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misseyla

Lv10

in Mechanical Engineering·

10 Jul 2022

When a man returns to his well-sealed house on a summer day, he finds that the house is at 32°C. He turns on the air conditioner, which cools the entire house to 20°C in 15 min. If COP of the air conditioner system is 2.5, determine the power drawn by the air conditioners. Assume the entire mass within the house is equivalent to 800 kg of air for which c = 0.72 kJ/kg – °C

5 answered

1 watching

misseyla

Lv10

in Mechanical Engineering·

10 Jul 2022

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 15 tons of cooling. If the high-loop temperature requires 10.12 kW compressor power and low loop 15.93 kW, determine the COP of the system.

4 answered

1 watching

misseyla

Lv10

in Mechanical Engineering·

10 Jul 2022

In an ammonia refrigeration system, the temperature in the evaporator is -12°C and the ammonia at the evaporator entry 0.1511 dry while at exit is 0.95 dry. If the rate of ammonia circulation is 5.64 kg/min, determine the refrigerating capacity of the system. Enthalpy of saturated liquid and vapor at -12°C is 144.929 kJ/kg and 1447.74 kJ/kg respectively.

4 answered

1 watching

misseyla

Lv10

in Mechanical Engineering·

10 Jul 2022

In an actual refrigeration cycle using R12 as working fluid, the refrigerant flow rate is 0.05 kg/s. Vapor enters the expansion valve at 1.15 MPa, 40°C (h = 238.5 kJ/kg) and leaves the evaporator at 175 kPa, -15°C (h = 345 kJ/kg). The electric iput to motor driving the compressor is measured and found 3.0 kW. Motor efficiency at this load 92% and mechanical efficiency 82%. Determine the actual coefficient of performance for this cycle.

5 answered

1 watching

misseyla

Lv10

in Mechanical Engineering·

10 Jul 2022

Saturated vapor ammonia at -16°C (h = 1442.60 kJ/kg) leaves the evaporator and enters the compressor at -6°C (h = 1465 kJ/kg). The refrigerant leaves the condenser as saturated liquid at 40°C (h = 390.6 kJ/kg) and enters the expansion valve at 35°C (h = 366.1 kJ/kg). Heat rejected from the condenser amount to 50 kW. The work to compressor is 208 kJ/kg, while the heat loss from compressor is 33 kJ/kg. If 95 kJ/kg of heat are lost in the piping between the compressor discharge and condenser inlet, determine the refrigerating capacity of the system.

5 answered

1 watching

misseyla

Lv10

in Mechanical Engineering·

10 Jul 2022

Three thousand cubic feet per minute of air are circulated over an air-cooled condenser. If the load on the condenser is 64,800 Btu/hr, compute the temperature rise of the air passing over the condenser. Specific volume of standard air (13.34 ft /lb)

4 answered

1 watching

misseyla

Lv10

in Mechanical Engineering·

10 Jul 2022

A reversed Carnot has a refrigerating COP of 2.5. Determine the ratio TH/TL.

5 answered

1 watching

misseyla

Lv10

in Mechanical Engineering·

10 Jul 2022

A twin cylinder ammonia compressor with volume displacement of 14,726 cm operates at 300 rpm. Condenser and evaporator pressure are 1200 kPa and 227 kPa respectively. Specific volume of refrigerant at the entrance of compressor is 528.26 L/kg. Compression process is polytropic with n = 1.20 and clearance factor of compressor is 2 percent. Determine the horsepower required.

4 answered

1 watching

misseyla

Lv10

in Mechanical Engineering·

10 Jul 2022

The refrigerant volume flow rate at the entrance of compressor were obtained from a test on a twin cylinder, single acting 15 cm x 20 cm, 320 rpm compressor ammonia refrigerating plant to be 33 L/s. Determine the volumetric efficiency of the compressor.

5 answered

1 watching

misseyla

Lv10

in Mechanical Engineering·

10 Jul 2022

A Freon 22 air conditioning under standard operating conditions of 35°C condensing and 5°C evaporating temperatures. The volume flow rate entering the compressor is 23.72 L/s. Determine the refrigerating capacity if the refrigerating effect is 164 kJ/kg. From the table for R22 the specific volume at the compressor entrance is 40.46 L/kg.

4 answered

1 watching

misseyla

Lv10

in Mechanical Engineering·

10 Jul 2022

An ammonia ice plant operates between a condenser temperature of 35°C and evaporator of -15°C. It produces 10 metric tons of ice per day from water at 30°C to ice at -5°C. Assuming simple saturation cycle, determine the horsepower of the motor if the adiabatic efficiency of the compressor n = 0.85 and mechanical efficiency n = 0.95. The specific heat of ice is 2.094 kJ/kg-°C 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.

5 answered

1 watching

misseyla

Lv10

in Mechanical Engineering·

10 Jul 2022

An ammonia simple saturation cycle operates with a suction pressure of 291.6 kPa and a condenser pressure of 1204 kPa develops 15 tons of refrigeration. Determine the theoretical horsepower of the compressor. The following enthalpies have been found: condenser entrance = 1653 kJ/kg, exit = 346.6 kJ/kg; compressor entrance = 1450.2 kJ/kg, exit = 1653 kJ/kg.

4 answered

2 watching

misseyla

Lv10

in Mechanical Engineering·

10 Jul 2022

A house that was heated by electric resistance heaters consumed 1200 kWh of electric energy in a winter month. If this house were heated instead by a heat pump that has an average performance factor, PF of 2.4, determine how much money the homeowner would be saved that month. Assume a price of 0.085 $/kWh for electricity.

5 answered

1 watching

misseyla

Lv10

in Mechanical Engineering·

10 Jul 2022

A refrigeration system is to cool bread loaves with an average mass of 450 g from 22°C to – 10°C at a rate of 500 loaves per hour by refrigerated air. Taking the average specific and latent heats of bread to be 2.93 kJ/kg-°C and 109.3 kJ/kg, respectively, determine the product load.

4 answered

1 watching

misseyla

Lv10

in Mechanical Engineering·

10 Jul 2022

An air-conditioning system is used to maintain a house at 75°F when the temperature outside is 95°F. The house is gaining the heat through the walls and windows at a rate of 1250 Btu/min, and the heat generation rate within the house from people, lights, and appliances amounts to 350 Btu/min. Determine the minimum power input required for this air-conditioning system

5 answered

1 watching

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