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Mixed convection flow is investigated numerically for nanofluid flow and heat transfer in a horizontal channel considering two localized heat sources compared with pure fluid. The channel’s walls are insulated and the heat sources are at the center of the channel. Al2O3 nanoparticles are employed to modify the thermal conductivity of the base fluid. The effect of different parameters including Richardson number, Reynolds number, thermal conductivity, sources separation distance and the length-to-height ratio of heat sources is investigated. The results indicate that by enhancing the Richardson number from 1 to 10, the heat transfer from the source surfaces slightly increases; however, no significant effect is observed on thermal behavior. Increasing Reynolds number modifies heat transfer from sources and has a large effect on the streamlines and isotherms. In Richardson number of 5, for Reynolds number of 5, 50, 100, 150, the Nusselt number is 1.01, 4.50, 14.11 and 22.13, respectively. Furthermore, for a higher sources thermal conductivity, heat transfer increases due to the lower thermal resistance. The increase in average Nusselt number with changing the dimensionless thermal conductivity in the range of $$1 \le \bar{k} \le 100$$ is 314%. By examining the length-to-height ratio of heat sources, the results show that heat transfer decreases initially and then increases for higher values of length-to-height ratios. Furthermore, the heat sources separation distance shows a pronounce influence on heat transfer and thermal distribution. Besides, the results show that the effect of nanofluid concentration on average Nusselt number is more significant at low Reynolds number. The increase of average Nusselt number for Reynolds numbers of 5, 80 and 150 is 25%, 15% and 6.5%, respectively.

The objective of this study is to investigate the effects of using local waste materials on the properties of fresh and hardened high performance and self-compacting concrete. Crushed ceramic products and steel slag from electric-arc furnaces were used as partial replacements of traditional concrete raw materials in the production of self-compacting and high performance concrete, which were obtained from local factories in Kuwait. Preliminary results have shown that using crushed ceramic products (in the form of powder and 3/8” aggregates) increases the rate of strength gain as the concrete cures, while using electric-arc furnace slag increases the compressive strength of the benchmark concrete mix by up to 40%.

This paper presents a numerical analysis of the natural convective heat transfer of magnetite/graphite slurry non-Newtonian ferrofluid in a square enclosure under a variable external magnetic field...

In the current experimental investigation, the rheological behavior of antifreeze containing a grouping of graphene oxide (GO) and copper oxide (CuO) in temperatures from 25 to 50 °C was evaluated. Homogeneous and stable samples with dissimilar solid volume fractions were prepared by dispersing GO and CuO in an equal mixture of water and ethylene glycol consuming a two-step method. The results showed that the base fluid has Newtonian behavior. Such behavior was also observed for the nanofluid with the volume fractions up to 0.4%. However, for higher concentrations than 0.4 vol.%, the viscosity decreased by increasing the shear rate. This demonstrates that the existing hybrid nanofluid has a non-Newtonian behavior (power-law pseudoplastic fluid). Consequently, with the purpose of facilitating the calculation of the viscosity of the nanofluid, a correlation was derived at the temperature range of 25–50 °C and the volume fractions of 0.1, 0.2 and 0.4% through a curve fitting technique. In addition, not only the consistency index but also the power-law indexes were gained for non-Newtonian samples exerting the curve fitting technique. Comparisons between the correlation output and experimental data expressed the accurateness of anticipated correlations.

The effects of Joule heating, Hartman, Brinkman, and Reynolds numbers on the flow pattern and thermal characteristics of force convection flow through a parallel-plate microchannel are inve...

