Thermal Energy Systems Research Articles

Radiation-Assisted Formation of Metal Nanoparticles in Molten Salts.

Knowledge of structural and thermal properties of molten salts is crucial for understanding and predicting their stability in many applications such as thermal energy storage and nuclear energy systems. Probing the behavior of metal contaminants in molten salts is presently limited to either foreign ionic species or metal nanocrystals added to the melt. To bridge the gap between these two end states and follow the nucleation and growth of metal species in molten salt environment in situ, we use synchrotron X-rays as both a source of solvated electrons for reducing Ni2+ ions added to ZnCl2 melt and as an atomic-level probe for detecting formation of zerovalent Ni nanoparticles. By combining extended X-ray absorption fine structure analysis with X-ray absorption near edge structure modeling, we obtained the average size and structure of the nanoparticles and proposed a radiation-induced reduction mechanism of metal ions in molten salts.

Applications and technological challenges for heat recovery, storage and utilisation with latent thermal energy storage

Thermal energy storage (TES) technology is considered to have the greatest potential to balance the demand and supply overcoming the intermittency and fluctuation nature of real-world heat sources, making a more flexible, highly efficient and reliable thermal energy system. This article provides a comprehensive state-of-the-art review of latent thermal energy storage (LTES) technology with a particular focus on medium-high temperature phase change materials for heat recovery, storage and utilisation. This review aims to identify potential methods to design and optimise LTES heat exchangers for heat recovery and storage, bridging the knowledge gap between the present studies and future technological developments. The key focuses of current work can be described as follows: (1) Insight into moderate-high temperature phase change materials and thermal conductivity enhancement methods. (2) Various configurations of latent thermal energy storage heat exchangers and relevant heat transfer enhancement techniques (3) Applications of latent thermal energy storage heat exchangers with different thermal sources, including solar energy, industrial waste heat and engine waste heat, are discussed in detail.

A case study on morphological aspects of distinct magnetized 3D hybrid nanoparticles on fluid flow between two orthogonal rotating disks: An application of thermal energy systems

The consolidation power of different nanomaterials such as metallic nanoparticles and metallic-oxides nanoparticles in a new-fangled and energetic hybrid material should give rise to fascinating properties that combine the advantages of each of the nanocomponents. In this paper, developed an MHD-hybrid model for the thermal energy system with seven different types of nanoparticles. For this purpose, we simulate the thermal conductivity and viscosity hybridized nanocomponents modeled based on the shape and size factor of each nanoparticle. The effect of morphology for Metallic and non-Metallic nanoparticles on flow and heat transfer rate has been investigated through hybrid nanofluids flow. Mathematical modeling of the concerning problem is done in the form of the partial differential structure under the boundary layer theory. The intrinsic features of capitalized induced particles along with base fluid are presented by empirical relations and utilized during the formulation of work. These hybrid nanofluids flow passing through the two orthogonal moving up/down porous disks. Thermal enhancement performance is analyzed through variation of shape and size of the nanoparticles with convective conditions. A stable system of nonlinear differential equations is obtained by applying suitable transformation on governing partial differential equations. Consequences of pertinent parameters on axial velocity, radial velocity, tangential velocity, and temperature distribution are elaborated. Important results of non-dimensional parameters with different types of hybrid nanofluids are examined through porous orthogonal disks. We achieved that the carbon nanomaterial has significant results on thermal performance. Novel results are obtained on thermal conductivity and viscosity associated with the shape/size of the nanoparticles. Shear stress increases with the increase of values of MHD. For the injection case, the Nusselt number shows significant results. If we increase the size of the nanoparticles then Skin friction also increases. This research set a strong foundation in the field of nano-biomedical devices, and engineering nanotechnology oriented electronic computers.

에너지공유 커뮤니티 구현을 위한 중앙온수급탕 방식의 신재생 열에너지 시스템 적용성 분석

에너지공유 커뮤니티 구현을 위한 중앙온수급탕 방식의 신재생 열에너지 시스템 적용성 분석

Modern solar systems driven by nanoparticles-based fatty acids and paraffin wax phase change materials

Integrating a suitable thermal energy depository device is extremely necessary to enhance the performance of solar thermal energy systems by a reduction in the discrepancies between the supply and demand of electricity. The most effective and potential system for the conservation of solar thermal energy is the dependence on phase change materials (PCMs). Here, we focus on the preparation and characterization of nanoparticle (NP)-reinforced PCM-based composites. Fatty acids and paraffin wax PCM, reinforced with different NPs, are extensively discussed in this review. To describe the composition, morphology, and thermal characters of the arranged NPs and the composite PCM, scanning electron microscopy (SEM) and Fourier transmission infrared (FTIR) spectroscopy are employed. To define the chemical structure, chemical density, component size, and internal structure of composites and chemical characteristics, EDX/XPS is performed on a component PCM, respectively. Graphene incorporation improves the whole system's thermal conductivity. Both used in the TGA and DTG study were the thermal decomposition details and chemical absorption of the polymer PCM. This study, therefore, focuses on PCMs, their methods for the processing of the materials, materials, and thermal characterization during the last five years.

