Heat Transfer Profiles Research Articles

IMPACTS OF HEAT SOURCE/SINK AND ELECTROMAGNETIC FIELD ON HEAT TRANSFER IN FERROFLUID FLOW

The inspiration driving this article is to explore the impacts of electromagnetic field and heat source/sink on two dimensional nanofluid flow over a stretching cylinder. The effectively controlled nanofluid model utilized in the current assessment incorporates the nanoparticle fraction model. The nanoparticles specified here are Cobalt $Co$ and Gadolinium $Gd$. Cobalt, $Co$ is a shunt material in the thermomagnetic generator. Gadolinium, $Gd$ is the material first used practically in the thermomagnetic generator. Motor Oil has taken as a base fluid. The governing system of equations solved numerically utilizing MATLAB. The effect of electric field parameter on velocity profile, Heat source/sink on temperature and heat transfer profile, has examined. Further, we noticed that Gadolinium is the most suitable material for the thermomagnetic generator. Its temperature is close to room temperature.

Boundary Layer Flow, Heat and Mass Transfer of Cu-Water Nanofluid over a Moving Plate with Soret and Dufour Effects: Stability Analysis

Our main focus in this paper is to investigate the effects of Soret and Dufour known as thermodiffusion and diffusion-thermo on moving plate in copper water nanofluid. The set of partial differential equations are converted into set of ordinary differential equations using the appropriate similarity variables before being solved numerically using bvp4c code in Matlab software. The results of heat and mass transfer, temperature and concentration profiles on Soret as well as Dufour effects are presented graphically. Soret effect increases the heat transfer rate at the surface while Dufour effect decreases the mass transfer rate at the surface. Since the solutions exist in dual, we carry out the stability solutions to determine which solution is stable and hence the physical meaning is realized physically.

Thermal network modeling of tunnel cable considering circumferential heat transfer and tunnel curvature

Taking wind direction and flow separation into account, the circumferential temperature difference of cable laid in forced-ventilation tunnel is investigated. Combining the heat conduction, the convection and the radiation, the formula calculating the thermal resistance is derived, followed by cable thermal network model in tunnel. The circumferential heat transfer and temperature profile for tunnel cable is analyzed. The results indicate that the temperature of cable is not only transmitted radially, but also circumferentially. The temperature on the leeward side is higher than that on the windward side. As the load increases, the circumferential temperature difference rises. The larger the wind direction angle, the smaller the temperature difference. When the angle is greater than 40°, continue to increase the angle does not have a great impact on the heat dissipation and temperature difference. It suggests that the temperature calculated by IEC-60287 is conservative as it does not take account of multi-factor interactions. The transient thermal network is also established.

Investigation of Cu–water nano-fluid of natural convection hydro-magnetic heat transport in a Darcian porous regime with diffusion-thermo

A theoretical investigation for internal heat generation, suction/injection, diffusion-thermo and nano-particle volume fraction on a chemically reacting hydro-magnetic flow of Cu–water nano-fluid over a semi-infinite vertical surface is presented in this article. The surface has a uniform velocity which is placed in a saturated porous medium. Under thermal equilibrium state, here we consider that the nano-particles are of uniform shape and size. The small perturbation technique is utilized to solve the boundary layer equations, and the solutions are assumed to be oscillatory type. The significant outputs are presented via figures to explain the effects of different controlling variables on the velocity, temperature, concentration, shear stress and rate of heat transfer profiles. As the conductivity of Cupper particles are higher than those of water-based particles, and significantly it is found that the flow velocities are accelerated for the impact of diffusion-thermo/Grashof/internal heat generation. Increasing porosity parameter decelerate the flow velocity for both nano-fluid and base fluid, whereas enhance the temperature for the radiation parameter. For the impact of free convection and diffusion-thermo, growth values of flow velocity are detected for nano-fluid ( $$\mathrm{Cu}$$ ) than the base fluid (water). Furthermore, application of $$\mathrm{Cu}$$ nano-particles can be used in conductive coatings, medical devices, anti-biotic, and textiles. Comparison with previously published works in the limits shows excellent agreement.

