2 1. (a) Give three examples for each of natural (free) convection and forced convection which occur in industrial processes. (b) The Grashof number and the Reynolds number appear in most correlations...

2
1. (a) Give three examples for each of natural (free) convection and forced convection which occur in industrial processes.
(b) The Grashof number and the Reynolds number appear in most correlations of experimental data for convective heat transfer. Explain, in a maximum of 150 words, the mechanisms of natural and forced convection with particular reference to the above non-dimensional groups.
(c) An appropriate correlation for heat transfer by natural convection from a horizontal pipe to the atmosphere is
where
and
Nu = 0.5 3Gr0.25 pr0.25
ocp2d3 (Ts - Tf )g Gr = ju2
c au Pr = P k
Show that the above correlation can be simplified to
025 h w 1.34 Ts Tf W m-2 K
when air has the values listed below a = 3.077 x 10-3K-1, p =1.086 kg m-3, cp = 1.0063 kJ kg-1K-1 k = 2.816 x 10-5 kW m-11(-1, p. =1.962 10-5 kg m-1- s-1