Thermal Storage Research Articles

Investigating the Effects of PCM-Integrated Walls on Thermal Performance for UK Residential Buildings of Different Typologies

Phase change materials (PCMs) can improve the thermal performance of building facades. The integration position of a PCM in the facades is influenced by multiple factors including the material properties of the PCM, building types, and the internal and external conditions of a building. However, this has not been a focus within the UK dwelling stock, where many dwellings are not thermally protected. This paper, therefore, presents a numerical study with the aid of building simulation that comparatively analysed the thermal performance between four typical UK dwelling types (semi-detached house, terraced house, detached house, and apartment) situated in North East England. The PCM was implemented into the external wall of the dwellings with the positions altered to determine the most effective position. It was determined that the PCM positioned internally was the most effective for all the dwelling types. These results demonstrated that the PCM being implemented in the apartment, semi-detached, and terraced houses had only marginal heat loss reductions (by 8%, 14%, and 8%, respectively) in comparison with that of the detached house (by 30%). It was also found that the large external wall area of the detached house acted as significant thermal energy storage, which was capable of offsetting heat transmission and stabilising indoor thermal conditions. In summary, this paper contributes to the matters concerning the effect of PCMs on indoor thermal performance in dwellings of different typologies in the UK.

Recent Progress on Thermal Energy Storage for Coal-Fired Power Plant

Recent Progress on Thermal Energy Storage for Coal-Fired Power Plant

Understanding photo-thermal and melting mechanisms in optical charging of nano and micro particles laden organic PCMs

Engineering efficient optical charging process necessitates efficient photo-thermal energy conversion, transfer, as well as storage of the incident solar radiant energy. The present work is a determining step in deciphering, quantifying, and understanding the aforementioned steps involved in the optical charging of PCMs. Herein, the effect of particle size, concentration and thermochromism have been critically investigated. In particular, detailed optical characterization and photo-thermal experimentation pertinent to non-thermochromic nanoparticles laden PCM (referred to as NP-PCM) and thermochromic micro capsules laden PCM (referred to as TMCP-PCM) has been undertaken. Detailed optical analysis points out that opposed to NP-PCM, TMCP-PCM significantly scatter the incident radiations – the diffuse transmittance (at room temperature) in the two cases being approximately 2 % and 39 % respectively. Furthermore, whereas, optical properties of non-thermochromic nanoparticles are nearly invariant to temperature changes; in the case of thermochromic microcapsules, the magnitude of scattering further increases and diffuse transmittance reaches as high as 51 % at elevated temperatures. Although, thermochromism helps in enhancing the penetration depth at elevated temperatures, but, due to significant fraction of scattering, the photo-thermal energy conversion is not that effective. In terms of temperature field, spatial-temporal temperature distribution curves reveal that temperature spread (in the liquid phase) in case of optical charging of non-thermochromic particles (carbon soot nanoparticles) laden PCMs is significantly high (as high as approximately 24 °C) relative to that observed in case of thermochromic particles (microcapsules) laden PCMs (approximately, 4 °C). The magnitude of the temperature spread (being representative of the deviation from thermostatic optical charging) clearly points out that opposed to non-thermochromic laden PCMs, nearly thermostatic optical charging can be achieved in case of thermochromic particles laden PCMs.Furthermore, in case of optical charging without thermochromic assistance, the temperature spread, peak temperatures and the melting rates increase with increase in particles concentration. Whereas, in the latter case, although the temperature spread and peak temperatures are nearly independent; the melting rates do depend on the particles’ concentration. Overall, the present work is a significant step towards accelerated-thermostatic thermal energy storage.

Techno-Economic Comparative Assessment of High Temperature Heat Pump Architectures for Industrial Pumped Thermal Energy Storage