Simulator development of a rotary magnetocaloric refrigerator by stepwise regenerator modelling approach

Magnetic refrigeration has been seeing as a promising technology based on the magnetocaloric effect. One of its great advantages is it offers smaller global environmental impact relating to conventional refrigeration. Modeling and simulation of such processes can provide important data in the development and optimization of the experimental devices. Among existing designs, the rotary refrigerators presents several challenges in terms of complexity when comparing to reciprocating ones, which is compensated by several properties. A novel full process simulator of a magnetocaloric refrigerator processes was implemented to study the processes performance over different conditions. A stepwise modeling approach was applied, simplifying the phenomena of heat transfers. Gd was chosen as refrigerant material because of its magnetic transition temperature. The routine considered a rotating clockwise Gd wheel with an anticlockwise closed flow loop of water, which percolates the six Gd porous beds, hot and cold heat exchanger. The simulator was able to represent the transient aspects as well as the steady state conditions of the processes, considering both time performance and numerical stability. The inversion in heat transfer profiles along the process was used as a limit in the calculation of the maximum heat transfer absorption in the cold exchanger.

Laboratory exploration of heat transfer regimes in rapidly rotating turbulent convection

We report heat transfer and temperature profile measurements in laboratory experiments of rapidly rotating convection in water under intense thermal forcing (Rayleigh number $Ra$ as high as $\sim 10^{13}$) and unprecedentedly strong rotational influence (Ekman numbers $E$ as low as $10^{-8}$). Measurements of the mid-height vertical temperature gradient connect quantitatively to predictions from numerical models of asymptotically rapidly rotating convection, separating various flow phenomenologies. Past the limit of validity of the asymptotically-reduced models, we find novel behaviors in a regime we refer to as rotationally-influenced turbulence, where rotation is important but not as dominant as in the known geostrophic turbulence regime. The temperature gradients collapse to a Rayleigh-number scaling as $Ra^{-0.2}$ in this new regime. It is bounded from above by a critical convective Rossby number $Ro^*=0.06$ independent of domain aspect ratio $\Gamma$, clearly distinguishing it from well-studied rotation-affected convection.

Soret, Dufour and radiation effects of a viscoelastic fluid on an exponentially stretching surface using the Catteneo–Christov heat flux model

PurposeIn this paper, we studied the steady flow of a radiative magnetohydrodynamics viscoelastic fluid over an exponentially stretching sheet. This present work incorporated the effects of Soret, Dufour, thermal radiation and chemical reaction.Design/methodology/approachAn appropriate semi-analytical technique called homotopy analysis method (HAM) was used to solve the resulting nonlinear dimensionless boundary value problem, and the method was validated numerically using a finite difference scheme implemented on Maple software.FindingsIt was observed that apart from excellence agreement with the results in literature, the results obtained gave further insights into the behaviour of the system.Originality/valueThe purpose of this research is to investigate heat and mass transfer profiles of a MHD viscoelastic fluid flow over an exponentially stretching sheet in the influence of chemical reaction, thermal radiation and cross-diffusion which are hitherto neglected in previous studies.

Thermal Radiation and Variable Pressure Effects on Natural Convective Heat and Mass Transfer Fluid Flow in Porous Medium

The study investigates the interaction of free convective flow with thermal radiation and variable pressure on natural convective heat and mass transfer fluid flow in porous medium. Solutions for time dependent energy, concentration and momentum equations were obtained by the perturbation series method after transforming into ordinary differential equations. The effect of various flow parameters such as: suction/injection ( δ) radiation (R ) magnetic field (M ) heat source (S ) chemical reaction ( Rc) on the skin friction, rate of heat transfer, velocity, temperature, and concentration profile influencing the physical situation were discussed with the aid of line graphs.
 Keywords: Thermal Radiation, Variable pressure, Perturbation, Natural Convection

Heat transfer behavior of the immersed tubes and solid circulation rate of a conventional U type loop-seal with an in-line tube bundle in the recycle chamber with and without side aeration at the walls

A loop-seal having a horizontal immersed tube bundle in the recycle chamber with aeration at the bottom of the supply and return chambers or a conventional loop seal with heat exchanger (LSHE) was used for this study. Heat transfer behavior of the immersed tubes with aerations at the side walls of the recycle chamber and without side aerations was investigated. An experiment was carried out in a circulating fluidized bed system. The riser has a cross sectional area of 100mm × 100mm while the supply and return chambers of the loop seal have the same cross-sectional areas. The tube has a diameter of 12.7mm. Sand having an average diameter of 310μm was used as bed particles. In all cases, heat transfer tends to be highest and lowest at the tube bottom and the tube crest, respectively. The side aeration can improve particle mobility in the stagnant zone at the tube crest, while bottom aeration cannot, even at a high velocity. Without the side aeration, there is a large difference in the local heat transfer profiles between the lower half and upper half of the tube. With the side aeration, the profiles tend to be comparable. As a result, the average heat transfer coefficient around the tube in this case is higher, and thermal stress due to temperature difference in the tube is lower than for the case without side aeration. In addition, the LSHE with side aeration has higher responsivities to thermal load and solid circulation rate variation than that without side h aeration.

