Cold Energy Storage Research Articles

Regulating Cold Energy from the Universe by Bifunctional Phase Change Materials for Sustainable Cooling

AbstractHarvesting cold energy from the universe by radiative cooling (RC) is a promising zero‐carbon route for green cooling. However, low power density and spatiotemporal energy mismatch of RC are great challenges for realizing efficient space cooling. Herein, a facile strategy for regulating cold energy from the universe by bifunctional phase change materials (PCM) for sustainable cooling is proposed. A bifunctional phase‐change composite film (PCCF) by integrating RC coating with PCM for 24‐h cold energy harvesting, storage, and utilization is demonstrated. The bifunctional PCCF can harvest cold energy from the universe and regulate the redundant cold energy generated by nighttime RC to compensate for the cold shortage of daytime RC, realizing flexible regulation of all‐day RC and setting new records of cooling power up to 180 W m−2 with sub‐ambient temperature drop of 11.95 °C. The work offers a promising strategy for zero‐carbon sustainable cooling by maximizing RC with cold energy storage.

Analysis of conduction mode in cold energy storage using a tank filled with nanomaterial

The intensification of freezing rates through the incorporation of nano-sized powders and fins through a cold storage unit was examined. The Galerkin method with special meshing was utilized to solve equations, which were based on the supposition of conduction mode dominance. Additives of varying diameters (dp) and three different concentration levels (ϕ) were implemented. The findings are presented through ice front visualization, contour plots, and scalar curves. The computational code demonstrated high accuracy during the validation phase. The results reveal that as the dp increases, the solidification time initially drops by approximately 20 %, then subsequently increases by about 49.45 %. The optimal solidification time of 2951.17 s was achieved with medium-sized powders. Furthermore, an intensification in (ϕ) leads to a significant decrement in freezing time by about 41.43 %, with the most pronounced effect observed for nano-powders with dp = 40 nm.

A Computational Study on Utilizing Phase Change Material With a Condenser to Improve air Conditioning System Performance

ABSTRACTThe efficacy of employing multiple cylindrical phase change materials (PCM) to enhance the performance of an air conditioning (AC) unit is examined in this study. The objective of the present study is to examine the effects of combining an AC unit with a cylindrical PCM container configuration on the PCM discharge process and the performance of the AC system. The procedure involves the connection of a heat exchanger with a cold energy storage PCM to the condenser of the AC. During the daytime, the warm surrounding air is cooled and then transmitted to the AC unit's condenser. Four different turbulence models, that is, the SST , standard , Realizable and RNG have been considered for the present computational study. The investigation has been performed for different air flow rates, that is, 33.6, 42, and 49 for a constant inlet air temperature of 308.15 K. The present outcomes indicate that as the flow rate rises, the air temperature inside the domain increases and the solid PCM starts melting. It is noted that complete discharging time for multi‐cylindrical PCM reduces as the air flow rate rises which are around 13.36, 11.03, and 9.94 h for airflow rates of 33.6, 42, and 49 , respectively. The maximum achieved increase in the COP is around 94.49%, 88.68%, and 87.57% at airflow rates of 33.6, 42, and 49 L/s, respectively, for the multi‐cylindrical PCM throughout the summer. It is found that for the same temperature, as the airflow rate rises, the consumed power saving rises.

Thermodynamic performance of air-cooled seasonal cold energy storage for space cooling: A case study

With the improvement in people's living standards, there is a growing demand for cooling, making it urgent to develop a low-carbon and energy-efficient refrigeration system. Therefore, this paper proposes an air-cooled seasonal energy storage (ACSES) system. The heat transfer model of the system is constructed. The impact of relevant parameters on the system's cold storage performance was analyzed. The results show that larger glycol flow rates, windward velocity, number of tube passes and tube rows, and the volume ratio of ethylene glycol to water (VR) are beneficial for improving cold storage performance. However, excessively large parameters do not significantly enhance cold storage performance. The influence of ambient temperature on cold storage performance is greater than that of ice thickness. When VR is 0.02, the cold storage performance is relatively superior. To demonstrate the energy-saving performance of the system, the energy consumption saving rate (ECSR) indicator was proposed. The ECSR of the ACSES system is 72.75 %. The system can significantly conserve resources and reduce energy consumption.

