Cold Energy Storage Research Articles

Utilization of Carbon-Based Nanomaterials and Plate-Fin Networks in a Cold PCM Container with Application in Air Conditioning of Buildings.

Cold energy storage devices are widely used for coping with the mismatch between thermal energy production and demand. These devices can store cold thermal energy and return it when required. Besides the countless advantages of these devices, their freezing rate is sluggish, therefore researchers are continuously searching for techniques to improve their operating speed. This paper tries to address this problem by simultaneously combining a network of plate fins and various types of carbon-based nanomaterials (NMs) in a series of complex computational fluid dynamics (CFD) simulations that are validated by published experimental results. Horizontal, vertical, and the combination of these two plate-fin arrangements are tested and compared to the base model. Subsequently, several carbon-based NMs, including SWCNT, MWCNT, and graphene-oxide NMs are utilized to further improve the process. The influence of these fin networks, nanoparticle types, and their volume- and mass-based concentrations within the PCM container are studied and discussed. According to the results, carbon-based NMs exhibit superior performance compared to metal-oxide NMs, so that at identical NM volume and mass fractions, MWCNT particles present a 2.77% and 17.72% faster freezing rate than the CuO particles. The combination of plate-fin network and MWCNT particles is a promising technique that can expedite the ice formation rate by up to 70.14%.

System Performance and Economic Analysis of a Phase Change Material Based Cold Energy Storage Container for Cold Chain Transportation

We studied a shipping container integrated with phase change material (PCM) based thermal energy storage (TES) units for cold chain transportation applications. A 40 ft container was used, which was installed with ten plate-like TES units containing PCM and a charging loop. An appropriate PCM was selected for meeting the requirement of the transportation of fresh vegetables (7-12°C). The charging loop was linked to a separate charging facility via quick coupling valves. The discharging performance of the container under dynamic conditions was investigated. The COP of the system was estimated to be 1.73. Economic analyses showed that energy and operation costs of the PCM-based container were, respectively, 71.3% and 85.6% lower than the same container but powered by a diesel engine (called reefer container). The results also showed that the PCM-based container was able to maintain not only the temperature range (7-12°C) but also the humidity range (85-95%), leading to better quality and longer shelf-life of the goods.

Thermal analysis of a solar-powered absorption air-conditioning system: Case study for a tent in Mina zone, Saudi Arabia

The present study used a TRNSYS simulation for solar cooling with cold energy storage. It was applied to a tent hypothetically located in Mina zone, KSA, where millions of pilgrims stay in tents for a few days once a year. The required cooling demand was calculated for a tent that can be occupied by 150 pilgrims for 7 days representing Makkah climatic region. The system consisted of a solar thermal system, absorption cooling chiller matched with a cooling tower, storage tank, and fan coil units. The results show that the required cooling capacity for the tent is about 70 kW (20 tons refrigeration) to keep the zone air temperature at 24 °C during summer days where the cooling demand for the tent for 7 days in June is around 8,850 kWh. In addition, the effect of a cold-water storage on the system performance was studied. Using a chilled water tank of 500 m 3 will reduce the absorption chiller capacity from 20 tons to 4.7 ton. Moreover, a PV system was designed to cover the electrical load of the considered absorption system with performance ratio of 70%.

Highly-efficient cold energy storage enabled by brine phase change material gels towards smart cold chain logistics

Cold chain logistics is an important technology to ensure the quality and preservation of food, drugs and biological samples. In this work, novel brine phase change material gels (BPCMGs) are proposed by loading the eutectic brine in super absorbent polymer (SAP) to realize the highly-efficient cold energy storage towards the cold chain transportation. Potassium chloride (KCl) and ammonium chloride (NH4Cl) are dissolved in water to form the eutectic brine PCM on account of its phase change temperature near −21 °C for the refrigerated transport of aquatic products and biological samples. SAP with excellent brine adsorption capacity can provide the free-standing feature for the BPCMGs. The resulted BPCMGs demonstrate eliminated supercooling, high latent heat of 230.62 Jg−1, high thermal conductivity of 0.589 Wm−1 K−1 and high cost-effectiveness of 7.63 × 10−6 $J−1. The BPCMGs also possess stable thermophysical properties after 200 cycles. Taking advantages of the above merits, the BPCMGs are applied in the cold chain logistics of aquatic products and biological samples. The cold storage times reach 21.44 h and 16.37 h for aquatic products and biological samples when the stored cold energy is 691,800 J. Furthermore, the temperatures and locations of the cold storage box can be real-time monitored remotely by equipping with temperature sensor, GPS positioning system and a smart phone. This work creates a state-of-the-art alternative for the next-generation cold energy storage materials and cold energy storage equipment.

