Cold Thermal Energy Research Articles

Multi-component Fluid Cycles in Liquid Air Energy Storage

With the penetration of renewable energy sources into the energy market, an emerging problem is the energy stability during energy supply and delivery. Energy storage technologies have the ability to overcome the intermittent nature of energy sources (such as wind and solar energy) and respond to unexpected situations like power failure. Liquid air energy storage (LAES) achieves good round-trip efficiencies by using hot and cold energy storages for heat transfer between the charging and discharging operations. In this work, the LAES technology has been studied and multi-component fluid cycles (MCFCs) are considered for the first time to replace the previously suggested single-component fluids in the cold thermal energy storage cycles to increase the performance of the cold cycles. Two case studies related to single MCFC and dual MCFC are simulated, optimized and compared. The optimal composition for the multi-component fluids is determined by using a particle swarm optimization (PSO) method. The objective function is to maximize the round-trip efficiency of the process. The results indicate that the LAES process with dual MCFC is superior to the case with single MCFC in terms of liquid yield (95.1 % vs. 87.1 %), exergy efficiency (86.1 % vs. 82.4 % for charging and 85.5 % vs. 78.5 % for discharging) and round-trip efficiency (61.8 % vs. 53.9 %).

Effect of surfactants on solidification characteristics of DI water based PCM for Cold Thermal Energy Storage

Cold Thermal Energy Storage is an upcoming need for sustainable energy consumption and storage. It finds application in wide variety of energy need in the sub-zero temperature zone. This work aims to study the effect of various surfactants on solidification characteristics of spherically encapsulated DI water with different surfactants. A constant temperature bath at -7°C is used to charge spherical encapsulated PCM using VCR system. Tween 80, Gum Arabic (also known as Gum Acacia) and PVP K30 are selected as surfactants and samples are prepared at various concentrations. To check the feasibility of the sample for thermal energy storage application its thermal properties are determined. Tween 80 and Gum Arabic showed no super cooling and subsequent reduction in super cooling was observed in case of PVP.

Characterization of wire arc additive manufactured products: A comparison between as-deposited and inter-layer cold worked specimens

The presence of large dendrites and alloy segregation in as-deposited wire arc additive manufacturing (WAAM) products results in a wide range of mechanical properties that are often inferior to wrought ones. In this study, the effect of inter-layer cold working on the microstructure and mechanical properties of AISI 347 samples manufactured by WAAM has been investigated. The average hardness of single-pass welding, as-deposited, and cold worked WAAM samples were 190 HV, 249 HV, and 323 HV, respectively. Inter-layer cold working has led to an increase in ultimate tensile strength from 576 MPa to 803 MPa and yield strength from 395 MPa to 697 MPa. Also, Inter-layer cold working and thermal energy due to the deposition of subsequent layers have resulted in microstructural evolution and grain refinement through recrystallization. Besides, a semi-quantitative analysis has shown that increasing the amount of cold working by four times resulted in 64 % decrease in average recrystallized grain size.

Lauryl alcohol and stearyl alcohol eutectic for cold thermal energy storage in buildings: Preparation, thermophysical studies and performance analysis

Abstract Energy storage is recognized as being of pivotal importance in development of sustainable buildings. This research focuses on exploration of a novel cold thermal energy storage material that effectively imparts thermal comfort in buildings. The newly identified eutectic phase change material (PCM) comprises of lauryl alcohol and stearyl alcohol in the composition 90:10. For enabling its use in various cooling applications, the thermophysical properties of the identified PCM requires careful examination. By Differential Scanning Calorimetry analysis, the melting point and latent heat of fusion of the new eutectic are 22.93 °C and 205.79 J g − 1, fitting the intended application. Thermal conductivity studies, thermogravimetric analysis and thermal cycling tests ascertain the material competency. The new eutectic also accounts for successful performance during its charge-discharge studies in a thermal energy storage integrated prototype test chamber. It is concluded that the developed PCM is an able material for thermal energy storage and indoor comfort in buildings.