Life cycle assessment and comparative exergoenvironmental evaluation of a micro-trigeneration system

The cascading use of energy distinguishes trigeneration systems from simple heat recovery strategies and conventional separate electric and thermal energy systems. Small-scale trigeneration is referred to as micro-trigeneration, and is a potentially sustainable energy solution. Despite the demonstrated benefits from economic, energy, and environmental perspectives, the adoption of micro-trigeneration systems has been undoubtedly underexplored in the tertiary sector. This study presents a detailed Life Cycle Assessment for a natural gas-fueled micro-trigeneration system, encompassing the equipment and energy flows. Two endpoint environmental assessment methods were employed, the Eco-indicator 99 and ReCiPe. The environmental data was utilized to develop exergoenvironmental assessments. The specific environmental impact for both methods, despite presenting different absolute values, show the same behavior. The highest environmental impacts are found at the internal combustion engine and steam generator. Regarding the evaluation of exergoenvironmental parameters, the absorber heat exchanger and steam generator should be the focus of improvement efforts. This study contributes to improving the understanding of which processes within a micro-trigeneration system contribute the most to exergy destruction and generation of environmental impacts.

Performance assessment of an oil-based packed bed thermal energy storage unit in a demonstration concentrated solar power plant

Small scale concentrated solar power plants (1–5 MWe) are a suitable alternative for regions with limited space for land occupation or applications requiring a low capital investment. A successful approach for these plants is the use of Linear Fresnel collectors together with organic Rankine cycles, mainly, due to their lower investment cost and flexibility in operation. To improve the dispatchability of the plant, a thermal energy storage is normally incorporated. The well-known thermal energy storage technology based on a double tank configuration using molten salts is not suitable for these systems, due to the operation temperatures. A promising alternative is the use of a packed bed thermal energy storage system, as they allow a wide operation temperature range and the implementation of low-cost heat storage materials. This work investigates a packed bed using Magnetite ore as heat storage media and a thermal oil, Delcoterm Solar E15, as heat transfer fluid. This oil is also used in the Linear-Fresnel-type solar field. The performance of this thermal energy storage solution is addressed for the particular case of the 1 MWe concentrating solar plant available in Ben Guerir (Morocco). The present work is part of the ORC-PLUS project, which targets to provide this plant with a thermal energy storage system able to supply up to 16 MWht to the power block. Overall, this work aims at demonstrating the potential in terms of thermal performance and cost-effectiveness of a packed bed thermal energy system for small-scale CSP plants using thermal oil as heat transfer fluid.

A Passive High-Temperature High-Pressure Solar Steam Generator for Medical Sterilization

Summary Saturated steam (>121°C and >205 kPa) is widely used in the medical sterilization process known as autoclaving. However, solar-driven steam generation at such high temperature and pressure requires expensive optical concentrators. We demonstrate a passive solar thermal device mostly built from low-cost off-the-shelf components capable of delivering saturated and pressurized steam to drive sterilization cycles even under hazy and partly cloudy weather. Enabled by an optimized ultra-transparent silica aerogel, the device utilizes an efficient thermal concentration strategy to locally increase the heat flux and temperature obviating the need for active optical concentrators. With almost 2× higher energy efficiency (47%) than those previously reported at 100°C, the device demonstrated successful sterilization in a field test performed in Mumbai, India. In addition to enabling passive sterilization, this work promises the development of solar thermal energy systems for saturated steam generation in energy conversion, storage, and transport applications.

