10 Thermodynamic Analysis of Activated Carbon–Ethanol …
193
Figure 10.3 shows the effect of varying maximum desorption temperature (T c )
and heat capacity ratio (R m ) on COP of the basic cycle keeping all other input
parameters constant i.e. T a = T csat = 300 K and T esat = 273 K for both the working
pairs. From Fig. 10.3a and b, it is clear that with the increase in maximum desorption
temperature, COP also increases and attains maxima for a particular value of T c
(370 K for Activated carbon ethanol and around 450 K for Zeolite–water pair) but
with further increase in temperature it starts decreasing because a fixed amount of
refrigerant is adsorbed inside the adsorbent and no more desorption occurs after a
particular temperature. With the increase heat capacity ratio more amount of input
heat will be absorbed by the structural material and it will affect the COP adversely
which can also be seen from Fig. 10.3.
Figure 10.4 shows the effect of varying maximum desorption temperature (T c ) and
heat capacity ratio (R m ) on COP of the heat recovery cycle keeping all other input
parameters constant i.e. T a = T csat = 300 K and T esat = 273 K for both the working
pairs. Heat recovery cycle also follows the same trend with respect to maximum
desorption temperature as followed by the basic cycle. Heat recovery cycle resulted
in higher COP as compared to basic cycle. From Fig. 10.4a and b, it can be noticed
that there is a sudden change in the COP gradient with respect to T c at T c = 365 K
(activated carbon–ethanol) and T c = 360 K (zeolite–water). This change is due to the
fact that condition T b ≥ T d prevails till T c = 365 K (activated carbon–ethanol) and
T c = 360 K (zeolite–water), and the estimation of equilibrium bed temperature T eq
is obtained from Eq. 10.16 pertaining to sensible heating and cooling. On the other
hand, for T c > 365 K (activated carbon–ethanol) and T c > 360 K (zeolite–water)
the condition T b < T d gets satisfied and estimation of T eq is obtained from Eq. 10.17
involving adsorption and desorption cooling along with sensible heating or cooling
process.
Figure 10.5 shows the effect of varying minimum adsorption temperature on
COP while all other parameters are kept constant i.e. T c = 370 K (activated carbon–ethanol), T c = 450 K (Zeolite–water), T csat = 300 K, and T esat = 273 K. It is
evident from Fig. 10.5a and b that with the increase in minimum adsorption temperature COP, increases and is maximum at T a = T csat = 300 K. With further increase
in temperature COP starts decreasing, this can be explained using Eqs. 10.6 and
10.8–10.10, when T a approaches T csat , Q
Q co (Eq. 10.8) but the net effect is increase in SCE and COP values. For the case
when T a is greater than T csat , Q
T a and T csat should be kept same.
193
Figure 10.3 shows the effect of varying maximum desorption temperature (T c )
and heat capacity ratio (R m ) on COP of the basic cycle keeping all other input
parameters constant i.e. T a = T csat = 300 K and T esat = 273 K for both the working
pairs. From Fig. 10.3a and b, it is clear that with the increase in maximum desorption
temperature, COP also increases and attains maxima for a particular value of T c
(370 K for Activated carbon ethanol and around 450 K for Zeolite–water pair) but
with further increase in temperature it starts decreasing because a fixed amount of
refrigerant is adsorbed inside the adsorbent and no more desorption occurs after a
particular temperature. With the increase heat capacity ratio more amount of input
heat will be absorbed by the structural material and it will affect the COP adversely
which can also be seen from Fig. 10.3.
Figure 10.4 shows the effect of varying maximum desorption temperature (T c ) and
heat capacity ratio (R m ) on COP of the heat recovery cycle keeping all other input
parameters constant i.e. T a = T csat = 300 K and T esat = 273 K for both the working
pairs. Heat recovery cycle also follows the same trend with respect to maximum
desorption temperature as followed by the basic cycle. Heat recovery cycle resulted
in higher COP as compared to basic cycle. From Fig. 10.4a and b, it can be noticed
that there is a sudden change in the COP gradient with respect to T c at T c = 365 K
(activated carbon–ethanol) and T c = 360 K (zeolite–water). This change is due to the
fact that condition T b ≥ T d prevails till T c = 365 K (activated carbon–ethanol) and
T c = 360 K (zeolite–water), and the estimation of equilibrium bed temperature T eq
is obtained from Eq. 10.16 pertaining to sensible heating and cooling. On the other
hand, for T c > 365 K (activated carbon–ethanol) and T c > 360 K (zeolite–water)
the condition T b < T d gets satisfied and estimation of T eq is obtained from Eq. 10.17
involving adsorption and desorption cooling along with sensible heating or cooling
process.
Figure 10.5 shows the effect of varying minimum adsorption temperature on
COP while all other parameters are kept constant i.e. T c = 370 K (activated carbon–ethanol), T c = 450 K (Zeolite–water), T csat = 300 K, and T esat = 273 K. It is
evident from Fig. 10.5a and b that with the increase in minimum adsorption temperature COP, increases and is maximum at T a = T csat = 300 K. With further increase
in temperature COP starts decreasing, this can be explained using Eqs. 10.6 and
10.8–10.10, when T a approaches T csat , Q
Q co (Eq. 10.8) but the net effect is increase in SCE and COP values. For the case
when T a is greater than T csat , Q
T a and T csat should be kept same.