A cold storage wall (3m*6m) is contructed of 15 cm thick concrete (thermal conductivity =1.37 w/ m c). Insulation must he provided to maintain a heat transfer rate through the wall at or below 500 w (fig.E4.8). If the thermal conductivity of the insulation is 0.04 w/m c, compute the reguired thickness of the insulation. The outside surface temperature of the wall is 38 c, and the inside wall temperature is 5 c.