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In the canning process, sealed cans of food are sterilized with pressurized steam to kill any

microorganisms initially present in the food and thereby prolong the shelf life of the food. A

cylindrical can of food has a diameter of 4 cm and height of 4 cm. The food material can be treated

as a solid with heat capacity of 4000 J/kgK, density of 1200 kg/m³, and thermal conductivity of 0.6

W/mK. In the process, steam at 120°C is used to sterilize the can. The convective heat-transfer

coefficient is 60 W/m² K. The can and contents initially are at a uniform temperature of 20 °C.

A. If the heat-transfer resistance offered by the thin can walls is neglected and the can ends are

thermally insulated, how long will it take for the center of the can to reach a temperature of 80

°C, which is sufficient to kill all microorganisms? Hint: You will need to use one of the charts

in Appendix F of Welty et al.

B. What is the required time if the ends of the can are not insulated but are instead exposed to the

steam? Hint: See Section 18.2 of Welty et al. for an approximate approach to this two-

dimensional problem. It is tricky, though, as you know the left-hand-side of Eq. 18.24, but not

the two terms on the right-hand-side. Thus, you will need iterate by making two educated guesses

for the time required, then calculate the right-hand-side and then interpolate (or extrapolate) to

get an improved estimate. Also, the variable a for this equation is the half-height of the can.