Cooling Methods Flashcards
Commercial methods of cooling: (6)
Room Force air Hydrocooling Package icing Vacuum cooling Transit cooling
Describe room cooling:
produce in refrigerated room
cold air from ceiling -> cool produce
warmed air rises -> carries heat to cooling coils
repeat
What is important for room cooling to be effective?
proper stacking/spacing (use pallets) - need some airflow
advantages of room cooling: (4)
less handling
simple
moderate refrigeration load
moderate air flow
disadvantages of room cooling:
slow
If air flow is too fast, _____
If air flow is too slow, ______
fast -> dessication
slow -> longer cooling
What should air flow be in a cooling room, vs a storage room?
cooling: 200-400fpm
storage: 50-75fpm
True/False: There should be plenty of empty space in a cooling room
false; should minimize
but ensure good ventilation
What are examples of modified room cooling?
Ceiling jets (air from jets direct to produce - better circulation) Cooling bays (individually controlled rooms)
Forced air cooling is also known as _____. It is based on:
suction/pressure cooling
force high velocity cool air flow, using NEGATIVE PRESSURE
How does air flow differ in room vs forced air cooling?
room: air flow AROUND packages
forced air: air flow THROUGH packages (need ventilation slits)
What is an essential component of forced air cooling systems?
fans/blowers to pull air away, creating negative pressure and drawing more cool air through
“cold-wall” and “serpentine” coolers are examples of modified ____ cooling
forced air
increasing ventilation in a package will have the negative effect of:
decreasing strength
What is hydrocooling and what are the advantages? (3)
use water as cooling medium
better heat transfer than air (h)
no moisture loss
cleansing
Hydrocooling can be a ___ or ____ process, and can be a ____ or ___ system
continuous/batch
spray/immersion
Important considerations/limitations of hydrocooling: (4)
not good for packaged goods (unless water tolerant)
need clean water
produce should be Cl resistant (from water)
must transfer to cold storage quick
Important considerations for package icing:
water resistant package
drainage holes
cold environment
advantages of package icing:
fast cooling (vaporization + contact cooling)
tight packing OK
High RH -> less moisture loss
When was vacuum cooling developed?
1940s
How does vacuum cooling work?
vacuum lowers partial pressure of air (Pwa)
MUCH HIGHER WVPD -> bigger driving force for evaporation!
RAPID EVAP. of water (flashing) -> cooling + moisture loss
What happens to wet bulb temperature and wet bulb depression as the vacuum increases?
wet bulb: decrease
wet bulb depression: increase
As the vacuum increases, the boil pt. of water will ____. This results in:
decrease
flashing (rapid evaporation)
What are the basic components of a vacuum cooling system?
strong vacuum chamber (leak proof)
vacuum device (mechanical/steam injection)
condenser (water/coils)
What can be done to make vacuum cooling even more effective?
wetting of produce
Factors affecting vacuum cooling: (4)
surface area
porosity
degree of vacuum
water availability
Vacuum cooling systems are best suited for: _____, and are (low/high) cost.
produce with large SA:volume ratio
high