Lecture 6: Heat Penetration Behaviour (Formula Methods)

Question 1

what are uses of general method?

Answer 1

graphical or numerical integration of heat penetration curve

Question 2

how do you use the formula method

Answer 2

• use heat penetration parameters from the heat penetration curve
• integrate destruction kinetics with heat penetration parameters

Question 3

what is transient time

Answer 3

temp data obtained at the cold spot location in the container during a process test

Question 4

in heating and cooling curves, temp and time have a ___ relationship

Answer 4

semi log

Question 5

in heating and cooling curves, log (temp) vs time have a ____ relationship

Answer 5

linear

Question 6

what defines the intercept of the heating curve?

Answer 6

log (Tr-Tpih)

Question 7

what is Tr?

Answer 7

retort temp

Question 8

what is Tih?

Answer 8

product initial temp

Question 9

what is T?

Answer 9

product temp at time t

Question 10

what is Tpih?

Answer 10

pseudo initial temperature (intercept of the straight line)

Question 11

what defines where the process actually starts?

Answer 11

log (Tr-Tih)

Question 12

define the slope of the heating curve

Answer 12

[log(Tr-T1) - log (Tr-T2)]/ (t1-t2)

Question 13

what is fh?

Answer 13

heating rate index (the time to pass one log cycle)

Question 14

in the heating curve, what is slope defined as?

Answer 14

slope = - 1/fh

Question 15

what is jch?

Answer 15

lag factor

jch = (Tr-Tpih) / Tr-Tih)

Question 16

what is g?

Answer 16

Tr - T

Question 17

what is Ih?

Answer 17

Tr - Tih (temp difference during heating)

Question 18

what is Tw?

Answer 18

water temperature

Question 19

what is Tic?

Answer 19

product initial cooling temp

Question 20

what represents the intercept of straight portion of the cooling curve?

Answer 20

log (Tpic-Tw)

Question 21

what defines the slope of the cooling curve?

Answer 21

slope = -1/fc

Question 22

what defines the point where the process actually starts?

Answer 22

log (Tic-Tw)

Question 23

what is Tpic?

Answer 23

pseudo initial cooling temp (the point where the linear portion of the cooling curve is a zero)

Question 24

what does Fc = Fh mean?

Answer 24

the product is heating and cooling at the same rate

Question 25

what is CUT?

Answer 25

come up time

• the time to reach the operating temperature
• not the same as processing time
• contributes to some warming of the product
• using some of the CUT can reduce the process time

Question 26

when can you ignore CUT?

Answer 26

as a safety factor, CUT can be ignored

Question 27

how much of the CUT did Ball determine to be effective?

Answer 27

the last 42% of CUT is effective and can be used as processing time

Question 28

how much of the CUT did Ball determine to be NOT effective?

Answer 28

• the first 58% of CUT

- should be discarded

Question 29

if your CUT is 10 mins, ____ is not useful

Answer 29

first 6 mins

Question 30

the come up time means the time scale should be shifted _____

Answer 30

forward

eg. shift the Xzero to the new point at X = 0.58CUT

Question 31

how are cooling curves affected by CUT?

Answer 31

cooling curves are not adjusted because cooling times are not used in process calculations

Question 32

what is B? what does this include? what equation represents this?

Answer 32

ball process time

includes: effective portion of the CUT + operators process time

B = Pt + 0.42CUT

Question 33

what is Pt?

Answer 33

operator’s process time

the total heating time - CUT

Question 34

what is the ball formula method based on?

Answer 34

heat penetration curve

Question 35

what is Bb

Answer 35

ball’s process time

Question 36

what is considered an industry standard?

Answer 36

ball formula method

Question 37

what are 4 assumptions made in the ball method?

Answer 37

1. z = 18F
2. heating rate index (fh) = cooling rate index (fc)
3. cooling curve lag factor: jcc = 1.41
4. CUT effectiveness = 42%

Question 38

what is used to related heating to lethality?

Answer 38

ball tables related Fh/U to log(g)

Question 39

when should you not use the ball method? why?

Answer 39

when Fh > Fc

ie. when cooling is faster than heating

using ball method would underestimate

Question 40

when jcc < 1.41, what method should you use?

Answer 40

ball

Question 41

when jcc = 1.41, what method should you use?

Answer 41

doesn’t matter

Question 42

if jcc > 1.41, what method should you use?

Answer 42

stumbo

the ball method would underestimate the processing time

Question 43

what is the stumbo method based on?

Answer 43

• heating and cooling curves
• jcc and jch values
• assumes Fh = Fc

Question 44

in the stumbo method, Fh = what?

Answer 44

Fh = Fc

Question 45

when Fh > Fc, what method should you use?

Answer 45

general methods