Lecture 8: Cold Storage Systems Flashcards
what components must be controlled in a storage system?
temp RH air velocity air composition insulation refrigeration capacity
simple systems are used for what?
ventilated storages (for potato, carrot, dry onion)
what do simple systems take into account?
insulation
air circulation
ventilation
simple systems uses what atmosphere storage?
RA storage = regular atmosphere storage
what needs to be taken into account for complex systems?
insulation air tightness vapor barrier price control of temp RH air comp
what are examples of complex systems?
CA storage
hypobaric storage
separate storage chambers for each produce is ideal but not practical. What is more common instead? What must be taken into account?
- mixed loads
- compatibility of temp, ethylene, RH, odor
what should be used to estimate quality loss?
Q10 concept
temp fluctuations should be what?
why?
low +/- 2C
b/c large fluctuations means a loss of quality
warm produce coming in contact with cold air results in what?
- dessication, if air is not saturated
- produce sweating, if air is saturated
warm air coming in contact with cold produce results in what?
- dessication if WVPD is positive
- condensation if WVPD is negative
adequate refrigeration capacity should be able to handle ____ and ___ loads
normal and unexpected loads
how can storage life of incoming commodities be maximized?
by precooling incoming produce to storage temp
storage life of all commodities will be at risk when….?
warm products are brought in. This causes large temp fluctuations and product warming
if the refrigeration capacity is undersized, what occurs?
- slow cooling
- product warming
- large temp fluctuations = larger quality loss
why should refrigeration capacity not be oversized?
more expensive
refrigeration temp should be close to _____
why?
room temp
what kind of cooling surface area of cooling coils is best?
larger surface area = more efficient heat transfer
what can be used to increase surface area?
fins
why is good air velocity important?
for proper temp distribution
at high flow rate, dessication occurs
at low flow rates, improper cooling occurs
thus, moderate rate is the best
why is adequate thermal insulation imp?
prevents heat gain from walls, doors, floor, etc…
how can moisture loss be reduced?
- having a smaller temp diff between coil and air
- smaller temp fluctuation
- humidifying air externally using special technique for storage: jacketed storage, filacell storage, fog spray system
describe the jacketed storage system
conserves moisture to better deal with high RH
describe the filacell storage system
humidifies air leaving cooling coil
describe the fog-spray system
- direct addition of moisture to air stream
- can make use of sonication as well
air circulation can be ___ or ___
which is more common?
natural or forced
forced is more common
air circulation promotes what?
- efficient heat and mass transfer
is heat transfer desirable?
is mass transfer desireable?
yes
no
air velocity is important for what?
- maintaining proper temp
- establishing homogenous CA conditions
proper air circulation depends on what?
- fan type and capacity
- air delivery
- package design and stacking
describe regular atmospheric systems
- atmosphere not controlled
- build up of CO2 and ethylene should be prevented
- O2 depletion should be prevented
what is CA? what is MA?
what is RA?
CA = controlled atmosphere
MA = modified atm
RA = regular atm
describe CA/MA storage systems
- altered atmosphere inside the storage chamber
- lower O2 levels
- higher CO2 levels
- removal of ethylene (to slower ripening of produce)
what are 2 types of RA?
jacketed storage
filacell system
describe RA
insulated vapor proof structures with mechanical refrigeration units
why are CA storage systems imp?
it can alter the gaseous environment inside the storage chamber
what are desirable effects of CA storage?
- lowered resp rate
- slowed senescence
- slowed ethylene production rate
- lower fruit sensitivity to ethylene
- alleviation of physiological disorders
- suppressed pathogen activity
what are undesirable effects of CA storage
- can promote some physiological disorders
- can induce irregular ripening
- can favor development of off flavours
- can favor stimulation of sprouting
what are 2 imp aspects of CA/MA storage?
- CA generation: lowering O2 level, increasing CO2 level
2. CA maintenance: CO2, O2, ethylene removal, etc…
what are 2 methods of CA generation?
- passive process: via produce respiration
2. active process: via external means
what are 2 types of of O2 control systems?
- external gas generators: operates by open flame burners or catalytic converters
- N generators: gas or liquid N cylinders; Smit-oxydrain
what is Smit-oxydrain?
- Ammonia is converted to N
- becomes N2 + H2
- H2 combines with O2 to form H2O
- N2 purges or replaces O2
how does CA generation remove CO2?
by scrubbing systems
- hydrated lime (absorbs lime)
- water (solubilizes CO2)
- brine water
- activated carbon