Discharging process and performance of a portable cold thermal energy storage panel driven by embedded heat pipes

By recent interest in overcoming heat transfer limitations of phase change materials (PCMs), latent thermal energy storage devices that assisted by embedded heat pipes (HPs) have received much attentions. Due to coupling with HPs, phase change process of PCMs can be enhanced and be better managed. In this study, a cold thermal energy storage panel for portable applications that embedded HPs into PCM is investigated experimentally. An effective way to control the cold energy supply of the panel is to control air temperature and air velocity. However, air properties varied with temperature as well as layout of HPs in the airside have influence on energy supply, which is implicit to the control of the panel. Therefore, the average effectiveness-NTU method is utilized to indicate the connection between air properties to the cold energy supply performance. The model validation results show that the effectiveness-NTU technique can describe the variation of refrigeration capacity with inlet air temperature and air velocity. The calculation error of the model is below ±9.0%. This method can be used as a design tool and is expected to provide a framework for designing portable cold thermal energy storage device with manageable cold energy supply.

Numerical study of a Phase Change Material (PCM) embedded solar thermal energy operated cool store: A feasibility study

Solar energy has proved to be an ideal alternative for fossil fuels, however, due to its intermittency in availability, systems operated by solar energy face serious limitations. In this study, a simplified dynamic model is developed to investigate the behavior of a PCM-embedded cool store. The main application of this type of cool store is to be operated with a solar thermal refrigeration system to compensate for the intermittency in energy availability. 8640 kg of crops (potatoes) is considered to be stored inside the cool store along with PCM cold thermal energy storage units. 9 h of active and 15 h of inactive period are considered for 24 h operation of the refrigeration system based on the solar energy availability data. During the active period, PCM units charge, and during the inactive period, they discharge and regulate the temperature inside the cool store. It was revealed that by choosing the right properties, PCM can keep the temperature of the crops in the desired range during the inactive period of the refrigeration system. Also, it was observed that the amount of PCM used and the phase change temperature of the PCM has a significant impact on the performance of the system. The lowest temperature obtained for the crops during the inactive period of the refrigeration system is for the case with PCM to crops amount ratio of 0.026 with PCM phase change temperature of 9 °C in which the discharge process finishes around the end of the inactive period of the refrigeration.

Effect of phase separation and supercooling on the storage capacity in a commercial latent heat thermal energy storage: Experimental cycling of a salt hydrate PCM

• Experimental study of a novel latent cold storage design in a laboratory unit. • Phase separation and supercooling has been determined to cause a significant storage capacity decrease as soon as after the first cycle. • The phase separation and supercooling effects in the storage is reversible and repeatable results are presented. • A sample analysis only on material scale is not enough to predict this storage decrease. Latent heat storage technologies offer process benefits like daily peak shaving. In this work a commercial storage design for storing cold thermal energy has been studied using a laboratory prototype containing 168 kg of a commercial salt-hydrate phase change material (PCM). The storage was charged and discharged with subsequent cycles at different mass flow rates over a fixed temperature range and duration. It was found that the PCM TES design exhibits phase separation and increased supercooling with continuous cycling. Both phenomena lead to a gradual decrease of the effective storage capacity. With later cycles only the bottom part stores latent heat, while the top and middle parts of the storage remain liquid. The results were repeatable and are consistent with T-History measurements of samples from the PCM TES before and after cycling. It is likely that the PCM itself does not suffer from incongruent melting. Instead, the phase separation is likely to occur due to a segregation of different liquid phases across the height of the storage. It was found that T-History measurements alone are not able to predict this behavior. Moreover, it is shown that phase separation in the storage can be reversed by increasing the PCM temperature and mechanical mixing of the liquid phase. This phase separation has to be prevented in future work in order to achieve stable performance with the studied storage design.

