Impingement air cooling/freezing on belt
Impingement air cooling/freezing on belt
(OP)
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
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
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





RE: Impingement air cooling/freezing on belt
Ken
Ken
KE5DFR
RE: Impingement air cooling/freezing on belt
"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
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
RE: Impingement air cooling/freezing on belt
Ken
Ken
KE5DFR
RE: Impingement air cooling/freezing on belt
This statement, which you have made twice, really gives me pause:
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
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RE: Impingement air cooling/freezing on belt
we have designed the first system and it works sufficiently (3rd time
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
RE: Impingement air cooling/freezing on belt
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
------------------------------------
there's no place like gnome.
RE: Impingement air cooling/freezing on belt
Thank you for your efforts.
Kind regards
virk
RE: Impingement air cooling/freezing on belt
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:
h
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.
RE: Impingement air cooling/freezing on belt
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
RE: Impingement air cooling/freezing on belt
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
RE: Impingement air cooling/freezing on belt
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
------------------------------------
there's no place like gnome.