Heat Storage Capacity Research Articles

Numerical study of an energy storage unit based on zeolite-water adsorption for mobilized thermal energy storage

Mobile energy storage heating trucks present a promising solution to address current challenges associated with low energy utilization and reliance on a singular heat supply method. This technology seamlessly integrates waste heat recovery and thermal energy utilization, offering potential advantages such as streamlining construction cycles and providing timely energy supply in scenarios with diverse energy demands. To enhance the energy delivery efficiency of mobile heating, this paper employs computational fluid dynamics (CFD) simulation to thoroughly examine the heat accumulator at the core of an adsorption-based mobilized thermal energy storage. Furthermore, the paper conducts simulations and analyses of heat and mass transfer within a zeolite-water accumulator, closely scrutinizing variations in temperature, vapor content, and water content within the zeolite field. The results indicate that, during the heat storage process in the 3 m/s to 5 m/s system, the zeolite sensible heat storage capacity increases by 6.48 %, accompanied by a reduction in latent heat. Specifically, when the inlet steam velocity is 5 m/s compared to 3 m/s, the equilibrium heat transfer time shortens by 24.6 %. Furthermore, for an inlet steam temperature ranging from 180 °C to 220 °C, the average temperature can be elevated by 28.8 °C, resulting in a 10.6 % increase in sensible heat storage capacity. However, the heat storage time experiences a 3.4 % increase. In the exothermic process, with an inlet air velocity of 5 m/s compared to 3 m/s, there is a 22.2 % reduction in latent heat exothermic and a 16.7 % reduction in exothermic time. The inlet air temperature during the exothermic process is 8.9 °C lower than the final temperature of 20 °C, leading to a 3.2 % increase in exothermic quantity and a 20 % improvement in exothermic efficiency.

Integrated demand response method for heating multiple rooms based on fuzzy logic considering dynamic price

We consider an educational building heated by a combination of district heating (DH) and a local air source heat pump. We have developed an integrated demand response method for multiple rooms, consisting of an optimization layer and a control layer, to maintain thermal comfort and save energy and costs. For the optimization layer, we apply fuzzy logic to adjust indoor temperature setpoints to respond to dynamic heat prices and propose an optimal heat supply method to find optimal heat supply schemes. For the control layer, a multi-objective model predictive control (MPC) has been developed to manage indoor thermal conditions across multiple rooms. To test and verify the integrated demand response method, we build a multi-room simulation model using the CARNOT Toolbox. The results show that adopting different indoor temperature setpoints during working and nonworking hours, combined with the MPC method, has an energy-saving potential of 9.1 % compared to maintaining a constant indoor temperature using DH alone. Adjusting temperature setpoints using fuzzy logic utilizes the building's heat storage capacity to increase energy flexibility, reaching 16.0 % savings in energy and reducing 12.6 % heating costs.

Effects of longitudinal ventilation and GHEs on geothermal energy extraction and HRC in high geothermal tunnels

With the excavation of deep tunnels, the problem of high geothermal heat is becoming more and more prominent. However, high geothermal heat can be utilized as a renewable energy source. In order to effectively reduce thermal damage and utilize geothermal energy, it is necessary to study the effects of longitudinal ventilation and ground heat exchanges (GHEs) on the heat-regulating circle of the surrounding rock. In this study, an experimental platform was designed and constructed in a laboratory to test different geothermal heat exchanger flow rates and ventilation air velocities and to monitor the heat extraction from the geothermal heat exchanger, the ventilation heat extraction, and the temperature field of the surrounding rock. The experimental results show that when the temperature field tends to be stabilized, the flow rate and ventilation velocity of the GHEs are closely related to the temperature distribution of the surrounding rock. The initial heat storage and heat replenishment capacity of the enclosing rock have a great influence on the heat extraction efficiency. Ventilation has a great influence on the heat extraction efficiency of GHEs, and the optimal wind speed range is 1.5∼2 m/s considering the cooling and heat extraction efficiency. When the wind speed is less than 1.5 m/s, the heat extraction efficiency of GHEs can be improved, and the total heat transfer can be increased. When the wind speed is greater than 1.5 m/s, the situation is reversed. The thermal entropy theory for circular tunnels is not fully applicable to arched tunnels containing GHEs.