Stability, thermal conductivity and supercooling behavior of novel β-CD-TiO2-Ag cooling medium-based nanofluids for eco-friendly cold thermal energy storage

The functionalized TiO2 nanoparticles(β-CD-TiO2-Ag) were manufactured and their characteristics were studied. The thermal storage characteristics of β-CD-TiO2-Ag cooling medium-based nanofluids as an innovative kind of phase change material for eco-friendly cold thermal energy systems were investigated. Dispersion stability is an important research focus for the cooling medium with nanoparticles and this research demonstrated that cooling medium-based nanofluids had good stability. The thermal conductivity of cooling medium-based nanofluids was measured, which was an evident method to improve cold thermal energy storage characteristics. The supercooling behavior of cooling medium-based nanofluids containing β-CD-TiO2-Ag, TiO2 and pure cooling medium was investigated. The experimental results showed that β-CD-TiO2-Ag nanofluids had an observably lower supercooling degree than both of the pure cooling medium and TiO2 nanofluids with the same volume fraction. Moreover, the total freezing time of β-CD-TiO2-Ag nanofluids was less than that of pure cooling medium with volume fraction increased. Supercooling degree could decrease by 63% from 14.6 °C to 5.4 °C with the addition of 0.1 vol% β-CD-TiO2-Ag nanoparticles. These promising results indicated that this research has huge potential in improving the performance of eco-friendly cold thermal energy storage systems and saving resources protecting environment.

Investigating the performance of a thermal energy storage unit with paraffin as phase change material, targeting buildings’ cooling needs: an experimental approach

Abstract For the reduction of the electricity cost for cooling buildings in hot climate zones, thermal energy storage at low temperature using phase change materials is a potential solution. The storage medium can be cooled during periods of low electricity cost and then absorb the cooling load any time of the day. In this study, an experimental cold thermal energy storage system using organic phase change materials (A9 and A14) with melting temperature of 9 or 14 °C is investigated. The system is designed for real application conditions coupled with a heat pump which cools down the organic material through the circulation of water in the pipes and fan coil units which dissipate their thermal load in the initially cooled storage medium. It comprises of a thermal energy storage tank, inside which is positioned a staggered heat exchanger with finned tubes immersed in phase change material. The results from the experiments yielded shorter process duration (for both melting and solidification) and higher heat transfer rate when the feed rate was higher. Moreover, the temperature of the water entering and exiting the tank is more than 5 °C for A9 organic material for more than half the capacity of the tank thus, using A9, the fan coil units can operate efficiently for a long time. The heat transfer rate exceeds 5 kW for 32 and 24 min using A9 and A14 respectively and the thermal load that the tank can absorb from the fan coils is above 6 kWh per tank. During the heat pump operation, A9 results to a more constant water outlet temperature over the time compared to A14 which in addition is not affected significantly by the water flow rate. Moreover, the staggered heat exchanger transfers less than 10 kW of heat when the water outlet temperature ranges between 5 and 10°C, a power value which can easily be provided by a typical commercial heat pump.

Cooling performance of a thermal energy storage-based portable box for cold chain applications

Cooling performance of a portable box integrating with phase change material (PCM)-based cold thermal energy storage (TES) modules was studied and reported in this paper. The effects of locations of the PCM modules, melting point of the PCM, and insulation materials on the cooling duration of the box were numerically investigated with an experimentally validated model. Five configurations of PCM modules inside the box were examined: Case 1 - 100 % of the PCM located at the top; Case 2 - 20 % at the top and 20 % on each of side walls; Case 3 - 25 % on each of the side walls; Case 4 - 20 % on each of the side walls and 20 % at the bottom; and Case 5 - 100 % at the bottom. Five different PCMs with melting points at 2 °C, 3 °C, 4 °C, 5 °C and 8 °C were considered. A comparison was made between two different insulation materials (polyurethane, vacuum insulated panels) on the cooling performance. It was found that the configuration of PCM modules, the PCM melting point, and the type of insulation material all affected the cooling durations. The configuration of PCM with 20 % located at the top and 20 % on each of the side walls, with the melting point at 2 °C and the vacuum insulated panel (VIP) gave the longest duration time. The maximum cooling time was up to 46.5 h with the maximum discharging efficiency at 90.7 % and the highest discharging depth at 99.4 %, offering a great potnetial for cold chain applications.