A fundamental unified framework to quantify and characterise energy flexibility of residential buildings with multiple electrical and thermal energy systems

To date, the energy flexibility assessment of multicomponent electrical and thermal systems in residential buildings is hindered by the lack of adequate indicators due to the different interpretations, properties, and requirements that characterise an energy flexible building. This paper addresses this knowledge gap by presenting a fundamental energy flexibility quantification framework applicable to various energy systems commonly found in residential buildings (i.e., heat pumps, renewables, thermal and electrical storage systems). Using this framework, the interactions between these systems are analysed, as well as assessing the net energy cost of providing flexibility arising from demand response actions where onsite electricity production is present. A calibrated white-box model of a residential building developed using EnergyPlus (including inter alia a ground source heat pump, a battery storage system, and an electric vehicle) is utilised. To acquire daily energy flexibility mappings, hourly independent, and consecutive demand response actions are imposed for each energy system, using the proposed indicators. The obtained flexibility maps give insights into both the energy volumes associated with demand response actions and qualitative characteristics of the modulated electricity consumption curves. The flexibility potential of each studied energy system is determined by weather and occupant thermal comfort preferences as well as the use of appliances, lighting, etc. Finally, simulations show that zone and water tank thermostat modulations can be suitably combined to shift rebound occurrences away from peak demand periods. These insights can be used by electricity aggregators to evaluate a portfolio of buildings or optimally harness the flexibility of each energy system to shift peak demand consumption to off-peak periods or periods of excess onsite electricity generation.

Development of a Coupled TRNSYS-MATLAB Simulation Framework for Model Predictive Control of Integrated Electrical and Thermal Residential Renewable Energy System

An integrated electrical and thermal residential renewable energy system consisting of solar thermal collectors, gas boiler, fuel cell combined heat and power, a photovoltaic system with battery, inverter, and thermal storage for a single-family house of Sonnenhaus standard is investigated with a model predictive controller (MPC). The main focus of this article is to define a multi-objective mathematical function, develop a coupled simulation framework for the nonlinear time-varying deterministic discrete-time problem of the energy system using TRNSYS and MATLAB. With the developed methodology, a sensitivity analysis of maximum optimization time, swarm (or population or mesh) size of a typical spring day and a typical summer day assuming a 100% accurate weather and load forecast with three different algorithms: particle swarm optimization (PSO), genetic algorithm (GA) and global pattern search (GPS) are analyzed. Finally, the obtained results are compared with a status quo controller. Results show that the PSO algorithm optimizer performs the best in this MPC for such a complex and time-consuming MPC model in both the spring day and the summer day. The obtained results show that the PSO with swarm size 50 in the selected typical spring day and the PSO with swarm size 40 in the selected summer day reduces the objective function’s fitness value from 413 to −177 within 6 h optimization time and from 1396 to 1090 in 4 h optimization time respectively.

Analysis of gravel back-filled borehole heat exchanger in karst fractured limestone aquifer at local scale

In designing and sizing of borehole thermal energy system, natural groundwater movement and temperature driven flow have a great importance on the borehole heat exchanger efficiency. The efficiency of double U – tube arrangement in gravel – backfilled borehole installed in a fractured limestone aquifer has been analyzed by means of three – dimensional numerical simulations. The numerical model is representative of 1 m deep of gravel back – filled borehole surrounded by the fractured aquifer. Several simulations have been carried out in order to evaluate the effect of aquifer parameters and boundary conditions on heat exchange efficiency by varying the mean temperature within the double U - tube. The fractured limestone aquifer of the industrial area of Bari (Italy) has been chosen as field site in order to identify the aquifer parameter range and the respective combinations. The results highlight that borehole thermal energy system efficiency is strictly dependent on aquifer transmissivity and groundwater Darcian velocity. The conducted analysis shows that, under lower Darcian groundwater flow and lower aquifer transmissivity, heat transfer efficiency increases at least by 25% compared to stagnant water, whereas heat transfer in the aquifer is governed by heat conduction. The increase of aquifer transmissivity induces the thermosiphon effect enhancing heat transfer processes both in the gravel back-filled borehole and aquifer. At higher values of groundwater Darcian velocity (> 0.1 m/d) advection due to groundwater flow is not negligible and mixed with free convection enhancing heat transfer further. Based on the results, discussion on the performance and environmental constraint of gravel back – filled borehole at field site has been presented.

Thermal energy management optimization of solar thermal energy system based on small parabolic trough collectors for bitumen maintaining on heat process

Solar energy integration in heat consuming processes is a promising replacement for fossil energy. We are interested in a small Solar Parabolic Trough Collectors field combined with a sensible heat storage reservoir. Unfortunately, such a system has a higher cost than fossil energy and is challenging to optimize. Therefore, this work's main objective is to provide an optimized design and management to minimize energy cost (EC) and maximize renewable energy utilization fraction (REF). This study is done by optimizing the sizing and the thermal energy flow management of a hybrid solar-fossil fuel energy system. The optimization problem is formulated based on mass and energy conservation equations, heat transfer phenomena modeling, correlations, and economic data. We resolved it by combining trial and error method, multi-node calculation procedure, and genetic algorithm. To evaluate our method, we studied a hybrid solar-fossil fuel energy system used for the bitumen heat maintaining process in Rabat region-Morocco. The evaluation considered different thermal storage capacities. Using our optimization, we reached REF ≥ 40% and EC < 0.05US$/kWh for small thermal capacities and REF ≥ 85% and EC less than 0.2US$/kWh for large thermal capacities. This is equivalent to saving, respectively, more than 0.75 and 1.5 tons of CO2 emissions/year/kW for small and large thermal storage capacities. Other important recommendations are also provided in this work.

