Figs. 1 and 2 show a schematic and the corresponding p-h
diagram of the conventional cascade refrigeration cycle and a
novel cascade refrigeration cycle with two ejectors and heat
exchanger, respectively.
The high temperature NH3 enters the compressor at pressure
P1 at state 1 in which it is compressed to the pressure of P2,
with an isentropic efficiency,hc subsequently the compressed
fluid at state 2 is cooled in the Condenser to the temperature of
T3. The NH3 at state 3 enters the ejector nozzle and expands
with a nozzle efficiency ofhn. The saturated Secondary vapor
stream enters the ejector at pressure of P9 in accordance with
state 9. The two streams mix at constant pressure in the final
state of the mixture according to state 5. It is necessary to know
that after that the mixture goes through the ejector diffuser
with a diffuser efficiency of hd, in which recovers to the pressure
P6 at state 6, the stream leaves the ejector and then flows
Nomenclature
COP coefficient of performance
h specific enthalpy (kJ kg1)
HTC high temperature circuit
I_des exergy destruction rate (kW)
LTC Low temperature circuit
m_ Mass flow rate (kg s1)
P pressure (MPa)
_Q
heat transfer rate (kW)
_S
gen entropy generation(kW K1)
s specific entropy [kJ (kg K)1]
T Temperature (C or K)
u velocity (m s1)
U entrainment ratio
_W
work (kW)
X quality
Subscripts
0 reference environment
1, 2, 3 … Cycle location
c compressor
cond condenser
d diffuser, discharge
eje ejector
eva evaporator
exp expansion valve
HEX heat exchanger
m mixing chamber
max maximum
MC Middle condenser
ME Middle evaporator
n nozzle
opt optimization
rev reversible process
s isentropic process
t total
Greek Symbol
h Efficiency (%)
J Stream exergy, [(kJ kg1)]
i n t e rna t i onal journal o f r e f r i g e r a t i o n 4 6 ( 2 0 1 4 ) 2 6 e3 6 27
into the separator, where it is separated to two distinct states;
saturated liquid and saturated vapor, while the saturated
liquid stream enters the conventional expansion valve and
expands to pressure Peva at state 8, the saturated vapor enters
to the compressor. The low temperature CO2 experiences the
same process, and at the lower temperature it exchanges its
energy to the NH3 through the heat exchanger.
Figs. 1 and 2 show a schematic and the corresponding p-h
diagram of the conventional cascade refrigeration cycle and a
novel cascade refrigeration cycle with two ejectors and heat
exchanger, respectively.
The high temperature NH3 enters the compressor at pressure
P1 at state 1 in which it is compressed to the pressure of P2,
with an isentropic efficiency,hc subsequently the compressed
fluid at state 2 is cooled in the Condenser to the temperature of
T3. The NH3 at state 3 enters the ejector nozzle and expands
with a nozzle efficiency ofhn. The saturated Secondary vapor
stream enters the ejector at pressure of P9 in accordance with
state 9. The two streams mix at constant pressure in the final
state of the mixture according to state 5. It is necessary to know
that after that the mixture goes through the ejector diffuser
with a diffuser efficiency of hd, in which recovers to the pressure
P6 at state 6, the stream leaves the ejector and then flows
Nomenclature
COP coefficient of performance
h specific enthalpy (kJ kg1)
HTC high temperature circuit
I_des exergy destruction rate (kW)
LTC Low temperature circuit
m_ Mass flow rate (kg s1)
P pressure (MPa)
_Q
heat transfer rate (kW)
_S
gen entropy generation(kW K1)
s specific entropy [kJ (kg K)1]
T Temperature (C or K)
u velocity (m s1)
U entrainment ratio
_W
work (kW)
X quality
Subscripts
0 reference environment
1, 2, 3 … Cycle location
c compressor
cond condenser
d diffuser, discharge
eje ejector
eva evaporator
exp expansion valve
HEX heat exchanger
m mixing chamber
max maximum
MC Middle condenser
ME Middle evaporator
n nozzle
opt optimization
rev reversible process
s isentropic process
t total
Greek Symbol
h Efficiency (%)
J Stream exergy, [(kJ kg1)]
i n t e rna t i onal journal o f r e f r i g e r a t i o n 4 6 ( 2 0 1 4 ) 2 6 e3 6 27
into the separator, where it is separated to two distinct states;
saturated liquid and saturated vapor, while the saturated
liquid stream enters the conventional expansion valve and
expands to pressure Peva at state 8, the saturated vapor enters
to the compressor. The low temperature CO2 experiences the
same process, and at the lower temperature it exchanges its
energy to the NH3 through the heat exchanger.
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