Degradation of rhodamine B photocatalyzed by Eu-doped CdS nanowires illuminated by visible radiation

CdS nanowires doped with different contents of Eu dopant were synthesized by solvothermal method. XRD, SEM, TEM and Raman analyses certified that the as-synthesized samples were hexagonal CdS uniform nanowires. The pure CdS nanowires were 1–3 ?μm long and 80 ?nm diameter with the 1st and 2nd order longitudinal phonon modes at 298 and 594 ?cm^?1. The 3% Eu-doped CdS wires were 800 ?nm–2.5 ?μm long and 75 ?nm diameter with the 1st and 2nd order longitudinal phonon modes at 296 and 593 ?cm^?1. CdS nanowires grew along the [001] direction due to the surface energy effect. The photocatalytic properties of CdS and Eu-doped CdS nanowires were investigated for the degradation of rhodamine B (RhB) illuminated by visible radiation. In this research, Eu dopant played the role in promoting the photocatalytic kinetics because Eu³⁺ ions act as an electron acceptor to promote charge separation and photocatalytic activity. Both ^●OH and ^●O₂^? were the main active radicals used to transform RhB molecules into CO₂, H₂O and other intermediates.     

Optimization and sensitivity analysis of magneto-hydrodynamic natural convection nanofluid flow inside a square enclosure using response surface methodology

This article studies buoyancy-driven natural convection of a nanofluid affected by a magnetic field within a square enclosure with an individual conductive pin fin. The effects of electromagnetic forces, thermal conductivity, and inclination angle of pin fin were investigated using non-dimensional parameters. An extensive sensitivity analysis was conducted seeking an optimal heat transfer setting. The novelty of this work lies in including different contributing factors in heat transfer analysis, rigorous analysis of design parameters, and comprehensive mathematical analysis of solution domain for optimization. Results showed that magnetic strength diminished the heat transfer efficacy, while higher relative thermal conductivity of pin fin improved it. Based on the problem settings, we also obtained the relative conductivity value in which the heat transfer is optimal. Higher sensitivity of heat transfer was, though, noticed for both magnetic strength and fin thermal conductivity in comparison to fin inclination angle. Further studies, specifically with realistic geometrical configurations and heat transfer settings, are urged to translate current findings to industrial applications.

     

Optimization of the finned double-pipe heat exchanger using nanofluids as working fluids

Journal of Thermal Analysis and Calorimetry - The heat exchanger pipe diameter has a significant effect on the flow characteristics as well as on the initial investment, operation and overall cost....     

Pd nanoparticle-modified Bi2WO6 nanoplates used for visible-light-driven photocatalyst

Pd nanoparticles supported on Bi₂WO₆ nanoplates used for visible-light-driven photocatalyst were successfully synthesized by photoreduction deposition method under visible-light irradiation. Different analytical techniques including X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy and photoluminescence spectroscopy revealed that face-centered cubic metallic Pd nanoparticles were uniformly loaded on top of orthorhombic Bi₂WO₆ nanoplates to form heterostructure Pd/Bi₂WO₆ nanocomposites. Photocatalytic activities of pure Bi₂WO₆ sample and heterostructure Pd/Bi₂WO₆ nanocomposites were studied through the photodegradation of rhodamine B (RhB) under visible-light irradiation. The photocatalytic efficiency of Bi₂WO₆ was increased to the highest by being loaded with 5 wt% Pd and then decreased by being loaded with 10 wt% Pd. The improved photocatalytic efficiency caused by high-efficiency diffusion and separation of photo-generated charge carriers was explained and can lead to superior photodegradation of RhB under visible-light irradiation.

     

Effect of fin pattern on the air-side performance of herringbone wavy fin-and-tube heat exchangers

In the present study, new experimental data on the air-side performance of fin-and-tube heat exchangers having herringbone wavy fin configuration are presented. Different from most previous studies, the present experiments have been performed to determine the effects of fin patterns and edge corrugations on the air-side performance of the heat exchangers. The experimental apparatus consists essentially of a well-insulated open wind tunnel and herringbone wavy fin-and-tube heat exchangers made from aluminium wavy finned, copper tube. Two types of wavy fin patterns commonly in industrial use are investigated. Air and hot water are used as working fluids in air-side and tube-side, respectively. From the experimental results, it is found that the fin pattern has a significant effect on the heat transfer and flow characteristics. The corrugation at the fin edge enables the Colburn factor to decrease but it has almost no effect on the friction factor.     

