what should be my TD between product temperature and room temperature.

Thanks for your help and waiting for your reply. Hopefully you will have and answer or at least and idea for me

Robert

[Bob45]

Oh by the way this is a clean room to.

[US Iceman]

Hi Robert,

OK then. You have a real situation to sort out. First of all, 2 weeks does not leave hardly any time to get the refrigeration equipment. Hopefully a stocking distributor will have what you need. This has all the makings of an uphill battle and missed start up times.

Will the jars full of hot cream be placed on a conveyor belt and then run through the cooling tunnel? Are you intending to build the cooling tunnel out of commercially available products (wood, insulation board, or a commercial walk-in cooler structure)?

The main issue is how to cool a single jar from 70C to 20C in 40 minutes. Once we get that determined, the cooling load for the total jars per minute can be calculated. I suppose the client wants a guarantee on cooling time and temperature also, heh?

Cooling a single jar from 70C to 20C in 40 minutes will determine the lower temperature for cooling. If the refrigerated air temperature is not low enough, the jars will not be cooled sufficiently in the time span allowed.

This will require a lot of air flow over the jars with sufficient clearance between the jars for adequate air flow. A high velocity air flow is required to pull the heat out of the jars in addition to the lower temperature that needs to be found.

What is the weight of each jar?

How many jars per minute need to be cooled?

What is the jar spacing on the conveyor (if one is used)?

I just saw your last post. A clean room also????

The plot thickens...

[Bob45]

Yea a clean room. But just have to be carefull about the dust. This is a body cream, so can't get dust particule on top of it. But that is not drastic as such.

Ok for the rest.

1 Jar is 200 grammes. I took a specific heat of 0.85 btu/lbs*°F which should be acceptable since the cream is 70% water.

They will be feeding 40 jars/minutes so at the same time you will have 1600 jars in the room.

This will be on a conveyor 1 jars behind the other so air will be able to move on top, around and some on the bottom of the jar.

The cold room is going to be 20' x 9' x 9' with and entrance and an exit for the conveyor.

My load with the coolroom gain in heat and 50 cfm of fresh air to keep positive pressure in the room is approximately 115,000 btu.

For the question of delivery time and production start, this customer is always like that second time he does that to me. So he will have to live with the time frame. heh!

The conveyor will be coming in at about 3 feet from the ground and will go around and up to about 7 feet in the room than come back down to about 3 feet before going out.

My concern is. Sure I can bring the temperature down to 0°F but that will freeze the top of the product which is unacceptable so I have to keep my supply air at a minimum of 35 °F. with a TD of 10°F so room temperature of 45°F

But by doing so I don't know if it will be enough to bring the cream to the temperature desired.

I would like to get some kind of spec that would give me a hint about that so at least I can advise the customer up front.

Because like you know he will try to keep me responsable if it doesn't work even that I already advised him that I cannot guaranty the output temperature because there is no calculation possible and only testing would determine if it would work and I'm not equiped to do some testing and the time is to short.


Bob

[chemi-cool]

Hi,
take into consideration that if the jars are sealed when the cream is hot, it will be very difficult to open them later.

On the other hand, if you cool them with the lid open, you might get cream all over......


Chemi

[Bob45]

Hi Chemi,

Sorry, didn't specify, cover will be put on after.

Bob

Hi,
take into consideration that if the jars are sealed when the cream is hot, it will be very difficult to open them later.

On the other hand, if you cool them with the lid open, you might get cream all over......


Chemi

[Bob45]

About the cream all over I guess I'll have to be carefull about the distribution of air. Mind you the air will be travelling at approximately 250 f/m if you take in concideration the size of the room 9' wide x 9' high with approx 10,000 cfm from one end to the other and back

I do not see any problem about the speed of air.

Thank Chemi

Bob

[US Iceman]

The conveyor will be coming in at about 3 feet from the ground and will go around and up to about 7 feet in the room than come back down to about 3 feet before going out.

What is the diameter of the spiral belt? Do you have sufficient room fo rthe cooling coils and fan sections?

