An automobile air conditioner uses refrigerant-134a as the cooling fluid. The evaporator operates at 100 kPa gage and the condenser operates at 1.5 MPa gage. The compressor requires a power input of 6 kW and has an isentropic efficiency of 85 percent. Atmospheric air at 25°C and 60 percent relative humidity enters the evaporator and leaves at 8°C and 90 percent relative humidity. Determine the volume flow rate of the atmospheric air entering the evaporator of the air conditioner, in m3/min.
The volume flow rate of the air at the inlet of the evaporator.
Answer to Problem 134RP
The volume flow rate of the air at the inlet of the evaporator is
Explanation of Solution
Express the mass flow rate of dry air at state 1.
Here, volume flow rate at state 1 is
Write the formula for mass flow rate of condensate water.
Here, specific humidity at state 1 and 2 is
Write the formula for an energy balance on the control volume.
Here, the rate of heat absorbed by the R-134a is
Write the formula of the mass flow rate of the refrigerant.
Here, the mass flow rate of refrigerant is
Write the formula for the rate of heat absorbed by the R-134ain the evaporator.
Here, the enthalpy of the state 4 in the refrigerant is
Conclusion:
Refer Figure A-31, “psychometric chart at
Substitute
Substitute
Refer Table A-4, “saturated water-temperature table”, and write the specific enthalpy of condensate water at state 2 at temperature of
Here, entropy of saturation liquid at temperature of
Write the formula of interpolation method of two variables.
Here, the variables denote by x and y is temperature and specific enthalpy of condensate water at state 2 respectively.
Show the specific enthalpy of condensate water at state 2 corresponding to temperature as in Table (1).
Temperature |
Specific enthalpy at state 2 |
5 | 21.02 |
8 | |
10 | 42.022 |
Substitute
Substitute
Substitute
From the Table A-12 “Saturated Refrigerant-134a-Pressure Table”, obtain the value of the specific enthalpy and entropy at the inlet of the compressor for isentropic process at 200 kPa of pressure and dryness fraction of 1 as
Refer Table A-12 “Saturated Refrigerant-134a-Pressure Table”, and write the specific enthalpy at the exit of the compressor for isentropic process at 1600 kPa of pressure and entropy of
From the Table A-12 “Saturated Refrigerant-134a-Pressure Table”, obtain the value of the specific enthalpy at the inlet of the compressor for isentropic process at 1600 kPa of pressure as:
Here, the specific enthalpy at the state 4 and 3 are equal in the refrigerant.
Substitute 6 KW for
Substitute
Substitute
Thus, the volume flow rate of the air at the inlet of the evaporator is
Want to see more full solutions like this?
Chapter 14 Solutions
Thermodynamics: An Engineering Approach
- Problem 2: An air-conditioning system operates at a total pressure of 1 atm and consists of a heating section and a humidifier that supplies wet steam (saturated water vapor) at 100 degrees celsius. Air enters the heating section at 10 degrees celsius and 70 percent relative humidity at a rate of 35 m^3/min, and it leaves the humidifying section at 20 degree celcius and 60 percent relative humidity. Heating coils Leeeeeeee 10°℃ 70% 35 m³/min AIR P = 1 atm Sat. vapor 100°C Humidifier 20°C 60% a. Humidity ratio at inlet b. Relative humidity at the exit c. Humidity ratio at exit d. Rate at which water is added to humidifying sectionarrow_forwardOn a hot summer day, the temperature is 35 ° C, barometric pressure 103 kPa and relative humidity 90%. One The air conditioner draws the outside air and cools it to 20 ° C and raises the air to 12500 L / h. Calculate the condensation rate of the moisture (kg / h) and the flow rate of the air drawn from the outside.arrow_forwardAn air-conditioner cools a flow of ambient moist air at 30°C and 80% relative humidity with 0.24 kg/s flow. The exit temperature is 12°C and 40% relative humidity. Pressure is at 100 kPa throughout the system. Condensed water from the moist air intake leaves the air-conditioner at a temperature of 6°C. Find the flow rate of water from the system and the amounts of heat transfer rates needed to condense the water, cool the water vapor, cool the air, and the total heat transfer rate.arrow_forward
- Water leaving a thermoelectric plant condenser at 36 °C enters a cooling tower at a mass flow rate of 3.6x107 kg/h. A flow of cooled water returns to the condenser from the tower at a temperature of 30 °C and with the same flow rate. Make-up water is added separately at 20°C. Atmospheric air is admitted to the cooling tower at 25 °C and with 36% relative humidity. Moist air leaves the tower at 90% relative humidity and 35°C.Determine the mass flow rate of dry air and make-up water, in kg/h. Neglect heat exchanges and fan power. Assume permanent regime.arrow_forwardAn air-conditioning system operates at a total pressure of 1 atm and consists of a heating section and a humidifier that supplies wet steam (saturated water vapor) at 100 degrees celsius. Air enters the heating section at 10 degrees celsius and 70 percent relative humidity at a rate of 35 m^3/min, and it leaves the humidifying section at 20 degree celcius and 60 percent relative humidity. Heating coils Loooooooo 10°C 70% 35 m³/min AIR P = 1 atm Sat. vapor 100°C Humidifier € 20°C 60% a. Humidity ratio at inlet b. Relative humidity at the exit c. Humidity ratio at exit d. Rate at which water is added to humidifying sectionarrow_forwardRequired information NOTE: This is a multi-part question. Once an answer is submitted, you will be unable to return to this part. An air-conditioning system operates at a total pressure of 1 atm and consists of a heating section and a humidifier that supplies wet steam (saturated water vapor) at 100°C. Air enters the heating section at 10°C and 70 percent relative humidity at a rate of 32 m /min, and it leaves the humidifying section at 20°C and 60 percent relative humidity. Use data from the tables. Sat. vapor 100°C Heating coils Humidifier 10°C Air 20°C 70% 60% ymYmin P=1 atm Determine the temperature and relative humidity of air when leaves the heating section. The temperature is °C. The relative humidity is %.arrow_forward
