temperatures. However, the destructive consequences of the
artificial refrigerants such as ODP (ozone depletion) appear
great interest so as to replace them by the appropriate alternatives,
which one of them is natural material like CO2 as well
as NH3. Although NH3 has not been recommended because of
its toxic feature, its availability and low flammability appeal
us to function it effectively (Lorentzen and Pettersen, 1990;
Lorentzen, 1995). Furthermore, it has relatively large swept
volume requirements under 35 C (Person, 2001), and the
evaporating pressure of NH3 system is below the atmospheric
pressure under 35 C that causes air to leak into the system.