Along, uninsulated steam line with a diameter of 100 mm and a surface emissivity of 0.8 transports steam at 150°c and is exposed to atmospheric air and large surroundings at an equivalent temperature of 20°c. (a) calculate the rate of heat loss per unit length for a calm day. (b) calculate the rate of heat loss on a breezy day when the wind speed is 8 m/s. (c) for the conditions of part (a), calculate the rate of heat loss with a 20-mm-thick layer of insulation (k = 0.08 w/m ⋅ k). would the heat loss change significantly with an appreciable wind speed?

scattering of light by tiny particles in air to produce the colors we see on sky, is dependent on the following factors:

(i) wavelength of light

(ii) size of the scattering particle  

(iii) distance traveled by light through the atmosphere.

according to rayleigh's law of scattering, the amount of scattering is inversely proportional to the fourth power of its wavelength. shorter the wavelength, greater is its scattering. hence violet/blue light is scattered more than red.

sun's light is a composite light ( visible light) with wavelengths in the range 400 nm (violet) to 700 nm (red). as sunlight passes through our atmosphere, the molecules of air scatter light according to their wavelengths. during sunrise and sunset, the sun's position is below the horizon. hence light from the sun travels a greater distance in the atmosphere when compared to its position a noon.

as sunlight enters the earth's atmosphere, blue light is scattered away and at the end of its journey in the sky, only red and orange wavelengths remain in the beam.

hence at sunrise and sunset, the sky appears reddish orange.