Experimental and Numerical Investigations of Heat Transfer Characteristics for Impinging Swirl Flow

This paper reports experimental and computational fluid dynamics (CFD) modelling studies to investigate the effect of the swirl intensity on the heat transfer characteristics of conventional and swirl impingement air jets at a constant nozzle-to-plate distance (L = 2D). The experiments were performed using classical twisted tape inserts in a nozzle jet with three twist ratios (y = 2.93, 3.91, and 4.89) and Reynolds numbers that varied from 4000 to 16000. The results indicate that the radial uniformity of Nusselt number (Nu) of swirl impingement air jets (SIJ) depended on the values of the swirl intensity and the air Reynolds number. The results also revealed that the SIJ that was fitted with an insert of y = 4.89, which corresponds to the swirl number Sw = 0.671, provided much more uniform local heat transfer distribution on the surface. The CFD-predicted results help to explain the experimental measurements in terms of the turbulence intensity. Furthermore, the predicted and measured local Nusselt numbers were consistent with each other

Numerical Investigation of Heat Transfer and Friction Factor Characteristics in a Circular Tube Fitted with V-Cut Twisted Tape Inserts

Numerical investigation of the heat transfer and friction factor characteristics of a circular fitted with V-cut twisted tape (VCT) insert with twist ratio (y=2.93) and different cut depths (w=0.5, 1, and 1.5 cm) were studied for laminar flow using CFD package (FLUENT-6.3.26). The data obtained from plain tube were verified with the literature correlation to ensure the validation of simulation results. Classical twisted tape (CTT) with different twist ratios (y=2.93, 3.91, 4.89) were also studied for comparison. The results show that the enhancement of heat transfer rate induced by the classical and V-cut twisted tape inserts increases with the Reynolds number and decreases with twist ratio. The results also revealed that the V-cut twisted tape with twist ratio y=2.93 and cut depth w=0.5 cm offered higher heat transfer rate with significant increases in friction factor than other tapes. In addition the results of V-cut twist tape compared with experimental and simulated data of right-left helical tape inserts (RLT), it is found that the V-cut twist tape offered better thermal contact between the surface and the fluid which ultimately leads to a high heat transfer coefficient. Consequently, 107% of maximum heat transfer was obtained by using this configuration

Heat Transfer Enhancement of Laminar Nanofluids Flow in a Circular Tube Fitted with Parabolic-Cut Twisted Tape Inserts

Numerical investigation has been carried out on heat transfer and friction factor characteristics of copper-water nanofluid flow in a constant heat-fluxed tube with the existence of new configuration of vortex generator using Computational Fluid Dynamics (CFD) simulation. Two types of swirl flow generator: Classical twisted tape (CTT) and Parabolic-cut twisted tape (PCT) with a different twist ratio (y = 2.93, 3.91 and 4.89) and different cut depth (w = 0.5, 1.0 and 1.5 cm) with 2% and 4% volume concentration of CuO nanofluid were used for simulation. The effect of different parameters such as flow Reynolds number, twist ratio, cut depth and nanofluid were considered. The results show that the enhancement of heat transfer rate and the friction factor induced by the Classical (CTT) and Parabolic-cut (PCT) inserts increases with twist ratio and cut depth decreases. The results also revealed that the heat transfer enhancement increases with an increase in the volume fraction of the CuO nanoparticle. Furthermore, the twisted tape with twist ratio (y = 2.93) and cut depth w = 0.5 cm offered 10% enhancement of the average Nusselt number with significant increases in friction factor than those of Classical twisted tape

Evaluation of Green Corrosion Inhibition by Extracts of Citrus aurantium Leaves Against Carbon Steel in 1 M HCl Medium Complemented with Quantum Chemical Assessment

Employing plants as corrosion inhibitors is a physical direction to detect less expensive green friendly inhibitors. Researchers found that the Citrus aurantium leaves extracts are mixtures containing vitamins, minerals, phenolic compounds and terpenoids. The flavonoids contained in C. aurantium can be divided into four groups, including flavones, flavanones, flavonols, and anthocyanins. These compounds indicate the extracts of Citrus aurantium leaves are appropriate to be applied as green corrosion inhibitors. Extracts of Citrus aurantium leaves have been researched by utilizing EIS, gravimetric and SEM techniques as novel eco-friendly corrosion inhibitors for carbon steel in corrosive environments. Inhibition effectiveness of tested extract depends on different concentrations of extract, starting from 0 to 40% v/v. Inhibition effectiveness of 81.2% is reached at the concentration of 20% v/v of the extract in 1 M corrosive solution for three hours at 25℃. Temperature effects and activation parameters have been investigated. A theoretical investigation of Citrus aurantium leaves extract isomers as corrosion inhibitors have been done using DFT/ B3LYP density functional theory. The results shows that, in general, Citrus aurantium leaves have good inhibiting activities at relatively low concentrations. Phenolic groups of Citrus aurantium leaves were picked for examination as substituents of the four inhibitors. Hydroxyl groups of the studied extract compounds result in an increase in inhibition effectiveness, while methylation of the hydroxyl group leads to decrease in inhibitive effectiveness. Citrus aurantium leaves extracted isomers symbolize a considerable enhancement in the inhibition performance

