Thermal Storage Tank Research Articles

Effect of phase change heat storage tank with gradient fin structure on solar energy storage: A numerical study

In this paper, the heat storage process of a latent heat thermal energy storage (LHTES) tank is studied numerically. A new type of gradient fin is added to the heat storage process in a latent heat storage tank to improve the heat transfer performance of the internal phase change material (PCM). The numerical model is verified by the experimental data. The influences of different structures on the melting rate, temperature distribution, velocity distribution, and maximum melting rate of PCM in LHTES tank are investigated, and the influence of natural convection on the energy storage system is further quantified. The results show that the melting time can be significantly reduced by 16.9% by using the four straight fins with gradient shape, and the melting time can be further reduced by 41.1% by reconstruction of the gradient fin position. The deformation in the opposite direction will slow down the melting speed and extend the melting time by more than 4.66 times. The convection criterion for judging the buoyancy convection of the melt in this paper shows that natural convection is dominant in both the upper and lower part of the melt. The closer the convection coefficient is to the overall heat transfer coefficient, the better the melting efficiency and energy efficiency will be.

Insulated concrete form foundation wall as solar thermal energy storage for Cold-Climate building heating system

Employing green energies for building energy sector decarbonization has captured the world’s attention in the current century. However, the imbalance between energy demand and availability necessitates designing reliable and cost-effective energy storage systems. The present study aims to propose an innovative building-integrated solar thermal storage method using insulated concrete form (ICF) foundation walls for residential buildings in cold climates such as that of Canada. Surplus solar thermal energy is stored inside the ICF wall, which has a high thermal capacity and mass and is integrated into the building envelope. The ICF wall and solar thermal collectors are coupled with a water-to-water heat pump to meet building space heating load and domestic hot water demand. Different configurations integrating the ICF wall are modeled and simulated in TRNSYS software to perform a yearly transient analysis. It is shown that a system with ICF walls has an 11% higher solar fraction (SF) than a similar system with a large water thermal storage tank. By replacing the solar thermal collector with a hybrid photovoltaic/thermal collector, the overall system solar fraction can increase to 20% above that of a similar system with a large water thermal storage tank system. An ICF-based system with a 16 m2 solar collector can completely cover nine months of space heating and domestic hot water load for a single-family house in London, Ontario. A detailed sensitivity analysis shows that the proposed ICF-based systems achieve an optimum solar fraction at high tilt angles (65-70°), unlike a similar design with an extensive water thermal storage tank system. Because of their ability to achieve a high SF at high tilt angles, ICF systems are suitable for vertically mounted solar systems typically required by high-rise buildings due to limited roof area. As part of the building envelope, ICF foundation walls have no additional cost and can be considered a feasible strategy for reducing the residential sector’s carbon footprint..

Impact of buoyant jet entrainment on the thermocline behavior in a single-medium thermal energy storage tank

This paper presents the characterization and management of dynamic thermocline behaviors in a single-medium thermocline (SMT) thermal energy storage tank with the aim of its performance improvement. In particular, the flow mixing induced by the entering thermal jet, its impact on the temperature stratification and its mitigation measure are systematically explored by both numerical and experimental methods. Results of CFD simulation and Particle Image Velocimetry (PIV) visualization clearly demonstrate the jet entrainment phenomenon and the typical flow patterns featured by the rising buoyant plumes. For the storage tank with simple inlet port, this thermal jet would cause the thermal overturning, the strong fluid mixing and convection heat transfer, resulting in the degradation of temperature stratification and the thermocline decay (Rigradient<0.25 at certain positions of the tank). It has also been shown by PIV measurement that the impact of thermal jet, characterized by the jet penetration length, becomes stronger with the increasing injecting flow rate and with the decreasing temperature difference between the injecting and existing fluids.Orifice baffle-type distributor has then been proposed and optimized, showing clearly its effectiveness for mitigating the impact of thermal jet on the temperature stratification. Both the initial uniform orifice baffle and the optimized orifice baffle distributors are then fabricated and installed into a lab-scale cuboid SMT storage tank. Charging operations are performed under different inlet flow rates (Qin: 0.3 to 1.5 L·min−1) and temperature differences between hot and cold fluids (∆T: 30 to 50 K). Experimental results obtained show that the optimized distributor could always lead to the better thermal performance (capacity ratio up to 0.94 and charging efficiency up to 0.8) than the initial uniform baffle distributor, providing more flexible operating conditions of the SMT storage systems in different industrial sectors.

