A spherical, cryosurgical probe may be imbedded in diseased tissue for the purpose of freezing, and thereby destroying, the tissue. Consider a probe of 3-mm diameter whose surface is maintained at −30 °C when imbedded in tissue that is at 37 °C. A spherical layer of frozen tissue forms around the probe, with a temperature of 0 °C existing at the phase front (interface) between the frozen and normal tissue. If the thermal conductivity of frozen tissue is approximately 1.5 W/m · K and heat transfer at the phase front may be characterized by an effective convection coefficient of 50 W/m2 · K, what is the thickness of the layer of frozen tissue (assuming negligible perfusion)? 5