Assessment of an intermediate working medium and cold energy storage (IWM-CES) system for LNG cold energy utilization under real regasification case

Owing to the fluctuating liquified natural gas (LNG) regasification rates in receiving terminals, LNG cold energy utilization systems face low recovery rate issue. In this work, an intermediate working medium and cold energy storage (IWM-CES) system is proposed to improve the operational flexibility and recovery rate for LNG cold energy utilization under actual regasification case. The proposed system comprises two modules, namely, cold energy recovery module and cold energy storage module. The cold energy recovery module recovers deep and shallow LNG cold energies using intermediate working mediums. The cold energy storage module acts as a buffer to promote stable cooling output. Key results revealed the maximum stable cooling output of conventional system (without cold energy storage) is constrained by the minimum regasification rate, which causes a relatively low recovery rate. On the contrary, the proposed system realizes a larger stable cooling output and enhances the cold recovery rate from 33.2% to 80.3%. Economically, the proposed system requires the injection of additional capital cost but can achieve better lifecycle profit. Environmental benefits are conducted and ultimately evaluated from users' perspective. Compared to the conventional system, the proposed system achieves the improvement of daily CO2 emissions reduction spanning 75.2 tons/day to 453.8 tons/day.

Study on the selection method of solid cold energy storage medium for liquid air energy storage

Liquid air energy storage (LAES) is a promising large-scale energy storage technology. A packed bed cryogenic regenerator was investigated for cold energy storage in the LAES system. As the thermophysical properties of the filling material directly affects the performance of the regenerator, sensitivity analyses of the specific heat capacity and thermal conductivity were carried out. Results show that the thickness of the thermocline in the packed bed can be reduced by increasing the specific heat capacity and decreasing the thermal conductivity. Furthermore, the synergy effect of the specific heat capacity and thermal conductivity on the system was considered. In the case of simultaneous changes of the two parameters, the selection method of the solid material was proposed innovatively, and the feasibility of the method was verified by theoretical calculation of various materials.

Thermodynamic analysis of the non-ideal cryogenic packed bed regenerator for the liquid air energy storage system

Liquid air energy storage (LAES) is one of the most recent technologies introduced for grid-scale energy storage. The cryogenic regenerator, which can greatly affect the system efficiency, is the key component of the system. A non-ideal packed bed regenerator for the LAES system was investigated. The cold energy loss and the axial heat conduction of the packed bed regenerator exist in the intermittent period between the charging and discharging process, which significantly degrades the system performance. With rock particles used as the cold energy storage medium, the axial temperature distributions of the packed bed regenerator with different initial temperatures and intermittent periods were compared. Also, the cold energy loss with different boundary conditions was analysed. The results show that the intermittent period exacerbates the negative impact of the axial heat conduction on the performance of the packed bed, and the thickness of the thermocline decreases as the inlet temperature of the cold end decreases. Moreover, as the cold energy loss increases, the cold energy storage efficiency of the packed bed decreases significantly.

Preface

Due to recent pandemic, 2022 6th International Conference on Hydrodynamics, Energy and Electric Power System (HEEPS 2022) was held virtually online during March 25-27, 2022. The decision to hold the virtual conference was made in compliance with many restrictions and regulations that were imposed by countries around the globe. Such restrictions were made to minimize the risk of people contracting or spreading the COVID-19 through physical contact. There were 100 individuals who attended this online conference, represented many countries including China, India, Mexico, Australia and Italy.The conference is an international conference for the presentation of technological advances and research results in the fields of Hydrodynamics, Energy and Electric Power System. The conference brings together leading researchers, engineers and scientists in the domain of interest from around the world. We warmly welcome previous and prospected authors submit your new research papers to HEEPS 2022, and share the valuable experiences with the scientists and scholars around the world.During the conference, the conference model was divided into three sessions, including oral presentations, keynote speeches, and online Q&A discussion. In the first part, some scholars, whose submissions were selected as the excellent papers, were given about 5-10 minutes to perform their oral presentations one by one. Then in the second part, keynote speakers were each allocated 30-45 minutes to hold their speeches. In the second part, we invited four professors as our keynote speakers. Prof. Abdul Hasib Chowdhury, Bangladesh University of Engineering and Technology, Bangladeshi, performed a speech: Improving frequency resilience of power systems through dynamic-adaptive load shedding. And then we had Prof. Chuanchang Li, Changsha University of Science & Technology, China. He delivered a speech: Emerging composite phase change materials for thermal and cold energy storage. Prof. Zong Zhi, Dalian University of Technology, China. He shared a speech: Configuration Hydrodynamics of Trimaran ships. Lastly, we were glad to invite Assoc Prof. Pengcheng Lin, Guangdong University of Technology, China. He made a wonderful speech: Phase change gel: from organic to inorganic, from foundation to application. Their insightful speeches had triggered heated discussion in the third session of the conference. Every participant praised this conference for disseminating useful and insightful knowledge.List of Committee member is available in this pdf.

