Heat Storage Medium Research Articles

Transient Thermo-mechanical analysis of a shell and tube latent heat thermal energy storage for CSP plants

The structural integrity of a lab-scale shell and tube latent heat thermal energy storage under transient conditions was investigated. The system was designed to use sodium at 750 °C as a heat transfer fluid with a high temperature phase change material, melting at 705.8 °C, as the heat storage medium. Stainless steel 347H (SS347H) was used as the tube and shell material. One quarter of the lab-scale system was used for the CFD model (using ANSYS Fluent) while a temperature profile was generated from the CFD modelling which was then linked to the validated ANSYS FEA model. The operating pressure of the system was below 1 bar, therefore, the thermally induced stress–strain due to high temperature gradient (up to 100 K) was the determining factor. The difference between the thermal expansion coefficient of the PCM and metal tubes was found to be of lesser influence as the ullage area provided sufficient space for expansion of the PCM. In the case of 50 K temperature gradients, a thermoelastic analysis showed that the maximum equivalent stress is approximately 106 MPa, which is below the allowable design stress for SS347H. However, the maximum equivalent stress under the 100 K temperature difference was 250 MPa, well above the allowable stress. Therefore, the structural integrity of the system is sound under transient operating conditions within a 50 K temperature gradient for 1000 h. Furthermore, an elastic–plastic (bilinear) analysis showed similar results for operation within a temperature difference of 50 K, however, a lower equivalent stress of 140 MPa for 100 K. Therefore, operation under a higher temperature gradient of up to 100 K is possible considering plastic strain and deformation while the system is reasonably protected against creep failure during the first 1000 h of operation. The current study provides new knowledge and insight into the structural integrity of a shell and tube system, in particular a system using an austenitic steel material, under high operating temperature which can assist in the design of a cost-effective latent heat thermal energy storage system.

Development and assessment of a solar driven trigeneration system with storage for electricity, ammonia and fresh water production

This research paper designs and analyzes a novel integrated solar-driven system for ammonia synthesis, freshwater production and power generation. The trigeneration system contains a solar thermal subsystem, a thermal energy storage system where the molten salt is used as a heat transfer fluid and storage medium, a solar energy-driven Rankine cycle, a multistage flash distillation, a proton exchange membrane electrolyser array, and an ammonia synthesis unit. The proposed integrated system uses solar energy to charge the molten salt, which flows through a heat exchanger and generates steam for the topping cycle. The exhaust stream of the steam turbine provides heat for the multistage flash distillation (MFD) process. A 20 stage MFD unit is proposed where the seawater is utilized as the feedwater in this study. A portion of the produced freshwater is sent to the PEM electroylzer array for hydrogen production, which is used for ammonia production via the Haber-Bosch process. The thermodynamic analysis of the solar driven multigeneration system is analyzed through the Engineering Equation Solver (EES) and Aspen Plus software packages. The novelty of this study relies on the development of a new solar energy-based integrated system and its application for a selected community with over 10,000 residents to meet all of their needs to be self-sufficient and sustainable. Ammonia (for multiple purposes, such as fuel, energy carrier and feedstock), freshwater and electricity are the useful outputs as targeted in this paper. The study incorporates the phase change materials into the system for thermal energy storage purposes. The performance assessments based on energy and exergy efficiencies are carried out for the overall system and its components. Furthermore, the power, freshwater and ammonia production capacities are studied for better demand coverage. The overall exergy efficiency of the system is determined as 12.1 %, where the ammonia synthesis, power generation, and freshwater production capacities are 0.85 kg/s, 17.6 MW, and 143.97 kg/h respectively. Moreover, the study investigates the energy and exergy efficiencies with and without the presence of an air separation unit. The study results show that the air separation unit has less than 0.3% effect on the overall energy and exergy efficiencies.