Resurrection of carbon dioxide as refrigerant in solar thermal absorption cooling systems

The existing air conditioning and cold storage systems use conventional compressor based systems, compelling more electricity and greenhouse gasses (GHG) emissions. The incumbent cooling system uses synthetic refrigerants (CFCs, HCFC, and HFCs) that outperform natural refrigerants but are banned or under time bared permission due to their harmful effects. The global community of (196 parties till 2017) has ratified Paris Accord to limit GHG emissions and use low Global Warming Potential (GWP) refrigerants, and after the ban on existing synthetic refrigerants, quested for suitable natural working fluids and retrofitting in the existing system. Among ASHRAE envisaged natural refrigerants, CO2 has resurrected as an emerging refrigerant after the availability of high pressure technologies. The proposed design of solar assisted absorption chiller employing CO2 as a heat transfer fluid for a commercial dwelling is simulated for a dwelling in the hot and humid, moderate and sun adverse region (Lahore, 31.5204° N, 74.3587° E) to assess the thermal properties of the proposed design. A thermal storage tank with immersed heat exchangers augmented to meet the intermittency of solar energy. A solar evacuated glass tube collector (EGTC) with U-shaped copper tubes is used to collect solar heat energy. Integration of renewable energy (RE) systems is inevitable due to the persistent energy crisis and climate change situations. Solar energy is a promising source of energy abundantly available in hot areas. CO2 is a natural refrigerant that outperforms ASHRAE envisaged natural refrigerants due to the low critical point. A solar thermal cooling system employing a 35.2 kW absorption chiller driven via heat energy harnessed with EGTC using R-744 supported by an auxiliary furnace is simulated in a TRNSYS® Simulation environment. The simulated system covers the cooling requirements of a large three-room dwelling in Lahore, Pakistan. The proposed design comprises an R-744-based solar heating system combined with a hot water-fired absorption chiller. The results were dynamically simulated for the hot climate of Lahore, Pakistan, with average yearly maintained temperatures of 23 °C, 26 °C, and 21 °C for the three rooms and 0.21 solar fraction for the whole year.

Studies on enhancing the heat transfer rate of a multitemperature phase change materials-integrated thermal storage tank

ABSTRACT The thermal energy storage (TES) system operates more effectively when employing multitemperature PCMs. This research aims to increase the efficiency of TES systems. There are two types of TES in the proposed system: one is packed with a D-mannitol PCM for the capacity of 5000 kJ and referred to as a single PCM storage system. The additional systems are packed with Erythritol and Xylitol with similar capacity, and referred as multitemperature PCM system. To ensure that the numerical model values are accurate, tests are performed and verified that the findings are consistent with one another and that the percentage of fluctuation is between 4% and 6%. The findings showed that multiple-temperature PCM systems are more effective than single PCM storage systems and provide constant heat flux throughout the fluid flow passage.

