A large slab of aluminium at a uniform temperature of 200C suddenly has its surface temperature dropped to 70C. What is the total heat removed from the slab per unit surface area when the temperature at a depth of 4cm has dropped to 120C ? If the slab is suddenly exposed to a convection-surface environment of 70C, with heat transfer coefficient of 525W/m2K. Calculate the time required for the temperature to reach 120C at the depth of 4cm for this circumstance? Hint: Use equation i=TiT0T(x,t)T0=erf(2tx) to determine the time. Then the instantaneous flow rate at the surface is integrated over the determined time