A tube-by-tube reduction method for simultaneous heat and mass transfer characteristics for plain fin-and-tube heat exchangers in dehumidifying conditions

This study proposed a new method, namely a tube-by-tube reduction method to analyze the performance of fin-and-tube heat exchangers having plain fin configuration under dehumidifying conditions. The mass transfer coefficients which seldom reported in the open literature, are also presented. For fully wet conditions, it is found that the reduced results for both sensible heat transfer performance and the mass transfer performance by the present method are insensitive to change of inlet humidity. Unlike those tested in fully dry condition, the sensible heat transfer performance under dehumidification is comparatively independent of fin pitch. The ratio of the heat transfer characteristic to mass transfer characteristic (h_c,o/h_d,o C_p,a) is in the range of 0.6~1.0, and the ratio is insensitive to change of fin spacing at low Reynolds number. However, a slight drop of the ratio of (h_c,o/h_d,o C_p,a) is seen with the decrease of fin spacing when the Reynolds number is sufficient high. This is associated with the more pronounced influence due to condensate removal by the vapor shear. Correlations are proposed to describe the heat and mass performance for the present plate fin configurations. These correlations can describe 89% of the Chilton Colburn j-factor of the heat transfer (j_h) within 15% and can correlate 81% of the Chilton Colburn j-factor of the mass transfer (j_m) within 20%.     

Thermal conductivity modeling of MgO/EG nanofluids using experimental data and artificial neural network

The application of nanofluids in energy systems is developing day by day. Before using a nanofluid in an energy system, it is necessary to measure the properties of nanofluids. In this paper, first the results of experiments on the thermal conductivity of MgO/ethylene glycol (EG) nanofluids in a temperature range of 25–55 °C and volume concentrations up to 5 % are presented. Different sizes of MgO nanoparticles are selected to disperse in EG, including 20, 40, 50, and 60 nm. Based on the results, an empirical correlation is presented as a function of temperature, volume fraction, and nanoparticle size. Next, the model of thermal conductivity enhancement in terms of volume fraction, particle size, and temperature was developed via neural network based on the measured data. It is observed that neural network can be used as a powerful tool to predict the thermal conductivity of nanofluids.     

Low-Pressure Chromatographic Separation of p-Hydroxybenzoates Using Sequential Injection with Lab-on-Valve System and Miniature Monolithic Column

The use of a small guard column (5-mm length) as a miniature analytical column in low-pressure liquid chromatography based on a sequential injection with lab-on-valve system was demonstrated. A strong initial mobile phase was used to rapidly deliver the sample zone to the column prior to simultaneous separation of analytes with weaker mobile phase. Separation of methyl-, ethyl-, propyl-, and butyl-4-hydroxybenzoates (MP, EP, PP, and BP) was achieved within about 120 s with sufficient peak resolution (all higher than 1.3) using 2,500 µL of mobile phase (composed of 1,087 µL of MeOH) per run. Detection limits were found to be 6.5, 8.0, 0.5, and 0.6 μmol L^?1 for MP, EP, PP, and BP, respectively. The system was tested with common commercially available skin lotions and wet wipe products. The analysis results were in good agreement with those obtained from the high-performance liquid chromatography with a 10-cm-length packed column.     

The effects of channel diameter on flow pattern,void fraction and pressure drop of two-phase air–water flow in circular micro-channels

Two-phase air–water flow characteristics are experimentally investigated in horizontal circular micro-channels. Test sections are made of fused silica. The experiments are conducted based on three different inner diameters of 0.53, 0.22 and 0.15 mm with the corresponding lengths of 320, 120 and 104 mm, respectively. The test runs are done at superficial velocities of gas and liquid ranging between 0.37–42.36 and 0.005–3.04 m/s, respectively. The flow visualisation is facilitated by systems mainly including stereozoom microscope and high-speed camera. The flow regime maps developed from the observed flow patterns are presented. The void fractions are determined based on image analysis. New correlation for two-phase frictional multiplier is also proposed for practical applications.     

Superparamagnetic and ferromagnetic behavior of ZnFe2O4 nanoparticles synthesized by microwave-assisted hydrothermal method

Zinc ferrite (ZnFe₂O₄) nanoparticles were successfully synthesized from Zn(NO₃)₂ · 6H₂O and Fe(NO₃)₃ · 9H₂O by microwave hydrothermal method at 150°C for 1 h. Cubic ZnFe₂O₄ with particle size below 7 nm was formed in the solution at pH ≥ 6. The crystallinity and particle size of ZnFe₂O₄ nanoparticles were increased after calcination. The effects of pH of the precursor solution and calcination on the particle size and crystallinity of the particles were studied. At room temperature the products show superparamagnetic and ferromagnetic properties, determined by their size. The formation mechanism of ZnFe₂O₄ was also discussed according to the experimental results.