• Energy Research
• 2016-2025close
• IN close
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• Energy Conversion and Management close

Abstract Thermal energy storage systems based on Phase change materials (PCM) are an attractive option to bridge the temporal and spatial gap between the energy demand and supply. But, these systems possess poor thermal conductivity causing reduced rate of heat transfer. The objective of the present study is to numerically analyze the melting process in an optimized finned latent heat storage system dispersed with varying volume fraction of Graphene nano plates (GNP). The individual effect of incorporating fins, GNP and a combination of both at different volume fraction has been studied. Effective thermal conductivity of nano-composite PCM has been theoretically evaluated including the effect of aspect ratio, interfacial thermal resistance, anisotropy, non-linear effects as well as concentration for the dispersed GNP. In this work, Dynamic differential scanning calorimetry tests are performed to evaluate the phase change temperature, latent heat and specific heat of the sugar alcohol (d- mannitol). Transient variation of liquid fraction, average temperature and radial/longitudinal temperature differentials are presented which would be useful for designing medium temperature (160–200 °C) storage systems for various applications. Fin height is varied to obtain an optimum fin size such that natural convection currents are not impeded. Various heat transfer models (including natural convection) are analysed using the actual plant data of a double effect solar absorption system at different arrangements of fins and GNP. Effect of Reynolds number and inlet temperature of HTF on the system performance have also been studied. A reduction of 68% in total melting time is observed in finned LHSS with 5% GNP as compared to a conventional system.

Horizontal axis tidal turbines (HATT) are promising candidates for hydroelectric power extraction in coastal urban applications. Currently, concerns around the fluid–structure interaction (FSI) performance of turbines limit their industrial deployment while an efficient FSI prediction model can mitigate these concepts. In this paper, we present an innovative predictive model, TurbineNet, designed to accurately forecast the FSI characteristics of diverse composite tidal turbine blade structures, thereby facilitating its performance optimization. The TurbineNet model utilizes blade mesh information as input to predict HATT performance through a neural network framework. By integrating mesh convolution and fully connected layers, the model delineates the hydrodynamic behavior of deformed blades which then couples with the finite element method (FEM) for a comprehensive dynamic FSI analysis of composite material blades. Through the generation and training of a database of deformed blades, the new TurbineNet/FEM model is capable of precisely predicting the hydrodynamic performance under various structural parameters. This approach significantly streamlines the computational process associated with traditional FSI models, reducing prediction times by nearly 18 times compared to static FSI calculations using established platforms like Ansys Workbench, while maintaining high accuracy. Based on the innovative TurbineNet/FEM model, we analyzed the FSI characteristics of three different web structures. The incorporation of web structures can substantially reduce local stress and enhance the structural stability of the blades, thus preventing vibrations. Our high-efficiency predictive FSI tool and results can aid HATTs in increasing their much-needed contribution to stability optimization design. It has the potential to significantly optimize energy conversion in tidal turbines by refining blade designs to efficiently convert the kinetic energy of tidal currents into electrical energy.

Abstract Paraffins constitute a class of solid-liquid organic phase change materials (PCMs). However, low thermal conductivity limits their feasibility in thermal energy storage (TES) applications. Carbon nano tubes (CNTs) are one of the best materials to increase the thermal conductivity of paraffins. In this regard, the present study is focus on the preparation, characterization, and improvement of thermal conductivity using CNTs as well as determination of TES properties of expanded perlite (ExP)/ n -eicosane (C20) composite as a novel type of form-stable composite PCM (F-SCPCM). It was found that the ExP could retain C20 at weight fraction of 60% without leakage. The SEM and FTIR analyses were carried out to characterize the microstructure and chemical properties of the composite PCM. The TES properties of the prepared F-SCPCM were determined using DSC and TG analyses. The analysis results showed that the components of the composite are in good compatibleness and C20 used as PCM are well-infiltrated into the structure of ExP/CNTs matrix. The DSC analysis indicated that the ExP/C20/CNTs (1 wt%) composite has a melting point of 36.12 °C and latent heat of 157.43 J/g. The TG analysis indicated that the F-SCPCM has better thermal durability compared with pure C20 and also it has good long term-TES reliability. In addition, the effects of CNTs on the thermal conductivity of the composite PCM were investigated. Compared to ExP/C20 composite, the use of CNTs has apparent improving effect for the thermal conductivity without considerably affecting the compatibility of components, TES properties, and thermal stability.

