Abstract
Heat energy storage is one of the most common technical solutions in the conditions of operation of low-potential and renewable energy sources. Adsorption heat energy storage devices based on the composite media “silica gel – salt” are the most effective in these conditions. The technique and technology of sol-gel synthesis of the composite adsorption materials “silica gel – sodium sulfate” and “silica gel – sodium acetate” have been developed. A special feature of this technique is a two-stage process involving the formation of silicon phase nuclei in the interaction of aqueous solutions of silicate glass and sulphuric or acetic acids in the presence of a polymeric quaternary ammonium salt and subsequent coarsening of the particles with the gradual addition of solutions of silicate glass and the corresponding acids. The essence of the technology consists in successive stages of formation and integration of the silicic phase nuclei, hydrolysis of functional OH- groups, filtration and drying of the fine precipitate. A qualitative difference in the adsorption properties of the synthesized composites and the mechanical mixture of salt – silica gel with sorption capacity inferior to them on average by 30% is revealed by differential thermal analysis. The processes of application of the composite adsorption materials “silica gel – sodium sulfate” and “silica gel – sodium acetate” obtained by the sol-gel method have been studied. A qualitative difference in the kinetics of adsorption of water by the composite adsorbents is shown as compared to massive salts. It is established that the amount of heat of adsorption of water vapor by the composite adsorbents of the materials “silica gel – sodium sulfate” and “silica gel – sodium acetate” is approximately 30 % greater than the linear superposition of salt and silica gel.
Highlights
Adsorption conversion of heat energy based on the thermal effects of adsorption on solid sorbents is one of the promising technical solutions that allow optimizing the operation of renewable energy sources, as well as absorption, accumulation and transformation of low-potential thermal energy
Manufacturing is associated with the use of rather complex impregnation technologies with solutions of crystalline hydrates of porous media, often expensive, which impedes commercialization in energy storage devices [5, 7]. This problem can be solved by synthesizing composites such as silica gel – crystalline hydrate by the sol-gel method [14,15,16]
The introduction of crystals of sodium sulfate or sodium acetate salts into the porous silicon dioxide matrix obviously results in an increase in the sorption capacity of the composite sorbents
Summary
Adsorption conversion of heat energy based on the thermal effects of adsorption on solid sorbents is one of the promising technical solutions that allow optimizing the operation of renewable energy sources, as well as absorption, accumulation and transformation of low-potential thermal energy. According to [1], the working pairs CaCl2–H2O, SrBr2– H2O, Na2S–H2O, MgCl2–H2O could be promising for the accumulation of thermal energy. They allow realizing the energy storage density of 1.9–2.7 GJ/m3 of crystalline hydrate. Their application is limited by physical and chemical instability along with the corrosive activity of these salts at high temperatures, instability in repeated cycling, degradation in time, and an underdeveloped heat exchange surface. The task-oriented development of heat-storage devices based on adsorption heat-accumulating materials becomes the task of current interest
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