Question

A Newtonian liquid food with a viscosity of 2.5 cP and a density of 1020 kg/m3 is to be pasteurized in a HTST system that heats the liquid food to 80°C followed by holding it in a 0.02 m diameter pipe for a minimum time of 0.07 min.

a. Calculate maximum velocity and the length of the holding tube required, given that the flow rate is 35 L/min.

b. The temperature at the cold spot for a liquid food in a can is as follows (Table Q2). The sterilization process is being applied to a microbial population with D121 of 1.1 min and z = 11°C. Calculate the total lethality for the sterilization process.

Time (min) 0 1 2 3 4 5 6

Temperature (°C) 80 105 130 135 125 115 105

Answer #1

Flow Rate = Area of Pipe* Velocity of Fluid

Hence the maximum velocity achievable in a pipe= 2*v = 2*1.8568
= **3.7136 m/s**

And the length of the pipe then shall be 2*8 = **16
m**

Lethality :

Time(min) | Δt | T(^0C) | Lethality (L) | F0(min) |

0 | 0 | 80 | 0.0001835 | 0 |

1 | 1 | 105 | 0.034384573 | 0.034384573 |

2 | 1 | 130 | 6.44304121 | 6.44304121 |

3 | 1 | 135 | 18.35001247 | 18.35001247 |

4 | 1 | 125 | 2.262275304 | 2.262275304 |

5 | 1 | 115 | 0.278903873 | 0.278903873 |

6 | 1 | 105 | 0.034384573 | 0.034384573 |

Sum = 27.403003 |

Total F0 = 27.403003 minutes

Hence Lethality :

Please comment for any doubts :)

A Newtonian liquid food with a viscosity of 4 cP and a density
of 1026 kg/m3 is to be pasteurized in a HTST system that heats the
liquid food to 90°C followed by holding it in a 0.0275 m diameter
pipe for a minimum time of 0.06 min. Calculate the maximum velocity
and the length of the holding tube required, given that the flow
rate is 30 L/min.

The temperature at the cold spot for a liquid food in a can is
as follows. The sterilization process is being applied to a
microbial population with D121 of 1.1 min and z = 11°C. Calculate
the total lethality for the sterilization process.
Time (min) 0 1 2 3 4 5 6
Temperature (°C) 85 110 135 140 130 120 110

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