Verification of hydrothermal stability of adsorbent materials for thermal energy storage

n/

experimental comparison of two heat exchanger concepts for latent heat storage applications

Abstract In the present work, two different types of heat exchangers are experimentally compared, namely a fin-and-tubes custom made HEX and a commercial asymmetric plate heat exchanger, for the application with phase change materials. In particular, the two devices were tested in a specifically designed testing rig located at CNR-ITAE and suitable for the characterization of thermal energy storages. The testing bench allows simulating a heat source up to 100°C (e.g. solar thermal collectors, low-grade waste heat) and to set the desired discharge temperature in the range 20°C-80°C. The phase change material with which the exchangers were filled, is a commercial paraffin (Plus ICE A82), having a nominal melting temperature of 82°C. The experimental results on charge and discharge tests, realized with the same protocol, were used for a comparison of the systems, through the identification of suitable performance figures and Key Performance Indicators, such as material-to-metal ratio, heat storage density, maximum and average power achievable and effectiveness of the system. The results show that, for the tested material, characterised by a very low thermal conductivity (i.e. about 0.2 W/mK), the selected plate heat exchanger allows a better exploitation of the heat stored inside the material, letting at the same time to reach a power output in the range 1-10 kW

Morphological and Structural Evaluation of Hydration/Dehydration Stages of MgSO4 Filled Composite Silicone Foam for Thermal Energy Storage Applications

Salt hydrates, such as MgSO4·7H2O, are considered attractive materials for thermal energy storage, thanks to their high theoretical storage density. However, pure salt hydrates present some challenges in real application due to agglomeration, corrosion and swelling problems during hydration/dehydration cycles. In order to overcome these limitations, a composite material based on silicone vapor-permeable foam filled with the salt hydrate is here presented. For its characterization, a real-time in situ environmental scanning electron microscopy (ESEM) investigation was carried out in controlled temperature and humidity conditions. The specific set-up was proposed as an innovative method in order to evaluate the morphological evolution of the composite material during the hydrating and dehydrating stages of the salt. The results evidenced an effective micro-thermal stability of the material. Furthermore, dehydration thermogravimetric/differential scanning calorimetric (TG/DSC) analysis confirmed the improved reactivity of the realized composite foam compared to pure MgSO4·7H2O.This work was partially funded by the Ministerio de Ciencia, Innovación y Universidades de España (RTI2018-093849-B-C31). This work was partially supported by ICREA under the ICREA Academia program

Atomistic modelling of water transport and adsorption mechanisms in silicoaluminophosphate for thermal energy storage

SAPO-34 – a silicoaluminophosphate microporous material – has recently attracted a great attention in the field of sorption thermal storage, since it is characterized by good water adsorption behavior (i.e. type V adsorption isotherms) and low regeneration temperature (i.e. 80 °C, for instance available by standard solar thermal energy collectors). However, the nanoscale mechanisms of water transport and adsorption in the microporous framework of SAPO-34 cannot be fully unveiled by experiments alone. In this work, water adsorption onto SAPO-34 is for the first time studied by means of an atomistic model built upon experimental evidence. First, Monte Carlo simulations are employed to set up a convenient atomistic model of water/SAPO-34 interactions, and numerical adsorption isotherms are validated against experimental measures. Second, the validated model is used to study the water diffusion through SAPO-34 by molecular dynamics simulations, and to visualize preferential adsorption sites with atomistic detail. Such atomistic model validated against experiments may ease the investigation and in silico discovery of silicoaluminophosphates for thermal storage applications with tailored adsorption characteristics

MgSO4·7H2O filled macro cellular foams: An innovative composite sorbent for thermo-chemical energy storage applications for solar buildings

