Question Five

$($a$)$ A one meter square insulation board cover of a cooler is made of three layers, the middle one being packed glass wool of thickness $100$ mm sandwiched between two plywood boards of $20$ mm thickness. The insulation board is held together by four steel bolts of $10$ mm diameter at the corners. If the surface temperatures are $5C$ and $20C,$ determine the heat flow across the board.

$(8$ marks$)$

Take the thermal conductivities of glass wool, plywood and steel as $0\mathrm{.}02,0\mathrm{.}12$ and $40\frac{W}{m}C,$ respectively.