- 上一篇：商业公共建筑暖通空调系统英文文献和翻译
- 下一篇：冷冲压模具设计英文文献和翻译
nineAstakhov equation.
3. Properties of the adsorbent and the adsorbate
For cooling purposes, the adsorbent should have high adsorptive
capacity at ambient temperature and low pressures, maintaining
small capacity of adsorption at high temperatures and pressures. The
required temperature at the evaporator depends on the adsorptive
capacity under small pressures; it is the property that allows the
adsorbent, at a given temperature, to retain vapors from a fluid at
lower temperature.Onthe otherhand, themore intense this property
is, the higher the level temperature for regenerating the adsorbent.- it can evaporate at a temperature largely below 0
C (its
melting point is e 94
C);
- its enthalpy of vaporization is high (w1200 kJ/kg, at e 5
C);
- itsmolecule is small enogh (4 104
mm) to be easily adsorbed
into micropores, with a diameter smaller than 2 103
mm;
- its normal boiling point (w65
C) is much higher the room
temperatures;
- its working pressure is always lower than the atmospheric one,
which means a safety factor in case of leakage.
The activated carbon has been selected as the adsorbent
material because of its affinity with methanol; the thermo physical
properties are those of the AC-35, produced by CECA (France).
These data and those concerning the thermodynamic equilibrium
e the isosters e of the AC-35/methanol pair are well known [20].
The activated carbon AC-35 is obtained from pinewood by heating
it to 950 C in the presence of water vapor. It has a significant
micropores volume, the empty spaces of which correspond to 78%
of the total volume. The adsorbent bed is made up of cylindrical
grains of 2 mm diameter and is 3 mm long in average. The
maximum adsorption capacity of the activated carbonemethanol
pair is about 0.3 kg of absorbate/kg of absorbent. According to
experimental studies, the regenerating temperature of the acti-
vated carbon AC-35 at this temperature ranges from 65 Cto
100 C [21].
4. Functioning principle and the ideal thermodynamic cycle
The adsorption refrigeration cycle consists of two well-defined
stages: one is described as the adsorber cooling, with its conse-
quent adsorption process, when the evaporation of the working
fluid (the adsorbate) takes place. The other stage consists of the
solid medium (the adsorbent) regeneration, when the adsorbate is
desorbed and condensed (Fig. 1a). The ideal thermodynamic cycle
can be represented by two isosters (isolineswith constant adsorbed
phase concentration, a) and two intercalated isobars, as shown in
Fig. 1b.
The adsorber cooling corresponds to the isosteric process 1e2,
depending on the ambient conditions. This process continues until
the adsorber pressure reaches itsminimumvalue (point 2), when it
becomes equal to the evaporator pressure. At this point, the
adsorption process starts and prolongs until its temperature rea-
ches the minimum value (point 3). Then, the adsorber is heated,
corresponding to another isosteric process (3e4), until its pressure
reaches a maximumvalue (point 4). Desorption starts at this point,
and goes on until the adsorber temperature reaches its maximum
value (point 1), completing, in this way, the cycle.
5. Energy equations
The energy equations related to the adsorber, which will be
given next, correspond to a multi-tubular system, whose outer
surface exchanges heat with the water coming fromthe hot storage
tank or from the water supply network, depending on the stage of
the cycle. The adsorbent occupies an annular space delimited by the
wall of the tube and a metal screen through which the adsorbate
flows.
For the heat transfer in the adsorbent medium, the following