REFRIGERATION

Suppose that 30 gpm of water are removed from 60℉ to 40℉. Calculate the heat energy removed in Btu per hour

-299,880 Btu/hr

A basic refrigeration cycle requires 25 kW when operating at a condenser temperature of 70°C and a COP of 3.50. Determine the sink temperature.

-6.22 C

A simple saturated refrigeration cycle for R-12 system operates at an evaporating temperature of - 5℃ and a condensing temperature of 40℃. Determine the volume flow rate for a refrigerant capacity of 1 kW. Properties of R-12 At -5℃, h1 = hg = 349.3 kJ/kg V1 = vg = 0.06496 m3 /kg At 40℃, h3 = hf = 238.5 kJ/kg

0.0005866 m3 /s

What is the specific volume of refrigerant HFC-134a with an enthalpy of 570 kJ/kg and a pressure of 0.6 MPa?

0.06 m3 /kg

A refrigerator using refrigerant R-12. The input power is 585 W. Heat absorbed from the cooled space is 450 Btu/hr (0.13 kW). The coefficient of performance is most nearly

0.2

A refrigeration system using R-22 has a capacity of 320 kW of refrigeration. The evaporating temperature is -10℃ and the condensing temperature is 40℃. Calculate the fraction of vapor in the mixture before the evaporator. Properties of R-22: At -10℃; hg = 401.60 kJ/kg, hf =188.43 kJ/kg At 40℃; hf - 249.69 kJ/kg

0.287

A water cooler uses 50 lb/hr of melting ice to cool running water from 80 F to 42 F. Based on te inside coil area, U1 = 110 Btu/hr-ft2-F . Find the gpm of water cooled

0.38 gpm

An air refrigeration cycle compresses air from 70℉ (20℃) and 14.7 psia (101 kPa) to 60 psia (400 kPa) in a 70% efficient compressor. The air is cooled to 25℉(-4.0℃) in a constant pressure process before entering a turbine with isentropic efficient of 0.80. Assume air is an ideal gas. The coefficient of performance of the cycle is most nearly

0.7

A simple vapor compression cycle develops 15 tons of refrigeration using Ammonia as refrigerant and operating at condensing temperature of 24℃ and evaporating temperature of -18℃ and assuming compression are isentropic and that the gas leaving the condenser is saturated, find the power per ton. Properties of Ammonia: At 24℃: hf = 312.87 kJ/kg h2 = 1665 kJ/kg At -18℃: hg = 1439.94 kJ/kg

0.702 kW/ton

A refrigeration cycle has a coeffcient of performance 80% of the value of a Carnot refrigerator operating between the temperature limits of 50℃ and -5℃. For 3 kW of cooling, what power input is required?

0.77 kW

A refrigerator is 2 m high, 1.2 m wide and 1 m deep. The over-all heat transfer coefficient is 0.532 W/m2℃. How many kilograms of 0℃ ice will melt per hour if the inside temperature is maintained at 10℃ while the surrounding air temperature is at 35℃?

1.60 kg

A heat pump operates on the Carnot cycle between 40℉ and 700℉ (4℃ and 370℃). The coeffcient of performance is most nearly

1.8

Calculate the tons of refrigeration required to freeze in 4 hrs. 3mm of 10℃ water on a skating rink 61 m x 30 m if the ground temperature is 10℃ and the air temperature above the rink is 16℃. The heat transfer coefficient from the air to 0℃ ice is 6.8 W/m2℃, and the heat transfer coefficient from the ground -6℃ ice is 0.3402 W/ m2℃

101.69

A vapor compression refrigerator cycle shown. The fluid used is Freon -12. State 1 is saturated vapor at 0℉, and P2 is 114.5 psia. If the isentropic effciency is 0.8 and the coeffcient of performance (COP is 4, then what is the cooling produced by 2 lbm of vapor?