For seasonal energy storage using solar energy in buildings heating and DHW, thermochemical technology represents the most promising alternative due to the virtually absence of heat losses during storage period. This work focuses on silicone foams, filled by MgSO4·7H2O, as innovative composite sorbents for sorption thermal energy storage applications. The necessity to enclose the salt hydrate in the polymeric foam arises for overcoming the issue of swelling, agglomeration, and/or deliquescence of the salt during its de/hydration process. Indeed, the foam with its flexible structure allows the safe volume expansion during the hydration phase of the salt. The foam samples presented in this paper were obtained by mixing the salt hydrate at various percentages (from 40 wt% up to 70 wt%) with a mixture of two water vapour permeable silicones. The foams were characterized by a complete physicochemical and morphological examination in order to evaluate their actual application in sorption energy storage systems. It was demonstrated that a good link seems to be established between the foam and the salt, and that the de/hydration capacity of the salt is not hindered by the foaming process, storage ability and storage density of the composites are expected to be in line with those of the pure material.The present work has been partially funded by PON “Ricerca e Competitività 2007-13” PON03PE_00206_2 S5 – Smart Small Scale Solar Systems and by the Spanish government (ENE2015-64117-C5-1-R (MINECO/FEDER)). The authors from the University of Lleida would like to thank the Catalan Government for the quality accreditation given to their research group (2014 SGR 123). Aran Solé would like to thank Ministerio de Economía y Competitividad de España for Grant Juan de la Cierva, FJCI-2015-25741

Synthesis and Characterization of Graphite Composite Foams for Oil Spill Recovery Application

The aim of this paper is the synthesis and characterization of a composite silicone foam filled with expanded graphite (EG) for oil spill recovery applications. The EG foams were obtained using a foaming slurry consisting of a mixture of siloxane compounds as the matrix with an EG filler. The effect of the filler content’s performance on an innovative composite silicone-based foam was investigated. All the obtained samples exhibited an open cell morphology. Each foam was evaluated in four commonly used oils (kerosene, pump oil, naphtha and crude oil). Additionally, kinetics was studied in order to investigate the physical, chemical and mass transport mechanisms that act during the absorption phenomenon and uptake evolution of the contaminants. Foam filled with 3% of EG exhibited the highest absorption capacity, particularly with light oils kerosene and virgin naphtha (854 and 1016 wt.%, respectively). Furthermore, the kinetic study showed that pseudo-second order mechanisms better fitted the composite absorption performances, suggesting that the oil sorption into EG filled polydimethylsiloxane (PDMS) foams could be related to chemisorption mechanism. The results evidenced a good oil sorption capability and water/oil selectivity indicating this class of materials as a potentially applicable material for oil spill remediation

Unified Methodology to Identify the Potential Application of Seasonal Sorption Storage Technology

In this study, the definition of a new methodology for a preliminary evaluation of the working boundary conditions under which a seasonal thermal energy storage (STES) system operates is described. The approach starts by considering the building features as well as the reference heating system in terms of solar thermal collectors’ technology, ambient heat sinks/source, and space heating distribution systems employed. Furthermore, it is based on a deep climatic analysis of the place where the STES needs to be installed, to identify both winter and summer operating conditions. In particular, the STES energy density is evaluated considering different space heating demands covered by the STES (ranging from 10% up to 60%). The obtained results demonstrate that this approach allows for the careful estimation of the achievable STES density, which is varies significantly both with the space heating coverage guaranteed by the STES as well as with the ambient heat source/sink that is employed in the system. This confirms the need for careful preliminary analysis to avoid the overestimation of the STES material volume. The proposed approach was then applied for different climatic conditions (e.g., Germany and Sweden) and the volume of one of the most attractive composite sorbent materials reported in the literature, i.e., multi-wall carbon nanotubes (MWCNT)-LiCl, using water as the working fluid, needed for covering the variable space heating demand in a Nearly Zero Energy Building (NZEB) was calculated. In the case of Swedish buildings, it ranges from about 3.5 m3 when 10% of the space heating demand is provided by the STES, up to 11.1 m3 when 30% of the space heating demand is provided by the STES