Investigation on heat transfer and phase transition in phase change material (PCM) balls and cold energy storage tank

The phase-change based energy storage provides an excellent solution for the mismatch of energy production and consumption. Cold energy storage tanks filled with PCM balls could be applied in energy-efficient air-conditioning systems. The main advantage lies in the reduction of energy storage space demand compared with water-based cold energy storage. Clarifying the pattern of freezing process within the PCM balls is of critical importance for the design of energy storage tank. In the present work, experimental measurement is conducted to obtain the temperature variance and phase transition process of one PCM ball. With the aid of CFD simulation software, physical model of one PCM ball is established and well-validated with experimental data. The validated model is then used to simulate the thermal performance of cold energy storage tank filled with multiple PCM balls. Meanwhile, the influences of parameters involving in the diameter of the PCM balls (90, 90&60, and 60 mm), and the flow rate of chilled water in the tank are evaluated. The results indicated that higher freezing rate of PCM ball can be achieved by smaller diameter of the ball and faster flow rate of chilled water. Under the conditions set in this study, the optimal diameter of phase change balls is determined to be 90&60 mm. and the best inlet flow rate is 2.196 m/h. When PCM balls are concerned for cold storage systems, it is proposed to set the diameter carefully in terms of the capacity of cold energy (flow rate of chilled water) and the limit of freezing duration.

Experimental research and numerical simulation of the thermal performance of a tube-fin cold energy storage unit using water/modified expanded graphite as the phase change material

In this study, experimental and numerical investigations were conducted on a tube-fin heat-exchanger latent-heat cold energy storage unit. The fin side of the heat exchanger was filled with water as the energy storage medium, and modified expanded graphite (MEG) was employed to improve the thermal characteristics of water. The water contact angle of the expanded graphite decreased from 106.31° to 0°, and the hydrophilicity and the absorption rate of water significantly improved after the modification. Moreover, the experimental analyses of the charge/discharge process showed that the cooling capacity of the system filled with 90 wt.% water/MEG was 80.8% of that of pure water, whereas its cooling time was only 69.7% of that of pure water. The average power increased by 15.9% compared with that of water. The system filled with 90 wt.% water/MEG completed two energy charging and discharging cycles, whereas the system filled with water completed only 1.5 cycles within 15000 s. Furthermore, the effects of the flow rate and inlet temperature of the heat transfer fluid on the charging process were explored. Finally, a numerical model was built and validated to investigate the phase change behavior and the effect of the structure size on the performance of the system. The heat-exchanger fin spacing had no significant effect on the cold energy storage unit, whereas the vertical spacing of the tube pass had the highest effect. It can be concluded that the heat exchanger combined with high-thermal-conductivity water/MEG exhibits better energy storage capacity and working power, showing a wide application prospect in the field of cold energy storage.

Melting of hybrid nano-enhanced phase change material in an inclined finned rectangular cavity for cold energy storage

The aim of this paper is to study the potential of two heat transfer enhancement techniques, namely adding fins and hybrid nanoparticle (Cu and Al2O3), for improvement of the melting process of PCM (water) in an inclined rectangular enclosure as model of cold energy storage systems. Phase change and heat transfer of PCM are modelled using an in-house built code based on Lattice Boltzmann Method, which is validated with experimental and numerical results from literature. Enhancement effect is investigated through the main parameters including number of fins, fin length ratio (W/H) and nanoparticle volume fraction (ϕ). Heat transfer and fluid flow, liquid fraction, transient evolution of melting front, required time for full melting, and thermal energy storage are analysed in detail. The results show that the melting rate is about two times higher for the fin length ratio of W/H = 0.75, compared to W/H = 0.25. Besides, nanoparticle loading further enhances the melting rate. The highest melting rate is attained in the case of 3-fins and nanoparticle concentration of ϕ = 6 vol% with a 33.5% reduction in the complete melting time. Incrementing the fin length ratio increases the thermal energy stored, and the melting time can be shortened by up to 64%.

High‐Performance Charging Method for Cold Energy Storage Using Foam Freezing

Foam freezing has an obvious advantage over the current conventional phase change cold energy storage method in charging performance. The maximum theoretical cold energy charging coefficient of foam freezing is as high as 237.1 W/m2K. Foam freezing brings a new dawn for solving the problem of gradual attenuation of the phase change cold storage charging rate. More details can be found in article number 2100647, Zhaoliang Jiang and co-workers.