Development of phase change eco-composite materials from eggshell waste

ABSTRACT The consumption of eggshell powder (ES) as an affluent source of calcium carbonate (CaCO3) can efficiently solve both ecological and financial interest. The use of eggshell waste in eco-composite materials (ECPCMs) is an attempt to reduce waste's negative effects. Eco-composite powders of polyethylene glycol (PEG) and calcium carbonate (CaCO3) were obtained by mechanical grinding. Compression molding was used to produce plates from the ground powders. FTIR spectroscopy and X-ray diffraction analysis showed that the ECPCMs were physically combined and the crystallinity of the two components was affected. According to TGA, the thermal stability of ECPCMs was improved, thanks to the use of eggshell waste powder. On the other hand, the results of the DSC showed that ECPCM with the addition of 90 wt% of PEG in the mixture provides excellent thermal stability and high energy storage density. In light of its high latent heat storage capacity of 156.1 J/g as well as its ability to prevent PEG exudation. Significant enhancement in melting-solidification time shows an improvement in Thermal Energy Storage (TES) response time by adding ES to the PCM. The obtained results indicate a good potential for industrially applied ECPCMs.

Review of organic and inorganic waste-based phase change composites in latent thermal energy storage: Thermal properties and applications

Systematization and analysis of standalone waste materials that can serve as phase change materials (PCMs), and composites consisting of commercially available PCMs combined with organic and inorganic waste materials is presented. Within the conducted review research, obtained thermal properties of so far investigated waste-derived PCMs were presented, assessing, among other, their latent heat storage capacity, thermal conductivity, and thermal and cyclic stability. Refined coconut oil and Allanblackia oil exhibited exceptional thermal and cyclic stability along with high values of latent heat, amounting 105 kJ kg−1 and 81 kJ kg−1, respectively. In some cases incorporation of waste materials significantly improved thermal properties, e.g. the addition of carbonized waste tire rubber to dodecyl alcohol increased its thermal conductivity to 0.431 W m−1K−1, representing an increase by a factor of 2.3. This enhancement led to a 17.2 % reduction in heating times and a 20 % reduction in cooling times compared to using pure PCM. Besides providing extensive data on thermophysical properties of phase change composites, the study provides a comprehensive overview of their applications, economic feasibility, and environmental implications. This extensive review shows the potential of waste-derived PCMs to contribute to a circular economy by repurposing waste materials for sustainable energy solutions and reducing environmental impacts. The findings indicate that while valorising wastes or by-products as latent thermal energy storage materials is feasible, more research efforts are required towards potential commercialization.

Highly dispersed Ag quantum dots anchored on palmitic acid/ graphitic carbon nitride composite phase change materials for enhanced photo-thermal storage

Phase change materials (PCM) have attracted much attention in the field of thermal energy storage because of exceptional heat storage capacity, stable operating temperature, and recyclability. However, organic phase change materials, represented by palmitic acid (PA), are limited by inherent leakage problem, unsatisfactory thermal responsiveness and inefficient photo-thermal storage capacity, which severely hamper the development of PCMs technology. As a means of addressing these challenges, we developed one novel support material with 2D/0D structure for palmitic acid via thermal polymerization, specifically, in which highly dispersed Ag quantum dots (Ag QDs) was firmly anchored on graphitic carbon nitride (g-C3N4). PA was further infiltrated into the layered structure of nanoporous g-C3N4/Ag QDs to successfully synthesize novel shape-stabilized PA/g-C3N4/Ag QDs composite phase change materials (CPCM). On the one hand, benefiting from the tightly stacked porous structure of g-C3N4/Ag QDs, PA is effectively encapsulated to avoid leakage problem during the solid-liquid transition with a superior adsorption capacity up to 65 %. On the other hand, the combination of g-C3N4 and Ag QDs in PA/g-C3N4/Ag QDs CPCM demonstrated a synergistic effect resulting in faster heat transfer capability and more efficient solar energy capture capability compared to pure PA, which is capable of dual utilization of heat and solar energy. The newly developed PA/g-C3N4/Ag QDs CPCM features a high melting latent heat and an appropriate phase change temperature, which are 128.35 J/g and 61.92 °C, respectively. The corresponding solidification enthalpy and temperature are 121.70 J/g and 60.02 °C. The photo-thermal conversion efficiency of the material is improved to 78.6 %, facilitating a rapid capture and storage of solar energy. Furthermore, through the optimization of the preparation process, Ag QDs are densely anchored on the surface of g-C3N4, which retains the excellent properties of metallic silver while eliminates the metal agglomeration phenomenon after repeated utilization of CPCMs. PA/g-C3N4/Ag QDs CPCM is proved to be extremely recyclable and thermally stable after massive thermal cycles. This innovative and operational encapsulation modified method significantly optimizes the practicality of phase change materials. The obtained shape-stabilized PA/g-C3N4/Ag QDs CPCM is more versatile, and its unique comprehensive properties can provide high-quality materials for photo-thermal storage systems.

