Crystals

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11 pages, 2599 KiB

Open AccessArticle

Molecular Dynamics Simulation of the Crystallization Behavior of Octadecane on a Homogeneous Nucleus

by Stefanie Tafelmeier and Stefan Hiebler

Crystals 2022, 12(7), 987; https://doi.org/10.3390/cryst12070987 - 15 Jul 2022

Cited by 4 | Viewed by 2888

Latent heat storages have the ability to contribute to a more sustainable energy supply network. However, phase change materials (PCM) used for latent heat storages often show supercooling. This phenomenon takes place whenever the PCM begins crystallizing below the freezing point and is [...] Read more.

Latent heat storages have the ability to contribute to a more sustainable energy supply network. However, phase change materials (PCM) used for latent heat storages often show supercooling. This phenomenon takes place whenever the PCM begins crystallizing below the freezing point and is one of the biggest drawbacks holding back the widespread use of PCM. Nucleation agents (NA) can be used to avoid the supercooling, yet the choice of an effective NA is not straightforward. In this work, molecular dynamics (MD) simulation was tested in order to simulate the crystallization of Octadecane on a NA. The simulation results include density, phase change temperature and enthalpy as well as the crystal structure and lie in good agreement with literature values and the authors’ own experimental data. Further simulations of the crystallization process on different surfaces of homogeneous nuclei acting as a NA were performed. The results reflect the hypothesis that liquid molecules start crystallizing easier on surfaces exposing the whole chain side rather than the chain ends. With the result, that the choice of parameters for the MD simulation represent the Octadecane system reliably and further studies can be performed including heterogeneous NA. Full article

(This article belongs to the Special Issue Crystals for Thermal Energy Storage)

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11 pages, 2798 KiB

Open AccessArticle

Evaluation of ZIF-8 and ZIF-90 as Heat Storage Materials by Using Water, Methanol and Ethanol as Working Fluids

by Ciara Byrne, Alenka Ristić, Suzana Mal, Mojca Opresnik and Nataša Zabukovec Logar

Crystals 2021, 11(11), 1422; https://doi.org/10.3390/cryst11111422 - 20 Nov 2021

Cited by 9 | Viewed by 4898

Abstract

The increasing demand for heating/cooling is of grave concern due to the ever-increasing population. One method that addresses this issue and uses renewable energy is Thermochemical Energy Storage (TCES), which is based on the reversible chemical reactions and/or sorption processes of gases in [...] Read more.

The increasing demand for heating/cooling is of grave concern due to the ever-increasing population. One method that addresses this issue and uses renewable energy is Thermochemical Energy Storage (TCES), which is based on the reversible chemical reactions and/or sorption processes of gases in solids or liquids. Zeolitic imidazolate frameworks (ZIFs), composed of transition metal ions (Zn, Co, etc.) and imidazolate linkers, have gained significant interest recently as porous adsorbents in low temperature sorption-based TES (sun/waste heat). In this study, we examined two different sodalite-type ZIF structures (ZIF-8 and ZIF-90) for their potential heat storage applications, based on the adsorption of water, methanol and ethanol as adsorbates. Both ZIF structures were analysed using PXRD, TGA, SEM and N₂ physisorption while the % adsorbate uptake and desorption enthalpy was evaluated using TGA and DSC analysis, respectively. Among the studied adsorbent–adsorbate pairs, ZIF-90-water showed the highest desorption enthalpy, the fastest sorption kinetics and, therefore, the best potential for use in heat storage/reallocation applications. This was due to its significantly smaller particle size and higher specific surface area, and the presence of mesoporosity as well as polar groups in ZIF-90 when compared to ZIF-8. Full article

(This article belongs to the Special Issue Crystals for Thermal Energy Storage)

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34 pages, 4886 KiB

Open AccessArticle

Thermal Energy Storage Materials (TESMs)—What Does It Take to Make Them Fly?

by Saman Nimali Gunasekara, Camila Barreneche, A. Inés Fernández, Alejandro Calderón, Rebecca Ravotti, Alenka Ristić, Peter Weinberger, Halime Ömur Paksoy, Burcu Koçak, Christoph Rathgeber, Justin Ningwei Chiu and Anastasia Stamatiou

Crystals 2021, 11(11), 1276; https://doi.org/10.3390/cryst11111276 - 21 Oct 2021

Cited by 24 | Viewed by 9089

Abstract

Thermal Energy Storage Materials (TESMs) may be the missing link to the “carbon neutral future” of our dreams. TESMs already cater to many renewable heating, cooling and thermal management applications. However, many challenges remain in finding optimal TESMs for specific requirements. Here, we [...] Read more.

