We need to size the cooling unit for a new refrigerator design. One step in finding the cooling capacity is to find the heat infiltration through the fridge walls. Consider one vertical side of the exterior of the fridge that is 66 inches tall and 28 inches wide. If ambient air is at 90oF and the fridge outer wall temp is 70oF, what is the heat flow to the wall by convection from the air? (This is natural convection from air to a vertical plate. Find air properties at film temp, then find Gr, Pr and GrPr to determine constants from Table 12.4 to be used in Eqn. 12.74 to find ho. Heat infiltration can be estimated from q = h_o AT_o where A is the surface area of fridge wall.) Ans: Gr ~ 7x109; Nu ~ 220; ho ~ 3.4W/m2.K; q ~ 45W ~ 155 BTU/hr