766 ENGINEERING THERMODYNAMICS
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\M-therm\Th14-4.pm5
R-1130 — Dichloroethylene (C 2 H 4 Cl 2 )
R-1150 — Ethylene (C 3 H 6 )
R-1270 — Propylene.
14.5.2. Desirable properties of an ideal refrigerant
An ideal refrigerant should possess the following properties :
- Thermodynamic properties :
(i) Low boiling point
(ii) Low freezing point
(iii)Positive pressures (but not very high) in condenser and evaporator.
(iv) High saturation temperature
(v) High latent heat of vapourisation.
- Chemical Properties :
(i) Non-toxicity
(ii) Non-flammable and non-explosive
(iii) Non-corrosiveness
(iv) Chemical stability in reacting
(v) No effect on the quality of stored (food and other) products like flowers, with other materials
i.e., furs and fabrics.
(vi) Non-irritating and odourless.
- Physical Properties :
(i) Low specific volume of vapour
(ii) Low specific heat
(iii) High thermal conductivity
(iv) Low viscosity
(v) High electrical insulation.
- Other Properties :
(i) Ease of leakage location
(ii) Availability and low cost
(iii) Ease of handling
(iv) High C.O.P.
(v) Low power consumption per tonne of refrigeration.
(vi) Low pressure ratio and pressure difference.
Some important properties (mentioned above) are discussed below :
Freezing point. As the refrigerant must operate in the cycle above its freezing point, it is
evident that the same for the refrigerant must be lower than system temperatures. It is found that
except in the case of water for which the freezing point is 0°C, other refrigerants have reasonably
low values. Water, therefore, can be used only in air-conditioning applications which are above
0°C.
