Ashwinkumar S. Dhoble

CFD Analysis to Study Effect of Circular Vortex Generator Placed in Inlet Section to Investigate Heat Transfer Aspects of Solar Air Heater

CFD analysis of 2-dimensional artificially roughened solar air heater duct with additional circular vortex generator, inserted in inlet section is carried out. Circular transverse ribs on the absorber plate are placed as usual. The analysis is done to investigate the effect of inserting additional vortex generator on the heat transfer and flow friction characteristics inside the solar air heater duct. This investigation covers relative roughness pitch in the range of 10 ≤ P/e ≤ 25 and relevant Reynolds numbers in the range of 3800 ≤ Re ≤ 18000. Relative roughness height (e/D) is kept constant as 0.03 for analysis. The turbulence created due to additional circular vortex generator increases the heat transfer rate and at the same time there is also increase in friction factor values. For combined arrangement of ribs and vortex generator, maximum Nusselt number is found to be 2.05 times that of the smooth duct. The enhancement in Nusselt number with ribs and additional vortex generator is found to be 1.06 times that of duct using ribs alone. The maximum increase in friction factor with ribs and circular vortex generator is found to be 2.91 times that of the smooth duct. Friction factor in a combined arrangement is 1.114 times that in a duct with ribs alone on the absorber plate. The augmentation in Thermal Enhancement Factor (TEF) with vortex generator in inlet section is found to be 1.06 times more than with circular ribs alone on the absorber plate.

Investigations of Different Liquid Based Spectrum Beam Splitters for Combined Solar Photovoltaic Thermal Systems

In the spectrum beam split approach of combined solar photovoltaic thermal system (PVT), the complete solar spectrum is splitted. The unwanted part of the solar spectrum for photovoltaic (PV) applications is filtered out and is used separately as heat. In this work, some inexpensive, clear, and easily available selective fluids are identified which can be used as both volumetric heat absorbers and selective spectrum filters for C-Si-based PVT. The electrical performance of a C-Si solar PV cell using these fluid-based filters is analyzed using a solar simulator at 1 Sun, AM 1.5 G. To check the volumetric heat absorbing potential, the required thermophysical properties of these selected fluids are estimated using a solar radiation pyranometer and standard experiments. The study concludes that water, coconut oil, and hydrotreated silicone transformer oil are some of the potential beam splitters and heat absorbers suitable for C-Si based spectrum beam split PVT applications.

Removal of arsenic(III) from water by magnetic binary oxide particles (MBOP): Experimental studies on fixed bed column

Magnetic binary oxide particles (MBOP) were prepared by template method using chitosan in the laboratory for the removal of As(III) from water. The prepared MBOP has super paramagnetic property which is sufficient for magnetic separation. Column study was performed at two different flow rates of 2.0ml/min and 5.0ml/min and comparison was made with regenerated MBOP, commercial activated carbon and commercial activated alumina. It is observed that fresh MBOP has higher breakthrough time and capacity than regenerated MBOP by a factor of 1.25 and 1.37 respectively. In Logit method, the values of K (adsorption rate constant) and N (adsorption capacity coefficient) were obtained as 0.2066 (L/mgh) and 1014(mg/L) for 5.0ml/min flow rate. All the drinking water parameters are within the limit of BIS 10500-2012. Toxicity characteristic leaching procedure (TCLP) and semi dynamic tests were performed for the mix ratios of 01:02:01, 01:02:05 and 01:02:10 and were found safe for the disposal.

Effect of austenitic fillers on microstructural and mechanical properties of ultra-low nickel austenitic stainless steel

In the present investigation effect of austenitic fillers namely E308, E309 and E310 on microstructural and mechanical properties of ultra-low nickel austenitic stainless steel weldment was analysed. The WRC-1992 diagram has been used to predict δ-ferrite and solidification mode of weld metal. Microstructural exploration confers the variation in magnitude and morphologies of δ-ferrite for different Creq/Nieq ratio. It was observed that greater amount of δ-ferrite resulted in improved tensile strength. On the other hand, it lowered the impact strength of weld joint. The results indicated that E308 exhibits higher hardness and tensile strength, whereas E310 demonstrates higher impact strength and this may be attributed to the variation in δ-ferrite content and solidification mode. During tensile test joints failed in heat affected zone for all weld specimen. Surface morphology of fragmented specimens was analysed using scanning electron microscopy and different morphologies were recognised for samples failed before and after Strauss test.