107.3 Btu

A Freon 12 waste water system operating at 5℃ suction temperature and a 40℃ condensing temperature has an evaporator load of 5 tons. If the condenser is selected for a 7℃ water temperature rise, how many gpm must be circulated through the condenser? The following enthalpies have been found: condenser entrance = 377 kJ/kg, exit = 238.5 kJ/kg; evaporator entrance = 238.5 kJ/kg, exit = 353.6 kJ/kg.

11.46

In an ammonia condensing machine ( compressor plus condenser) the water used for condensing is 55℉ and the evaporator is at 15℉. Calculate the ideal COP.

11.875

In a Freon-12 vapor compression system, liquid refrigerant leaves the condenser at 40℃ and is then admitted into an internal heat exchanger at 30℃. The evaporator temperature is -20℃. Determine the cooling effect per unit mass of refrigerant.

115 kJ/kg

A newly installed refrigeration system produces 250 Btu/lb of cooling. Calculate the mass of refrigerant shall be used in the refrigeration system to have a rating of one ton of refrigeration.

1152 lb/day

In order to cool 1 ton (1000 kg) of water at 20°C in an insulated tank, a person pours 80 kg of ice at -5°C into the water. Determine the final equilibrium temperature in the tank. The melting temperature and the heat of fusion of ice at atmospheric pressure are 0°C and 333.7 kJ/kg, respectively.

12.43 C

A thermoelectric refrigerator that resembles a small ice chest is powered by a car battery, and has a COP of 0.10. If the refrigerator cools a 0.350 L canned drink from 20°C to 4°C in 30 min, determine the average electric power consumed by the thermoelectric refrigerator.

130 watts

A vapor compression refrigeration system is designed to have a capacity of 150 tons of refrigeration. It produces chilled water from 22°C to 2°C. Its actual coefficient of performance is 5.86 and 35% of the power supplied to the compressor is lost in the form of friction and cylinder cooling losses. Determine the condenser cooling water required for a temperature rise of 10°C.

14.75 kg/s

A supply of 50 kg of chicken at 6°C contained in a box is to be frozen to -18°C in a freezer. Determine the amount of heat that needs to be removed. The latent heat of the chicken is 247 kJ/kg, and its specific heat is 3.32 kJ/kg-°C above freezing and 1.77 kJ/kg-°C below freezing. The container box is 1.5 kg, and the specific heat of the box material is 1.4 kJ/kg-°C. Also the freezing temperature of chicken is -2.8°C.

15,206.4 kJ

A refrigerator cools a continuous aqueous solution (Cp= 1 Btu/lbm-℉; 4.19 kJ/kg℃) flow of 100 gal/min (0.4m3 /min) from 80℉(25℃) to 20℉(25℃) environment. The minimum power requirement is most nearly

150 hp(94 kW)

A refrigeration system operates on the reversed Carnot cycle. The minimum and maximum temperatures are -25℃ and 72℃, respectively If the heat rejected at the condenser is 6000 kJ/min, find the power input required.

1686.83 kJ/min

For efficient operation, the condensing temperature should not be more than

17 C

A Carnot refrigerating system receives heat from a cold reservoir at 0℃. The power input is 1750 W per ton of refrigeration. The system's coeffcient of performance is

2.0

A household window air conditioner has an energy effciency rating of 7.5 kJ/W-hr. What is the coeffcient of performance for the unit?

2.1

How much refrigeration capacity is required to cool 2000 cfm of air from 85℉ to 70℉?

2.7 TOR

Five hundred kilograms of poultry enter a chiller at 8℃ and are frozen and chilled to a final temperature of -18℃ for storage in 15 hours. The specific heat above and below freezing are 3.18 kJ/kg℃ and 1.55 kJ/kg℃ respectively. The latent heat is 246 kJ/kg and the freezing temperature is -5℃. Compute the product load.

2.85 kW

A heat pump takes heat from groundwater at 7℃ and maintains a room at 21℃. What is the maximum coeffcient of performance possible for this heat pump?

