Thermal Energy Systems Research Articles

Computational single‐phase comparative study of a Williamson nanofluid in a parabolic trough solar collector via the Keller box method

A solar thermal collector collects heat by absorbing sunlight and converting this incoming radiation into useful thermal energy. The parabolic trough solar sollector (PTSC) is widely installed in concentrated solar power technology with a temperature range of 325-700 K. The thermodynamic efficiency of the PTSC can be intensified by using nanofluids owing to their enhanced thermophysical properties. In this paper, the two-dimensional flow over a stretched sheet in PTSC under Williamson nanofluid effects is explored. With the help of useful transformations, the partial differential equations arising from boundary layer equations of the Williamson nanofluid model are changed into nonlinear ordinary differential equations. The Keller box numerical scheme is then used to find the solution of the resulting nonlinear ordinary differential equations. Two nanofluids, copper-engine oil (Cu-EO) and alumina-engine oil (Al2O3-EO) are considered to address the performance analysis of PTSC in this study. It is observed that the parameters of the porous media reduced the heat transfer rate but increased the velocity gradient. In order to examine the effect on various performance parameters of the device, the nanoparticle concentration is also varied. With the increase in the Reynolds and Brinkman numbers, the entropy is found to increase. The thermodynamic performance of the Cu-EO nanofluid is remarkably better than that of the Al2O3-EO nanofluid under the same conditions. The thermal efficiency of Cu-EO over Al2O3-EO is seen with a minimum of 1.5% and a maximum of 9.1%. The theoretical simulations documented here may be effective in improving solar thermal energy systems.

Special Issue: The State of the Art of Thermochemical Heat Storage

Nowadays, thermal energy storage (TES) is gaining a crucial role in the development of highly efficient thermal energy systems [...]

Induced MHD impact on exponentially varying viscosity of Williamson fluid flow with variable conductivity and diffusivity

In this study, we assumed a thermal energy system with variable controlling properties which effect the entire system. One of the best applications of thermal energy system is heat exchanger. A good heat exchanger is a big challenge over the past years, due to enlarged public request on improving energy efficiency and decreasing energy. Normally, heat exchangers are used in the transmission of heat between two or more fluids [46]. Furthermore, the analysis of MHD flow of an electrically conducting fluid due to the thermal system is significant in current metallurgy and metal-working methods. Due to large amount of applications, variable thermo-physical properties of induced magnetic field in Williamson fluid flow is studied. The achieved system is partial differential, which is converted into ordinary differential equations by using the transformations. Then the attained system is solved by using shooting method. The thermal extrusion system contains velocity, concentration, and temperature fields. The associated controlling parameters contain small parameter, magnetic field, the reciprocal magnetic Prandtl number, variable viscosity parameter, Williamson parameter, small concentration parameter and Schmidt number. The outlined results deliver good thermal impact on entire system for minor and big values of these pertinent parameters. Williamson fluid model is executed to examine the properties of shear thinning fluids. It is noticed that a big reduction is noticed in velocity profile for large values of variable viscosity parameter, Williamson parameter and magnetic parameter. Moreover, the reciprocal magnetic Prandtl number reduces the magnetic profile. The temperature and concentration small parameters show enhanced impact on temperature and concentration profiles. Comparison of present thermal system is considered for limited values of these parameters.

Thermal Performance Evaluation of Circular-Stadium Double Pipe Thermal Energy Storage Systems

Thermal Energy Storage (TES) systems are employed in numerous practical applications, owing to their capability to solve the problems related to the reliability of thermal energy systems by using phase change materials (PCM). In this study, the charging and discharging processes of N-eicosane in a circular-stadium double pipe TES system for various aspect ratios (1, 0.35, 0.25, and 0.15) and angular orientations (0°, 30°, 60°, and 90°) of the inner stadium tube are numerically investigated using enthalpy-porosity formulation. The zero-heat flux is applied to the outer tube of TES systems while the inner tube wall is retained at constant temperatures. The numerical results are compared with the experimental results of the concentric double-pipe TES system which shows an accuracy with 2.34% error. The findings revealed that the best thermal performance is provided by the X/Y=0.15 case with 90° angular orientation which contributes the highest increase in the charging rate while the discharging rate is not substantially affected by aspect ratio and angular orientation. The melting time decreases by 59% and solidification time raises by 27%. The overall efficiency of the TES system is 75% which is 26% higher than a base case (X/Y=1). The results further conceived that gravitational acceleration plays an important role in the natural convection heat transfer during the charging process of PCM.

