Thermal Energy Storage Tank Research Articles

Experimental and computational analysis of packed-bed thermal energy storage tank designed for adiabatic compressed air energy storage system

The growing importance of decarbonization and renewable energy sources to national power systems has brought about a need to implement large-scale energy storage technology. Adiabatic Compressed Air Energy Storage (A-CAES) systems comport with the environmental requirements of renewable energy storage better than traditional CAES systems because they eliminate the combustion of auxiliary fuel during discharge. This benefit is achieved with a Thermal Energy Storage (TES) tank that heats up during the air compression step, stores the thermal energy, and then releases it during discharge by heating the expanding air. This process increases the overall energy efficiency of the A-CAES system since a large portion of the heat of compression is used rather than lost. The subject of this paper is an experimental and numerical study of a slender basalt-filled TES tank designed for installation in decommissioned mine shafts. Storing energy in such otherwise unused, already depreciated infrastructure represents a unique application and economic opportunity for highly urbanized industrial areas. Situating A-CAES systems in mine shafts also significantly reduces their cost due to natural stress compensation from high air pressure. The slenderness of the reservoir compared to existing and previously studied systems has a positive effect on the efficiency of heat storage in the basalt due to the reduced heat conduction field, but results in a greater pressure drop of the flowing air. To investigate the performance of the TES storage tank, a laboratory bench was constructed with basalt grit as the accumulation material. The experimental results obtained were used to verify the numerical model used in ANSYS Fluent. The numerical model showed a theory–experiment discrepancy in the basalt temperature rise results of only 1.91% for the entire curves and 2.29% for the most intense temperature rise phase, and the difference between the pressure drop results did not exceed 4%. The flexibility of the numerical model was tested for various input parameters. A high level of model validation was achieved by selecting an accurate correlation for the Nusselt number, as well as implementation of temperature-dependent thermodynamic parameters for the storage material.

Evaluation of the energy potential of an adiabatic compressed air energy storage system based on a novel thermal energy storage system in a post mining shaft

The paper describes an energy storage system that uses compressed air and thermal energy storage, enabling installation in a post-exploitation mine shaft. The paper presents the concept and construction of thermal energy and compressed air hybrid storage system. Storage potential and effectiveness of the compressed air energy storage (CAES) system are demonstrated. The main motivation for undertaking the research was to manage post-mining infrastructure, especially in highly urbanized areas, and to propose a system to compensate for power fluctuations in the power system. The analyzed system includes a two-section air compressor, one compressed air reservoir with built-in two-section thermal energy system and a two-section air expander. The proposed energy storage system uses a post-mine shaft with a volume of about 60,000 m3 and the proposed thermal energy and compressed air storage system can be characterized by energy capacities of 140 MWh at a moderate pressure of 5 MPa. Important features of the system that determine high values of electric energy storage efficiency, in excess of 70 %, are identified. A numerical investigation of the Thermal Energy Storage (TES) tank supported by experimental studies is also presented, and the energy efficiency of the TES was calculated to be 95 %. This paper provides a detailed description of the concept, discusses its advantages and limitations, and highlights areas for future research.

Experimental investigation of heat dispatch controllability through simultaneous charging-discharging and stand-alone discharging operations in vertical cylindrical sensible heat storage tank

