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A comprehensive 2-D transient heat and mass transfer analysis is carried out to identify the best reactor configuration in terms of better charge and discharge characteristics for a CO2-activated carbon (Maxsorb III)-based sorption systems. Reactors with different aspect ratios (AR) ranging from 0.35 to 7.8 are analysed for a wide range of convective heat transfer coefficient (h), constant pressure charging, and discharging cases. Effects of external cooling/heating fluid temperature, convective heat transfer coefficient (h), operating pressures are studied for both the charging (1–100 bar) and discharging (65–110 bar) cases. The adsorption cell with AR= 7.8 showed the best performance for CO2 adsorption/desorption in a fixed charge/discharge time of 300 s. For charging at 100 bar pressure, the reactor with AR= 7.8 resulted in an increment of 23.34% in CO2 uptake and reduction in maximum bed temperature by 27 K compared to that of the reactor with AR = 0.35. For h = 700 and 500 W/m2 K, the reactor with AR = 7.8 adsorbs 1300 g and desorbs 832 g of CO2/kg of adsorbent at 100 bar and 65 bar for external cooling and heating fluid temperature of 293 K and 800 K, respectively. The study concludes that better discharge performance can be attained by proper selection of AR even at a lower heating fluid temperature as the reactor with AR = 7.8 at 600 K can desorb 46 to 131 g of extra CO2 w.r.t. all ARs at 800 K. The proposed reactor configurations are supposed to play a vital role in designing of adsorption-based green refrigeration and carbon capture systems. [ABSTRACT FROM AUTHOR]

• Four different configurations of adsorption cooling cycles are studied for improved performance for subcritical and transcritical cycles. • Detailed thermodynamic analysis is carried out for 5 different adsorbent materials for all the configurations. • Effect of various parameters are studied on system performance. • Out of all the adsorbents used, Maxsorb III showed better system performance. • Various co-relations have been developed for various intermediate temperatures and COP. In the present investigation, thermodynamic analysis of four different adsorption cooling cycles; basic, internal heat recovery, mass recovery, and heat & mass recovery cycles are carried out employing CO 2 as the refrigerant. The said investigation is done for five different adsorbent materials i.e. a highly microporous activated carbon (Maxsorb III), Maxsorb III based composite, Activated carbon fibre (ACF) A-20, BPL activated carbon (AC), and Norit AC. The study stretches the analysis from subcritical to supercritical zone for evaporator temperature ranging from −5 °C to 15 °C. For subcritical cycle, generator and condenser temperatures are varied between 65 °C to 91 °C and 20 °C to 30 °C, and for transcritical cycle, generator and gas cooler exit temperatures are varied from 90 °C to 120 °C and 35 °C to 40 °C, respectively. The maximum COP and specific cooling effect (SCE) achieved by incorporating both heat and mass recovery to the basic cycle are 0.305 and 105 kJ/kg, respectively. The improvement in COP and 2nd law efficiency of the same cycle w.r.t. other cycles are in the range of 7% to 84% and 38% to 77%, respectively for subcritical cycles. Similarly, for transcritical cycles, improvements in COPs of HMRC are in range of 17% to 75%. Analysis showed better system performance for Maxsorb III and it's composite as compared to other adsorbents. Various regression equations are developed to predict the different intermediate temperatures and COP for the mentioned modified subcritical and transcritical cycles. [ABSTRACT FROM AUTHOR]

• 4-Bed CO 2 -based adsorption cooling system is analyzed with various sorbent reactors. • Variable aspect ratios of cylindrical reactors with longitudinal fins are explored. • The study is carried out for subcritical and transcritical cyclic operations. • Results show system performance is strongly dependent on reactor geometry. • 23–98 % COP improvement is achieved during transcritical and subcritical operations. The present investigation expounds on the effects of the reactor geometry, cycle time and heating/cooling fluid temperatures on the performance of a 4-bed CO 2 adsorption cooling system. Cylindrical adsorbent reactors of varying aspect ratios (AR) with an optimum number of internal longitudinal fins and non-finned reactors are compared. The study confirms the substantial effect of reactor configuration on the system COP, specific cooling effect (SCE) and power, energy interactions during various processes and the total cycle time (TCT), which the equilibrium or lumped system analysis fails to predict. An increment of 98 % and 189 % in system COP and SCE is attained by varying the aspect ratio of the reactor with fins under subcritical operations. In continuation, a reduction of 41 % in TCT is observed. The study confirms the optimum adsorption/desorption time for which the COP and SCE are maximum, especially for higher AR reactors. It is noteworthy that proper selection of reactor aspect ratio results in a better system COP, even at lower heating fluid temperatures. During the transcritical operations, an increment of 23 % in COP and 6 % in SCE is achieved for a gas cooler exit temperature of 35 °C. Moreover, the reactor configuration also affects the optimum gas cooler pressure for the transcritical cycle, like the gas cooler exit temperature. One of the crucial observations is that, for a given combination of reactor configuration, heating/cooling fluid temperatures, and operating pressures, there exists a minimum cycle time below which a cyclic steady-state condition is impossible to achieve. During the subcritical and transcritical operations, a maximum COP of 0.1 and 0.052 is achieved for the proposed adsorption chiller configuration, respectively. [ABSTRACT FROM AUTHOR]

• 12 adsorbent composites are synthesized with enhanced thermophysical properties. • Composites are employed in post-combustion CO 2 capture applications. • 6–606% increment in thermal conductivity is achieved. • 5 isotherm models have been used to correlate the measured isotherm data. • Thermodynamic performance is investigated under different operation conditions. The present investigation aims at developing consolidated adsorbent composites with enhanced thermophysical and transport properties at the cost of a minimum sacrifice in equilibrium CO 2 uptake. Twelve samples are synthesized using a coconut shell-derived activated carbon (CSAC) as the parent material, graphite, graphene nanoplatelets, and CuO as the additives and PVA as the binder. All the synthesized had undergone a proper characterization using N 2 adsorption/ desorption and FE-SEM to highlight the changes in the BET surface area, pore volume, pore size distribution, and pore networking compared to the parent activated carbon and surface morphology. The thermophysical (specific heat capacity) and transport properties (thermal conductivity and thermal diffusivity) of all the composites of various mass fractions of the additives (10–40%) are measured using a TPS-2500 S transient hot disk method. The experimental results show that maximum thermal conductivity of 1.72 W/m K is achieved with graphite as the additive with a ratio of CSAC: graphite: PVA (Composite 4) of 50:40:10 wt%, corresponding to an increment of 606% compared to parent CSAC. The increment is comparable and better than the other consolidated adsorbent composites reported in the literature. All the constants of various isotherm models are obtained based on the experimentally obtained pressure-temperature and concentration data using the non-linear regression analysis. Based on the R2 values, the Toth model is identified as the best model for all the composites. A detailed thermodynamic analysis is further carried out, and important thermodynamic parameters, i.e., Enthalpy, Entropy, Gibbs free energy change associated with the adsorption process and the Isosteric heat of adsorption are obtained. The estimated thermodynamic parameters, isotherm and thermophysical data are crucial for the actual design and development of compact systems suitable for adsorption-based CO 2 capture applications. [Display omitted] [ABSTRACT FROM AUTHOR]