Question

The total heat transfer from a spherical copper ball of diameter 15 cm initially at 220 °C, and its environment at a constant temperature of 25°C and convection coefficient h = 100 W/$m^2$K, during the first 20 min of cooling is calculated to be 2400 kJ. Assuming the properties of the copper to be k = 400 W/mK, $\rho$ = 8933 kg/$m^3$ and $c_p$ = 385 J/kgK. This result is

Answer 1

$q_{max}=m{c}_p(T_i-T_{\infty })$

$=8933\times \frac{4}{3}\pi (0.075{)}^3\times 0.385\times (220-25)$

$=1185kJ$

$q_{calculated}>q_{max}\Rightarrow$Result is not possible