Using a vertical cylindrical thermal energy storage (TES) tank with helical discharging coil fitted inside, the present study experimentally investigates the scarcely studied simultaneous charging and discharging (SCAD) mode, as well as the discharging-alone operation following a substantial stand-alone period. The temperature distributions within the tank, coil outlet temperature and primary thermocline thickness serve as the key performance trackers for the storage tank. The primary thermocline thickness increases with increasing coil side flow rate during the SCAD operation. The SCAD operation exhibited the splitting of the primary thermocline, leading to the formation of a secondary thermocline in the lower half of the tank. The sustenance of secondary thermocline, thermal gradients across the tank height, and the discharging efficiency are found to decrease with increasing charging flow rate, whereas the coil outlet temperature and the primary thermocline thickness increase. The highest average discharging efficiency of 80.1 % is observed for the TES charging at 0.5 L/min at 70 °C, accompanied by the 2 L/min discharging flow rate. The average thermal energy stored is the maximum (1758 kJ) for the TES charging at 1.25 L/min at 70 °C, with discharging rate of 0.5 L/min. The stand-alone period prior to the discharging-alone operation exhibits the heat content retention capability of the storage and allows for the thermocline formation. The time required for thermal stratification is more with the higher initial charging temperature. The time required for the complete discharging of the TES storage tank decreases with increasing coil-side flow rate. These modes provide ample operational flexibility and heat content dispatch controllability, resulting in the versatility of the system.

Melting assessment on the effect of nonuniform Y-shaped fin upon solid–liquid phase change in a thermal storage tank

This study provides an alternative solution to the improvement on solid–liquid phase change by designing a Y-shaped fin in a nonuniform pattern along the gravity direction. A numerical model is established and validated through the present measurement and data in literature. Six cases with different Y-shaped fins and locations are designed and compared to the original straight fin case. Thermal assessments on the melting fraction, temperature field, velocity distribution, and uniformity for melting are made. Results demonstrate that the nonuniform melting features caused by the local natural convection are significantly eliminated by the novel nonuniform fin structure. The time required for melting the lower PCM is found to occupy more than 50% of the completely melting time. The accurate local heat transfer enhancement measures (bottom enhancement) are conducive to markedly reduce the full melting time by 21.5%, compared to the uniform fin pattern. Upon using finned thermal storage tank for a mobilized thermal storage truck (bare tube tank), the initial investment increases by 44.9% but the profit increases by 393.6% and the payback period reduces by 69.2%. The use of fin tube in heat storage tank can quickly obtain higher returns based on a small increase in initial investment. This work provides new insights into the understandings of the transient phase change process and the strategies for guiding the design for thermal energy storage tank.

Study on the thermal performance of thermal energy storage and heating module based on a novel embedded heat pipe

A novel embedded heat pipe (HP) for electric thermal energy storage (TES) utilization was designed, which is conveniently embedded in the TES tank, and the evaporation surface and condensation surface are embedded in it. Besides, it can be used with multistage heat pipes. An electric TES heating module for building heating based on the HP was established. The start-up, the temperature uniformity, and heat transfer performance of the HP and the heat storage/release characteristic of the TES module were both studied experimentally. It is found that the novel embedded HP has good heat transfer performance and temperature uniformity. Under the condition of measured heating power, the minimum thermal resistance is as low as 0.077 °C/W, and the equivalent thermal conductivity is up to 91,273 W/(m·°C). In the heat storage process of the TES module, the paraffin completely melts from the top to the bottom, and the axial temperature of the TES module is uniform. But the radial temperature difference is relatively large. In the heat release process, the overall temperature uniformity of the TES module is good. The maximum temperature difference in the radial direction and the axial direction are less than 5 °C and 12 °C, respectively. Besides, the PCM temperature changes rapidly by adjusting the wind speed, and the thermal response of the TES module is quick. In the application of building heating, this TES module can adapt to the need of simultaneous heat storage and heating.

