• Energy Research

AbstractThermal energy storage (TES) systems have been a subject of growing interest due to their potential to address the challenges of intermittent renewable energy sources. In this context, cementitious materials are emerging as a promising TES media because of their relative low cost, good thermal properties and ease of handling. This article presents a comprehensive review of studies exploring the use of cementitious materials, particularly concrete, as sensible heat storage media at varying scales, ranging from laboratory investigations to prototype evaluations. Starting from the different kinds of energy storage systems and applications where concrete has been used as a storage media, this article reviews the important properties which makes them a suitable material for the purpose. Reported observations are discussed and summarised based on concrete mix composition/design, aggregate/addition type, size gradation, etc., and performance of these materials. Finally, different cement-based prototypes are examined highlighting their strengths and weaknesses, and general conclusions are drawn.

Geopolymer (GEO) concrete emerges as a potential high-temperature thermal energy storage (TES) material, offering a remarkable thermal storage capacity, approximately 3.5 times higher than regular Portland cement (OPC) concrete, without compromising its environmentally benign nature. This research dissects the application of GEO concrete as a high-temperature TES material, primarily focusing on its optimization and scalability. The introductory part of the study involves the development and validation of a three-dimensional numerical model using computational fluid dynamics (CFD). The model demonstrated an average accuracy rate of 5 %, as justified by empirical data. Later, a two-tiered investigation to determine the optimal design for GEO concrete TES systems was investigated. Three different geometries plus the impact of crucial parameters such as air velocity, tube diameter, and module size on the thermal storage capacity (Q) studied. It further extends into a parametric examination, exploring a variety of tube sizes, arrangements, and configurations. It is found that air velocity primarily influences Q. A subsequent phase provides an analysis of the thermodynamic effects brought by the inclusion of tubes within TES modules through an equivalent parametric study. It exposes the thermal resistance resulting from tube insertion. The study reinforces the superior thermal performance of tubeless GEO concrete TES configurations, as signified by overall heat transfer rate (Q̇). The study also signals the significant roles of key parameters in determining the temperature (T) and Q within TES unit using Pearson's correlation coefficient equation. As a final observation, this work emphasizes the sustained significance of on-site evaluations to consistently monitor the interplay between TES materials and high-temperature fluids (HTFs) over extended periods for viability analysis purposes. This work was born under the umbrella of the project “Energy storage solutions based on concrete (E-CRETE)” (RTI2018-098554-B-I00) funded by MCIN/AEI/10.13039/501100011033 (Program I+D+i RETOS INVESTIGACIÓN 2018). Mohammad Rahjoo acknowledges the grant PRE2019-087676 funded by MCIN/AEI/10.13039/501100011033 and co-financed by the European Social Fund under the 2019 call for grants for predoctoral contracts for the training of doctors contemplated in the State Training Subprogram of the State Program for the Promotion of Talent and its Employability in R&D&I, within the framework of the State Plan for Scientific and Technical Research and Innovation 2017–2020. In addition, the economic support from POVAZSKA is acknowledged. Jorge S. Dolado acknowledges the funding from the Gobierno Vasco UPV/EHU (project no. IT1569-22). Peer reviewed

Understanding the mechanism that controls cement hydration and its stages is a long-standing challenge. Over a decade ago, the mineral dissolution theory was adopted from geochemistry to explain the hydration rate evolution of alite. The theory is not fully accepted by the community and deserves further investigation. In this work, we apply Kinetic Monte Carlo (KMC) simulations with the mineral dissolution theory as a conceptual framework to investigate and discuss alite dissolution. We build a Kossel crystal model system and parameterize the dissolution activation energies and frequencies based on experimental data. The resulting KMC model is capable of reproducing the dissolution rate and activation energies as a function of the dissolution free energy. The simulations indicate that mineral dissolution theory easily explains the induction and acceleration stages due to a continuous increase of the reactive area as the etch pits open. However, the deceleration stage is hardly reconcilable with the mechanism suggested in the literature, i.e. dislocation coalescence. Still, within the mineral dissolution theory umbrella, we propose and discuss an alternative mechanism based on dislocation exhaustion. The authors would like to acknowledge funding from ‘Departamento de Educación, Política Lingüística y Cultura del Gobierno Vasco’ (Grant No. IT1458-22), the Transnational Common Laboratory ‘Aquitaine- Euskadi Network in Green Concrete and Cement-based Materials’ (LTCGreen Concrete) and the technical and human support provided by the Scientific Computing Service of SGIker (UPV/EHU/ERDF, EU). P.M. also acknowledges the postdoctoral fellowship ‘Margaritas Salas scholarship NEXT GENERATION EU.’ from ‘ministerio de universidades de España’. MJAQ acknowledges funding from the United States’ National Science Foundation under awards CMMI-2145537 and CMMI-2103125.

