Optical techniques for fluid flow and heat transfer

The present research aims to improve the convective thermal transport rate of a hybrid nanofluid within an inverted T‐shaped porous enclosure using strategically placed cold circular cylinders. Different locations of circular cylinders in the physical domain are distinguished with nomenclatures as Cases C0‐C4. The mathematical model, based on the Darcy–Brinkman–Forchheimer equation, is numerically simulated through the penalty finite element method. Fluid flow and heat transfer characteristics are depicted graphically, showcasing streamlines, isotherms, mean Nusselt number (), and heat transfer enhancement percentage (En%) across varied thermo‐physical parameters, including Rayleigh number (), Darcy number (), and porosity values (). Notably, the presence of two circular cylinders at the bottom flow zones (Case C4) demonstrates superior heat transfer compared to other spatial cylinder arrangements with increasing . Furthermore, augmenting flow parameters () in the case C4 model intensifies convective heat and fluid flow phenomena. A comparative analysis of thermal transport activity between Case C4 and the simple physical domain (Case C0) reveals maximum thermal enhancement of 166%, 167%, and 36% across varying , , and values. This comprehensive analysis suggests that two circular cylinders (Case C4) at the bottom flow section of the porous enclosure provide an effective strategy for enhancing convective fluid and thermal transport phenomena in an inverted T‐shaped porous enclosure. Moreover, this research significantly contributes in optimizing the thermal transport engineering of T‐shaped applications like solar collectors, exchangers, and heat storage.

Numerical simulations were conducted to study the fluid flow and heat transfer through a partially filled square enclosure with a horizontal porous layer at the bottom. The vertical walls of the enclosure were subjected to uniform heating and cooling at specified temperatures TH and TC, respectively. The problem formulation was based on the Darcy–Brinkman model, which took into account density variation using the Mach number law approximation and incorporated variable properties. Based on the developed code, a parametric study of fluid flow and heat transfer inside the cavity was carried out to examine the effects of temperature difference, medium permeability, and Darcy number. Additionally, the variation of the Nusselt number on the hot and cold walls was provided to demonstrate the overall nature of heat transfer within the enclosure. The results of this study highlight that fluid flow and heat transfer are influenced by the temperature difference between the vertical walls and the characteristic parameters of the porous layer.

This paper reports on the results of a numerical study of convection flow and heat transfer in a rectangular porous cavity filled with a phase change material under steady state conditions. The two vertical walls of the cavity are subject respectively to temperatures below and above the melting point of the PCM while adiabatic conditions are imposed on the horizontal walls. The porous medium is characterized by an anisotropic permeability tensor with the principal axes arbitrarily oriented with respect to the gravity vector. The problem is governed by the aspect ratioA, the Rayleigh numberRa, the anisotropy ratioR and the orientation angle θ of the permeability tensor. Attention is focused on these two latter parameters in order to investigate the effects of the anisotropic permeability on the fluid flow and heat transfer of the liquid/solid phase change process. The method of solution is based on the control volume approach in conjunction with the Landau-transformation to map the irregular flow domain into a rectangular one. The results are obtained for the flow field, temperature distribution, interface position and heat transfer rate forA=2.5,Ra=40, 0≤θ≤π, 0.25≤R≤4.

Microchannels are of current interest for use in heat exchangers where very high heat transfer performance is desired. Microchannels provide very high heat transfer coefficients because of their small hydraulic diameters. In this study, an investigation of fluid flow and heat transfer in microchannels is conducted. A review of the literature published regarding fluid flow and heat transfer in microchannels is provided in this study. A thorough background on the theory of internal convective heat transfer is provided as well. A critical analysis of some of the published heat transfer experiments on microchannels is also given. It was found that some of the experimental methods published recently employ experimental and data reduction techniques which may result in errors for reported Nusselt numbers. A brief computational fluid dynamics (CFD) investigation into the heat transfer and fluid flow performance of some channels with designed bumps is also presented. It was found that designed channels offer enhanced Nusselt numbers in the turbulent regime at the cost of a higher friction factor when compared to a plain channel. Fluid flow and heat transfer experiments were conducted on a copper microchannel heat exchanger (MHE). An experimental method of imposing a constant surface temperature to the MHE was used. A description of the experimental apparatus and procedure is provided. The friction factor results from the experiments agree fairly well with theoretical correlations. The experimental Nusselt number results agree with theory very well in the transition/turbulent regime, but the results show a higher Nusselt number in the laminar regime than predicted by theoretical correlations. A full description of the data reduction and analysis of the experimental data is given. A CFD model was created to simulate the fluid in the inlet plenum and the microchannels. The results from these simulations are presented, and they show good agreement with the experimental data in the transition/turbulent regime as well as with theoretical correlations for laminar and turbulent flow.

