Showing papers in "Journal of Thermal Analysis and Calorimetry in 2020"

Conjugate natural convection flow of Ag–MgO/water hybrid nanofluid in a square cavity

Abstract: The conjugate natural convection of a new type of hybrid nanofluid (Ag–MgO/water hybrid nanofluid) inside a square cavity is addressed. A thick layer of conductive solid is considered over the hot wall. The governing partial differential equations (PDEs) representing the physical model of the natural convection of the hybrid nanofluid along with the boundary conditions are reported. The thermophysical properties of the nanofluid are directly calculated using experimental data. The governing PDEs are transformed into a dimensionless form and solved by the finite element method. The effect of the variation of key parameters, such as the volume fraction of nanoparticles, Rayleigh number, and the ratio between the thermal conductivity of the wall and the thermal conductivity of the hybrid nanofluid (Rk), is studied. Furthermore, the effects of the key parameters are investigated on the temperature distribution, local Nusselt number, and average Nusselt number. The results of this study show that the heat transfer rate increases by adding hybrid nanoparticles for a conduction-dominant regime (low Rayleigh number). The heat transfer rate is an increasing function of both the Rayleigh number and the thermal conductivity ratio (Rk). In the case of a convective-dominant flow (high Rayleigh number flow) and an excellent thermally conductive wall, the local Nusselt number at the surface of the conjugate wall decreases substantially by moving from the bottom of the cavity toward the top.

Numerical study on mixed convection of a non-Newtonian nanofluid with porous media in a two lid-driven square cavity

Abstract: In the present numerical study, mixed flow of the non-Newtonian water/Al2O3 nanofluid with 0–4% nanoparticles volume fractions (φ) inside a two-dimensional square cavity with hot and cold lid-driven motion and porous media is simulated at Richardson numbers (Ri) of 0.01, 10 and 100 and Darcy numbers (Da) of 10−4 ≤ Da ≤ 10−2 using Fortran computer code. The obtained results for temperature domain, velocity, Nusselt number and streamlines indicate that by increasing Richardson number and decreasing axial velocity parameter of walls and similarity of flow behavior to natural flow mechanism, variations of velocity are reduced, which is due to the reduction in fluid momentum. By increasing Darcy number, penetrability of fluid motion enhances and fluid lightly moves along the cavity. Figuration of streamlines at lower Richardson numbers highly depends on the Darcy number changes. In case (2), due to the counterflow motion and buoyancy force, distinction of flow domain profiles is more obvious. On the other hand, this issue causes more velocity gradients and vortexes in special sections of cavity (central regions of cavity). In case (2), the behavior of streamlines is affected by some parameters such as variations of Darcy number, nanoparticles volume fraction and Richardson number more than case (1). By increasing Darcy number, flow lightly passes among hot and cold sources and leads to improve the heat transfer. Moreover, reduction in flow penetrability in cavity results in the reduction in fluid flow in its direction, sectional distribution and regions with higher temperature. Consequently, in these regions the growth of thermal boundary layer is more significant. In case (2), at lower Richardson numbers compared to higher ones, the affectability of lid-driven motion contrary to buoyancy force caused by density variations is less because of higher fluid momentum. At Ri = 0.01, because of the strength of lid-driven motion, flow direction is compatible with lid-driven motion. Also, temperature distribution is not uniform, and in these regions, fluid has the minimum velocity which leads to the enhancement of dimensionless temperature. In both studied cases, the increment of nanoparticles volume fraction as well as Darcy number and reduction in Richardson number result in the improvement of temperature distribution and decrease in dimensionless temperature.

Effect of thermal radiation on MHD Casson fluid flow over an exponentially stretching curved sheet

Abstract: This paper presents the flow and heat transfer characteristics of an electrically conducting Casson fluid past an exponentially stretching curved surface with convective boundary condition. The fluid motion is assumed to be laminar and time dependent. The effects of temperature-dependent thermal conductivity, Joule heating, thermal radiation, and variable heat source/sink are deemed. Suitable transformations are considered to transform the governing partial differential equations as ordinary ones and then solved by the numerical procedures like shooting and Runge–Kutta method. Graphs are outlined to describe the influence of various dimensionless parameters on the fields of velocity and temperature and observe that there is an enhancement in the field of temperature with the radiation, temperature-dependent thermal conductivity, and irregular heat parameters. Also, the Casson parameter has a tendency to suppress the distribution of momentum but an inverse development is noticed for the curvature parameter. Attained outcomes are also compared with the existing literature in the limiting case, and good agreement is perceived.