An experimental study on a solar-assisted heat pump incorporated with PCM based thermal energy storage unit

Considering the storage of solar energy, which is intermittent in nature, and its usage even when it is absence, this study deals with the evaluation of thermal performance of a water-to-water heat pump (HP) system with a thermal energy storage (TES) unit integration. For this purpose, a TES unit is designed and integrated to a HP experimental rig. Different volume flow rates of the heat transfer fluid at the condenser side (V˙ = 400, 600, 800, 1000, and 1200 L/h) and water temperatures in the thermal storage tank (Tst = 35, 45, and 55 °C) were taken into account along with the consideration of phase change material (PCM). The temperature variations in the tank, total heating time, compressor operation time ratio, and coefficient of performance (COP) values are obtained from the experimental data and discussed accordingly. The results showed that the PCM inclusion can significantly improve the heating time up to 30.6% and COP up to 33.9% at Tst = 35 °C, while it can have an adverse impact at Tst = 55 °C. Besides, compressor operation time can be reduced by up to 16.5% at Tst = 35 °C, while it is increased by up to 15.7% at Tst = 55 °C. The trade-off between the sensible and latent heat storage is emphasized in the present work.

Analysis of a solar-assisted heat pump system with hybrid energy storage for space heating

Insufficient heating capacity and low coefficient of performance have always been obstacles that inhibit the application of air source heat pump systems in cold regions. This study proposes an indirect expansion solar-assisted air source heat pump system to improve the heating performance of the air source heat pump. The indirect expansion solar-assisted air source heat pump system consists of solar collectors, a hybrid thermal energy storage tank, and a dual-source heat pump. An optimized control method is proposed to tackle the refrigerant redistribution problem for the dual-source heat pump. An experiment is carried out to study the thermodynamic performance of the indirect expansion solar-assisted air source heat pump. The experimental results indicate that the average coefficient of performance of the solar heat pump mode is increased by 50.0% compared to the air source heat pump mode due to the higher evaporating temperature. Based on the experimental results, a techno-economic and environmental analysis of the indirect expansion solar-assisted air source heat pump system for space heating is conducted in six northern cities in China. The indirect expansion solar-assisted air source heat pump system has the highest annual average coefficient of performance of 2.53 in Jinan, which is increased by 18.8% compared to Harbin. The payback period of the indirect expansion solar-assisted air source heat pump system is shortest in Xining and is reduced by 53.45% compared to Jinan. Applying the IX-SAASHP system in the northwest region is suitable for improving its energy and economic performance. The analysis results indicate that the IX-SAASHP system is beneficial for reducing carbon emissions from space heating systems in the northeast region.

Optimization of capsule diameters in cascade packed-bed thermal energy storage tank with radial porosity oscillations based on genetic algorithm

The packed-bed thermal energy storage system (PBTES) has broad application prospects in renewable energy, such as for solar, hydraulics, biomass, and geothermal. This study varied the capsule diameter arrangement of the PBTES using a genetic algorithm (GA) to optimize the thermal performance of the cascaded three-layer PBTES during charging. When considering the oscillatory distribution of the radial porosity, the thermal energy storage (TES) rate density was used as an objective function to evaluate the system’s thermal performance. The TES rate density of PBTES was calculated for more than 4000 capsule diameter arrangements. The results indicate that the tank-to-capsule diameter ratio significantly affects the radial porosity distribution, velocity, and temperature distribution of PBTES. The optimal capsule diameter arrangement in the range of 15 mm ≤d≤ 40 mm was obtained as d1 = 15.58 mm, d2 = 21.78 mm, and d3 = 27.68 mm. Compared with the original model, the optimal model’s charging time was reduced by 33.90%, the TES rate density improved by 37.07%, and the cost per unit of heat storage increased by 92.41%. The results show that the GA is a powerful tool for optimizing PBTES structures.

Comprehensive thermoeconomic study of a new solar thermosyphon-assisted multigeneration system