KIMERA is a scientific tool for the study of mineral dissolution. It implements a reversible Kinetic Monte Carlo (KMC) method to study the time evolution of a dissolving system, obtaining the dissolution rate and information about the atomic scale dissolution mechanisms. KIMERA allows to define the dissolution process in multiple ways, using a wide diversity of event types to mimic the dissolution reactions, and define the mineral structure in great detail, including topographic defects, dislocations, and point defects. Therefore, KIMERA ensures to perform numerous studies with great versatility. In addition, it offers a good performance thanks to its parallelization and efficient algorithms within the KMC method. In this manuscript, we present the code features and show some examples of its capabilities. KIMERA is controllable via user commands, it is written in object-oriented C++, and it is distributed as open-source software.

L'ajout de différents types de matériaux à changement de phase (PCM) aux matériaux à base de ciment pour le stockage de l'énergie thermique a été largement étudié dans la littérature. De nombreuses études ont étudié l'ajout de PCM organiques et les performances thermiques du système PCM-ciment. Cependant, les inconvénients tels que les fuites et la mauvaise conductivité thermique des PCM ont stimulé les études visant à améliorer les propriétés thermiques au sein du système PCM-ciment. Parmi les différentes solutions, l'ajout de matériaux carbonés (tels que le graphite et les nanotubes de carbone) pour améliorer la conductivité thermique des PCM a été étudié. Dans le travail actuel, un système innovant contenant des PCM microencapsulés (MPCM) et de l'oxyde de graphène réduit (rGO) synthétisé à dessein a été conçu et évalué. L'ajout de rGO a deux objectifs. La première consiste à accélérer la vitesse de stockage/libération de chaleur en améliorant la conductivité thermique de l'ensemble du système. La seconde consiste à améliorer la conductivité électrique du système afin de pouvoir activer activement (en appliquant une tension) la fonction de stockage/libération thermique. À la connaissance des auteurs, il s'agit d'une nouvelle approche pour le développement de systèmes de stockage d'énergie thermique à base de ciment PCM actif. En outre, dans la présente étude, l'utilisation des PCM paraffiniques a été comparée à celle des PCM biosourcés afin de fournir une solution plus durable à la conception d'éléments à base de ciment pour les applications du bâtiment. Une caractérisation thermique complète (capacité de stockage thermique, conductivité thermique et diffusivité) a été réalisée ainsi qu'une caractérisation microstructurale. De plus, la spectroscopie diélectrique à large bande a été utilisée pour caractériser la conductivité électrique du nouveau système MPCM-rGO-cement. La adición de diferentes tipos de materiales de cambio de fase (PCM) a los materiales a base de cemento para el almacenamiento de energía térmica se ha investigado ampliamente en la literatura. Muchos estudios han investigado la adición de PCM orgánicos y el rendimiento térmico del sistema PCM-cemento. Sin embargo, inconvenientes como las fugas y la mala conductividad térmica de los PCM han estimulado estudios para mejorar las propiedades térmicas dentro del sistema PCM-cemento. Entre las diferentes soluciones, se ha investigado la adición de materiales carbonosos (como el grafito y los nanotubos de carbono) para mejorar la conductividad térmica de los PCM. En el trabajo actual, se ha diseñado y evaluado un sistema innovador que contiene PCM microencapsulados (MPCM) y óxido de grafeno reducido (rGO) sintetizado a propósito. La adición de rGO tiene dos objetivos. La primera es acelerar la velocidad de almacenamiento/liberación de calor mejorando la conductividad térmica de todo el sistema. El segundo es mejorar la conductividad eléctrica del sistema para poder activar activamente (aplicando voltaje) la función de almacenamiento/liberación térmica. Hasta donde saben los autores, este es un enfoque novedoso para el desarrollo de sistemas activos de almacenamiento de energía térmica basados en PCM-cemento. Además, en el presente estudio, el uso de PCM parafínicos se comparó con el de PCM de base biológica para proporcionar una solución más sostenible al diseño de elementos a base de cemento para aplicaciones en edificios. Se ha realizado una caracterización térmica integral (capacidad de almacenamiento de calor, conductividad térmica y difusividad) así como una caracterización microestructural. Además, se utilizó la espectroscopia