REVIEW OF LAMINAR FORCED CONVECTION IN DIFFERENT SHAPE CHANNEL WITH NANOFLUID SUOERPOSED IN POROU MEDIA

Second-law analysis (SLA) is an important concept in thermodynamics, which basically assesses energy by its value in terms of its convertibility from one form to another.[...]

Transport Processes in a Rapidly Changing World.- Modelling of Transport Phenomena in Porous Media.- Fundamentals of Mechanics of Saturated Porous Media: Basic Equations and Waves.- The Stability of Convective Flows in Porous Media.- Free Convection Heat and Mass Transfer in a Porous Medium.- Natural Convection in a Vertical Porous Annulus.- Non-Darcy Natural Convection in Saturated Porous Media.- Mixed Convection in Saturated Porous Media.- Forced Convective Flow and Heat Transfer Through a Porous Medium Exposed to a Flat Plate or a Channel.- Forced Convection Heat Transfer in a Porous Medium.- Radiation Transport in Porous or Fibrous Media.- Fundamentals of Drying of Capillary-Porous Bodies.- Heat Transfer During Unsaturated Flow in Porous Media.- Buoyancy-Induced Flow and Heat Transfer in Saturated Fissured Media.- Effect of Randomness on Heat and Mass Transfer in Porous Media.- Analytical Solutions to Transient Convective Mass Transfer Within Porous Media.- Natural Convection in Porous Media with Variable Porosity and Thermal Dispersion Effects.- Convective Flow Interaction and Heat Transfer Between Fluid and Porous Layers.- Temperature Distribution in a Porous Slab with Random Thermophysical Characteristic.- Forced Convection in Packed Tubes and Channels with Variable Porosity and Thermal Dispersion Effects.- Transient Double Diffusive Convection in a Horizontal Fluid Layer Situated on top of a Porous Substrate.- Drying of Wood Residues in a Fixed Bed.- Heat and Mass Transfer in Adsorbent Beds.- Solidification of a Binary Mixture Saturating a Bed of Glass Spheres.- Melting in the Presence of Natural Convection in a Saturated Porous Medium.- Air-Water Two-Phase Flow Pressure Drop in Large Scale Porous Media.- Boiling and Dryout in Unconsolidated Porous Media.- Heat Transfer from a Surface Covered with Hair.- Measurements of Thermal Conductivity in Porous Media.- Determination of Velocity Vectors in Porous Media with Fluorescent Particle Image Velocimetry (FPIV).- Non Invasive Measurement Techniques in Porous Media.- Flash Method of Measuring Thermal Diffusivity and Conductivity.- Mechanics, Heat and Mass Transfer in Saturated Porous Media. Application to Petroleum Technology.- Drying Complex Porous Materials-Modelling and Experiments.- Some Geophysical Problems Involving Convection in Porous Media.- Porous Surface Boiling and Its Application to Cooling Microelectronic Chips.- Heat and Mass Transfer in Spouted Beds.- Liquid Seeping into Porous Ground.- Future Research Needs in Convective Heat and Mass Transport in Porous Media.

PurposeFluid flow and heat transfer in a dual scale porous media is investigated to determine the interfacial convective heat transfer coefficient, numerically. The studied porous media is a periodic dual scale porous media. It consists of the square rods which are permeable in an aligned arrangement. It is aimed to observe the enhancement of heat transfer through the porous media, which is important for thermal designers, by inserting intra-pores into the square rods. A special attention is given to the roles of size and number of intra-pores on the heat transfer enhancement through the dual scale porous media. The role of intra-pores on the pressure drop of air flow through porous media is also investigated by calculation and comparison of the friction coefficient.Design/methodology/approachTo calculate the interfacial convective heat transfer coefficient, the governing equations which are continuity, momentum and energy equations are solved to determine velocity, pressure and temperature fields. As the dual scale porous structure is periodic, a representative elementary volume is generated, and the governing equations are numerically solved for the selected representative volume. By using the obtained velocity, pressure and temperature fields and using volume average definition, the volume average of aforementioned parameters is calculated and upscaled. Then, the interfacial convective heat transfer coefficient and the friction coefficient is numerically determined. The interparticle porosity is changed between 0.4 and 0.75, while the intraparticle varies between 0.2 and 0.75 to explore the effect of intra-pore on heat transfer enhancement.FindingsThe obtained Nusselt number values are compared with corresponding mono-scale porous media, and it is found that heat transfer through a porous medium can be enhanced threefold (without the increase of pressure drop) by inserting intraparticle pores in flow direction. For the porous media with low values of interparticle porosity (i.e. = 0.4), an optimum intraparticle porosity exists for which the highest heat transfer enhancement can be achieved. This value was found around 0.3 when the interparticle porosity was 0.4.Research limitations/implicationsThe results of the study are interesting, especially from heat transfer enhancement point of view. However, further studies are required. For instance, studies should be performed to analyze the rate of the heat transfer enhancement for different shapes and arrangements of particles and a wider range of porosity. The other important parameter influencing heat transfer enhancement is the direction of pores. In the present study, the intraparticle pores are in flow direction; hence, the enhancement rate of heat transfer for different directions of pores must also be investigated.Practical implicationsThe application of dual scale porous media is widely faced in daily life, nature and industry. The flowing of a fluid through a fiber mat, woven fiber bundles, multifilament textile fibers, oil filters and fractured porous media are some examples for the application of the heat and fluid flow through a dual scale porous media. Heat transfer enhancement.Social implicationsThe enhancement of heat transfer is a significant topic that gained the attention of researchers in recent years. The importance of topic increases day-by-day because of further demands for downsizing of thermal equipment and heat recovery devices. The aim of thermal designers is to enhance heat transfer rate in thermal devices and to reduce their volume (and/or weight in some applications) by using lower mechanical power for cooling.Originality/valueThe present study might be the first study on determination of thermal transport properties of dual scale porous media yielded interesting results such as considerable enhancement of heat transfer by using proper intraparticle channels in a porous medium.