Thermal conductivity prediction of nanofluids containing CuO nanoparticles by using correlation and artificial neural network

Abstract: Nanofluids are employed in different thermal devices due to their enhanced thermophysical features which lead to noticeable heat transfer augmentation. One of the major reasons of the heat transfer improvement by using the nanofluids is their increased thermal conductivity. Several methods have been applied to estimate this property of nanofluids such as correlations and artificial neural networks (ANNs). In the present paper, group method of data handling (GMDH) and a mathematical correlation are proposed for forecasting the thermal conductivity of nanofluids containing CuO nanoparticles. The inputs of the both models are the base fluids’ thermal conductivities, concentration, temperature and nanoparticle dimension. Comparison of the forecasted data by these two approaches revealed more favorable performance of GMDH. The values of R-squared in the cases where polynomial and ANN were utilized were 0.9862 and 0.9996, respectively. Moreover, the average absolute relative deviation values were 5.25% and 0.881% for the indicated methods, respectively. According to these statistical values, it is concluded that employing the ANN-based regression leads to more confident model for forecasting the TC of the nanofluids containing CuO nanoparticles.

Comparing various machine learning approaches in modeling the dynamic viscosity of CuO/water nanofluid

Abstract: Nanofluids are broadly employed in heat transfer mediums to enhance their efficiency and heat transfer capacity. Thermophysical properties of nanofluids play a crucial role in their thermal behavior. Among various properties, the dynamic viscosity is one of the most crucial ones due to its impact on fluid motion and friction. Applying appropriate models can facilitate the design of nanofluidics thermal devices. In the present study, various machine learning methods including MPR, MARS, ANN-MLP, GMDH, and M5-tree are used for modeling the dynamic viscosity of CuO/water nanofluid based on the temperature, concentration, and size of nanostructures. The input data are extracted from various experimental studies to propose a comprehensive model, applicable in wide ranges of input variables. Moreover, the relative importance of each variable is evaluated to figure out the priority of the variables and their influences on the dynamic viscosity. Finally, the accuracy of the models is compared by employing the statistical criteria such as R-squared value. The models’ outputs disclosed that employing ANN-MLP approach leads to the most precise model. R-square value and average absolute percent relative error (AAPR) value of the model by using ANN-MLP model are 0.9997 and 1.312%, respectively. According to these values, ANN-MLP is a reliable approach for predicting the dynamic viscosity of the studied nanofluid. Additionally, based on the relative importance of the input variables, it is concluded that concentration has the highest relative importance; while the influence of size is the lowest one.

Entropy generation analysis due to MHD natural convection flow in a cavity occupied with hybrid nanofluid and equipped with a conducting hollow cylinder

Abstract: The main objective of this numerical investigation was to analyze the entropy generation and natural convection flow under magnetic field in a square enclosure filled with Cu–Al2O3/water hybrid nanofluid. The enclosure is equipped with a conducting hollow cylinder. The free convective flow in the enclosure is created by a horizontal temperature difference between the vertical left hot wall and the right cold wall under the Boussinesq approximation. The dimensionless equations of steady laminar natural convection flow for Newtonian and incompressible mixture are discretized using the finite volume method. The effective thermal conductivity and viscosity of the hybrid nanofluid are calculated using Corcione correlations taking into consideration the Brownian motion of nanoparticles. Numerical solutions were performed for different values of the nanoparticles volumic concentration, Hartmann number, Rayleigh number, radius ratio, and solid–fluid thermal conductivity ratio. The analyzed results show that inserting a hollow conducting cylinder plays an important role in controlling flow characteristic and heat transfer rate as well as irreversibilities within the cavity.

Natural convection analysis in a square enclosure with a wavy circular heater under magnetic field and nanoparticles

Abstract: The aim of the current study is to investigate the natural convection heat transfer in a square enclosure with a wavy circular heater under magnetic field and nanoparticles. The governing equations that are expressed in dimensionless form are solved by means of control volume finite element method employing a validated FORTRAN code. The dimensionless controlling parameters of the present investigation are shape factor of nanoparticles (m), Hartmann number (Ha), Rayleigh number (Ra), and nanoparticle volume fraction (ϕ). In this study, the amplitude A and number of undulations N are fixed at a constant value of 0.2 and 8, respectively. The obtained results portray that in the presence of waves on the inner wall of the annulus, the heat transfer rate is an ascending function of Rayleigh number, nanoparticle volume fraction and less obvious function of their shape factor, while it is a descending function of the Hartmann number.