RETRACTED: Development of correlations for Nusselt number and friction factor of packed bed solar thermal energy storage system having spheres with pores as packing elements

Solar energy is an emerging alternative of fossil fuels to fulfill the global energy demand as it is available in plenty and eco-friendly in behaviour. However, solar energy systems requires storage unit due to its intermittent nature. The packed bed storage system (PBSS) as storage unit is considered to be a feasible option for solar thermal energy systems having operating temperature range under 100°C. The heat transfer and pressure drop within PBSS are influenced by shape of packing element as convective heat transfer coefficient is a function of it. Under the current study, correlations are developed for Nusselt number as well as friction factor using the results obtained through experimental investigation for the PBSS built up of spherical shaped packing elements having pores on the surface. The developed correlations are the function of Reynolds number, ratio of pore diameter to sphere diameter (d/D), perforation index (PI) and ratio of pore depth to sphere diameter (t/D) within range of 200 to 800, 0.066 to 0.2, 0.06 to 0.22 and 0.05 to 0.2, respectively. Values obtained from the developed correlations are compared with the values obtained through experimentations and it is found that the correlations for Nusselt number and friction factor can predict the values with mean absolute deviation of 6.7% and 7.5%, respectively. These correlations may be helpful for the researchers working in the same research area and manufacturers developing the low temperature solar thermal energy systems. This study may also be useful to investigate the effect of similar shape of packing elements in latent heat based PBSSs.

Unsteady 3D mixed convection flow of a chemically reactive Oldroyd‐B nanofluid configured by a periodically accelerated surface

AbstractFundamental developments in nanotechnology have attracted the attention of scientists towards the interaction of nanoparticles due to their fascinating applications in thermal engineering and solar energy systems. Convinced by such motivating applications, the current research project addresses the utilization of nanoparticles in the unsteady three‐dimensional chemically reactive flow of an Oldroyd‐B fluid induced by a bidirectional oscillatory stretching surface. The effects of mixed convection are also considered here. The prime features of the nanofluid namely thermophoresis and Brownian motion characteristics are explored by introducing the famous Buongiorno's nanofluid model. The relevant equations for the formulated theoretical model have been reduced by the appropriate transformations for which the analytic solution is deliberated via the homotopic technique. Later on, a complete graphical analysis for distinct flow parameters is deliberated for dimensionless velocities, concentration, and temperature distributions with the relevant physical implications. Moreover, stimulating physical quantities like local Nusselt and Sherwood numbers are numerically calculated and discussed. The study emphasizes that decreasing variation in both components of velocities has been reported with an increment of relaxation time, while the impact of the retardation time constant is quite opposite. It is further claimed that the velocity distribution has an increasing tendency in the horizontal direction for a higher buoyancy ratio and mixed convection parameters. Moreover, an increment in thermophoresis parameter enhances both temperature and concentration distributions.

Energy, Exergy, Economic and Environmental Analyses of Air-Based High-Temperature Thermal Energy and Electricity Storage: Impacts of Off-Design Operation

Abstract The present study presents a comprehensive assessment of the impacts of the off-design operation of an air-based high-temperature thermal energy and electricity storage (also known as high-temperature heat and power storage) system on its energy, exergy, economic, and environmental aspects. Here, the effects of load variations on the mass flowrate, pressure ratio, and isentropic efficiency of the turbomachinery are considered to give the most accurate possible picture of the techno-economic aspects of the performance of the system. The results of such an assessment will be extremely useful in achieving the optimal performance of the energy storage system while working parallel with solar and wind power plants. The results prove that the system will present high overall energy and exergy efficiencies of 91.5% and 88.16% when working at full load all the time. These indices, however, will be as low as 67.8% and 65.9% at an annual average operation load of 70% and even further lower to 34% and 32.7% at 40% load, respectively. The payback period of the system will decrease from 11 to 23 years when the operation load falls from 100% to 80%. The environmental effects of such an energy storage unit for an energy market like Denmark (for instance) will be about 6355, 3227, and 823 tonnes of reduced equivalent carbon-dioxide when working at 100%, 70%, and 40% loads, respectively.