21

Boiling point of Freon - 12 at atmospheric pressure is

21 F

Ammonia is used in a reversed Carnot cycle refrigerator with reservoirs at 110℉(45℃) and 10℉(-10℃). 1000 Btu/hr (1000 kJ/h) are to be removed. The work input is most nearly.

210 Btu/hr (210 kJ/h)

Magnolia Dairy products plant must cool 4000 gallons of fresh milk received from the farm per day from an initial temperature of 80℉ to a temperature of 38℉ in 5 hours. If the density of milk is 8.6 lb/gal, specific gravity is 1.03 and specific heat is 0.935, what must be the capacity of the refrigerating machine in tons?

22.515

A household refrigerator that has a power input of 450 watts and a COP of 2.5 is to cool five large watermelons, 10 kg each, to 8⁰C. If the watermelons are initially at 20⁰C, determine how long will it take for the refrigerator to cool them. The watermelons can be treated as water whose specific heat is 4.2 KJ/kg-⁰K.

2240s

A San Miguel Corporation processing plant that requires cooling of 120 gpm of water from 15.6C to 10C, the cooler heat transfer surface area has 5.5C differential between the chilled water leaving the cooler and the R-12 evaporating temperature. Assume that the condenser heat transfer surface area will enable a 5.5℃ differential between the condenser water out and R-12 condensing temperature. Water for the condensing medium at 29.4℃ inlet and 35℃ outlet. Find the tons of refrigeration.

50.49

In a CO2 refrigerating plant, the specific enthalpy of the refrigerant as it leaves the condenser is 135 kJ/kg and as it leaves the evaporator it is 320 kJ/kg. If the mass flow of the refrigerant is 5 kg/min, calculate the refrigerating effect per hour.

55 500 kJ/hr

Determine the heat extracted from 1350 kg of water from 25℃ to ice at -10℃

621, 150 kJ

Which of the following in CHU/hr is equivalent to ten tons of refrigeration (TOR)?

66,666.67

A 10 m3 uninsulated tank contains nitrogen at 2 MPa and 250℃. The temperature of the environment surrounding the tank is 35℃. Disregard the mass of the tank. What entropy change do the surroundings experience after a long period of time?

67 kJ/K

A Carnot cycle refrigerator operates between -11℃ and 22℃. What is the coefficient of performance

7.9

A cylindrical flash tank mounted with its axis horizontal is used to separate liquid ammonia from ammonia vapor. The ammonia bubbles through the liquid with 70 m3 /min leaving the disengaging surface. The disengaging rate is limited to 60 m/min and the liquid level is to operate with the liquid level one-third to the diameter from the top. Determine the diameter if the tank is 1.5 m long.

830 mm

Determine the heat extracted from 2000 kg of water from 25°C to ice at -10°C

921,150 kJ

A refrigerating system operates on the reversed Carnot Cycle. The higher temperature of the refrigerant in the system is 120℉ and the lower is 10℉. The capcity is 20 tons. Neglect losses. Determine the network in Btu/min.

936.21 Btu/min

Which of the following is also known as refrigerant (R-600)

Butane

A type of refrigerant control typically used in household refrigeration

Capillary Tube

What is refrigerant R-744?

Carbon dioxide

What is the other name for the Refrigerant R-40?

Chloromethane

Mass of ice at -4℃ is needed to cool 115 kg of vegetables in a bunker for 24 hours. The initial temperature of vegetables is assumed to be 30℃. It is also assumed that the average temperature inside the bunker is 7℃ within 24 hour period. If the heat gained per hour in the bunker is 30% of the heat removed to cool the vegetable from 30℃ to 7℃, what would be the required mass of ice? Note: Cp of ice = 1.935 kJ/kg-K Cp of veggies = 3.35 kJ/kg-K Cp of water = 4.186 kJ/kg-K Lf of ice = 33

23.82 kg

The weight of ammonia circulated in a machine is found to be 21.8 lb/hr. if the vapor enters the compressor with a specific volume of 9.6 ft3 /lb, calculate the piston displacement, assuming 80% percent volume efficiency.