Effects of different shapes of nanoparticles on peristaltic flow of MHD nanofluids filled in an asymmetric channel

Abstract: An innovative approach to escalate the heat generation in peristalsis flow of MHD nanofluids filled in an asymmetric channel is proposed. Three different shapes of nanoparticles, namely (1) spherical, (2) disc and (3) cylindrical are utilized. Results for temperature, velocity and concentrations have been obtained analytically. The physical features for heat generation, concentration, pressure gradient, pressure rise and magnetic parameter have been elaborated graphically, whereas effects of Nusselt number and skin friction have been numerically computed by using the MATLAB software. For bolus features, trapping phenomena are also inspected by dint of stream lines. It is found that cylindrical shapes of nanoparticles have very low thermal conductivity as compared to spherical and disc shapes. Moreover, it is seen that the heat generation parameter always increases the temperature of nanofluid, and consequently, the trapping phenomena produce more boluses for larger values of heat source parameter.

Numerical simulation of hydrothermal features of Cu–H2O nanofluid natural convection within a porous annulus considering diverse configurations of heater

Abstract: The purpose of the current study is to numerically investigate the effects of shape factors of nanoparticles on natural convection in a fluid-saturated porous annulus developed between the elliptical cylinder and square enclosure. A numerical method called the control volume-based finite element method is implemented for solving the governing equations. The modified flow and thermal structures and corresponding heat transfer features are investigated. Numerical outcomes reveal very good grid independency and excellent agreement with the existing studies. The obtained results convey that at a certain aspect ratio, an increment in Rayleigh and Darcy numbers significantly augments the heat transfer and average Nusselt number. Further, enhancement of Rayleigh number increases the velocity of nanofluid, while that of aspect ratio of the elliptical cylinder shows the opposite trend.

Influence of viscous dissipation on MHD flow of micropolar fluid over a slendering stretching surface with modified heat flux model

Abstract: The current research article delivers a numerical study of an electrically conducting magnetohydrodynamic nonlinear convection flow of micropolar fluid over a slendering stretching surface. The flow is laminar and time independent. The influence of viscous dissipation, Joule heating, non-uniform heat source or sink, temperature-dependent thermal conductivity and thermal radiation is deemed. Heat-transfer characteristics are scrutinized with the aid of modified Fourier’s law. We presented simultaneous solutions for a flat surface and variable thickened surface. At first, appropriate similarity transformations are considered to convert the basic partial differential equations as ordinary ones and then solved by the successive application of numerical procedures such as shooting and fourth-order Runge–Kutta method. Graphs are delineated to observe the influence of diverse nondimensional parameters on the flow fields. Along with the skin friction coefficient, couple stress coefficient and local Nusselt number are also discussed and bestowed with the support of the table. Results stipulate that the distribution of temperature increases with thermal relaxation and radiation parameters, but a contradictory outcome is spotted for Prandtl number. Also, the microrotation velocity is suppressed with an enhancement in magnetic field parameter, but an opposite trend is observed for buoyancy force.

Investigation of energy performance in a U-shaped evacuated solar tube collector using oxide added nanoparticles through the emitter, absorber and transmittal environments via discrete ordinates radiation method

Abstract: This work is a three-dimensional numerical study of a U-shaped evacuated tube solar collector employing different types of oxide nanofluids including water–Al2O3, water–CuO and water–TiO2 under the steady-state condition. The simulation is performed using the single-phase method for nanofluid modeling, the DO method for radiation modeling, incompressible and fluid flow laminar regime. The thermo-physical properties of the water are considered as a function of temperature ranging from 0 to 150 °C. The obtained results showed that increasing both length and diameter of the U-shaped tubes of the solar collector enhances its thermal efficiency. Moreover, it is found that using oxide nanofluids results in an enhancement in the collector thermal performance which using water–CuO nanofluid causes 13.8, 1.5 and 1.3% higher collector thermal efficiency in comparison with employing pure water, water–TiO2 and water–Al2O3 nanofluids, respectively. It is also observed that the working fluid heat capacity plays an important role in the thermal performance of the evacuated tube solar collector.

