Q$.7$ A rectangular black rubber bag $1m1m0\mathrm{.}1m$ with walls $5$ mm thick is filled with $100$

litre of water, supported on a thin, nonconductive, horizontal grid well above the ground,

and exposed to a solar irradiance $G=750W{m}^{-2}($Figure $1).$ The ambient temperature Ta

is $20C,$ and the wind speed is $5\frac{m}{s}.$ Given the convective heat transfer coefficient,

$h_v=24\mathrm{.}7W{m}^{-2}{K}^{-1}.$

Draw the electrical circuit analogy and calculate

$($i$)$ The resistance to heat losses from the bag.

$($ii$)$ The time taken to reach the maximum average temperature of the water.