Abstract The industrial sector is a key global source of wealth, but it is also recognized as a major challenge toward worldwide decarbonization. Today the industrial sector requires more than 22 % of the global energy demand as thermal energy and produces for this about 40 % of the total CO2 emissions. Solutions to efficiently decarbonize the industrial sector are deemed. This work presents a comparative techno-economic performance assessment of a high temperature heat pump integration within a molten salts based power to heat system for industrial heat flexible generation. The main system performance is reported in terms of required working conditions and temperature for the heat pump and thermal demand size as well as reduction of the attainable levelized cost of heat (LCoH) against non-flexible electric boiler based systems. The impact of different industrial load profiles, electricity prices, heat pump capital cost and heat pump real to Carnot efficiency ratio are also presented. The results highlight that the proposed system can be cost-competitive, particularly for thermal demand around 10 MW and waste heat temperatures above 80°C. Under these conditions LCoH reductions higher than 15 %, with respect to the considered non-flexible electric boiler alternative, are attainable. These LCoH reductions are primarily driven by savings in electrical consumption as high as 30 %. This study sets the ground for further power-to-heat techno-economic investigations addressing different industrial sectors and identifies main system and components design strategies, integrations, and targets.

Solar-enhanced DCMD: Dual-tank system for superior efficiency and viability

ABSTRACT This study investigates a novel solar-powered direct contact membrane distillation (DCMD) system designed to significantly enhance desalination efficiency and economic feasibility. The system features a dual-tank configuration integrated with a solar collector, which optimizes thermal energy storage and ensures consistent feedwater temperatures. Therefore, continuous operation is possible despite fluctuations in solar radiation. An assessment of the system's performance under various solar radiation conditions predicted an average daily permeate flux of 14.4 kg/m2 and a specific energy consumption of 1810 kJ/kg, indicating superior thermal efficiency. The economic analysis revealed a competitive levelized water cost of $25.75 per cubic meter, highlighting the system's potential as a viable alternative to conventional desalination technologies. These findings suggest that the proposed DCMD system is a leading technology in the pursuit of sustainable desalination. Considering its thermal management and cost-effectiveness, the system presents a transformative solution for sustainable freshwater production in regions with abundant solar resources.

Solutions and case studies for thermally driven reactive transport and porosity evolution in geothermal systems (reactive Lauwerier problem)

Abstract. Subsurface non-isothermal fluid injection is a ubiquitous scenario in energy and water resource applications, which can lead to geochemical disequilibrium and thermally driven solubility changes and reactions. Depending on the nature of the solubility of a mineral, the thermal change can lead to either mineral dissolution or precipitation (due to undersaturation or supersaturation conditions). Here, by considering this thermo-hydro-chemical (THC) scenario and by calculating the temperature-dependent solubility using a non-isothermal solution (the so-called Lauwerier solution), thermally driven reactive transport solutions are derived for a confined aquifer. The coupled solutions, hereafter termed the “reactive Lauwerier problem”, are developed for axisymmetric and Cartesian symmetries and additionally provide the porosity evolution in the aquifer. The solutions are then used to study two common cases: (I) hot CO2-rich water injection into a carbonate aquifer and (II) hot silica-rich water injection into a sandstone aquifer, leading to mineral dissolution and precipitation, respectively. We discuss the timescales of such fluid–rock interactions and the changes in hydraulic system properties. The solutions and findings contribute to the understanding and management of subsurface energy and water resources, such as aquifer thermal energy storage, aquifer storage and recovery and reinjection of used geothermal water. The solutions are also useful for developing and benchmarking complex coupled numerical codes.

Study on Phase Change Materials’ Heat Transfer Characteristics of Medium Temperature Solar Energy Collection System

Within the next five years, renewable energy is expected to account for approximately 80% of the new global power generation capacity, with solar power contributing to more than half of this growth. However, the intermittent nature of solar energy remains a significant challenge to fully realizing its potential. Thus, efficient energy storage is crucial for optimizing the effectiveness and dependability of renewable energy. Phase-change materials (PCMs) can play an important role in solar energy storage due to their low cost and high volumetric energy storage density. The low thermal conductivity of PCMs restricts their use for energy storage, despite their immense potential. Hence, the primary goal of this study is to experimentally investigate the energy storage capacity of two blended phase-change materials (paraffin and barium hydroxide octahydrate) through integration with a medium-temperature solar heat collection system. The experimental findings reveal that the blended PCMs possess the highest cumulative charge fraction (0.59), energy capacity, and low energy loss compared to each PCM alone. Furthermore, the phase change storage tank achieves higher heat storage (27%) and exergy storage efficiency (18%) compared to the stored tank water without any PCMs. The blended PCMs enhanced their performance, exhibiting improved interaction and excellent thermal storage properties across a range of temperatures, offering an opportunity for the design of an energy-efficient, low-cost storage system.