Thermal management of photovoltaic panels using phase change materials and hierarchical ZnO/expanded graphite nanofillers

Although PV panels are widely used to generate electricity from solar energy, their most important defect is the reduction of electrical efficiency with the increase of their temperature. The aims of this research is thermal management of a PV panel using phase change materials (PCM) and hierarchical ZnO/expanded graphite (EG) nanofillers to increase its production capacity. Two types of ZnO nanoparticles (rod- and flower-shaped) are synthesized using sonochemical method, and doped on EG particles to improve the thermal conductivity of the PCMs. A new bio-PCM consisting of oleic acid and beeswax is prepared and its performance is compared with paraffin and beeswax. The effect of PCM thickness (h=10-30 mm) and weight fraction of nanoparticles (ϕ = 1–5%wt) on temperature (Ts,ave), open-circuit voltage, current, and electrical performance of the PV panel is investigated. Results show that Ts,ave for pure paraffin, beeswax and bio-PCM has decreased from 64.23oC (without cooling) to 54.11oC, 57.15oC and 51.41oC, respectively. For all PCMs, adding flower-shaped ZnO/EG particles shows better results compared to rod-shaped one. The composite of bio-PCM with ZnO/EG has a higher positive effect on Ts,ave reduction and in generating voltage compared to paraffin and beeswax. PCMs composed of ZnO/EG particles with ϕ=5 wt% exhibited the minimum values of electrical efficiency. In addition, Ts,ave decreased intensively from h=10 mm to h=25 mm, but no significant difference is observed between h=25 mm and h=30 mm. The bio-PCM has proper melting point and heat storage capacity to cool down PV panel, which led to high power production. The maximum electrical efficiency is achieved using composite of bio-PCM and flower-shaped ZnO/EG particles at h=25 mm, which is circa 12.88 %.

Optimal design and thermal performance evaluation of phase change material filling position for solar air collectors

Unreasonable filling positions of phase-change materials (PCMs) significantly reduce the heat storage capacity, heat release time, output temperature difference, heat collection efficiency, and heat peak migration capacity of PCM-based solar–air collectors in building heating systems, thereby affecting the comprehensive heating requirements of building users. To solve this problem and obtain the optimal filling position of the PCM, four PCM filling schemes were designed in this experiment: Type I was a solar air collector with the PCM filled in the upper portion, Type II was filled in the middle portion, Type III was filled on both sides, and Type IV was filled in the bottom portion. Subsequently, the four models were compared. A comparative analysis of the thermal performance evaluation index showed that compared with the other three types of collectors, the heat storage layer of Type I stored 1.505 × 106J of heat in 1.42h, indicating that the Type I solar–air collector had the best heat storage speed rate. When the solar energy supply was terminated, the continuous heat release time of the Type I collector was 13.92h, and the ratio of the heat release time to the non-solar time was 96 %. The Type I collector had the lowest output temperature and the slightest temperature fluctuation, which could increase indoor thermal comfort. The average daily heat collection efficiency of the Type I collector was the lowest, at only 38.11 %, indicating that the Type I collector has the strongest “peak cutting and valley filling” ability, which allows for transferring more heat for nighttime release. Therefore, filling the upper portion is the optimal filling scheme that can provide technical benefits for the application and development of collectors.

Effects of firebricks for industrial process heat on the cost of matching all-sector energy demand with 100% wind-water-solar supply in 149 countries.