Performance and economy of trigenerative adiabatic compressed air energy storage system based on multi-parameter analysis

The trigeneration combined the electricity, cooling and heating makes adiabatic compressed air energy storage system (ACAES) popular as an energy storage technology. Based on thermodynamic analysis, this paper studies the influence on the system performance of four variable factors, including compression stages, expansion stages, water (heat storage medium) mass flow rates in charging process and discharging process to provide a guidance for the design of ACAES for different user demand. The results show that changing these four factors can achieve different energy output distributions in a very wide range (power supply ratio is 0.50–0.86, heating output ratio is 0.00–0.39, cooling supply ratio is 0.00–0.41). Simulation results also indicate that fewer compression and expansion stages are suggested for the cases requiring shorter running time. Furthermore, according to this study, less compression stages than expansion is good for electricity generation and more compression stages is good for cooling supply. And for large heating supply demand, less compression is suggest. Besides, the energy efficiencies for different configurations of trigenerative ACAES are also achieved which are changed from 0.62 to 0.87 and the best configurations with highest system efficiency are also presented. Finally, by economic analysis, the most economic condition is achieved.

Nanosized n-tetracosane as heat storage media: adjustable phase transition temperature and thermal property

Nanosized n-tetracosane as heat storage media: adjustable phase transition temperature and thermal property

Development and Characterization of Concrete/PCM/Diatomite Composites for Thermal Energy Storage in CSP/CST Applications

Thermal energy storage (TES) systems for concentrated solar power plants are essential for the convenience of renewable energy sources in terms of energy dispatchability, economical aspects and their larger use. TES systems based on the use of concrete have been demonstrated to possess good heat exchange characteristics, wide availability of the heat storage medium and low cost. Therefore, the purpose of this work was the development and characterization of a new concrete-based heat storage material containing a concrete mix capable of operating at medium–high temperatures with improved performance. In this work, a small amount of shape-stabilized phase change material (PCM) was included, thus developing a new material capable of storing energy both as sensible and latent heat. This material was therefore characterized thermally and mechanically and showed increased thermal properties such as stored energy density (up to +7%, with a temperature difference of 100 °C at an average operating temperature of 250 °C) when 5 wt% of PCM was added. By taking advantage of these characteristics, particularly the higher energy density, thermal energy storage systems that are more compact and economically feasible can be built to operate within a temperature range of approximately 150–350 °C with a reduction, compared to a concrete-only based thermal energy storage system, of approximately 7% for the required volume and cost.

Thermal and electrical performance analysis of induction heating based‐thermochemical reactor for heat storage integration into power systems

In this study, the thermal and electrical performance analysis of an induction heating based-thermochemical reactor is investigated for high-temperature heat storage. The induction-heating model is built with Maxwell equations, and the surface-to-surface (S2S) radiation model is used for the induced and diffused thermal energy flow transport in the fluid phase within the reactor inner cavity. The effects of operating and structural parameters in terms of the coil turn number, coil current intensity and frequency, the conductive plate, and the coil's relative permeability, electrical conductivity, and emissivity could affect the heat generation, input power demand, and energy consumption of the proposed reactor performance are sufficiently investigated. It is found that the reactor temperature distribution resulted from the homogenized multi-turn coil magnetomotive force and frequency with the current intensity 48% more effective in reaching the desired temperature at the heat storage medium. However, the conductive plate relative permeability, electrical conductivity, and surface emissivity significantly affect the induction heating system's thermal power, with the relative permeability having the highest impact of 13% in the storage medium's temperature increasing at low current intensity. Moreover, the surface emissivity shows remarkable effects when the inducting heating operates at a high current. Significant energy consumption, more than 159%, is observed when the induction heating generator operates at steady-state mode. The reactor heating region temperature increases when the reactor operating current and frequency get high. It is observed that the more the induced heat was applied to the reactor, the more the reactor is heating up to a steady-state. The instantaneous temperature distribution inside the reactor depicted the rise in the temperature is caused by convection and radiation heat transfer. Higher and more uniform temperature distribution inside the reactor is obtained by optimizing the reactor operating and structural parameters.

