UNIVERSITY OF CEBU-MAIN
MECHANICAL ENGINEERING DEPARTMENT
AIR CONDITIONING
Problem Set
1. Find the enthalpy of air with wet bulb temperature of 25 oC and dry bulb temperature of
32 oC using psychrometric chart.
A. 65.45 KJ/kg B. 76.50 KJ/kg C. 74.29 KJ/kg D. 78.40 KJ/kg
2. Find the enthalpy of air with wet bulb temperature of 25 oC and 60% RH using
psychrometric chart.
A. 74.56 KJ/kg B. 60.34 KJ/kg C. 76.50 KJ/kg D. 77.40 KJ/kg
3. Find the dew point temperature of air with dry bulb temperature of 303 oK and RH of
80% usingpsychrometric chart.
A. 26.50 oC B. 24.50 oC C. 85.25 oC D. 32 oC
4. At 30 oC, air-vapor mixture has a relative humidity of 75%. Find the humidity ratio if
barometric pressure is 100 kpa. At 30 oC, Psat = 4.246 kpa
A. 0.123 B. 0.0205 C. 0.054 D. 0.019
5. The humidity ratio of air is 0.05. If barometric pressure is 99 kpa, find the partial
pressure of water vapor.
A. 4.23 kpa B. 7.37 kpa C. 6.81 kpa D. 5.23 kpa
6. Air at 32 oC and pressure of 101 kpa has a density of 1.10 kg/m3. Find the humidity
ratio of air.
A. 0.0304 B. 0.6350 C. 0.0635 D. 0.0173
7. What is the enthalpy of the air-vapor mixture at 70% RH and 33 oC when the barometric
pressure is 101 kpa? At 33 oC: Psat = 5.628, hg = 2565.3
A. 97.76 KJ/kg B. 74.23 KJ/kg C. 67.34 KJ/kg D. 53.34 KJ/kg
8. Air-vapor mixture has an enthalpy of 73 KJ/kg at 31 oC. Find the partial pressure of
water vapor. At 31 oC: hg = 2556.3 KJ/kg
A. 6.34 kpa B. 1.34 kpa C. 4.231 kpa D. 2.61 kpa
9. An ammonia ice plant operates between a condenser temperature of 35oC and
evaporator of –15oC. It produces 12 metric tons of ice per day from water at 30oC to ice at
–5oC. Assuming simple saturation cycle, determine the horsepower of the motor if the
adiabatic efficiency of the compressor ηc = 0.87 and mechanical efficiency ηm = 0.96. The
specific heat of ice is 2.094 kJ/kg.oC and the latent heat is 335 kJ/kg. From the table for
ammonia the following enthalpies are: condenser entrance = 1703 kJ/kg, exit =366.1
kJ/kg; compressor entrance = 1443.9 kJ/kg, exit = 1703 kJ/kg
A. 17.68 hp B. 18.61 hp C. 15.5 hp D. 25.2 hp
10. A two stage cascade vapor compression refrigeration system uses ammonia in the low-
temperature loop and R-12 in the high-temperature loop. The ammonia provides 18 tons
cooling. If the high-loop temperature requires 10.12 kW compressor power and low-loop
15.93 kW, determine the COP of the system.
A. 2.429 B. 5.22 TR C. 3.314 TR D. 9.1 TR
11. Air in an airconditioner enters at 65% RH with w = 0.025 and leaves at 25 oC dry bulb
and 16 oC wet bulb. If mass of air is 10 kg/s, find the refrigeration capacity in tons of
refrigeration.
At 65% RH, w = 0.025: h = 85 KJ/kg, v = 0.803 m3/kg At 25 oC db, 16 oC wb: h = 43
KJ/kg;
A. 134.34 TR B. 119.45 TR C. 102.45 TR D. 98.34 TR
