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Thread: Capacity calculation
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01-07-2006, 05:57 PM #1
Capacity calculation
How do I calculate the needed capacity to cool 5000 kg/h vegetables in a cooling tunnel from 20°C to 1°C with a time in the tunnel of 6 minutes?
5000 kg/hx 0.8 cal/kg°C x 19Kbut what about the latent heat?
It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.
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01-07-2006, 06:28 PM #2
Re: Capacity calculation
5000kg/h = 500kg per 6 minutes so your calc should be for 500kg (the actual load in the tunnel at any one time.
The latent process can be ignored as you are not going below freezing (phase change)
So, your calc should be
Q = m x C x dT all divided by the time is seconds and chilling factor.
What vegetables are they Peter?
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01-07-2006, 06:40 PM #3
Re: Capacity calculation
Originally Posted by Peter_1
No allowance for air change or infiltration in that.
Probably a 125kW tunnel and plant, giving a good safety factor
Kind Regards AndyIf you can't fix it leave it that no one else will:rolleyes:
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01-07-2006, 11:15 PM #4
Re: Capacity calculation
I explained/translated it the wrong way I see now.
It should have been respiration heat, due to the fact that vegetables are a living metabolism and produce heat, other then meat.It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.
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01-07-2006, 11:20 PM #5
Re: Capacity calculation
Originally Posted by Peter_1
Have a revision look in Dossat.
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01-07-2006, 11:24 PM #6
Re: Capacity calculation
Using a chilling factor of 0.85 I get 114.8KW. Add to that a safety factor and I agree with Andy's suggestion of 125kw.
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01-07-2006, 11:27 PM #7
Re: Capacity calculation
See once this link http://www.agr.gc.ca/cal/epub/1532e/1532-0026_e.html
It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.
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01-07-2006, 11:40 PM #8
Re: Capacity calculation
Thats alright but you are talking about 6 MINUTES so I think you can ignore it
the following was taken from your link
he longer the time required to cool the produce, the greater the total respiration heat.
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01-07-2006, 11:52 PM #9
Re: Capacity calculation
Hi, Peter_1
Originally Posted by Peter_1
Best regards, Josip
It's impossible to make anything foolproof because fools are so ingenious...
Don't ever underestimate the power of stupid people when they are in large groups.
Please, don't teach me how to be stupid....
No job is as important as to jeopardize the safety of you or those that you work with.
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02-07-2006, 07:59 AM #10
Re: Capacity calculation
Thanks all,
I need to use figures which are correct.
It's for the case with the potatoes cooling tunnel.
I had a small problem with the HD in my head
I had a table which gave BTU/lb and thought there was something wrong with it and I see now that should have been BTU/lb/hour.
Is following calculation then correct if I count the load per hour
5.000 kg/hour (11.023 lb/hour) entering at 20°C (68°F) and leaving at 1°C (33.8°F), specific heat of 0.8 and a respiration heat of 0.028 kcal/kg°C (or 0.028 BTU/lb/hour)
gives (5000 x (20-19) x 0.8) + (5000 x 0.028 x 19) = 76.000 kcal + 2.660 kcal = 78.660 kcal or 91 kW + eventually additional load like Andy said for the fans but the motor of the fans are outside the tunnel and the fanblade itselves is connected to the inside via a long shaft/rod on the motor.
Or (11.023 x (68-33.8) x 0.8 ) + (5000 x (68-33.8) x 0.028 = 301589 + 10555 = 312144 BTU/hour)It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.
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02-07-2006, 10:58 AM #11
Re: Capacity calculation
Hi, Peter_1
Are you sure you can cool 5000 kg of potato from 20C down to 1C in one hour
Maybe I miss something
http://www.uidaho.edu/ag/plantdisease/pstore.htm
http://www.uidaho.edu/ag/plantdiseas...re.htm#anchor4
Best regards, Josip
It's impossible to make anything foolproof because fools are so ingenious...
Don't ever underestimate the power of stupid people when they are in large groups.
Please, don't teach me how to be stupid....
No job is as important as to jeopardize the safety of you or those that you work with.
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02-07-2006, 12:22 PM #12
Re: Capacity calculation
It are in fact fresh French Fries, at a rate of 5.000 kg/u. Tehy have to be cooled down to 1°C before packing.
It's a coninue line from raw potatoes till packed FF.It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.
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02-07-2006, 12:36 PM #13
Re: Capacity calculation
Hi, Peter_1
Originally Posted by Peter_1
Best regards, Josip
It's impossible to make anything foolproof because fools are so ingenious...
Don't ever underestimate the power of stupid people when they are in large groups.
Please, don't teach me how to be stupid....
No job is as important as to jeopardize the safety of you or those that you work with.
-
02-07-2006, 08:09 PM #14
Re: Capacity calculation
Peter,
You were asking for some comments on the load calculations. I see you are still working on the french fry cooling tunnel problem.
...for the fans but the motor of the fans are outside the tunnel and the fan blade itselves is connected to the inside via a long shaft/rod on the motor.
The fan motors will have some inefficiency, this is the heat that is produced by the motor. Since this is external to the tunnel this heat does not become part of the refrigeration load. This is normally about 15-20% for small motors.
The remaining energy is used to turn the fan blades. Since the fan blades are inside of the cooling tunnel, the majority of the energy used by the motors is absorbed by the air.
Does this cooling tunnel also have an exhaust fan to remove the CO2 or nitrogen ( I forgot which one you were using) from the tunnel. The volume of air this fan moves could also be considered part of the cooling load (at least as far as the cyrogen is considered).
You will also have some air cooling load that enters the tunnel. This might be part of the exhaust fan volume flow, I'm not sure what you have.
Also, the respiration heat is based on Energy/Mass-Time. So in IP units, you are looking at Btu/pound-time (the time rate could be minutes, hours, or 24 hours).
In your calculation you show:
(11.023 x (68-33.8) x 0.8 ) + (5000 x (68-33.8) x 0.028 = 301589 + 10555 = 312144 BTU/hour)
If the respiration heat is 0.028 Btu/lb-hr, then you should be multiplying 11.023 pounds X 0.028 Btu/pound-hr to get 308.6 Btu/hr. The pounds(mass) cancel out each other, so you are left Btu/hr.
If you multiple 11.023 pounds per hour X 0.028 Btu/pound-hr X dT the units get scrambled up into something that does not makes sense. (Btu-F/hr)
Does that help?Last edited by US Iceman; 02-07-2006 at 11:19 PM.
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02-07-2006, 08:19 PM #15
Re: Capacity calculation
Corrected givest his:
5.000 kg/hour (11.023 lb/hour) entering at 20°C (68°F) and leaving at 1°C (33.8°F), specific heat of 0.8 and a respiration heat of 0.028 kcal/kg°C (or 0.028 BTU/lb/hour)
gives (5000 x (20-19) x 0.8) + (5000 x 0.028) = 76.000 kcal + 140 kcal = 76.140 or 88.5 kW + eventually additional load like Andy said for the fans but the motor of the fans are outside the tunnel and the fanblade itselves is connected to the inside via a long shaft/rod on the motor.
Or (11.023 x (68-33.8) x 0.8 ) + (11.023 x 0.028) = 301589 + 309 = 301897 BTU/hour
Im' busy with the report this Sunday. Already 35 pages.It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.
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02-07-2006, 11:23 PM #16
Re: Capacity calculation
Hi Peter,
The last post you made I agree with. You should also add any additional motor power input to the load calc.'s, i.e., conveyor, etc.
Good luck with the report.
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