tarea de ciclo de refrigeracion y maquinas termicas (1)

7/28/2019 Tarea de Ciclo de Refrigeracion y Maquinas Termicas (1)

1/4

DIEGO MEJIA

MAYO DEL 2013

CICLOS TRMICOS-CICLO DE REFRIGERACIN

in a vapor-compression refrigeration cycle, ammonia exits the evaporator as saturated vapor at _22C. The refrigerant enters the condenser at 16 bar and 160C, and saturated liquid exits at 16bar. There is no significant heat transfer between thecompressor and its surroundings, and therefrigerant passesthrough the evaporator with a negligible change in pressure. If therefrigerating capacity is 150 kW, determine:(a) the mass flow rate of refrigerant, in kg/s.(b) the power input to the compressor, in kW.(c) the coefficient of performance.(d) the isentropic compressor efficiency.

SOLUCION

a) H

C

H

C

T T

QQ

J Q K T K T H H C 3

1045.6,520,300

J K K

J T T

QQ H

C H C

33 1072.3520300

)1045.6(

b) J J J QQW C H 333 1073.21072.31045.6

d) %3.42100423.0423.01045.61073.2

3

3

J J

QW

e H

c)


2/4

DIEGO MEJIA

MAYO DEL 2013

table de valores para variaciones y condiciones Termicas

T 1 K

T 2 K

T 3 K

T 4 K

P1 kPa

P2 kPa

P3 kPa

P4 kPa

300 662.46 1400 883.56 100 1000 1000 100W C /m kJ/kg

W T /m kJ/kg

Q In /m kJ/kg

bwr %

W net /m kJ/kg

h Net Power MW

-372.91 600.88 842.32 62.0 227.97 27.1 1.32

MAQUINAS TRMICAS.

Air enters the compressor of an ideal air-standard Brayton cycle at 100 kPa, 300 K, with a volumetricflow rate of 5 m 3 /s. The turbine inlet temperature is 1400 K. For compressor pressure ratios ranging

from 2 to 20, plot :(a) the thermal efficiency of the cycle.(b) the back work ratio.(c) the net power developed, in kW.


3/4

DIEGO MEJIA

MAYO DEL 2013

(1) (2): Isentropic Compression(2) (3): Constant Pressure Heat Addition(3) (4): Isentropic Expansion(4) (1): Constant Pressure Heat Rejection.

Th e Br ayton Cycle: The air- standard Brayton cycle is the ideal cycle for gas turbines.

All 4 processes are internally reversible:

Air-standard gas turbine cycle [2]


4/4

DIEGO MEJIA

MAYO DEL 2013

The following table summarizes the solution:

T 1

K

T 2

K

T 3

K

T 4

K

P1

kPa

P2

kPa

P3

kPa

P4

kPa300 574.1 1400 787.7 100 1000 1000 100W C /m kJ/kg

W T /m kJ/kg

Q In /m kJ/kg

bwr %

W net /m kJ/kg

h Net Power MW

-279.68 706.92 935.55 39.6 427.24 45.67 2.48

Note that because of irreversibilities in the compressor and in the turbine:The efficiency has dropped substantially from 45.7% to 27.1 %The cycle net capacity has dropped from 427 kJ/kg to 228 kJ/kg.

The back work ratio has increased from 39.6 % to 62% whileThe net power developed has dropped from 2.48 MW to 1.32 MW, a decrease of 47

%.

tarea de ciclo de refrigeracion y maquinas termicas (1)

Documents