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work on the following:
Mass to be frozen = 30.5 Metric Tons
Product = fish Fillets
I know it is difficult to catch only one species but the specific heat depends on the type of fish.
I’ll suppose 101 W/kg from +10° to -18°C.
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Freezing time per day = 3hr + 15min for loading and unloading
Time depends on many factors and you don’t give any information to make assumptions. So freezing time is something you will have to determine.
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From this it worked out to be 8 cycles per day.
The weight that will be frozen at each cycle will be 3813kg/cycle.
So I will require 5 x 30 stations plate freezers (vertical plate freezers).
My refrigerant will be Ammonia that will enter the plates at -18C and the fish is +10C.
So far OK. This gives me 3813 kg/cycle x 101 W/kg = 385 kW
for 30 stations => 12.8 kW/station.
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From what I calculated (which I know I made an error somewhere but do not know where) I get a total refrigerant capacity of 47.21kw. For 1 x 30 station.
The plate freezers will have headers.
According to the suppliers specifications for ammonia the pump circulation rate will be 67 litres / Hour per 1000 K Cals.
I posted all my calculation so that all can help and check if they are correct.
According to this 385 kW = 331 (1000 kcal/h) * 67 Liters/h (1000 kcal) = 22177 Liters/h =22.2 m3/h
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How will I know if my refrigeration capacity is adequate enough?
Density of ammonia @ -38°C saturated = 688 kg/m3
Enthalpy of vaporization = 1383 kJ/kg
1h = 3600s
So 22.2 m3/h x 1/3600 h/s x 688 kg/m3 x 1383 kJ/kg = 5568 kJ/s = 5568 kW > 331 kW
This means that you will evaporate only 1/16.8 th of the pumped liquid or 1318 Liters/h.
You have more than enough capacity.
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And how do I calculate the pump circulation rate as the litres / Hour per 1000 K Cals confuses me.
, because i know how to convert kW to kCals/h.
1. Just want to correct something, the product Temp in is +10C and after the freezinf the core temp must be -18C. The evaporating Temp -38C.
It confuses me too: the units are not correct and these numbers are not usual for a plate freezer.
The only person that can assure how to do the calculations is the manufacturer of the plates or its rep.