Investigation of the effect of physical factors on exergy efficiency of a photovoltaic thermal (PV/T) with air cooling

Thermal photovoltaic systems are used to harness solar energy to generate electricity and thermal at the same time. In this technology, electrical efficiency is very low compared to thermal efficiency; as the cell surface temperature rises, the electrical efficiency decreases, so one of the ways to achieve high efficiency is exergy analysis. Exergy analysis of a process or system shows how much of the ability to perform the work or input exergy has been consumed by that process or system. In this research, an ordinary thermal photovoltaic panel with air cooling has been examined for exergy. To do this, it has identified the effective performance variables from a mechanical point of view, which are inlet air temperature, inlet air flow, and length (number of modules that are connected in series). The effect of changing each of the variables based on Saveh weather conditions has been simulated using MATLAB software. The results show that the exergy efficiency of the panel decreases with the inlet air temperature increasing. It was also observed that the optimal airflow is 0012 (kg/s) and will have the highest efficiency per 8.8 m length.http://www.hindawi.com/journals/ijpMechanical and Aeronautical Engineerin

A review of thermal conductivity models for nanofluids

Nanofluids, as new heat transfer fluids, are at the center of attention of researchers, while their measured thermal conductivities are more than for conventional heat transfer fluids. Unfortunately, conventional theoretical and empirical models cannot explain the enhancement of the thermal conductivity of nanofluids. Therefore, it is important to understand the fundamental mechanisms as well as the important parameters that influence the heat transfer in nanofluids. Nanofluids’ thermal conductivity enhancement consists of four major mechanisms: Brownian motion of the nanoparticle, nanolayer, clustering, and the nature of heat transport in the nanoparticles. Important factors that affect the thermal conductivity modeling of nanofluids are particle volume fraction, temperature, particles size, pH, and the size and property of nanolayer. In this paper, each mechanism is explained and proposed models are critically reviewed. It is concluded that there is a lack of a reliable hybrid model that includes all mechanisms and influenced parameters for thermal conductivity of nanofluids. Furthermore, more work needs to be conducted on the nature of heat transfer in nanofluids. A reliable database and experimental data are also needed on the properties of nanoparticles.http://www.tandfonline.com/loi/uhte202016-09-30hb201

Unsteady Darcian Natural Convection within Porous Media of Square Enclosure at Various Rayleigh Numbers

Transient natural convection within a 2D square cavity filled with a porous medium is numerically investigated. The left wall is suddenly heated to a constant temperature Th, while the right wall is suddenly cooled to a constant temperature Tc. Both the horizontal walls are insulated. The Finite Volume numerical method is used to solve the dimensionless governing equations. The results are obtained for the initial transient state assuaging to the steady state, and for Rayleigh number values of 102-104. It is indicated that the average Nusselt number showing an undershoot during the transient period and that the time needed to reach the steady state is longer for low Rayleigh number and shorter for high Rayleigh number.</p

Enhancing energy efficiency in zero energy buildings: Analyzing the impacts of phase change material-filled enclosures and outlet air distance on solar wall performance

This paper presents a study on solar walls integrated with phase change material (PCM) to enhance energy efficiency in zero-energy buildings. The research focuses on expanding the surface area with PCM-filled compartments to improve thermal performance. The effects of different expanded surface shapes and outlet air distances on the solar wall's temperature and PCM solidification process are investigated through numerical simulations. The findings show that semicircular surfaces with a 30 cm outlet air distance have the highest temperatures, while rectangular surfaces with the same distance have the lowest temperatures. Semicircular surfaces take the longest time to freeze PCM completely, whereas rectangular surfaces with a 30 cm gap achieve the fastest solidification. These insights provide valuable guidance for optimizing solar wall design and energy efficiency in zero-energy buildings. Finally, it was seen that by changing the shape of the extended surfaces and the air gap, the outlet air temperature changes up to 1.15° and the wall temperature changes up to 1.21°

Influence of Preparation Characteristics on Stability, Properties, and Performance of Mono- and Hybrid Nanofluids: Current and Future Perspective

Nanofluids (NFs) synthesized via the suspension of diverse nanoparticles into conventional thermal fluids are known to exhibit better thermal, optical, tribological, and convective properties, photothermal conversion, and heat transfer performance in comparison with traditional thermal fluids. Stability is pivotal to NF preparation, properties, performance, and application. NF preparation is not as easy as it appears, but complex in that obtaining a stable NF comes with the harnessing of different preparation parameters. These parameters include stirring duration and speed, volume, density, base fluid type, weight/volume concentration, density, nano-size, type of mono or hybrid nanoparticles used, type and quantity of surfactant used, and sonication time, temperature, mode, frequency, and amplitude. The effect of these preparation parameters on the stability of mono and hybrid NFs consequently affects the thermal, optical, rheological, and convective properties, and photothermal conversion and heat transfer performances of NFs in various applications. A comprehensive overview of the influence of these preparation characteristics on the thermal, optical, rheological, and properties, photothermal conversion, and heat transfer performance is presented in this paper. This is imperative due to the extensive study on mono and hybrid NFs and their acceptance as advanced thermal fluids along with the critical importance of stability to their properties and performance. The various preparation, characterization, and stability methods deployed in NF studies have been compiled and discussed herein. In addition, the effect of the various preparation characteristics on the properties (thermal, optical, rheological, and convective), photothermal conversion, and heat transfer performances of mono and hybrid NFs have been reviewed. The need to achieve optimum stability of NFs by optimizing the preparation characteristics is observed to be critical to the obtained results for the properties, photothermal conversion, and heat transfer performance studies. As noticed that the preparation characteristics data are not detailed in most of the published works and thus making it mostly impossible to reproduce NF experimental studies, stability, and results; future research is expected to address this gap. In addition, the research community should be concerned about the aging and reusability of NFs (mono and hybrid) in the nearest future