This paper presents a numerical study on the unsteady natural convective flow of Newtonian and non-Newtonian fluids in a square enclosure. A heat source with oscillating heat flux is located on the bottom wall of the enclosure. The top wall is thermally insulated and the other walls are at a relatively low temperature. The continuity, momentum, and energy equations for a computational domain encompassing the enclosure are solved numerically using the SIMPLE algorithm. The flow and temperature fields and the heat transfer performance are examined for different non-Newtonian fluids and heat source locations. The results are presented for different values of power-law index, Rayleigh number, and fluctuation period. It is found that the flow and temperature fields vary as the oscillating heat flux is changed. The pseudoplastic non-Newtonian fluid $$(n < 1)$$ is associated with a higher heat transfer, and the dilatant non-Newtonian fluid $$(n > 1)$$ is associated with a lower heat transfer with respect to the Newtonian fluid. The heat source oscillation period significantly affects the maximum flow temperature in the enclosure. This study provides useful information for the designers of electronic cooling systems using non-Newtonian fluids.

The coupling of MoS2 with In2O3 is a well-known challenge due to the lower stability of MoS2 in the presence of oxygen at high temperature. In the present work, stable mesoporous MoS2@In2O3 composites were designed by a sonochemical reaction and a low temperature hydrothermal method, in which MoS2 nanosheets (NSs) were vertically planted on highly mesoporous In2O3 nanocubes. The mesoporous MoS2@In2O3-II nanocomposite with a MoS2 and In2O3 mass ratio of 1:1 exhibited a high response of 10.3–100 ppm NOx, and ultrafast response time of 1–9 s from 100 to 0.1 ppm. The enhance gas response of MoS2@In2O3-II reveals the synergistic effect of the interfacial transfer of electrons from In2O3 nanocubes to MoS2 NSs, and the highly exposed active edges of vertically aligned MoS2 NSs. The MoS2@In2O3-II sensor is a promising candidate as a gas sensing material due to its excellent structure and outstanding properties at room temperature (RT).

Data loss problems severely effect the performance of state estimation in most of communication and control systems. The normal techniques adopted for compensation in the process of state estimation are Open-loop Kalman filter and compensating closed-loop Kalman filter. The compensated closed-loop Kalman filtering scheme employs three (03) strategies namely Normal Equation, Levionson-Durbin and Leroux-Gueguen algorithms, using Autoregressive (AR) model, where only previous measurements are used. In this paper, the compensated vector is proposed based on Autoregressive Moving Average or ARMA model instead of AR model. This model contains more information than Autoregressive model, i.e. measurement and input signals, which is believed to generate more efficient results. Necessary steps including the computation of linear prediction coefficients have been taken to accommodate the input signal. Computation of this extra linear prediction coefficient however, bears an observable increase in computation time. The selection of AR and ARMA models is a trade-off between computation time and improved performance, which is the ultimate consequence of extra input signal. A standard mass-spring-damper case study is simulated to provide a comprehensive comparison in light of various parameters including state estimation, error, gain elements etc.

The role of magnetic field and natural convection on the solid–liquid interface motion, flow, and heat transfer during melting of gallium on a vertical wall is reported in this paper. The classical geometry consisting of a rectangular cavity with uniform but different temperatures imposed at two opposite side walls, insulated top, and bottom walls is considered. The magnetic field is imposed in the horizontal direction. A numerical code is developed to solve for natural convection coupled to solid–liquid phase transition and magnetic effects. The corresponding streamlines and isotherms predicted by the numerical model serve to visualize the complicated flow and temperature field. The interplay between the conduction and convection modes of heat transfer stimulated by the combination of the buoyancy-driven flow and the Lorentz force on the fluid due to the magnetic field are studied. The results show that the increase of Rayleigh number promotes heat transfer by convection, while the increase of Hartmann number dampens the strength of circulating convective currents and the heat transfer is then mainly due to heat conduction. These results are applicable in general to electrically conducting fluids and we show that magnetic field is a vital external control parameter in solid–liquid interface motion.