261.6 ft3 /hr

An ammonia compressor is used in a heat pump cycle. Suction pressure is 30 psia (300 kPa). Discharge pressure is 160 psia (1.0 MPa). Saturated liquid ammonia enters the throttle valve. The refrigeration effect is 500 Btu/lbm (1200 kJ/kg) ammonia. The coefficient of performance as a heat pump is most nearly.

5.3

A heat pump using refrigerant R-12 operates on the Carnot cycle. The refrigerant evaporates and is compressed at 35.7 psia and 172.4 psia ( 246 kPa and 1190 kPa), respectively. The coeffcient of performance is most nearly.

5.8

Which of the following is a proper statement of the second law of thermodynamics?

It is impossible for a system working in a complete cycle to accomplish, as its sole effect, the transfer of heat from a body at a given temperature to a body at a higher temperature.

Which of the following is NOT a part of low pressure side in refrigeration system?

Liquid line

Which of the following Refrigerants designated by chemical formula CF3CH2F?

R134a

Which of the following Refrigerants that is represented by the chemical formula CHClF2?

R22

Which compressors are used in small, medium size refrigerators?

Reciprocating compressors

Tubing that is unenclosed and therefore exposed to crushing, abrasion, puncture, or similar damage after installation.

Unprotected Tubing

Large leaks in a Freon system cannot always be detected with a halide torch because it changes color with the slightest amount of Freon present. A large leak can be detected easier by applying

a soapsuds solution, mixed with a little glycerin to hold the solution together, and watch for bubbles

If the compressor short-cycles on the low-pressure cutout, the trouble might be

any of these

What operates low-pressure cutout switch?

bellows

Refrigerants consisting of mixtures of two or more different chemical compounds, often used individually as refrigerants for other applications

blends

What is the major problem of heat pump?

frosting

Superheating the refrigerant in refrigeration system, without useful cooling, the refrigeration effect per unit mass will

increase

A Freon unit will tend to short-cycle when operating under

light loads

The purpose of relief valves on refrigeration machines is to

prevent excessive pressure in case of stoppage on the discharge side of the system

By subcooling the refrigerant in refrigeration system, the compressor power per unit mass will

remain the same

Low suction pressure is caused by

solenoid valve not functioning properly

If the cooling water to the condenser suddenly fails?

the compressor will shut down

What does the term "tonnage" refer to in regard to refrigeration cycles? A. the rate at which heat is removed from a refrigeration cycle B. the coeticient of performance of a refrigeration cycle C. the energy effciency rating of a refrigeration cycle D. the enthalpy change of a refrigeration cycle

the rate at which heat is removed from a refrigeration cycle

The cooling-water side of the condenser should be opened for inspection every

three months

Sweating of the crankcase is caused by which of the following?

too much oil in the system

Which of the following is the usual cause of slugging?

too much refrigerant in the system

The refrigerant use in steam jet cooling is

water

The power requirement of a Carnot refrigerator in maintaining a low temperature region at 300 K is 1.5 kW per ton. Find the heat rejected.

5.02 kW

A refrigeration system using ammonia and the refrigerant has a condensing temperature of 27℃ and an evaporating temperature of -18℃. If it uses wet compression, calculate its coefficient of performance

5.01

A single-stage ammonia compressor is producing 10 tons of refrigeration and the power consumed is 15 Hp. Suction pressure is 25 psi, condensing pressure is 180 psi. Brine temperature is 20℉ of brine cooler. Determine the actual coefficient of performance.

3.14

An air compression refrigeration system is to have an air pressure of 100 psia in the brine tank and an allowable air temperature increase of 60F. For standard vapor compression cycle temperatures of 77F entering the expansion cylinder and 14 F entering the compression cylinder, calculate the coefficient of performance

3.3

If the energy efficiency ratio of the refrigeration system is 12.6, what is the COP of the system?

