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Grading Sheet~~~~~~~~~~~~~~

MIME 3470—Thermal Science Laboratory~~~~~~~~~~~~~~Laboratory №. 17

REFRIGERATION CYCLE ANALYSISStudents’ Names / Section №

POINTS SCORE TOTALPRESENTATION—Applicable to Both MS Word and Mathcad Sections GENERAL APPEARANCE 5 ORGANIZATION 5 ENGLISH / GRAMMAR 5ORDERED DATA, CALCULATIONS & RESULTS TABLE OF PROPERTIES FOR THE 8 STATES 10 PLOT IDEAL CYCLE (W/ BLOCK ARROWS) USING PRESSURES 3 & 8 10 PLOT ACTUAL CYCLE (W/ BLOCK ARROWS) 10 CALCULATE & 10TECHNICAL WRITTEN CONTENT DISCUSSION—GENERAL DISCUSSION OF CALCULATIONS 5 EXPLAIN IN TERMS OF 1ST & 2ND LAWS THE DISCREPENCIES BETWEEN THE TWO PLOTS ABOVE 10 ARE THE DISCREPENCIES IN THE PROPER DIRECTION(S)? 10 SHOULD THERE BE DIFFERENCES BETWEEN THE ACTUAL & IDEAL CYCLES? 10 CONCLUSIONS 5ORIGINAL DATASHEET 5

TOTAL 100

COMMENTS

GRADER—d

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MIME 3470—Thermal Science Laboratory~~~~~~~~~~~~~~Laboratory №. 17