The three dimensional (3D) interlayer rGO/SnO2/PPy nanohybrids, based on reduced graphene oxide (rGO) obtained from expanded graphene (EG), SnO2 nanoparticles (NPs) and polypyrrole (PPy) were obtained by facile method. The rGO/SnO2/PPy nanohybrid electrodes were composed of a thin conducting film of PPy on the surface of rGO/SnO2 (EG: Sn molar ratio of 1.2:1), used for the determination of ultra-trace ions (Cd2+, Cu2+, Hg2+ and Pb2+) with the square wave anodic stripping voltammetry (SWASV) technique. Among the rGO/SnO2/PPy, rGO/SnO2 (rGS), rGO/PPy (rGP) and pure polypyrrole (PPy) samples, the sensitivity and current density of rGO/SnO2/PPy-4 (rGS: PPy mass ratio of 1:4), have shown excellent performance for the recognition of above ultra-trace heavy metal ions (HMIs). The limit of detection (3σ method) of the rGO/SnO2/PPy-4 nanohybrids modified electrode toward Cd2+, Cu2+, Hg2+ and Pb2+ ions was 7.5 × 10−13, 8.3 × 10−13, 8.1 × 10−13 and 8.8 × 10−13 mol L-1 (M), respectively. The 3D interlayer rGO/SnO2/PPy nanohybrid is a favorable material constructed for multiple functionalities having the advantages of conducting material PPy, active site SnO2 NPs and outstanding electrical substrate graphene nanosheet (obtained from EG) in electrochemical detection of HMIs.

To fabricate sensors that are capable of ultrasensitive detection of NOx as well as optimize their synthetic route, highly porous and hierarchically structured Co3O4/CuO nanosheets were synthesized by a facile hydrothermal-calcination route. The CC2-1 sample synthesized with the 2:1 molar ratio of Co(NO3)2·6H2O and CuCl2·2H2O has the most abundant porosity. Structural measurements found that the size of pore is 3.37 nm, the specific surface area is 24.04 m2g−1, and the average slice thickness is about 5 nm. This optimum sample presented excellent NOx sensing performance at room temperature (RT = 21 °C), which has not only the highest response (14.16–1000 ppm), the shortest response time (2 s to 1000 ppm), and the minimum detection limit (0.01 ppm), but also good reversibility and selectivity. The superior property arises from the appropriate CuO ratio and the addition of pore-forming agent NaHCO3, and all together resulted in the unique hierarchical heterojunction structure, endowed with abundant porosity and a large number of defects, which eventually engender the remarkable chemisorbed ability to oxygen species.

The present study aims to investigate the transient natural convection in an air-filled square cavity based on the effects of fluid-structure interaction (FSI). The Prandtl number of air is assumed to be 0.71. A thin deformable baffle is horizontally located in the center of the cavity and the top wall of the cavity is also elastic. The horizontal walls are completely insulated. Initially, the cavity is set at T c temperature, then the left side wall temperature is raised to T h . The arbitrary Lagrangian-Eulerian approach is implemented to study the flow field in the presented model. The fluid field equations are discretized by Galerkin finite element method. Further, the dimensionless equations of flexible parts of the cavity are solved using the Newton-Raphson method. The study examines the effects of Rayleigh number and baffle length on flow and temperature fields, heat transfer rate and deformation of elastic parts of the cavity. The results show that an increase in the Rayleigh number enhances the natural convection and increases the elastic parts deformations. Finally, the increase of baffle length has different effects on thermal performance of cavity depending on the Rayleigh number and rigidness or flexibility of the system.

To further develop sensing materials for the detection of reducing gases like NH 3 and H 2 S and improve their response efficiency and selectivity, mesoporous In 2 O 3 @CuO composite multijunctions nanofibers (ICCNs) was synthesized by an electrospinning approach with a subsequent thermal treatment. Comparison was made with the one-dimensional (1D) pristine CuO multijunctions nanofibers (NFs). It was found that the CuO NFs have many p-p homojunctions and lots of chemisorbed oxygen, allowing for excellent gas sensing behaviors towards H 2 S at room temperature (RT). Interestingly, the ICCNs’ sensors favor to detect NH 3 gas. Amongst them, ICCN-5 (short for the sensor composite where the molar ratio of Cu: In is 100: 5) behaves very fast response, excellent selectivity and good stability (within 30 days) toward 10 ppm NH 3 at RT. The significantly enhanced sensing property of ICCNs to NH 3 could be attributed to the synergistic effect of In 2 O 3 promoter, multijunctions and unique mesoporous structure of NFs. Our studies demonstrated that 1D-CuO and ICCN-5 sensors were promising candidates of practical detectors to H 2 S and NH 3 at RT.