Impact of Large-scale concentrated solar power on energy and auxiliary markets

Concentrated solar power (CSP) generation has been widely regarded as a promising technology to increase the penetration of renewable energy-based generation units in power systems. Numerous research studies have been conducted in various ways to promote the participation of a CSP generator as a price-taker in electricity markets. However, it remains an open question as to how the strategic behavior of a CSP generator as a price-maker affects electricity markets. To this end, we conducted a numerical analysis to quantify the impact of a strategic large-scale CSP generator on energy and auxiliary markets. A three-stage stochastic bi-level model is proposed to describe the strategic behavior of a CSP generator as a price-maker in electricity markets. The impact of the risk-averse level of a CSP generator is also incorporated. Moreover, network constraints are considered to make our conclusion more realistic. The proposed bi-level model is recast into a mathematical programming with equilibrium constraints form firstly by using Karush-Kuhn-Tucker conditions and then a mixed-integer-liner-programming form by using the strong duality theory, and big-M method. Case studies based on an IEEE-56 bus system demonstrate that a price-maker CSP generator can decrease the price of both energy markets and reserve markets. However, an associated thermal energy storage tank can alleviate the negative impact of a CSP generator on electricity markets. Additionally, the high risk-averse level of a CSP generator will lead to an increased equilibrium price.

Chemical compatibility of hollow ceramic cenospheres as thermal insulation for high-temperature thermal energy storage applications with molten nitrate salt

An effective insulation material that is both thermally and chemically stable in molten salts could transform the design of molten-salt-based thermal energy storage (TES) tanks. Most current molten salt TES tanks hold the metallic tank structure in direct contact with hot salt inventory, a design which leads to thermal expansion of the tank and triggers stresses that can lead to thermomechanical failures. With an internal insulation to lower the temperature at the tank structure, the extent of thermal expansion can be reduced, thereby reducing expansion-induced stresses and allowing for consideration of lower-cost tank structure materials. Conventional insulation materials are either 1) too porous and allow molten salts to permeate into the matrix, which significantly increases the thermal conductivity or 2) too dense and have a thermal conductivity that cannot provide sufficient thermal insulation. This paper presents an alternative thermal insulation concept using cenospheres which have an alumino-silicate structure. The cost analysis suggests that the low-density cenospheres can be one of the cheapest materials to provide cost-effective thermal insulation. The chemical compatibility of cenospheres is investigated in molten 60 wt% NaNO 3 /40 wt% KNO 3 salt which is close to industrial-grade Solar Salt. This paper shows that diffusion of the sodium and potassium cations from the salt into the cenospheres occurs based on weight analysis, energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and Fourier-transform infrared (FTIR) spectroscopy. The cation diffusion breaks the bridging oxygen bonds and causes volume expansion of the microstructure which is responsible for the failure of the cenosphere particles. The chemical composition of the cenospheres is found to affect their compatibility with molten nitrate salt. A cenosphere product with low iron content showed the best compatibility with an average survival rate of 77.9% ± 9.8% after 7 days of immersion in the molten nitrate salt. While even the low-iron cenospheres appear to require protection from direct molten salt contact, their slow degradation rate, closed-cell porosity, and low cost hold potential for effective use as internal tank insulation. • Hollow cenospheres are investigated as insulation for molten nitrate salt storage. • Low level of impurities in cenospheres should improve chemical stability. • Cenospheres can provide cost-effective insulation. • Cenospheres can be fail-safer than conventional materials.

Predication of the sensitivity of a novel daily triple-periodic solar-based electricity/hydrogen cogeneration system with storage units: Dual parametric analysis and NSGA-II optimization

Solar systems are vital toward green cities; however, owing to their higher irreversibilities, it is important to modify the previous configurations. Hence, this study is motivated to design a novel solar-based cogeneration system utilizing different energy storage equipment arranged to diminish the irreversibilities innovatively. Therefore, the suggested system producing electricity and hydrogen is planned in a daily triple-periodic framework employing a heliostat field with thermal energy storage tanks using high-temperature molten salt. Meanwhile, a gas turbine cycle, an organic Rankine cycle, a low-temperature electrolyzer, and a compressed air energy storage are efficiently combined. As an assumption, the unsteady condition of solar power is divided into three different steady operational modes, namely storing, charging, and discharging. The methods of sole and dual parametric analyses and non-dominated sorting genetic algorithm-II for multi-objective optimization are applied. It is inferred that the system has the potential to increase the performance of previous similar systems. According to the results, direct normal irradiation as the effective parameter can increase the electricity generation capacity by 2.1 times. Besides, the optimum electricity and hydrogen production capacities (objective functions) are 6.58 MW and 690 kg/h leading to the optimum round-trip and exergetic round-trip efficiencies of 41.0% and 25.0, respectively.