Optimum selection of phase change material for solar box cooker integrated with thermal energy storage unit using multi-criteria decision-making technique

Various thermal energy storage (TES) materials are used to increase the efficacy of solar cooker in off-sun hours. For the past few decades, phase change materials (PCMs) used as heat storage medium have become research interest. Selection of optimum PCM is important for the effective and efficient heat storage. Therefore, the main objective of the current study is to select the optimum PCM among the alternatives to be used for TES unit incorporated in solar box cooker (SBC). The PCMs are pre-screened among the alternatives used in earlier works based on the melting temperature. The optimum PCM is then selected with the aid of different multi-criteria decision -making (MCDM) techniques like TOPSIS, EDAS and MOORA. The criteria weights required for the optimization algorithm is found by using AHP, ENTROPY and CRITIC methods. Also, compromised values between the weights obtained through these methods are computed. The optimization algorithms are solved using MATLAB. The results of all MCDM techniques show that erythritol is the best alternative for the TES medium incorporated in the SBC. Further, the optimum mass of PCM and dimensions of the TES unit required for the SBC to operate during sun down hours for some specific duration is calculated by using a simple iterative solver developed with MATLAB. There is good agreement between the computational procedure and experimental study using paraffin wax as the TES medium. The iterative solution procedure also selects erythritol to be the best alternative as it required lesser quantity compared with other PCMs. Therefore, we recommend erythritol as the best PCM for the SBC incorporated with TES unit.

PENINGKATAN KAPASITAS TERMAL PENAMPUNG AIR PANAS SOLAR HEATER MENGGUNAKAN CAPSULATED PARAFFIN

Solar power is considered as the most essential renewable energy in human life, particularly for daily activities. The application of solar water heater is significantly able to reduce the electric load of water heating so that this method is indirectly able to save energy needs. The biggest challenge is increasing the energy density of warm water storage. The best storage medium is paraffin, but it is constrained by the low thermal conductivity of the paraffin and also the wrapping media. This study focuses on efforts to improve thermal conductivity of paraffin as a heat storage medium by using nickel mixture at a ratio (volume) of 10 - 50%. Samples of paraffin and nickel paraffin mixture are inserted into the wrapper of aluminum 6063 material and then tested for heat absorption and release process. The best heat absorption is shown by the sample with the most nickel content, while in the heat release process the best performing sample is shown with a nickel mixture between 20–40%. These results are directly related to the power rate of each sample. The results of this study can be used as a reference for increasing the thermal capacity of warm water storage from solar water heaters.

Comparative study on high temperature thermal stability of quaternary nitrate-nitrite mixed salt and Solar salt

Molten salts are applied in solar thermal power plant as heat transfer and heat storage medium. In this work, the thermal stability of quaternary nitrate-nitrite (QNN) mixed salt and Solar salt are studied under three constant temperature conditions (500 °C, 565 °C, 600 °C) for 1008h. The results show that the mass ratio of N O 2 − 1 / N O 3 − 1 plays an important role in the thermal physical properties of nitrite/nitrate molten salt. The mass ratio of N O 2 − 1 / N O 3 − 1 in Solar salt increases with the increasing of working temperature, which results in the decreasing of melting point and initial crystal temperature and the increasing of decomposition temperature. The average values of melting point and initial crystal temperature of QNN mixed salt are maximum 119 °C and 24 °C lower than that of Solar salt. Meanwhile, the maximum increase of average values of specific heat and thermal conductivity of QNN mixed salt are 14.26%, 8.18% compared with its base salt, respectively. When the working temperature is higher than decomposition temperature, average values of specific heat and thermal conductivity of Solar salt decrease because of the acceleration of nitrite formation. The viscosity values of QNN mixed salt and Solar salt decrease with the increasing of temperature. Based on the comparative analysis, QNN mixed salt has good application value in practical engineering applications. • The long-time thermal stability of QNN mixed salt and Solar salt are studied. • Nitrite/nitrate ratio plays an vital role in molten salt thermal physical property. • The thermal physical performance of QNN mixed salt is better than Solar salt.

Numerical simulation of the performance of passive and active solar still with corrugated absorber surface as heat storage medium for sustainable solar desalination technology

