Search

In this study, two wind-solar-based polygeneration systems namely CES-1 and CES-2 are developed, modeled, and analyzed thermodynamically. CES-1 hybridizes a heliostat based CSP system with wind turbines while CES-2 integrates heliostat-based CPVT with wind turbines. This study aims to compare the production and thermodynamics performance of two heliostat based concentrated solar power technologies when hybridized with wind turbines. The systems have been modeled to produce, freshwater, hot water, electricity, hydrogen, and cooling with different cycles/subsystems. While the overall objective of the study is to model two polygeneration systems with improved energy and exergy performances, the performances of two solar technologies are compared. The wind turbine system integrated with the comprehensive energy systems will produce 1.14 MW of electricity and it has 72.2% energy and exergy efficiency. Also, based on the same solar energy input, the performance of the heliostat integrated CPVT system (CES-2) is found to be better than that of the CSP based system (CES-1). The polygeneration thermal and exergy efficiencies for the two systems respectively are 48.08% and 31.67% for CES-1; 59.7% and 43.91% for CES-2. Also, the electric power produced by CES-2 is 280 kW higher in comparison to CES-1.

The growing interest in hybrid nanofluids is due to the synergistic effects of nanoparticles, which could give them better heat transfer properties as compared to base fluids, and conventional nanofluids. Several factors like temperature and volume fraction have been used in explaining the behaviours of hybrid nanofluids, however, the need to investigate comprehensively, the mixing ratios of hybrid nanofluids, remains a critical research area in the development of efficient nanofluids as heat transfer fluids. In this study, three mixture ratios of 1:1:1 (33.3% Al2O3, 33.3% ZnO, 33.3% Fe3O4), 1:2:1 (25% Al2O3, 50% ZnO, 25% Fe3O4), and 1:1:2 (25% Al2O3, 25% ZnO,50% Fe3O4) ternary hybrid nanofluid (THNF) are synthesized at volume concentrations of 0.5%, 0.75%, 1%, and 1.25%. All experiments were carried out at a temperature range between 25 °C-65 °C. The effect of temperature, volume concentration, mixture ratio, are examined, as well as the development of a machine learning model for accurate prediction. The thermal conductivity and dynamic viscosity behaviour of the THNF were investigated. The result showed that temperature and volume concentration significantly affected the thermophysical properties of the fluid. The optimum Thermal Conductivity enhancement (TCE) was retrieved for the 1:1:1 THNF, at 36.018%. The 2:1:1, and 1:2:1 mixture ratios had a 32.92%, and 31.68% TCE respectively. At 1% volume concentration, the optimum TCE (as compared with water) for the mono, hybrid, and THNF measured are 18.98%, 28.58%, and 32.45% respectively. It is seen that the least viscosity was recorded for the 1:1:1 mixture ratio (0.001 Pa.s), while the highest viscosity was measured for the 2:1:1 THNF mixture ratio (0.021 Pa. s). The Gaussian process regression (GPR) gave an excellent prediction showing an R2 value of 0.9656, and 0.934 for the thermal conductivity and dynamic viscosity prediction respectively. In terms of application to solar thermal systems, the low viscosity of 1:1:1 Al2O3–ZnO-Fe3O4 THNF makes that a low-pressure drop and pump work is required in practical applications of the 1:1:1 Al2O3–ZnO-Fe3O4 THNF.

Unlike previous studies where models/methods used in determining the carbon emission are presented, in this paper, a detailed analysis of the causes, trends, and solutions to carbon emission in Africa is presented. Economic development plays a crucial role in the well-being of a country/continent, thereby, affecting energy consumption. The impact of economic development on Africa's carbon (CO2) emissions trend is first investigated. After which, three neural network models are developed to predict the future trend of total CO2 emission in the continent. Then, the use of renewable energy (RE) sources for power generation is analyzed/proposed as a viable solution for CO2 emission reduction in Africa. Finally, the impact of battery electric vehicles (BEVs) integration and hydrogen production in maximizing RE production in Africa's largest economy is analyzed. Secondary data of the economic indicators for twenty-five different African countries have been used to justify the effect of economic development on their carbon emission. From the results of the analyses, gross national income and carbon emissions in all sectors were found to be significantly positively correlated. That is, as national wealth across Africa increases, carbon emissions in the continent increase. Also, the predicted total annual CO2 emission showed that most countries will witness an increase in total CO2 emission by 2022 in comparison to 2018. The proposed RE-based method for power generation showed that the CO2 emission from the power industry can be reduced to zero for an African country. Nevertheless, the use of BEVs and the production of hydrogen will be integral in achieving this.