Chapter 10 - Multiphase Fluid and Heat Flow in Porous Media

In order to enhance the heat transfer in a double-pipe counterflow heat exchanger, the use of porous media and nanofluid is analyzed. The effect of complete filling of one or both channels of the heat exchanger with porous metal foams on the heat transfer and pumping power has been studied, considering laminar flow with various Reynolds numbers (Re = 100 to 2000) and porous media (Da = 0.1 to 10−4). As a novelty, in order to select proper porous media with an appropriate Reynolds number in each channel, this study focused on the coupling of Re asymmetry and porous medium properties used in the inner and outer channels of the heat exchanger. Flow through porous media is simulated by the non-Darcy law and two-phase mixture model used for the nanofluid flow. Results are presented and investigated in terms of the effectiveness (e-NTU method) and the performance evaluation criterion (PEC). It is shown that the effectiveness could only depict the thermal performance, while the PEC reflects the influences of the porous media on both the pumping power and the heat transfer. Use of porous media in both channels (case D) has led to the highest effectiveness (between 0.6 and 1). In addition, PEC study reveals that the optimal Re values exist for flow in each one of the channels and that case D has the highest PEC (more than 4). To maximize the PEC, for the cases with only one porous channel (B and C), the channel which does not include porous media should have the highest Re, while a low or moderate Re should be selected for the porous channel. However, for case D, Rei should have its highest value, while Reo has an optimal value in the range of 500 to 1000.

Pore-scale analysis of two-phase nanofluid flow and heat transfer in open-cell metal foams considering Brownian motion

In this paper, a combination of Monte Carlo ray tracing (MCRT) and finite volume method (FVM) was utilized to numerically investigate the application of CuO/water nanofluid and porous media (as volumetric absorber agents) in a direct absorption parabolic trough solar collector (DAPTC). The main purpose of this study is the numerical evaluation of the effect of the nanofluid and porous media (separately and simultaneously) to compare their influences on the efficiency of DAPTCs using Ansys Fluent software. The effects of volume fraction, porosity, pore diameter, input temperature, and flow rate on the collector thermal performance are also examined. The results indicated 40.5% and 49.9% improvement in the thermal efficiency of the collector due to the use of nanofluid and porous media, respectively. Thermal efficiency showed a reduction with increasing the inlet temperature as well as decreasing the flow rate. Applying the porous media can reduce the temperature concentration near the absorber tube wall, which will decrement the heat loss. However, using full porous media as a volumetric absorber leads to a great pressure drop. Results showed that the use of porous media enhanced the friction factor of pure water without metal foam 1500-1750 times. Therefore, nanofluids and partially filled porous media can be simultaneously used for their synergistic benefits. The combination of direct absorbers can increment the thermal efficiency up to 69.5%. The numerical simulation is validated with available experimental data.

Heat flow modelling: a generalized two-dimensional diffusive and convective numerical model for the Exmouth Plateau, offshore Northwest Australia

Thermal performance of microchannel heat sink integrated with porous medium, slip coefficient and phase change material and machine learning approach

Viscous dissipative forced convection in thermal non-equilibrium nanofluid-saturated porous media embedded in microchannels