Nowadays, due to the global energy crisis, limited reservoirs of fossil fuels, and their negative environmental effects, the use of renewable energy sources and multigeneration systems have become good alternatives for conventional thermodynamic systems. One of these resources, whose technology has developed rapidly in recent years, is the use of solar energy for the simultaneous generation of various products. Therefore, in this research, a multigeneration system with several subsystems is introduced. The proposed system includes a solar energy collector to receive thermal energy, two thermal energy storage tanks, an organic Rankine cycle, and a Kalina cycle to generate electricity, a multi-effect distillation unit to produce fresh water, an electrolyzer to produce hydrogen, as well as heat recovery for hot water and hot air generation. In this multigeneration system, the cooling unit is designed with the help of a thermosyphon. The performance of the proposed system is studied from energy, exergy, environmental, and exergoeconomic viewpoints using Aspen HYSYS and EES software. The obtained results show that due to the addition of the thermosyphon unit to the refrigeration system, the exergy efficiency increases from 55.62% to 70.26%. As a result of this combination, the performance of the whole system is improved and the amount of costs are reduced. In addition, the parabolic collector system has the highest exergy destruction ratio, 39%, among the subsystems. Furthermore, the results of the exergoeconomic analysis indicate that the PEM water heater with 33.3% and the ejector with 22.7% own the highest cost destruction rates.

Thermal performance characterization of a thermal energy storage tank with various phase change materials

Thermal performance characterization of a thermal energy storage tank with various phase change materials

Corrigendum: Optimization method of wind power consumption based on thermal storage tanks against the background of stepped carbon trading

CORRECTION article Front. Energy Res., 18 April 2023Sec. Wind Energy Volume 11 - 2023 | https://doi.org/10.3389/fenrg.2023.1186881

Effect of filling height of metal foam on improving energy storage for a thermal storage tank

Heat storage eliminates the imbalance of supply and demand for renewable energies. Metal foam holds phase change materials (PCMs) inside the porous network through both enhancing conduction and enlarging heat transfer area. To synergically utilize the buoyancy convection in the molten PCM as well as the heat conduction penetration by the porous matrix, a partially filling configuration on the metal foam was proposed to enhance the energy efficiency for the storage tank. Numerical models were established and verified by comparing with experimental results. Metal foams with five different porosities were filled in the tank, under nine filling ratios ranging from 60% to 100% in an interval of 5%. By evaluating the melting characteristics of the different cases, the influences of both the filling ratio and porosity upon the melting performance were analyzed. Results demonstrated that there existed an optimal filling ratio to maximally reduce the complete melting time, and this ratio decreased with an increase in porosity. The full melting time under a high porosity of 0.98 was the least affected by different filling ratios. However, excessively reducing the filling ratio significantly retarded the melting process regardless of the filling porosities. Upon saving 5% mass for the metal foam, a reduction of 15.7% in complete melting time was achieved. The partially filling design provided a competitive solution to thermal applications by improving the energy storage efficiency and reducing the material consumption.

Evaluation of solar thermal energy capture and storage alternatives for indirect steam generation: A case study

AbstractThis study analyzes the integration of a solar thermal plant for indirect steam generation in a typical industrial process with thermal energy requirements. Solar irradiation is computed using a validated predictive model in Santa Fe province, Argentina. Three configurations are proposed, consisting of parabolic trough collectors and thermal storage tanks. Performance indicators, such as generated energy, resulting solar fraction (the fraction of the industrial process' thermal requirements met by solar energy), and necessary solar field area, are evaluated for each configuration. A specific energy map is generated, showing the solar generation potential at each location. For required solar fractions of 20%‐25%, incorporating a thermal storage system does not provide any benefits as the solar plant does not produce enough energy to contribute to the industrial process during winter months. For required solar fractions of 30%‐35%, the resulting solar fraction can be increased to 42%‐45% with additional capture area and thermal storage capacity. For required solar fractions of 37%‐40%, the thermal storage improves the efficiency of the solar plant, resulting in a solar fraction of 50%‐60%, allowing the industrial process to receive energy for at least 6 h a day throughout the year. It is concluded that these configurations are suitable for providing a portion of the industrial process' thermal requirements.