Study on the heat transfer performance of coaxial casing heat exchanger for medium and deep geothermal energy in cold regions

To accurately assess the heat transfer performance of a medium-depth coaxial casing heat exchanger, this study introduced the concepts of the annual stabilized mining stage and the effective thermal influence distance for each layer of non-homogeneous thermal storage. The study area was stratified into six layers based on the geothermal temperature gradient fitting results. The findings revealed that the maximum injected circulating fluid temperature for the mid-depth coaxial casing geothermal system was 37 °C, with a maximum mass flow rate of 16.67 kg/s. When the injected circulating fluid temperature increased from 2 °C to 25 °C, the duration of the annual stabilized exploitation stage extended from 23 to 26 years. Similarly, increasing the injected circulating fluid mass flow rate from 2.78 kg/s to 16.67 kg/s prolonged the maintenance period in the annual stable mining stage from 22 to 28 years. The study further indicated that the effective thermal influence distance for each layer of thermal storage was significantly impacted by varying injection circulating fluid temperatures. These results offered theoretical insights into the heat transfer performance of medium-depth coaxial casing geothermal systems under both short- and long-term operational conditions.

Numerical Investigation of Solar Collector Performance with Encapsulated PCM: A Transient, 3D Approach

This study presents a comprehensive numerical investigation into the thermal performance of solar collectors integrated with encapsulated phase change materials (PCMs) using a transient three-dimensional (3D) approach. The performance of two distinct PCMs—paraffin wax and RT60—was evaluated under varying operational conditions, including seasonal variations, inlet pipe velocities, and inlet temperatures. The results indicate that paraffin wax exhibits a higher peak temperature, reaching approximately 360 K, compared to RT60’s peak of 345 K, making paraffin wax more effective for consistent thermal energy storage. Paraffin wax also maintained higher fluid fractions, with a maximum of 0.9 in summer, indicating superior heat absorption and retention capabilities. In contrast, RT60 demonstrated a quicker phase transition, fully liquefying at a lower fluid fraction, which is advantageous for rapid heat release. Seasonal variations significantly impacted system efficiency, with the highest efficiency observed in June at 365 K and the lowest in December at 340 K. The study also found that lower inlet velocities (e.g., 0.25 L/s) significantly improved heat retention, resulting in higher outlet temperatures, while increasing the inlet temperature from 290 K to 310 K led to a marked increase in outlet temperatures throughout the day. These findings underscore the importance of optimizing PCM selection, inlet velocity, and temperature in enhancing the performance of solar thermal systems, offering quantitative insights that contribute to the development of more efficient and reliable renewable energy solutions.

Molecular simulations of increased thermal energy storage in metal–organic heat carriers with R1234ze(E)/R32 mixtures combined with IRMOF-1

Metal-organic heat carrier (MOHC) nanofluids offer a promising solution to enhance the efficiency of Organic Rankine Cycle systems. In this study, we developed a computational model to assess the thermal energy storage capacity of MOHC nanofluids using a base fluid mixture of R1234ze(E) and R32 refrigerants. Through Grand Canonical Monte Carlo and molecular dynamics simulations, we examined the adsorption characteristics, desorption heat, and thermodynamic properties of MOHCs. Our findings reveal that R32 molecules are preferentially adsorbed in IRMOF-1 compared to R1234ze(E), with adsorption selectivity of R32 over R1234ze(E) increasing under higher adsorption pressures. When the temperature during the endothermic process surpasses the phase transition point of the base fluid, the latent heat of phase transition can be fully exploited to enhance energy storage. Moreover, the inclusion of IRMOF-1 nanoparticles significantly improves the energy storage properties of both R32 and R1234ze(E), as well as their mixtures. The energy storage enhancement provided by IRMOF-1 is particularly pronounced under high working pressures and low temperature differences. These insights offer valuable guidance for selecting appropriate base fluids in MOHC systems, thereby optimizing the utilization of low-grade energy sources.