Role of metal foam on ice storage performance for a cold thermal energy storage (CTES) system

The cold thermal energy storage (CTES) is of great significance for the sake of decline of fossil energy usage. However, there exhibits a low energy charging and discharging efficiency, due to the poor thermal conductivity of phase change material (PCM). In this context, the metal foam is utilized to improve the ice storage performance of the CTES device in this paper. The solidification performance of PCM in a horizontal shell-tube CTES system with fins is numerically studied with consideration of natural convection. The ice front evolutions and the dynamic temperature distribution for the case with metal foam is analyzed and compared with these without metal foam. Moreover, the influence of the porosity on the ice storage performance for the CTES system with metal foams is analyzed as well. The results imply that the addition of metal foam effectively improves the thermal performance of the CTES system, the distribution of the temperature in the shell-tube CTES system is more uniform and the freezing speed of PCM is faster due to coupled effects of thermal conduction enhancement and the suppression of the natural convection. The porosity of the metal foam plays an essential role in the ice storage performance of the CTES system. The smaller porosity of the metal foam induces faster freezing speed and more uniform temperature distribution. Therefore, a smaller porosity is recommended for faster energy discharging rate in practical engineering applications.

Investigation of the cold thermal energy storage reefer container for cold chain application

Investigation of the cold thermal energy storage reefer container for cold chain application

Experimental Study on Phase Change Materials for Cold Energy Storage System

Cold Thermal Energy Storage (CTES) is a technology with a high potential for different cooling applications. Many previous works have investigated energy efficiency of different cold units by applying CTES systems using phase change materials (PCMs). Phase change materials (PCMs) are generally regarded as a promising material for storing thermal energy. This work presents an experimental study on phase change materials for cold storage application. The experimental process of phase-change materials is based on the following chemicals: water, propylene glycol (C₃H₈O₂), glycerin (C₃H₈O₃), parrafin oil (white oil LP-70), and sodium polyacrylate (C₃H₃NaO₂)_n. The temperature changes over time as ice charging and discharging the phase-change materials are investigated. At the same time, the work try to analyze the physical and chemical properties of the aforementioned phase-change materials. The results indicate that the discharging process of paraffin and glycol is rapid. As for water and sodium polyacrylate, the discharging time is slower than that of paraffin and glycol. And finally, for glycerin, the loading time is slowest compared to other chemicals, the discharging time is also slowest compared to the other four chemicals. This indicates that the latent heat of glycerin has high value, long melting time and deep ice storage temperature. This is a suitable material for use in cold storage systems as a phase change material.

The Effect of Heat Transfer Fluid Velocity on Heat Exchange Efficiency in Cold Energy Storage Tank: A Numerical Simulation Study

Developing a cold thermal energy storage (CTES) technology is one of the most effective methods to solve energy shortage and environmental pollution all over the world. The current study deals with the modelling and simulation of a cold thermal energy storage tank consisting of an polyvinyl chloride pipe (PVC) heat exchanger partially filled with a phase change material (PCM). Water, as the heat transfer fluid (HTF), flows through the inner tubes and the outer one while propylene glycol as the phase change material fills. This paper focuses on studying the effect of the velocity characteristics on the heat transfer efficiency of polyvinyl chloride pipe (PVC) heat exchanger in cold thermal energy storage system by the numerical simulation. In this paper, the detail of heat transfer performance within the heat exchanger is numerically solved using computational fluid dynamics (CFD), for various velocity as well as different heat transfer for optimal design. Several results of changes in the temperature field at the outlet of the cold thermal energy storage tank are presented when the inlet water velocity changes from 1 m/s to 1.4 m/s. The results indicate that low input water velocity will provide better heat exchange efficiency. However, it is required to make sure that the flow inside the heat exchanger is the turbulent flow because the study uses turbulent flow modules.