REFRIGERATION CYCLE ANALYSIS~~~~~~~~~~~~~~

LAB PARTNERS: NAME NAMENAME NAMENAME NAME

SECTION №EXPERIMENT TIME/DATE: TIME, DATE

~~~~~~~~~~~~~~OBJECTIVE—of this exercise is to determine the various coefficients of performance, COP. Specifically, these are the ideal and actual cycle COPs using the attached thermodynamic diagram for Refrigerant-12 (R12). INTRODUCTION—A refrigeration cycle is a cycle which transfers heat from a low temperature sink to a high temperature sink by the application of energy from a third source. A refrigeration cycle differs from what is commonly called a heat pump in that the desired output is the heat transfer from the cold sink rather than the heat transfer to the hot sink.

The most common type of refrigeration cycle is the mechanical vapor compression cycle. This cycle is essentially a Rankine Cycle run backwards. A schematic and a T-s diagram of the cycle appears in Figure 1. The cycle is referred to as a mechanical compression because the compression process (States 1 to 2) is accomplished by a mechanical compressor that is driven by an external power source. This source is usually an electric motor.

Figure 1— Schematic and T-s process diagram of an ideal vapor-compression refrigeration cycle

ANALYSIS—The performance of a refrigeration cycle is given in terms of the Coefficient of Performance or COP and the cooling capacity . The overall COP for the cycle is

(1)

where, = electric power to the compressor motor. From the First Law, the cooling capacity is

(2)

where, = mass flow of air through the evaporator

= specific heat of air

= temperature of air entering the evaporator

= temperature of air leaving the evaporatorThe refrigeration cycle in Figure 1 is an ideal cycle. It is ideal

because the compression process is isentropic (States 1 to 2) and there are no pressure losses across either the evaporator (States 4 to 1) or the condenser (States 2 to 3). The power to the compressor and the cooling capacity for the ideal refrigeration cycle are

(3)

(4)

where, = mass flow of refrigerant through the system.Therefore, from Equation 1, the ideal COP is

. (5)

Figure 2— Schematic and T-s diagram for a vapor-compression refrigeration cycle including irreversibilities in all components

The refrigeration cycle for an actual cycle is presented in Figure 2. This cycle varies from the ideal in that the compression process is non-isentropic (States 1 to 2) and there are pressure losses across both the evaporator (States 7 to 8) and the condenser (States 3 to 4). The cooling capacity, , and the heat load from the condenser,

, are

(6)

and (7)

and (8)

Equation 8 is obtained from an energy balance across the air side of the condenser. The temperatures and are the air temperatures in and out of the condenser.

Equation 3 would be valid for an actual cycle only if the compression and combination compressor-motor efficiencies were both unity. The compression efficiency, , and the compressor-

motor efficiency, , are defined by

(9)

and (10)

Therefore, the cycle overall COP for actual cycle is

(11)

PROCEDURE—Turn on and study the cycle and the components of the refrigeration unit shown in Figure 3. Trace the R12 flow path and identify the compressor, evaporator, condenser, and expansion valve inlets and outlets. Make sure that the flow path is correct by opening and closing the proper valves. For the unit to act on a refrigeration cycle, the flow from the evaporator must go to the top of the compressor. After the unit has stabilized, take temperature and pressure data for flows into and out of the

a. Compressor (States 1 and 2)b. Condenser (States 3 and 4)

Evaporator

Condenser

Valve

Throttling

Expansion

)(

condQ

evapQ

T

s

hConstant

pConstant

pConstant

Compressor

compW

Evaporator

CondensercondQ

evapQ

T

s

Compressor

compW

1p8p

2p

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c. Expansion valve (States 5 and 6)d. Evaporator (States 7 and 8).

Figure 3— Refrigeration cycle experimental setup

For the ReportNOTE: This experiment is to be done in English units only. This is because the only pressure-enthalpy diagram for Freon-12 we have access to is in English units. 1. Make a table (supplied below) of state properties (p, T, v, h,

and s) for the eight states of the cycle. 2. On the supplied p-h chart, plot the ideal cycle for the appro-

priate conditions of our experimental data. The student is to use Pressures 3 and 8 to determine the ideal cycle. Be sure to indicate with block arrows across the lines the occurrences of

, , and .3. Redo Item 2 using the actual cycle data points. This plot

should appear on the same sheet as that of Item 2. 4. Calculate and

5. Explain in terms of the First and Second Laws of Thermodynamics, the nature of the discrepancies between the cycle paths in Items 2 and 3. Are the discrepancies in the proper direction(s)? Should there be differences between the actual and ideal cycles?

ORDERED DATA, CALCULATIONS, and RESULTS REMEMBER: DO THIS ONE IN ENGLISH UNITS ONLYRequirement 1 : Make a table of state properties (p, T, v, h, and s) for the eight states of the cycle.

StateData

Compressor

In

Compressor

Out

Condenser

In

Condenser

Out

ExpansionValve In

ExpansionValve Out

Evaporator

In

Evaporator

Outp(psi)gagep(psi)

absolute (+14.7psi)

T(F)v(ft3/lbm)

h(Btu/lbm)s(Btu/

lbmR)

Requirement 4.Calculate and . The student may want to use the Mathcad object (below) for this. Otherwise, feel free to delete the object.

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Requirements 2 & 3. On the supplied p-h chart, plot the ideal cycle for the appropriate conditions of our experimental data. The student is to use Pressures 3 and 8 to determine the ideal cycle. Be sure to indicate with block arrows across the lines the occurrences of ,

, and . Redo Item 2 using the actual cycle data points. This plot should appear on the same sheet as that of Item 2.

mQcond

IDEAL CYCLEACTUAL CYCLE

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DISCUSSION OF RESULTS

Explain in terms of 1st and 2nd Laws the discrepencies between the two plots. Answer:

Are the discrepencies in the proper directions? Answer:

Should there be differences between the actual and ideal cycles? Answer:

CONCLUSIONS

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APPENDICES APPENDIX A— DATA SHEET FOR REFRIGERATION CYCLE ANALYSIS NOTE: 1. THE CONDENSOR IS ON THE HIGH PRESSURE SIDE

WHILE THE EVAPORATOR IS ON THE LOW PRESSURE SIDE2. ALL PRESSURE DATA ARE GAGE PRESSURES ; HOWEVER,

THE PROPERTY TABLES USE ABSOLUTE PRESSURE —BE SURETO CONVERT TO ABSOLUTE BEFORE LOOKING UP PROPERTIES.

Time/Date: ___________________________

Lab Partners: ___________________________ ___________________________

___________________________ ___________________________

___________________________ ___________________________

StateData

Compressor

In

Compressor

Out

Condenser

In

Condenser

Out

ExpansionValve In

