8/13/2019 Tut - Basic Refrigeration

1/3

THERMOFLUIDS II BASIC REFRIGERATION TGK 2011

Note: In question 3 you are asked to use the P-h diagram. Use data from theThermodynamic and Transport Properties of Fluids for the other questions.

1. Refrigerant 13a is the !orking fluid in a "arnot #apour refrigeration cycle. Thee#aporator temperature is -1$ $". %aturated #apour enters the condenser at $ $" andsaturated liquid e&its at the same temperature. If the mass flo! rate of refrigerant is 3kg'min calculate(

)i* the refrigeration effect.)ii* the !ork done +y the compressor)iii* the coefficient of performance.

),. k/0 1.,3 k/0 .,*

. In a #apour compression refrigeration cycle the refrigerant enters the compressor asa dry saturated #apour at -1 $" and lea#es the condenser as a saturated liquid at $". The compression is isentropic.

2ra! a schematic of the plant and the thermodynamic cycle on T-s and p-h a&is.

"alculate the refrigeration effect and the "P for(a* Refrigerant 1+* Refrigerant 414 )ammonia*c* Refrigerant 13a

)11.4 k5'kg0 .30 114 k5'kg0 .,0 1 k5'kg0 .3*

3. 6 #apour compression refrigerator using refrigerant 13a operates +et!een thepressure le#els $.4 +ar and 7 +ar. The !orking fluid enters the compressor at -1$ $"and lea#es the condenser as saturated liquid. The isentropic efficiency of thecompressor is $..

a* sketch the cycle on T-s and P-h diagrams.+* use the R13a P-h chart to find(

)i* the e&it temperature from the compressor)ii* the refrigeration effect)iii* the "P

)34 80 13 k5'kg0 1.*

. 6 heat pump using ammonia as the !orking fluid takes in heat at $" ."ondensation takes place at 3 $". The fluid lea#es the compressor !hich can +econsidered isentropic0 in a superheated condition at $". It lea#es the condenser assaturated liquid.%ketch the cycle on T-s and P-h a&is and calculate(

)i* the condition of the ammonia at thecompressor suction.

)ii* the compression !ork input per kg.

8/13/2019 Tut - Basic Refrigeration

2/3

)iii* the "P

)dryness fraction9$.70 1.3 k5'kg0 7.3*. 6 #apour compression heat pump system uses refrigerant 13a as the !orking fluid.The refrigerant enters the compressor at . +ar0 $ $" !ith a mass flo! rate of 1.kg'min and lea#es at 1$.1,3 +ar and ,$ $". %aturated liquid e&its the condenser.

"alculate()i* the po!er input to the compressor)ii* the heating capacity of the system

)iii* the isentropic efficiency of the compressor.)$.1 k/0 3.4 k/0 $.*

,. 6 #apour compression refrigeration system uses R13a as the !orking fluid and isdesigned to meet a cooling load of k/. The refrigerant enters the compressor at .+ar and $$". 6t the e&it of the compressor the pressure is 11., +ar. The isentropicefficiency of the compressor is $.. 6ssume that the liquid after condensation isundercooled +y 1$ 8.

2ra! the cycle on T-s and p-h a&is and calculate()i* the temperature at the e&it of the compressor)ii* the mass flo! rate of the refrigerant)iii* the "P of the cycle.),., o"0 $.$33 kg's0 3.3*

4. 6 refrigeration system uses R13a as the !orking fluid and includes a liquid-to-suction heat e&changer. The heat e&changer can !arm the saturated #apour comingfrom the e#aporator from -1$o" to $o" using saturated liquid !hich e&its the condenserat 3o".

)i* "alculate the "P !ith and !ithout the heat e&changer.)ii* If the compressor is capa+le of pumping 1 l's of refrigerant measured at thecompressor suction calculate the refrigeration effect !ith and !ithout the heate&changer

6ssume that the compressor is isentropic).10 .0 14.7 k/0 17.74 k/*

. 6 t!o-stage heat pump operating on the cascade principle dra!s lo! grade heatfrom ri#er !ater for the supply of $$ k/ of high grade heat to a hospital. Usingammonia as the !orking fluid0 the e#aporator operates at o" saturation temperature.The !orking fluid in the condenser coil is R13a and is at o" saturation temperatureand lea#es the condenser !ith $ 8 su+cooling. In the cascade heat e&changer0 thesaturation temperature of ammonia and R13a are $ o" and 3o" respecti#ely !ith nosu+cooiling of the ammonia.

2ra! the cycles on T-s and P-h a&is.6ssuming that +oth refrigerants enter the compressors as saturated #apour0 and theisentropic efficiency of compression is $:0 determine(

8/13/2019 Tut - Basic Refrigeration

3/3

)i* the po!er input to the compressors)ii* the heat remo#ed from the ri#er !ater

)1 k/0 31., k/*