**Question **# (a) Differentiate between free and forced convection with examples. b) Define Nusselt (Nu), Prandtl (Pr), Reynolds (Re) and Grashof (Gr)dimensionless numbers. State which numbers are used in free and forcedconvection to determine the heat transfer coefficient. (c) A vertical pipe 75 mm diameter and 1.5 m height is maintained at aconstant temperature of 125 °C. The pipe is surrounded by stillatmospheric air at 25 °C. Find heat loss by natural convection. Properties of water at 75 °C: Density = 1.1145 kg/m³10-6 Kinematic viscosity = 21.55 x10 m²/s Prandtl number (Pr) = 0.751% Thermal conductivity (k) = 33.06 x 10³ W/m K \text { Grashof number, } G r=\frac{g \times \beta \times L^{3} \times \Delta T}{V^{2}} N u=0.10(G r P r)^{0.333}