Freezing process involves a change in phase as water converts into ice crystals. This process involves unsteady state heat transfer, with a change in thermal and physical properties. Perhaps the most important aspect of the mathematical description of freezing is the changing physical and thermal properties. The change in properties as a function of temperature is often modeled using appropriate mathematical functions. A typical freezing curve is shown as follows. Note that during most of the freezing time, latent heat must be removed to accomplish change of phase.