Experimental investigation on semicircular, triangular and rectangular shaped absorber of solar still with nano-based PCM

This paper shows the results of a novel research conducted with the overall aim of developing a system that can provide continuous desalination. Productivity enhancement of solar stills is regarded as the main purpose of the investigators in desalination field. This paper represents the experimental results in a new approach of paraffin + graphene oxide nanoparticles mixture. The paraffin mixture in a semicircular, triangular and rectangular absorber with paraffin +graphene oxide of 0.1, 0.3 and 0.5 wt% has been investigated. The finding indicated that for all absorbers, the use of paraffin + graphene oxide in higher weight fractions enhances daily freshwater production. The results showed that the thermal performances are greater applying graphene oxide + paraffin of 0.5%wt with semicircular absorber compared to triangular and rectangular absorber. The achievement of the present paper can be implemented to design more efficient absorbers for solar still parts

Natural convection in triangular enclosures with protruding isothermal heater

Natural convection heat transfer from a protruding heater located in a triangular enclosure has been analyzed numerically. Temperature of inclined boundary of the triangle is lower than the temperature of the heater, which has constant temperature boundary condition. The remaining walls are insulated. The study is formulated in terms of the vorticity-stream function procedure and numerical solution was performed using the finite difference method. Air was chosen as working fluid with Pr = 0.71. Governing parameters, which are effective on flow field and temperature distribution, are; Rayleigh number, aspect ratio of triangle enclosure, dimensionless height of heater, dimensionless location of heater and dimensionless width of heater. Streamlines, isotherms, velocity profiles, local and mean Nusselt numbers are presented. It is found that all parameters related with geometrical dimensions of the heater are effective on temperature distribution, flow field and heat transfer. © 2007 Elsevier Ltd. All rights reserved

Effects of different fin parameters on temperature and efficiency for cooling of photovoltaic panels under natural convection

The photovoltaic panels are one of the most efficient energy systems that generate electricity by absorbing the solar radiation. Nevertheless, when the sun's rays are converted to electricity, a high amount of waste heat is generated. Therefore, the efficiency of photovoltaic (PV) panels needs to be studied to minimize the amount of waste heat. There is a non-linear relationship between the temperature, the current and the voltage values produced by the PV panels. In the present study, the performance of 75 W PV panels with polycrystalline cell structure under Elazig, Turkey climatic conditions were experimentally investigated. The system performances such as temperature, power and efficiencies were analyzed by applying different fin parameters (length, sequences) to PV panels. The aluminum fins were applied with 10 different configurations as given by A1-A10. The cell temperatures, output powers, power loss ratios and energy-exergy efficiencies were calculated based on measurements of the experimental study. It was observed that the temperature did not distributed homogeneously on the PV panel. In terms of the efficiency, the fins are designed as staggered array and the 7 cm × 20 cm dimensions showed the best results. The highest energy and exergy efficiencies values of the finned panels (A5) were calculated as 11.55%, and 10.91%, respectively. © 201

Experimental study for the application of different cooling techniques in photovoltaic (PV) panels

This article contains the experimental investigations of different cooling methods used for photovoltaic (PV) panels. Phase change material (PCM), thermoelectric (TE) and aluminum fins were chosen as the cooling methods. The CaCl2·6H2O is chosen as one of the PCM which is widely used in the cooling of PVs and the other is the PCM with melting temperature above the surface temperature of the PV panel. By using TE material in different numbers (6, 8 and 12) and aluminum fins in different layouts, surface temperatures and output powers of PV panels were compared. It is observed that the PCM which is not chosen appropriately has insulation feature in the PV panel and enhances the temperature of the panel and decreases the output power. When the most successful cooling methods were tested under the same environmental conditions, PV with fin system produced the highest power generation of 47.88 W while PV with PCM and TEM produced the lowest power generation of 44.26 W. © 2020 Elsevier Lt

Pulsating flow of CNT–water nanofluid mixed convection in a vented trapezoidal cavity with an inner conductive T-shaped object and magnetic field effects