Refractory bricks are bricks that can withstand high temperatures without damage to their structures. They have been used to insulate kilns, furnaces, and other hot enclosures for thousands of years. Firebricks are refractory bricks that can, with one composition, store heat, and with another, insulate the firebricks that store the heat. Because firebricks are made from common materials, the cost per kilowatt-hour-thermal of a firebrick storage system is less than one-tenth the cost per kilowatt-hour-electricity of a battery system. It has thus been hypothesized that using excess renewable electricity to produce and store industrial process heat in firebricks can provide a low-cost source of continuous heat for industry. Here, it is hypothesized further that, upon a transition to 100% clean, renewable energy worldwide, using firebricks to store industrial process heat can reduce electricity generator, electricity storage, and low-temperature heat storage needs, thereby reducing overall energy cost. Both hypotheses are tested across 149 countries combined into 29 world regions. Results suggest, relative to a base case with no firebricks, using firebricks may reduce, among all 149 countries, 2050 battery capacity by ∼14.5%, annual hydrogen production for grid electricity by ∼31%, underground low-temperature heat storage capacity by ∼27.3%; onshore wind nameplate capacity by ∼1.2%, land needs by ∼0.4%, and overall annual energy cost by ∼1.8%. In sum, the use of firebricks for storing industrial process heat appears to be a remarkable tool in reducing the cost of transitioning to clean, renewable energy across all energy sectors.

Phase Change Materials for Thermal Energy Storage: A Concise Review

Thermal energy and its storage systems play an extensive role in day-to-day life. They store renewable energy and are capable of recovering generated heat from different systems. Storage of thermal energy can be classified into three types: sensible, latent and sorption heat storages. Thermal heat storages use different types of materials based on their capacity of heat storage, stability of duration and thermal conductivity. Various phase change materials (PCMs) that are suitable for thermal storage are reported. Low conversion ability limits their effectiveness. We reviewed some of the traditional materials synthesized recently that are used for thermal energy storage (TES). Recently developed TES materials exhibit high thermal conductivity, reduced super cooling and multiple phase change temperatures. Nano-enhanced PCMs produced an increase in thermal conductivity up to 32% with a reduction in latent heat by 32%. At this juncture, MXenes with high performance and extraordinary properties (thermal, mechanical, etc.) are of special significance. MXenes displayed an increased thermal conductivity up to 16% and 94% efficiency. In view of their structure and adaptability to be used in thermal storage systems, an attempt was made to review their role also in thermal storage applications. It is observed that MXenes highly impact storage and efficiency. Apart from MXenes, various types of PCMs along with their thermal characteristics are presented.

Preparation and thermal properties of latent functional thermal fluid based on size-controllable phase change nanocapsules

Size-controllable 1-octadecanol@polystyrene phase change nanocapsules (NEPCMs) were prepared using the miniemulsion polymerization and dispersed in deionized water containing multi-walled carbon nanotubes to prepare a latent functional thermal fluid (LFTF). The results demonstrate that the NEPCMs exhibit a typical core-shell structure. The average particle size (55.28–143.8 nm) of the NEPCMs can be regulated by controlling the content of compound emulsifiers. The optimal phase change enthalpy has an excellent heat storage capacity of about 222.7 J/g, the encapsulation efficiency is up to 80.63 %, and the average particle size is about 88.3 nm. The heating/cooling cycles results show that NEPCMs have excellent cycle stability. LFTF containing 10 wt% NEPCMs was considered the optimal choice for its excellent photothermal conversion efficiency (up to 64.91 %), excellent dispersion stability (zeta potential 39.17 mV) and thermal storage capacity (peak specific heat capacity 5.72 J g−1 K−1). Under the influence of solar radiation, the temperature rise curve of LFTF exhibited a rapid initial warming rate followed by a plateau period of approximately 76 min upon reaching the melting point of the NEPCMs, whose photothermal conversion efficiency is roughly 2.18 times that of water. The experimental findings demonstrate the potential application of LFTF based on NEPCMs in the solar thermal industry.

