Formula Sheet: RAC | Thermodynamics - Mechanical Engineering PDF Download

 Page 1


Refrigeration and Air Conditioning F orm ula Sheet
Refrigeration Cycles
• V ap or Compression Refrigeration Cycle :
– Co e?icien t of P erformance (COP) :
COP
R
=
Q
L
W
net
=
h
1
-h
4
h
2
-h
1
whereQ
L
is heat absorb ed (Jkg
-1
),W
net
is compressor w ork (Jkg
-1
),h is sp ecific
en thalp y (Jkg
-1
).
– Refrigeration Effect : Heat absorb ed in the ev ap orator.
Q
L
=m(h
1
-h
4
)
where m is mass flo w rate ( kgs
-1
).
– Compressor W ork :
W
comp
=m(h
2
-h
1
)
• Carnot Refrigeration COP : Ideal rev ersible cycle.
COP
Carnot
=
T
L
T
H
-T
L
where T
L
is ev ap orator temp erature, T
H
is condenser temp erature (K ).
• V ap or Absorption Refrigeration :
COP=
Q
L
Q
gen
+W
pump
where Q
gen
is heat input to generator (J ), W
pump
is pump w ork (J ).
Psyc hrometrics
• Dry Bulb T emp erature (T
db
) : Air temp erature (
?
C or K ).
• W et Bulb T emp erature (T
wb
) : T emp erature at saturation due to ev ap oration.
• Relativ e Humidit y (? ) :
?=
P
v
P
sat
×100
where P
v
is partial pre ssure of w ater v ap or, P
sat
is saturation pressure at T
db
(Pa ).
• Humidit y Ratio (W ) : Mass of w ater v ap or p er unit mass of dry air.
W =
m
v
m
d
=
0.622P
v
P-P
v
where P is total pressure (Pa ).
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Page 2


Refrigeration and Air Conditioning F orm ula Sheet
Refrigeration Cycles
• V ap or Compression Refrigeration Cycle :
– Co e?icien t of P erformance (COP) :
COP
R
=
Q
L
W
net
=
h
1
-h
4
h
2
-h
1
whereQ
L
is heat absorb ed (Jkg
-1
),W
net
is compressor w ork (Jkg
-1
),h is sp ecific
en thalp y (Jkg
-1
).
– Refrigeration Effect : Heat absorb ed in the ev ap orator.
Q
L
=m(h
1
-h
4
)
where m is mass flo w rate ( kgs
-1
).
– Compressor W ork :
W
comp
=m(h
2
-h
1
)
• Carnot Refrigeration COP : Ideal rev ersible cycle.
COP
Carnot
=
T
L
T
H
-T
L
where T
L
is ev ap orator temp erature, T
H
is condenser temp erature (K ).
• V ap or Absorption Refrigeration :
COP=
Q
L
Q
gen
+W
pump
where Q
gen
is heat input to generator (J ), W
pump
is pump w ork (J ).
Psyc hrometrics
• Dry Bulb T emp erature (T
db
) : Air temp erature (
?
C or K ).
• W et Bulb T emp erature (T
wb
) : T emp erature at saturation due to ev ap oration.
• Relativ e Humidit y (? ) :
?=
P
v
P
sat
×100
where P
v
is partial pre ssure of w ater v ap or, P
sat
is saturation pressure at T
db
(Pa ).
• Humidit y Ratio (W ) : Mass of w ater v ap or p er unit mass of dry air.
W =
m
v
m
d
=
0.622P
v
P-P
v
where P is total pressure (Pa ).
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• Degree of Saturation :
µ=
W
W
s
where W
s
is h umidit y ratio at saturation.
• Sp ecific En thalp y of Moist Air :
h=c
p
T
db
+Wh
g
where c
p
˜1.005kJkg
-1
K , h
g
is en thalp y of saturated v ap or (Jkg
-1
).
Air C onditioning Pro cesses
• Sensible Heating/Co oling :
Q=m
d
c
p
(T
2
-T
1
)
where m
d
is mass flo w rate of dry a ir ( kgs
-1
), T
1
,T
2
are dry bulb temp eratures (K ).
• Laten t Heating/Co oling :
Q=m
d
h
fg
(W
2
-W
1
)
where h
fg
is laten t heat of v ap orization (Jkg
-1
).
• T otal Heat T ransfer :
Q
total
=m
d
(h
2
-h
1
)
• A diabatic Mixing of Air Streams :
m
1
h
1
+m
2
h
2
=m
3
h
3
, m
1
W
1
+m
2
W
2
=m
3
W
3
where m
1
,m
2
,m
3
are mass flo w rates of dry air ( kgs
-1
).
• Sensible Heat F actor (SHF) :
SHF=
Q
sensible
Q
total
Co oling Load Calculations
• Co oling Load : T otal heat to b e remo v ed.
Q
load
=Q
sensible
+Q
laten t
+Q
v en tilation
• V en tilation Load :
Q
v en t
=m
d
(h
out
-h
in
)
• T onnage of Refrigeration : 1 TR = 3.517kW = 12000h
-1
.
Q
TR
=
Q
load
3.517kW
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