Impact of nano-powders on conduction mechanism during solidification through cold storage tank

In this article, numerical modeling with the aim of decreasing the solidification time is presented. The solidification process is primarily influenced by conduction, leading to the application of two techniques aimed at enhancing this mechanism: the install of fins and the addition of nano-powders. Various shapes and fractions of alumina nanoparticles are introduced into the H2O to accelerate the solidification. To predict the properties of the nanoparticle-infused mixture, single-phase formulations are employed. The Finite Element Method (FEM) is then hired to model the system, with an adaptive grid implemented to enhance accuracy. Validation against previous works demonstrates the capability of the developed code for the present study. The incorporation of nanoparticles results in a significant 32.7 % increase in the freezing rate, highlighting the effectiveness of this approach. Additionally, altering the shape of the nanoparticles can further increase the process rate by approximately 10.73 %. The transition from a water-based system to one infused with nanomaterials leads to a notable decrement in freezing time, from 957.64 s to 6447.35 s. These outputs emphasize the potential of nanomaterial-enhanced cold energy storage systems to significantly improve efficiency and performance. In summary, the study showcases the effectiveness of numerical simulation in optimizing cold energy saving processes through the strategic utilization of nanoparticles.

Surfactant hydrophilic modification of expanded graphite to fabricate water-based composite phase change material with high latent heat for cold energy storage

Glycine water-based (GW) phase change material (PCM) is considered a promising candidate for cold energy storage due to its lower cost and high latent heat. However, low thermal conductivity hinders its practical application. Adding high thermal conductive fillers can effectively enhance the thermal conductivity of PCM, but it also leads to a decrease in enthalpy. Thus, the study employed a non-covalent functionalization method to modify the thermal conductivity filler of expanded graphite (EG) using the surfactant Triton X-100 (TX-100) in this study. The hydrophilic groups in TX-100 facilitated the formation of hydrogen bonds between modified expanded graphite (MEG) and GW PCM, thereby inhibiting the enthalpy loss of GW/MEG materials. The prepared GW/MEG composites containing 2 to 8 wt% of MEG exhibited thermal conductivities ranging from 0.88 to 1.28 W/(m·K), representing an increase of 46.47 % ∼ 113.35 %. Simultaneously, the melting temperature ranged from −5.35 to −5.65 °C, with a high melting latent heat of 284.6 to 264.5 J/g. After 100 thermal cycles, only minor fluctuations in melting temperature (−1.62 % ∼ +2.20 %) and latent heat (−2.18 % ∼ −4.66 %) were observed. Furthermore, the application of GW/MEG2 in cold storage of strawberries resulted in a significant reduction in pre-cooling time by 56.60 % compared to that of ice storage. The GW/MEG2 materials allow strawberries to be refrigerated for up to 17.86 h within the temperature range of 1.54 ∼ 3.39 °C. This study provides an effective solution for short-distance transportation of perishable food within cold chain logistics system.

Comparative analysis of charging and discharging characteristics in novel cold and hot simultaneous energy storage tanks

Energy storage technology is instrumental in reducing energy costs and crucial for balancing demand and supply. This study proposes a cold and hot simultaneous energy storage tank (CAHSEST) for the first time, although its heat transfer characteristics are not yet clear. The objective is to explore the heat transfer properties of CAHSEST. Utilizing computational fluid dynamics (CFD) software, three-dimensional models for five distinct tanks were developed and comparative analyses were performed focusing on temperature distribution, velocity distribution, thermocline thickness and storage efficiency. The findings indicate that tanks with separated cold and hot water (cases 3–5) exhibit significantly better stratification than those with mixed water (cases 1 and 2), showing higher energy storage efficiency. At a heating time of 3600 s, cases 3 and 5 shows higher heat charging efficiency than other cases. In addition, case 3 achieves the highest cold discharging efficiency of 90.25 %, whereas case 2 has the lowest, at only 15.94 %. Overall, case 3 emerges as the optimal configuration. This research offers technical assistance for the design and understanding heat transfer characteristics of CAHSEST, and provides new directions for achieving long-term heat storage and short-term cold storage.