Nanoparticles dispersed in a phase change material alter the thermo-physical properties of the base material, such as thermal conductivity, viscosity, and specific heat capacity. These properties combined with the configuration of the cavity, and the location of the heat source, influence the melting characteristics of the phase change material. In this paper, an assessment of the influence of the nanoparticles in the base material subjected to a heat generating source located in the center of an insulated square cavity, which is a common configuration in thermal capacitors for temporal heat storage is investigated. The interplay between heat conduction enhanced due to an increase in thermal conduction and buoyancy driven heat convection damped by the increase in viscosity of nanoparticles dispersed in the phase change materials is studied with the calculated streamlines and isotherms. We observed three regimes during the melting process, first at an early time duration dominated by heat conduction, later by buoyancy driven convection till the melting front levels with the center of the cavity, and lastly once again heat conduction in the bottom portion of the cavity. During the first two regimes, addition of nanoparticles have no significant performance gain on the heat storage cavity, quantified by maximum temperature of the heat source and average Nusselt number at the faces of the heat source. In the late regime, nanoparticles provide a slight performance gain and this is attributed to the increase in the specific heat of the melt due to the nanoparticles.

NiO@CuO nanocomposite was synthesized through a simple reflux and hydrothermal method. NiO@CuO gas sensor has been fabricated and investigated. The result revealed that the NiO:CuO molar ratio 1:1 of NiO@CuO (NC-1) sensor shows the fast response time which was 2 s to 100 ppm NO 2 gas at room temperature (RT), which is better from NC-2 and NC-4 which have NiO:CuO molar ratios of 2:1 and 4:1, respectively. This valuable gas sensing properties could be attributed to the combined action of the high specific surface, highly porous structure, and interactions between high conductivity of NiO nanosheets (NSs) and CuO nanoparticles (NPs), which is salutary for diffuse and adsorption-desorption of gas on the surface of the NC-1. The high gas sensing performance of NiO@CuO sensors described here will be a promising material towards the detection of NO 2 gas in environmental supervising.

In this work, highly crystalline mesoporous In 2 O 3 nanowires (NWs) doped with K 2 O, ZnCl 2 or CaCl 2 were synthesized by template-calcined method using SBA-16 as template. The mesoporous K 2 O-In 2 O 3 NWs (INW-K2), which was synthesized by mixing 0.2 mol L −1 In(NO 3 ) 3 solution with 0.02 g KNO 3 so that In(NO 3 ) 3 and KNO 3 mass ratio was 30:1, has high density of chemisorbed oxygen. Its diameter is about 4–8 nm and pore size is 3–5 nm. For INW-K2, K 2 O doped on its surfaces serves as alkaline center and benefits the adsorption and diffusion of acidic NO x . Meanwhile, the INW-K2 provides large number of active centers for gaseous reactions on the surface of the nanowires. Therefore, the gas sensing property of INW-K2 is significantly improved, the response of NO x to 97 ppm is about 151.78 and response time is only 12 s, the detection limitation decreased to 48.5 ppb at room temperature (RT). The highly crystalline mesoporous K 2 O-In 2 O 3 nanowires might offer a new opportunity for synthesizing multifunctional sensing materials in future.

