A small flexible bag contains 0.1 kg ammonia at -100 C and 3 bar. The bag material is such that the pressure inside varies linearly with volume. The bag is left in open space where the incident solar radiation is 75 W. The heat energy lost to the ground and surrounding air from bag is at the rate of 25 W. After a while, it is found that the bag is heated to 300 C at which time the pressure of ammonia is 10 bar. Estimate (i) the amount of heat energy infiltrated into the bag and (ii) the elapsed time.
Properties of ammonia:
(a) Compressed liquid ammonia at -100 C, 3 bar : specific volume of saturated liquid, vf = 0.001002 m3/kg, specific internal energy of saturated liquid, uf = 134 kJ/kg.
(b) Superheated ammonia vapour at 300 C, 10 bar : specific volume = 0.1321 m3/kg, specific internal energy = 1347 kJ/kg.