Viability of hybrid and alkali-activated slag materials for thermal energy storage: Analysis of the evolution of mechanical and thermal properties

Technological progress is needed to develop renewable energies. Improvements should be especially focused on the energy storage element to help correct the mismatch between energy supply and demand. In concentrated solar power (CSP) plants, ordinary concrete made of Portland cement (PC) has been proven to be a good thermal energy storage (TES) medium. However, the substantial environmental impact of PC manufacturing makes it necessary to develop new materials. Thus, in this work, alternative alkali-activated mortars (AAM) and hybrid materials (HM) have been developed using blast furnace slag to replace PC. This has been done in order to study their stability at high temperature (up to 500 °C) and their viability to operate as TES, undergoing thermal cycles between 200 °C and 400 °C, as they would in CSP technologies. Studying the mechanical and thermal properties after the thermal treatments has revealed that the alternative materials offer improved mechanical properties as well as very good thermal conductivity and storage capacity values. In particular, the best results in terms of mechanical properties were achieved by the AAM system, where the compressive strength value is increased with respect to the reference PC sample by 195% after exposure to 500 °C and by almost 97% after 20 thermal cycles between 200 °C and 400 °C. Furthermore, in terms of thermal properties, the AAM system showed a 31% increase in thermal conductivity after thermal exposure compared to PC. In addition, both AAM and HM systems demonstrated substantial improvements in specific heat and thermal storage capacity, outperforming PC by up to 46% during CSP-like thermal cycles. These promising results open new doors to the study of these alternative materials, such as TES, as they are more suitable than PC from an operational point of view.

Quantifying the massive depletion of heat storage capacity of Lake Urmia

The catastrophic drying of Lake Urmia, once the world’s second-largest saline lake, has led to the degradation of its vital ecosystem services, including microclimate regulation. This study investigates the variation of Lake Urmia’s heat storage, a key driver of its microclimate regulation function, from 2001 to 2020. We analyze Lake Urmia’s monthly energy and water balances considering the spatial variation of hydro-meteorological variables over the lake and explicitly accounting for lake salinity. We found that the heat storage capacity of Lake Urmia has exponentially depleted with its shrinkage. The NRMSE values of the proposed equations for Lake Urmia’s maximum and minimum heat storage were 0.24 and 0.20, respectively. As a potential consequence, the maximum air temperature over the lake has increased while the minimum temperature has remained constant. The reviled role of Lake Urmia’s heat storage capacity in hindering the maximum annual temperature of the area can provide valuable insights into the role of lake conservation in mitigating climate warming.

Critical analysis of enhanced photovoltaic thermal systems: a comparative experimental study of PCM, TEG, and nanofluid applications

Phase change materials (PCM), thermoelectric generators (TEG), and nanofluids are popular methods investigated for improving conventional photovoltaic thermal (PVT) systems. These methods are particularly used in warm climates where high temperatures negatively impact photovoltaic (PV) power output and energy efficiency. This experimental study evaluated the effects of 32 °C melting point PCM and TEG integration on PVT units, as well as 42 °C melting point PCM and nanofluid incorporation on concentrated PVT (CPVT) units. Technical, exergetic, and economic performance were compared using a small-scale PVT module. Low-cost commercially available materials were used to construct all PVT units. Industrial metal waste was introduced to enhance the thermal conductivity of paraffin wax and salt hydrate PCMs. The results indicated that applying PCMs, porous media, and concentrator plates increased energy generation, potentially offsetting their higher initial cost and achieving an energy cost of approximately $0.135/kWh. However, TEG and nanofluid implementation remained uneconomical, leading to a 15–35 % increase in energy cost. The water-based CPVT unit, enhanced with paraffin wax and copper fins, demonstrated the best technical performance. This unit achieved electrical, thermal, and exergy efficiencies of approximately 15.5 %, 37.4 %, and 16.7 %, respectively, with more than a 20 % reduction in cell temperature. The study also revealed that severe structural changes caused by corrosion of metallic materials in hydrated PCMs could alter the melting point by more than 30 %. This change negatively impacts heat storage capacity. Conversely, incorporating metal chips in non-hydrated PCMs improved the time to reach the melting point state by 30–60 minutes.

