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Showing papers on "Heat transfer published in 2004"


Journal ArticleDOI
TL;DR: In this paper, a review of the phase change materials (PCM) and their application in energy storage is presented, where the main advantages of encapsulation are providing large heat transfer area, reduction of the PCMs reactivity towards the outside environment and controlling the changes in volume of the storage materials as phase change occurs.

2,636 citations


Book
01 Oct 2004
TL;DR: In this paper, the authors define heat transfer and its applications: heat transfer by conduction principles of heat flow in fluids, heat transfer to fluids without phase change heat transfer in fluids with heat change radiation heat transfer heat-exchange equipment evaporation.
Abstract: Part 1 Introduction: definitions and principles. Part 2 Fluid mechanics: fluid statics and its applications fluid flow phenomena basic equations of fluid flow flow of incompressible fluids in conduits and thin layers flow of compressible fluids flow past immersed bodies transportation and metering of fluids agitation and mixing of liquids. Part 3 Heat transfer and its applications: heat transfer by conduction principles of heat flow in fluids heat transfer to fluids without phase change heat transfer to fluids with heat change radiation heat transfer heat-exchange equipment evaporation. Part 4 Mass transfer and its applications: equilibrium stage operations distillation introduction to multicomponent distillation leaching and extraction principles of diffusion and mass transfer between phases gas absorption humidification operations drying of solids adsorption membrane separation processes crystallization. Part 5 Operations involving particulate solids properties, handling and mixing of particulate solids size reduction mechanical separations.

2,424 citations


Journal ArticleDOI
TL;DR: In this article, an experimental work on the convective heat transfer of nanofluids, made of γ-Al2O3 nanoparticles and de-ionized water, flowing through a copper tube in the laminar flow regime was conducted.

1,545 citations


Journal ArticleDOI
TL;DR: In this article, the iterative algorithm of Feldman for heat flow in layered structures is solved in cylindrical coordinates for surface heating and temperature measurement by Gaussian-shaped laser beams.
Abstract: The iterative algorithm of Feldman for heat flow in layered structures is solved in cylindrical coordinates for surface heating and temperature measurement by Gaussian-shaped laser beams. This solution for the frequency-domain temperature response is then used to model the lock-in amplifier signals acquired in time-domain thermoreflectance measurements of thermal properties.

1,264 citations


Journal ArticleDOI
TL;DR: Theoretical studies of the possible heat transfer mechanisms have been initiated, but to date obtaining an atomic and microscale-level understanding of how heat is transferred in nanofluids remains the greatest challenge that must be overcome in order to realize the full potential of this new class of heat transfer as mentioned in this paper.
Abstract: ▪ Abstract Nanofluids, consisting of nanometer-sized solid particles and fibers dispersed in liquids, have recently been demonstrated to have great potential for improving the heat transfer properties of liquids. Several characteristic behaviors of nanofluids have been identified, including the possibility of obtaining large increases in thermal conductivity compared with liquids without nanoparticles, strong temperature-dependent effects, and significant increases in critical heat flux. Observed behavior is in many cases anomalous with respect to the predictions of existing macroscopic theories, indicating the need for a new theory that properly accounts for the unique features of nanofluids. Theoretical studies of the possible heat transfer mechanisms have been initiated, but to date obtaining an atomic- and microscale-level understanding of how heat is transferred in nanofluids remains the greatest challenge that must be overcome in order to realize the full potential of this new class of heat transfer...