Thermal performance study of PCM embedded radiant cooling ceiling assisted by infrared-transparent silicon wafers

Phase change materials embedded radiant chilled ceiling (PCM-RCC) systems are great for cutting peak power demand and boosting energy efficiency, but they might not work as well in really humid areas due to condensation issues. Infrared-transparent silicon wafer-assisted PCM-RCC (ISW-assisted PCM-RCC) is proposed to improve the cooling capacity in this study. A heat transfer model of ISW-assisted PCM-RCC is established and its reliability is verified. Effects of thermal conductivity, phase change temperature, and control strategy on the thermal performance of ISW-assisted PCM-RCC are discussed by using the model. The simulation results show that the thermal conductivity of PCM is recommended to be above 0.6 W/(m·K), and the temperature difference between the lower limit of the selected PCM phase transition temperature range and the chilled water temperature should not be less than 1℃. The maximum cooling power of the system is more than 80 W/m2, 46 % higher than the non-condensing cooling capacity of traditional RCC at 70 % relative humidity conditions. Interestingly, the prolonged cold energy storage strategy at night should be avoided which is not friendly to the energy efficiency of the system. In short, the combination with ISW is an effective means to increase the cooling capacity of the PCM-RCC.

A self-satisfying cooling system based on cold energy storage for the locomotive in a high geothermal tunnel

Effective thermal management of locomotive systems is crucial for ensuring the safe operation of trains through high geothermal tunnels. By taking advantage of the frequent alternation of high-temperature tunnels and cold climate environment, a self-satisfying cooling system based on cold energy storage is proposed, in which a phase change heat exchanger between air and phase change material (succinic acid with 20 wt% expanded graphite) is developed to store cold energy outside tunnels and improve air-cooling efficiency inside tunnels. Numerical models are established to examine the thermal environment in a typical tunnel and the effectiveness of the proposed cooling system. The results indicate that because of the heat exhausted from the train and the thermal dissipation from the surrounding hot rock, the air temperature in the tunnel can rise above 50 °C. The proposed cooling system can release the cold energy from phase change material to keep the air outlet temperature below 40 °C, increasing the energy efficiency and reliability of locomotive operation. By examining the effects of locomotive operating conditions and orthogonal analysis of multi-factors, the heat exchanger structure and other operating conditions are recommended for the self-satisfying cooling system. Finally, the cooling system’s effectiveness is confirmed for the full-line operation of the locomotive along the Ya’an-Nyingchi section of the Sichuan-Tibet Railway in both summer and winter climatic conditions. This study is significant because it provides a novel design scheme for locomotive’s thermal management in high geothermal tunnels and other similar engineering conditions with natural cold sources.

Cold energy storage enhancement and phase transition temperature regulation

The objective of this study is to prepare a highly adjustable ester phase change material (PCM) and further optimize its cold storage properties using a simple and controllable physical method. Initially, lauric acid (LA) and polyethylene glycol 200 (PEG 200) are selected as raw materials, and a non-toxic and environmentally friendly polyethylene glycol laurate (PLE) with a tiny supercooling is prepared under the condition of acid-alcohol molar ratio of 1:3. To further regulate the cold storage property of PLE, a series of PCMs with different melting temperatures are successfully prepared using PLE blended with ethanol (EA). Among them, the lowest melting temperature in the study reaches −15.2 °C, which is about 94.6 % lower compared to −7.81 °C for PLE, and the highest latent heat of melting is 81.56 J/g. It is also observed that the supercooling of a range of samples is also optimized compared to the PLE, with a maximum reduction of 27.1 %. Additionally, the prepared samples not only exhibit excellent stability but also demonstrate outstanding application potential in temperature control and preservation experiments. This innovative achievement provides a richer selection of PCMs for the cold storage field. More crucially, this is the first report utilizing EA to regulate the temperature range of ester-based PCMs. This method is simple, easy to operate, and highly reproducible. It paves the way for the refinement, diversification, and customization of refrigeration technology.

