Fossil fuels are sharing a large portion of energy demand. Conventional energy sources emit a huge amount of greenhouse gas into the atmosphere, which creates energy and environmental challenges for ...the ecosystem. To fulfill the world energy demand and to support environmental as well as economic development in a sustainable way, with the utilization of technological advancement of renewable energy resources, algae are presently believed as most adaptable feedstock materials for bioenergy production. Algae has a high fixation rate of atmospheric carbon dioxide which supports to fast growth rate with high productivity per unit area in the form of renewable algal biomass. The present article aims to elaborate on the three generations of biofuels, sustainable microalgae biomass production, cultivation systems, and a wide range of growth parameters. The microalgae harvesting methods and their challenges are also discussed, with a special focus on lipid extraction methods and future r recommendations. The upstream and downstream processes of microalgae could help to harness the microalgae energy in an eco-friendly manner and will help in achieving overall sustainable development.
•Microalgal biomass is a sustainable feedstock for biofuel and bioproducts.•Optimization of upstream and downstream processes enhance produces of microalgae.•Important biotic and abiotic factors of microalgae cultivation are summarized.•Critical steps of harvesting and transesterification of microalgal are discussed.•The key challenges with future recommendations of algal cultivation are briefed.
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•Comparative experimental study on PV and PV/T systems.•Two-sided serpentine-flow thermal absorber to cover more heat transfer surface.•PV/T performance assessment based on both energy and exergy ...analysis.•Thermal efficiencies of PV/T system were 74.62%.•A 5.76% enhancement in electrical efficiency of PV/T as compared to PV.
Photovoltaic (PV) technology suffers from the major drawback of poor energy conversion efficiency that is further worsened by overheating of the module. Hybrid photovoltaic thermal (PV/T) collectors have brought about a notable change in this technology by enabling the extraction of both electricity and heat from the same module, thereby improving the overall efficiency. However, there are some technical challenges with these devices that obstacles their wide-scale application. The major shortcoming of conventional water based PV/T collector is that their operation is limited only in the daytime. To overcome these challenges, novel parallel serpentine pipe flow based PV/T has been designed, developed and studied. The experiments were performed at different volume flow rates viz. 0.5–4 L per minutes (LPM) to optimize the designed and developed PV/T. Maximum thermal efficiency of PV/T system was found to be as 76.58% at 2 LPM. Electrical efficiency of PV and PV/T-only was found to be 9.89% and 10.46% respectively. The maximum exergy efficiency of PV and PV/T system has been found 7.16% and 12.98% (0.5LPM) respectively.
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In present work, techno-economic and thermodynamic analysis of an ETC with/without PCM has been undertaken. The results approved that for all selected flow rates, ETC/S obtained higher energy and ...exergy efficiencies in comparison to the ETC/WS design. The maximum attained value of average daily energy efficiency for ETC/S and ETC/WS was 78.36% and 54.10% respectively with a high flow rate (24 L/h). Also, at this flow rate, ETC/S and ETC/WS attained peak value of average daily exergy efficiency of 23.15% and 20.06% respectively. The average daily energy efficiency of ETC/S was found to be 53.46%, 30.87%, and 44.85% higher in comparison to ETC/WS for low (8 L/h), medium (16 L/h) and high (24 L/h) flow rate respectively. Hence, the integration of SA (stearic acid) as energy storage material with HP-ETC not only stored the thermal energy but also enhanced the system performance.
Furthermore, the techno-economic study revealed that the cost of production of hot water by ETC/S has been found to be lowest compared with ETC/WS and electric geyser. This analysis showed that ETC/S system has a promising potential in terms of supply of hot water from low to medium temperature range at a cheaper rate at lower payback period.
•Thermal performance of the developed systems is influenced by the flow rates.•Performance of evacuated tube collector with/without storage was investigated.•Economic viability of developed systems is done by techno-economic analysis.•HP-ETC with phase change material having good performance.