731 citations


Book
28 May 2004
TL;DR: In this paper, the authors proposed a method for heat transfer in a composite slab with the Galerkin method and the Finite Element Method (FEM) to solve the heat transfer problem.
Abstract: Preface. 1 Introduction. 1.1 Importance of Heat Transfer. 1.2 Heat Transfer Modes. 1.3 The Laws of Heat Transfer. 1.4 Formulation of Heat Transfer Problems. 1.4.1 Heat transfer from a plate exposed to solar heat flux. 1.4.2 Incandescent lamp. 1.4.3 Systems with a relative motion and internal heat generation. 1.5 Heat Conduction Equation. 1.6 Boundary and Initial Conditions. 1.7 Solution Methodology. 1.8 Summary. 1.9 Exercise. Bibliography. 2 Some Basic Discrete Systems. 2.1 Introduction. 2.2 Steady State Problems. 2.2.1 Heat flow in a composite slab. 2.2.2 Fluid flow network. 2.2.3 Heat transfer in heat sinks (combined conduction-convection). 2.2.4 Analysis of a heat exchanger. 2.3 Transient Heat Transfer Problem (Propagation Problem). 2.4 Summary. 2.5 Exercise. Bibliography. 3 The Finite Elemen t Method. 3.1 Introduction. 3.2 Elements and Shape Functions. 3.2.1 One-dimensional linear element. 3.2.2 One-dimensional quadratic element. 3.2.3 Two-dimensional linear triangular elements. 3.2.4 Area coordinates. 3.2.5 Quadratic triangular elements. 3.2.6 Two-dimensional quadrilateral elements. 3.2.7 Isoparametric elements. 3.2.8 Three-dimensional elements. 3.3 Formulation (Element Characteristics). 3.3.1 Ritz method (Heat balance integral method-Goodman's method). 3.3.2 Rayleigh-Ritz method (Variational method). 3.3.3 The method of weighted residuals. 3.3.4 Galerkin finite element method. 3.4 Formulation for the Heat Conduction Equation. 3.4.1 Variational approach. 3.4.2 The Galerkin method. 3.5 Requirements for Interpolation Functions. 3.6 Summary. 3.7 Exercise. Bibliography. 4 Steady State Heat Conduction in One Dimension. 4.1 Introduction. 4.2 Plane Walls. 4.2.1 Homogeneous wall. 4.2.2 Composite wall. 4.2.3 Finite element discretization. 4.2.4 Wall with varying cross-sectional area. 4.2.5 Plane wall with a heat source: solution by linear elements. 4.2.6 Plane wall with a heat source: solution by quadratic elements. 4.2.7 Plane wall with a heat source: solution by modified quadratic equations (static condensation). 4.3 Radial Heat Flow in a Cylinder. 4.3.1 Cylinder with heat source. 4.4 Conduction-Convection Systems. 4.5 Summary. 4.6 Exercise. Bibliography. 5 Steady State Heat Conduction in Multi-dimensions. 5.1 Introduction. 5.2 Two-dimensional Plane Problems. 5.2.1 Triangular elements. 5.3 Rectangular Elements. 5.4 Plate with Variable Thickness. 5.5 Three-dimensional Problems. 5.6 Axisymmetric Problems. 5.6.1 Galerkin's method for linear triangular axisymmetric elements. 5.7 Summary. 5.8 Exercise. Bibliography. 6 Transient Heat Conduction Analysis. 6.1 Introduction. 6.2 Lumped Heat Capacity System. 6.3 Numerical Solution. 6.3.1 Transient governing equations and boundary and initial conditions. 6.3.2 The Galerkin method. 6.4 One-dimensional Transient State Problem. 6.4.1 Time discretization using the Finite Difference Method (FDM). 6.4.2 Time discretization using the Finite Element Method (FEM). 6.5 Stability. 6.6 Multi-dimensional Transient Heat Conduction. 6.7 Phase Change Problems-Solidification and Melting. 6.7.1 The governing equations. 6.7.2 Enthalpy formulation. 6.8 Inverse Heat Conduction Problems. 6.8.1 One-dimensional heat conduction. 6.9 Summary. 6.10 Exercise. Bibliography. 7 Convection Heat Transfer 173 7.1 Introduction. 7.1.1 Types of fluid-motion-assisted heat transport. 7.2 Navier-Stokes Equations. 7.2.1 Conservation of mass or continuity equation. 7.2.2 Conservation of momentum. 7.2.3 Energy equation. 7.3 Non-dimensional Form of the Governing Equations. 7.3.1 Forced convection. 7.3.2 Natural convection (Buoyancy-driven convection). 7.3.3 Mixed convection. 7.4 The Transient Convection-diffusion Problem. 7.4.1 Finite element solution to convection-diffusion equation. 7.4.2 Extension to multi-dimensions. 7.5 Stability Conditions. 7.6 Characteristic-based Split (CBS) Scheme. 7.6.1 Spatial discretization. 7.6.2 Time-step calculation. 7.6.3 Boundary and initial conditions. 7.6.4 Steady and transient solution methods. 7.7 Artificial Compressibility Scheme. 7.8 Nusselt Number, Drag and Stream Function. 7.8.1 Nusselt number. 7.8.2 Drag calculation. 7.8.3 Stream function. 7.9 Mesh Convergence. 7.10 Laminar Isothermal Flow. 7.10.1 Geometry, boundary and initial conditions. 7.10.2 Solution. 7.11 Laminar Non-isothermal Flow. 7.11.1 Forced convection heat transfer. 7.11.2 Buoyancy-driven convection heat transfer. 7.11.3 Mixed convection heat transfer. 7.12 Introduction to Turbulent Flow. 7.12.1 Solution procedure and result. 7.13 Extension to Axisymmetric Problems. 7.14 Summary. 7.15 Exercise. Bibliography. 8 Convection in Porous Media. 8.1 Introduction. 8.2 Generalized Porous Medium Flow Approach. 8.2.1 Non-dimensional scales. 8.2.2 Limiting cases. 8.3 Discretization Procedure. 8.3.1 Temporal discretization. 8.3.2 Spatial discretization. 8.3.3 Semi- and quasi-implicit forms. 8.4 Non-isothermal Flows. 8.5 Forced Convection. 8.6 Natural Convection. 8.6.1 Constant porosity medium. 8.7 Summary. 8.8 Exercise. Bibliography. 9 Some Examples of Fluid Flow and Heat Transfer Problems. 9.1 Introduction. 9.2 Isothermal Flow Problems. 9.2.1 Steady state problems. 9.2.2 Transient flow. 9.3 Non-isothermal Benchmark Flow Problem. 9.3.1 Backward-facing step. 9.4 Thermal Conduction in an Electronic Package. 9.5 Forced Convection Heat Transfer From Heat Sources. 9.6 Summary. 9.7 Exercise. Bibliography. 10 Implementation of Computer Code. 10.1 Introduction. 10.2 Preprocessing. 10.2.1 Mesh generation. 10.2.2 Linear triangular element data. 10.2.3 Element size calculation. 10.2.4 Shape functions and their derivatives. 10.2.5 Boundary normal calculation. 10.2.6 Mass matrix and mass lumping. 10.2.7 Implicit pressure or heat conduction matrix. 10.3 Main Unit. 10.3.1 Time-step calculation. 10.3.2 Element loop and assembly. 10.3.3 Updating solution. 10.3.4 Boundary conditions. 10.3.5 Monitoring steady state. 10.4 Postprocessing. 10.4.1 Interpolation of data. 10.5 Summary. Bibliography. A Green's Lemma. B Integration Formulae. B.1 Linear Triangles. B.2 Linear Tetrahedron. C Finite Element Assembly Procedure. D Simplified Form of the Navier-Stokes Equations. Index.

