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Subject:
Engineering
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Coursework
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English (U.S.)
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Topic:

Thermal Processing, Drying, and Evaporation

Coursework Instructions:

Please answer the following FOUR questions. 

Problem 1 (25 marks) The F0 for 99.999% inactivation (one survivor from 100,000) of Clostridium botulinum is 1.1 minutes. Calculate F0 for 8D inactivation, and the F value at 135°C. What is the lethal rate? 

Problem 2 (25 marks) Air with a wet bulb temperature of 27 °C and a relative humidity of 20% is fed into a dryer at a rate of 5,000 m3/hr to dry slices of persimmons. The air leaving the dryer is saturated and cannot hold any more water vapor. The persimmons enter the dryer at a rate of 55 kg (wet weight)/hr with a moisture content of 1000% (dry weight basis). What is the wet basis moisture content of the persimmons leaving the dryer?  Approach: Use psychrometric chart to find specific volume of inlet air as well as moisture content of inlet and outlet air. Use a water mass balance to solve for the moisture content of the dried fruit. 

Problem 3 (25 marks) A bin holds 1800 kg of wet grain containing 450 kg of water. This grain is to be dried to a final moisture content of 15% (wet basis). a) What are the initial and final moisture contents of the grain in dry basis? b) How much water is removed during drying? 

Problem 4 (25 marks) Orange juice at 15 °C is to be concentrated from 7% solids to 42% solids in a single effect evaporator. Due to quality reasons, the temperature of orange juice cannot exceed 60 °C. Saturated steam at 170 kPa is used to heat the evaporator.  If the desired production rate of concentrated orange juice is 2000 kg/h, calculate (a) the surface area of the evaporator, (b) steam mass flow rate, and (c) the steam economy. Assume the overall heat transfer coefficient is 4000 W/[m2 °C], the specific heat of solids is 1500 J/[kg °C] .   Hint for Problem 4 1. Calculate the mass flow rates of feed (

Coursework Sample Content Preview:
FOODSCI 306 2023 Semester 1
Assignment – Thermal Processing, Drying, and Evaporation
Problem 1
99.999% inactivation corresponds to 5D
The D value (time required for 1 log reduction or 90% inactivation) at reference temperature (121.1°C) is: D0 = F0/5 = 1.1/5 = 0.22 minutes.
For an 8D inactivation, F0 = SD0 = 8(0.22) = 1.76 minutes.
Calculating D at 135°C (or 275°F):
Reference temperature T0 is 121.1°C (or 250°F). If z is the temperature change required for a 10-fold change in D and is given as 10°C, then we can calculate D at 135°C using the equation: D = D0 × 10^((T0 - T)/z), where T is the new temperature.
Substituting in the values:
D at 135°C = D0 × 10^ ((121.1-135)/10) = 0.22 × 10 ^ (-1.39) = 0.086 minutes.
The F value at 135°C would then be F135 = 8 × D at 135°C = 8 × 0.086 = 0.688 minutes.
Lethal Rate
k = log (D0/D) ………. where D is the D-value at the temperature of interest
D is the D-value at 135°C (0.086 minutes)
Lethal rate is k = log (0.22/0.086) = 0.96
Problem 2
Using psychrometric chart:
Humidity ratios:w₁ = 0.034 kg water/kg dry air for inlet air
w₂ = 0.072 kg water/kg dry air for outlet air
We have two main components to consider here:
* Inlet and outlet air streams.
* Persimmons themselves.
Using a water mass balance over the system, inlet water (from the inlet air and the persimmons) equals the outlet water (from the outlet air and the dried persimmons).
Assuming average conditions for air (approximately 1.2 kg/m³):
Air mass flow rate: = volume flow rate / specific volume
= 5,000 m³/hr / 1.2 kg/m³ = 4,166.67 kg/hr
Then the inlet and outlet water in the air streams can be found by multiplying the air mass flow rate by the humidity ratios.
Inlet water from air = w₁ × air mass flow rate = 0.034 kg water/kg dry air × 4,166.67 kg/hr = 141.67 kg/hr
Outlet water from air = w₂ × air mass flow rate
= 0.072 kg water/kg dry air × 4,166.67 kg/hr
= 300 kg/hr
Moisture content of the persimmons on a dry basis is given as 1000%
Thus 10 kg of water for every 1 kg of dry persimmons.
So, inlet water from persimmons = persimmons mass flow rate * (1000% / (100% + 1000%))
= 55 kg/hr * (10 / 11) = 50 kg/hr
Applying water balance:
Inlet water = Outlet water Inlet water from air + Inlet water from persimmons
= Outlet water from air + Outlet water from persimmons 141.67 kg/hr + 50 kg/hr = 300 kg/hr + Outlet water from persimmons
Outlet water from persimmons = 108.33 kg/hr.
Moisture content on a wet basis (Mw) of the persimmons leaving the dryer can be calculated as follows:
Mw = (Outlet water from persimmons / (Outlet water from persimmons + persimmons dry mass flow rate)) × 100%
Mw = (108.33 kg/hr / (108.33 kg/hr + 55 kg/hr × (1 / 11))) × 100% = 80.86%
Thus, the wet basis moisture content of the persimmons leaving the dryer is approximately 80...
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