Impingement air cooling/freezing on belt 1

[virk]

Hello!

Above a belt of about 20m length and 2 m width we will install an impingement cooling "system" with cold air for to cool down the product being transported on this belt.
We already installed one of these systems successfully, so there is already some experience.
I want to learn more about this process in order not to oversize next system too much Maybe somebody of you can give some hints to literature, companies, etc.

Especially I would like to know somewhat more about the sizing of the channel where the "used" air has to disappear. My literature (VDI-Wärmeatlas, German) does not inform sufficiently.

Any hints welcome!

Kind regards

virk

 

[TXiceman]

There are a lot of parameters that goes into a blast cooler design. Air velocity is a major item. There are tables published on cooling of food products in blast coolers. Other wise, it is best to test a new product and determine at what velocity and air temperature you will obtain the optimum cooling.

Ken

Ken
KE5DFR

 

[virk]

Thank you Ken for your statement:

"There are a lot of parameters that goes into a blast cooler design. Air velocity is a major item."

Yes, we know about that. Maybe there is somebody out there with a hint...

"There are tables published on cooling of food products in blast coolers"

...to these tables etc.

"Other wise, it is best to test a new product and determine at what velocity and air temperature you will obtain the optimum cooling."

Of course it will be a test installation But if it works, nothing will be changed with this installation. So I need additional information/point of view for to ensure that this "test installation" will 1st work sufficiently and 2nd be not oversized to much.

As I already wrote, we already designed one of these systems, but do not know how it works but only know that it works sufficiently.

So, if there is any info available kindly let me know!

Kind regards

virk

 

[TXiceman]

Some of the companies that manufacturer the coils and air units for the freezers and coolers have test data from previous experiments that they had run. I know Krack Corp. used to have a lab that they would actually run cooling/freezing test for customers if they provided all of the test material. All of the old timers are pretty well gone, but the information should still be there. You might try contacting Chuck Koran at Krack.

Ken

Ken
KE5DFR

 

[vpl]

virk

This statement, which you have made twice, really gives me pause:

As I already wrote, we already designed one of these systems, but do not know how it works but only know that it works sufficiently.

It would seem your best place to start to get the information you need is with those in-house people who designed your original system.

Otherwise, there does not seem to be enough information here for anyone to help you. Besides the important air velocity, parameters such as the speed of the belt and the initial and final temperature of the components being cooled also are important.



Patricia Lougheed

Please see FAQ731-376 for tips on how to make the best use of the Eng-Tips Forums.

 

[virk]

Patricia,

we have designed the first system and it works sufficiently (3rd time). Now I want to get more information about why it works sufficiently and how to improve it, make it cheaper and less energy consuming. (We do not have access to the running system)
I do not want anybody to calculate anything, this is why I did not feed you with more accurate information. I have literature which was written by "Holger Martin" in the 70th. So my question is whether anybody has any information besides this.

Thank you

virk

 

[magicme]

we used impingement cooling inside turbines.
the effects of "spent" flow (or "crossflow") are significant.

an important paper(maybe the best) is:
Steamwise flow and Heat Transfer Distributions for Jet Array Impingement with Cross Flow, by Florschuetz, Truman, Metzger, ASME, 1981. (specifically equations 11a and 11b)

also

Effects of Crossflow on Impingement Heat TRansfer, by Metzger, Korstad (Journal of Engineering for Power, 1972)

also

Multiple Jet Impingement Heat Transfer Characteristics...etc...etc, by Florschuetz, Metzger, Takeuchi, Berry (NASA Contract Report 3217, 1980)


also

Heat TRansfer by a Square Array of Round Air Jets Impinging...etc etc, by Kercher, Tabakoff (Journal of Engineering for Power, 1970,


that should overload you with info... (hope it helps)


magicme


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there's no place like gnome.

 

[virk]

Dear magicme!

Thank you for your efforts.

Kind regards

virk

 

[magicme]

virk

i took this question a step further, and added impingement to my class notes (which i have wanted to do for years!)

this is a simplified version of the first paper that i quoted here, but it will get your first calculations in the ballpark.
i would NOT design critical parts to this, because i simplified the cross flow effects (to introduce students to this topic).

anyway .... i put my notes here:

http://myweb.wit.edu/leod1/MECH594/Impingement.html

and if you can't get the ASME paper i quoted, at least you may have a ballpark number.

regards,

magicme




------------------------------------
there's no place like gnome.

 

[virk]

magicme

Thank you for your link. I will work through it within the next days and also make an spreadsheet of your equations, after I have understood what they are telling me

Kind regards

virk

 

[virk]

Dear magicme

One further remark. I had a first look at your link. The "air" speed through the holes in your table seems to be quite high. Do you really trust these high velocities. In my calculation your much higher than sound speed at these large Reynolds numbers.

Kind regards

virk

 

[magicme]

virk

i wrote that yesterday and threw some numbers in there to get the spreadsheet running. in fact, i am still writing up that topic (just added more stuff this morning, if you check the web page again).

regarding the velocity ... note that the mass flow rate per hole (mdot) is a user input value. this is actually driven by the applied pressure drop across the impingement hole plate. in this case, i just dropped a number in for mdot and did not check what the velocity through the holes would be.

you must definitely use realistic numbers, and remember that this is compressible flow thru those holes, so the flow-pressure relation must account for compressibility. i glossed over that issue as well.

the acid test is after my students get it and find another dozen "glitches" that i missed !!

regards

magicme



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there's no place like gnome.