The retention time will be 40 minutes right? The first jar into the tunnel will be the first jar out in 40 minutes?

Whose blast cooler are you using? Have you asked the manufacturer what the expected cooling load might be? OR, is this a home grown project using a bunch of pieces that hopefully works?

This will be on a conveyor 1 jars behind the other so air will be able to move on top, around and some on the bottom of the jar.

Most of the surface area for heat transfer are the sides of the jars. The air flow should be directed to impinge on as much surface area of the jars as possible.

Do you have a sketch of the intended (or existing) construction of the tunnel? Hopefully showing the air flow direction.

so I have to keep my supply air at a minimum of 35 °F. with a TD of 10°F so room temperature of 45°F

How did you determine this? Will this guarantee a jar core temperature of 20C?

because there is no calculation possible

There are calculations for estimating purposes, but if the owner wants a guaranteed time and core temperature he is asking you to assume total responsibility, which I would not do in any circumstances.

For any idea of the calculations look in a heat transfer handbook for transient conduction heat transfer.

It sounds like you are basing your assumptions on steady state heat transfer.

[US Iceman]

The cold room is going to be 20' x 9' x 9'

Which dimension is the length and width of the room?

[Bob45]

Hi Iceman,

I lost track somewhere here. What do you mean by the diameter of the spiral belt? The jar is about 5" diameter and the conveyor is 5" wide. It will run in spiral in a cold room of 9' x 20' x 9' going up and back down to give it enough length so the product stays in 40 minutes.

And yes first jar in first jar out 40 minutes later.

Concerning the supply air and room temperature. My TD will be of 10°F on the evaporator, which will be a blast cooler evap not determined yet but probably an 8' wide evap with fans. The 35°F supply is more a guess because I have 2 concerned. Bring the temperature down but I cannot freeze the top of the product. So on the safe side air at 35°F will not freeze the top of the product. Concerning the guarantee of temperature at the end there is no guarantee, just a approximation but I like to give approximation that are as close as possible.

I have to keep high humidity in the room to prevent drying the product.

For the load calculation I use the Keeprite refrigeration book.

I'll probably supply them with a pre-fab cold room not determined yet, or they will build there own with my specifications of insulation and vapor barrier.

[US Iceman]

Another question for you: What are the jars made of?

Plastic, glass, or metal?

[Bob45]

Plastic Jars

Another question for you: What are the jars made of?

Plastic, glass, or metal?

[US Iceman]

What do you mean by the diameter of the spiral belt?

Sorry, my fault. I assumed the belt was a circular conveyor belt based on the use of the word "spiral".

If the jars are 5" in diameter and the conveyor is 5" wide, are the jars relatively captive in the conveyor? What I'm looking for is this: Will the jars be susceptible to being blown out of the conveyor if the air velocity is too high?

This is an interesting project...

[Bob45]

Well as far as I know by what I've seen on the conveyors they already use. Yes the jars would fly if you should supply to much air at the bottom and the cream would fly if you supply to much air on the top.

Sorry, my fault. I assumed the belt was a circular conveyor belt based on the use of the word "spiral".

If the jars are 5" in diameter and the conveyor is 5" wide, are the jars relatively captive in the conveyor? What I'm looking for is this: Will the jars be susceptible to being blown out of the conveyor if the air velocity is too high?

This is an interesting project...

[US Iceman]

I will spend a little time on this and see what I can come up with for a product cooling load in the 40 minute time frame allowed.

Check back later...

[Bob45]

I will spend a little time on this and see what I can come up with for a product cooling load in the 40 minute time frame allowed.

Check back later...

Hi Iceman,

Here is a little test I did with the cream this morning outdoor 50°F with slight wind.

Temperature test.JPG

[US Iceman]

Hello Bob,

Have not forgotten you.

I've run into some difficulties on my end for spare time at the present. If I can get to your problem over the weekend I'll have a go at it.

I did however want to respond back to you as promised.
I noticed on your chart that the core temperature reduction in the time frame would exceed the 40 minutes allowed.