The significant research has seen with nano fluid flow and heat transfer. But still there is a wide scope of research in mass transfer with nano fluids due to Brownian motion of particles. A theoretical investigation has attempted in this paper to study the chemical reaction effects during mass transfer. We have studied convective heat and mass transfer of MHD nano fluid flow past inclined, oscillating permeable flat plate with radiation and Abstract: The significant research has seen with nano fluid flow and heat transfer. But still there is a wide scope of research in mass transfer with nano fluids due to Brownian motion of particles. A theoretical investigation has attempted in this paper to study the chemical reaction effects during mass transfer. We have studied convective heat and mass transfer of MHD nano fluid flow past inclined, oscillating permeable flat plate with radiation and Abstract: The significant research has seen with nano fluid flow and heat transfer. But still there is a wide scope of research in mass transfer with nano fluids due to Brownian motion of particles. A theoretical investigation has attempted in this paper to study the chemical reaction effects during mass transfer. We have studied convective heat and mass transfer of MHD nano fluid flow past inclined, oscillating permeable flat plate with radiation and

Purpose The purpose of this paper is to develop a combined method for three-dimensional incompressible flow and heat transfer by the spectral collocation method (SCM) and the artificial compressibility method (ACM), and further to study the performance of the combined method SCM-ACM for three-dimensional incompressible flow and heat transfer. Design/methodology/approach The partial differentials in space are discretized by the SCM with Chebyshev polynomial and Chebyshev–Gauss–Lobbatto collocation points. The unsteady artificial compressibility equations are solved to obtain the steady results by the ACM. Three-dimensional exact solutions with trigonometric function form and exponential function form are constructed to test the accuracy of the combined method. Findings The SCM-ACM is developed successfully for three-dimensional incompressible flow and heat transfer with high accuracy that the minimum value of variance can reach. The accuracy increases exponentially along with time marching steps. The accuracy is also improved exponentially with the increasing of nodes before stable accuracy is achieved, while it keeps stably with the increasing of the time step. The central processing unit time increases exponentially with the increasing of nodes and decreasing of the time step. Research limitations/implications It is difficult for the implementation of the implicit scheme by the developed SCM-ACM. The SCM-ACM can be used for solving unsteady impressible fluid flow and heat transfer. Practical implications The SCM-ACM is applied for two classic cases of lid-driven cavity flow and natural convection in cubic cavities. The present results show good agreement with the published results with much fewer nodes. Originality/value The combined method SCM-ACM is developed, firstly, for solving three-dimensional incompressible fluid flow and heat transfer by the SCM and ACM. The performance of SCM-ACM is investigated. This combined method provides a new choice for solving three-dimensional fluid flow and heat transfer with high accuracy.

Fluid flow and heat transfer in a nanochannel may depart from the traditional behavior due to the scale effect, and the velocity slip and temperature jump at the fluid-solid interface must be taken into account. A lot of papers about fluid flows in nanochannels with the same wettability at two surfaces have been published. It is necessary to investigate fluid flow and heat transfer in nanochannels with the asymmetric wettability by the molecular dynamics method. The fluid velocity and temperature distributions, interfacial velocity slip and temperature jump in a rough nanochannel are evaluated. The effects of asymmetric wettability on the velocity slip, temperature jump and internal fluid heat transfer are analyzed. The results indicate that the velocity of the fluid flow under an external force in a nanochannel in a bulk region is of a parabolic distribution, but the parabolic distribution is not centrosymmetric because of the centrosymmetric density profile. The difference in density distribution can affect the fluid flow. Viscous dissipation due to shear flow will increase the fluid temperature. The range that is affected by the interaction between solid and liquid is small. So the wettability of the cold wall hardly affects the velocity of the fluid near the hot wall, and the slip velocity is almost constant. At this time, the negative slip will take place at the fluid-solid interface near the hot wall. But the velocity of the fluid near the cold wall comes up with the increasing hydrophobicity of the cold wall, and the slip velocity increases. The temperature jump on both sides of interface increases with the increasing hydrophobicity of the cold wall, but the degree of temperature jump at a liquid-cold solid interface is higher than that at a liquid-hot solid interface. Then the fluid temperature near the cold wall gradually exceeds the fluid temperature near the hot wall. The internal heat flow of the fluid will be reversed. The inverted temperature profile of the fluid will appear. The inverted temperature profile becomes more obvious when the degree of asymmetric wettability increases.