The effect of a wedge angle on the MHD laminar momentum and thermal boundary layer decelerating forced flow of a water-Cu nanofluid flow over a constant temperature wedge is investigated numerically for different nanoparticle volume fractions. The thermal conductivity and viscosity of the nanofluid are computed by considering the Brownian motion of the particles. The momentum and energy equations are solved by the Keller-Box method. The averaged friction coefficient and the Nusselt number are analyzed to explore boundary layer and heat transfer behaviours. Two regression models are obtained by using the response surface methodology for various magnetic parameters ( $0.5\le M\le 2.5$ ), wedge angles ( $ 90^{\circ}\le \beta\le 180^{\circ}$ ) and nanoparticle volume fractions ( $ 0.01\le \varphi\le 0.07$ ). Then, a sensitivity analysis is carried out to gain further insight into the impact of the factors on the problem. Finally, an optimization process is conducted in order to determine the maximum heat transfer rate and the minimum surface friction. The obtained results show that both the magnetic parameter and the wedge angle decrease the thicknesses of the hydrodynamic and thermal boundary layers, so that the averaged surface friction and the Nusselt number reduce. Surprisingly, adding nanoparticles is found to have a decreasing impact on the averaged Nusselt number by enlarging the thermal boundary layer thickness at high magnetic strength. The sensitivity analysis outcomes reveal that M, $ \beta$ , and $ \varphi$ have increasing effects on the surface friction. Also, the sensitivity of $ \overline{Nu}$ to the wedge angle is found to be independent of the magnetic parameter. The optimum condition occurs when M = 0.62, $ \beta=166.71^{\circ}$ , and $ \varphi$ = 0.052, wherein $ \overline{Nu}$ = 1.176 and $ \overline{C}_{f}=3.2601$ , with a maximum error of 0.33%.

In this paper, natural convection and radiation heat transfer of alumina-water nano-fluid in a square chamber at 45° has been simulated. The right wall of the chamber is cold, and there is a warm vane in the chamber. The vane can change form into horizontal ellipse, vertical ellipse, and circle. The other parts of the walls are insulated. The simulation was performed by using the algebraic control volume method and the SIMPLE algorithm. The effective parameters include the Rayleigh number, the radiation parameter, the nanoparticle volume percentage, and the vane dimensions. The paper focuses on finding the best vane size for maximum heat transfer. The results show that the intensification of the Rayleigh Number and addition of nanoparticles augments heat transfer. As the Rayleigh number enhances by up to 105, the Nusselt number increases up to 3 times. The intensification of nanoparticles concentration up to 4% also increases the Nusselt by 2.5% compared to water. Adding radiation heat transfer to the chamber can significantly increase heat transfer. Increasing the radiation parameter from 0 to 3 has increased the Nusselt number by more than 7 times. The Nusselt number increases with increases in both vane diameters. Nevertheless, it is strongly dependent on the horizontal diameter, and changes in the vertical diameter have little effect on the average Nusselt Number (Nuave).

In this paper, a less studied factor in the asymmetrical rolling process of sheets, namely the rolls horizontal displacement, is investigated using an analytical approach based on the slab method analysis. The presented method is capable of computing the force and torque of the process under different asymmetrical factors such as the rolls horizontal displacement, the interface friction inequality, and the rolls speed mismatch. A formula is presented to predict the outgoing sheet curvature induced by the rolls horizontal displacement. The results can be potentially used in producing curved sheets of various shapes by the asymmetrical rolling process. The analytical model is compared with a verified finite element code and good agreement has been observed.

Plastic anisotropy of ultrafine-grained (UFG) Cu–30%Zn tubes fabricated by parallel tubular channel angular pressing (PTCAP) process was investigated. The results showed that there was a severe anisotropy in UFG tubes in comparison with course grained counterparts. The PTCAP processed tube showed a very high strength of about 1220 MPa along the peripheral direction while it is about 580 MPa along the axial direction. Ultimate strength increased about 66% and 106% along the axial and peripheral directions, respectively. Comparison between the yield strength of CG and UFG tubes shows that the yield strength increases from ~106 MPa to ~344 MPa along the axial direction and ~359–1013 MPa along the peripheral direction. In the other word, the yield strength increases about 224% and 182% along the axial and peripheral directions, respectively. The hardness in the peripheral direction was almost greater than that in the axial direction which is in a good agreement with anisotropy of tensile properties. The corresponding textures verified this severe anisotropic in mechanical properties. The {111} plane was rotated about 90° with reorientation toward the radial direction after PTCAP processing while it is almost dispersal with a small texture to the extrusion direction in the annealed sample.