Multifunctional 3D-Printed Thermoplastic Polyurethane (TPU)/Multiwalled Carbon Nanotube (MWCNT) Nanocomposites for Thermal Management Applications

In this work, multiwalled carbon nanotubes (MWCNTs) were melt-compounded into a novel thermal energy storage system consisting of a microencapsulated paraffin, with a melting temperature of 6 °C (M6D), dispersed within a flexible thermoplastic polyurethane (TPU) matrix. The resulting materials were then processed via Fused Filament Fabrication (FFF), and their thermo-mechanical properties were comprehensively evaluated. After an optimization of the processing parameters, good adhesion between the polymeric layers was obtained. Field-Emission Scanning Electron Microscopy (FESEM) images of the 3D-printed samples highlighted a uniform distribution of the microcapsules within the polymer matrix, without an evident MWCNT agglomeration. The thermal energy storage/release capability provided by the paraffin microcapsules, evaluated through Differential Scanning Calorimetry (DSC), was slightly lowered by the FFF process but remained at an acceptable level (i.e., >80% with respect to the neat M6D capsules). The novelty of this work lies in the successful integration of MWCNTs and PCMs into a TPU matrix, followed by 3D printing via FFF technology. This approach combines the high thermal conductivity of MWCNTs with the thermal energy storage capabilities of PCMs, creating a multifunctional nanocomposite material with unique thermal management properties.

Integrating MXene Film With Recyclable Polyethylene Glycol-co-Polyphosphazene Copolymer as Solid-Solid Phase Change Material for Versatile Applications.

Phase-change materials (PCMs) stand a pivotal advancement in thermal energy storage and management due to their reversible phase transitions to store and release an abundance of heat energy. However, conventional solid-liquid PCMs suffer from fluidity and leakage in their molten state, limiting their applications at advanced levels. Herein, a novel Zn2+-crosslinked polyethylene glycol-co-polyphosphazene copolymer (PCEPN-Zn) as a solid-solid PCM through dynamic metal-ligand coordination is first designed and synthesized. The as-synthesized PCEPN-Zn is further integrated with an MXene film to construct a double-layered phase-change composite through layer-by layer adhesion. Owing to the introduction of MXene film with low emissivity, good light absorptivity, and nonflammability, the resultant phase-change composite not only presents a high latent-heat capacity, good thermal stability, high thermal reliability, and excellent shape stability, but also exhibits a superior self-healing ability, good recyclability, high adhesivity, and good flame-retardant performance. It can be easily adhered to on most objects for various application scenarios. With a combination of the excellent functions derived from PCEPN-Zn and MXene film, the developed phase-change composite exhibits broad prospects for versatile applications in the thermal management of CPUs and Li-ion batteries, thermal infrared stealth of high-temperature objects, heat therapy in the clinic, and fire-safety for various scenarios.

Fins-nanoparticle combination for phase change material enhancement in a triplex tube heat exchanger: A numerical approach to thermal sustainability

Many phase change materials exhibit low thermal conductivity, leading to incomplete melting and solidification processes. To address this issue, researchers have numerically explored the integration of alumina nanoparticles (Al2O3) with paraffin (RT82), a phase change material with a solidification temperature of 65 °C, in a triplex-tube heat exchanger. The phase change material model with internal longitudinal fins employed the both-sides freezing technique and was conducted using Ansys Fluent software, employing the enthalpy-porosity method within a finite-volume framework to model the phase change material behavior during both melting and solidification phases. This methodology aims to significantly improve the thermal performance of thermal energy storage systems by enhancing heat transfer efficiency within the phase change material (PCM), thereby ensuring more effective utilization of stored thermal energy. The numerical findings show that the pure PCM completely solidified in 780 min. By dispersing 1 %, 4 %, 7 %, and 10 % of Al2O3 in the PCM, thermal conductivity improved by 3 %, 12.5 %, 22.5 %, and 32.5 %, respectively. Additionally, the inclusion of nano-PCM reduced the solidification time. This research also compares the overall energy release in two different situations: PCM with and without nanoparticles. The computer-generated simulation results closely correlated with the practical experimentation results.