HVAC Best Practices in Arctic Climates

Arctic climates provide unique challenges for designers of HVAC, plumbing, and thermal energy systems. The importance of considering the operation outside air temperatures, system reliability, and building resiliency cannot be understated. The paper describes best practice examples of robust and reliable systems with the emphasis on their redundancy, durability, and functionality. The paper also discusses the most common heating and ventilation system approaches used in arctic climate with the emphasis on the importance of a maintenance program that allows building operators to successfully troubleshoot and maintain buildings in the arctic. More detailed discussion of concepts presented in this paper can be found in the Guide [1] where these concepts are illustrated by best practice examples from U.S. military bases in Alaska and Søndre Strømfjord, the international airport of Greenland that previously was used as a U.S. military base. The paper results from experts’ discussions during the Consultation Forum “Thermal Energy Systems Resilience in Cold/Arctic Climates” [2] and research conducted under the IEA EBC Annex 73, the Environmental Security Technology Certification Program (ESTCP) Project “Technologies Integration to Achieve Resilient, Low-Energy Military Installations” and U.S. Army Program project 633734T1500 under Military Engineering Technology Demonstration. The paper is complementary to the ASHRAE Cold Climate Design Guide [3] with a focus on resilience of thermal energy systems.

Analyzing the Factors that Effect Maximum Time to Repair Thermal Energy Systems in Cold/Arctic Climates

Resilient energy systems are those that can prepare for and adapt to changing conditions, and recover rapidly from disruptions including deliberate attacks, accidents, and naturally occurring threats. This makes thermal energy systems resilience especially important in extreme climates such as arctic or tropical environments. While metrics and requirements for availability, reliability, and quality of power systems have been established (DoD 2020), similar metrics and requirements for thermal energy systems are not well understood. In one of the first attempts to address this deficiency, a study was conducted to better understand the factors that affect maximum time to repair thermal energy systems. Maximum time to repair of thermal systems can be defined in terms of how long the process can be maintained or the building remains habitable or protected against damage from freezing of water pipes, sewer, fire suppression system, protect sensitive content, or start growing mold during extended loss of energy supply with extreme weather events. The purpose of this paper is to present the methodology and results of a novel temperature decay test conducted during the winter, along with blower door tests on five representative military buildings in Alaska. The results from the field tests described in this paper show that the distribution of temperature decay is not uniform throughout the building and that it will vary depending on solar position, building features and wind direction. This demonstrates that strategic placement of personnel, equipment and facilities that are critical to building operations, can extend operation time during a thermal energy disruption.

CURRENT TRENDS IN ENSURING SUSTAINABLE DEVELOPMENT OF THE TRANSPORT AND ENERGY SYSTEM OF UKRAINE

The article considers the peculiarities of the development of the transport and energy system of Ukraine in the conditions of external geopolitical and pandemic threats to energy security. The main problems of development of thermal energy and gas transmission system of Ukraine are analyzed. The directions of improving the management of the transport and energy system of Ukraine based on the need to comply with national interests in the European energy market are substantiated. The aim of the article is to study the current state of functioning of the transport and energy system of Ukraine and to form recommendations for improving its efficiency in the context of solving the problems of energy security of the state. Research methods. Methods of scientific analysis are used - in the critical assessment of scientific sources to determine the essence of the transport and energy system; comparison - in the study of the dynamics of energy production and the formation of coal reserves in thermal power plants; graphical method for displaying and comparing indicators of development of the transport and energy system of Ukraine; method of generalization in the development of proposals to improve the efficiency of the transport and energy system of Ukraine. Results. The directions of improving the management of the transport and energy system of Ukraine in the conditions of geopolitical and pandemic threats to energy security are proposed, in particular: the necessity of mass transition of apartment buildings to individual heating is substantiated, which will significantly reduce heat consumption; proposed vectors to stimulate the installation of gas boilers for individual heating through the introduction of special credit programs of banks and state target programs; the expediency of developing shale gas fields and increasing its production is substantiated; the expediency of intensifying the development of energy with the use of renewable energy sources is argued.

