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S. Sangwan and P. R. Chakraborty
Basic requirements for the selection of adsorbate are as follows:
1. Should have high latent heat of vaporization to minimize the amount of adsorbent
needed.
2. The saturation pressure corresponding to the evaporating temperature should be
above atmospheric pressure so that the system always runs on positive pressure.
3. The saturation pressure corresponding to the condensing temperature should be
as low as possible.
4. Should be thermally and chemically stable.
5. Non-toxic, non-flammable and should have low cost.
10.5 Adsorption Refrigeration Cycle
An adsorption refrigeration cycle consist of adsorber/desorber, a condenser, an evaporator and an expansion valve (Meunier 2001). The mechanical compressor which
is an integral part of traditional VCR systems is replaced by low grade energy driven
adsorbent bed. Single bed adsorption refrigeration cycle is intermittent in nature and
consists of four processes.
I. Sensible Heating
II. Desorption and Condensation
III. Sensible Cooling
IV. Adsorption and Evaporation
The desorption and adsorption occurs at constant pressure (isobaric process), whereas
the sensible heating and cooling occurs at constant concentration (isosteric process).
To deal with the problem of intermittent nature of single bed cycle, we are considering two bed system in which both the beds will work simultaneously, one will
undergo adsorption process, at the same time other will undergo desorption process.
Schematic of two bed adsorption refrigeration system (Basic cycle) with uniform
bed temperature assumption and representative ideal thermodynamic cycle for the
beds is shown in Fig. 10.1, the system operates in the following way.
Sensible Heating
This is the period from a to b as shown in Fig. 10.1. During this process concentration
of refrigerant or adsorbate remains constant or at maximum (x a = x b ) and the bed is
sensibly heated from T a to T b , resulting an increase in pressure from P e (evaporating
pressure) to P c (condensing pressure).
Heating, Desorption and Condensation
This is the period from b to c as shown in Fig. 10.1. At T b pressure in the adsorber
is equal to the condensing pressure P c and desorption starts. During desorption
temperature of the bed increases along isobar until the refrigerant concentration
reaches X min . This desorbed refrigerant get condensed in the condenser releasing
the latent heat of condensation to atmosphere.
S. Sangwan and P. R. Chakraborty
Basic requirements for the selection of adsorbate are as follows:
1. Should have high latent heat of vaporization to minimize the amount of adsorbent
needed.
2. The saturation pressure corresponding to the evaporating temperature should be
above atmospheric pressure so that the system always runs on positive pressure.
3. The saturation pressure corresponding to the condensing temperature should be
as low as possible.
4. Should be thermally and chemically stable.
5. Non-toxic, non-flammable and should have low cost.
10.5 Adsorption Refrigeration Cycle
An adsorption refrigeration cycle consist of adsorber/desorber, a condenser, an evaporator and an expansion valve (Meunier 2001). The mechanical compressor which
is an integral part of traditional VCR systems is replaced by low grade energy driven
adsorbent bed. Single bed adsorption refrigeration cycle is intermittent in nature and
consists of four processes.
I. Sensible Heating
II. Desorption and Condensation
III. Sensible Cooling
IV. Adsorption and Evaporation
The desorption and adsorption occurs at constant pressure (isobaric process), whereas
the sensible heating and cooling occurs at constant concentration (isosteric process).
To deal with the problem of intermittent nature of single bed cycle, we are considering two bed system in which both the beds will work simultaneously, one will
undergo adsorption process, at the same time other will undergo desorption process.
Schematic of two bed adsorption refrigeration system (Basic cycle) with uniform
bed temperature assumption and representative ideal thermodynamic cycle for the
beds is shown in Fig. 10.1, the system operates in the following way.
Sensible Heating
This is the period from a to b as shown in Fig. 10.1. During this process concentration
of refrigerant or adsorbate remains constant or at maximum (x a = x b ) and the bed is
sensibly heated from T a to T b , resulting an increase in pressure from P e (evaporating
pressure) to P c (condensing pressure).
Heating, Desorption and Condensation
This is the period from b to c as shown in Fig. 10.1. At T b pressure in the adsorber
is equal to the condensing pressure P c and desorption starts. During desorption
temperature of the bed increases along isobar until the refrigerant concentration
reaches X min . This desorbed refrigerant get condensed in the condenser releasing
the latent heat of condensation to atmosphere.