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M. Muttakin et al.
where d in represents the diameter of the absorber tube that contains the fluid.
Thus Eqs. (8.27)–(8.29) are the governing dynamic equations to determine the
temperatures of the glass cover, absorber plate and working fluid (with both time and
position) respectively.
8.5 Modelling of an Adsorption Chiller
The major components of a two-bed adsorption chiller are evaporator, condenser and
two adsorber beds. An adsorber bed is necessarily a heat exchanger, filled with the
adsorbent material, e.g., silica gel, packed between the fins of that finned tube heat
exchanger. Adsorption and desorption are exothermic and endothermic processes,
respectively. To extract the heat of adsorption, it is necessary to circulate cooling water
through the tubes of the adsorber bed during the adsorption process. Furthermore,
during this process, the bed is connected to the evaporator in order to receive the
adsorbate vapor, e.g., water vapor, to be adsorbed by the adsorbent. Consequently,
the other bed goes through the desorption process and is connected to the condenser.
The hot water, flowing through its tubes, provide the necessary heat required for
desorption.
Thus an adsorption chiller works in a cyclic manner. Each cycle consists of three
operating modes (a) adsorption/desorption, (b) mass recovery and (c) heat recovery. This section will state the lumped analytical simulation model equations of an
adsorption chiller that uses silica gel as the adsorbent and water as the adsorbate.
The model is based on the following assumptions,
• The porous properties of the adsorbent are constant.
• The kinetics parameters, i.e. the diffusivity and activation energy, are independent
of temperature and pressure.
• At the first time step of any phase, the model does not consider the water flow
condition within the bed in the previous time step.
• The isotherm and kinetics equations for adsorption and desorption are same.
8.5.1 Description of Operating Modes
8.5.1.1 Mode (a): Adsorption/Desorption
In the operating mode (a) (see Fig. 8.7), Bed 1 goes through the desorption phase,
and adsorption is taking place in Bed 2. Bed 1 is heated up by the hot water streams,
which also raises the pressure of Bed 1.
The connecting valve between Bed 1 and condenser is open at this stage, and
the desorbed vapor is then condensed in the condenser and returned back to the
evaporator through an expansion valve. The other bed (Bed 2) is connected to the
M. Muttakin et al.
where d in represents the diameter of the absorber tube that contains the fluid.
Thus Eqs. (8.27)–(8.29) are the governing dynamic equations to determine the
temperatures of the glass cover, absorber plate and working fluid (with both time and
position) respectively.
8.5 Modelling of an Adsorption Chiller
The major components of a two-bed adsorption chiller are evaporator, condenser and
two adsorber beds. An adsorber bed is necessarily a heat exchanger, filled with the
adsorbent material, e.g., silica gel, packed between the fins of that finned tube heat
exchanger. Adsorption and desorption are exothermic and endothermic processes,
respectively. To extract the heat of adsorption, it is necessary to circulate cooling water
through the tubes of the adsorber bed during the adsorption process. Furthermore,
during this process, the bed is connected to the evaporator in order to receive the
adsorbate vapor, e.g., water vapor, to be adsorbed by the adsorbent. Consequently,
the other bed goes through the desorption process and is connected to the condenser.
The hot water, flowing through its tubes, provide the necessary heat required for
desorption.
Thus an adsorption chiller works in a cyclic manner. Each cycle consists of three
operating modes (a) adsorption/desorption, (b) mass recovery and (c) heat recovery. This section will state the lumped analytical simulation model equations of an
adsorption chiller that uses silica gel as the adsorbent and water as the adsorbate.
The model is based on the following assumptions,
• The porous properties of the adsorbent are constant.
• The kinetics parameters, i.e. the diffusivity and activation energy, are independent
of temperature and pressure.
• At the first time step of any phase, the model does not consider the water flow
condition within the bed in the previous time step.
• The isotherm and kinetics equations for adsorption and desorption are same.
8.5.1 Description of Operating Modes
8.5.1.1 Mode (a): Adsorption/Desorption
In the operating mode (a) (see Fig. 8.7), Bed 1 goes through the desorption phase,
and adsorption is taking place in Bed 2. Bed 1 is heated up by the hot water streams,
which also raises the pressure of Bed 1.
The connecting valve between Bed 1 and condenser is open at this stage, and
the desorbed vapor is then condensed in the condenser and returned back to the
evaporator through an expansion valve. The other bed (Bed 2) is connected to the