Effect of Nanoconvection due to Brownian Motion on Thermal Conductivity of Nanofluids

A nanofluid is a new class of heat transfer fluids that contain a base fluid and nanoparticles. The use of additives is a technique applied to enhance the heat transfer performance of base fluids. The thermal conductivity of the ordinary heat transfer fluids is not adequate to meet today's cooling rate requirements. Nanofluids have been shown to increase the thermal conductivity and convective heat transfer performance of the base liquids. One of the possible mechanisms for anomalous increase in the thermal conductivity of nanofluids is the Brownian motions of the nanoparticles inside the base fluids. It is shown in this Study that the heat diffusion assumption that has been used in the macro- and micro- composite systems is not valid in the nanofluid systems. Apart from heat diffusion the nanoconvection diffusion that it is due to the indirect effect of Brownian motion is responsible of enhancement in thermal conductivity Of nanofluid systems

The impact of renewable energy sources on the sustainable development of the economy and greenhouse gas emissions

Growing population and limited energy resources have impacted energy consumption. Limited fossil fuel resources and increased pollution threaten national and human societies. These elements emphasize energy sources. Renewable energy use affects growth. All new energy sources, including renewables, are crucial for global economic growth. Economic and environmental issues have led to new approaches in international environmental law, including the green economy. This study employs structural vector auto-regression (SVAR) to compare the effects and outcomes of increasing the use of renewable energy in the context of economic growth and greenhouse gas emissions in middle income countries (MICs) and high income countries (HICs). The results show that these indicators demonstrate that the production of energy from renewable sources has positive short-term and long-term economic effects with varying contributions. However, renewable energies have a greater impact on the green economy in selected MICs than in selected HICs. Therefore, the promotion of macroeconomic indicators is viewed as one of the reasons for the development of policies to increase energy production from renewable sources in selected countries

Numerical study and optimization of thermal efficiency for a pin fin heatsink with nanofluid flow by modifying heatsink geometry

This paper presents a numerical study on the thermal efficiency of a pin fin heatsink (HEK). The working fluid used is an alumina/water nanofluid, which enters the HEK in a laminar flow regime and exits from its surroundings. This study involves varying the distance between circular pin fins, their height, and their diameter. By altering these parameters, we determine the values of thermal resistance (THR) and temperature uniformity (Teta) on the HEK, along with the heat transfer coefficient (HTC). We further optimize the obtained results using artificial intelligence techniques to minimize the THR of the HEK, maximize the HTC, and achieve the best Teta on the HEK. This numerical investigation employs a two-phase approach to model nanofluid flow within the HEK. The optimization process yields predictions with an accuracy of less than 4%. The findings reveal that increasing the height of the pin fins reduces the HTC and the heat capacity of the HEK, while simultaneously improving the Teta on the HEK. Expanding the distance between pin fins enhances the HTC, decreases the THR of the HEK, and further improves the Teta on the HEK. Similarly, augmenting the diameter of the pin fins amplifies the HTC, reduces the THR, and enhances the Teta on the HEK

A detailed review on the performance of photovoltaic/thermal system using various cooling methods

As an emerging technology, photovoltaic (PV) panels have made a vital energy source to meet increased energy consumption demand and to replace the associated scarcity of traditional energy resources. PV modules have electrical efficiency from 4 to 26%, depending on their materials. The PV panel transforms about 50–60% of total solar radiation into heat, leading to high temperatures during the operation of the PV panel. Due to high temperature, there is a decrease in electrical conversion efficiency and thermal stress in PV panels continue for a more extended period. In this context, a photovoltaic/thermal (PV/T) system is suggested to decrease the thermal stress of the PV panel by removal of heat and make it useful at high PV module temperature. This comprehensive literature review reports PV cooling techniques, research gaps and difficulties encountered by various researchers in this technology. To counter this drawback, active and passive methods of cooling have been studied, including jet impingement, airflow cooling, immersion cooling using liquids, thermoelectric based cooling, microchannel cooling, phase change materials (PCM) based cooling, water/liquid cooling and heat pipe cooling. This research study intends to present a modern, systematic review of PV/T cooling techniques and challenges associated with these methods. Furthermore, techno-economic analysis and the role of artificial intelligence in PV/T systems are also summarized.http://www.elsevier.com/locate/seta2023-12-30hj2023Mechanical and Aeronautical Engineerin