Groundwater is the most important and valuable water resource in arid and semi-arid regions. Nevertheless, the high salinity of these resources remains the major constraint. To remedy this problem, the present study aims to investigate and develop a novel sustainable solar desalination technology. A passive and active single slope solar still, combined with phase change material (PCM) for the thermal energy storage system, have been numerically modeled and simulated. The active system has been made by coupling passive solar still with a parabolic trough collector (PTC) via a heat exchanger, as an external heat source. For each desalination system, a flat absorber and others with corrugated surfaces (rectangular, triangular, and spherical) were tested to compare their performances and the effect of absorber shape on both passive and active systems. Conservation equations of the two models were solved using Comsol Multiphysics software. Simulation results showed that for the passive system the corrugated surface with rectangular ripples increases pure water productivity by 109% and 42% by comparison with the conventional distiller, and the distiller with an absorber of flatform with storage system, respectively. Furthermore, it was revealed that solar still integrated with PTC and modified by different absorber geometry has higher freshwater productivity of 15.39 and 15.01 kg/m2/day compared to 2.37 and 2.11 kg/m2/day for the passive still by using rectangular and spherical absorbers respectively. Consequently, the percentage improvement of the developed active system is about 549.36% and 611.37% respectively. From this investigation, it is observed that the passive solar still with rectangular absorber is the most suitable for household use; however, by coupling PTC to the modified passive solar still with rectangular absorber configuration, we have the appropriate design for industrial applications such as hospitals, irrigation processes for agricultural greenhouses in arid and semi arid regions.

Distributed Thermal Energy Storage Configuration of an Urban Electric and Heat Integrated Energy System Considering Medium Temperature Characteristics

Distributed thermal energy storage (DTES) provides specific opportunities to realize the sustainable and economic operation of urban electric heat integrated energy systems (UEHIES). However, the construction of the theory of the model and the configuration method of thermal storage for distributed application are still challenging. This paper analyzes the heat absorption and release process between the DTES internal heat storage medium and the heat network transfer medium, refines the relationship between heat transfer power and temperature characteristics, and establishes a water thermal energy storage and electric heater phase change thermal energy storage model, considering medium temperature characteristics. Combined with the temperature transmission delay characteristics of a heat network, a two-stage optimal configuration model of DTES for UEHIES is proposed. The results show that considering the temperature characteristics in the configuration method can accurately reflect the performance of DTES, enhance wind power utilization, improve the operation efficiency of energy equipment, and reduce the cost of the system.

Transient simulation and thermodynamic analysis of pumped thermal electricity storage based on packed-bed latent heat/cold stores

Pumped thermal electricity storage is a promising large-scale electricity storage technology that uses thermodynamic cycles and thermal energy storage to achieve electricity storage and release. At present, for pumped thermal electricity storage based on the Joule-Brayton cycle, packed beds filled with sensible heat storage media are widely adopted as the thermal store, while they usually suffer from low energy storage densities and large volumes. In this paper, the thermodynamic feasibility of packed-bed latent heat/cold stores is explored to replace the packed-bed sensible heat/cold stores in pumped thermal electricity storage. A numerical model of a 10.5 MW/5 h storage system based on packed-bed latent heat/cold stores is established. The energy and exergy analysis of components is carried out. The effect of compression ratios, porosities, isentropic efficiencies, and inlet velocities on the systematic thermodynamic performance is investigated and optimal conditions are also investigated. It is concluded that the energy storage density of the system increases from 232.5 kWh/m3 to 245.4 kWh/m3 when packed-bed sensible heat/cold stores are replaced by latent ones. Furthermore, the power density of the system based on packed-bed latent heat/cold stores is 216.5 kW/m3, and the round-trip efficiency reaches 84.7%, which is competitive in large-scale electricity storage technologies.

Thermal properties of KCl–MgCl2 eutectic salt for high-temperature heat transfer and thermal storage system

Molten chloride salt is recognized as a promising heat transfer and storage medium in concentrating solar power (CSP) in recent years, but there is a serious lack for thermal property data of molten chloride salts under high-temperature condition. In this work, temperature and component dependence of local structure and physical properties for binary KCl–MgCl2 mixture were computed by molecular dynamics simulations (MD) method based on Born–Mayer–Huggins (BMH) potential. As the temperature rises, the distances between ions change and the structures turn into loose state, thus the density, thermal conductivity and the shear viscosity decrease, which also agree well with the experimental results. The calculation errors of thermal properties are mainly within 8%. The results show that density and thermal conductivity have negative linear correlation with temperature. Specific heat capacity is invariant with temperature at a constant pressure. When K+ increases in the salt, thermal conductivity is significantly improved, and shear viscosity and specific heat capacity decrease. The formulas of temperature-thermal properties-component correlations are obtained, which provide the fundamental property database for the precise design of high-temperature thermal storage system.

