Yuri I. Aristov

New composite sorbent CaCl2 in mesopores for sorption cooling/heating

New working material “CaCl2 confined to mesoporous host matrix MCM-41” is synthesised and studied keeping in mind its application for the sorption cooling/heating. For this mesoporous system the isobars, isosters and isotherms of the water sorption are obtained at the temperatures 293–423 K and the vapour partial pressures 8.7–50.3 mbar. The water sorption is found to be a combination of a liquid absorption and a heterogeneous adsorption. The obtained results evidence the considerable change of the salt properties due to its confinement to the MCM-41 nanopores. A brief comparison of this sorbent with a pure silica gel for the cooling/heating application is made.

Doping Magnesium Hydroxide with Sodium Nitrate: A New Approach to Tune the Dehydration Reactivity of Heat-Storage Materials

Thermochemical energy storage (TES) provides a challenging approach for improving the efficiency of various energy systems. Magnesium hydroxide, Mg(OH)2, is known as a suitable material for TES at temperature T>300 °C. In this work, the thermal decomposition of Mg(OH)2 in the absence and presence of sodium nitrate (NaNO3) is investigated to adapt this material for TES at T<300 °C. The most notable observations described for the doped Mg(OH)2 are (1) a significant reduction of the decomposition temperature Td that allows tuning the dehydration reactivity by varying the NaNO3 content. The Td decrease by 25 °C is revealed at a salt content Y≤2.0 wt %. The maximum Td depression of some 50 °C is observed at Y=15-20 wt %; (2) the NaNO3-doped Mg(OH)2 decomposes considerably faster under conditions typical for closed TES cycles (at T>300 °C in vapor atmosphere) than a pure Mg(OH)2; (3) the morphology of the dehydration product (MgO) dramatically changes. Differential scanning calorimetry, high-resolution transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and vibrational spectroscopy (IR and Raman) are used to study the observed effects and to elucidate possible ways the NaNO3 influences the Mg(OH)2 dehydration and morphology of the dehydration product. The mechanism involving a chemical interaction between the salt and the hydroxide accompanied by nitrate embedding into brucite layers is discussed.

Calcium hydroxide doped by KNO3 as a promising candidate for thermochemical storage of solar heat

New materials for thermochemical storage of concentrated solar heat are highly desirable for making this emerging technology competitive with the traditional sensible and latent heat storage. Keeping this in mind, we have prepared calcium hydroxide modified with potassium nitrate and studied its de-/rehydration dynamics by differential scanning calorimetry and thermogravimetry techniques. The following notable observations are described for the modified Ca(OH)2: (1) an acceleration of the dehydration and reduction of its temperature as compared with the pure hydroxide; (2) the temperature reduction depends on the KNO3 content Y and reaches 35 °C at Y = 5 wt%; (3) the addition of KNO3 only slightly reduces the dehydration heat which remains promising for heat storage applications. Fast rehydration of the doped CaO is observed at T = 290–360 °C and P(H2O) = 23–128 mbar, and its rate strongly depends on both temperature and pressure. De- and rehydrated products were studied by the BET analysis and IR-spectroscopy to elucidate possible ways for the salt to influence the Ca(OH)2 dehydration. The mechanism involving a chemical interaction between the salt and the hydroxide is discussed. The new material exhibits a large heat storage density, fast de-/rehydration and adjustable decomposition temperature, and may be considered as a promising candidate for thermochemical storage of concentrated solar energy.

Experimental Findings: Main Factors Affecting the Adsorptive Temperature-Driven Cycle Dynamics

In Chap. 2, the two main methods to study the sorption dynamics for AHT cycles were widely described: (i) the Large Pressure Jump (LPJ) method, in which adsorption is initiated by a jump of pressure over the sample, is the most adequate for pressure-driven AHT cycles; (ii) the Large Temperature Jump (LTJ) method, in which adsorption is enabled by a temperature swing of a heat exchanger wall that is in contact with the adsorbent under an almost isobaric ad/desorption stage, is the proper choice for temperature-driven AHT cycles (see Chaps. 1 and 2). In this chapter, the main factors affecting the sorption dynamics will be highlighted for temperature-driven AHT cycles by the analysis of results achieved by the two versions (namely V-LTJ and G-LTJ) of the LTJ method.

Optimization of an “Adsorbent/Heat Exchanger” Unit

Despite significant progress, the AHT technology as yet remains unfinished and expensive, so that there is still a big room for its improvement [1, 2]. This concerns, first of all, enhancement of the AHT dynamics, like the ad/desorption rate and finally the specific power that is the main figure of merit of the AHT dynamic performance. Therefore, further R&D activity is necessary to realize the potential economic and ecological advantages of the AHT technology [3]. The optimization of the AHT dynamic performance is a multi-purpose task that includes, first of all, the improvement of the “adsorbent–heat exchanger” unit.

Adsorptive Heat Transformation and Storage: Thermodynamic and Kinetic Aspects

At present, the majority of thermodynamic cycles of heat engines are high-temperature cycles that are realized by internal combustion engines, steam and gas turbines, etc. (Cengel, Boles in Thermodynamics: an engineering approach, 4th edn. McGray-Hill Inc., New York, 2002). Traditional heat engine cycles are mainly based on burning of organic fuel that may result in dramatic increase of CO2 emissions and global warming. The world community has realized the gravity of these problems and taken initiatives to alleviate or reverse this situation. Fulfilment of these initiatives requires, first of all, the replacement of fossil fuels with renewable energy sources (e.g. the sun, wind, ambient heat, natural water basins, soil, air). These new heat sources have significantly lower temperature potential than that achieved by burning of fossil fuels which opens a niche for applying adsorption technologies for heat transformation and storage (Pons et al in Int J Refrig 22:5–17, 1999).

Measurement of Adsorption Dynamics: An Overview

Analysis of the Ad-HEx dynamic behaviour is of pivotal importance in development of advanced adsorber concepts, enabling reduction of weight and volume of the real adsorption heat pump/chiller unit, as well as its energy density enhancement.

Extraction of Water from the Atmosphere in Arid Areas by Employing Composites “A Salt Inside a Porous Matrix”

This communication is addressed to sorptive extraction of water from the atmosphere in arid areas. The method includes (a) sorption of water vapour in an adsorber in the night-time when the air relative humidity is comparatively high, and (b) desorption of the stored water and its subsequent collection in a condenser in the day-time. New materials adapted to this process are highly welcome. Composites “a salt inside a porous matrix” (CSPMs) have enhanced water sorption capacity and their properties may be intently varied in a wide range. In this communication, we make a preliminary analysis of CSPMs application for extraction of water from the atmosphere. Firstly, a general scheme of the water extraction is described. Then, we form a mental representation of an ideal solid sorbent that is optimal for the extraction of water from the atmosphere. Finally, we discuss how to design a real CSPM with properties meeting the formulated requirements, what are roles of the salt and the matrix, etc.