Innovative dodecane-hexadecane/expanded graphite composite phase change material for sub-zero cold storage applications

Utilization of phase change materials (PCMs) for cold energy storage has garnered increasing attention. This study focuses on the development of a composite PCM by integrating a novel eutectic dodecane-hexadecane (DD-HD) PCM into expanded graphite (EG), to cater to the demands of sub-zero cold energy storage applications, such as cold chain logistics. The study identified the optimal mass ratio of DD-HD as 80:20. A series of DD-HD/EG composites were fabricated through a combination of high-speed emulsification and physical adsorption methods. The adsorption capacity of EG for the eutectic PCM mixture was evaluated by examining the impact of EG fraction on the leakage of the composite PCM, revealing that the optimum EG fraction is 10 wt%. The composite PCM displayed a sub-zero phase change temperature of -12.09 ℃, a high melting enthalpy of 178.75 kJ/kg, and a high thermal conductivity of 5.18 W/(m•K). The thermal conductivity of the composite was enhanced by 22.52 times compared to the base PCM. Thermogravimetric analysis indicated that the decomposition temperature of DD-HD/EG was significantly higher than that of the base PCM. The composite demonstrated outstanding thermal reliability, as evidenced by thermal cycle tests. With its impressive thermal characteristics, this composite shows great potential for various cold energy storage applications.

Thermo-economic analysis of a pumped thermal energy storage combining cooling, heating and power system coupled with photovoltaic thermal collector: Exploration of low-grade thermal energy storage

As renewable energy penetration grows, traditional power systems face significant challenges due to their intermittency and volatility. Pumped thermal energy storage (PTES) is a potential energy storage technology that has a low specific cost and geographical restriction. In this paper, a PTES system which is coupled with solar photovoltaic thermal (PVT) collectors is proposed to satisfy the demand for cooling, heating and electricity supply, and achieve energy cascade utilization. An ejector refrigeration cycle and the turbine extraction heating are accompanied with a PTES system. Thermodynamic analysis of the system is performed by evaluating the influence of key parameters on system performances for 1 MW power output. The economic analysis adopted levelized cost of energy storage (LCOS), which mainly includes investment costs, operation and maintenance costs and system depreciation. The results show that the maximum amplification of roundtrip efficiency with PVT is 12.04 % compared to the system without PVT. Moreover, the maximum average power generation benefit of PVT is 4.85 %. The increase in cold energy storage tank temperature can effectively improve the roundtrip efficiency of the system. The lower cold energy storage tank temperature and higher hot energy storage tank temperature have a negative impact on system thermal efficiency (ηthermal) but benefits for LCOS. Multi-objective optimization is carried out to obtain the optimal design performance that ηthermal and LCOS are 51.06 % and 0.533$/kWh respectively.

Solar photovoltaic refrigeration system coupled with a flexible, cost-effective and high-energy-density chemisorption cold energy storage module

Owing to the environmental pollution and high costs associated with lead-acid batteries, this paper proposes a solar photovoltaic (PV) refrigeration system coupled with a flexible, cost-effective and high-energy-density chemisorption cold energy storage module. Its operation mode includes daytime solar PV refrigeration/cold energy charging mode and nighttime cold energy discharging mode. A novel composite sorbent SrCl2 is developed using expanded natural graphite as matrix and carbon coated aluminum as additive, exhibiting superior heat and mass transfer performance. A sorbent performance test bench is constructed, demonstrating that the cold energy storage density reaches 503.6 kJ/kg at an evaporating temperature of −15 °C, 1.5 times of ice storage. Compression-assisted desorption is adopted to regulate desorption temperature, so that 75–90 °C solar hot water from low-cost non-concentrating solar collectors can be utilized as the driving heat source. For an evaporating temperature of −10 °C and a solar hot water temperature of 90 °C, the electrical coefficient of performance for cold energy storage unit reaches 3.72, representing a 33 % improvement compared to conventional solar PV refrigeration systems. This novel system features characteristics such as low cost, high efficiency and eco-friendliness, offering a promising solution for solar refrigeration.

