Question $3$

Consider a thin $16-cm-$long and $20-cm-$wide horizontal plate

suspended in air at $20C.$ The plate is equipped with electric

resistance heating elements with a rating of $20$ W $.$ Now the heater

is turned on and the plate temperature rises so that the surface

temperature of both sides of the plate is maintained at $50C.$ Use

the following properties for air at the film temperature of $35C$ :

$k=0\mathrm{.}02625\frac{W}{m}.K$;$v=1\mathrm{.}655{10}^{-5}\frac{m^2}{s}$;$Pr=0\mathrm{.}7268,$ and

Determine:

i$.$ The convective heat transfer from the top surface $($W$).$

ii$.$ The convective heat transfer from the bottom surface $($W$).$

iii. The net heat loss by radiation to the surrounding $($W$).$

iv$.$ The expected emissivity of the plate assuming that both sides exchange radiation with a surrounding

sky temperature which is also at $20C.$