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TRG-TRC012-EN 17
period two
Refrigeration Cycle
notes
separated from the mixture and routed directly to the suction side of the
compressor and the remaining liquid refrigerant enters the evaporator.
In the evaporator, the liquid refrigerant boils as it absorbs heat from water. The
resulting vapor is drawn back to the compressor to repeat the cycle.
The pressure-enthalpy chart is simply a plot of the saturated properties of a
refrigerant. It plots refrigerant pressure (vertical axis) versus enthalpy
(horizontal axis). Enthalpy is a measurement of the heat content, both sensible
and latent, per pound [kg] of refrigerant.
For example, A represents the heat content of saturated
liquid
HFC-134a
refrigerant at 147.5 psia [1.02 MPa] and 104°F [40°C]. B represents the heat
content of saturated
vapor
HFC-134a refrigerant at the same pressure and
temperature. The difference in heat content, or enthalpy, between A and B—
that is, 70.2 Btu/pound [163.2 kJ/kg]—is the amount of heat required to
transform 1 pound [1 kg] of saturated liquid refrigerant to saturated refrigerant
vapor at the same pressure and temperature.
If the heat content of the refrigerant at any pressure falls to the right of the
curve, the vapor is superheated. Similarly, if the heat content of the refrigerant
falls to the left of the curve, the liquid is subcooled. Finally, when the heat
content of the refrigerant falls inside the curve the refrigerant exists as a liquid/
vapor mixture.
Pressure–Enthalpy (
p-h)
Chart
enthalpy
enthalpy
subcooled
subcooled
liquid
liquid
mixture of
mixture of
liquid and
liquid and
vapor
vapor
pressure
pressure
superheated
superheated
vapor
vapor
%
$
46.4 Btu/
46.4 Btu/
lb
lb
[256.4 kJ/kg]
[256.4 kJ/kg]
147.5
147.5
psia
psia
[1.02
[1.02
MPa
MPa
]
]
116.6 Btu/
116.6 Btu/
lb
lb
[419.6 kJ/kg]
[419.6 kJ/kg]
Figure 27