The performance, emissions, and combustion characteristics of an unmodified diesel engine running on the ternary blends of pentanol/safflower oil biodiesel/diesel fuel

Abstract: The objective of the present study is to scrutinize the influence of a binary blend of diesel–safflower oil biodiesel and ternary blends of diesel–biodiesel–pentanol on performance, emission and combustion characteristics of a diesel power generator. The test fuels were prepared on volume basis by splash blending and named as follows: B20, B20P5, B20P10, B20P15, and B20P20. The tests were carried out on a single-cylinder, four-stroke, naturally aspirated, and direct-injection diesel engine at four engine loads with a constant engine speed of 3000 rpm. According to the results, ternary blends vaguely reduced BTE while increased BSFC up to 13.90% as compared to diesel. In addition, an increase in pentanol concentration has a considerable effect on the decrease in NOX emissions. It is noted that the addition of pentanol to diesel–biodiesel blend caused to lower emissions (CO, HC, and smoke), whereas CO2 emission increased noticeably thanks to the more complete combustion due to the excess oxygen content. Reviewing combustion analysis results, pentanol addition led to decrease heat release rate and lower ignition delay up to 15% blend ratio compared to diesel. Based on the present study, pentanol can be evaluated as a promising type of higher alcohol for the compression ignition engines in the near future.

Magnetohydrodynamic natural convection and entropy generation analyses inside a nanofluid-filled incinerator-shaped porous cavity with wavy heater block

Abstract: The aim of the current study is natural convection analysis conjugated with entropy generation analysis in an incinerator shaped permeable enclosure loaded with Al2O3–H2O nanofluid subjected to the magnetic field with a rectangular wavy heater block positioned on the bottom of the cavity wall. The bottom and top horizontal walls are adiabatic; the inclined and vertical walls are thought to be cooled. Firstly, the governing expressions and standard k–e turbulence model are rewritten from dimensional form to non-dimensional form using dimensionless parameters such as vorticity and stream function. In the next step, the equation of entropy generation is written in dimensionless form. Then, the system of non-dimensional governing equations is solved by the finite volume method (FVM) conjugated with a non-dimensionalization scheme using ANSYS Fluent. Fine grids (wall y+ < 2) with inflated layers have been used for the higher Rayleigh number. The effects of the Rayleigh number in the laminar region (Ra = 103, 104, and 105) and turbulent region (Ra = 108, 0.5 × 109, and 109), Darcy number (Da = 0.01 and 100), Hartmann number (Ha = 0 and 40), and the nanoparticles ( $$ \phi = 2{{\% }} $$ ) on the entropy generation number and natural convection are investigated. The validation results were in good agreement with those of the literature. The results demonstrate that for the laminar region, the Nusselt number and entropy generation number increase as the Rayleigh number and the Darcy number grow, whereas both of them abate as Hartmann number increases. In the turbulent region, the average Nusselt number decreases by ascending the Darcy number. Also, for turbulent region (Ra = 109), convection flow strength decreases 6.28% when Hartmann number increases from 0 to 40, whereas the entropy generation number increases 31.5% at Da = 0.01.

Numerical investigation of turbulent flow and heat transfer of nanofluid inside a wavy microchannel with different wavelengths

Abstract: In the present study, turbulent flow and heat transfer inside a three-dimensional wavy microchannel with different wavelengths have been numerically simulated. The main purpose of this study is to investigate the effects of changing the wavelength of the sinusoidal microchannel and CuO nanoparticle concentration on flow and heat transfer properties. For this reason, flow is simulated at Reynolds numbers of 3000, 4500, 6000, and 7500 with volume fractions of 0, 1.5, and 3% in three different geometries and the effects of each parameter have been investigated. Validation of the results showed there is an excellent agreement between the presented results with the previous studies. The average Nusselt number, pressure loss ratio, performance evaluation criterion, and local Nusselt number have been presented. Moreover, the distribution of the static temperature contour has been presented. In the flow with lower Reynolds numbers, the Nusselt number is not changed significantly; however, in flow with Reynolds number of 7500, the Nusselt number is increased. The performance evaluation criterion has the highest value in nanofluid flow with the volume fraction of 3%, indicating the effects of heat transfer with pressure drop caused by nanoparticles, and from engineering and economic perspectives, using nanoparticles in the wavy microchannel is recommended.