The process of rotational moulding consists in manufacturing plastic parts by heating a polymer powder in a biaxial rotating mould. In order to optimise the production cycle of this process, a complete simulation model has to be used. This model should describe the phenomena of heat and mass transfer in a moving granular media with phase change, coalescence, sintering, air evacuation and crystallization during the cooling stage. This paper focus on the study of heat and mass transfer in a quiescent polymer powder during the heating stage. An experimental device has been built. It consists in an open plane static mold on which an initial thickness, e, of a polymer powder is deposited. This powder is then heated until it melts. An inverse heat conduction method is used to determine the heat flux and temperature at the interface between the mold and the powder. This interfacial heat flux is taken as a boundary condition in a numerical heat transfer model witch takes into account the heat transfer in granular media with phase change, coalescence, sintering, air bubbles evacuation and rheological behaviour of the polymer. For the numerical simulation of the heat transfer, the apparent specific heat method is used. This approach allows to solve the same energy equation for all the material phases, so one do not have to calculate the melting front evolution. This fine modelling, close to the real physical phenomena makes it possible to estimate the temperature profile and the evolution of the polymer powder characteristics (phase change, air diffusion, viscosity, evolution of the thermophysical properties of the equivalent homogeneous medium, thickness reduction, air volume fraction...). Several results are then presented, and the influence of different parameters, like the thermal contact resistance, the process initial conditions and the polymer’s rheological characteristics are studied and commented. Indeed the predictions of the temperature rises in the polymer bed, agree well with the experimental measurements.

This article presents flow, heat and mass transfer phenomena in Bingham plastic fluid. The flow channel is considered to be a rotating disk with a slip which is different in span and streamwise directions, and heat transfer is investigated using dissipation term of the fluid. Arrhenius activation energy and binary chemical reaction are the imperative features of the study of mass transfer. Bingham plastic fluid and anisotropic slip are the key factors of the study due to their numerous applications in manufacturing industries. On the other hand, the radiative heat transfer phenomenon is considered which is widely used in nuclear and power generating systems. The partial differential equations that govern the flow, and heat and mass transfer are converted into ordinary differential equations by utilizing von Kármán's similarity transformation for rotating disk flows. The velocity, temperature, and concentration profiles and some important physical quantities are examined against important flow parameters. It is observed that the thermal radiation showed an increasing effect on temperature profile and the activation energy enhanced the mass transfer rate. The radial slip increased the volumetric flow rate and reduced the boundary layer thickness. The tangential slip reduced the volumetric flow rate and increased the boundary layer thickness.

The study of stagnation point flow and heat transfer over a stretching/shrinking sheet in a hybrid nanofluid has numerous possible applications such as microelectronics cooling design and, heat transfer in atmospheric re-entry. This study needs to solve the governing mathematical model (partial differential equations) to explore the properties of fluid flow and heat transfer. The model is converted into a system of ordinary differential equations by using similarity variables. In order to solve these nonlinear ordinary differential equations, the study uses numerical collocation method of Haar wavelets. By employing this method, the study can forecast several significant fluid flow and heat transfer characteristics, such as the local Nusselt number, skin friction coefficient, and temperature and velocity profiles. The numerical results show that dual solutions can appear for certain values of the shrinking parameter. It is also noted that the slip parameter, suction/injection parameter, and nonlinear parameter contribute to widening the range of possible solutions to allow for more variations in the fluid behaviour under different conditions.

Pipe cable is considered as an important form for underground transmission line. The maximum electrical current (ampacity) of power cable system mostly depends on the cable conductor temperature. Therefore, accurate calculation of temperature distribution in the power cable system is quite important to extract the cable ampacity. In the present paper, the fluid flow and heat transfer characteristics in the pipe cable with alternating current were numerically studied by using commercial code COMSOL MULTIPHYSICS based on finite element method (FEM). The cable core loss and eddy current loss in the cable were coupled for the heat transfer simulation, and the difference of heat transfer performances with pure natural convection model and radiation-convection model was compared and analysed in detail. Meanwhile, for the radiation-convection model, the effects caused by radiant emissivity of cable surface and pipe inner surface, as well as the cable location in the pipe, were also discussed. Firstly, it is revealed that the radiation and natural convection heat flux on the cable surface would be of the same order of magnitude, and the radiation heat transfer on the cable surface should not be ignored. Otherwise, the cable ampacity would be underestimated. Secondly, it is found that the overall heat transfer rate on the cable surface increases as the cable surface emissivity increases, and this is more remarkable to the upper cable. While the effect caused by the radiant emissivity on the pipe inner surface would be relatively small. Furthermore, it is demonstrated that, as cable location in the pipe falls, the natural convection heat transfer would be enhanced. These results would be meaningful for the ampacity prediction and optimum design for the pipe cable.