Thermal storage investigation of a two-layered latent-sensible packed bed with PCM and rock spheres

To improve the thermal performance of concentrated solar power (CSP) plants, this study establishes a novel two-layered latent-sensible packed bed to extend the application scope. The major innovation lies in the combination of nitrate-encapsulated phase change material (PCM) capsules and rock spheres in a two-layered configuration, which enhances operational efficiency and minimizes heat transfer temperature differences. A transient concentric-dispersion model is used for numerical simulations to study temperature evolution, thermocline temperature configurations, liquid fraction, sensible and latent energy storage, exergy rate, and exergy efficiency. Four configurations were evaluated: two-layered packed beds with PCM and rock spheres (Cases A and B) and single-layered packed beds with either PCM or rock spheres (Cases C and D). The analysis focuses on the dynamic behavior of thermal energy exchange within the PCM and rock sphere layers, highlighting the advantages and limitations of each configuration. The results show that the two-layered configurations have lower thermocline degradation and higher thermal efficiency. Specifically, the heat storage capacity increased by 15.18 MJ in the two-layered configurations. The exergy input time extended to 350 min in Case A and 342 min in Case B, compared to 260 min in Case C. Results indicate that this hybrid approach significantly reduces thermocline degradation and enhances the overall energy storage capacity and efficiency. The proposed two-layered latent-sensible TES showed higher exergy efficiency and energy storage density than both single-layered LHTES and SHTES, demonstrating improved thermal storage performance.

Enhancing the performance of parabolic trough solar collectors: Cost-effective innovative designs for sustainable energy harvesting

This study aims to improve the performance and stability of parabolic trough solar collectors (PTSC), especially those with heat storage capacity. Three different receiver tube designs have been meticulously developed to achieve this goal. As a result of the research, the Black surface (BS) -PTSC and PTSC- Paraffin wax (PW) systems achieved 26.5% and 56.8% more thermal energy flow, respectively, compared to the conventional PTSC. In addition, while the average thermal efficiencies of the PTSC, BS-PTSC, and PTSC-PW systems were found to be 11.2%, 14.1%, and 16.9%, respectively, the average exergy efficiencies of the PTSC, BS-PTSC, and PTSC-PW were 1.4%, 1.9%, and 2.3%. Painting the black copper pipe and filling the receiver tube with paraffin wax PCM increased thermal and exergy efficiency. Besides, comparing the temperature differences based on the PTSC system, it was found that BS-PTSC and PTSC-PW systems have 12.3% and 16.4% higher tank temperatures, respectively. The findings of this research have demonstrated the potential of parabolic trough solar collectors equipped with heat storage. It has also increased the sustainability index in terms of sustainability and reduced CO2 emissions into the atmosphere. Furthermore, it has been shown that these simple and inexpensive designs, without significant modifications to the system, can achieve high thermal performance without unnecessary expensive components.

Optimization of fin arrangement in solar thermal storage devices and convolutional neural network modeling

Solar energy, a renewable and eco-friendly source, faces challenges in aligning energy production with storage durations. Phase change materials (PCMs) effectively tackle this issue, yet their poor thermal conductivity limits solar thermal storage device performance. Conventional solutions involve adding fins, but limited volume compromises overall heat storage capacity. Our study enhances device performance by rearranging fins while maintaining the same area. The H/R = 0.5 fin arrangement with equal spacing significantly improves heat storage, reducing total melting time by 54.31% with a higher entropy value. Further, arranging five fins, predominantly in the lower part, shortens PCM melting time without compromising upper material melting, enhancing device temperature uniformity. Utilizing computed data, we trained a Convolutional Neural Network (CNN) model, maintaining a maximum error within 5%, with an actual maximum error of only 1.56%. The efficacy of CNN in addressing prediction challenges is noteworthy, showcasing improved solar thermal storage device performance.

Heat transfer characteristics of topological latent heat storage systems based on optimization objectives

In order to improve the heat storage efficiency and shorten the heat storage/release time in latent heat storage (LHS) systems, topology optimization of heat transfer problems has been applied to LHS systems. The choice of the optimization objective determines the structure of the topology fins. In this paper, the topology generation process was analyzed using the mean temperature, the mean square deviation (MSD) of the mean temperature, and the multi-objective entropy depletion as the optimization objectives. In this way, a method for selecting the optimization objectives according to the design requirements was obtained. The multi-objective topological structure (Case 3) with uniform tree-shaped fins (Case 4) and gradient tree-shaped fins (Case 5) was applied to the LHS system, and the finite element analysis method was used to construct a mathematical model of the LHS system to comprehensively analyze the heat storage/release process. The results showed that the complete melting times for Case 3, Case 4, and Case 5 were 751 s, 1005 s, and 920 s, respectively. At 751 s, the average heat storage capacities for Case 3, Case 4, and Case 5 are 296.81 W, 216.94 W, and 238.92 W, respectively. Compared to Case 4, Case 3 decreased the complete melting time by 25.27 % and increased the average heat storage capacity by 36.82 %. At heat-releasing times of 500 s, 1000 s, 1500 s, and 2000 s, the maximum differences in liquid phase rates for the three models were 10.93 %, 11.97 %, 11.51 %, and 9.57 %, respectively. From the perspective of the field synergy, Case 3 showed a better heat transfer path and the optimal heat transfer effect considering the temperature, liquid phase rate, heat storage/release time, and heat storage/release capacity. In addition, the dimensionless criterion equation affecting the liquid phase rate was obtained by segmented fitting of the heat transfer process of the topology-optimized LHS system. The findings of the study can facilitate the promotion of topology-optimized structures for practical engineering applications in LHS systems.