Thermal Energy Storage Materials (TESMs) may be the missing link to the “carbon neutral future” of our dreams. TESMs already cater to many renewable heating, cooling and thermal management applications. However, many challenges remain in finding optimal TESMs for specific requirements. Here, we combine literature, a bibliometric analysis and our experiences to elaborate on the true potential of TESMs. This starts with the evolution, fundamentals, and categorization of TESMs: phase change materials (PCMs), thermochemical heat storage materials (TCMs) and sensible thermal energy storage materials (STESMs). PCMs are the most researched, followed by STESMs and TCMs. China, the European Union (EU), the USA, India and the UK lead TESM publications globally, with Spain, France, Germany, Italy and Sweden leading in the EU. Dissemination and communication gaps on TESMs appear to hinder their deployment. Salt hydrates, alkanes, fatty acids, polyols, and esters lead amongst PCMs. Salt hydrates, hydroxides, hydrides, carbonates, ammines and composites dominate TCMs. Besides water, ceramics, rocks and molten salts lead as STESMs for large-scale applications. We discuss TESMs’ trends, gaps and barriers for commercialization, plus missing links from laboratory-to-applications. In conclusion, we present research paths and tasks to make these remarkable materials fly on the market by unveiling their potential to realize a carbon neutral future. Full article

(This article belongs to the Special Issue Crystals for Thermal Energy Storage)

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11 pages, 3728 KiB

Open AccessArticle

Pyrolysis Preparation Process of CeO₂ with the Addition of Citric Acid: A Fundamental Study

by Chao Lv, Ming-He Sun, Hong-Xin Yin, Zhen-Feng Wang and Tian-Yuan Xia

Crystals 2021, 11(8), 912; https://doi.org/10.3390/cryst11080912 - 3 Aug 2021

Cited by 2 | Viewed by 2120

Abstract

CeO₂ is an important energy storage material that can be used in solid fuel cells. Adding citric acid can improve the particle distribution of the pyrolytic preparation of CeO₂ inside the reactor. Through Fluent, this paper investigated the pyrolysis preparation of [...] Read more.

CeO₂ is an important energy storage material that can be used in solid fuel cells. Adding citric acid can improve the particle distribution of the pyrolytic preparation of CeO₂ inside the reactor. Through Fluent, this paper investigated the pyrolysis preparation of CeO₂ with the addition of citric acid by adopting the Eulerian multiphase flow model, component transportation model, and standard k-ε turbulence model. The experimental and simulation results suggest that the addition of citric acid can alter the pressure, temperature, and component distributions inside the reactor. When the mass fraction of O₂ is 0.3, the concentration distribution effect of the CeO₂ component is optimal and its conversation rate is the highest. When the mass fraction of citric acid is 0.04, the concentration distribution effect of the CeO₂ component is the best, as witnessed by the high CeO₂ concentration at the exit. It was found that an O₂ content of 30 wt % and citric acid content of 4 wt % were optimal operating conditions for this technology. Full article

(This article belongs to the Special Issue Crystals for Thermal Energy Storage)

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12 pages, 30762 KiB

Open AccessArticle

Tailoring Water Adsorption Capacity of APO-Tric

by Suzana Mal, Alenka Ristić, Amalija Golobič and Nataša Zabukovec Logar

Crystals 2021, 11(7), 773; https://doi.org/10.3390/cryst11070773 - 2 Jul 2021

Cited by 3 | Viewed by 2348

Abstract

Microporous triclinic AlPO₄-34, known as APO-Tric, serves as an excellent water adsorbent in thermal energy storage, especially for low temperature thermochemical energy storage. Increased water adsorption capacity of thermochemical material usually leads to higher thermal energy storage capacity, thus offering improved [...] Read more.

Microporous triclinic AlPO₄-34, known as APO-Tric, serves as an excellent water adsorbent in thermal energy storage, especially for low temperature thermochemical energy storage. Increased water adsorption capacity of thermochemical material usually leads to higher thermal energy storage capacity, thus offering improved performance of the adsorbent. The main disadvantage of aluminophosphate-based TCM materials is their high cost due to the use of expensive organic templates acting as structure directing agents. Using ionic liquids as low cost solvents with associated structure directing role can increase the availability of these water adsorbents for TES applications. Here, a green synthesis of APO-Tric crystals at elevated and ambient pressure by using 1-ethyl-3-methyl imidazolium bromide ionic liquid is presented. Large 200 µm romboid shaped monocrystals were obtained at 200 °C after 6 days. The structure of APO-Tric and the presence of 1,3-dimetylimidazolium cation in the micropores were determined by single crystal XRD at room temperature and 150 K. Water sorption capacity of APO-Tric prepared by ionothermal synthesis at elevated pressure increased in comparison to the material obtained at hydrothermal synthesis most probably due to additional structural defects obtained after calcination. The reuse of exhausted ionic liquid was also confirmed, which adds to the reduction of toxicity and cost production of the aluminophosphate synthesis. Full article

(This article belongs to the Special Issue Crystals for Thermal Energy Storage)

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20 pages, 6363 KiB

Open AccessArticle

Experimental Comparison of Innovative Composite Sorbents for Space Heating and Domestic Hot Water Storage

by Vincenza Brancato, Larisa G. Gordeeva, Angela Caprì, Alexandra D. Grekova and Andrea Frazzica

Crystals 2021, 11(5), 476; https://doi.org/10.3390/cryst11050476 - 24 Apr 2021

Cited by 14 | Viewed by 2600

Abstract

In this study, the development and comparative characterization of different composite sorbents for thermal energy storage applications is reported. Two different applications were targeted, namely, low-temperature space heating (SH) and domestic hot water (DHW) provision. From a literature analysis, the most promising hygroscopic [...] Read more.