Off-design and flexibility analyses of combined cooling and power based liquified natural gas (LNG) cold energy utilization system under fluctuating regasification rates

The Liquified Natural Gas (LNG) regasification rate tends to fluctuate during the diurnal period due to the varying demand of natural gas. This fluctuation leads to the energy mismatch between LNG cold energy utilization system and users. Consequently, the actual LNG cold energy utilization efficiency deteriorates significantly. In this study, a novel cold storage-based combined cooling and power system has been designed to improve the efficiency and versatility of LNG cold energy utilization under fluctuating regasification rates. The system incorporates a CO2 based Rankine cycle, a direct expansion unit, and cooling recovery units. The waste heat (90 °C) harnessed from gas power plants instead of seawater (15 °C) is employed as the heat source to improve the Rankine cycle performance. Further, cold energy storage tanks are adopted to decouple the power and cooling outputs from the fluctuating regasification rates. Off-design performance of the system is investigated under the different regasification rates. Key results have revealed that the power output profile from the conventional system is monotonous and the valley-to-peak ratio of power is as low as 0.05, resulting in potential downtime for downstream users. In contrast, the proposed system implements a versatile power and cooling strategy to satisfy different users’ demands. Results from two case studies demonstrate that the valley-to-peak ratio of power can be markedly improved to values spanning 0.4 to 1. The daily cold recovery rate, exergy efficiency, and reducing CO2 emission approach 53.45%, 25.26%, and 645.13 tons/day, respectively, for a 3 megatons per annum regasification LNG plant. The payback period for the proposed system is 0.67 years, which is almost half of the conventional system’s period.

Preliminary thermodynamic analysis of a carbon dioxide binary mixture cycled energy storage system with low pressure stores

The liquid CO2 energy storage has considerable potential for power supply-demand management, but its low energy density, harsh condensation condition and high operation pressure are substantial obstacles. It is the first time to design energy storage system with high energy density and low-pressure stores by cycling the CO2 binary mixtures. By using CO2 mixtures, the pressure in storage tanks can be as low as ambient pressure (0.1 MPa) and two-tank cold energy storage with liquid storage materials can be used to complete the evaporation and condensation processes of working fluid in subcritical pressure. A large number of refrigerants are discussed and nine of them are selected as preliminary candidate additives into CO2. The performance of newly proposed system cycled with these additives is further analyzed by utilizing an in-house code developed with established thermodynamic models. The numerical results demonstrate that the mass fraction of additives is suggested to be higher than 0.12, otherwise there is high required capacity of cold storage material although a larger energy density. By and large, the mixtures CO2/R161 (0.7/0.3) and CO2/R1270 (0.82/0.18) are the first two most suitable selections among the CO2 mixtures, the round trip efficiency and energy density of which at basic design condition are 52.95% and 29.74 kWh/m3 and 52.12% and 29.83 kWh/m3, respectively. Both the optimal charge and discharge pressures can be identified for round trip efficiency while the energy density increases monotonically with charge pressure and the increasing trend is first steep and gradually becomes slow.

Investigation and evaluation of building energy flexibility with energy storage system in hot summer and cold winter zones

The dramatically increasing energy demand of building air-conditioning in hot summer and cold winter zones fluctuates greatly, especially during the period of cooling and heating in summer and winter, which exerts strict operation burden and challenge on power-grid system stability. In order to realize building energy flexibility, this paper proposes a type of energy utilization system including electricity chiller, gas-boiler, electricity heater, cold and thermal energy storage tank (case II), on the basis of electricity chiller and gas-boiler for cooling and heating demand (case I), which is commonly used as cold and heat source in hot summer and cold winter zones. The total cost of the whole life period and annual carbon emission of energy systems are served as objective function is optimized. Furthermore, the system capacity confirmation and load demand management control are analyzed and discussed, the characteristics of energy-flexibility with and without energy storage are presented, the load coefficient is introduced to evaluate the impact of case II on building energy flexibility. Compared with case I, with the deployment of cold and thermal energy storage, the cost-effectiveness of case II is 16.5% and carbon emission is reduced by 30.9% compared with case I .In case II, the load coefficient of electricity chiller and electricity heater is 83.34% and 30.65% respectively, which means that energy storage system enables to promote building energy flexibility improvement and grid-friendliness enhancement. This paper provides methods and theoretical guidance for the planning-operation of building energy system and building energy flexibility in hot summer and cold winter zones.

