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A detailed performance evaluation of modified transcritical CO 2 adsorption refrigeration systems integrated with an ejector and a thermoelectric sub-cooler is carried out using simplified thermodynamic models. The simultaneous effect of subcooling and the lift produced by the ejector on system COP and the specific cooling effect (SCE) is expounded. It is observed that the proposed system yields an identical COP with that of heat and mass recovery systems with reduced design and operational complexity. However, the heat and mass recovery systems clubbed with ejector and thermoelectric sub-cooler yield the best system performance with a maximum increment of 126% in COP. The gas cooler pressure and subcooling temperature strongly affect the entrainment ratio; however, COP and SCE strongly depend on gas cooler pressure, evaporator and generator temperatures. The maximum COP attained (i.e., 0.353) using the novel adsorbent (M-AC C-500) in the modified system can be used as a benchmark. [Display omitted] • Thermodynamic study is done on a CO 2 -based transcritical adsorption cooling system. • Enhanced system performance is achieved by various cycle modifications. • different activated carbon-CO 2 pairs are compared for best cycle modification. • M-AC C-500 yields the maximum COP of 0.353 and SCE of 123.10 kJ/kg. • Effects of critical design and operating parameters are studied in detail. [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]

A novel micro-mesoporous activated carbon (SBL AC-700) is synthesized from subabul (Leucaena leucocephala) sawdust waste by direct single-stage physical activation at 700 °C for 1 h for carbon capture applications. The synthesized AC is characterized to explore various physiochemical properties like elemental composition, surface morphology and crystallinity, presence of functional groups, surface area, pore size, and pore volume. Additionally, emphasis is given to exploring the thermophysical aspects of the novel AC, the literature regarding which is scarce in the open domain. The CO 2 adsorption study is carried out for a 0–1 bar pressure for temperatures ranging from 0 to 75 °C. The analysis revealed that the AC possesses a surface area of 590 m2/g and pore volume and width of 0.27 cm3/g and 1.85 nm, corresponding to a 70% microporosity with a well-developed porous structure. At 25 °C and 1 bar, a CO 2 uptake of 40.54 cm3/g is achieved, corresponding to an increment of 6–202% compared to other commercials, chemically and physically activated carbons. Moreover, SBL AC-700 has a thermal conductivity of 0.095 W/m K, 8–131% higher than other benchmarks ACs and much lower specific heat of 0.82 kJ/kg K corresponding to lesser regeneration energy requirements. Experimental data are fitted with various isotherm models, i.e., Langmuir, Freundlich, Sips, R–P, and Toth, out of which R–P and Toth models exhibit the best fit. In continuation, adsorption kinetics is studied to explore the dynamic performance of the SBL AC-700 by using Pseudo-first-order, Pseudo-second-order, Elovich, and intraparticle diffusion kinetic models. [Display omitted] • AC SBL AC-700 from subabul sawdust waste is synthesized successfully. • Novel AC is prepared by eco-friendly single-step direct CO 2 activation. • The ability of CO 2 uptake at 25 °C and 1 bar is 40.54 cm3/g. • SBL AC-700 has a thermal conductivity of 0.095 W/m K, 8–131% higher than other ACs. • Isotherm, kinetics, and thermodynamic modeling is done for the AC-CO 2 pair. [ABSTRACT FROM AUTHOR]