Question

A block of tofu (5 cm × 2.5 cm × 1.25 cm) needs to be sterilized to make it shelf stable. Typically holding this product at 120 C for 2.5 minute is adequate to sterilize this product. This is accomplished by keeping the product in high pressure retort containing steam at 121 °C. Calculate the process time for this operation if the convective heat transfer coefficient of steam is 200 W/m2, and thermal conductivity of the tofu is 2 W/m2. The density of product is 1300 kg/m3 and specific heat is 3800 J/kg C. Condition: You cannot assume a black of tofu as an infinite slab of one characteristic thickness. assume the initial temperature of Tofu block to be 4 C. You must assume a finite slab Hint: assuming a certain time point, calculate the Fourier number for each infinite slab(s) of unique characteristic thickness and estimate the unaccomplished temperature fraction for each infinite slab. Using these temperature fractions, predict the temperature at the center of tofu using a formula discussed in class at that time. This process can be repeated until the temperature at the center of tofu reached 120 C.

Answer 1