In this study, the development and comparative characterization of different composite sorbents for thermal energy storage applications is reported. Two different applications were targeted, namely, low-temperature space heating (SH) and domestic hot water (DHW) provision. From a literature analysis, the most promising hygroscopic salts were selected for these conditions, being LiCl for SH and LiBr for DHW. Furthermore, two mesoporous silica gel matrixes and a macroporous vermiculite were acquired to prepare the composites. A complete characterization was performed by investigating the porous structure of the composites before and after impregnation, through N₂ physisorption, as well as checking the phase composition of the composites at different temperatures through X-ray powder diffraction (XRD) analysis. Furthermore, sorption equilibrium curves were measured in water vapor atmosphere to evaluate the adsorption capacity of the samples and a detailed calorimetric analysis was carried out to evaluate the reaction evolution under real operating conditions as well as the sorption heat of each sample. The results demonstrated a slower reaction kinetic in the vermiculite-based composites, due to the larger size of salt grains embedded in the pores, while promising volumetric storage densities of 0.7 GJ/m³ and 0.4 GJ/m³ in silica gel-based composites were achieved for SH and DHW applications, respectively. Full article

(This article belongs to the Special Issue Crystals for Thermal Energy Storage)

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10 pages, 3654 KiB

Open AccessArticle

High Anisotropic Thermal Conductivity, Long Durability Form-Stable Phase Change Composite Enhanced by a Carbon Fiber Network Structure

by Kaixin Dong, Nan Sheng, Deqiu Zou, Cheng Wang, Xuemei Yi and Takahiro Nomura

Crystals 2021, 11(3), 230; https://doi.org/10.3390/cryst11030230 - 25 Feb 2021

Cited by 6 | Viewed by 2403

Abstract

To address the drawback of low thermal conductivity of conventional organic phase change materials (PCMs), a paraffin-wax-based phase change composite (PCC) was assembled via a vacuum impregnation method, using a new type of carbon fiber network material as the supporting matrix. The carbon [...] Read more.

To address the drawback of low thermal conductivity of conventional organic phase change materials (PCMs), a paraffin-wax-based phase change composite (PCC) was assembled via a vacuum impregnation method, using a new type of carbon fiber network material as the supporting matrix. The carbon fiber sheet (CFS) material exhibited a network structure comprising high-thermal-conductivity carbon fibers, beneficial for enhancing the heat transfer properties of the PCC. The sheet-shaped carbon fiber material was stacked and compressed, and then impregnated with the liquid paraffin wax PCM to form the composite. The thermal conductivity, durability, shape stability, chemical stability, and heat storage characteristics of the PCC specimen were carefully analyzed. The maximum thermal conductivity of the PCC was 11.68 W·m⁻¹·K⁻¹ (4670% compared to that of pure paraffin) in the radial direction, and 0.93 W·m⁻¹·K⁻¹ in the axial direction of the sample, with 17.44 vol % of added CFS. The thermal conductivity retention rate after 200 thermal cycles was 78.6%. The PCC also displayed good stability in terms of chemical structure, shape, and heat storage ability. This study offers insights and a possible strategy for the development of anisotropic high-thermal-conductivity PCCs for potential applications in latent heat storage systems. Full article

(This article belongs to the Special Issue Crystals for Thermal Energy Storage)

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22 pages, 17654 KiB

Open AccessArticle

Assessment of the Thermal Properties of Aromatic Esters as Novel Phase Change Materials

by Rebecca Ravotti, Oliver Fellmann, Ludger J. Fischer, Jörg Worlitschek and Anastasia Stamatiou

Crystals 2020, 10(10), 919; https://doi.org/10.3390/cryst10100919 - 10 Oct 2020

Cited by 10 | Viewed by 7884

Abstract

In the quest for a decarbonized energy system, the development of highly efficient technologies that allow the integration of renewables is of the utmost importance. Latent Heat Storage systems with Phase Change Materials (PCM) can contribute to solving the issue of the mismatch [...] Read more.

In the quest for a decarbonized energy system, the development of highly efficient technologies that allow the integration of renewables is of the utmost importance. Latent Heat Storage systems with Phase Change Materials (PCM) can contribute to solving the issue of the mismatch between demand and supply brought forward by renewable energies. Despite possessing promising thermal properties, organic PCMs and esters in particular have rarely been investigated. In the present study, eight commercial aromatic esters are assessed as possible PCM candidates. To do so, their thermal properties, such as phase change temperature, enthalpy of fusion, density, and thermal conductivity, alongside sustainability and toxicity issues, are considered. The aromatic esters are found to possess phase change temperatures between −16

^{\circ}

C and 190

^{\circ}

C and maximum enthalpies of fusion of 160 J/g. This, alongside densities above 1 g/mL, makes them interesting candidates for high-temperature applications, where, typically, salts and ceramics or metals dominate as PCMs. Full article

(This article belongs to the Special Issue Crystals for Thermal Energy Storage)

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