Melting and solidification of phase change materials in metal foam filled thermal energy storage tank: Evaluation on gradient in pore structure

Solar energy as a renewable energy has sufficient development potential in energy supply applications, with the help of heat storage equipment that deals with its intermittence problem. To further improve melting/solidification efficiency, a novel energy storage tank filled by phase change materials with graded metal foams is proposed. Three gradient structures (positive gradient, non-gradient, and negative gradient) in porosity or pore density are designed. Three pieces of metal foam with the fixed porosity of 0.94 but varying pore densities of 15, 45, and 75 pore per inch is packed to form gradient in pore density design. For gradient in porosity, three selected porosities of 0.90, 0.94, and 0.98 are employed. A test bench for the phase interface visualization is set up and experiment on melting/solidification evolution and temperature are carried out. Achieving satisfactory agreement with experiments, numerical models are employed to explore the thermal features for phase change materials embedded in various kinds of graded metal foams during melting and solidification procedures. Results demonstrate that gradient design in pore density does not affect the melting and solidification procedures, while graded porosity helps notably the melting and solidification processes. Design on graded porosity reduces the complete melting time by 21.1% compared with the non-gradient structure. The global phase change process can be strengthened only if the melting is strengthened. The optimal gradient in porosity reduces the overall cycle of melting and solidification time by 10.9%, compared to the uniform filling pattern.

Optimization methodology of thermal energy storage systems for domestic water heating applications with different configurations

This paper develops an optimization methodology for the Thermal Energy Storage (TES) tank embedded with Phase Change Materials (PCMs) for domestic water heating applications with respect to the design parameter constraints and tank size. It presents the optimum design conditions for two different TES configurations considering different control strategies for the conventional cascaded system and the multiple entry independent PCM modules. The optimum configurations are determined using adaptive simulated annealing algorithm aimed to enhance the energy content and compare the systems outputs, namely the available energy and the heat transfer fluid outlet temperature at the optimum conditions for the two systems. The present study is conducted during a complete melting and solidification processes. It simultaneously validates the effectiveness of the multiple entry independent PCM modules in satisfying the low and high user requirements of domestic hot water and highlights the reduction in the electric power consumption throughout the year compared to the conventional TES system.

Surrogate modeling and optimization for the unequal diameter radial diffuser of stratified thermal energy storage tanks

AbstractStratified thermal energy storage (TES) tanks are widely used in thermal power plants to enhance the electric power peak load shifting capability and integrate high renewable energy shares. In this study, a data‐driven surrogate modeling and optimization study of the unequal diameter radial diffuser previously proposed by the present authors is conducted. First, based on the orthogonal experimental design, numerical experiments are performed to generate the performance database. Then, the database is used to establish the data‐driven surrogate model via the support vector machine. Subsequently, the single‐objective optimization and multiobjective optimization of an unequal diameter radial diffuser are conducted using the genetic algorithm. For the single‐objective optimization, the optimal thermocline thickness is 0.829 m when the diameter ratio of the long baffle and the tank is 0.426, the diameter ratio of the short baffle and the long baffle is 0.823, and the distance between the two baffles is 228.51 mm. For multiobjective optimization, the obtained Pareto optimal solutions are obtained. Under the premise of maintaining excellent thermal stratification, the selected Point C can reduce the steel cost by 88.1%. The research results are helpful for designing efficient and economical unequal diameter radial diffusers for TES tanks.