Robust and comprehensive predictive models for methane hydrate formation condition in the presence of brines using black-box and white-box intelligent techniques

Accurate estimation of gas hydrate formation condition is crucial for many reasons. In one hand, the gas hydrate formation is a promising approach for gas separation, cold energy storage, seawater desalination, etc. On the other hand, in some industries, this phenomenon may cause some challenges, such as pipelines blockage. The current study was undertaken to develop trustworthy predictive tools for methane hydrate formation temperature (MHFT) in the presence of brines. To achieve this target, 1051 experimental data pertinent to the methane hydrate equilibrium in 26 single and multiple brines over an extensive range of operating conditions were amassed from published studies. Four simple factors, including pressure, brine concentration, salt molecular weight and salt melting temperature were defined as the input variables, and the black-box intelligent techniques, including gaussian process regression (GPR), multilayer perceptron (MLP) and radial basis function (RBF) were employed to link MHFT to the mentioned factors. A plethora of graphical and statistically-based assessments were performed to determine the accuracy level of the proposed models. While all intelligent models had excellent performances, the one established by the GPR method showed the best agreements with experimental data, and gave the AARE and R2 values of 0.14% and 99.17%, respectively, in the testing step. The foregoing model was capable of predicting MHFT over a broad range of conditions with relative deviations mostly below 0.10%. Additionally, it showed an excellent performance in describing the physical variations of MHFT versus operating factors. The authority of the analyzed databank and the presented model was asserted via the William's plot investigation. Moreover, a sensitivity analysis was undertaken in order to determine the most fundamental factors in controlling MHFT. Eventually, a simple mathematical correlation was also derived based on the white-box intelligent approach of gene expression programming (GEP), which allowed the accurate estimation of MHFT with an AARE of 0.56%.

Evaluation of thermal storage system during freezing and loading nano-powders

In pursuit of advancing the efficiency of cold energy storage, a uniquely designed curved container has been employed, filled with a water-nanoparticle mixtureQ. The container is equipped with fins, strategically leveraging the enhanced conduction facilitated by the presence of nanoparticles. The simulation of the intricate unsteady phenomena in this study has been conducted using the finite element technique, providing a robust analytical framework. The incorporation of an adaptive grid ensures a refined resolution, particularly in the vicinity of the ice front region. The nanoparticle fraction (ϕ) emerges as a pivotal factor directly influencing the rate of solidifying. The dispersion of nano-powders leads to a noteworthy reduction in completion time, demonstrating a substantial 33.21% improvement. The diameter of the nano-powders (dp) introduces diverse effects on the solidification process, primarily due to its significant influence on the conductivity of the nanomaterial. An in-depth exploration of the impact of dp reveals compelling insights. As the dp increases from its smallest size to 40 nm, there is a commendable 15.12% reduction in the required freezing time. However, a subsequent increment in dp beyond this threshold results in a notable 36.56% increase in the freezing time. The findings presented here not only contribute to the fundamental understanding of freezing processes but also hold practical implications for the design and optimization of cold storage systems.

Simulation of storage of cold energy considering unsteady conduction mechanism in mathematical model

To enhance system productivity, fins were incorporated into the container, and PCM (phase change material) infused with alumina nanoparticles was introduced. Mathematical modeling was employed to evaluate the current problem, with a specific focus on utilizing water as the PCM for achieving the fastest solidification process. The integration of fins, PCM, and nano-powders introduces a novel dimension to the research, providing unique insights into enhancing solidification processes. The surrounding cold walls of the container play a crucial role in solidification, primarily through conduction. The low speed of H2O allows its neglect in simulation. The developed mathematical model for this work comprises two equations. While considering larger powder sizes improves particle interaction, the negative impact of sedimentation diminishes conductivity. The addition of nanoparticles results in a 41.34 % enhancement in the solidification rate. Furthermore, altering the powder diameter from thirty to 40 nm reduces the completion time about 19.98 %, whereas an increase from 40 to 50 nm elevates it by about 49.37 %.