Unlike steam and gas cycles, the Kalina cycle system can utilize low-grade heat to produce electricity with water-ammonia solution and other mixed working fluids with similar thermal properties. Concentrated photovoltaic thermal systems have proven to be a technology that can be used to maximize solar energy conversion and utilization. In this study, the integration of Kalina cycle with a concentrated photovoltaic thermal system for multigeneration and hydrogen production is investigated. The purpose of this research is to develop a system that can generate more electricity from a solar photovoltaic thermal/Kalina system hybridization while multigeneration and producing hydrogen. With this aim, two different system configurations are modeled and presented in this study to compare the performance of a concentrated photovoltaic thermal integrated multigeneration system with and without a Kalina system. The modeled systems will generate hot water, hydrogen, hot air, electricity, and cooling effect with photovoltaic cells, a Kalina cycle, a hot water tank, a proton exchange membrane electrolyzer, a single effect absorption system, and a hot air tank. The environmental benefit of two multigeneration systems modeled in terms of carbon emission reduction and fossil fuel savings is also studied. The energy and exergy efficiencies of the heliostat used in concentrating solar radiation onto the photovoltaic thermal system are 90% and 89.5% respectively, while the hydrogen production from the two multigeneration system configurations is 10.6 L/s. The concentrated photovoltaic thermal system has a 74% energy efficiency and 45.75% exergy efficiency, while the hot air production chamber has an 85% and 62.3% energy and exergy efficiencies, respectively. Results from this study showed that the overall energy efficiency of the multigeneration system increases from 68.73% to 70.08% with the integration of the Kalina system. Also, an additional 417 kW of electricity is produced with the integration of the Kalina system and this justifies the importance of the configuration. The production of hot air at the condensing stage of the photovoltaic thermal/Kalina hybrid system is integral to the overall performance of the system.

The performance analysis of a novel multi-generation (MG) system that is developed for electricity, cooling, hot water and hydrogen production is presented in this study. MG systems in literature are predominantly built on a gas cycle, integrated with other thermodynamic cycles. The aim of this study is to achieve better thermodynamic (energy and exergy) performance using a MG system (without a gas cycle) that produces hydrogen. A proton exchange membrane (PEM) utilizes some of the electricity generated by the MG system to produce hydrogen. Two Rankine cycles with regeneration and reheat principles are used in the MG configuration. Double effect and single effect absorption cycles are also used to produce cooling. The electricity, hot water, cooling effect, and hydrogen production from the multi-generation are 1027 kW, 188.5 kW, 11.23 kg/s and 0.9785 kg/h respectively. An overall energy and exergy efficiency of 71.6% and 24.5% respectively is achieved considering the solar parabolic trough collector (PTC) input and this can increase to 93.3% and 31.9% if the input source is 100% efficient. The greenhouse gas emission reduction of this MG system is also analyzed.

Ternary nanofluids are a new type of fluids with three nanoparticles dispersed in a base fluid, and they have been experimentally shown to have improved thermophysical and rheological properties as compared to conventional or hybrid nanofluids. This study presents a numerical computation of investigating the performance of Photovoltaic/thermal collectors by utilizing Al2O3-ZnO-Fe3O4/water ternary nanofluid. The preparation of the nanofluid was done using a two-step method and analyzed for stability using Zeta potential analysis. The effect of the mixture ratio of the nanofluid on the thermal and electrical efficiency of the Photovoltaic/thermal system is investigated. The price-performance factor of the ternary nanofluid is firstly computed to determine the optimum volume concentration for practical application. This study also investigates the effect of nanofluid mass flow rate, volume fraction, mixture ratio and solar irradiation on the Photovoltaic/thermal system. From an economic standpoint, the system was estimated using the Price-performance factor and results showed that the 0.5 vol% Al2O3-ZnO-Fe3O4 ternary hybrid nanofluid was most suitable for laminar flow and turbulent flow regimes. The optimum electrical and thermal efficiency measured in this study was 13.75% and 59.38% respectively. This study also recorded an optimum cell temperature reduction of 8.81 °C. The mixture ratio measured for optimum PV/T performance was 0.33. The maximum exergy efficiency and PV/T total exergy efficiency recorded are 1.53% and 14.77%. The ternary nanofluid based PV/T system saved 19948.04 kgCO2 annually, as compared to 18719.88 kgCO2 when water was used as heat transfer fluid. The payback period was calculated to be 2.63 years for the ternary hybrid nanofluid based PV/T system.