dieléctrica de banda ancha para caracterizar la conductividad eléctrica del nuevo sistema de cemento MPCM-rGO. Addition of different types of phase change materials (PCMs) to cement-based materials for thermal energy storage has been broadly investigated in the literature. Many studies have researched the addition of organic PCMs and the thermal performance of the PCM-cement system. However, drawbacks such as leakage and poor thermal conductivity of the PCMs have stimulated studies to improve thermal properties within the PCM-cement system. Among the different solutions, addition of carbonous materials (such as graphite and carbon nanotubes) to improve thermal conductivity of the PCMs have been investigated. In the current work, an innovative system that contains microencapsulated PCMs (MPCMs) and purposely synthesized reduced graphene oxide (rGO) has been designed and assessed. The addition of rGO has two aims. The first one is to speed up the heat storage/release velocity by improving the thermal conductivity of the whole system. The second one is to improve the electrical conductivity of the system in order to actively (by applying voltage) be able to turn on the thermal storage/release feature. Up to the authors' knowledge, this is a novel approach for the development of active PCM-cement based thermal energy storage systems. Furthermore, in the present study, the use of paraffinic PCMs was compared with that of biobased PCMs in order to provide a more sustainable solution to the design of cement-based elements for buildings applications. A comprehensive thermal characterization (heat storage capacity, thermal conductivity and diffusivity) has been carried out as well as microstructural characterization. Moreover, broadband dielectric spectroscopy was used to characterize the electrical conductivity of the novel MPCM-rGO-cement system. تم التحقيق على نطاق واسع في إضافة أنواع مختلفة من مواد تغيير الطور (PCMS) إلى المواد القائمة على الأسمنت لتخزين الطاقة الحرارية في الأدبيات. وقد بحثت العديد من الدراسات في إضافة PCMs العضوية والأداء الحراري لنظام الأسمنت PCM. ومع ذلك، فإن العيوب مثل التسرب وضعف الموصلية الحرارية لـ PCMs قد حفزت الدراسات لتحسين الخصائص الحرارية داخل نظام الأسمنت PCM. ومن بين الحلول المختلفة، تم التحقيق في إضافة مواد كربونية (مثل الجرافيت والأنابيب النانوية الكربونية) لتحسين الموصلية الحرارية لـ PCMS. في العمل الحالي، تم تصميم وتقييم نظام مبتكر يحتوي على PCMs المغلفة الدقيقة (MPCMs) وأكسيد الجرافين المنخفض المركب عن قصد (rGO). إضافة rGO لها هدفان. الأول هو تسريع سرعة تخزين/إطلاق الحرارة من خلال تحسين الموصلية الحرارية للنظام بأكمله. والثاني هو تحسين الموصلية الكهربائية للنظام من أجل أن يكون قادرًا بنشاط (من خلال تطبيق الجهد) على تشغيل ميزة التخزين/التحرير الحراري. على حد علم المؤلفين، يعد هذا نهجًا جديدًا لتطوير أنظمة تخزين الطاقة الحرارية النشطة القائمة على الأسمنت PCM. علاوة على ذلك، في هذه الدراسة، تمت مقارنة استخدام PCMs البرافينية مع استخدام PCMs الحيوي من أجل توفير حل أكثر استدامة لتصميم العناصر القائمة على الأسمنت لتطبيقات المباني. تم تنفيذ توصيف حراري شامل (سعة تخزين الحرارة والموصلية الحرارية والانتشار) بالإضافة إلى التوصيف الهيكلي الدقيق. علاوة على ذلك، تم استخدام التحليل الطيفي العازل عريض النطاق لتوصيف الموصلية الكهربائية لنظام الأسمنت MPCM - RGO الجديد.

Thermal energy storage (TES) systems are dependent on materials capable of operating at elevated temperatures for their performance and for prevailing as an integral part of industries. High-temperature TES assists in increasing the dispatchability of present power plants as well as increasing the efficiency in heat industry applications. Ordinary Portland cement (OPC)-based concretes are widely used as a sensible TES material in different applications. However, their performance is limited to operation temperatures below 400 °C due to the thermal degradation processes in its structure. In the present work, the performance and heat storage capacity of geopolymer-based concrete (GEO) have been studied experimentally and a comparison was carried out with OPC-based materials. Two thermal scenarios were examined, and results indicate that GEO withstand high running temperatures, higher than 500 °C, revealing higher thermal storage capacity than OPC-based materials. The high thermal energy storage, along with the high thermal diffusion coefficient at high temperatures, makes GEO a potential material that has good competitive properties compared with OPC-based TES. Experiments show the ability of geopolymer-based concrete for thermal energy storage applications, especially in industries that require feasible material for operation at high temperatures.