653 citations


Journal ArticleDOI
TL;DR: In this article, a bibliographical review on the convective heat transfer through microchannels is presented, highlighting the main results obtained on the friction factor, on the laminar-to-turbulent transition and on the Nusselt number in channels having a hydraulic diameter less than 1 mm.

647 citations


13 Jun 2004
TL;DR: In this paper, the authors compared the performance of nano-fluids with pure water on a smooth horizontal flat surface (roughness of a few tens nano-meters) and showed that nano-particles have poor heat transfer performance compared to pure water.
Abstract: Abstract Boiling heat transfer characteristics of nano-fluids with nano-particles suspended in water are studied using different volume concentrations of alumina nano-particles. Pool boiling heat transfer coefficients and phenomena of nano-fluids are compared with those of pure water, which are acquired on a smooth horizontal flat surface (roughness of a few tens nano-meters). The experimental results show that these nano-fluids have poor heat transfer performance compared to pure water in natural convection and nucleate boiling. On the other hand, CHF has been enhanced in not only horizontal but also vertical pool boiling. This is related to a change of surface characteristics by the deposition of nano-particles. In addition, comparisons between the heat transfer data and the Rhosenow correlation show that the correlation can potentially predict the performance with an appropriate modified liquid-surface combination factor and changed physical properties of the base liquid.