Transient study of thermal stratification of full-scale chilled water storage tank during optimum discharge condition

Thermal stratification of full-scale Chilled Water Storage Tanks (5855 m3) with 18 m tank diameter, and 23 m water depth during discharge mode and optimum condition was studied. The experimental and numerical analyse of stratified thermal storage tank in full-scale dimension and discharge mode has been studied. A 3D and 2D numerical model was performed. The case simplified to divide into two parts, the first part was to simulate flow in pipes and radial diffuser, and the second part included simulation in the tank according to the part one results. The optimum operation condition which found from many tests of tank operation conditions according to high thermal stratification and low thermal mixing inside the tank. Validation test with experimental data obtained from the present work and literature. The results included to analyse the thermal stratification and the flow characteristics during the discharging mode. Also, thermal performance parameters such as discharge efficiency, Richardson number, stratification efficiency, thermocline thickness, the average temperature in the tank, and discharge temperature were presented. The important result of the above analysis was the optimum stratification phenomena in the tank with low thermal mixing. The contribution of this study was the numerical modelling and simulation setting to capture the experimental results of these phenomena in the full-scale thermal storage tank, moreover to specify the optimum condition of thermal stratification of this tank dimension, diffuser type, and flow rate.

The effect of conical shell and converging/diverging tube on the charging performance of shell and tube latent heat thermal energy storage system

Latent heat storage is a promising method to overcome the problem of the intermittent nature of renewable sources. However, the main challenge in utilizing phase change materials is their poor thermal conductivity which leads to the slow charging and discharging of latent heat thermal energy storage tanks. Geometric optimization is a passive method to enhance the charging and discharging rate. In this paper, the geometric optimization of a shell and tube storage tank is studied numerically. Different configurations, including conical shell and tube, cylindrical shell and diffuser, cylindrical shell and nozzle, and a combination of conical shell and diffuser with different tilting angles is investigated. The height of all cases is assumed to be a constant number. The melting process is modeled by the enthalpy-porosity method, and the Boussinesq approximation is employed to consider the effect of natural convection. The governing equations are solved by a spatially and temporally second-order finite volume method. It is found that the main determining parameter is the cross-sectional area ratio of the phase change material at the top to its value at the bottom of the tank. By increasing this ratio, the effect of conductive heat transfer is attenuated, but natural convection is augmented. Since the charging rate is affected by these two heat transfer mechanisms, an optimum value of around 10 is obtained for this shape factor which results in an increased storage rate of 25 % compared to the case of cylindrical shell and tube storage tank. The optimum shape factor can be obtained either by a conical shell and tube or by combining a conical shell and a diffuser.

Determination of Thermocline Heat Transfer Coefficient by Using CFD Simulation

This article deals with a thermal energy storage system in the form of a water tank with a thermocline. The well-known thermocline phenomenon is modeled using computational fluid dynamics (CFD). However, the reservoir model proposed in this article is zero-dimensional. This is due to the fact that the aim of this article is to build a mathematical model that will be more useful in mathematical models of complex energy systems in which a hot water tank is one of many elements of the system. In such a zero-dimensional mathematical model, the hot water tank will be modeled using equations describing heat transfer, and the thermocline itself will be treated as a heat transfer surface with known dimensions and heat transfer coefficient. A novelty of this paper is that it addresses heat loss across the thermocline as defined in this manner. A CFD model of a thermal storage tank is created, validated with available experimental data, and used to obtain the heat transfer coefficient U. The resulting value is then analyzed quantitatively and qualitatively and the changes in the thickness of the thermocline are accounted for in the equation. The results from this groundbreaking work can be used to analyze heat storage in the form of thermocline water tanks at the level of system modeling, e.g., for the purpose of configuring the structure of other devices and control systems.