Multi-objective non-simultaneous dynamic optimal control for an ejector expansion heat pump with thermal storages

This study is to enhance the overall performances of a transcritical CO2 heat pump coupled with hot and cold thermal energy storages (HPTES) during energy charging by using a controllable ejector to replace an expansion valve (ExV) in heat pump and a new multi-objective non-simultaneous dynamic optimization strategy. A Modelica-based dynamic simulation model was developed and validated for an ejector expansion CO2 heat pump with thermal storages during charging process, and a model-based multi-objective non-simultaneous dynamic optimization strategy was proposed. Under a single-objective dynamic optimal control strategy, the overall coefficient of performance (COP) can be increased 22.0%, energy consumption can be reduced 17.3%, and charging time can be reduced significantly during charging process of thermal storages by using an ejector expansion heat pump compared to an ExV heat pump. Charging performances of the ejector HPTES system can be enhanced further by using a multi-objective non-simultaneous dynamic optimal control strategy, in which multiple transient performance parameters of the HPTES system, instead of energy consumption and cost as in the literature, were used as multi-objective functions. The mechanisms of dynamic performance enhancements of an ejector HPTES were revealed. This study would be useful for a dynamic optimal control of other coupled energy systems under unsteady conditions.

Concentrated solar energy system and cold thermal energy storage (process development and energy analysis)

The storage of refrigeration produced in the refrigeration cycle during unnecessary hours and its use during busy hours can be a good way to reduce the cost of energy consumption in the industrial. In this study, a hybrid solar driven refrigeration system using cold thermal energy storage is introduced and investigated. Water-ammonia absorption refrigeration system at a temperature of −23.5 °C is used as refrigeration system. The cycle modified for use in an integrated structure. Solar dish collectors are applied for supplying the required duty in the absorption refrigeration system generator. This integrated process is capable to produce 373.7 kW of refrigeration. Indeed, in this system, a portion of the produced refrigeration is directly used in the refrigerator during the day and another portion is stored in a phase-change material (PCM) system. Moreover, the amount of stored refrigeration in the low-temperature PCM during the night is injected into the refrigerator. In this paper, TRNSYS, HYSYS, and MATLAB software utilized for simulating of the integrated system based on the weather data of the coastal city of Bandar Abbas, Iran. Exergy analyses of the process demonstrate that solar collectors with 77.33% and HX3 with 5.07% have the most exergy destruction rate.

Supercooling characteristics of mannitol phase transition system under heterogeneous nucleation

Supercooling of phase change materials (PCMs) during solidification is a major problem in cold thermal energy storage (CTES), which reduces energy efficiency and aggravates energy waste. This study focuses on the supercooling characteristics of PCMs under heterogeneous nucleation, which provides a new idea for researching the influence of different dispersants on the supercooling degree of aqueous solution. The optimal ratios of CNTs water dispersant (TNWDIS) and polymer polyacrylic acid sodium (PAAS) to multi-walled carbon nanotubes (MWCNTs) in mannitol aqueous solution are determined through microstructure and cooling characteristics. How these two surfactants and MWCNTs with different concentrations and particle sizes influence the supercooling degree of nanofluids are investigated. The results indicate that the effect of PAAS is greater than that of TNWDIS. Furthermore, under the action of two dispersants and particle sizes of MWCNTs, the fitting equations of supercooling changing with the concentration of MWCNTs are obtained. In the light of the heterogeneous nucleation theory, with the enlargement of the particle size and the diminution of the contact angle affected by the dispersants, the interfacial free energy of heterogeneous nucleation of PCMs on the surface of nanoparticles is reduced. The supercooling degree therefore decreases. Specifically, the nucleation mechanism is deduced and analyzed through the contact angle and nucleation free energy formula.

