A $3cm$ thick slab of lean meat is placed inside a freezer in which the temperature is $-25C.$

The coefficient of heat transfer by convection from the surface of the meat is $15\frac{J}{s{m}^{2}C}.$

Determine the time needed to freeze the meat slab if $70\%$ of its weight is water.

$($Hint: the latent heat of fusion of water to ice is $335k\frac{J}{k}g)$

Data: Properties of lean meat

Thermal conductivity $1\mathrm{.}7\frac{J}{smC}.$

Specific heat $2\mathrm{.}1k\frac{J}{kgC}.$

Density $995k\frac{g}{m^3}$

The initial freezing temperature for lean meat is $T_F=-2\mathrm{.}2C$