Investigation of the effect of lattice structure on the fluid flow and heat transfer of supercritical CO2 in tubes

Synthetic MAP Tomographic Reconstruction of Turbulent Flow FieldsDavid W. WattUniversity of New Hampshire, Department of Mechanical EngineeringKingsbury Hall, Durham, New Hampshire 03824ABSTRACTTomographic reconstruction from both interferometric and absorption data is a potentially powerful tool forexperimental observations of compressible fluid mechanics, combustion, and heat transfer. In many of these cases,both flow field images and ensemble statistics are desired. The use of an ensemble of noisy tomographic data setsto synthesize image statistics and stabilize individual reconstructions using a Maximum A Posterior! (MAP)reconstruction technique is presented. The MAP technique uses the ensemble mean and variances of the sourcefunction to constrain individual reconstructions of the ensemble. In this paper, we show that by synthesizing themean and variances using preliminary algebraic reconstructions, the reconstruction of the individual realizations canbe improved. The technique is demonstrated using a group of source images generated with a fractal sum of pulses(FSP) technique. The images have similar statistical properties and appearances to the flow field images producedin turbulent jets. The paper discusses a fractal model for turblent mixing field images, the selection of thepreliminary reconstruction technique, and the results of MAP and synthetic MAP reconstructions.1 . INTRODUCTION: INTERFEROMETRIC AND ABSORPTION TOMOGRAPHY FOR FLOW VISUALIZATIONOptical tomography or projection imaging is a family of techniques for obtaining multidimensional scalarmeasurements from a group of projection integrals. The projections are obtained using probe beams passingthrough the field of interest, which causes either an optical phase delay due to the inhomogeneous refractive indexor an attenuation of the beam due to absorption. In either, case the magnitude of the signal is proportional to a lineintegral of the concentration of some scalar quantity such as density or concentration of an absorbing species. Ifthese projections are obtained from a range of viewing angles (see Figure 1 ), the integrals may be inverted to obtainan image of the original scalar distribution, using a procedure known as tomographic reconstruction.The appeal of tomography in experimental fluid mechanics, heat transfer and combustion is that spatially-resolved measurements of density (and by extension pressure or temperature) or concentration can be obtainednon-intrusively. Its advantages in some applications relative to planar imaging techniques are that it can providethree-dimensional scalar measurements and that it is superior for obtaining information normal to the flow direction.The cost of these advantages is a much more complex optical and image acquisition system that requires anadditional computational reconstruction step. Furthermore, the computational reconstruction method, the complexityof field being imaged, and the imaging geometry all affect the accuracy of the measurements. It is common toattempt to enhance the accuracy of tomographic reconstructions by the use of prior information.In the current work, the application of prior information is discussed in the context of an algebraic representationof the projection and reconstruction operations. In this context, the scalar field is represented by a discrete sum oforthogonal basis functions whose amplitudes are denoted by the vector f. The projection measurements aredenoted by the discrete vector R which is related to f using

PurposeStudying the effect of localized wall discharge on the fluid flow and heat transfer for a flow over backward facing step is the main purpose of this paper. Jet is used to control the reattachment length which controls the fluid flow and heat transfer downstream the step. Several parameters are to be investigated: geometric; expansion ratio, location of the jet, and jet angle flow; Reynolds number, jet velocity.Design/methodology/approachNumerical simulation using both the standard K−ε and renormalized group turbulence theory (RNG) K−ε models are used to model flow in the computational domain. The energy equation is also used to model the heat transfer characteristics of the flow. The model equations are solved numerically using a finite volume code.FindingsIt is found that the presence of the wall jet at a proper location can significantly influence the flow and heat characteristics of the problem. Furthermore, varying the ratio of the jet velocity to the main stream velocity could play an important role in controlling the size of the circulating bubble and, therefore, the fluid and heat transfer characteristics of the flow, whereas, the expansion ratio has less influence. It is also found that increasing Reynolds number increases the value of maximum heat transfer but has less influence on either its location or the reattachment length.Research limitations/implicationsThe range of the Reynolds number considered in this research covers only the turbulent regime. The research does not cover laminar flows. The results and conclusions cover only three values of expansion ratios. Namely (expansion ratio (ER)=1.67, 1.8 and 2). Conclusions should not be read beyond these values of ER.Practical implicationsThis work gives designers of similar flows a new method of controlling the fluid flow and heat transfer by varying jet angle.Originality/valueThis work has not been done before and it can initiate additional research projects as investigating the effect of applying wall jets in combustors.

Chapter 3 - Heat and Mass Transfer, Basic Principles