Thin film flow of the water‐based carbon nanotubes hybrid nanofluid under the magnetic effects

AbstractIn this article, the effects of magnetic field versus the thin liquid film water‐based ferrum oxide (Fe3O4) and carbon nanotubes (CNTs) nanofluids have been studied through stretching cylinder. The iron oxide and CNTs (single‐wall [SWCNTs] or multi‐wall [MWCNTs]) have been used as nanoparticles in carrier fluid water (H2O). To the flow field, magnetic effects are applied vertically. The modeled system of partial differential equations are transformed to nonlinear ordinary differential equations by selecting variables. The analytic solution has been obtained through homotopy analysis method. The obtained results are further compared with the numerical ND‐solve method. The embedded constraints impacts are focused on pressure distribution, velocity profile, heat transfer, Nusselt number, and Skin friction through graphical illustration and tables. The dispersion of Fe3O4 and CNTs in base fluid significantly enhanced the mechanism of heat transfer. Moreover, from the results, it has been observed that the MWCNTs have a greater impact on heat transfer, velocity, and pressure profile.

Flame pattern analysis for [formula omitted] flames under conventional air-fired and oxy-fuel conditions for two different types of coal

The present work is dedicated to the experimental investigation of the influence of fuel-type and oxidizer composition upon flame structure and behaviour of swirl-stabilized pulverized coal flames. Detailed flame measurements are conducted by employing a combination of flame-intrusive and non-intrusive measurement techniques which can provide complementary data about flow fields, major product species and radiative heat transfer from the flames. Four flames with constant thermal output (60kWth) and stoichiometry are employed. While previous studies of the same configuration were limited to one fuel (Rhenish lignite), the influence of fuel type is investigated here by additionally measuring the same set of parameter for Prosper Haniel bituminous coal. Two reactive atmospheres (conventional air and oxy-fuel with an O2/CO2 ratio of 25/75vol%) are employed to investigate the impact of changes in oxidizer. The combined analysis of measurement results show that flame length is predominantly controlled by the effective swirl intensity when the flame ignites and stabilizes in the vicinity of the burner. Further on, measurements from narrow-band flame imaging and heat flux measurements show that the location of peak combustion intensity is determined by the flow inlet conditions (at the burner). This being key parameters, that could be employed to match heat transfer profiles when transitioning from conventional air firing to oxy-fuel in existing power plants.

Variations of heat transfer mechanism and flow structure in a heat exchanger tube fitted with 30° inclined ring

Flow prediction, heat transfer pattern, and thermo-hydraulic efficiency in a heat exchanger tube fitted with vortex generator are chosen for the present research. The 30° inclined ring is opted to develop the performance of the heat exchanger tube. The effects of inclined ring configuration and placement in the heat exchanger tube on the patterns of flow and heat transfer are investigated. The Reynolds number (at the entry zone of the periodic model) in the range of around 100–2000 (laminar flow region) is discussed. The heat transfer ability, pressure loss, and efficiency of the heat exchanger tube fitted with 30° inclined ring are analyzed with the numerical method (finite volume method). The SIMPLE algorithm of the commercial code is picked for the present study. The simulated results in the heat exchanger tube fitted with 30° inclined ring are offered in patterns of streamlines, temperature contour, and Nusselt number contour. From the preliminary result, it is found that the creation model of the heat exchanger tube fitted with 30° inclined ring has sufficient reliance to measure flow and heat transfer profiles. The installment of the 30° inclined ring in the heat exchanger tube leads to greater heat transfer ability and thermo-hydraulic performance because of the creation of the vortex flow and thermal boundary layer disturbance on the heat exchanger tube surface. The heat transfer ability in the heat exchanger tube fitted with 30° inclined ring is found to be around 1.00–10.56 times above the plain circular tube. In addition, the installation of the 30° inclined ring in the heat exchanger tube gives the maximum thermal enhancement factor around 3.18.

Effects of Longitudinal Vortices on Turbulent Junction Flow Heat Transfer

Turbulent junction flow is a vortex system upstream of a blockage embedded in a turbulent boundary layer, which leads to augmented heat transfer near the blockage. Vortex legs wrap around the blockage and travel downstream as longitudinal vortices. In multistage axial turbines or multiple row tube heat exchangers, these longitudinal vortices can collide with junction flow vortices further downstream. Furthermore, these devices often augment mixing and increase heat transfer with high freestream turbulence. A comprehensive study on how longitudinal vortices affect junction flow heat transfer for different Reynolds numbers, freestream turbulence values, and longitudinal vortex configurations was performed. Longitudinal vortices were generated upstream of a symmetric airfoil using delta winglet vortex generators. Spatially resolved endwall heat transfer coefficients upstream and around the junction were measured using infrared thermography. Time-averaged flowfield measurements of the incoming longitudinal vortices were taken using stereo particle image velocimetry. Longitudinal vortices provided limited heat transfer augmentation around the junction and did not disrupt the time-averaged horseshoe vortex. These interactions were identical at high turbulence, but longitudinal vortices were less effective at augmenting heat transfer, likely due to an increase in vortex wandering. Vortex wandering also led to a broadening in lateral heat transfer profiles.