3.69

An ice plant produces 20 tons of ice per day at - 15oC from water at 25oC. If the miscellaneous losses are 12% of the freezing and chilling loads, calculate the refrigeration capacity of the plant in tons of refrigeration

31.5

Seventy-five hundred pounds of fresh beef enter a chilling cooler at 102℉ and are chilled to 45℉ each day. Compute the product load in Btu per 24 hours. The specific heat of beef above freezing is 0.75 Btu/lb-℉.

320,600 Btu

A refrigeration system using refrigerant 22 is to have a refrigerating capacity of 80 kW. The evaporating temperature is -10℃ and the condensing temperature is 42℃, determine the volume flow rate of refrigerant at inlet to the compressor.

35 L/s

A refrigeration system produces 348.9 kJ/kg of cooling. In order to have a rating of 1 ton of refrigeration, What must be the mass floow rate of the vapor? (1 ton of refrigeration = 12.66 MJ/hr, approximately the rate required to freeze 2000 lbm of ice in a day.)

36.29 kg/hr

A creamery must cool 20,000 liters of milk received each day from an initial temperature of 29°C to a final temperature of 2°C in 5 hours. If refrigeration losses amount to 10 percent of the cooling load, what must be the capacity of their refrigerating machine? Note: specific heat of milk is 3.9 kJ/kg-K and SG = 1.05.

38.5 TOR

Ammonia is used in a reversed Carnot cycle refrigerator with reservoirs at 110℉(45℃) and 10℉(-10℃). 1000 Btu/hr (1000 kJ/h) are to be removed. The coefficient of performance is most nearly.

4.7

An ideal vapor compression cycle requires 2.5 kW to power the compressor. You have found the following data for the cycle; the enthalpy at the condenser entrance - 203 kJ/kg, exit =55 kJ/kg; evaporator entrance =55 kJ/kg, exit = 178 kJ/kg. If the mass flow rate of the refrigerant is 0.10 kg/s, then the coefficient of performance of this refrigeration cycle is most nearly:

4.92

A single acting, twin cylinder, Ammonia compressor with bore equal to stroke is driven by an engine at 250 rpm. The machine is installed in a chilling plant to produce 700 kW of refrigeration at -18°C evaporating temperature. At this temperature the cooling effect per kg mass is 1160 kJ. The specific volume of vapor entering the compressor is 0.592 m3 per kilogram. Assume 85% volumetric efficiency, determine the bore in mm

400 mm

A 200 mm x 300 mm water cooled compressor runs at 1200 rpm and receives ammonia refrigerant at 200 kPa (-10℃) where h = 1442 kJ/kg, & specific volume of 619.9 L/kg. It compresses to a final pressure of ammonia where h = 1759 kJ/kg-K. Compute the work of the compressor in horsepower given n of ammonia is 1.12 and the mass flow rate of 1 kg/

425

A refrigeration system operates on an ideal vapor compression using R-12 with an evaporator temperature of -30℃ and a condenser exit temperature of 49.30℃ and requires 74.6 kW motor to drive the compressor. What is the capacity of the refrigerator in tons of refrigeration? Enthalpy at condenser entrance = 382 kJ/kg, exit = 248.15 kJ/kg, at evaporator entrance = 248.15 kJ/kg, exit - 338.14 kJ/kg.

43.1

To cool farm products, 300 kg of ice at -4.4℃ are placed in bunker. Twenty four hours later the ice have melted into water at 7.2℃. What is the average rate of cooling provided by the ice in kJ/hr?

4679.28 kJ/hr

Refrigerant HFC-134a is ideally throttled from an enthalpy of 480 kJ/kg at the evaporator pressure of 0.2 MPa to a pressure of 0.02 MPa. What is the final enthalpy?

480 kJ/kg

A refrigeration system consumed 28,000 kw-hr per month of energy. There are 20 % of energy is lost due to cooling system of compressor and motor efficiency is 90 %. If COP of the system is 6, find the tons of refrigeration of the system.

49.15 TR

For efficient operation, the condensing temperature should not be lower than

5 C

Modern way of detecting air compressor leak is by using

Acoustic leak detector

Which of the following is a reversed Brayton cycle?

Air refrigeration cycle