A comprehensive review on the natural, forced, and mixed convection of non-Newtonian fluids (nanofluids) inside different cavities

Abstract: Convection heat transfer in cavities has attracted much attention from researchers. Many kinds of nanofluids have exhibited non-Newtonian behavior and been employed as heat transfer fluids in cavities. In a non-Newtonian fluid, shear stress and strain do not have a linear relationship. Such fluids do not follow Newton’s law of shear stress. As a result, researchers have used such models as the power-law or Bingham to formulate the behavior of non-Newtonian fluids and provide a numerical solution. In this study, first the non-Newtonian nanofluids were summarized. And then two well-known models, namely the power-law and Bingham models, are introduced, which was followed by empirical studies in non-Newtonian fluids or nanofluids. Then a summary of studies on nanofluids and non-Newtonian fluids inside different types of cavities was provided. Moreover, some tables are presented summarizing numerical studies into cavities containing nanofluids or non-Newtonian fluids and their significant findings.

Significance of bioconvection in chemical reactive flow of magnetized Carreau–Yasuda nanofluid with thermal radiation and second-order slip

Abstract: Several non-Newtonian fluids are of practical interest, and it is fascinating to examine the rheology of such fluids with various flow features. In this study, the flow of Carreau–Yasuda nanofluid has been analyzed in the presence of gyrotactic microorganisms. The impressive features of nanofluid are displayed by abiding the thermophoresis and Brownian motion aspects. The second-order velocity slip effects are decomposed in the mathematical simulations. Further, the governing flow problem governed the impact of thermal radiation, chemical reaction and convective Nield boundary conditions. Although some attempts are available in the literature which examines the rheological features of Carreau–Yasuda nanofluid, whereas the analysis for bioconvection of flow of this non-Newtonian fluid model in the presence of second-order slip features is not proposed yet. Further, it has been noticed that many investigators used first-order or partial slip effects associated with their flow problems. The flow problem becomes more realistic due to the interaction of second-order slip constrains and subsequently develops a more stable boundary layer. The governing equations for the formulated flow problem are partial differential equations. Standard dimensionless quantities are recommended to alter the flow equations in dimensionless forms. The solution of the locally similar problem has been computed numerically via shooting technique. All the computations are performed by using bvp4c with the help of MATLAB software. Following the iterative procedure, the solution is accurate up to convincing accuracy of $$ 10^{ - 4} . $$ The step size for the present simulation is taken as $$ \Delta \eta = 1 \times 10^{ - 4} . $$ The results are also verified by comparing with already reported numerical computation and found a convincible accuracy. The implication of each parameter is executed for velocity, temperature, concentration and microorganisms’ distributions. Moreover, the substantial quantities, namely skin friction coefficient, motile density number, local Nusselt number, and local Sherwood number numerically evaluated and are overviewed for various parameters. The study reveals that velocity distribution decays with the presence of first-order slip parameter and Rayleigh number, while an enhanced velocity profile has been noted for variation of Weissenberg number. An improved nanoparticle temperature and concentration distributions have been found with the utilization of the second-order slip factor and combine parameter. It is further observed that the density of motile microorganisms declined with Peclet number and bioconvection Lewis number. In recent days, a growing interest has been developed from scientists toward the significance of nanoparticles because of their diverse engineering, industrial and commercial applications. The proposed observations can be useful in extrusion systems applications, biomolecules, biomimetic systems, energy production improvement and enhancement of manufacturing processes.

Review on the recent progress in the preparation and stability of graphene-based nanofluids

Abstract: Graphene has attracted much attention from the science world because of its mechanical, thermal, and physical properties. Graphene nanofluid is well known for its easy synthesis, longer suspension stability, higher heat conductivity, lower erosion, corrosion, larger surface area/volume ratio, and lower demand for pumping power. This article is an audit of experimental outcome about the preparation and stability of graphene-based nanofluids. Numerous researches to prepare and stabilize graphene-based nanofluids have been developed, and it is indispensable to create a complete list of the approaches. This research work outlines the advancement on preparation and assessment methods and the techniques to enhance the stability of graphene nanofluids and outlook prospects.

Effect of irregular heat source/sink on the radiative thin film flow of MHD hybrid ferrofluid

Abstract: Ferrofluids are the colloidal suspensions of magnetic nanoparticles and base fluids. It has several medical applications like drug targeting, cell separation, magnetic resonance imaging, etc. The dispersion of more than one magnetic nanoparticle into the convectional fluid is called hybrid nanofluid. It has various technological applications like damping, dynamic sealing, heat dissipation, etc. Due to the immense applications of the ferrofluids, in this analysis, we examined the liquid film flow and heat transfer of hybrid ferrofluid in the attendance of radiation and irregular heat source/sink. We considered the magnetite (Fe3O4) and cobalt ferrite (CoFe2O4) nanoparticles and suspended them into water–ethylene glycol (EG) mixture (50–50%). A mathematical model is developed for the present investigation and solved numerically after applying the suitable similarity transformations. The impact of various governing non-dimensional parameters on the momentum, energy fields, and local Nusselt number of ferro- and hybrid ferrofluids is studied with the aid of graphical illustrations. It is perceived that the rate of heat transfer is higher in hybrid ferrofluid than that of ferrofluid.

