Two horizontal steam pipes have diameters 100 mm and 300 mm and are kept in a boiler house such that mutual heat transfer is negligible. The surface temperature of each pipe is 475°C. Given the temperature of ambient air is 35°C. The ratio of heat transfer coefficients of the smaller diameter to the larger diameter pipe is ________
\(Nu = 0.59{\left( {Gr.Pr} \right)^{\frac{1}{4}}}\)Enter numerical value using the virtual keypad. Round off where necessary.