A topology optimization framework to facilitate adoption of advanced district thermal energy systems

Advanced district thermal energy systems, which circulate water at temperatures near ambient conditions, and facilitate the utilization of waste heat and renewable thermal sources, can lower the carbon-intensity of urban districts, advancing the U.N. Sustainable Development Goals. Optimization of the network topology — the selection of the best subset of buildings and the best network to connect them, to minimize life cycle cost — can increase adoption of these system in appropriate applications. The potential “solution space” of the topology optimization problem grows factorially with the number of buildings in the district, motivating the consideration of a design heuristic. In this study, a heuristic for the network selection was evaluated with an exhaustive search, for a prototypical four-building district. For the prototypical district considered, the heuristic was effective in selecting an optimal network topology. Additionally, it was found that, in this case, the selection of the subset of buildings was more influential on the life cycle cost than the selection of the network topology. This work is part of a larger effort to develop a topology optimization framework for district thermal energy systems, which is anticipated to address barriers to adoption of ambient-temperature systems.

Desalination process using humidification–dehumidification technique: A detailed review

The lack of fresh water resources is one of the important reasons obstructing progress all over the world. To overcome this crucial situation, the water desalination system (WDS) is progressed, enhanced, and modified. The desalination plant is mostly powered by nonrenewable energy resources, mainly by fossil fuels that make it an expensive and high-energy-consuming technology. Therefore, it is indispensable to depend on renewable energy supplies to drive desalination systems. Recently, the total thermal energy desired to operate the humidification–dehumidification desalination systems can be gained from renewable/sustainable energy resources such as geothermal energy and solar energy. Among the different desalination techniques, the HDH is considered one of the most effective desalination techniques to manage the critical issue of shortage of drinking water. The current paper presents a comprehensive review of diverse types of HDH desalination systems as well as their fundamental components. The present work revealed that the seawater HDH system is a promising technology to produce fresh water, particularly for decentralized demand. The packed bed humidifier is the most utilized type in the HDH water desalination system than other types of humidifiers. Furthermore, the direct dehumidifier enhances the performance of HDH desalination system compared to the indirect one. The present study concludes that the hybrid energy systems have the highest gain output ratio, while the thermal energy systems have the lowest gain output ratio. Water heating with solar energy has a significant enhancement in system productivity compared with solar air heating. The HDH WDS incorporated with heat pump achieves appropriate system productivity and gain output ratio with the lowest cost per liter.

Optimal planning of thermal energy systems in a microgrid with seasonal storage and piecewise affine cost functions

The optimal design of microgrids with thermal energy system requires optimization techniques that can provide investment and scheduling of the technology portfolio involved. In the modeling of such systems with seasonal storage capability, the two main challenges include the low temporal resolution of available data and the non-linear cost versus capacity relationship of solar thermal and heat storage technologies. This work overcomes these challenges by developing two different optimization models based on mixed-integer linear programming with objectives to minimize the total energy costs and carbon dioxide emissions. Piecewise affine functions are used to approximate the non-linear cost versus capacity behavior. The developed methods are applied to the optimal planning of a case study in Austria. The results of the models are compared based on the accuracy and real-time performance together with the impact of piecewise affine cost functions versus non-piecewise affine fixed cost functions. The results show that the investment decisions of both models are in good agreement with each other while the computational time for the 8760-h based model is significantly greater than the model having three representative periods. The models with piecewise affine cost functions show larger capacities of technologies than non-piecewise affine fixed cost function based models.

