3. (a) What is the physical interpretation of the Grashof number? (b) A glass-door firescreen, used to reduce exfiltration of room air through a chimney, has a height of 0.71 m and a width of 1.02 m and reaches a temperature of 232C. If the room temperature is 23C, estimate the convection heat rate from the fireplace to the room. (Assume air properties: k= 33.8 x10 W/mK, v = 26.4x10 m/s, a = 38.3x10-6 m/s, Pr= 0.69) 5+2