Famco Danfoss Maneurop MT, Руководство пользователя

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Application guidelines
13
FRCC.PC.004.A9.22
Operating envelopes
Refrigerant mixtures can be either zeotropic or
azeotropic.
An azeotropic mixture (like R502 or R507)
behaves like a pure refrigerant. During a phase
transition (from vapor to liquid or from liquid to
vapor) the composition of vapor and liquid stays
the same.
In a zeotropic mixture (like R407C) on the other
hand the composition of vapor and liquid
changes during the phase transition. When the
effect of this phase transition is very small, the
mixture is often called a near-azeotropic mixture.
R404A is such a near-azeotropic mixture.
The composition change causes phase shift and
temperature glide.
Phase shift
Temperature glide
Dew temperature and Mean
temperature for R407A/C/F
In system components where both vapor and
liquid phase are present (evaporator, condenser,
liquid receiver), the liquid phase and vapor phase
do not have the same composition. In fact both
phases form two different refrigerants. Therefore
zeotropic refrigerants need some special attention. Zeotropic refrigerants must always be
charged in liquid phase. Flooded evaporators
and suction accumulators should not be applied
in systems with zeotropic refrigerants. This also
applies to near-azeotropic mixtures.
During the evaporating process and the
condensing process at constant pressure,
the refrigerant temperature will decrease
in the condenser and rise in the evaporator.
Therefore when speaking about evaporating
and condensing temperatures, it is important to
indicate whether this is a dew point temperature
or a mean point value. In the figure below, the
dotted lines are lines of constant temperature.
They do not correspond to the lines of constant
pressure.
Points A and B are dew point values. These are
temperatures on the saturated vapor line.
Points C and D are mean point values. These are
temperatures which correspond more or less with
the average temperature during the evaporating
and condensing process. For the same cycle,
mean point temperatures are typically about
3.6°F lower than dew point temperatures.
According to Asercom recommendations,
Danfoss Commercial Compressors uses dew
point temperatures for selection tables and
application envelopes etc.
To obtain exact capacity data at mean point
temperatures, the mean point temperatures
must be converted to dew point temperatures
with help of refrigerant data tables from the
refrigerant manufacturer.
Zeotropic refrigerant
mixtures