Problem 3 174 in your text page 34 Calculate the density of

Problem 3 (1.74 in your text, page 34). Calculate the density of air inside a house and outside a house using 20°C inside and -25°C outside. Use an atmospheric pressure of 85 kPa (kilo Pascals, kilo is 103). Do you think there would be a movement of air from the inside to the outside (infiltration), even without a wind? Explairn.

Solution

density of air inside house

D = P / RT

R = specific gas constant = 287.058 J /kg .K

T = 20C = 293 K

P = 85 *10^3 pascals

             D = 1.010 kg / m ^3 inside

density of air outside house where T = -25C = 248K

              D = 1.193 kg / m^3 outside

the density of air is inversely praportional to the temperature , hence the air move from out side to insider , i.e from high density to low density.