Multicriteria Analysis of a Solar-Assisted Space Heating Unit with a High-Temperature Heat Pump for the Greek Climate Conditions

The goal of this investigation is the thorough analysis and optimization of a solar-assisted heat pump heating unit for covering the space heating demand for a building in Athens, Greece. The novelty of the studied system is the use of a high-temperature heat pump that can operate with radiative terminal units, leading to high thermal comfort standards. The examined system includes flat-plate solar thermal collectors, an insulated thermal storage tank, auxiliary electrical thermal resistance in the tank and a high-temperature heat pump. The economic optimization indicates that the optimal design includes 35 m2 of solar thermal collectors connected with a storage tank of 2 m3 for facing the total heating demand of 6785 kWh. In this case, the life cycle cost was calculated at 22,694 EUR, the seasonal system coefficient of performance at 2.95 and the mean solar thermal efficiency at 31.60%. On the other hand, the multi-objective optimization indicates the optimum design is the selection of 50 m2 of solar field connected to a thermal tank of 3 m3. In this scenario, the life cycle cost was calculated at 24,084 EUR, the seasonal system coefficient of performance at 4.07 and the mean solar thermal efficiency at 25.33%.

An analytical study on transient thermal behavior of a packed-bed molten salt thermocline thermal storage

A volume averaged set of the governing equations for local thermal non-equilibrium fluid saturated porous media was applied to study transient thermal behavior of convection and conduction within a packed-bed thermocline thermal storage tank. General analytical expressions, which agree well with numerical results, were derived for the prediction of transient temperature fields of molten salt and granulated material. Three important dimensionless parameters, namely, the solid fluid heat capacity ratio, interstitial Stanton number and Peclet number based on the effective thermal diffusivity, are identified to investigate their effects on the thermal response of the packed-bed thermocline thermal storage tank. An explicit analytical expression for the effective discharging efficiency has been derived as a function of the three important dimensionless parameters. The expression may serve as a powerful tool to design a packed-bed thermocline thermal storage tank according to required operational conditions.

Performance evaluation of external compound parabolic concentrator integrated with thermal storage tank for domestic solar refrigeration system.

The aim of this research was to develop a model for a solar refrigeration system (SRS) that utilizes an External Compound Parabolic Collector and a thermal energy storage system (TESS) for solar water heating in Chennai, India. The system parameters were optimized using TRNSYS software by varying factors such as collector area, mass flow rate of heat transfer fluid, and storage system volume and height. The resulting optimized system was found to meet 80% of hot water requirements for the application on an annual basis, with an annual collector energy efficiency of 58% and an annual TESS exergy efficiency of 64% for a discharge period of 6h per day. In addition, the thermal performance of 3.5kW SRS was studied by connecting it to an optimized solar water heating system (SWHS). The system was found to generate an average cooling energy of 12.26MJ/h annually, with a coefficient of performance of 0.59. By demonstrating the ability to efficiently generate both hot water and cooling energy, the results of this study indicate the potential for utilizing a SWHS in combination with STST and SRS. The optimization of system parameters and the use of exergy analysis provide valuable insights into the thermal behavior and performance of the system, which can inform future designs and improve the overall efficiency of similar systems.

Experimental validation of a solar system based on hybrid photovoltaic-thermal collectors and a reversible heat pump for the energy provision in non-residential buildings

This work aims to validate a transient model of a solar hybrid pilot plant based on photovoltaic-thermal (PV-T) collectors integrated via thermal storage tanks with an air-to-water reversible heat pump (rev-HP). The pilot plant is in operation and provides space heating, cooling, domestic hot water (DHW) and electricity to an industrial building located in Zaragoza (Spain). The plant consists of eight uncovered PV-T collectors (2.6 kWe, 13.6 m2), two water tanks and a rev-HP with a nominal thermal power of 16 kW for heating and 10.5 kW for cooling. The validation results show that the transient model fits the experimental performance of the PV-T collectors, with an average error of -16% and 3%, for the thermal and electrical generation respectively. The accuracy of the estimated rev-HP performance depends on the operation mode. The estimated COP in cooling mode has an average error of 14%, while in heating mode has an average error of -10%. The results show that the integration of the thermal and electrical generation of the PV-T collectors with a high-performance rev-HP allows the solar PV-T system to be self-sufficient to satisfy the building energy demand.