Application of phase change material on solar-greenhouse back wall and its effects on indoor thermal environment and cucumber production in winter

The configuration of the solar greenhouse building wall and the thermal properties of the building materials directly impact wall insulation, heat storage characteristics, and, consequently, the thermal environment within the greenhouse. To address the variations in wall heat storage during the design and construction of solar greenhouses, this study aims to integrate solar energy effectively with phase change heat storage technology. Utilizing Energy Plus, the study simulates and verifies the heat storage and release performance of phase change materials on the greenhouse's back wall. The research also explores the warming effect of these materials on cucumber growth. The findings reveal that the composite phase change greenhouse (PC) wall exhibits an average heat release of 60.47 W/m2, maintaining an average temperature of 21.09 °C. In comparison, the heat release from the back wall of the traditional greenhouse (CK) increases by 14.03 W/m2, resulting in a temperature rise of 1.91 °C. Additionally, the substantial heat released by the phase change wall raises the average ground temperature to 18.26 °C through heat conduction, exceeding CK by 3.07 °C. Despite this, the maximum temperature remains below 25 °C, creating an ideal growth temperature for cucumbers and fostering vigorous growth. Furthermore, cucumber quality indicators, such as soluble sugar and VC content, significantly improve, demonstrating a 28.5 % increase in the single fruit weight of cucumbers. In conclusion, the composite phase change greenhouse outperforms the traditional greenhouse in heat storage capacity. The heat storage wall effectively enhances the overall thermal environment, insulation, and heat storage performance, ultimately leading to increased cucumber yield and quality.

Multi-index modeling and optimization of thermal performance of shell-and-tube heat accumulator based on MANOVA

The heat storage process of composite phase change heat accumulators is a complex phenomenon that requires multiple indicators to comprehensively reflect their thermal performance. Current research in this area is not comprehensive enough. There are also limitations in the evaluation indicators used. In this paper, the multi-index modeling, comprehensive evaluation and optimization methods of the heat storage performance of heat accumulators are studied. First, the basic vectors in the vector set of parameters reflecting the heat storage performance are selected as indicator functions, such as heat storage capacity, heat storage time and heat storage residue. Several independent variables are selected from the three aspects of the geometric parameters of the heat accumulator, the operating conditions, and the rib parameters as factors affecting the thermal storage performance. These multi-index dependent variables and independent variables constitute the multi-index form mathematical model group. Second, multivariate analysis of variance (MANOVA) was used to study the constituent terms of the multi-indicator formal mathematical model group. The MANOVA method was used to identify the effects of each independent variable on the thermal performance of the heat accumulators. The MANOVA method was also used to analyze the effect of the interaction between the factors on the multiple indicators of the thermal performance of the thermal storage. Multivariate nonlinear regression analysis was used to construct the multi-indicator mathematical model group reflecting the thermal storage performance based on MANOVA. Finally, the mathematical model group of multiple indicators is normalized and converted into a group of multiple indicator effectiveness functions, and the group of multiple indicator effectiveness functions is mathematically transformed to construct a comprehensive evaluation function that comprehensively responds to the thermal storage performance and seeks an optimization scheme for the thermal storage performance. The maximum value of its comprehensive index is 0.9988, and the corresponding optimal solutions of independent variables are X1 = 24 mm, X2 = 66.7 mm, X3 = 1600 mm, X4 = 0.2 m/s, X5 = 2 mm, X6 = 6.4 mm, and X7 = 46.8 mm.