Chapter 3, Problem 3.17P

Consider the oven of Problem 1.54. The walls of the oven consist of $L=30\text{-mm}$ -thick layers of insulation characterized by $k_{ins}=0.03\text{W/m}\cdot \text{K}$ that are sandwiched between two thin layers of sheet metal. The exterior surface of the oven is exposed to air at 23°C with $h_{ext}=2{\text{W/m}}^{\text{2}}\cdot \text{K}\text{.}$ The interior oven air temperature is 180°C. Neglecting radiation heat transfer, determine the steady-state heat flux through the oven walls when the convection mode is disabled and the free convection coefficient at the inner oven surface is $h_{fr}=3{\text{W/m}}^{\text{2}}\cdot \text{K}\text{.}$ Determine the heat flux through the oven walls when the convection mode is activated. in which case the forced convection coefficient at the inner oven surface is $h_{fo}=27{\text{W/m}}^{\text{2}}\cdot \text{K}\text{.}$ Does operation of the oven in its convection mode result in significantly increased heat losses from the oven to the kitchen? Would your conclusion change if radiation were included in your analysis?