How effective is carbon offset Assessment of carbon dioxide reduction methods by using MCDM techniques: a case study of global automotive factory

In order to reduce CO2 emissions, industrial enterprises try to utilise various methods such as obtaining energy from renewable power plants, afforestation and carbon offset. In this study, it was aimed to determine the most appropriate method to reduce CO2 emissions caused by the energy consumption of an automotive industry company. With this study conducted, analytical hierarchy and multimoora methods, which are among the multi-criteria decision-making techniques, were used together to select the optimum method among the CO2 reduction methods. As a result of the study that assesses the effectiveness of hydroelectric power station, solar electrical system, solar thermal energy system, afforestation and carbon offset alternatives from various angles, it is concluded that hydroelectric power plant is the most suitable option for ensuring CO2 reduction for the automotive company. It has been revealed that carbon offset, which is often preferred by companies, is not such an effective alternative.

Modelling of A Solar Thermal Energy System For Energy Efficiency Improvement In A Ceramic Plant

The thermal energy use in the manufacturing plants is the most representative parcel of the total energy consumption within the European industry. Such is mainly attributed to the operation of high energy intensive thermal processes such as furnaces and boilers. The implementation of heat recovery technologies is a solution with a great potential to improve the operation of these processes and improve the overall energy efficiency in a plant. On the other hand, the use of renewable energy resources such as solar energy is highly relevant measure to decrease the use of fossil fuels, such as natural gas. This paper presents the modelling of a solar thermal energy system (STES) established by a water circuit and solar thermal collector for the heat supply to two boilers installed in a ceramic plant. Such system has been conceptualised in the scope of industrial practices, proposing solar heat for industrial processes (SHIP). The practical work in this paper aims to the development of a customised simulation tool for the modelling of heat recovery networks and thermal processes in manufacturing industry plants using the Modelica language. The system model has been developed using existing and newly developed equipment models. The simulation results were validated with measured data in the industrial plant, being consistent with the real values (e.g. highest deviation of about 0.01%). In addition to the boilers, the performed simulation allowed to achieve the sizing of the components of the water circuit, in particular for the pumping system (with a required supply of 0.747 kW of electric energy). A techno-economic assessment has been performed to evaluate the viability of the cproposed solution, showing a payback time of approximately 3 years, a total annual economic savings of about 25209 € and associated reduction of equivalent carbon dioxide emissions of about 170 ton/year.

Heat integration applied on low thermal energy system: Building complex case study

The tertiary-building sector is one of the most important energy consumers in the Morocco, especially thermal energy. Its intensive use of energy is highly related to the building’s inefficient processes. The Moroccan strategy for energy efficiency aims mainly to save 12% of energy consumption by 2020 and 15% by 2030, which reinforce the appearance of many energy saving alternatives ranging from sensitization and construction laws to engineering applications. The present paper addresses the problem of the building complex energy efficiency in order to improve its performance thermally. The proposed approach in this work is based on the pinch technology which is a technique widely used to integrate and optimize the energy of thermal systems and which has demonstrated its successfulness for industrial process. The simulation results reveals that the potential thermal energy saving reaches 21.16%, with heat exchange network design initially proposed to clearly show the potential recovered. Based on the composite curves (CCs), the problem table algorithm (PTA) and the grand composite curve (GCC), the pinch point temperature is turned out to be 15°C with 316,99 kW of hot utility. The obtained results reveal that the proposed pinch technology perform its effectiveness not only in the industrial sector but also in the building-tertiary.