Statistical wind prediction and fatigue analysis for horizontal-axis wind turbine composite material blade under dynamic loads:

The purpose of this article is to analyze various wind speed-forecasting methods, select the appropriate method for developing synthetic wind speed for 1-year period at Salem in Tamilnadu state in India, and use it for the structural and fatigue analysis of a small horizontal-axis wind turbine blade made of composite material. Various forecasting models such as Markov chain, Kalman filter, and autoregressive integrated moving average are evaluated, and a long-term wind speed pattern at Salem is developed using Markov chain. This wind pattern is used to create time-varying loads using the blade element momentum on blade sections. Then, the fatigue analysis of the blade is carried out using the stress life approach. The blade is found to have available life of about 20 years and the critical area for fatigue is found on the skin near the root of the blade. Various blade skin materials are also compared for fatigue performance. A cohesive zone model of the adhesively joined root joint is also developed and analyzed for fatigue at the metal–composite joint. Thus, an integrated methodology involving high-fidelity modeling of the blade, wind forecasting, and static and fatigue analysis is developed for horizontal-axis wind turbine blade for locations where historically wind speed measurements are available for short time.

Evaluation of Microstructure, Mechanical Properties and Corrosion Resistance of Friction Stir-Welded Aluminum and Magnesium Dissimilar Alloys

Microstructure, mechanical properties and corrosion resistance of dissimilar friction stir-welded aluminum and magnesium alloys were investigated by applying three different rotational speeds at two different travel speeds. Sound joints were obtained in all the conditions. The microstructure was examined by an optical and scanning electron microscope, whereas localized chemical information was studied by energy-dispersive spectroscopy. Stir zone microstructure showed mixed bands of Al and Mg with coarse and fine equiaxed grains. Grain size of stir zone reduced compared to base metals, indicated by dynamic recrystallization. More Al patches were observed in the stir zone as rotational speed increased. X-ray diffraction showed the presence of intermetallics in the stir zone. Higher tensile strength and hardness were obtained at a high rotational speed corresponding to low travel speed. Tensile fractured surface indicated brittle nature of joints. Dissimilar friction stir weld joints showed different behaviors in different corrosive environments, and better corrosion resistance was observed at a high rotational speed corresponding to low travel speed (FW3) in a sulfuric and chloride environments. Increasing travel speed did not significantly affect on microstructure, mechanical properties and corrosion resistance as much as the rotational speed.

Deep neural network-based wind speed forecasting and fatigue analysis of a large composite wind turbine blade

The purpose of this paper is to analyze the modern deep neural networks such as nonlinear autoregressive network with external inputs and a recurrent neural network called long short-term memory for wind speed forecast for long-term and use the prediction for fatigue analysis of a large 5 MW wind turbine blade made of composite materials. The use of machine learning algorithms of advanced neural network applied for engineering problems is increasing recently. The present paper therefore brings as important connection between these latest machine learning methods and engineering analysis of complex wind turbine blades which are also the focus of researchers in renewable system design and analysis. First, a nonlinear autoregressive network with external inputs neural network model using Levenberg–Marquardt back propagation feed forward algorithm is developed with 5 years of environment parameters as input. Similarly, a long short-term memory based model is developed and compared. The chosen long short-term memory model is used for developing two-year wind speed forecast. This wind pattern is used to create time varying loads on blade sections and cross-verified with National Renewable Energy Laboratory tools. A high-fidelity CAD model of the NREL 5 MW blade is developed and the fatigue analysis of the blade is carried out using the stress life approach with load ratio based on cohesive zone modeling. The blade is found to have available life of about 23.6 years. Thus, an integrated methodology is developed involving high-fidelity modeling of the composite material blade, wind speed forecasting using multiple environmental parameters using latest deep learning methods for machine learning, dynamic wind load calculation, and fatigue analysis for National Renewable Energy Laboratory blade.

