Cooked mashed potato is cooled on large rectangular trays in a chilling unit with refrigerated air at 2C blown over the product surface at high velocity. The depth of the product is 30 mm and the initial temperature of the product is 95C. The product has a thermal conductivity of 0.37 W/(m K), specific heat capacity of 3.7 kJ/(kg K), and density of 1000 kg/m3. Assume heat loss from the mashed potato only occurs on the top and bottom faces of the product in the tray. Assume negligible resistance to transfer at the surface.

Calculate product temperature at the center after 30 minutes of cooling. (use Heisler chart)