This paper introduces an irradiance loss factor that quantifies the relationship between irradiance, tilt angle and power output of a soiled panel with the soil particle size composition. Artificial soiling experiments were performed using four soil samples at irradiance levels between 200 and 1200 W/m2 at 18 tilt angles. Biharmonic interpolation was used to develop power contours in terms of irradiance and tilt angle from experimentally obtained data. These contours were compared with ideal ones of a clean panel to observe deviation in the nature of contours for a soiled panel. A correction factor in terms of particle size composition (as a coefficient to tilt angle) was proposed to calculate power output of a tilted soiled panel. The angular loss on a panel with soil sample containing 150 μm particle size in abundance was observed to be 22% and for sample containing 75 μm particles in majority, the loss is 24%. Presence of 300 μm particle size in abundance causes a 23.7% loss, while 52% angular loss was observed for soil with highest composition of less than 75 μm particle size.

Abstract Single-stage cultivation strategy is more favorable than two-stage cultivation owing to the lesser technical obstacles and being more cost-effective in the microalgal biodiesel production. Hence, in this study, mixotrophically grown Chlorella minutissima MCC 27 biomass was optimized for synergistic maximization of biomass yield and intracellular lipid accumulation using Central Composite Rotatable Design (CCRD). The effect of mix-carbon sources (glucose + acetate), nitrate concentration and culture time on biomass accumulation and lipid content (% DCW) was evaluated separately using Response Surface Methodology (RSM). Out of the three strategies, viz., biomass optimization (BO), lipid content (% DCW), and simultaneous production of biomass and lipid content and their maximization, the third strategy was found to be most effective to obtain the maximum lipid productivity (108.81 mg L−1 d−1), which was approximately 10-fold higher than the autotrophically grown C. minutissima culture. The optimized conditions for maximum lipid productivity were found to be 5.96 g L−1 glucose, 4.12 g L−1 acetate, 0.73 g L−1 nitrate and incubation period of 10 days. Palmitic acid was the principal FAME composite followed by oleic acid and the ratio of saturated fatty acids (SFA):monounsaturated fatty acids (MUFA) and polyunsaturated fatty acids (PUFA) was found to be 1.9:1.8:1. Accordingly, simultaneous biomass and lipid content optimization was found to be a better strategy for the maximization of lipid yield as compared to the other strategies followed in the present study.

Fatty acid methyl esters (FAMEs) are useful as biodiesel and have environmental benefits compared to conventional diesel. In this study, these esters were synthesized non-catalytically from non-edible vegetable oils: neem oil and mahua oil with two different methylating agents: methanol and methyl tertbutyl ether (MTBE). The effects of temperature, pressure, time and molar ratio on the conversion of triglycerides were studied. The temperature was varied in the range of 523-723 K with molar ratios upto 50:1 and a reaction time of upto 150 min. Conversion of neem and mahua oil to FAMEs with Supercritical methanol was found to be 83% in 15 min and 99% in 10 min, respectively at 698 K. Further, a conversion of 46% of mahua oil and 59% of neem oil was obtained in 15 min at 723 K using supercritical MTBE. The rate constants evaluated using pseudo first order reaction kinetics were in the range of 4.7 x 10(-6) to 1.0 x 10(-3) for the investigated range of temperatures. The activation energies obtained were in the range of 62-113 kJ/mol for the reaction systems investigated. The supercritical synthesis was found to be superior to the catalytic synthesis of the corresponding FAMEs.(C) 2017 Elsevier Ltd. All rights reserved.