Decade research on nanofluids have solidified the claim that they have excellent heat transfer properties. The properties of mono nanofluids can be optimized by varying the volume concentration of the nanoparticle, however, there is a limit to this due to the challenge of the trade-off of the net negative of viscosity increase. In resolving this limitation, hybrid nanofluids have been synthesized by researchers to maximize the unique properties of different types of nanoparticles. The early days of hybrid nanofluid experimentations consisted of two-particle nanofluids, however, in recent years, a new class of working fluids has been discovered and extensively explored, consisting of three solid nanoparticles dispersed in a conventional fluid. These fluids are referred to as ‘ternary nanofluid, 'ternary hybrid nanofluid’ or ‘trihybrid nanofluids’. This paper gives a comprehensive review of all studies that have synthesized this new class of nanofluids. The major focus in this study was given to their synthesis methods, characterizations, stability tests, thermophysical properties (thermal conductivity, specific heat capacity, and viscosity). This study also reviews the heat transfer applications of ternary nanofluids. The ternary nanofluids are shown to significantly increase the thermal conductivity and heat transfer properties of base fluids. The type and sizes, as well as mixture ratio of nanoparticles are important factors that determine the effectiveness of ternary nanofluids. Several areas still need to be covered for proper understanding of the hybridization effects of three particle nanofluids, like the effect of combining different nanoparticle types, particle sizes, nanoparticle shape, and base fluids.

Nanofluids have gained tremendous research interests in diverse fields of study due to their improved properties, especially as heat transfer fluids. Numerous studies have revealed the characteristics, limitations, and applicability of single type nanoparticles and the attributes of their colloidal mixtures. The discovery of the synergistic effect of nanoparticles, as relating to their improved thermophysical properties have been further explored in experimental and numerical studies of hybrid nanofluids. While the major focus has been on thermal conductivity, and viscosity, another extremely important property that gets little study attention is the specific heat capacity, which is a key thermal property in energy systems. Proper understanding of the specific heat capacity (SHC) of hybrid nanofluids is a sine qua non for proper decisions for heat transfer and heat storage applications. The crux of this review study is to give a detailed and comprehensive review of the specific heat capacity of hybrid nanofluids. The synthesis, characterization, and stability of hybrid nanofluids are presented. Furthermore, the different effects like temperature, volume concentration, mixture ratio, and particle size that influence the SHC behaviour of hybrid nanofluids are analyzed in this study. A compilation and discussion on correlation and machine learning models developed for hybrid nanofluids are also presented. Results suggest that volume concentration have an inverse relationship with the SHC of hybrid nanofluids, an increase in temperature improves the SHC of hybrid nanofluids, and this is more significant at temperatures above 50 ℃. Finally, although scarcely researched, the SHC is also affected by the size of the nanoparticles.

The utilization of solar thermal collectors has increased significantly in the last decade. The heat transfer fluids that is used in the design of these systems has notable effects on their performance. The recent discoveries of hybridized nanofluids, give a promising approach for investigating the performance of parabolic trough collectors (PTC), especially at different design conditions and environmental parameters. This study investigates the thermodynamic performance of a Kalina cycle incorporated with a parabolic trough collector that utilizes ternary nanofluid as a heat transfer fluid. The use of mono, hybrid and ternary nanofluids (THNF) in the parabolic trough collector is examined based on their impact on the efficiency of thermal system. The nanofluids considered are Al2O3, Al2O3–Fe, Al2O3–ZnO, and CuO–MgO–TiO2. The performance of integrated cycle based on the effect of solar irradiation and volume fraction of the nanofluids are studied and compared with conventional fluids namely: thermal VP1 oil, DowThermal oil, and Salt (7NaNO3, 40NaNO2, 53KNO2). In addition, an optimization study is conducted using genetic algorithm to maximize the net power output of the Kalina cycle and the exergetic efficiency of overall system. The results showed that performance of the system which uses nanofluids as a working fluid was higher than the systems using conventional fluids. Furthermore, the results demonstrate that maximum net power output of the system is recorded when Al2O3, Al2O3–Fe, Al2O3–ZnO, and CuO–MgO–TiO2 nanoparticles are used. The power outputs were evaluated as 59.72 kW, 56.64 kW, 54.54 kW, and 61.21 kW respectively. The optimization study reveals that the optimum exergetic efficiency when Al2O3, Al2O3–Fe, Al2O3–ZnO, and CuO–MgO–TiO2 nanofluids are used can reach up to 21.0%, 17.2%, 10.8%, and 25.1% respectively.