The present study shows that nanostructured (NS) thin-walled tubes possess an excellent energy absorption capacity, which was increased about four times compared to their course grained counterparts. Different deformation modes of axisymmetric concertina folding, three lobes diamond, and two lobe diamond forms were observed in annealed, single pass and two pass parallel tubular channel angular pressing (PTCAP) processed tubes, respectively.

This paper examines the natural convection in an enclosure that is filled with a water-Al2O3 nanofluid and is influenced by a magnetic field. The enclosure is bounded by two isothermal vertical walls at temperatures Th and Tc and by two horizontal adiabatic walls. Based upon numerical predictions, the effects of pertinent parameters such as the Rayleigh number (103 ≤ Ra ≤ 107), the solid volume fraction (0 ≤ ϕ ≤ 0.06) and the Hartmann number (0 ≤ Ha ≤ 60) on the flow and temperature fields and the heat transfer performance of the enclosure are examined. Prandtl number is considered to be Pr = 6.2. The results show that the heat transfer rate increases with an increase of the Rayleigh number but it decreases with an increase of the Hartmann number. An increase of the solid volume fraction may result in enhancement or deterioration of the heat transfer performance depending on the value of Hartmann and Rayleigh numbers.

This article provides numerically study of the thermal performance of a microchannel, cooled with either pure water or a Cu-water nanofluid, while considering the effects of both slip and no-slip boundary conditions on the flow field and heat transfer. The microchannel is partially heated at a constant temperature and cooled by forced convection of a laminar flow at a relatively lower temperature. The effects of pertinent parameters such as Reynolds number, solid volume fraction, and slip velocity coefficient on the thermal performance of the microchannel are studied. The results of the numerical simulation indicate that the heat transfer rate is significantly affected by the solid volume fraction and slip velocity coefficient at high Reynolds numbers.

Thin films of semiconductors are being used in microelectronic devices. These structures experience very high transient thermal loads during operation. Phonons are the main heat carriers in these ultrafine layers. The interfaces in these structures also affect their thermophysical properties through reflection and transmission of heat carriers. This work focuses on the transient heat transport in the direction perpendicular to the plane of a double layer thinfilm structure. The analysis is based on the equation of phonon radiative transport (EPRT). This integrodifferential equation is numerically solved for the double layer. The results for the transient temperature distribution as well as the heat flow across the layers are presented.

Heating and melting of a semi-infinite body due to volumetric absorption of a moving laser radiation were studied. The problem is essentially a transient three-dimensional conduction problem with a moving heat source and a moving phase boundary. An explicit finite difference technique was used to solve for the temperature distribution and the melt pool size. In order to save computing time the solution domain was divided into inner and outer regions. The inner region was sized to contain the maximum pool size. A fine grid pattern was used for the inner region, where the temperature gradient is large and where the accurate location of the solid-liquid interface is desired. In order to validate the numerical results, comparisons were made with experimental data. The results show that the heat-affected zone and the melt pool size decrease as the translational speed of the beam increases.

This technical brief numerically examines the mixed convection heat transfer of a Cu-water nanofluid in a parallel-plate vertical channel that is influenced by a magnetic field. An upward flow of Cu-water nanofluid enters the channel at a relatively low temperature and a uniform velocity. It is found that the magnetic field has dissimilar effects on the heat transfer rate at different Richardson numbers. The increase of solid volume fraction results in an increase of the heat transfer rate especially at low Richardson numbers.