Mixed convection of carbon-nanotube/water nanofluid in a vented cavity with an inner conductive T-shaped object was examined under pulsating flow conditions under magnetic field effects with finite element method. Effects of different parameters such as Richardson number (between 0.05 and 50), Hartmann number (between 0 and 30), cavity wall inclination (between 0◦ and 10◦), size (between 0.1 H and 0.4 H) and orientation (between −90◦ and 90◦) of the T-shaped object, and amplitude (between 0.5 and 0.9) and frequency (Strouhal number between 0.25 and 5) of pulsating flow on the convective flow features were studied. It was observed that the average Nusselt number enhanced with the rise of strength of magnetic field, solid nanoparticle volume fraction, and amplitude of the pulsation, while the effect was opposite for higher values of Ri number and cavity wall inclination angle. The presence of the T-shaped object and adjusting its size and orientation had significant impact on the main flow stream from inlet to outlet and recirculations around the T-shaped object and in the vicinity of hot wall of the cavity along with the magnetic field strength. Pulsating flow resulted in heat transfer enhancement as compared to steady flow case for all configurations. However, the amount of increment was different depending on the variation of the parameters of interest. Heat transfer enhancements were 41.85% and 20.81% when the size of the T-shaped object was increased from 0.1 H to 0.4 H. The T-shaped object can be utilized in the vented cavity as an excellent tool for convective heat transfer control. As highly conductive CNT particles were used in water, significant enhancements in the average Nusselt number between 97% and 108% were obtained both in steady flow and in pulsating flow cases when magnetic field was absent or present. © 2020 by the authors

MHD conjugate natural convection in a porous cavity involving a curved conductive partition and estimations by using Long Short-Term Memory Networks

In this study, MHD conjugate free convection of a porous cavity having a curved shape conductive partition is numerically analyzed by using the Galerkin weighted residual finite element method. The numerical simulation is performed for different values of pertinent parameters: Rayleigh number (between 10 4 and 10 6), Hartmann number (between 0 and 60), Darcy number (between 5 × 10 - 4 and 0.05), porosity of the medium (between 0.25 and 0.75), curvature of the partition (minor axis radius of the horizontal ellipse, between 0.01H and 0.3H) and conductivity ratio (between 0.05 and 50). It was observed that the heat transfer rate enhances locally and in average for higher values of Rayleigh number, Darcy number, porosity of the medium and conductivity ratio, whereas the impact is opposite for higher values of Hartmann number. The amount of average Nusselt number reduction is obtained as 22 % when Hartmann number is changed from 0 to 60 at Rayleigh number of 10 5. Curvature and conductivity of the curved partition affect the variation in fluid flow and heat transfer characteristics. Maximum of 7 % variation in the average Nusselt number is achieved when the curvature of the conductive partition is varied but the effects of thermal conductivity ratio on heat transfer rate are higher. Long Short-Term Memory Networks are used for estimation of the velocity and temperatures in the computational domain for various values of pertinent input parameters variation in the system which includes conjugate heat transfer mechanism in a porous enclosure with complex-shaped conductive partition under the effects of magnetic field. © 2019, Akadémiai Kiadó, Budapest, Hungary

Investigation of pollutant reduction by simulation of turbulent non-premixed pulverized coal combustion

In this work, a computational model was developed and used to study NOx reduction during pulverized coal combustion. The finite volume method with a structured grid arrangement and a SIMPLE algorithm were utilized to model the pulverized coal combustion process. The effect of dilution of the oxidizer by participating gases including Air, Helium, Argon, Steam and CO2 were studied, and the corresponding reductions in the rate of NO,, production are compared. The cases when 10 and 20 percent of oxidizer was diluted by the participating gases were analyzed. The Probability Density Function (PDF) model was used for modeling the interaction between turbulence and chemistry, and the Discrete Phase Model (DPM) model was used for modeling the solid particle trajectory analysis including the interaction with turbulence. A QUICK scheme was adopted for the discretization of all convective terms of the advective transport equations. The static temperature, mass fraction of pollutant NOx, and velocity distribution along the centerline of the burner as well as temperature and NOx contours for different dilution percentages were presented. It was shown that as result of injection of CO2 into the oxidizer the peak temperature and/or flow velocities of the combustion gases decrease more as compared to injection of steam or other neutral gases. Also, the results showed that the NOx reduction in pulverized coal combustion was highest due to injection of CO2 into the oxidizer in comparison to injection of steam, Argon or Helium. (C) 2014 Elsevier Ltd. All rights reserved

A brief review of natural convection in enclosures under localized heating with and without nanofluids

International audienceIn this work, natural convection heat transfer and fluid flow is reviewed in different types ofenclosures with localized heating, considering the working fluid as a simple fluid or a nanofluid.Experimental findings are considered in addition to two and three dimensional numerical studies.The common objective of the reviewed work is to investigate the effects of type and location oflocal heat sources as well as the effects of the different configurations of cavities and boundaryconditions on the enclosed fluid flow and heat transfer. Important correlations, concluded fromthese studies, are summarized