Simulation of Cattaneo–Christov heat flux on the flow of single and multi-walled carbon nanotubes between two stretchable coaxial rotating disks

Abstract: With an objective to unfold the flow and heat transfer characteristics of carbon nanotubes between two stretchable coaxial rotating disks, the present investigation has been carried out. The behavior of single- and multi-walled carbon nanotubes (SWCNTs and MWCNTs) taking water as the base fluid is analyzed. To formulate the energy equation, we have incorporated Cattaneo–Christov heat flux model. Consideration of such kind of model accounts the contribution by thermal relaxation. von Karman transformation has been implemented in order to reconstruct the governing partial differential equations into a system of ordinary differential equations. Employing optimal homotopy analysis method series solutions are obtained. Error analysis has also been performed and presented in tabular form. The physical clarifications for the behavior of fluid velocity, temperature, skin friction coefficient and Nusselt number are well demonstrated with the help of graphs and contour plots. One of the major outcomes of the present study signifies that water-based SWCNTs have a tendency to cause less drag and higher rate of heat transfer as compared to water-based MWCNTs. This investigation finds numerous applications in different mechanisms of thermal conversion for nuclear propulsion and spacecraft.

Nanoparticles for water desalination in solar heat exchanger

Abstract: Producing potable water is a critical issue due to the lack of access to clean H2O and the increasing demands of environment. One of the main technologies for water purification is solar still using the sustainable and green source of energy. To augment the efficiency of solar unit, nanoparticles are combined with the saline water. Nanofluids are suspended materials that besides the different geometries (single slope, double slope, tubular…) of the solar stills have a significant impact on improvement of the thermal conductivity of the brackish H2O. Further, combining nanomaterial with solar energy system appears to be more cost-effective approach for potable water production since they boost the evaporation and condensation rate. This paper is a comprehensive literature on different types of nanofluid and various numerical, experimental and analytical methods that researchers have applied to augment the efficiency of system.

Investigation on the effect of cottonseed oil blended with different percentages of octanol and suspended MWCNT nanoparticles on diesel engine characteristics

Abstract: In the present work, a series of experiments were designed and conducted to prepare biodiesel from cottonseed oil and to blend it with octanol. The thermal and mass transfer characteristics of the biodiesel were further improved by adding functionalized multi-walled carbon nanotubes (MWCNTs). The performance of the engine with the blended fuel was analyzed through characterization and measurement of the gas emissions from the engine. Four blends of cottonseed oil (B20, B40, B60, and B100) were prepared initially, and each blend was added with octanol additive of 5%, 10%, and 15% together with 3% of functionalized MWCNTs by mass. The performance analysis showed that B20 with 5%, 10%, and 15% octanol represented relatively lower brake specific fuel consumption relative to all test fuels. Likewise, the addition of MWCNT nanoparticle further stabilized the rate of fuel consumption and brake thermal efficiency. It was also identified that at larger values of diesel and biodiesel blends, the performance and also the quantity of gas emission were the same.

Significance of exponential space- and thermal-dependent heat source effects on nanofluid flow due to radially elongated disk with Coriolis and Lorentz forces

Abstract: In this paper, the nanofluid flow near an infinite disk which stretches in the radial direction in the presence of exponential space-based heat source (ESHS) and thermal-based heat source (THS) is investigated. The Brownian motion and thermophoresis effects are accounted to study the nanofluids. Effects of radial magnetism and the Coriolis force are also deployed. The pertinent nonlinear equations are approximated under boundary layer notion and modified von Karman transformations. The subsequent nonlinear differential system is treated via shooting method. The impacts of controlling parameters on flow profiles are discussed and depicted with the aid of graphs. Results show that as the ESHS and THS parameters increase, the thermal field increases. However, ESHS phenomenon is highly influential than THS phenomenon on energy transport and its gradient. Further, it is found that thermophoresis slip mechanism has more effect on heat transport rate than the Brownian motion.