Convective nonlinear thermally developed flow of thixotropic nanoliquid configured by Riga surface with gyrotactic microorganism and activation energy: A bio-technology and thermal extrusion model

The thermal performances of base materials with thermal radiation, variable heat transportation features and activation energy are quite progressive which allow many industrial, engineering and technological applications. The scientists are still focusing to discover the cheap and friendly environment energy resources. On this end, the utilization of nanoparticles as a energy resource is intended much attention of researcher in recent decade. Moreover, the bioconvection of nano-materials is also a fundamental approach to improve the nanoparticles stability and many bio-technology applications like enzymes, petroleum engineering application, bio-fuels, bio-sensors and many more. Present analysis aim to discover the complex rheological characteristics of thixotropic nanofluid in presence of gyrotactic microorganisms over a Riga surface. The most fascinating features of nonlinear thermal radiation and activation energy are also carried out to improve the heat and mass transportation process. The formulated flow problem is preceded by using convective Nield boundary conditions. After successfully attaining the dimensionless form of formulated set of flow equations, a famous shooting numerical scheme is followed with appliances of MATLAB computational software. The involved flow parameters significance is graphically underline with well justified physical consequences. All physical quantities determining the heat, mass and microorganisms transportations are comprehensively studied via graphs and tables. The key observations revealed from this novel numerical continuation lead to many thermal engineering and solar energy systems applications, energy resources and consumptions, enzymes, bio-sensors and bio-technology.

Progress in heat transfer research for high-temperature solar thermal applications

High-temperature solar thermal energy systems make use of concentrated solar radiation to generate electricity, produce chemical fuels, and drive energy-intensive processing of materials. Heat transfer analyses are essential for system design and optimisation. This article reviews the progress, challenges and opportunities in heat transfer research as applied to high-temperature solar thermal and thermochemical energy systems. The topics discussed include fundamentals of concentrated solar energy collection, convective heat transfer in solar receivers, application of liquid metals as heat transfer media, and heat transfer in non-reacting and reacting two-phase solid–gas systems such as particle–gas flows and gas-saturated porous structures.

A Monte Carlo based approach for exergo-economic modeling of solar water heater

ABSTRACT In life-cycle costing of thermal energy systems, the basis of costing could be mass or exergy and the approach followed could be deterministic or stochastics. In thermal energy systems with end products/services such as hot air, hot water, steam etc. the value addition is due to higher exergy content; therefore, exergy is a logical basis of costing and stochastics is a practical approach capturing uncertainties of input variables. This paper proposes a novel framework named as stochastic Monte Carlo-based exergy costing (SMXC) for assessment of solar hot water systems. The annual hours of operation, maintenance cost, service life, and capital cost have been identified as highly sensitive input variables. The costs based on mass and exergy content of hot water in deterministic life-cycle costing method are estimated at 0.296 and 0.304 US cent/kg, respectively. The mean values of mass and exergy costs of hot water using Monte Carlo-based stochastics life-cycle costing method are 0.302 and 0.310 US cent/kg. A very low value (i.e. 2.4%) of the exergo-economic factor (f) for the solar water heater indicates the poor exergetic efficiency; therefore, capital investment to improve its efficiency is justified. The methodological approach can be extended to examine the probabilistic exergo-economic cost of array of thermal energy products when the parametric uncertainties play a key role.

Flexible phase change materials with enhanced tensile strength, thermal conductivity and photo-thermal performance

Phase change materials are most potential candidates for storing solar thermal energy with large enthalpy and high exergy. However, the intrinsic drawback such as poor optical absorptive capacity, low thermal conductivity and poor tensile strength restrict the thermal efficiency of phase change materials. To overcome drawback, expanded graphite is used to encapsulate the paraffin then thermoplastic elastomer is used to mix with the powders with twin-screw extrusion technology. The highly flexible phase change composite shows a melting enthalpy of 124.6 J g−1 and a thermal conductivity of 2.2 W m−1 K−1 with 70% of expanded graphite/paraffin. The tensile strength of 2.1 MPa and a breaking elongation of 220%. This flexible phase change composite demonstrates good photo-thermal energy charging/discharging property and shows much larger exergy than traditional fluids in the solar thermal energy systems.

Energy-Positive House: Performance Assessment through Simulation and Measurement

This paper presents the results for the operating energy performance of the smart operation for a low carbon energy region (SOLCER) house. The house design is based on a ‘systems’ approach, which integrates the building technologies for electrical and thermal energy systems, together with the architectural design. It is based on the concept of ‘energy positive’ buildings, utilising renewable energy systems which form part of the building envelope construction. The paper describes how the building energy model HTB2, with a range of additional ‘plugins’, has been used to simulate specific elements of the design and the overall energy performance of the house. Measurement data have been used in combination with the energy simulation results to evaluate the performance of the building together with its systems, and identifying the energy performance of individual components of the building. The study has indicated that an energy-positive performance can be achieved through an integrative systems approach. The analysis has indicated that the house, under normal occupancy, needs to import about 26% of its energy from the grid, but over the year its potential export to import ratio can reach 1.3:1. The paper discusses the performance gap between design and operation. It also considers the contribution of a transpired solar air collector (TSC) to space heating. The results have been used to gain a detailed understanding of energy-positive performance.