Cold thermal energy storage with lauryl alcohol and cetyl alcohol eutectic mixture: Thermophysical studies and experimental investigation

Abstract The surging demand for thermal energy storage (TES) directs considerable attention towards the development of phase change materials (PCMs). This study has the objective to develop a eutectic PCM for effective cold thermal energy storage. The work involves preparation, thermophysical property analysis and experimental studies of a novel binary eutectic mixture. The technique of Differential Scanning Calorimetry is used in determination of thermophysical properties of the prepared eutectic. Results show that the 80:20 eutectic composition of lauryl alcohol and cetyl alcohol with melting temperature of 20.01 °C and latent heat of 191.63 J g−1 is fit for use in cold thermal energy storage. The material also proves to have good thermal conductivity. Thermal stability and reliability studies which are carried out using accelerated thermal cycling tests and thermo gravimetric analysis provide positive reports for the new mixture. An experimental investigation on the effectiveness of the identified PCM is carried out by using it in a cold storage chamber. Experimental studies report a solid improvement in cold energy containment of the PCM incorporated storage chamber resulting in considerable energy savings.

Enhancement of thermal conductivity and thermal stability of capric-lauric acid eutectic phase change material using carbonaceous materials

This paper investigates the effect of adding carbon based nano additives viz., graphene oxide (GO), multi-walled carbon nanotubes (MWCNT) and activated carbon (AC) to capric-lauric acid (CA-LA) eutectic phase change material (PCM) in order to prepare nanoenhanced PCMs (NEPCMs). Field emission scanning electron microscopy images showed that GO has a sheet, MWCNT has a tube, and AC has a sheet with porous like structures, which influence the shape stability of eutectic PCM. The CA-LA has melting and solidification temperature at 18.92 °C and 18.30 °C, corresponding latent heat values were 107.9 J g−1 and 106.8 J g−1 analyzed by differential scanning calorimetry. The addition of carbonaceous materials shows a slight decrease in the latent heat values for NEPCMs which is quashed by its improved heat transfer rate. Thermal stability of NEPCMs were studied by thermogravimetric analysis. As-prepared carbonaceous materials had excellent thermo-physical properties in that MWCNT has higher thermal conductivity compared to GO and AC due to it light weight. Therefore, NEPCMs has acceptable thermal properties which are suitable for cold thermal energy storage.

Analysis of a phase change material-based unit and of an aluminum foam/phase change material composite-based unit for cold thermal energy storage by numerical simulation

Thermal energy storage systems have increasingly attracted researchers and engineers in the last decades, not only because they permit to overcome the mismatch between thermal energy supply and demand in solar thermal systems, but also because they have the potential to improve the power grid reliability and flexibility, as they allow, for example, to store the heat or the cooling energy produced by residential electric heat pumps for a later use. In this context, this work analyses the cooling energy charging and discharging of two different cold thermal energy storage units, based on the use of a phase change material (PCM), by numerical simulation. One unit consists of an aluminum cylindrical container partially filled with a biological PCM. The other one is similar, with the only difference that it also includes an aluminum metal foam immersed in the PCM. Two different 2D axisymmetric models have been developed, both based on the effective heat capacity method in order to account for the PCM latent heat, for the numerical simulation of the two different units, and the numerical results are compared with experimental ones, obtained by means of a climatic chamber, in order to assess, in each case, the best set of the model arbitrary parameters among the considered ones. Moreover, for each simulation model, a sensitivity analysis is performed to show the effects of two arbitrary model parameters on the numerical results. Simulation results relative to the unit with only the PCM indicate that the cooling energy charging is most affected by conductive heat transfer, and in particular by the thermally resistive layer of solid PCM that forms at the lateral wall of the aluminum container, and that heat transfer by free convection plays a crucial role in the cooling energy discharging process. As concerns the unit with the PCM and the aluminum foam, numerical results show that the charging process and the discharging one are about four times and two times faster than without the foam, respectively. Furthermore, numerical results show that, with the employed aluminum foam, free convection within the PCM is negligible in both the cooling energy charging and discharging process.