Problem $3\mathrm{.}4$

Most solar$-$thermal collectors are 'glazed' meaning they are contained within a shallow

box with a glass cover to insulate the absorber from heat loss by convection $($e$.$g$.$ from

wind$)$ while allowing the majority of the solar radiation to pass through to the absorber$.$

Flat$-$plate solar collectors are typically tilted to optimise their solar energy absorption$.$

The tilt angle affects the rate at which heat is lost from the collector due to natural

convection. A collector is $0\mathrm{.}96$ m high and $2\mathrm{.}4$ m wide and has a gap between the

absorber and glass of $24$ mm $.$ Assuming the absorber plate $($the surface that heats the

water$)$ is maintained at $90C$ and the inside surface of the glass cover is maintained at

$30C,$ calculate the rate of heat loss by natural convection between the absorber plate

and glass cover for a tilt angles of $40$ from horizontal.