- HUMIDIFIER: MASS BALANCE On a hot summer day, the air is at 30.6 ° C and 80% relative humidity. The air conditioning in a building supplies 30 m3 / min of air at 13 ° C to keep the air inside the building at an average temperature of 24 ° C and 40% relative humidity. If the ventilation switch of the air conditioner is “open”, the air from outside enters the unit as shown in the drawing (I): The air conditioner cools the air to a temperature low enough to condense the required amount of water and reheat it to 13 ° C (unsaturated current), at which point it has the same absolute humidity as the air in the building. Calculate: a. the speed at which condenses water (kg / min) b. the temperature at which the air must be cooled to condense water at this rate. Do the calculations without using the psychrometric chart (although 1 atm of current pressure can be assumed). If the ventilation switch is closed, as normal, the air from inside the building would be recirculated in the air…arrow_forwardThe design condition for a space is 77oF db and 50% relative humidity with 55oF db supply air at 90% relative humidity. A 50-ton, constant-volume space air- conditioning system uses face and bypass and water temperature control. Outdoor air is supplied at 95oF db, 60% relative humidity with a ratio of 1 lbm to 5 lbm re-circulated air. A part-load condition exists where the total space load is decreased by 50% and the SHF is increased to 90%. The outdoor air condition changes to 85oF db and 70% relative humidity. Assume sea-level conditions. a) At full – load conditions:a. Show all the processes on a psychrometric chart.b. Determine the temperature must the air be supplied to the space at fullload conditions.c. Determine the apparatus dew point temperature at full load conditions. b)At part – load conditions:a. Show all the processes on a psychrometric chart.b. Determine the temperature must the air be supplied to the space at partload conditions.c. Determine the apparatus dew point…arrow_forwardTo eliminate dust, air with a dry bulb temperature of 38 oC and a wet bulb temperature of 27 oC scrubbed with water. The water temperature is kept at 25 degrees Celsius. The air that is expelled from the scrubber is in balance with water. It is then heated to 93 degrees Celsius in an air preheater before being admitted to an adiabatic rotary dryer. The air exits the drier at 49 degrees Celsius. Moisture is lost at a rate of 0.05 kg of water per kg of product. The total product capacity is 1000 kg/h. Calculate the following (using a psychrometric chart): is a. Total weight of dry air used per hour. b. Total volume of air leaving the dryer.arrow_forward
- The sensible effectiveness of a heat recovery ventilator is 53.6%. The inlet temperature of fresh air is 35°C and relative humidity is 50%. The inlet temperature of exhaust air is 24°C and relative humidity is 60%. The mass flow rates of fresh air and exhaust air are 1.3 kg/s and 1.5 kg/s, respectively. Calculate the outlet fresh air temperature and estimate the energy saving ratio of adopting heat recovery ventilator.arrow_forwardP=19 Moist air goes into air-conditioning unit at a degree-30 C and 70% relative humidity, and it is cooled to 20-degree C and 20% relative humidity at a constant pressure of 1.01325 bar. The mass flow rate of dry air is mda=63 kg/s The unit applies refrigerant R-134a as the cooling fluid that enters inside the tubes of the cooling coil at 3.6 bar with a quality of 0.2 and leaves as a saturated vapor at the same pressure of 3.6 bar. Use the psychometric chart to determine: a) Mass flow rate of condensed water in kg/s b) The heat transfer rate from the air to the cooling coil in kW (Use the psychometric chart) c) The mass flow rate of R-134a that is needed in kg/sarrow_forwardIn an air conditioning system 30 emm of fresh out door air is introduced at 43°C DBT and 30% RH. The remaining air is recirculated from the room maintained at 25°C DBT and 50% RH. The bypass factor of cooling coil is 0.15 and apparatus dew point Is 11.8°C, RSH 100 kW and RLH 15 kW. Determine: (1) Humidity ratios for outdoor and Room conditions. (2) OASH & OALH (3) ERSH and ERLH (iv) Supply air temperature (v) Supply air volume flow rate using ERSH (vi) Temperature at inlet to cooling coil by assuming density of niside and outside air sanie Given that saturation pressures of water at 25°C and 43C are 3.1693 KP and 8.6459 KPa respectively. Show the process on psychrometric chart standard atmospheric pressure=1.01325 bar.arrow_forward
- Elements Of ElectromagneticsMechanical EngineeringISBN:9780190698614Author:Sadiku, Matthew N. O.Publisher:Oxford University PressMechanics of Materials (10th Edition)Mechanical EngineeringISBN:9780134319650Author:Russell C. HibbelerPublisher:PEARSONThermodynamics: An Engineering ApproachMechanical EngineeringISBN:9781259822674Author:Yunus A. Cengel Dr., Michael A. BolesPublisher:McGraw-Hill Education
- Control Systems EngineeringMechanical EngineeringISBN:9781118170519Author:Norman S. NisePublisher:WILEYMechanics of Materials (MindTap Course List)Mechanical EngineeringISBN:9781337093347Author:Barry J. Goodno, James M. GerePublisher:Cengage LearningEngineering Mechanics: StaticsMechanical EngineeringISBN:9781118807330Author:James L. Meriam, L. G. Kraige, J. N. BoltonPublisher:WILEY