Granted the air temperature was only 50F and the air movement was very minimal. Trying to project out the time to cool the core temperature would probably be in excess of 2 hours at this rate.

So this presents a case of how much airflow is required with the additional 15 degrees of temperature reduction (50F minus 35F air stated earlier).

At the present time I think the air velocity is the key ingredient. My starting point for this would be about 500 ft/minute.

To obtain reasonable results from the test, the jar should be rotated so that the entire surface area is exposed to moving air. I would try a fan to increase the velocity and re-run the test in the evening when the air temperature is colder.

My best guess right now is the air temperature might have to be colder than 35F.

I'll reply back when I have something more scientific. Sorry for the delay.

[Bob45]

Thanks Iceman.

And yes I was thinking of something around 500 feet/min to which I believe would make sense. And with the temperature droped to 35°F I believe that I won't be far from the result needed. Because If you look at the chart you can see a certain stability. After 15 min it's start droping by 6°F every 5 min and then to 3°F per 5 min. So I believe that if my temperature is at 35°F I could get a decrease of 6°F per 5 min for a longer period.

I a bit concerned about droping my temperature under 35°F this could create frost on top of the product at the end of the tunnel.

Mind you that by the test I've noticed to that and air flow of 500 feet/min when the product is hot and very liquid is ok. But once it get down to about 110°F the top is harder and could probably run more air on it.

Or what I could do is split the tunnel in 2 sections, first section running at 0°F or less, and second section runnin at 35°F with more air speed.

[US Iceman]

Bob,

They method I wanted to look at became more complicated than I have time to spare right now. If we look at this as a steady state cooling load, the product cooling load will be approximately 7 Tons based on a 40 minute pull down time. Or about 9 Tons with a 30 minute window. (I like the shorter time duration as this helps to build in some wiggle room; a fancy name for safety factor )

This is for the mass of cream being cooled only. The mass of the jars may be significant also. The jars being plastic add in a layer of resistance to heat transfer also.

With this you would also have the fan motor heat, fresh air load, and envelope load.

Is the operation of this system cyclical? Once started it continues to operate, or, does the system work for a while to cool off 1600 jars and then shut off for some undetermined time frame until the next batch of 1600 jars is ready?

Another part of the heat loads are the mass of floor (concrete or pre-fab panels), the mass of the wall and ceiling panels, and the conveyor itself. All of these contribute to the total cooling load. Their impact would of course be minimized if the operation requirements are constant. The mass of the building structure is a one time load, if the process is continuous.

Having said that my guess is the total load will end up around 15-20 Tons. This is a guess right now since there are still unknown requirements existing and this is a lot of supposition on my part.

If you approach this as a two temperature system (once for each of the two sections) I would recommend each system be capable of the providing the lower temperature. Let's say the total load is 20 Tons for a discussion point.

(Note: you may also need some capacity reduction ability for the compressors if the installed capacity is too great for the cooling load. You certainly don't want the compressor cycling or shutting off!)

Each system could be designed to provide 10 Tons at say 20F evaporating temperature with a 10 degree TD for the evaporators to limit moisture loss.

The evaporators should be selected for a large volume of air flow to achieve 500 ft/minute air velocity over the jars, but low velocity on the face area of the coil.

Each system could be operated at a higher or lower evaporating temperature depending on how the whole process works. Of course the compressor, condenser, and TXV's would also have to be selected for a range of operating conditions.

With the degree of uncertainty that exists with this problem the use of two identical systems provides a degree of flexibility to overcome unknowns.

If the system is designed to operate through a range of evaporating temperatures say 20 to 35F and you have two systems, this might provide sufficient latitude for adjustment of the systems to meet the operational requirements of the tunnel.

This is one of those problems that you need at least a week to develop properly. Hopefully our discussion will prove to be of some value to you.

[Bob45]

That ok Iceman,

Thanks for the time spent and the feed, I will work with that and I'm sure it's going make me think of stuff that I didn't think about.