Chapter 3, Problem 3.17P

Consider the oven of Problem 1.54. The walls of theoven consist of $L=30\text{-mm-thick}$ layers of insulationcharacterized by $k_{\text{ins}}=0.03\text{W/m}\cdot \text{K}$ that are sandwichedbetween two thin layers of sheet metal. Theexterior surface of the oven is exposed to air at $23°\text{C}$ with $h_{\text{ext}}=2{\text{W/m}}^2\cdot \text{K}\text{.}$ The interior oven air temperatureis $180°\text{C}\text{.}$ Neglecting radiation heat transfer, determinethe steadystate heat flux through the oven wallswhen the convection mode is disabled and the free convectioncoefficient at the inner ovensurface is $h_{\text{fr}}=3{\text{W/m}}^2\cdot \text{K}\text{.}$ Determine the heat flux through theoven walls when the convection mode is activated, inwhich case the forced convection coefficient at theinner oven surface is $h_{\text{fo}}=27{\text{W/m}}^2\cdot \text{K}\text{.}$ Does operationof the oven in its convection mode result in significantlyincreased heat losses from the oven to thekitchen? Would your conclusion change if radiationwere included in your analysis?