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•ETC and ETC-HP system is discussed with possible applications.•Performance of heat pipe ETC is higher compared to direct flow ETC.•PCMs application in ETC system proves it more efficient as compared ...to without PCM.•Heat Pipe ETC found more suitable for industrial/domestic applications.•Thermal Analysis of ETC-HP and direct flow ETC is discussed.
Sun is the prime source of energy. There are two types of technologies available for the harnessing of solar energy i.e. Solar Thermal and Solar photovoltaic. Solar thermal energy having a potential to provide the domestic and industrial energy demand for hot water, air heating, solar cooling, solar drying etc. Among multiple applications of solar energy, water heating, space heating, and cooling are consuming more energy. The energy consumption in production of hot water represents a large contribution of total building energy consumption. The Collector is the important aspect for efficient energy needs for these applications. Among all thermal collectors specifically for low/medium temperature applications, evacuated tube collector is found to have the best efficiency. This paper addresses the advancement, different types of evacuated tube collectors and its low/medium temperature applications. The use of heat pipe in evacuated tube has been studied by many researchers around the globe to overcome the lower performance issue in direct flow evacuated tube collector. This turns out to be one of the most important advancement in this area. Another, important advancements in this research have been found to be integration of phase change materials with evacuated tube collector which has the great impact on its performance. This makes the evacuated tube technology more efficient, reliable and user-friendly. This review covers the recent research areas of the direct flow and heat pipe evacuated tube collector with different applications and comprehensive knowledge of the theoretical analysis. This paper also provides financial advantages, classification with and without thermal energy storage, advantages and drawbacks of evacuated technology and future recommendation for future improvement and recent research trend have also incorporated in this manuscript for researchers and practice engineers.
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45.
Mechanisms of homocysteine-induced oxidative stress Tyagi, Neetu; Sedoris, Kara C; Steed, Mesia ...
American journal of physiology. Heart and circulatory physiology,
12/2005, Volume:
289, Issue:
6
Journal Article
Peer reviewed
Department of Physiology and Biophysics, University of Louisville School of Medicine, Louisville, Kentucky
Submitted 24 May 2005
; accepted in final form 1 August 2005
Hyperhomocysteinemia decreases ...vascular reactivity and is associated with cardiovascular morbidity and mortality. However, pathogenic mechanisms that increase oxidative stress by homocysteine (Hcy) are unsubstantiated. The aim of this study was to examine the molecular mechanism by which Hcy triggers oxidative stress and reduces bioavailability of nitric oxide (NO) in cardiac microvascular endothelial cells (MVEC). MVEC were cultured for 024 h with 0100 µM Hcy. Differential expression of protease-activated receptors (PARs), thioredoxin, NADPH oxidase, endothelial NO synthase, inducible NO synthase, neuronal NO synthase, and dimethylarginine-dimethylaminohydrolase (DDAH) were measured by real-time quantitative RT-PCR. Reactive oxygen species were measured by using a fluorescent probe, 2',7'-dichlorofluorescein diacetate. Levels of asymmetric dimethylarginine (ADMA) were measured by ELISA and NO levels by the Griess method in the cultured MVEC. There were no alterations in the basal NO levels with 0100 µM Hcy and 024 h of treatment. However, Hcy significantly induced inducible NO synthase and decreased endothelial NO synthase without altering neuronal NO synthase levels. There was significant accumulation of ADMA, in part because of reduced DDAH expression by Hcy in MVEC. Nitrotyrosine expression was increased significantly by Hcy. The results suggest that Hcy activates PAR-4, which induces production of reactive oxygen species by increasing NADPH oxidase and decreasing thioredoxin expression and reduces NO bioavailability in cultured MVEC by 1 ) increasing NO 2 -tyrosine formation and 2 ) accumulating ADMA by decreasing DDAH expression.