Energy consumption reduction in a building by free cooling using phase change material (PCM)

It is significantly important to implement energy storage systems nowadays. Latent heat thermal energy storage (LHTES) systems contain numerous advantages as a result of their small temperature variation and higher energy storage densities during storage. The present paper deals with the cooling load of a room in Zanjan, Iran using Carrier software. Then, a free cooling system using commercial paraffin RT25 was numerically analyzed as phase change material (PCM) while investigating the effects of the flow rate of the storage tank and inlet air temperature overcharging and discharging procedures. Based on cold energy storage simulation, by airflow with the temperature of 20°C at night, the paraffin is solidified in 4 h. Stored cold energy of 1.4 kW in PCM releases energy through a free cooling system within 2.1 h of July afternoon in the room.

Cold Energy Storage via Hydrates Production with Pure CO2 and CO2/N2 (70/30 and 50/50 vol%) Mixtures: Quantification and Comparison between Energy Stored and Energy Spent

Cold Energy Storage via Hydrates Production with Pure CO2 and CO2/N2 (70/30 and 50/50 vol%) Mixtures: Quantification and Comparison between Energy Stored and Energy Spent

Hectorite aerogel stabilized NaCl solution as composite phase change materials for subzero cold energy storage

Inorganic phase change cold storage materials have garnered significant interest in cold chain transportation due to their high energy storage density. Nevertheless, practical applications have been hindered by inherent limitations such as high supercooling and susceptibility to phase separation. To address these challenges, this study devised 3D-Hectorite/sodium chloride (NaCl) composite phase change cold storage materials by utilizing 3D-Hectorite aerogel to adsorb NaCl solution, effectively mitigating the issue of phase separation common in such materials. Additionally, various concentrations of nucleating agents such as SrCl2·6H2O, borax, and diatomite were introduced for step cooling curve tests, establishing 0.03% diatomite as the optimal concentration for nucleation, reducing the supercooling of the NaCl solution to 1.1 °C. The results showed that the latent heat and thermal conductivity of 3D-Hectorite/NaCl were 215.30 J/g and 0.6315 ± 0.013 W/mK, respectively. The phase transition temperature could be adjusted in the range of -33~0 °C by changing the concentration of NaCl to meet the different temperature requirements. Furthermore, exceptional cyclic stability was observed even after subjecting the material to ten dissolution-solidification cycles. Analyzing the temperature change of the air inside the insulation bag showed that, compared with ice, 3D-Hectorite/NaCl can be applied to meet lower cooling temperature requirements, demonstrating good prospects for its application in cold chain transportation.

Form-stable oleic acid based polyHIPE/nanoclay framework supported composite phase change materials for low‐temperature latent heat storage

Latent heat storage, one of the promising methods in energy storage, is an important option for the sustainable use of energy and is attracting more attention day by day. Phase change materials (PCMs) produced for this purpose allow the storage/release of latent heat due to the temperature of the medium and can be obtained using various methods. In this work, the preparation of a new fatty acid based composite phase change material was accomplished by applying simple two-step approach. Here, oleic acid (OA) was employed as PCM, and emulsion templated macroporous polymers (polyHIPEs) as supporting matrices. Furthermore, macroporous supports were also fabricated in the presence of surface modified montmorillonite nanoclay to enhance thermal properties of the targeted composite PCMs. In this respect, a neat macroporous support and surface modified nanoclay enhanced macroporous support were synthesized. Then, the composite PCMs were prepared by filling the macropores of the obtained polymer foams with OA via a solvent-assisted impregnation approach for cold energy storage. The examinations on the thermal characteristics of the composite PCMs were performed through Differential Scanning Calorimetry (DSC), while the chemical structure was analyzed with FT-IR. Besides, polarizing optical microscopy (POM) was used to monitor the loading of OA to macroporous polymer supports. Additionally, the thermal behaviors of composite PCMs were investigated by the temperature-history (T-history) method and the findings were also found to be compatible with DSC. Furthermore, thermal stability of the composite PCMs was investigated through thermogravimetric analysis (TGA). According to DSC results, the prepared composite PCMs are candidates for utilizing cold thermal energy storage such as building cooling, cold protection and cold chain transportation applications with their proper melting temperatures (7.08 °C and 7.40 °C) and moderate latent heat capacities.