At the end of its manufacturing process, a silicon wafer of diameter d = 258 mm , thickness ô =1 mm is at an initial temperature of 325 C and is allowed to cool in quiescent, ambient air and large surroundings for which T =T= 25 C, What is the initial rate of cooling by convection (kJ/s) from the TOP surface ONLY (Watts)? 3 Silicon :p= 2330 kg/m , c = 813 J/kg · K, k= 87.8 W/m·K" 2 -6 Air: v = 32.15×10 m /s, k = 0.0372 W/m K, a = 46.8 ×10° m/s, Pr= 0.686 %3D Quiescent air T Tsur Silicon wafer D, 8, e, T

A food product wants to be produced in a small round shape (pellet) by freezing it in a water blast freezer freezer. Air freezer operates at -25 ° C. The initial product temperature is 25 ° C. The pellet has a diameter of 0.5 cm, and a density of 980 kg / m3. The initial freezing temperature is -2.5 ° C. The latent heat of freezing of the product is 280 kJ / kg. The thermal conductivity of the frozen product is 1.9 W / (m ° C). The convective heat transfer coefficient is 50 W / (m? K). Calculate the freeze time.