Comparison of Local Heat Transfer Distribution in Between Three-Dimensional Inclined Closed and Open Cavities

Abstract The phenomenon of natural convection is investigated in three-dimensional (3D) cavities with four adiabatic walls and one hot wall. The surface opposite to the hot wall is either a wall (closed cavity) at a lower constant temperature or is open to ambient at a lower temperature (open cavity). It is pointed out here that not only overall heat transfer is important, the distribution of local heat transfer is also important. To quantify the uniformity of heat transfer distribution, the ratio of maximum to average heat transfer is calculated for various Rayleigh numbers as well as inclination angles for open and closed cavities. A significant difference in the local heat transfer profile along the hot surface of the closed cavity in comparison to that in open cavity for small inclination angle (especially at higher values of Rayleigh number) is noted. However, the profile is remarkably similar in the case of vertical cavities. For inclined closed cavities, there is a buoyancy component of the flow acceleration normal to the hot and cold wall, which is absent in the case of vertical cavities. For lower inclinations, this component brings the three-dimensionality in the flow field and leads to the differences in the flow patterns. The fluid striking the cold wall in the case of the closed cavity causes significantly different flow patterns that, in turn, lead to nonuniform local heat transfer. To explain the flow behavior, iso-surfaces, stream ribbons, and the Y-components of the flow velocity are plotted at different surfaces of the closed cavity.

Radiation and Heat Source Effects on MHD Free Convection Flow over an Inclined Porous Plate in the Presence of Viscous Dissipation

This study analyzes radiation, viscous dissipation and heat source effects on magneto-hydrodynamic free convection flow, of a viscous incompressible fluid over an inclined porous plate. Applying the perturbation technique, the solution of a set of ordinary differential equations are gotten as a result of reducing the non-linear partial differential equations of motion, energy and diffusion, which is solved analytically for velocity, temperature and the concentration distribution. The effect of Radiation, viscous dissipation and heat source on the velocity, temperature, concentration, skin friction, heat transfer and rate of mass flux distribution is plotted graphically using Mathematica 12 software and discussed. It is observed that increased Magnetic field reduces the velocity profile, increases the temperature, skin friction and heat transfer profile. Increase in radiation reduces heat transfer causing a mixed effect on the velocity, temperature and skin friction while an increase in the heat source causes a turbulent effect on the velocity, temperature and skin friction profile. Increase in porosity reduces the velocity, temperature, skin friction and heat transfer profile and finally parameters such as Chemical reaction, Grashof concentration number and Schmidt number had no effect on the velocity, temperature, skin friction and heat transfer profile.

Numerical Calculations for a Boundary Layer Flow past a Moving Vertical Porous Plate with Suction/Injection and Thermal Radiation

The work presented herein investigates the velocity, heat transfer, Nusselt number and skin friction profiles involved in boundary layer flow past a moving vertical porous plate. Similarity transformations are employed to convert the governing nonlinear unsteady momentum and energy equations from their partial differential equation forms to boundary value ordinary differential equations. The resulting equations are then solved numerically by the Runge-Kutta fourth order method with the help of a shooting technique. Several features of the flow and heat transfer characteristics for different values of problem parameters are analyzed and discussed. These include the effects of the radiation parameter (R), suction and injection parameter (c), Grashof (Gr) and Prandtl (Pr) numbers on the flow and heat profiles. Numerical results show the impact of blowing and sucking as well as radation on boundary layer flows of this type. Both the skin frictions as well as the heat transfer rate are also significantly related to the radiation parameter. For all these cases; the numerical results are found to be in agreement with the physics of the problem.