Heat storage design and performance analysis of a parabolic trough thermal power generation system based on sectional heating collection

The integration of solar thermal utilization and energy cascade utilization can bring the possibility to increase the overall plant efficiency by decreasing the exergy loss while maintain a firm supply. This paper takes SEGS VI Plant and its improved plant using sectional heating as research object, two novel thermal energy storage subsystem structures were proposed and designed for the improved plant, to explore the enhancing effect of energy cascade utilization on commercial solar thermal power plants. Calculation models of the energy storage efficiency and collector field multiples of the thermal energy storage tank were established. This paper used the software Ebsilon to establish the simulation model of the commercial 30 MW solar thermal power plant with traditional thermal energy storage structure, the improved plants with two different thermal energy storage structures, and conducted the performance analysis of the plants under design and operating conditions. The results show that, compared with the system using traditional thermal energy storage structure, the overall plant efficiency of the improved plant adopt the novel thermal energy storage structure increased by 0.71% and 0.95% under design conditions day, the overall plant efficiency increased by 0.60% and 0.81% under operating conditions, which can realize the better use of energy. Simultaneously, the total capital investment cost and levelized cost of electricity also can be reduced by 6.77 M$ and 4c$/kWh, which has good application prospects.

Experimental analysis of artificial intelligence-based model predictive control for thermal energy storage under different cooling load conditions

As the global community seeks to reduce fossil fuel dependence, improving energy efficiency and developing an optimal operational strategy are high priorities in the building sector. Integrating thermal energy storage (TES) into building energy systems is desirable for improving energy flexibility and cost efficiency. However, an optimal control strategy for TES system operation is required to maximize its advantages of balancing energy supply and demand. This study proposed a model predictive control (MPC) scheme using artificial intelligence (AI) to control the TES system and validated it by the experimental analysis. To construct a reliable and computationally manageable MPC controller, an artificial neural network was utilized as a prediction model, and a metaheuristic algorithm of εDE-RJ was employed as an optimization solver. The AI-based MPC for cooling operation was examined using a reduced-scale experimental system consisting of a chiller, sensible TES tank, heat exchangers, and variable-speed pumps. AI-based MPC optimized the charging and discharging rates of the TES system to minimize the operating cost. Three cooling load profiles were tested for both MPC and rule-based control methods. The results showed that AI-based MPC was highly feasible by flexibly managing the different load levels and reducing the operating cost by 9.1–14.6%.

Optimization of the solar space heating system with thermal energy storage using data-driven approach

The employment of solar space heating is a significant measure to achieve carbon neutrality. However, the design of the solar space heating system usually leads to the dilemma of a trade-off between the economic benefit and environmental protection, which cannot be solved by single-objective optimization. In this work, in order to design a solar space heating system of a bungalow equipped with radiant floor heating, multi-objective optimization of the solar collector area and the volume of the water thermal energy storage (TES) tank is performed by coupling TRNSYS simulation, machine learning and genetic algorithm (GA). Simulation for the entire winter operation of the solar space heating system is conducted in TRNSYS, and a database with various combinations of the design variables are generated, based on which an artificial neural network (ANN) is constructed to capture the mapping of the design variables and the system performance indicators. After proper training and validation, the ANN model with satisfactory forecasting precision is utilized as the objective function for optimizing the system. GA is employed for searching the solutions of the multi-objective optimizations. This data-driven approach combining ANN and GA is helpful to achieve the optimal solutions. For the solar space heating system, the CO2 emission reduction can benefit most from the enlargement of the solar collector area and the TES tank volume, while the payback period reaches its minimum when both the solar collector area and the TES tank volume are small. By comparing single-objective with multi-objective optimizations, it is found that the single-objective optimization cannot reveal the interactions among the CO2 emission reduction, annualized life cycle cost (ALCC) and payback period (PBP) and that the optimization focusing on a single objective probably leads to apparent defects and inapplicability in reality. Better balance among the CO2 emission reduction, ALCC and PBP can be achieved from the Pareto optimums of the multi-objective optimization rather than the single-objective optimization. According to the TOPSIS evaluation, the most appropriate design scheme is obtained from the multi-objective optimization and has the potential to reduce the carbon emission by 5480.6 kgCO2eq/year while the ALCC and payback period are only 33.40 ¥/(m2·year) and 3.70 years, respectively.