Heat transfer enhancement of laminar flow in a circular tube using Swirl/vortex generator

Swirl/vortex fl ow generator is an important form of passive augmentation techniques consist of a variety of tube inserts, geometrically varied fl ow arrangements and duct geometry modifi cations that produce fl ows. Twisted-tape is one of the most important members of this form which used extensively in different type heat exchangers. This paper presents a research on heat transfer enhancement and friction factor characteristics in a circular tube using CFD simulation. Plain twisted tape inserts with twist ratios (y = 2.93, 3.91) and slant baffl ed twisted tape inserts with baffl e angle 30° and twist ratio (y = 2.93) have been used for the simulation. The results obtained by simulation matched with the literature correlations for plain tube with the discrepancy of less than ±8% for Nusselt number and ±6.25% for friction factor. The results have also revealed that the heat transfer in term of the Nusselt number enhanced with increases of Reynolds number, decreases of twist ratio. Among the various twist ratios, the slant baffl ed twisted tape with twist ratio of y = 2.93 has offered a maximum heat transfer enhancement with signifi cant friction factor

Inhibition of Mild Steel Corrosion by 4-benzyl-1-(4-oxo-4-phenylbutanoyl)thiosemicarbazide: Gravimetrical, Adsorption and Theoretical Studies

Gravimetric measurements were applied to study the inhibitory effect of 4-benzyl-1-(4-oxo-4-phenylbutanoyl)thiosemicarbazide (BOT) on the corrosion of mild steel in 1.0 M HCl. BOT has a good inhibitory efficacy of 92.5 percent at 500 ppm, according to weight loss results. The effect of inhibitor concentration on the mild corrosion behavior of steel was investigated and it was discovered that the higher the inhibitor concentration, the higher the damping efficiency. The results confirm that BOT is an effective corrosion inhibitor for mild steel in the presence of 1.0 M HCl. Furthermore, the higher protection efficiency with increasing temperature and the free energy value showed that BOT molecules participate in both chemisorption (coordination bonds between the active sites of BOT molecules and d-orbital of iron atoms) and physisorption (through the physical interactions on the mild steel surface). The adsorption mechanism on the mild steel surface obeys the Langmuir adsorption isotherm model. Quantum chemical calculations based on the DFT calculations were conducted on BOT. DFT calculations indicated that the protective efficacy of the tested inhibitor increased with the increase in energy of HOMO. The theoretical findings revealed that the broadly stretched linked functional groups (carbonyl and thionyl) and heteroatoms (sulfur, nitrogen and oxygen) in the structure of tested inhibitor molecules are responsible for the significant inhibitive performance, due to possible bonding with Fe atoms on the mild steel surface by donating electrons to the d-orbitals of Fe atoms. Both experimental and theoretical findings in the current investigation are in excellent harmony

Synthesis and characterisation of Co2+-incorporated ZnO nanoparticles prepared through a sol-gel method

The properties of ZnO nanoparticles were modified by doping them with cobalt ions (Co2+) in various compositions through a sol-gel route. The Co2+-doped ZnO nanoparticles were characterised using X-ray diffraction (XRD), UV/Vis spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and zeta potential measurements. A hexagonal wurtzite-phase structure of Co2+-doped ZnO was observed, with a slight decrease in particle size as the Co2+ doping concentration increased. Absorption by Co2+-doped ZnO was found to shift to longer wavelengths, towards the visible region, which was also confirmed by photoluminescence analysis. The band gap of the Co2+-doped ZnO samples decreased from 3.19 to 2.66�eV�as the content of dopant Co2+ increased from 0.0 to 1.0�wt.%. The zeta potential results showed slight effects of Co2+ doping compared with undoped ZnO, indicating that Co2+ doping influences the optical properties and morphology of pure ZnO nanoparticles. The photocatalytic activity of the Co2+-doped ZnO samples was evaluated for the removal of Congo red dye from aqueous solution under solar radiation. The Co2+-doped ZnO samples showed higher effective removal of the dye using the optimal doping of 0.50�wt.%, which produced higher efficiency (about 96%, compared with 80% for pure ZnO).This paper was made possible by a NPRP Grant # [ 5-1425-2-607 ] from the Qatar National Research Fund ? Qatar (a member of Qatar Foundation). The statements made herein are solely the responsibility of the authors. Also, one of the authors (Muneer M. Ba-abbad) is grateful to the Hadhramout University of Science & Technology , Yemen for financial support for his PhD study.Scopu