How effective is carbon offset Assessment of carbon dioxide reduction methods by using MCDM techniques: a case study of global automotive factory

In order to reduce CO2 emissions, industrial enterprises try to utilise various methods such as obtaining energy from renewable power plants, afforestation and carbon offset. In this study, it was aimed to determine the most appropriate method to reduce CO2 emissions caused by the energy consumption of an automotive industry company. With this study conducted, analytical hierarchy and multimoora methods, which are among the multi-criteria decision-making techniques, were used together to select the optimum method among the CO2 reduction methods. As a result of the study that assesses the effectiveness of hydroelectric power station, solar electrical system, solar thermal energy system, afforestation and carbon offset alternatives from various angles, it is concluded that hydroelectric power plant is the most suitable option for ensuring CO2 reduction for the automotive company. It has been revealed that carbon offset, which is often preferred by companies, is not such an effective alternative.

Requirements for Building Thermal Conditions under Emergency Operations in Cold Climates

This paper provides recommendations on thermal and moisture parameters in different types of buildings under emergency operation in cold/arctic climates. We consider three scenarios under normal operating conditions: occupied, temporarily unoccupied, and long-term unoccupied. These thermal parameters are necessary to: (1) perform required work safely and efficiently, (2) support building processes, and (3) support long-term integrity of the building under emergency conditions (i.e., interruption of fuel, steam, hot water, and electrical service that interrupts building space conditioning). Under emergency conditions, requirements of thermal parameters for different categories of buildings may change. Mission critical areas can be conditioned to levels that support the agility of personnel who perform critical operations, but not to optimal comfort levels. Critical process requirements are given priority. This paper was developed for military applications, based on research performed under the International Energy Agency’s Energy in Buildings and Communities Program, Annex 73; under the Department of Defense Environmental Security Technology Certification Program project EW18-D1-5281, “Technologies Integration to Achieve Resilient, Low-Energy Military Installations,” and under the Office of the Deputy Assistant Secretary of the Army project “Thermal Energy Systems Resiliency for Army Installations located in cold climates.” Results are applicable to similar public and private sector buildings.

Evaluation of vehicle engine thermal energy system detection effect based on target detection algorithm

The paper takes the front-mounted parallel structure of the transmission as an example and uses the target detection algorithm to introduce a real-time equivalent energy consumption control strategy for the vehicle engine thermal energy system. Based on studying the relationship between fuel thermal energy and electrical energy consumed when the vehicle is driving in a cycle, we elaborated on the strategy?s critical issue, namely, the equivalent method of the electrical energy of the battery pack and the fuel thermal energy consumption of the engine. Finally, the thesis carries out a simulation test on this strategy based on the vehicle simulation model and compares it with other control strategies.

Characterization of Unripe and Mature Avocado Seed Oil in Different Proportions as Phase Change Materials and Simulation of Their Cooling Storage.

Environmental problems have been associated with energy consumption and waste management. A solution is the development of renewable materials such as organic phase change materials. Characterization of new materials allows knowing their applications and simulations provide an idea of how they can developed. Consequently, this research is focused on the thermal and chemical characterization of five different avocado seed oils depending on the maturity stage of the seed: 100% unripe, 25% mature-75% unripe, 50% mature-50% unripe, 75% mature-25% unripe, and 100% mature. The characterization was performed by differential scanning calorimetry, Fourier transform infrared spectroscopy, and thermogravimetric analysis. The best oil for natural environments corresponded to 100% matured seed with an enthalpy of fusion of 52.93 , and a degradation temperature between 241–545 °C. In addition, the FTIR analysis shows that unripe seed oil seems to contain more lipids than a mature one. Furthermore, a simulation with an isothermal box was conducted with the characterized oil with an initial temperature of −14 °C for the isothermal box, −27 °C for the PCM box, and an ambient temperature of 25 °C. The results show that without the PCM the temperature can reach −8 °C and with it is −12 °C after 7 h, proving its application as a cold thermal energy system.

