Aluminum cans of a liquid baby formula are sterilized with steam in an autoclave before being shipped to wholesale distributors. A batch of the product consists of 500 cans, each of which has a tare (empty) mass of 1.00 times 10^2 g and contains 0.750 kg of formula. The cans are loaded into the autoclave at 35 degree C, and saturated steam at 2 bar is used to displace all the air from the autoclave and bring the cans and their contents to the same temperature as the steam. After the autoclave temperature has stabilized, it is held constant for 15 minutes, which is sufficient to achieve the required degree of sterilization. The steam is then vented, the pressure in the autoclave reduced to 1 atm, and the cans of formula are cooled to ambient temperature before being packaged for shipping. The heat capacities of the cans and formula are 0.91 kJ/(kg middot degree C) and 3.77kJ/(kg middot degree C), respectively. What is the highest temperature (degree C) in the autoclave? Estimate how much steam (kg) condenses as the cans go from their initial temperature to the value in Part (a). Why is more steam condensate produced in the actual operation than is calculated in Part (c)? Why is it important that the infant formula be held at the temperature from Part (a) for a period of 15 minutes?
a)At 2 bar, saturated steam has a temperature equalto the boiling point of 120.23 ( FROM TABLES)
b) The heat required to heat the cans and the food is that required to go from 35 deg C to 120 deg C
The sp heat of the can is .91 KJ/Kgdeg
The sp heat of the food is 3.77 KJ/Kg deg
The calories reqd is mass * sp heat * temp change
Putting in the values: For the Can : (50 Kg total) 50*.91*85 = 3867.5 KJ
For the food, 375 KG total, heat is 375*3.77*85 = 120168.75 KJ
Th elatent heat of steam at 2bar and 120 C is 2201.6 KJ/Kg,
Dividing the total heat extracted by the latent heat gives the mass of steam = 56.34 Kg
Due to condensation at latent heat, the pressure will fall, latent heat will fall and hence more amount if steam will be needed.
d) for Pasteurisatin /sterilisation - many bacteria are heat resistant.
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