4 Cooling Rate Half Cooling Time

Question 1

define cooling/precooling

Answer 1

used interchangeably; lowering of produce temp from field to storage conditions

Question 2

differentiate between: sensible, latent, field, and vital heat

Answer 2

• 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

Question 3

ideally, we want (fast/slow) cooling

Answer 3

fast

Question 4

advantages of fast cooling?

Answer 4

• reduction of RR, TR, microbiological/ethylene/chemical activity
• planning cold storage design

Question 5

what questions are asked pertaining to cooling?

Answer 5

• how much energy to cool?
• quantity of produce?
• speed?
• methods available?
• appropriate equipment?

Question 6

what do we use to determine how much energy needed?

Answer 6

Q = mCdT (answer in kJ)

Question 7

what do we use to determine how fast to cool?

Answer 7

rate of heat removal aka cooling rate (answer in kW/ton)

Question 8

what is the unit for refrigeration capacity?

Answer 8

ton

Question 9

true or false: a ton of refrigeration delineates the size of the refrigerator

Answer 9

false. it’s the heat needed to freeze one short ton (2000 pounds) of water to 32 degrees F in 24 H.

Question 10

what is one ton of refrigeration equal to in SI units?

Answer 10

3.52 kW

Question 11

how do you get cooling time?

Answer 11

heat (Q)/Rate(q)

Question 12

what product factors influence cooling time/rate?

Answer 12

size, shape, packing, packaging, type

Question 13

what system factors influence cooling time/rate?

Answer 13

size/capacity, medium temp, medium flowrate, medium type

Question 14

by what modes of heat transfer are produce cooled?

Answer 14

• within the produce: conduction
• from produce to air: convection
• from air to cooling coil: convection

Question 15

what law do we use for conduction?

Answer 15

Fourier’s law

Question 16

what law do we use for convection?

Answer 16

Newton’s law

Question 17

what law do we use for radiation?

Answer 17

Plank’s

Question 18

define conduction

Answer 18

heat transfer via molecular vibrations or compacted particles without involving any gross movement of particles

Question 19

rate of conduction is directly proportional to _____ and _____ _____

Answer 19

area and temperature gradient

Question 20

define convection

Answer 20

gross movement of molecules or particles either by density gradient or forced movement

Question 21

what dumb sentence should you remember for newton’s law for convection?

Answer 21

cute hat

q = hAdT

Question 22

define radiation

Answer 22

no medium involved; travels like other EM radiation. can be reflected, deflected, absorbed, or transmitted

Question 23

the state at which temperature at any given location does not change with time

Answer 23

steady state

Question 24

state at which temperature at any given location changes with time

Answer 24

unsteady state

Question 25

most common heat transfer processes are _____ state

Answer 25

unsteady

Question 26

the simple cooling curve is what shape?

Answer 26

semilog

Question 27

what are the units for cooling rate?

Answer 27

there are none

Question 28

how do you calculate CR?

Answer 28

negate the slope of the linear semi-log curve

Question 29

what is half cooling time?

Answer 29

time interval which reduces cooling load by half