For the refrigerating cycle a
➔
b
➔
e
➔
f as shown in Figure 7.7, if the cooling capacity of condenser increases by the
temperature down of saturated liquid, cooling water or air and then the temperature of condenser outlet
refrigerant liquid decreases, the refrigerating cycle will be a
➔
b
➔
e
➔
f. Likewisely, the temperature difference when
the temperature of condenser outlet refrigerant liquid is below the temperature of saturated liquid at that pressure
is called the degree of supercooling, which enhances the refrigerating effect. The effect of supercooling is as
follows.
2) Work of compression : The heat equivalent of work which
has compressed refrigerant 1kg is the difference of enthalpy
between compressive process A
➔
B as shown in Figure 7.9,
and the equation of calculation is as follows.
A
l
= i
B
- i
A
............................................................... (7.4)
3) Calorie of condensation : The calorie emitted from
condenser is the sum of the refrigerating effect and the heat
equivalent of work. (Figure 7.10)
q
e'
= q
e
+ A
l
qe
= (i
A
- i
D
) + (i
B
- i
A
) = i
B
- i
D
.................................. (7.5)
7.3 Calculation of refrigerating cycle
1) Refrigerating effect : Calories which evaporator absorbes, and the refrigerant flowing through evaporator is a
wet vapor and at outlet a superheat vapor. In D
➔
A process in Figure 7.8, refrigerant absorbs Calorie qe from
surroundings with evaporating.
q
e
=
i
A
-
i
D
.......................................................................................................................................... (7.1)
The refrigerating effect is one which is calculated by equation (7.1), and is expressed in calories which
refrigerant 1kg absorbs from evaporator during A
➔
B
➔
C
➔
D cycle.
The refrigerating effect when the state of refrigerant gas sucked into compressor is changed into A', A'' in
Figure 7.8 is as follows.
q
e'
=
i
A'
-
i
D
......................................................................................................................................... (7.2)
q
e"
=
i
A"
-
i
D
......................................................................................................................................... (7.3)
Standard
Supercooling rise
Refrigerating effect
q
e
=
i
a
-
i
g
<
q
e
'=
i
a
-
i
f
Coefficient of performance
<
q
e
=
i
a
-
i
d
A
l
i
b
-
i
a
q
e
'
=
i
a
-
i
f
A
l
i
b
-
i
a
P
C
B
A
q"
A"
D
A'
e
i"
A
i'
A
i
A
q'
e
q
e
C
i
D
i
i
P
C
B
A
AI
D
i
A
i
B
q
e
i
P
C
D
B
i
A
i
B
q
e
q
e'
= q
e
AI
A
AI
C
i
D
i
i
Figure 7.8 Refrigerating effect
Figure 7.9 Work of compression
Figure 7.10 Calorie of condensation
TCL Air Conditioner Service Manual
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