A novel building thermal energy storage PCM: lauric acid-palmitic acid- tetradecyl alcohol/vitrified beads

A novel building thermal energy storage PCM: lauric acid-palmitic acid- tetradecyl alcohol/vitrified beads

Short-cycle borehole thermal energy storage: Impact of thermal cycle duration on overall performance

Borehole thermal energy storage arrays are a common form of seasonal underground energy storage which relies on the thermal mass of subsurface rock or sediment to store hot or cold thermal energy. However in practice, typical seasonal operation seldom leads to cyclic energy recovery factors greater than 50%–60% due to significant thermal losses during prolonged periods between consecutive charges. In this paper, the impact of short cycle operation (down to a few days) on energy recovery and overall performance is investigated. Analytical and numerical models are used to estimate energy recovery as a function of cycle length for a typical array and for two distinct charging and discharging scenarios (constant temperature or thermal charge load), which is novel and has not been done before. The results show that shorter cycle duration yields increased recovery factors and storage capacity, which is ascribed to a greater rate of charge to rate of thermal loss ratio. In particular, short-cycle operation at the scale of days unlocks recovery factors in excess of 85 %. The results, supported by a numerical subsurface analysis of the temperature distribution, also show that the recovery efficiency increases with time as losses approach, but never fully reach, a steady-state.

Fabrication and evaluation of eicosane/poly(styrene-co-butylacrylate) microencapsulated phase change materials through ultrasonicated mini-emulsion technique

This study reports the synthesis and characterization of Microencapsulated Phase Change Materials for the pertinence of latent heat storage. Eicosane/ Poly(Styrene-co-Butylacrylate) [ESE/Poly(Sty-co-BA)] microcapsules were synthesized by encapsulating n-Eicosane (n-ESE) with a shell made of Poly(Styrene-co-Butylacrylate) [Poly(Sty-co-BA)] via employing ultrasonic-assistant mini-emulsion polymerization technique. The properties of the synthesized ESE/Poly(Sty-co-BA) microcapsules were analyzed by Differential scanning calorimetry (DSC),Thermogravimetric analysis (TGA), Transmission electron microscopy (TEM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR)spectroscopy. DSC results indicated that ESE/Poly(Sty-co-BA) exhibited a melting and crystallizing temperature of 35.72 and 32.27 °C, and latent heat of 220.53 and 218.57 J/g, respectively. The ESE/Poly(Sty-co-BA) microcapsules prepared in this work unveiled an effective encapsulation ratio (91.93 %), encapsulation efficiency (91.59 %) and displayed excellent thermal storage capacity (99.63 %). Various models such as Kissinger’s, Augis and Bennett’s approximation, Mahadevan and Arvami theory were employed to determine the effective activation energy value alongside the crystal growth of n-ESE and ESE/Poly(Sty-co-BA). TGA analysis revealed that ESE/Poly(Sty-co-BA) demonstrated three step degradation and exhibited good thermal stability. The findings of the work manifested a novel technique for producing the phase transition materials for TES that can be applied to a wide range of instances, including smart textiles, thermo-sensitized functional coatings, passive space cooling or heating.

Numerical and Design Study of Beehive in Building for Thermal Storage During Hours of Absence of Solar Radiation

This study investigates the numerical and design performance of Phase Change Materials (PCMs) embedded in a beehive structure within building envelopes for thermal energy storage during periods without solar radiation. Using Computational Fluid Dynamics (CFD) simulations in ANSYS Fluent, the study examines how the PCM system stabilizes indoor temperatures and improves energy efficiency. The research focuses on three months: January, November, and December, in Baghdad, Iraq, where diurnal solar radiation variations and temperature patterns are prevalent. Results reveal that the PCM-enhanced structure effectively absorbs heat during peak solar radiation hours, with solar radiation peaking at 574 W/m² in January, 596 W/m² in November, and 557 W/m² in December. The heat storage and release ability of the PCM keep up the interior temperature at its maximum of 309.96K and 310.04 K in Jan and Nov and 309.23 K in Dec with slightly less drop in the evening. The heat transfer coefficient was maximum in November 11.37 W/m²·K, while the PCM mass fractions showed significant phase change and the maximum value 0.425 in November. The thermal efficiency of the system was highest in November at 68.23% and also fluctuates slightly in the other remaining months. This study suggests that PCM systems, especially with the beehive structure, additionally improve isothermal stability and energy densities of the buildings in the changing climate, which is cost-effective and a more environmentally friendly strategy for regulating heating and cooling requirements.

