文档介绍：Engineering and thermal processing
Engineers are different from scientists
What do scientists do?
What do engineers do?
The importance of simplifying assumptions
examples
Engineers deal with
Heat transfer, always runs from hot to cold so refrigerators or freezers need pumps (energy input)
Mass transfer
Mass balance
Consider a simple drier
The 2nd Law of Thermodynamics: everything goes to maximum randomness (entropy)
Unless you put in energy
Electric, microwave, pressure, thermal, ionizing
Types of Heat Transfer (demo)
Conduction
Convection
Radiation
Most food processing involves the addition or removal of energy. Most types of food spoilage have engineering solutions.
Thermal Processing and Refrigeration
Heating and Cooling:
Heat transfer (heating or cooling) is driven by ΔT (the temperature difference)
ΔT (°F)
Boiling H2O
152
Oven 350°F
292
Broiler @ 2000°F
1940
Refrigerator 40°F
20
Household Freezer 10°F
50
Commercial Freezer -40°F
100
Liquid Nitrogen -380°F
440
Assume a Room Temperature of
60°F.
Pasteurization:
7 log kill for Salmonella in Milk = %
Pasteurization of eggs:
3 log reduction = % 145°F for 3 to 4 mins.
Fruit juices are pasteurized to reduce microbial count and inactivate enzymes; they were thought not to carry pathogens.
Temperature:
145°F (63C)
161°F (72C)
212°F (100C)
280°F (131C)
Time:
30 min
15 sec
6 sec
Log Numbers
Time (min)
# survivors
Log # survivors
1
1,000,000
6
2
100,000
5
3
10,000
4
4
1,000
3
5
100
2
6
10
1
7
1
0
8
-1
9
-2
10
-3
Log vs linear