644 citations


Journal ArticleDOI
TL;DR: In this article, a three-zone flow boiling model was proposed to describe evaporation of elongated bubbles in microchannels, and a time-averaged local heat transfer coefficient was obtained.

560 citations


Journal ArticleDOI
TL;DR: In this paper, a review of recent research on boiling in micro-channels is presented, which addresses the topics of macroscale versus micro-scale heat transfer, two-phase flow regimes, flow boiling heat transfer results for micro-channel, heat transfer mechanisms in microchannels and flow boiling models for micro channels.

553 citations


Journal ArticleDOI
TL;DR: In this paper, heat transfer measurements taken at atmospheric pressure in silica nano-solutions are compared to similar measurements taken in pure water and silica micro-solution, and the data include heat flux vs. superheat of a 0.4 mm diameter NiCr wire submerged in each solution, showing a marked increase in critical heat flux (CHF) for both nano- and micro-Solutions compared to water, but no appreciable differences in heat transfer for powers less than CHF.

Journal ArticleDOI
TL;DR: In this paper, the authors use classical molecular dynamics simulations to study the interfacial resistance for heat flow between a carbon nanotube and octane liquid and find that the thermal conductivity of carbon-nanotube polymer composites and organic suspensions will be limited by the interface thermal resistance.
Abstract: We use classical molecular dynamics simulations to study the interfacial resistance for heat flow between a carbon nanotube and octane liquid. We find a large value of the interfacial resistance associated with weak coupling between the rigid tube structure and the soft organic liquid. Our simulation demonstrates the key role played by the soft vibration modes in the mechanism of the heat flow. These results imply that the thermal conductivity of carbon-nanotube polymer composites and organic suspensions will be limited by the interface thermal resistance and are consistent with recent experiments.

Journal ArticleDOI
TL;DR: In this article, the authors deal with the preparation of paraffin/high density polyethylene (HDPE) composites as form-stable, solid liquid phase change material (PCM) for thermal energy storage and with determination of their thermal properties.

Journal ArticleDOI
TL;DR: In this paper, the effects of concentration of carbon nanotubes and temperature on effective thermal conductivity were investigated, and it was found that effective thermal conduction increased with increasing concentration of the carbon-nanotubes, and the dependence was nonlinear even at very low concentrations.
Abstract: This work is concerned with the effective thermal conductivity of aqueous suspensions of multiwalled carbon nanotubes (nanofluids). Stable nanofluids were made using sodium dodecylbenzene sulfonate as the dispersant. The effects of concentration of carbon nanotubes and temperature on effective thermal conductivity were investigated. It was found that effective thermal conductivity increased with increasing concentration of carbon nanotubes, and the dependence was nonlinear even at very low concentrations, which was different from the results for metal/metal oxide nanofluids. The effective thermal conductivity increased with increasing temperature, and the dependence was also nonlinear. At temperatures lower than ∼30 ◦ C, approximately linear dependence of the thermal conductivity enhancement on temperature was seen, but the dependence tended to level off above ∼30◦C. A comparison between the results of this work and those of published studies showed a large discrepancy in the effective thermal conductivity of carbon nanotube nanofluids. Differences in the interfacial resistances and thermal conductivities of carbon nanotubes used in these studies were proposed to be the main reasons. The experimental results were also compared with some classical macroscopic models for thermal conductivity of homogenous mixtures containing micrometer- or millimeter-sized particles. It was shown that the macroscopic models were inadequate for the prediction of the effective thermal conductivity of nanofluids. Analysis of possible mechanisms for thermal conduction enhancement suggested that networking of carbonnanotubes was likely to be responsible for the observed high effective thermal conductivity of carbon-nanotube nanofluids. Experiments at a temperature above 60‐70 ◦ C showed that the dispersant failed, which led to destabilization of nanofluids.

Journal ArticleDOI
TL;DR: In this paper, an eddy-viscosity model based on Durbin's elliptic relaxation concept is proposed, which solves a transport equation for the velocity scales ratio ζ=υ 2¯/k instead of υ2¯, thus making the model more robust and less sensitive to grid nonuniformities.