Operational Characteristics of Oscillating Heat Pipe at Sub-Zero Temperature for Cold Energy Storage

Operational Characteristics of Oscillating Heat Pipe at Sub-Zero Temperature for Cold Energy Storage

Performance Analysis of Sorption Thermal Battery for High-Density Cold Energy Storage Enabled by Novel Tube-Free Evaporator

Performance Analysis of Sorption Thermal Battery for High-Density Cold Energy Storage Enabled by Novel Tube-Free Evaporator

An electrical resistivity-based method for measuring semi-clathrate hydrate formation kinetics: Application for cold storage and transport

Tetra-n-butylammonium bromide (TBAB) semi-clathrate hydrate has a large latent heat and suitable phase transition temperatures to be used as a phase change material for cold energy storage and transport. The mass fraction of hydrates in the semi-clathrate hydrate slurry is a key parameter determining the cold carrying capacity and flow properties. We developed a new experimental methodology based on electrical resistivity to quantify the hydrate fraction in semi-clathrate hydrate slurry during hydrate formation. Relationship between electrical resistivity and hydrate fraction of semi-clathrate hydrate slurry was established based on Bruggeman’s effective-medium approximation. After validation, this method was employed to quantitatively investigate the effect of temperature on TBAB hydrate formation from 20 wt% TBAB/water system. As the temperature was lowered from 278.2 K to 274.2 K, the induction time was reduced by 97.8% and the hydrate growth rate was enhanced by over 2.5 times. At 274.2 K and 276.2 K, type A hydrates were preferentially formed followed by a structural transition to type B. At 278.2 K, only type A hydrates were observed. Furthermore, given an appropriate concentration, amino acid L-tryptophan was identified to be a good kinetic promoter for TBAB hydrate formation. The presence of 500 ppm L-tryptophan reduced the induction time by 60% and boost the hydrate growth rate by more than 32%. The electrical resistivity-based method developed in this work has shown simplicity, low cost, high accuracy, and repeatability. It would enable precise investigation of semi-clathrate hydrate kinetics in the future for cold energy applications and beyond.

Unsteady analysis of the cold energy storage heat exchanger in a liquid air energy storage system

Liquid air energy storage (LAES) is promising in the large scale energy storage field. The heat exchanger (Hex) in a LAES system using liquid phase working mediums for cold energy storage (CES) works discontinuously for the intermittent characteristic of the LAES. Variable temperature distribution exists in the Hex for CES (Hex-CES) in the intermittent process, and degrades the performance of the CES unit. In this paper, a computational model is constructed for the unsteady process in the Hex-CES of a 100 kW LAES system using liquid phase working mediums for CES to study the unsteady effect. The established steady temperature gradient is decreased gradually in the static process during which the LAES stops working and basically turns to zero gradient 12 h later. In the next operation cycle, it takes 34.8 min to reestablish the steady temperature gradient in the Hex-CES. Two methods to reduce the unsteady effect are proposed, the influence of key parameters on weakening the unsteady effect is investigated, and the optimal operation parameters in the static process are obtained. The results obtained in this paper are expected to provide the basis for the application of CES using liquid phase mediums and enhance the performance of LAES.

Nanoencapsulated n-tetradecane phase change materials with melamine–urea–formaldehyde–TiO2 hybrid shell for cold energy storage

A series of nanoencapsulated phase change materials with n-tetradecane as the core material and melamine–urea–formaldehyde (MUF)–TiO2 composite as the shell material was developed using a two-step method. Sol-gel and blending modification methods were respectively utilized after the in situ polymerization. The physical, chemical, and thermal properties of the nanoencapsulated phase change material (NEPCM) samples were characterized. Furthermore, a comprehensive performance evaluation system was established based on the efficacy coefficient method. The results indicated that the average diameter of the nanocapsules was significantly increased by the sol-gel modification and was slightly influenced by the blending method. All NEPCMs exhibited high chemical and thermal stability. The NEPCMs modified by the sol-gel method (C14@MUF–TiO2-S1) exhibited the best performance in terms of the encapsulation ratio, melting enthalpy, and onset decomposition temperature, which were 68.6%, 156.2 J·g-1, and 155.36 °C, respectively. C14@MUF–TiO2-S2 exhibited the lowest mass loss of 44.2% at 100 h. For the blending method, C14@MUF–TiO2-B1 had the highest yield of 53.87%. The thermal conductivity of C14@MUF–TiO2-B3 increased up to 88.15% compared with the unmodified NEPCMs. Therefore, modification by the sol-gel method with 2.2 g TiO2 sol had the highest total efficacy coefficient of 0.843 among the samples.