Thermo-economic assessment of flexible nuclear power plants in future low-carbon electricity systems: Role of thermal energy storage

The increasing penetration of intermittent renewable power will require additional flexibility from conventional plants, in order to follow the fluctuating renewable output while guaranteeing security of energy supply. In this context, coupling nuclear reactors with thermal energy storage could ensure a more continuous and efficient operation of nuclear power plants, while at other times allowing their operation to become more flexible and cost-effective. This study proposes options for upgrading a 1610-MWel nuclear power plant with the addition of a thermal energy storage system and secondary power generators. The total whole-system benefits of operating the proposed configuration are quantified for several scenarios in the context of the UK’s national electricity system using a whole-system model that minimises the total system costs. The proposed configuration allows the plant to generate up to 2130MWel during peak load, representing an increase of 32% in nominal rated power. This 520MWel of additional power is generated by secondary steam Rankine cycle systems (i.e., with optimised cycle thermal efficiencies of 24% and 30%) and by utilising thermal energy storage tanks with a total heat storage capacity of 1950MWhth. Replacing conventional with flexible nuclear power plants is found to generate whole-system cost savings between £24.3m/yr and £88.9m/yr, with the highest benefit achieved when stored heat is fully discharged in 0.5 h. At an estimated cost of added flexibility of £42.7m/yr, the proposed flexibility upgrades to such nuclear power plants appears to be economically justified with net system benefits ranging from £4.0m/yr to £31.6m/yr for the examined low-carbon scenarios, provided that the number of flexible nuclear plants in the system is small. This suggests that the value of this technology is system dependent, and that system characteristics should be adequately considered when evaluating the benefits of different flexible nuclear plant configurations and choosing the most cost-effective designs and operational characteristics.

Predictive control of a combined heat and power plant for grid flexibility under demand uncertainty

In recent years, the increasing penetration of non-programmable renewable energy technologies has made energy system flexibility essential for ensuring power grid stability, in terms of balance between power demand and supply. In particular, cogeneration plants can provide flexibility services by making a defined amount of power available at a given schedule, upon request. The grid operator can request it or not depending on the actual dispatch management. In the presence of this uncertain request, producers need smart controllers to meet thermal demand and, at the same time, to maximize profit while fulfilling the needs of the grid. This work presents a hierarchical predictive control architecture for optimal management of combined heat and power production sites equipped with a thermal energy storage tank supplying district heating networks. The feasibility of the proposed approach is investigated by simulating several scenarios with different degrees of uncertainty about the actual power request from the grid operator. It is shown that the controlled system is able to comply with the requirements to the maximum extent when the exact power dispatch is known a few hours in advance, also giving a profit increase as well as environmental benefits. While the grid operator request for flexibility is met up to 100%, the reduction in carbon emissions ranges from 3% to 7% and the operating margin is increased by 20%. This can be realized when the power availability is scheduled at periods of both maximum and minimum heat demand. Thus, the method is promising also in improving production planning of future integrated energy systems from the perspective of grid flexibility.

A newly developed solar-based cogeneration system with energy storage and heat recovery for sustainable data centers: Energy and exergy analyses

There is a strong need and hence specific challenges attached to this for data centers to bring holistic energy solutions for better operation, control and management in a more cost-effective, efficient and environmentally benign manner. The current study develops and investigates a solar-based novel integrated system to generate electricity and hence provide cooling in a sustainable way. The proposed system includes a parabolic trough-type concentrated solar plant with a Rankine cycle, bifacial photovoltaic plant, proton exchange membrane (PEM) fuel cell, PEM electrolyzer, Cu-Cl thermochemical hydrogen production cycle, Li-Br absorption refrigeration cycle. In order to prevent solar intermittency, thermal and chemical-based energy storage systems are integrated as molten salt cold and hot thermal energy storage tanks and hydrogen-based energy storage systems. The heat is recovered by the Rankine cycle and the Li-Br absorption refrigeration cycle in order to generate electricity and to provide cooling. The overall system is analyzed with thermodynamic approaches from the energy and exergy points of view. For further, the overall system is analyzed with the hourly ambient data in a time-dependent analysis for a data center in Calgary, Alberta, Canada. For the average ambient conditions, the energy and exergy efficiencies of the overall integrated system calculated as 35.98% and 31.24%, respectively. At least 10% of the overall energy efficiency is exceeded during a total of 8091 h of the year, whereas the overall exergy efficiency is exceeded 10% during the 7726 h in a year. Further to note that there are challenges for such systems to bring a holistic solution.