Proceedings ArticleDOI
TL;DR: In this article, an experimental study has been carried out to provide qualitative and quantitative insight into gas to wall heat transfer in a gasoline fueled homogeneous charge compression Ignition (HCCI) engine.
Abstract: An experimental study has been carried out to provide qualitative and quantitative insight into gas to wall heat transfer in a gasoline fueled Homogeneous Charge Compression Ignition (HCCI) engine. Fast response thermocouples are embedded in the piston top and cylinder head surface to measure instantaneous wall temperature and heat flux. Heat flux measurements obtained at multiple locations show small spatial variations, thus confirming relative uniformity of incylinder conditions in a HCCI engine operating with premixed charge. Consequently, the spatially-averaged heat flux represents well the global heat transfer from the gas to the combustion chamber walls in the premixed HCCI engine, as confirmed through the gross heat release analysis. Heat flux measurements were used for assessing several existing heat transfer correlations. One of the most popular models, the Woschni expression, was shown to be inadequate for the HCCI engine. The problem is traced back to the flame propagation term which is not appropriate for the HCCI combustion. Subsequently, a modified model is proposed which significantly improves the prediction of heat transfer in a gasoline HCCI engine and shows very good agreement over a range of conditions.

Journal ArticleDOI
TL;DR: In this article, a literature survey is devoted to the problem of heat transfer of fluids at supercritical pressures including near critical region, and a discussion on the general trends of various thermophysical properties at near critical and pseudocritical points is also included.

Book
29 Apr 2004
TL;DR: In this article, the authors present a model of a Porous Medium Model of a Storage System with Phase-Change Material (PMM) based on the Darcy Flow and more advanced models.
Abstract: Contents Preface 1 Porous Media Fundamentals 1.1 Structure 1.1.1 Microporous Media 1.1.2 Mesoporous Media 1.1.3 Macroporous Media 1.2 Mass Conservation 1.3 Darcy Flow and More Advanced Models 1.4 Energy Conservation 1.5 Heat and Mass Transfer 1.5.1 Fluid Flow 1.5.2 Heat Flow 2 Flows in Porous Media 2.1 Use Simple Methods First 2.2 Scale Analysis of Forced Convection Boundary Layers 2.3 Sphere and Cylinder with Forced Convection 2.4 Channels with Porous Media and Forced Convection 2.5 Scale Analysis of Natural Convection Boundary Layers 2.6 Thermal Stratification and Vertical Partitions 2.7 Horizontal Walls with Natural Convection 2.8 Sphere and Horizontal Cylinder with Natural Convection 2.9 Enclosures Heated from the Side 2.10 Enclosures Heated from Below 2.11 The Method of Intersecting the Asymptotes 2.11.1 The Many Counterflows Regime 2.11.2 The Few Plumes Regime 2.11.3 The Intersection of Asymptotes 3 Energy Engineering 3.1 Thermodynamics Fundamentals: Entropy Generation or Exergy Destruction 3.2 Exergy Analysis 3.3 Thermal Energy Storage 3.4 Sensible Heat Storage 3.5 Aquifer Thermal Energy Storage 3.6 Latent Heat Storage 3.7 Cold Thermal Energy Storage 3.8 Porous Medium Model of a Storage System with Phase-Change Material 3.9 Fuel Cell Principles and Operation 3.10 Fuel Cell Structure and Performance 3.11 The Concept of Exergy-Cost-Energy-Mass (EXCEM) Analysis 3.12 Exergy, Environment, and Sustainable Development 4 Environmental and Civil Engineering 4.1 The Energy-Environment Interface 4.2 Wakes: Concentrated Heat Sources in Forced Convection 4.3 Plumes: Concentrated Heat Sources in Natural Convection 4.4 Penetrative Convection 4.5 Aerosol Transport and Collection in Filters 4.6 Filter Efficiency and Filtration Theories 4.7 Pressure Drop, Permeability,and Filter Performance 4.8 Ionic Transport 4.9 Reactive Porous Media 4.10 Electrodiffusion 4.11 Tree-Shaped Flow Networks 4.12 Optimal Size of Flow Element 4.13 Hot Water Distribution Networks 4.14 Minimal Resistance Versus Minimal Flow Length 5 Compact Heat Transfer Flow Structures 5.1 Heat Exchangers as Porous Media 5.2 Optimal Spacings in Natural Convection 5.3 Optimal Spacings in Forced Convection 5.4 Pulsating Flow 5.5 Optimal Packing of Fibrous Insulation 5.6 Optimal Maldistribution: Tree-Shaped Flows 5.7 Dendritic Heat Exchangers 5.7.1 Elemental Volume 5.7.2 First Construct 5.7.3 Second Construct 5.8 Constructal Multiscale Structure for Maximal Heat Transfer Density 5.8.1 Heat Transfer 5.8.2 Fluid Friction 5.8.3 Heat Transfer Rate Density: The Smallest Scale 5.9 Concluding Remarks 6 Living Structures 6.1 Respiratory System 6.1.1 Airflow Within the Bronchial Tree 6.1.2 Alveolar Gas Diffusion 6.1.3 Particle Deposition 6.2 Blood and the Circulatory System 6.3 Biomembranes: Structure and Transport Mechanisms 6.3.1 Cell Membrane 6.3.2 Capillary Wall 6.4 Transport of Neutral Solutes Across Membranes 6.5 Transport of Charged Solutes Across Membranes 6.5.1 Membrane Potential 6.5.2 Electrical Equivalent Circuit 6.6 The Kidney and the Regulation of Blood Composition 6.6.1 Kidney Failure and Dialysis 6.6.2 Pumping Blood Through Semipermeable Membranes 7 Drying of Porous Materials 7.1 Introduction 7.2 Drying Equipment 7.3 Drying Periods 7.4 Basic Heat and Moisture Transfer Analysis 7.5 Wet Material 7.6 Types of Moisture Diffusion 7.7 Shrinkage 7.8 Modeling of Packed-Bed Drying 7.9 Diffusion in Porous Media with Low Moisture Content 7.10 Modeling of Heterogeneous Diffusion in Wet Solids 7.10.1 Mass Transfer 7.10.2 Heat Transfer 7.10.3 Boundary Cond