Agriculture and its corresponding farms are an integral part of every society/country. In recent years, the energy consumption by farms has risen as sophisticated technologies (that require a high amount of energy) are used for the pre-processing/storage of farm produce. In a bid to advance the transition toward cleaner energy consumption in farms, the thermodynamic assessment of two innovative high-performance solar-based multigeneration systems is presented in this study. Based on the identified most crucial energy needs in farms, the multigeneration systems are designed to produce electrical power, cooling/refrigeration effect, hydrogen, and domestic hot water. In comparison to existing literature, this study is novel as it analyzes the daily performance of the multigeneration systems based on the integration/comparison of two storage techniques. While thermal storage is integrated with one multigeneration system (MGS-TS), the power-to-hydrogen conversion and use of the hydrogen in a solid oxide fuel cell is considered as the storage mechanism in the second system (MGS-SOFC). To analyze the daily performance of the systems, solar parabolic trough collectors are used to produce the input thermal energy based on a 6-hour availability timeframe per day, and the storage systems are designed to power the system for the remaining 18 h. The multigeneration systems developed are analyzed using the energy/exergy approach while the economic costs of the systems are also compared. The effect of different crucial parameters including, ambient temperature, discharge periods, dispatch rates, etc. on key variables related to the systems is investigated. Based on the performance assessment of the two high-performance systems modeled in this study, the overall energetic and exergetic efficiencies are 55.37% and 53.70% for MGS-TS, and 51.12% and 46.82% for MGS-SOFC. The total daily electricity, cooling/refrigeration effect, and hot water useful outputs from the two multigeneration systems are 61,630 kWh/day, 7,939.1 kWh/day, and 125,178 Liters/day for MGS-TS; and 34,597 kWh/day, 15,504 kWh/day, and 129,686 L/day for MGS-SOFC respectively. While the performances of the two systems differ slightly, the unique advantages of each are embedded in their useful energy products.

In this experimental study, the specific heat capacity of water-based Fe3O4-Al2O3-ZnO was fabricated. Three mixture ratios of 1:1:1 (33.33%% Fe3O4, 33.33%% Al2O3, 33.33%% ZnO), 1:2:1 (25% Fe3O4, 50% Al2O3, 25% ZnO,) and 1:1:2 (25% Fe3O4, 25% Al2O3, 50% ZnO,) were synthesized at volume fraction of 0.5%, 0.75%, 1% and 1.25%. All the experiments were carried out at a temperature range of 25°C and 65°C. Zeta potential test and particle size analyzer were used in examining the dispersal stability of the nanofluids, and nanoparticle size, respectively. Also, a high-resolution scanning electron microscope was used in describing the morphological structure of the nanocomposites. The result of the study showed that there exists a linear effect of temperature on the specific heat capacity of the ternary hybrid nanofluid. Also, when the volume concentration increases, it causes the specific heat capacity to decrease. At the mixture ratio of 1:1:1(Fe3O4-Al2O3-ZnO), 1:2:1 (Fe3O4-Al2O3-ZnO) and 1:1:2 (Fe3O4-Al2O3-ZnO), the maximum specific heat capacity increment of 11.9399%, 14.6491% and 13.5572% respectively was recorded at 1.25% volume concentration and 25°C temperature, as compared to the base fluid. The experimental result showed a `peaking effect` in the specific heat capacity, which was measured at a mixture ratio of 1:1:1. The least specific heat capacity values recorded are for the mixture ratio of 1:2:1. Correlation and machine learning models were developed in this study, and the result showed that the most accurate prediction of the experimental data was obtained using the support vector regression model. When the support vector regression and correlation models were compared to the experimental results, the maximum deviation recorded was 0.2% and 12.467% respectively.

In light of the popular gain of renewable energy sources and solar energy technologies in particular, photovoltaic thermal systems present an interesting approach towards cogeneration of electricity and heat. The extraction of heat from the photovoltaic array for use also serves the purpose of reducing the operating temperature of the solar cells to improve their power conversion efficiency. This study analyzes the possibility of incorporating a PV/T system with an absorption system. Three different systems are considered; the single effect, double effect & triple effect absorption systems driven by heat from the PV/T. It is evident that the triple effect absorption cooling system has the highest coefficient of performance thus giving a greater cooling benefit for the same input energy from the PV/T.

