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[en] Highlights: • Multi-objective optimization of desiccant wheels is investigated. • Response surface method is used for establishing novel regression models. • Effects of operating variables on corresponding responses are comprehensively evaluated. • Optimum values of input variables have been derived to minimize process outlet temperature and humidity ratio. • A valuable equation for determination of Pareto-optimal points has been proposed. - Abstract: A two-step computational framework based on the combination of response surface methodology and multi-objective optimization is proposed to model the outlet-air state of desiccant wheels and subsequently optimize their operation. Regeneration temperature, surface area ratio, rotational speed, and wheel diameter are considered as decision parameters in the genetic algorithm. The central composite design and response surface methods have been employed to design experiments, establish predictive empirical models, and determine interactive effects of decision variables on response variables—process outlet temperature and humidity ratio. Several experiments have been performed to verify applicability of the proposed methodology and validate obtained results. A value of the coefficient of determination exceeding 0.95 demonstrates high reliability and accuracy of the modeling process involved in the proposed methodology. Results obtained demonstrate greater dominance of the surface area ratio compared to other decision variables in terms of their influence on response variables. After successful validation against experimental data, the developed models have been considered as a combination of two objective functions. A fast and elitist non-dominated sorted genetic algorithm II-based optimization technique has been employed to simultaneously determine optimum values of decision variables. A Pareto-optimum front has been presented to select the best value of each decision parameter from available points of optimum operation, and a valuable equation for Pareto-optimal points has been deduced for each material to assist designers develop an optimum design of desiccant cooling systems.
[en] In this paper, the economics analysis of water production by using different solid desiccant materials and composite materials through Scheffler reflector is presented. The experiments for water production have been performed at National Institute of Technology, Kurukshetra, Haryana, India [29°58′ (latitude) North and 76°53′ (longitude) East]. The various factors have been carried out to calculate the annual cost/liter in Indian currency. Total six cases are studied, and for each case, uniform procedure is adopted. The silica gel gives the best economical annual cost/liter compared to molecular sieve and activated alumina in case of solid desiccant, and for composite material, it is CaCl2/River Sand compared to LiCl/River Sand and LiBr/River sand.
[en] Polyamide 6-LiCl (PA 6-LiCl) electrospun nanofibrous membranes (NFMs) have been successfully prepared as novel solid desiccant materials. The PA 6 NFM with 20% LiCl mass ratio had a sorption capacity of 1.8 g g−1 at 25 °C and 95% relative humidity, which was 4 times more than that of silica gels. The desorption isobars of the NFMs indicated that over 85% of sorbed water in the NFMs can be desorbed at about 50 °C, and the low regeneration temperature made it promising as an energy-saving desiccant material. The experimental results manifested that the sorption/desorption kinetics of the NFMs better fit the pseudo-second order model. According to scanning electron microscope images and the cycle experiment, the NFMs were also found to possess notably improved stability against moisture and could be recycled with little degradation of performance, which confirmed the practicability of the new desiccant membranes. (paper)
[en] Highlights: • A novel hybrid desiccant cooling system with a condenser is studied. • Thermal balancing technique is applied for zero and single extraction systems. • A mathematical model of the proposed system using enthalpy pinch method is explained. • The coefficient of performance is improved by 85% using the single extraction. • The investigated hybrid system also produces fresh water as a by-product. - Abstract: This paper focuses on thermodynamic balancing of the regeneration process in a hybrid liquid desiccant cooling/desalination system. The thermal balancing technique is investigated by adding a single extraction between the system regenerator and condenser. This technique is considered as a potential method to reduce energy consumption and increase the hybrid system performance, dramatically. The mathematical procedure to model the proposed system using enthalpy pinch is outlined to study the effect of extraction on the hybrid system performance. The hybrid system, with a single extraction and without extraction (zero extraction), is analyzed in terms of the normalized entropy generation, local enthalpy losses, the coefficient of performance, and proper extraction location. The results show that at enthalpy pinch of 20 kJ per kg of dry air, single extraction system performance is 85.7% better than zero extraction. In addition, the single extraction produces 103.2 kg of fresh water per hour as a by-product compared to 94.2 kg per hour for the zero extraction system.
[en] The aim of the present work was to study Argentinean natural clays with different modifications and their use as desiccants. To this end, bentonite clays collected from different regions were characterized and modified by heat treatment and calcium addition, and the desiccant capacity, in the form of powder and pellets, was studied. In addition, the hydration degree reversibility of these materials was estimated. The mineralogical and structural characterization was performed by X-ray diffraction, Fourier-transform infrared spectroscopy, differential thermal analysis, and thermogravimetric analysis. The textural characterization was performed by adsorption-desorption of N2 , chemical composition by X-ray fluorescence and cation exchange capacity. The water adsorption was determined at 25 °C between 11-98% relative humidity. The results indicated that the desiccant power has a close relationship with the degree of clay purity, drying of the sample and the method of calcium incorporation. (author)