During heat treatment, cylindrical pieces of 25 mm diameter, 30 mm height and at 30 degree Celsius are placed in a furnace at 750 degree Celsius with convective coefficient 80 W/m2 degree. Find the value of biot number if thermal conductivity is 40 W/m degree

• A. 0.0082
• B. 0.0072
• C. 0.0062
• D. 0.0052