Design and Energy Analysis of a Solar Desiccant Evaporative Cooling System with Built-In Daily Energy Storage

Heat storage with thermochemical (TC) materials is a promising technology for solar energy storage. In this paper, a solar-driven desiccant evaporative cooling (DEC) system for air-conditioning is proposed, which converts solar heat energy into cooling with built-in daily storage. The system utilises thermochemical heat storage along with the DEC technology in a unique way. Magnesium Chloride (MgCl2·6H2O) has been used, which serves as both a desiccant and a thermochemical heat storage medium. The system has been designed for the subtropical climate of Lahore, Pakistan, for a bedroom with 8 h of cooling requirements during the night. MATLAB has been employed for modelling the system. The simulation results show that 57 kg of magnesium chloride is sufficient to meet 98.8% of cooling demand for the entire month of July at an elevated cooling requirement. It was found that the cooling output of the system increased with increasing heat exchanger effectiveness. The heat exchangers’ effectiveness was increased from 0.7 to 0.8, with the solar fraction increased from 70.4% to 82.44%. The cooled air supplied to the building meets the fresh air requirements for proper ventilation.

A novel thermal storage integrated evacuated tube heat pipe solar air heater: Energy, exergy, economic and environmental impact analysis

This study aims to present a novel thermal energy storage integrated evacuated tube heat pipe solar air heater suitable for high-temperature applications. A new heat pipe arrangement was introduced in this study by attaching all the evaporator tubes of heat pipes to a common condenser section. A thermal energy storage medium was kept in a chamber within the common condenser unit of the heat pipe to obtain uniform outlet air temperature from the system when there is fluctuation in solar radiation. Therminol 55 was used as the sensible heat storage medium in the system. The Performance evaluation of the system was conducted by varying four airflow rates 0.03 kg/s, 0.1 kg/s, 0.2 kg/s and 0.3 kg/s, respectively. 0.03 kg/s resulted in a maximum outlet air temperature of 128 °C and the system delivered more than 100 °C of hot air until 10 h of operation. The maximum thermal and exergy efficiency obtained during each airflow rate was 38%, 77%, 85%, 89%, and 5.01%, 5.21%, 5.34%, and 5.76% respectively. An average of 6200 kJ energy was collected by the present system during its operation. The total money saved per month during the operation of TS-ETHPSD was 445 INR. The Payback Period for the system is 69 months. The solar air heater can be considered as an environment-friendly device as it can save 73 kg/month of Co2 from entering the atmosphere.

Enhancing the Productivity of Tubular Solar Still by Using the Phase Change Material

In this article, a theoretical simulation of a modified tubular solar still (TSS) integrated with a rectangular basin painted black color was investigated. The simulation was conducted out using a 2-dimensional computational fluid dynamics by COMSOL metaphysics software. The two different types of phase change materials- PCMs have been used as a heat storage medium; paraffin wax and stearic acid. Influence of several parameters PCM mass, solar radiation, wind speed and temperature environment (ambient temperature) was studied. Therefore, a set of numerical simulations were displayed out to study the effect of heat transfer within the TSS. A series of this analysis in various real weather conditions (Najaf, latitude = 32° 1′ 38.55″ N, longitude = 44° 19′ 59.22″ E) on the TSS with seven PCM layers having a different thickness (tPCM = 5, 10, 20, 30, 40, 50 and 60 mm) were performed. The simulation results indicate that within the daytime, a more applicably performance of TSS was achieved with 40 mm PCM (2.664 kg of paraffin wax or 3.143 kg of stearic acid) compared to TSS without PCM. They are shown that the proposed solar system with PCM is significantly better due to thermal loss reduction. In general, the system including paraffin wax is most effective with or without stearic acid. The results of the analytical simulation were validated with experimental field results. It was found a good agreement between the numerical data obtained, and the experimental data have been obtained (rMBE = 0.022).

