Homework Answers

16. Find the dew point temperature of air whose humidity ratio is 0.0150 kg water/kg dry air.

15. An airconditioning system has a sensible heat load of 120 kw and latent heat load of 25 kw. Find the sensible heat factor.

14. A cooling tower cools water from 39oC to 24oC at the rate of 25 kg/s. Air enters the tower at 18oC at the rate of 35 kg/s. Find the temperature of air leaving the tower.

13. The evaporative condenser of an ammonia refrigeration plant has a water flow rate of 100 kg/s and enters a natural draft cooling tower at 43oC. The water is cooled to 30oC by air entering at 27oC db 24oC wet bulb. The air leaves the tower as 90% RH and 32oC db. Calculate the percent of make-up water needed the tower. At 27oC db and 24oC wb: h = 72.5 KJ/kg, w = 0.0178 At 90% RH and 32oC db: h = 102 KJ/kg, w = 0.0275.

12. A 120 tons refrigeration system with COP of 5 has a condenser which is to be cooled by means of a cooling tower. Air enters the tower at 25oC db and 50% RH and leaves at 35oC db and 80% RH. Find the volume of air needed m3/hr. At 25oC and 50% RH: h = 50 KJ/kg, v = 0.86 m3/kg At 350C db and 80% RH: h = 108

11. A 100 BHP diesel engine has a brake thermal efficiency of 30% and jacket water loss of 34%. The engine is to be cooled by means of a cooling tower having a range of 27oC. Find the mass of water leaving the tower.

10. Air enters the tower at the rate of 60 kg/s. The entrance enthalpy is 86 KJ/kg and exit enthalpy of 53 KJ/kg. Find the temperature range of the tower if mass flow rate of water is 30 kg/s.