An industrial freezer must keep the rate of thermal energy entering through a 10m2 panel below 150W when the temperature difference between the inside and outside surfaces is 30∘C. Two insulation materials are available:
• Material X: thermal conductivity 0.060W/(m⋅∘C), cost \$15 per square meter for each centimeter of thickness
• Material Y: thermal conductivity 0.025W/(m⋅∘C), cost \$30 per square meter for each centimeter of thickness
Which choice minimizes the cost per square meter while still meeting the thermal requirement?
a) Either material costs the same for the required thickness.
b) Use Material X only.
c) Use Material Y only.
d) Neither material can meet the thermal requirement.