A fruit juice containing 10% solids (initial temperature = 20 degree C) was plac
ID: 1452594 • Letter: A
Question
A fruit juice containing 10% solids (initial temperature = 20 degree C) was placed in a cylinder (height = 20 cm, radius = 5 cm) in a blast air freezer with an air temperature of -25 degreeC. The convective heat transfer coefficient between the air and the product is 1000 W/m^2 K. The specific heat, density, and thermal conductivity of the unfrozen product are 4000 J/kg K, 950 kg/m^3, and 0.6 W/m K respectively and that of the frozen product arc 3900 J/kg K, 900 kg/m^3, and 1.5 W/mK respectively. If it takes 53 minutes for the product to get to its initial freezing point, determine its initial freezing point Determine the time taken for the product to freeze once it gets to its initial freezing point. What are the assumptions that you need to make? Are these assumptions valid? Why or why not?Explanation / Answer
a) Here, 0.6 * 45 * 53 * 60 * 0.2 + 1.5 * 45 * 53 * 60 * 0.2 = 1000 * (3.14 * 0.05 * 0.05) * 53 * 60 * T
=> T = 2.40 degree celsius
=> initial freezing point = - 27.4 degree celsius
b) time taken = 60102/59911.2
= 60.19 minutes