Thermal management of low concentrated photovoltaic systems using extended surfaces in phase change materials

The applicability of phase change materials (PCMs) for the thermal management of low concentrated photovoltaic systems is explored in the current research work. Extended surfaces on the back surface of the PCM container are proposed with its small portion extruded to the outside. PCM thicknesses of 80 mm, 100 mm, and 120 mm are investigated, and an 80 mm thick PCM system is considered as the base configuration. Systems with 2 fins, 3 fins, and 4 fins are analyzed with two different fin lengths of 30 mm and 40 mm inside the PCM enclosure. Two-dimensional transient numerical analysis has been carried out with ANSYS FLUENT using the enthalpy porosity method. The nonuniform melting behavior of PCMs due to natural convection inside the molten PCMs is considered during the analysis using a Boussinesq approximation. The result shows that the proposed 4 fin configuration enhances the melting time by 6000 s compared to the no fin system, reduces the average PCM temperature inside the container by 18%, and decreases the heater surface temperature by 16%.The applicability of phase change materials (PCMs) for the thermal management of low concentrated photovoltaic systems is explored in the current research work. Extended surfaces on the back surface of the PCM container are proposed with its small portion extruded to the outside. PCM thicknesses of 80 mm, 100 mm, and 120 mm are investigated, and an 80 mm thick PCM system is considered as the base configuration. Systems with 2 fins, 3 fins, and 4 fins are analyzed with two different fin lengths of 30 mm and 40 mm inside the PCM enclosure. Two-dimensional transient numerical analysis has been carried out with ANSYS FLUENT using the enthalpy porosity method. The nonuniform melting behavior of PCMs due to natural convection inside the molten PCMs is considered during the analysis using a Boussinesq approximation. The result shows that the proposed 4 fin configuration enhances the melting time by 6000 s compared to the no fin system, reduces the average PCM temperature inside the container by 18%, and decrease...

A comparative analysis of thermo-hydraulic performance of a roughened solar air heater using various rib shapes

ABSTRACT The thermal efficiency of the solar air heater (S.A.H.) is enhanced by introducing various artificial roughness geometries on the absorber surface. Artificial roughnesses in the form of a chamfered rib, right angle triangular and reverse L-shaped ribs, invented from square rib are presented. A comparative thermohydraulic analysis of these ribs is carried out using experimental, Computational Fluid Dynamics (C.F.D.) and analytical investigation. The experiments are carried out using rib height (e = 0.7,1 and 1.4), relative roughness pitch (P/e = 7.14 to 35.71), relative roughness height (e/D = 0.021, 0.03 and 0.042), Reynolds number (Re = 3800 to 18000) and duct aspect ratio (W/H= 5).The effect of rib shape, rib height (e), pitch (P), relative roughness pitch (P/e), relative roughness height (e/D), chamfer angle (α) and Reynolds number (Re) on heat transfer and friction flow is evaluated. Experimental results are validated using C.F.D. code ANSYS FLUENT 14.5, by simulating two-dimensional computational domain of roughened S.A.H. Based on the experimental results correlations for the Nusselt number and friction factor are derived. A mathematical model has been developed to investigate the effect of geometrical and operating parameters on the thermal and effective efficiency of a roughened S.A.H.

Thermal performance evaluation of solar air heater using combined square and equilateral triangular rib roughness

ABSTRACT Heat transfer and fluid flow characteristics in roughened solar air heater duct with combined square and equilateral triangular ribs as roughness is investigated using experimental and computational fluid dynamics (CFD) approaches. Relative roughness pitch (7.14 ≤ P/e ≤ 17.86), roughness height (e/D = 0.042), Reynolds number (3800≤ Re ≤ 18,000) and heat flux (1000 W/m2) are used as operating parameters. Turbulent flow is simulated using ANSYS FLUENT code with RNG k-ɛ turbulence model. The vortices generated around the ribs and grooves are considered to be responsible for the enhancement in heat transfer rate. Thermo hydraulic performance parameter (THPP) has been evaluated for optimum configuration of the roughness element for given set of geometrical and operating parameters. A value of 1.86 has been recorded as an optimum value of THPP for the range of parameters investigated. Solar air heater with combined ribs shows better performance when compared with the individual rib performances.