Modeling and Simulation of Heat Transfer Phenomenon Related to Mold Heating during Investment Casting

Cast shape during investment casting process dictates properties and service life of the casting. These properties are the function of cast part parameters (both static and dynamic), part geometry and hence mold geometry, nature and type of metal being cast, properties (extrinsic and intrinsic) and processing parameters (rate of heating, rate of cooling, rate of pouring). Improper and inadequate manipulation and modification of mold properties degrade the properties and life of casting altogether. A mathematical model is developed using standard transport equations incorporating all heat transfer coefficients (HTCs) to determine the effect of external mold heating on the properties of the final casting and a simulation is performed in C++ to validate it against experimental results. Pure iron is casted in investment molds of silica sand with zircon coating. Airflow near the mold surfaces was partially restricted due to geometry of the molds and arrangement of the pieces around a tree. The variations in heat transfer coefficient contribute towards total heat transfer out of mold surface. External heating is found to be very effective for improved casting properties. The mold heat transfer profile is found to be in good agreement with experimental values validating the effectiveness of mold heating.

Improving lake mixing process simulations in the Community Land Model by using <i>K</i> profile parameterization

Abstract. We improved lake mixing process simulations by applying a vertical mixing scheme, K profile parameterization (KPP), in the Community Land Model (CLM) version 4.5, developed by the National Center for Atmospheric Research. Vertical mixing of the lake water column can significantly affect heat transfer and vertical temperature profiles. However, the current vertical mixing scheme in CLM requires an arbitrarily enlarged eddy diffusivity to enhance water mixing. The coupled CLM-KPP considers a boundary layer for eddy development, and in the lake interior water mixing is associated with internal wave activity and shear instability. We chose a lake in Arctic Alaska and a lake on the Tibetan Plateau to evaluate this improved lake model. Results demonstrated that CLM-KPP reproduced the observed lake mixing and significantly improved lake temperature simulations when compared to the original CLM. Our newly improved model better represents the transition between stratification and turnover. This improved lake model has great potential for reliable physical lake process predictions and better ecosystem services.

Mixed convection and stability analysis of stagnation-point boundary layer flow and heat transfer of hybrid nanofluids over a vertical plate

Purpose This study aims to study the mixed convection flow and heat transfer of Al2O3-Cu/water hybrid nanofluid over a vertical plate. Governing equations for conservation of mass, momentum and energy for the hybrid nanofluid over a vertical flat plate are introduced. Design/methodology/approach The similarity transformation approach is used to transform the set of partial differential equations into a set of non-dimensional ordinary differential equations. Finite-deference with collocation method is used to integrate the governing equations for the velocity and temperature profiles. Findings The results show that dual solutions exist for the case of opposing flow over the plate. Linear stability analysis was performed to identify a stable solution. The stability analysis shows that the lower branch of the solution is always unstable, while the upper branch of the solution is always stable. The results of boundary layer analysis are reported for the various volume fractions of composite nanoparticles and mixed convection parameter. The outcomes show that the composition of nanoparticles can notably influence the boundary layer flow and heat transfer profiles. It is also found that the trend of the variation of surface skin friction and heat transfer for each of the dual solution branches can be different. The critical values of the mixed convection parameter, λ, where the dual solution branches joint together, are also under the influence of the composition of hybrid nanoparticles. For instance, assuming a total volume fraction of 5 per cent for the mixture of Al2O3 and Cu nanoparticles, the critical value of mixing parameter of λ changes from −3.1940 to −3.2561 by changing the composition of nanofluids from Al2O3 (5 per cent) + Cu (0%) to Al2O3 (2.5%) + Cu (2.5 per cent). Originality/value The mixed convection stability analysis and heat transfer study of hybrid nanofluids for a stagnation-point boundary layer flow are addressed for the first time. The introduced hybrid nanofluid model and similarity solution are new and of interest in both mathematical and physical points of view.

LBM simulation of piezo fan in square enclosure

PurposeThis paper aims to investigate the use of a piezo fan in an enclosure on wall heat transfer and thermal boundary layer profile in constant wall temperature situation.Design/methodology/approachThe governing partial differential equations of mass, momentum and energy in addition to boundary conditions are solved by lattice Boltzmann method. The problem is solved numerically using D2Q9 population's model and Bhatnagar–Gross–Krook collision model with a code written in MATLAB.FindingsThe effects of Prandtl number (Pr) and the frequency of piezo fan vibrations are critically investigated on the hydrothermal characteristics of the square cavity. The mesh independency study and the validation of the proposed model are accomplished with numerical results of Ghia et al. (1982) and analytical solution of pure conduction very good agreement is found between present results and benchmark findings. Generally, with increasing beam frequency, the heat removal from heat source increased. It is found that, for all Prandtl numbers, wall Nusselt number will increase with the increase of the beam frequency. This enhancement is more intense in higher Prandtl number.Originality/valueBased on these results, the use of piezo fan in an enclosure can be classified as standalone as well as heat sink integrated cooling solution.