The ratio of the actual mass of water vapour in a unit mass of dry air to the mass of water vapour in the same mass of dry air when it is saturated at the same temperature and pressure, is called

Nusselt number (N_N) is given by

A. $${{\text{N}}_{\text{N}}} = \frac{{{\text{h}}l}}{{\text{k}}}$$

B. $${{\text{N}}_{\text{N}}} = \frac{{\mu {{\text{c}}_{\text{p}}}}}{{\text{k}}}$$

C. $${{\text{N}}_{\text{N}}} = \frac{{\rho {\text{V}}l}}{\mu }$$

D. $${{\text{N}}_{\text{N}}} = \frac{{{{\text{V}}^2}}}{{{\text{t}}{{\text{c}}_{\text{p}}}}}$$

In case of sensible heating of air, the coil efficiency is given by (where B.P.F. = Bypass factor)

A. B.P.F. - 1

B. 1 - B.P.F.

C. $$\frac{1}{{{\text{B}}{\text{.P}}{\text{.F}}{\text{.}}}}$$

D. 1 + B.P.F.

The undesirable property of a refrigerant is

A. Non-toxic

B. Non-flammable

C. Non-explosive

D. High boiling point

The desirable property of a refrigerant is

A. Low boiling point

B. High critical temperature

C. High latent heat of vaporisation

D. All of these