Emergence of asymmetric straight and branched fins in horizontally oriented latent heat thermal energy storage units

Mobilized thermal energy storage units have a vital role in reducing energy consumption in buildings by enabling industrial waste heat to be used in buildings. High conductive fins can enhance the heat transfer performance of mobilized thermal energy storage tanks which suffer significantly from the low thermal conductivity of phase change materials. On the other hand, investment costs of the mobilized thermal energy storage tanks need to be decreased to compete with fossil fuel-driven systems in buildings. The present study numerically investigates the effect of innovative fin structures on the melting performance for fixed fin material volume to disable cost increase. Two-dimensional models with phase change were simulated for shell-and-tube heat exchangers. The shell geometry was designed sufficiently large to observe the melting growth of phase change material independent from shell walls within the given charging time. Straight and Branched type fin structures with the fin numbers of Nfin=2, 4, and 6 were simulated to uncover the effect of shape and length scale of fins on natural convection-driven melting. It was found that Straight fin type is more suited than Branched fins as they do not show significant melting enhancement with increased complexity and cost. The fin structures in all cases performed better when located at the top of the heat transfer fluid tube, even though the literature considers that top-located fins inhibit natural convection circulations. Varying the number of fins from (2-fin) to (4-fin) causes 15.8% increase in melting ratio, but further increase in the fin number (6-fin) reduces melting ratio below the (4-fin) case. Within (4-fin) structures located at the top, using distinct fin lengths yields melting ratio to increase 28.1%. Overall, the results show that heat transfer could be improved by varying the fin structure without increasing total fin volume and cost. The melting region growth shape with optimized fin structure forms the basis for the multitube arrangement of mobilized thermal energy storage units to enhance heat transfer performance with low cost.

Thermoeconomic evaluation of using thermal energy storage tank in the cogeneration production system of heating, power (CHP), and freshwater

Thermoeconomic evaluation of using thermal energy storage tank in the cogeneration production system of heating, power (CHP), and freshwater

Response Surface Methodology-based prediction model for working fluid temperature during stand-alone operation of vertical cylindrical thermal energy storage tank

Domestic hot water applications rely on the stand-alone operation of thermal energy storage (TES), in which natural convection significantly affects the efficiency of a storage system. The present study develops a two-dimensional axisymmetric numerical model for detailed simulation. Subsequently, an effective prediction model for a vertical stand-alone cylindrical storage tank is formed. The results of the detailed model are found to have good agreement with the findings of the in-house experiments. The experimental and numerical results show the formation of temperature gradients with time, known as thermal stratification, which affects the storage efficiency and thermodynamic quality of the stored heat. A seven parameter three-level Box-Behnken Design (BBD) Response Surface Methodology (RSM) is used to develop a prediction model for the working fluid temperature inside the tank. Analysis of variance (ANOVA) is performed to evaluate the effects and interactions of the process parameters for selecting the statistically significant terms. Based on the ANOVA, a reduced prediction equation is generated. Various plots such as normal probability, predicted versus actual response, versus fits, versus order, Pareto charts, main effects and interaction effects are created to analyze the model. Comparing the results of the detailed model and prediction equation, it is concluded that the newly formulated scaling-based prediction equation can predict and characterize the performance of the TES under test with adequate accuracy.