ExpansionValve Out

Evaporator

In

Evaporator

Out

p(psi) dT(F) d

Evaporator

CondensercondQ

evapQ

Compressor

compW

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APPENDIX B— R-12 (CC l2F2) THERMODYNAMIC PROPERTIES v(ft3/lbm), u(Btu/lbm), h(Btu/lbm), s(Btu/lbm°R) Saturated

Superheated

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APPENDIX C— BIOGRAPHIC SKETCHES The Father of CoolWillis Haviland Carrier—The History of Air ConditioningBy Mary Bellis

“I fish only for edible fish, and hunt only for edible game even in the laboratory.” — Willis Haviland Carrier on being practical.

In 1902, only one year after Willis Haviland Carrier graduated from Cornell University with a Masters in Engineer-ing, the first air (temperature and humi-dity) conditioning was in operation, making one Brooklyn printing plant owner very happy. Fluctuations in heat and humidity in his plant had caused the dimensions of the printing paper to keep altering slightly, enough to ensure a mis-alignment of the colored inks. The new air conditioning machine created a stable environment and aligned four-color printing became possible. All thanks to the new employee at the Buffalo Forge Company, who started on a salary of only $10 per week.

The ‘Apparatus for Treating Air’ (U.S. Pat# 808897) granted in 1906, was the first of several patents awarded to Willis Haviland Carrier. The recognized ‘father of air conditioning’ is Carrier, but the term ‘air conditioning’ actually originated with textile engineer, Stuart H. Cramer. Cramer used the phrase ‘air conditioning’ in a 1906 patent claim filed for a device that added water vapor to the air in textile plants—to condition the yarn.

In 1911, Willis Haviland Carrier disclosed his basic Rational Psychrometric1

Formulae to the American Society of Mechanical Engineers. The formula still stands today as the basis in all funda-mental calculations for the air conditioning industry. Carrier said he received his ‘flash of genius’ while waiting for a train. It was a foggy night and he was going over in his mind the problem of temperature and humidity control. By the time the train arrived, Carrier had an understanding of the relationship between temperature, humidity and dew point.

Industries flourished with the new ability to control the temperature and humidity levels during and after production. Film, tobacco, pro-cessed meats, medical capsules, textiles and other products acquired significant improvements in quality with air conditioning. Willis and six other engineers formed the Carrier Engineering Corporation in 1915 with a starting capital of $35,000 (1995 sales topped $5 billion). The company was dedicated to improving air conditioning technology.

In 1921, Willis Haviland Carrier patented the centrifugal refrigeration machine. The ‘centrifugal chiller’ was the first practical method of air conditioning large spaces. Previous refrigeration machines used reci-procating-compressors (piston-driven) to pump refrigerant

1 psy·chrom·e·ter n. : a hygrometer consisting essentially of two similar thermometers with the bulb of one being kept wet so that the cooling that results from evaporation makes it register a lower temperature than the dry one and with the difference between the readings constituting a measure of the dryness of the atmosphere. psy·chro·met·ric adj. psy·chrom·e·try n.NOT TO BE CONFUSED WITHpsy·chom·e·try n. 1 : divination of facts concerning an object or its owner through contact with or proximity to the object.psy·cho·met·rics pl. n. but sing. in construction: the psychological theory or technique of mental measurement

http://www.merriam-webster.com

(often toxic and flammable ammonia) throughout the system. Carrier desig-ned a centrifugal-compressor similar to the centrifugal turning-blades of a water pump. The result was a safer and more efficient chiller.

Cooling for human comfort, rather than industrial need, began in 1924, noted by the three Carrier centrifugal chillers installed in the J.L. Hudson Department Store in Detroit, Michigan. Shoppers flocked to the air conditioned store. The boom in human cooling spread from the department stores to the movie theaters, most notably the Rivoli Theater in New York, whose summer film business skyrocketed when it heavily advertised the cool comfort. Demand increased for smaller units and the Carrier Company obliged.

In 1928, Willis Haviland Carrier developed the first residential

‘Weathermaker’, an air conditioner for private home use. The Great

Depression and then WW2 slowed the non-industrial use of air

conditioning. After the war, consumer sales started to grow again.

The rest is history, cool and comfortable history.

Willis Haviland Carrier did not invent the very first system to cool an

interior structure, however, his system was the first truly successful

and safe one that started the science of modern air conditioning.

Special thanks given to the Carrier Corporationhttp://inventors.about.com/library/weekly/aa081797.htm

WILLIS CARRIERby John H. Lienhard

It was a hot August day in San Antonio, Texas. I was there to name the Milam Building as a Mechanical Engineering Landmark. I went from the hot street into the cool halls of this fine old 21-story Art Deco building. As if by magic, the weather changed from awful to pleasant as I entered.

This was no ordinary magic. You see, this was the first air-conditioned office building in the world.

Inside, I met representatives of the Carrier Corporation. They were proud this day. In 1928, their company installed the original system here. Of course everyone invoked the name of Willis Carrier.

Carrier’s mother had some of that creative magic. For she had a mechanic’s instincts. Carrier learned about math and machines from his mother.

Carrier was poor. He waited tables, earned scholarships, and sold stereopticon slides to get through engineering school at Cornell. In 1901, he went on to work for the Buffalo Forge Company. There he designed heating and cooling equipment.

He soon saw how little we knew about regulating the temperature and humidity of air. He went to work on the problem. By 1911, he’d written the science of psychrometry. It describes air temperature and humidity.

But Carrier did much more. He’d already begun creating a technology for controlling air condition. In 1907, Buffalo Forge saw the value of his work. They formed The Carrier Air Conditioning Corporation of America as a subsidiary.

Air conditioning spread across America. First theaters and churches. Then more complex structures. If you’re old enough, you remember the early air-conditioned movie theaters. They used to paint blue ice cubes on their marquees.

Carrier died in 1950. Now the Houston temperature climbs. And I too say “Thank God!” for the magic that makes this sultry climate so pleasant—all year round.

Engines of Our Ingenuity, № 688

Willis Haviland Carrier

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http://www.uh.edu/engines/epi688.htm