NADPH oxidase; thioredoxin; nitric oxide; protease-activated receptor; nitric oxide synthase; 2',7'-dichlorofluorescein diacetate; asymmetric dimethylarginine; microvascular endothelial cells
Address for reprint requests and other correspondence: S. C. Tyagi, Dept. of Physiology and Biophysics, School of Medicine, 500 S. Preston St., 1115-A, Univ. of Louisville, Louisville, KY 40202 (e-mail: s0tyag01{at}louisville.edu )
•RSF/PEG mixture was developed as FS-LHSM.•CNF, CNT and GNP were used to enhance the thermal conductivity of the FS-LHSMs.•The obtained FS-LHSMs had melting temperature of 14–15 °C and latent heat of ...55–56 J/g.•Thermal conductivity of the FS-LHSMs was significantly enhanced by carbon nano additives.•Carbon nanomaterial doped FS-LHSMs can be utilized for solar building TES applications.
In the present study, raw silica fume (RSF) was evaluated as carrier matrix to create PEG-included form-stable latent heat storage materials (FS-LHSMs), and carbon nanofiber (CNF), carbon nanotube (CNT) and graphene nanoplatelet (GNP) were used for enhancing thermal conductivity of the developed FS-LHSMs. The obtained novel RSF/PEG, RSF/PEG/CNF, RSF/PEG/CNT and RSF/PEG/GNP form-stable (FS-LHSMs) displayed significantly thermal conductivity and well resistance against the leakage of PEG during their heating periods. The techniques of differential scanning calorimetry (DSC), thermal gravimetric analyzer (TGA), thermal conductivity meter, fourier transform infrared spectroscopy (FTIR), and scanning electron microscope (SEM) were employed in the characterizations. The form-stable loading of PEG in the fabricated FS-LHSMs was found to be 40 wt%. The FS-LHSMs are fundamentally physical mixes according to interactions revealed in the FTIR analysis. The melting temperature of synthesized FS-LHSMs was in the range of about 14–15 °C while their LH of fusion was in the range of about 55–56 J/g. The FS-LHSMs exhibited admirable thermal cycling reliability and thermal durability properties. The thermal conductivity of RSF/PEG composite was significantly improved by the CNF-CNT-GNP additives, and such improvements were also affirmed by the heat charging-discharging rate test. All the results exposed that the prepared FS-LHSMs can be utilized for engineering different building materials or elements with solar TES capability.
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Phase change materials (PCMs) can be applied to several different solar energy systems for the extended heat energy storage which is quite useful as the solar energy is intermittent in nature and is ...unavailable during the night period. Application of PCMs in solar energy systems allows the solar energy to be used at any time even in the absence of the natural solar radiation. Thus, the use of PCMs in the solar energy systems can bridge the demand and supply gap of the normal electrical energy. This paper deals with the recent advances in PCMs application in different solar energy systems and presents almost all of the emerging areas where the applications of PCM in solar energy systems are urgently required. The novel and most recent developments of PCMs in solar thermal energy systems, such as, solar thermal power plants, solar air heater, solar water heater and solar cooker have been duly covered. Furthermore, the application of PCMs in heating and cooling of buildings have been presented as well as the investigation of the PCM application in the solar photovoltaic systems for the performance enhancement of PCMs. Intrinsically important, from the study it has been found that PCMs have been in use in almost all of the solar energy systems even though their uses are still limited and commercially not available due to several economic and environmental constraints. Thus, the paper attempts to present recent and novel approaches by the authors around the world on PCMs applications in the solar energy in well documented forms. Based on the findings, future recommendations have also been given to provide the idea and pragmatic concepts for the researcher to work on the areas of research for further improvements in the systems.
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•Union of quantitative and qualitative aspects of energy.•MEG validation of PV/T and FPC collectors against HW model.•Minimum entropy generation corresponds to optimal irreversibility ...desired.•Internal irreversibilities seems to be deterministic for the tube size.•20 and 10 l/h were respectively the optimized flow rates of water in PV/T and FPC.
