4 Cooling Rate Half Cooling Time Flashcards
define cooling/precooling
used interchangeably; lowering of produce temp from field to storage conditions
differentiate between: sensible, latent, field, and vital heat
- sensible results in temp change
- latent results in phase change
- field is the heat of produce at harvest to be removed for storage
- vital is the heat of respiration
ideally, we want (fast/slow) cooling
fast
advantages of fast cooling?
- reduction of RR, TR, microbiological/ethylene/chemical activity
- planning cold storage design
what questions are asked pertaining to cooling?
- how much energy to cool?
- quantity of produce?
- speed?
- methods available?
- appropriate equipment?
what do we use to determine how much energy needed?
Q = mCdT (answer in kJ)
what do we use to determine how fast to cool?
rate of heat removal aka cooling rate (answer in kW/ton)
what is the unit for refrigeration capacity?
ton
true or false: a ton of refrigeration delineates the size of the refrigerator
false. it’s the heat needed to freeze one short ton (2000 pounds) of water to 32 degrees F in 24 H.
what is one ton of refrigeration equal to in SI units?
3.52 kW
how do you get cooling time?
heat (Q)/Rate(q)
what product factors influence cooling time/rate?
size, shape, packing, packaging, type
what system factors influence cooling time/rate?
size/capacity, medium temp, medium flowrate, medium type
by what modes of heat transfer are produce cooled?
- within the produce: conduction
- from produce to air: convection
- from air to cooling coil: convection
what law do we use for conduction?
Fourier’s law
what law do we use for convection?
Newton’s law
what law do we use for radiation?
Plank’s
define conduction
heat transfer via molecular vibrations or compacted particles without involving any gross movement of particles
rate of conduction is directly proportional to _____ and _____ _____
area and temperature gradient
define convection
gross movement of molecules or particles either by density gradient or forced movement
what dumb sentence should you remember for newton’s law for convection?
cute hat
q = hAdT
define radiation
no medium involved; travels like other EM radiation. can be reflected, deflected, absorbed, or transmitted
the state at which temperature at any given location does not change with time
steady state
state at which temperature at any given location changes with time
unsteady state
most common heat transfer processes are _____ state
unsteady
the simple cooling curve is what shape?
semilog
what are the units for cooling rate?
there are none
how do you calculate CR?
negate the slope of the linear semi-log curve
what is half cooling time?
time interval which reduces cooling load by half