Thermal evaluation of a heat pipe working with n-pentane-acetone and n-pentane-methanol binary mixtures

Abstract: In the present study, a set of experiments were accomplished to appraise the thermal performance and heat transfer of n-pentane-acetone and n-pentane-methanol mixtures inside a gravity-assisted thermosyphon heat pipe. Pure n-pentane, acetone and methanol were also tested as the carrying fluid to produce some reference data. The heat pipe was manufactured from copper with length and diameter of 290 and 20 mm, respectively. The effect of multiple factors covering the input heat to the evaporator section, the filling ratio of the carrying fluid, heat pipe tilt angle and also the type of the carrying fluid on temperature distribution and thermal performance of the heat pipe was investigated. The results demonstrated that the thermo-physical properties of the carrying fluid were the key factor controlling the heat pipe efficiency. The vapour pressure and boiling temperature of the carrying fluid controlled the thermal efficiency of the system such that for n-pentane-acetone, the highest thermal efficiency was obtained. Also, it was identified that the filling ratio of the system is a key operating factor such that the value of the filling ratio was small for the evaporative carrying fluid (binary mixtures), while it was large for the non-evaporative carrying fluids. Also, heat pipe tilt angle was impressed by the type of the carrying fluid; the optimum tilt angle was 55 degree for the binary mixtures, while it was 65° for the pure liquids.

A comprehensive review on nanofluid operated solar flat plate collectors

Abstract: The impact of population explosion and continuous upsurge on energy demand has resulted in the intimidating depletion of fossil fuel resources, increased environmental pollution, and elevated production and consumption cost. Hence, in the past two decades the demand for renewable energy has escalated. The solar energy is the most trending topic when talking about renewable energy sources, because of its ease of availability, reduced dependence on foreign fuels and negligible maintenance. This can be directly harnessed unlike other renewable energy sources. A solar flat plate collector converts the radiant solar energy from the sun into thermal energy; usually, copper or aluminium is used as heat absorbing material. However, to further enhance the performance and thermophysical properties of the heat exchanger liquids of flat plate solar collectors like radiative heat transfer and thermal conductivity, the nanofluids are used. The use of nanofluids as an innovative type of working fluids is reasonably a new development in solar flat plate collectors. They are prepared by mixing low concentration of solid particles, sized 1–100 nm with the base fluid. The objectives of this review paper is to recapitulate the investigations carried in the field of solar flat plate collectors using a range of nanofluids, the performance analysis of various flat plate collectors using numerous nanofluids and the challenges faced in developing an efficient thermal collector using nanofluids. Furthermore, the article discusses the opportunities for future research.

Enhancement of heat transfer in peristaltic flow in a permeable channel under induced magnetic field using different CNTs

Abstract: The flow of salt water as a base fluid containing nanoparticles of different shapes, viz. zigzag, chiral, and armchair, in an asymmetric permeable channel has been investigated. Such particles in peristaltic flow with a magnetic field have noteworthy medical applications. Two illustrative models, namely those of Hamilton and Crosser, are utilized. The set of governing partial differential equations is solved analytically to find exact solutions, and numerical results are obtained using computer software. A rich summary of the latest findings for pertinent parameters and trapping phenomena is presented using graphs, tables, and streamline diagrams.

On the flow patterns and thermal behaviour of hybrid nanofluid flow inside a microchannel in presence of radiative solar energy

Abstract: Solar radiative energy represents an important source of renewable energy. Of late, hybrid colloidal nanodispersion as an elevated heat transport agent acquires immense interest among researchers rather than unitary nanoliquids. The aim of this investigation was to quantify the flow patterns and heat transfer behaviour of hybrid nanoliquids in presence of nonlinear solar radiation for various solar thermal apparatus. Alumina–copper nanoingredients with water as host fluid are considered. The leading PDEs of our system are turned into ODEs by using prevalent similarity transformation. After that those ODEs have been solved by RK-4-based shooting method. Subsequently, the influences of relevant parameters on the heat transfer of fluid have been talked over on behalf of graphical and tabular approach. Extracted results are verified with experimental plus simulated data. Results communicate that solar radiation fosters heat transport in suction. Hybrid solution exhibits impressive increment in heat transport for suction. Though injection reduces the effect, the decay rate is slower for hybrid nanocomposite. Flipping nature of velocity is perceived for Reynolds number, rotational parameter, and nanoparticle concentration except the variations of suction/injection parameter. We believe that this comprehensive investigation will have potential applications in solar thermal power fabrication, solar ponds, solar thermo electric cells, etc.