Second Generation Zwitterionic Aza‐Diarylethene: Photoreversible CN Bond Formation, Three‐State Photoswitching, Thermal Energy Release, and Facile Photoinitiation of Polymerization

Diarylethenes are a well‐studied and optimized class of photoswitches with a wide range of applications, including data storage, smart materials, or photocontrolled catalysis and biological processes. Most recently, aza‐diarylethenes have been developed in which carbon‐carbon bond connections are replaced by carbon‐nitrogen connections. This structural elaboration opens an entire new structure and property space expanding versatility and applicability of diarylethenes. In this work, we present the second generation of zwitterionic aza‐diarylethenes, which finally allows for fully reversible photoswitching and precise control over all three switching states. High‐yielding photoswitching between the neutral open form and a zwitterionic Z isomer is achieved with two different wavelengths of light. The third zwitterionic E isomeric state can be reached up to 87% upon irradiation with a third wavelength. Its high energy content of >10 kcal/mol can be released thermally by deliberate solvent change as trigger mechanism, rendering aza‐diarylethenes into interesting candidates for molecular solar thermal energy storage (MOST) applications. The third state further serves as locking state, allowing to toggle light‐responsiveness reversibly between thermally labile and thermally stable switching. Further, irradiation of the zwitterionic states leads to highly efficient photopolymerization of methyl acrylate (MA), directly harnessing the unleashed chemical reactivity of aza‐diarylethene in materials applications.

Second Generation Zwitterionic Aza-Diarylethene: Photoreversible CN Bond Formation, Three-State Photoswitching, Thermal Energy Release, and Facile Photoinitiation of Polymerization.

Diarylethenes are a well-studied and optimized class of photoswitches with a wide range of applications, including data storage, smart materials, or photocontrolled catalysis and biological processes. Most recently, aza-diarylethenes have been developed in which carbon-carbon bond connections are replaced by carbon-nitrogen connections. This structural elaboration opens an entire new structure and property space expanding versatility and applicability of diarylethenes. In this work, we present the second generation of zwitterionic aza-diarylethenes, which finally allows for fully reversible photoswitching and precise control over all three switching states. High-yielding photoswitching between the neutral open form and a zwitterionicZisomer is achieved with two different wavelengths of light. The third zwitterionicEisomeric state can be reached up to 87% upon irradiation with a third wavelength. Its high energy content of >10 kcal/mol can be released thermally by deliberate solvent change as trigger mechanism, rendering aza-diarylethenes into interesting candidates for molecular solar thermal energystorage (MOST) applications. The third state further serves as locking state, allowing to toggle light-responsiveness reversibly between thermally labile and thermally stable switching. Further, irradiation of the zwitterionic states leads to highly efficient photopolymerization of methyl acrylate (MA),directly harnessing the unleashed chemical reactivity of aza-diarylethene in materials applications.

Preparation and thermal stability research of oxalic acid dihydrate-glutaric acid/PAMPS phase change gel for solar thermal energy utilization

Thermal energy storage technology based on phase change materials (PCMs) can address the temporal and spatial mismatches in solar thermal energy conversion, thereby enhancing solar energy utilization efficiency. However, the liquid flow and poor thermal reliability of PCMs limit their large-scale application in solar thermal systems. In this study, we employ a simple “one-pot method” to prepare a form-stable and thermally reliable oxalic acid dihydrate-glutaric acid/poly 2-Acrylamido-2-methyl-1-propanesulfonic acid (OAD-GA/PAMPS) phase change gel. The OAD-GA/PAMPS phase change gel melts at 64.5 °C with a phase change enthalpy of 193.6 kJ/kg, the tensile strength is 7.707 MPa, and the compressive strength is 16.940 MPa. By incorporating 5 wt% BN particles, the thermal conductivity of OAD-GA/PAMPS phase change gel reaches 0.63 W/(m·K). After 200 heating-cooling cycles, the phase change temperature of the OAD-GA/PAMPS phase change gel remains nearly unchanged, and the phase change enthalpy decreases by only 5.7 %. The photo-thermal conversion efficiency of the OAD-GA/PAMPS phase change gel is 82.7 %. The high thermal reliability and photo-thermal conversion efficiency of the OAD-GA/PAMPS phase change gel makes it suitable for solar thermal energy storage applications.