The present lecture summarizes some of the most recent joint research results from the cooperation between the Federal University of Rio de Janeiro, Brasil, and the University of Miami, USA, on the transient analysis of both fluid flow and heat transfer within microchannels. This collaborative link is a natural extension of a long term cooperation between the two groups, in the context of fundamental work on transient forced convection, aimed at the development of hybrid numerical-analytical techniques and the experimental validation of proposed models and methodologies [19]. The motivation of this new phase of the cooperation was thus to extend the previously developed hybrid tools to handle both transient flow and transient convection problems in microchannels within the slip flow regime. The analysis of internal flows in the slip-flow regime recently gained an important role in association with the fluid mechanics of various microelectromechanical systems (MEMS) applications, as well as in the thermal control of microelectronics, as reviewed in different sources [10-16]. For steady-state incompressible fully developed flow situations and laminar regime within simple geometries such as circular microtubes and parallel-plate microchannels, explicit expressions for the velocity field in terms of the Knudsen number are readily obtainable, and have been widely employed in the heat transfer analysis of microsystems, such as in [17-23]. Only quite recently, attention has been directed to the analysis of transient flow in microchannels [24-33]. Unsteady one-dimensional models have been extended from classical works, and analytical solutions have been sought for fully developed flows in simple geometries. These recent works are also concerned with situations in which a simple and well-defined functional form for the pressure gradient time variation is prescribed or for the time dependence of the wall imposed velocity, in the case of a Couette flow application. Research findings are yet to be further pursued in the analytical and robust solution of more generalized models, which will accommodate more general conditions and parameter specifications, and thus offer a wider validation range for the automatic general purpose numerical codes. Mikhailov and Ozisik [34] presented a unified solution for transient one-dimensional laminar flow models, with the usual no-slip boundary condition, based on the classical integral transform method. Their solution was then specialized to two situations: step change and periodically varying pressure gradient. The knowledge in regular size channels is therefore fairly well consolidated for models that use simple functional forms for the pressure gradient variation such as for the two cases cited above. One of the objectives of this paper is to illustrate the solution of a onedimensional mathematical model for transient laminar incompressible flow in microchannels such as circular tubes and parallel-plate channels, that accounts for a source term time variation in any functional form, including electrokinetic effects for liquid flows, by making use of the Generalized Integral Transform Technique (GITT) [35-40], and thus yielding analytical expressions for the time and space dependence of the velocity fields in the fully developed region. We then demonstrate this hybrid numerical-analytical solution for transient internal slip flow, obtained employing mixed symbolic-numerical computations with the Mathematica platform [41]. The goal here is to improve and complement existing analytical solution implementations to study laminar fully developed flows in micro-ducts subjected to arbitrary source term disturbances in space and time. On the other hand, the heat transfer literature of the last decade has demonstrated a vivid and growing interest in thermal analysis of flows in micro-channels, both through experimental and analytical approaches, in connection with cooling techniques of micro-electronics and with the development of micro-electromechanical sensors and actuators (MEMS), as also pointed out in recent reviews [12-16]. Since the available analytical information on heat transfer in ducts could not be directly extended to flows within microchannels with wall slip, a number of contributions have been recently directed towards the analysis of internal forced convection in the micro-scale. In the paper by Barron et al.

Conduction-combined forced and natural convection in lid-driven enclosures divided by a vertical solid partition

Through-air drying is commonly used in the drying of high-quality tissue and towel products. A representative elementary volume method was used to model the fluid flow and heat and mass transfer during through drying in heterogeneous porous biobased materials such as tissue and towel products. Results of flow both upstream and downstream of a modeled porous sheet allowed visualization of the effects of mixing at the top and bottom of the porous medium. The effect of initial nonuniformity on fluid flow and convective heat and mass transfer in heterogeneous porous media was studied. The effect of material nonhomogeneity and associated transport properties on moisture content of the porous material as a function of drying time was studied. Modeling results indicate that for the first time it is possible to simulate the effect of nonuniformity on fluid flow and convective heat and mass transfer in porous media during through-air drying of paper. Moisture and structural nonuniformity contributing to nonuniformity in air flow might contribute significantly to drying nonuniformity. Depending on the moisture regimes and degree of saturation of the convective medium, heat and mass transfer coefficients may have varying effects on the overall drying.

In a previous paper (Cope 1937)† an account was given of the simultaneous measurement of the heat transmission and friction coefficients of a series of smooth pipes of various shapes of cross-section. The results formed the first section of a comprehensive research into the problem of heat transmission. The present paper, which describes the results of tests on rough pipes, forms the second section. Three pipes were tested, their internal surfaces being artificially roughened by a special knurling process which produced a series of pyramids geometrically similar in form but varying in absolute size from pipe to pipe. The roughness ratios (radius of pipe/height of pyramid) were approximately 8/1, 15/1, and 45/1. The apparatus used was basically the same as that used in the previous tests; the working fluid was water, and the Reynolds number ranged from 2,000 to 60,000. The results indicate that when fully turbulent conditions are established the roughness has very little effect on the heat transmission coefficient, but that in the transition region between laminar and fully turbulent flow, the roughness may increase that coefficient to considerably more than its value for a smooth pipe; and that the heat transmission graphs for the three pipes are in better agreement if shearing force velocity is used instead of mean velocity, in forming the non-dimensional parameters used for plotting purposes. The broad conclusions from the practising engineer's standpoint are (1) for a given pressure drop across a heat transmission apparatus more heat will be transmitted if the pipes be smooth than if they be rough; (2) the velocity of the working fluid will, of course, be greater with smooth pipes; and (3) the smooth pipe is more efficient if the comparison is made on a basis of heat transmission for equal power.

Forced convection of nanofluids in metal foam: An essential review