Journal ArticleDOI
TL;DR: In this paper, the authors analyzed the forces due to surface tension and momentum change during evaporation in microchannels and derived two new non-dimensional groups, K1 and K2, relevant to flow boiling.
Abstract: The forces due to surface tension and momentum change during evaporation, in conjunction with the forces due to viscous shear and inertia, govern the two-phase flow patterns and the heat transfer characteristics during flow boiling in microchannels. These forces are analyzed in this paper, and two new nondimensional groups, K1 and K2 , relevant to flow boiling phenomenon are derived. These groups are able to represent some of the key flow boiling characteristics, including the CHF. In addition, a mechanistic description of the flow boiling phenomenon is presented. The small hydraulic dimensions of microchannel flow passages present a large frictional pressure drop in single-phase and two-phase flows. The small hydraulic diameter also leads to low Reynolds numbers, in the range 100‐1000, or even lower for smaller diameter channels. Such low Reynolds numbers are rarely employed during flow boiling in conventional channels. In these low Reynolds number flows, nucleate boiling systematically emerges as the dominant mode of heat transfer. The high degree of wall superheat required to initiate nucleation in microchannels leads to rapid evaporation and flow instabilities, often resulting in flow reversal in multiple parallel channel configuration. Aided by strong evaporation rates, the bubbles nucleating on the wall grow rapidly and fill the entire channel. The contact line between the bubble base and the channel wall surface now becomes the entire perimeter at both ends of the vapor slug. Evaporation occurs at the moving contact line of the expanding vapor slug as well as over the channel wall covered with a thin evaporating film surrounding the vapor core. The usual nucleate boiling heat transfer mechanisms, including liquid film evaporation and transient heat conduction in the liquid adjacent to the contact line region, play an important role. The liquid film under the large vapor slug evaporates completely at downstream locations thus presenting a dryout condition periodically with the passage of each large vapor slug. The experimental data and high speed visual observations confirm some of the key features presented in this paper. @DOI: 10.1115/1.1643090#