This particular research article is an attempt to unify two distinct classical theories i.e. (i)-principle of minimum entropy generation (MEG) and (ii)-Hottel Whillier (HW) model in view of thermal optimization of PV/T and FPC collectors. Solar conversion systems are highly susceptible to substantial exergy losses in particular to thermal exergy, hence it would be better to have some sort of generalized approach, which in this paper was put forward in the form of irreversibility. The entire canvass of the paper focuses to show that how the elementary concepts in thermodynamics can be validated against a heat transfer problem to yield almost similar results. Based on MEG principle and its HW validation it has been investigated that certain minimum amount of entropy generation is the necessary criterion in order to anticipate maximum exergetic values particularly associated with heat interactions. The optimized mass flow rates for PV/T and FPC using MEG and HW models were respectively found to be 17&20l/hPV/T and 8&10l/hFPC. However, the conclusive difference in the two approaches comes from the fact that MEG model take care of the universal entropy generation optimization, while HW model was system specific only. The transition in diameter which occurs towards asymptotic minimum entropy generation per unit length was found to be at 0.00875 m and 0.01 m for the two collectors particularly associated with laminar flow and constant heat flux source. The maximum temperature of the modeled PV module (255Wp) was ideally predicted to be reduce by 18 °C through the proposed design which corresponds to 8.6% increment in the electrical efficiency. A parameter χ based on useful thermal gain per unit cost of thermal management was maximized in order to optimize the center to center tube spacing.
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The energy supply to demand narrowing down day by day around the world, the growing demand of power has made the power plants of scientific interest, but most of the power plants are designed by the ...energetic performance criteria based on first law of thermodynamics only. The real useful energy loss cannot be justified by the fist law of thermodynamics, because it does not differentiate between the quality and quantity of energy. The present study deals with the comparison of energy and exergy analyses of thermal power plants stimulated by coal and gas. This article provides a detailed review of different studies on thermal power plants over the years. This review would also throw light on the scope for further research and recommendations for improvement in the existing thermal power plants.
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This article offers a trend of inventions and implementations of photocatalysis process, desalination technologies and solar disinfection techniques adapted particularly for treatment of industrial ...and domestic wastewater. Photocatalysis treatment of wastewater using solar energy is a promising renewable solution to reduce stresses on global water crisis. Rendering to the United Nation Environment Programme, 1/3 of world population live in water-stressed countries, while by 2025 about 2/3 of world population will face water scarcity. Major pollutants exhibited from numerous sources are critically discussed with focus on potential environmental impacts & hazards. Treatment of wastewater by photocatalysis technique, solar thermal electrochemical process, solar desalination of brackish water and solar advanced oxidation process have been presented and systematically analysed with challenges. Both heterogenous and homogenous photocatalysis techniques employed for wastewater treatment are critically reviewed. For treating domestic wastewater, solar desalination technologies adopted for purifying brackish water into potable water is presented along with key challenges and remedies. Advanced oxidation process using solar energy for degradation of organic pollutant is an important technique to be reviewed due to their effectiveness in wastewater treatment process. Present article focused on three key issues i.e. major pollutants, wastewater treatment techniques and environmental benefits of using solar power for removal of pollutants. The review also provides close ideas on further research needs and major concerns. Drawbacks associated with conventional wastewater treatment options and direct solar energy-based wastewater treatment with energy storage systems to make it convenient during day and night both listed. Although, energy storage systems increase the overall cost of the wastewater treatment plant it also increases the overall efficiency of the system on environmental cost. Cost-efficient wastewater treatment methods using solar power would significantly ensure effective water source utilization, thereby contributing towards sustainable development goals.
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•Recent trends on wastewater treatment using solar energy were reviewed.•Solar photocatalysis methods of wastewater treatment was studied and analysed.•Advanced oxidation methods using solar energy are found to be effective.•Technical limitations and environmental benefits are discussed.
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