A laboratory drying oven has a composite wall made of Plane Wall1 and Plane Wall 2 as shown above. A thin film heater (surface heatsource, thickness negligible) is sandwiched between the two planewalls 1 and 2. Plane Wall 1 has a thickness L1 = 0.02 m and athermal conductivity k1 = 0.05 W/m·K, while Plane Wall 2 has athickness L2 = 0.01 m and a thermal conductivity k2 = 0.1 W/m·K.During steady state operation, the oven air maintains a constanttemperature T∞,2 = 60 ËšC, while the heater layer is controlled at atemperature of TH = 90 ËšC. The drying oven is put inside a roomwhere the ambient air temperature T∞,1 = 30 ËšC, and the heattransfer coefficient between the outer surface of the Plane Wall 1and the ambient air h1 = 3 W/m2 ·K. First, assume the heat transfercoefficient between Plane Wall 2 and the oven air is h2 = 3.5 W/m2·K. For simplicity, assume that the drying oven has 4 side walls(each is 0.5 m long and 0.5 m high), and both the top and bottomsurfaces of the oven are perfectly insulated. Consider the oven airand ambient air as an ideal gas with density Ï = 1.13 kg/m3 ,specific heat capacity cp = 1000 J/kg·K, kinematic viscosity v =15x10-6 m2 /s, thermal conductivity ka = 0.027 W/m·K, volumeexpansion coefficient β = 3.4x10-3 (1/K) and a Prandtl number of Pr= 0.71. Contact resistances do not occur. Additionally, all effectsof thermal radiation may be neglected.