Journal ArticleDOI
01 Nov 2004
TL;DR: In this paper, a review on progress with passive heat transfer augmentation is presented, where inserts are used in the flow passage to augment the heat transfer rate, where the insert manufacturing process is simple and these techniques can be easily employed in an existing heat exchanger.
Abstract: Heat transfer augmentation techniques (passive, active or a combination of passive and active methods) are commonly used in areas such as process industries, heating and cooling in evaporators, thermal power plants, air-conditioning equipment, refrigerators, radiators for space vehicles, automobiles, etc Passive techniques, where inserts are used in the flow passage to augment the heat transfer rate, are advantageous compared with active techniques, because the insert manufacturing process is simple and these techniques can be easily employed in an existing heat exchanger In design of compact heat exchangers, passive techniques of heat transfer augmentation can play an important role if a proper passive insert configuration can be selected according to the heat exchanger working condition (both flow and heat transfer conditions) In the past decade, several studies on the passive techniques of heat transfer augmentation have been reported The present paper is a review on progress with the passi

Journal ArticleDOI
TL;DR: In this paper, an equation of conduction-advection is established for heat transfer in porous media, and an analytical transient solution is obtained for a line heat source in an infinite medium by means of the Green function analysis.

Journal ArticleDOI
13 Feb 2004-Science
TL;DR: This result suggests that high densities of interfaces between dissimilar materials may provide a route for the production of thermal barriers with ultra-low thermal conductivity.
Abstract: Atomic layer deposition and magnetron sputter deposition were used to synthesize thin-film multilayers of W/Al 2 O 3 . With individual layers only a few nanometers thick, the high interface density produced a strong impediment to heat transfer, giving rise to a thermal conductivity of ∼0.6 watts per meter per kelvin. This result suggests that high densities of interfaces between dissimilar materials may provide a route for the production of thermal barriers with ultra-low thermal conductivity.

Journal ArticleDOI
TL;DR: In this paper, the effect of mass flux, pressure, and heat flux on the heat transfer coefficient and pressure drop was measured for four horizontal cooling tubes with different inner diameters ranging from 1 to 6 mm.
Abstract: Heat transfer of supercritical carbon dioxide cooled in circular tubes was investigated experimentally. The effect of mass flux, pressure, and heat flux on the heat transfer coefficient and pressure drop was measured for four horizontal cooling tubes with different inner diameters ranging from 1 to 6 mm. The radial distribution of the thermophysical properties (i.e. specific heat, density, thermal conductivity and viscosity) in the tube cross-section was critical for interpreting the experimental results. A modified Gnielinski equation by selecting the reference temperature properly was then developed to predict the heat transfer coefficient of supercritical carbon dioxide under cooling conditions. This proposed correlation was accurate to within 20% of the experimental data.

Journal ArticleDOI
TL;DR: In this article, an ensemble of experimental phase change material (PCM) storages, with and without heat transfer enhancement structures, was designed and constructed, and the numerical predictions calculated with FEMLAB simulation software were compared to experimental data.

Journal ArticleDOI
TL;DR: In this paper, a phase change material (PCM) thermal management system was designed for an electric scooter, which can control the temperature excursions and maintain temperature uniformity in Li-ion batteries without the use of active cooling components such as a fan, a blower or a pump.

Journal ArticleDOI
TL;DR: In this article, a two-dimensional mixed convection problem in a vertical two-sided lid-driven differentially heated square cavity is investigated numerically and the Richardson number, Ri=Gr/Re2 emerges as a measure of relative importance of natural and forced convection modes on the heat transfer.

Journal ArticleDOI
TL;DR: In this paper, the authors consider the irreversibilities originating from finite-time and finite-size constraints in real thermal system optimization and consider the energy transfer between the system and its surroundings in the rate form.

Journal ArticleDOI
TL;DR: In this paper, a non-dimensional number quantifying the part of axial conduction in walls of a mini-micro counter-flow heat exchanger is proposed, which is shown to be a good approximation of the heat transfer coefficient.

Journal ArticleDOI
TL;DR: The statistics of heat exchange between two classical or quantum finite systems initially prepared at different temperatures are shown to obey a fluctuation theorem.
Abstract: The statistics of heat exchange between two classical or quantum finite systems initially prepared at different temperatures are shown to obey a fluctuation theorem.

Journal ArticleDOI
TL;DR: In this paper, the effects of microburner wall conductivity, external heat losses, burner dimensions, and operating conditions on combustion characteristics and the steady-state, self-sustained flame stability of propane/air mixtures were investigated.