This paper provides a theoretical comparative analysis for the thermodynamic performance of a cascade refrigeration system using different refrigerants paired with carbon dioxide (CO2). The cascade refrigeration system consists of a low-temperature loop and a high-temperature loop. The former loop uses CO2 as working fluid while the later loop uses four different refrigerants namely HFE7000, HFE7100, NH3 and R134a. HFE7000 and HFE7100 are new refrigerants called hydrofluroethers. A code is developed in engineering equation solver for the basic energy and exergy balance equations of the system. For the reference conditions; 223 K evaporator temperature and 308 K condenser temperature, the coefficient of performance was obtained as 1.398, 1.3363, 1.309, and 1.221 for refrigerant couples NH3/CO2, R134a/CO2, HFE7000/CO2, and HFE7100/CO2 respectively. The exergy efficiencies for the reference conditions were calculated as 47.01%, 45.84%, 44.30%, and 41.06% respectively for NH3, R134a, HFE7000, and HFE7100 refrigerants paired with CO2. The condenser and evaporator temperatures and heat exchanger effectiveness were varied to determine their effect on the cooling coefficient of performance and the exergy efficiency. The evaporator has been identified as the component having the highest rate of exergy destruction, whereas the expansion valve in the low temperature loop has the lowest rate of exergy destruction. The total equivalent warming impact (TEWI) values of the refrigerant pairs of the system are calculated and contrasted for the reference operating conditions for a cooling load of 175 kW. The HFE7000 is considered as a promising refrigerant according to the COP, exergy efficiency, and TEWI results for the proposed cascade refrigeration system, as it can be used as a substitute to R134a.

One of the main challenges in renewable energy integrated multigeneration and comprehensive system researches is the inability to study the transient performance analysis of the system. In this study, a novel wind-biomass comprehensive energy system for power, cogeneration, trigeneration, and multigeneration is proposed. This system is analyzed in both steady-state and transient conditions using energy and exergy approaches. Rice husk is considered as the raw material for biomass fuel. The comprehensive system is modeled to produce electricity, freshwater, hot water, and hydrogen with a steam cycle, an organic Rankine cycle, a double stage refrigeration system, a proton exchange membrane electrolyzer, and a hot water chamber. Electric vehicles are integrated with the system in time-based process modeling to ensure load stability and maximize electricity production. The overall exergy and energy efficiencies of the proposed comprehensive system increase from 24.91% and 27.42% while producing electricity to, 26.08% and 35.22% when multigenerating. Based on the transient analysis, this system is capable of meeting the energy demand of a rice-producing factory, campus, and its surrounding community. The process modeling also shows the hourly performance of the system and its load stability.

One of the challenges faced by renewable energy (RE) powered multigeneration system is the unavailability of RE resources at different times. In this research, a novel comprehensive energy system powered with wind turbines, concentrated photovoltaic/thermal and biogas is modelled and analyzed using energy and exergy approach. Multiple useful products such as electricity, hot air, hydrogen, fresh water, cooling effect and hot water will be produced by the system. Four different operational scenarios namely; CPVT/wind, wind/biogas, CPVT/biogas, and biogas only are considered for this comprehensive energy system. Thermal energy storage is incorporated with the system, in order to save thermal energy that will be used during hours without solar radiation. Furthermore, the CO2 emissions saved, in comparison with the use of different fossil fuel sources is analyzed. The maximum productions from the comprehensive system are: 3.4 MW of electricity; 12.41 L/sec of Hydrogen; 279.4 kW of cooling effect; 17.546 kg/s of hot air; 144.18 L/min of hot water and 10.31 L/min of fresh water. The overall energetic efficiency of the system considering all the case studies ranges from 64.91% to 71.06% while the exergetic efficiencies ranges from 31.80% to 53.81%. The CO2 emission analysis results show that the system is environmentally friendly.

We propose a method for residential end-use load analysis in developing countries. The times of use of home appliances were established by conducting face-to-face surveys, from which typical hourly load curves are obtained. For N. Cyprus, where the winter peak is the critical load, electrical heating of water and space is the dominant activity. DSM measures can reduce the peak by approximately 53 MW at the expense of US$12 million. A capital investment of $100 million for a new power plant may be deferred for 20 years.