Energy and exergy analyses of drying medicinal herb in a novel forced convection solar dryer integrated with SHSM and PCM

This article examined the performance of a low cost, economically viable and a novel forced convection solar drying system. To control the thermal fluctuations during the day-night drying process, solar air collector (SAC) was equipped with sensible heat storage medium (SHSM) while, drying unit contained paraffin RT-42 as a thermal energy storage (TES) medium. The experiment was conducted considering a sample size of 9.0 kg of Valerian rhizomes. The rhizomes were dehydrated to saturation value of 9% from preliminary moisture content of 89% on wet basis and took 120 (216) hours with (without) use of TES. The performance evaluation of each element of the dehydrating system was carried out on the basis of energy and exergy analyses. The mean values of energy and exergy efficiencies of SAC without (with) TES were computed to be 9.8(26.10) % and 0.14(0.81) % respectively. The overall drying rate without (with) applying TES was 0.028(0.051) kg/hour. The exergy efficiency of the drying unit was assessed to vary from 3.7% to 75.15% with a mean value of 30.28%. The specific energy consumption (SEC) of the rhizomes and the overall efficiency of the drying system were 11.33 kWh/ kg of moisture and 10.53%, respectively.

Supervisory model predictive control for combined electrical and thermal supply with multiple sources and storages

We present the design, implementation, and experimental validation of a supervisory model predictive control approach for the simultaneous optimization of thermal and electrical building energy supplies. The system comprises a heat pump, a photovoltaic system, an electric battery, and a thermal storage tank. The system uses a phase change slurry as both the heat storage and heat transfer medium, which, beyond an increased storage capacity, results in an improved performance of the heat pump and an increased load-shifting potential. In contrast to approaches that use volumetric flow rates as inputs, the supervisory model predictive control used here determines optimal energy flows. As a result, the online optimization problems do not require impractical computational power in spite of the system complexity. We show the control can be implemented on low-cost embedded hardware and validate it with an experimental demonstrator comprising an installation of the complete supply system, including all hydraulic and all electrical components. Experimental results demonstrate the feasibility of both, the heat pump based heating system with a phase change slurry, and the optimal control approach. The main control objectives, i.e., thermal comfort and maximum self-consumption of solar energy, can be met. In addition, the system and its controller provide a load shifting potential.

Research on Temperature Distribution of Single Tank Using Molten Salt for Thermal Storage

The temperature distribution of the storage tank with molten salt as the heat storage medium during the discharge process is introduced in the article. In order to analyze the temperature distribution of molten salt in a storage tank and improve the heat exchange effect, the exothermic process of a single thermal storage tank equipped with an immersion heat exchanger was studied. Fluent software was used in the analysis to study the influence of different heat transfer areas, structures and layouts on temperature distribution by means of numerical simulation. The results show that if the heat exchange area is increased, the temperature uniformity and heat transfer speed in the tank will strengthen. By reducing the tube diameter of heat exchanger, the temperature difference in the axial direction can be reduced. When the heat exchanger is arranged above, the temperature stratification in the tank will be improved, and the heat exchange will be more sufficient.

Performance Analysis of Photovoltaic Passive Heat Storage System with Microencapsulated Paraffin Wax for Thermoelectric Generation

The depletion of non-renewable energy sources and negative effects towards the environment push research towards the widespread adoption of renewable energy sources such as solar energy. The main drawback of solar panels is that temperatures above 27°C will result in an efficiency drop of 0.1-0.5%/°C. In previous studies, usage of photovoltaic thermal (PVT) systems was mainly for the purpose of heating water, warming buildings, and drying crops. This research will focus on the usage of a standalone PVT and thermoelectric generator (TEG) system whereby it uses heat extracted from the PVT system for thermoelectric generation. A passive standalone PVT-TEG system design with microencapsulated paraffin wax as a phase change material (PCM) as a heat storage medium was created. The heat stored in the PCM is used as a heat source for thermoelectric generation. To extract the heat from the PV panel, an aluminum heatsink underneath the PV panel is used as a heat absorber to passively extract heat without external power sources. This setup reduces the surface temperature by 22.7°C. Transient thermal analysis and thermoelectric simulation of the system was conducted through Computational Fluid Dynamics (CFD) using ANSYS 2019 software. The error recorded between the experimental and simulation results was 4.2%. This proposed system panel successfully increased the electrical efficiency of the PV panel by approximately 12.8%, where the overall electrical power produced shows a significant increase from 7.7W to 17.7W.