CFD Analysis of Heat Transfer and Friction Factor Characteristics in a Circular Tube Fitted with Quadrant-Cut Twisted Tape Inserts

This paper reports numerical investigations of heat transfer and friction factor characteristics in swirling flow conditions using CFD simulation. A commercial CFD package, FLUENT 6.3.26, was used in this study. 3D models for circular tube fitted with classical and quadrant-cut twisted tape (QCT) inserts with three twist ratios (y = 2.93, 3.91, and 4.89) and different cut depths (w = 0.5, 1.0, and 1.5 cm) were generated for the simulation. The data obtained from the CFD simulation were verified with the literature correlations of plain tube with the discrepancy of less than ±8% for Nusselt number and ±10% for friction factor. The results show that there was a significant increase in heat transfer coefficient and friction factor in the tube fitted with quadrant-cut twisted tape (QCT) with decreasing of twist ratio (y) and cut depth (w). Furthermore, the configuration of QCT insert with a twist ratio of y = 2.93 and a cut depth of w = 0.5 cm offered higher heat transfer rate and friction factor than other twist ratios

Arabic gum as green agent for ZnO nanoparticles synthesis: properties, mechanism and antibacterial activity

The size and morphology of ZnO nanoparticles (ZnO NPs) were controlled in the presence of the natural and green agent, Arabic gum. Lower amounts of Arabic gum showed a greater effect on the size and morphology as well as on the properties of ZnO NPs prepared by a sol–gel method. The hexagonal wurtzite crystal structure was found for all samples ZnO NPs with no other phase for impurities. The size of the spherically shaped ZnO NPs decreased with an increase in the amount of Arabic gum, up to an optimal 1.50 wt%. The smaller size of ZnO NPs of 16 nm was obtained with the optimal amount of Arabic gum, compared to 32 nm produced without Arabic gum. These results were attributed to the ready reaction between Arabic gum molecules and zinc ions within the nucleation and growth processes of ZnO NPs. The optical properties of ZnO NPs, with a band gap of 3.4 eV and enhanced intensity of blue emission, were the result of the smaller size of ZnO at the optimal amount of Arabic gum. According to the experimental results, a mechanism to elucidate the formation of ZnO NPs was proposed and explained. The antibacterial activity was tested against Escherichia coli against which higher activity, explained by smaller size of the ZnO NPs, was obtained.This paper was made possible by NPRP Grant # [5-1425-2-607] from the Qatar National Research Fund (a member of Qatar Foundation) and Research Centre for Sustainable Process Technology (CESPRO), Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia under project PKT-6/2012, iconic-2014-004. The statements made herein are solely the responsibility of the authors. One of the authors (Muneer M. Ba-Abbad) is grateful to Hadhramout University of Science &Technology, Yemen for its financial support for his PhD study. The authors would like to thank the Centre for Research and Instrumentation Management, UKM (CRIM) for XRD, TEM and PL analyses.Scopu

Comparative Studies on Thermal Performance of Conic Cut Twist Tape Inserts with SiO 2

This paper presents a comparison study on thermal performance conic cut twist tape inserts in laminar flow of nanofluids through a constant heat fluxed tube. Three tape configurations, namely, quadrant cut twisted tape (QCT), parabolic half cut twisted tape (PCT), and triangular cut twisted (VCT) of twist ratio y = 2.93 and cut depth de = 0.5 cm were used with 1% and 2% volume concentration of SiO2/water and TiO2/water nanofluids. Typical twist tape with twist ratio of y = 2.93 was used for comparison. The results show that the heat transfer was enhanced by increasing of Reynolds number and nanoparticles concentration of nanofluid. The results have also revealed that the use of twist tape enhanced the heat transfer coefficient significantly and maximum heat transfer enhancement was achieved by the presence of triangular cut twist tape insert with 2% volume concentration of SiO2 nanofluid. Over the range investigated, the maximum thermal performance factor of 5.13 is found with the simultaneous use of the SiO2 nanofluid at 2% volume concentration VCT at Reynolds number of 220. Furthermore, new empirical correlations for Nusselt number, friction factor, and thermal performance factor are developed and reported