Incorporating novel heat recovery units into an AHU for energy demand reduction-exergy analysis

Abstract: The building sector is the major energy consumer, accounting for over 40% of global energy demand. Heating and cooling together with domestic hot water energy consumption are estimated to account for 60% of the required energy for buildings’ maintenance and operation. Energy recovery is a suitable technique to tackle high energy consumption in the building. In this study, a new layout of heat recovery units installation (i.e., primary and secondary) is investigated. The main objective of this study is to reduce energy consumption in an air handling unit through the exergy analysis. Owing to adding heat recovery units, cooling and heating coil loads reduced by 7.8% and 43%, which in turn decreased the total required load of AHU by 17.84%. From the viewpoint of the second law and based on the results, incorporating the primary and secondary heat recovery units into the base AHU in hot and dry climate regions led to decrease in the total irreversibility up to 26.29%, while in hot and humid climate this figure is 14.25%. Consequently, the positive effect of using heat recovery units in the hot and dry climate region is superior to the hot and humid one.

Magnetohydrodynamic natural convection of hybrid nanofluid in a porous enclosure: numerical analysis of the entropy generation

Abstract: The effect on the entropy production and MHD convection of the hybrid nanofluid Al2O3–Cu/water (water with Cu and Al2O3 nanoparticles) in a porous square enclosure is studied numerically via Galerkin finite element method. The enclosure used for flow and natural convection analysis is subjected to sinusoidal varying temperatures at the boundaries. Calculations were performed for specific parameters of the Rayleigh number (Ra = 103–106), porosity ratio (e = 0.1–0.9), Darcy number (Da = 10−5–10−2), Hartmann number (Ha = 0–100) and nanoparticles concentration (φ = 0–0.08). The numerical results are presented by velocity profiles, isotherms, streamlines, and Nusselt number. They indicate that the isotherms subject to estimation variations under Ha boost from 0 to 100 as Ra enhances. At high Ha, the conduction transfer mechanism is more obvious. Also, it is seen that the convective heat transfer becomes stronger with the enhancement of the Ra while it detracts with the rise in Ha. Due to the Ra increase, the flow cell becomes stronger. For Ra = 106 and higher Hartmann numbers, the isotherms remain constant which is an indication of convection predominance.

Seasonal and annual performance analysis of PCM-integrated building brick under the climatic conditions of Marmara region

Abstract: In this work, thermal performance of a conventional brick incorporating phase change material (PCM) is studied. The influence of brick containing PCM on heating and cooling loads is examined considering different fusion temperatures, locations and quantities of PCM. Seasonal and annual thermal performance analysis of brick filled with PCM is evaluated and quantified for climatic conditions of Marmara region, Turkey, by an established and verified numerical model. The obtained results are compared with those of conventional brick and brick filled with phase stabilized material to identify the contribution of latent heat to energy saving. The results showed that filling the gaps of brick near the indoor ambient provides a higher energy conservation. The optimum fusion temperature of PCM varied from season to season in the range of 18–26 °C. An adverse effect of the latent heat activation was observed in summer season, causing higher cooling energy demand by an inappropriate selection of phase transition temperature. Then, an annual analysis was performed to determine the optimum melting temperature which was found to be 18 °C. By incorporating PCM to the brick, the annual thermal load decreased by 17.6%, 13.2% of which was attained due to the utilization of latent heat. The outcomes of this study suggest that the integration of PCM with optimum fusion temperature into the brick can reduce heating and cooling loads considerably in every season of the year and provide thermal comfort for the occupants.

Impact of a helical-twisting device on the thermal–hydraulic performance of a nanofluid flow through a tube

Abstract: Creating greater thermal efficiency is desirable yet challenging in many industrial applications. Employing nanofluids for increasing the thermal behavior of the working fluid and consequently the overall heat transfer rate is an interesting solution that has widely been studied in the literature. This study, however, proposes the use of a special geometry of disturber (i.e., a helical-twisting shape) for a circular duct with nanofluid (water–CuO) as the heat transfer medium and a forced convective flow for this objective. To assess the effect of this instrument, FVM is employed to simulate the hydrothermal performance of the flow through the duct and the disturber. The main parameters of the study include the effects of the width of the disturber blade and inlet velocity on Darcy factor and the heat transfer coefficient. The homogenous model was used for the properties of nanomaterial. The results of the simulations show that better turbulence, i.e., a greater performance, is observed as the width of the flow disturber blade increases and the Reynolds number picks up.