Internal energy change in Darcy-Forchheimer Carreau fluid model past a vertical stretching sheet with magnetic dipole and variable thermo-physical properties

In this research work, we consider a thermal energy system with a different controlling effects which impact the entire system. These controlling effects include the variable thermo-physical properties of Carreau fluid flow causing change in internal energy (viscous dissipation) of the permeable thermal conversion problem. The disturbance in fluid’s motion is created by applying magnetic dipole. After converting the thermal system from partial differential into ordinary differential, the developed system is solved by using midpoint method in combination with bisection. The thermal energy extrusion system consists of velocity and temperature fields. The related controlling parameters include variable thermal conductivity parameter, Darcy-Forchheimer parameter, Eckert number, mixed convection parameter, variable viscosity parameter, ferrohydrodynamic interaction variable, Weissenberg number, curie temperature and Prandtl number. The sketched results provides good thermal effects on entire system for small and large values of these parameters. Carreau fluid model is performed to analyse the properties of shear thinning and thickening. It is noticed that velocity distribution reduces for large values of Williamson parameter, ferrohydrodynamic interaction variable, porosity parameter and variable viscosity parameter but opposite behavior is achieved for large values of Darcy-Forchheimer parameter. The temperature profile shows great impact by emerging parameters appearing on it. The small parameter and Eckert number shows enhancement in temperature distribution, but large reduction is noticed in temperature distribution for greater values of Prandtl number and curie parameter. Comparison of current thermal system is calculated for limited values of these parameters.

Single and Hybrid Nanofluids to Enhance Performance of Flat Plate Solar Collectors: Application and Obstacles

Solar energy represents the best alternative for traditional energy sources used in many thermal energy systems. Among solar thermal systems, Flat Plate Solar Collectors (FPSCs) are the most utilized type implemented in low and medium-level thermal domestic applications. Recently, the usage of nanofluids (NFs) to enhance FPSCs is one of the newest technologies that has drawn the attention of researchers to improve the overall thermal efficiency of solar systems. This paper briefly reviews the recent studies carried on thermal performance enhancement of FPSCs by implementing NFs (single and hybrid NFs) considering the main influential parameters such as particle concentration, particle size, and collector area. Finally, the main obstacles reported by the researchers such as the instability, viscosity, concentration limit, corrosion effect and others are identified, which is believed to be useful for interested newcomers in this research area. Based on the studies investigated in this paper, NFs, even under low concentrations, can remarkably improve the energetic and exergetic efficiency of FPSCs.

Еconomic efficiency of implementation of passive solar systems for creation of necessary microclimate in greenhouses

The article investigates the mechanism of introduction of renewable energy sources to create the necessary microclimate in greenhouses. The organization of greenhouses and the cultivation of various types of crops is a very profitable business, in addition, useful on all sides. The existing relationship between greenhouses and energy companies is one-sided. Today, companies are asking to sign a contract for energy supply of greenhouses for five years ahead, taking into account the hourly limits of electricity. These requirements put greenhouses in an extremely difficult position, because the energy consumption of greenhouses is highly dependent on ambient temperature and weather, which is impossible to predict even a month aheadwith a high degree of probability. For indoor plants,the use of renewable energy sources is the highest priority. The purpose of the work is to propose a mechanism for the introduction of renewable energy sources to create the necessary microclimate in greenhouses and evaluate the economic efficiency of this mechanism. Based on the analysis of scientific sources, the article considers the theoretical foundations of renewable energy sources, summarizes the advantages and disadvantages of generating electricity from solar radiation. The probability and validity of the obtained results is due to the use of general scientific and special statistical methods. The study aims to propose and justify the design of a passive solar system with heataccumulators. The model of a greenhouse with closed passive solar systems is substantiated and its economic efficiency is estimated (costs for introduction of the offered complex solar installation for the enterprise of an agro-industrial complex are covered less than for 3 years that confirms economic efficiency of its introduction). To ensure favorable conditions for plant development, the energy supply system of the greenhouse complex must ensure the reliable operation of technical means for microclimate control, lighting and watering of plants. In the process of functioning of the greenhouse complex, it is influenced by environmental factors (wind speed, ambient temperature, intensity of solar radiation, length of daylight), as well as internal factors (multiplicity of air exchange, etc.), depending on which the needs change thermal and electric energy systems. This in turn affects the importance of energy efficiency indicators. The work is a completed study, which examines the scientificand technical solution of an important scientific andtechnical problem of the introduction of renewableenergy sources in greenhouses. The model of a greenhouse with closed passive solar systems is economically advantageous, so it is advisable to implement it to create the necessary microclimate in greenhouses.