Important Role In Heat Transfer Research Articles

Turbulent Characteristic of Liquid Around a Chain of Bubbles in Non-Newtonian Fluid

The turbulence behavior of gas-liquid two-phase flow plays an important role in heat transfer and mass transfer in many chemical processes. In this work, a 2D particle image velocimetry (PIV) was used to investigate the turbulent characteristic of fluid induced by a chain of bubbles rising in Newtonian and non-Newtonian fluids. The instantaneous flow field, turbulent kinetic energy (TKE) and TKE dissipation rate were measured. The results demonstrated that the TKE profiles were almost symmetrical along the column center and showed higher values in the central region of the column. The TKE was enhanced with the increase of gas flow and decrease of liquid viscosity. The maximum TKE dissipation rate appeared on both sides of the bubble chain, and increased with the increase of gas flow rate or liquid viscosity. These results provide an understanding for gas-liquid mass transfer in non-Newtonian fluids.

Influences of igneous intrusions on coal rank, coal quality and adsorption capacity in Hongyang, Handan and Huaibei coalfields, North China

article i nfo Localized igneous intrusions with varying types of intrusion patterns were found in the Pennsylvanian-Permian coals in north China. Five typical patterns, including dike cut-through (pattern-I), dike cut-in (pattern-II), floor intru- sion by sill (pattern-III), roof intrusion by sill (pattern-IV) and dual intrusions of roof and floor by sills (pattern-V), were investigated at five different underground profiles. It was found that the influence of localized intrusions on rank, petrology and coal quality characteristics are mainly related to the emplacement temperature, the style of heat transfer (convection or conduction), the intrusion forms (dike or sill) and size, the distance from the contact and the thermal properties of the surrounding rocks at the contact of the intrusion. Among the five patterns, only pattern-V was found to have two distinct contact metamorphic aureoles within a distance of 1-2timesofthethick- ness of the intrusion, whereas patterns I through IV show wave-like profiles of vitrinite-reflectance, ash and volatile matter. This resulted from the typical characteristics of multiphasic and superimposed thermal metamorphic evo- lution of north China coals. Except for the heat conduction by intrusion contact, the hydrothermal convection and tectonic-heat played important roles in heat transfer away from dike/sill. Intrusion-induced coal changes including coal rank, organic/inorganic composition and pore properties work together to influence the adsorption capacity of coals. The effect of intrusion upon the adsorption capacity of altered coals is related to the values of their altered coal ranks. Adsorption capacity is elevated from the Langmuir volume (VL) of 7.6 (pre-intrusion) to 17.5 m 3 /t (post-intrusion) for altered bituminous coals and semi-anthracites with VRrb2.1%. In contrast, the adsorption ca- pacity is moderately reduced from background levels of about 27.2 m

Assessment of homotopy perturbation method in nonlinear convective-radiative non-Fourier conduction heat transfer equation with variable coefficient

Analytical solutions play a very important role in heat transfer. In this paper, the He's homotopy perturbation method (HPM) has been applied to nonlinear convective-radiative non-Fourier conduction heat transfer equation with variable specific heat coefficient. The concept of the He's homotopy perturbation method are introduced briefly for applying this method for problem solving. The results of HPM as an analytical solution are then compared with those derived from the established numerical solution obtained by the fourth order Runge-Kutta method in order to verify the accuracy of the proposed method. The results reveal that the HPM is very effective and convenient in predicting the solution of such problems, and it is predicted that HPM can find a wide application in new engineering problems.

The Backing Bar Role in Heat Transfer on Aluminium Alloys Friction Stir Welding

Although new structural and advanced materials have been used in the automotive and aircraft industries, especially lightweight alloys and advanced high strength steels, the successful introduction of such materials depends on the availability of proven joining technologies that can provide high quality and performance joints. Solid-state joining techniques such as Friction Stir Welding (FSW) are a natural choice since their welds are produced at low temperatures, so the low heat input provides limited, slight distortion, microstructural and mechanical degradation. Great effort has currently been devoted to the joining of Al-Cu-Mg and the Al-Mg-Si alloys because of their high strength, improved formability, and application in airframe structures. FSW is a continuous, hot shear, autogenous process involving a non-consumable and rotating tool plunged between two abutting workpieces. The backing bar plays an important role in heat transfer from stir zone (SZ), which can influence the weld microstructure as well as the consolidation of material in the root of the join. This study aims at investigating issues concerning heat generation, within the SZ of friction stir welded aircraft aluminium alloys.

Study on Turbulent Behavior of Water Jet in Supersonic Steam Injector

One of the most interesting devices for light water reactor systems aimed at simplified system, improvement of safety and reliability is a supersonic steam injector. Supersonic steam injector is a passive jet pump without rotating machine and high efficient heat exchanger because of direct contact condensation between supersonic steam and a subcooled water jet. It is considered that flow behavior in the supersonic steam injector is related to complicated turbulent flow with large shear stress induced by velocity difference between steam and water and direct contact condensation. However, studies about turbulent flow under large shear stress with direct contact condensation are not enough. Especially, mechanisms of momentum and heat transfer are not clarified in detail. Objective of the present study is to investigate turbulent behaviors of a water jet and interface that play an important role in heat transfer and momentum transfer. Radial distribution of streamwise velocity and fluctuation of total pressure are measured by a pitot measurement. Visual measurement of the turbulent water jet is conducted by a high speed camera in order to identify location of unstable interface and its behavior. It is found that streamwise velocity increases as it approaches downstream of the mixing nozzle. Fluctuation of total pressure is large at water-steam mixture region. It is confirmed that waves propagated on the interface. And its velocity is obtained.

Interrelationships between leaf heat conductivity and tissue structures of different varieties of Populus tomentosa Carr.

Plant heat conductivity largely depends on tissue structure. Different structures lead to different heat conductivity. As well, water transfer also plays a very important role in heat transfer in plants. We have studied leaf heat conductivity and tissue structure of 3-and 30-year-old Populus tomentosa Carr. trees using infrared thermal imaging, steady state heat conductivity surveys and paraffin section and investigated the relationship between leaf heat conductivity, tissue structure and water content of leaves. The results show that the temperature on leaf surfaces among the various varieties of trees was almost the same. Leaf heat conductivity, temperature and water content of leaves are positively correlated. The thicker the leaf tissue structures, the larger the heat resistance. That is, the tighter the cells and the smaller the interspaces, the smaller the heat conductivity, which is not conducive for heat transfer.

Connection between Eurasian and North Atlantic climate anomalies and natural variations in the Atlantic thermohaline circulation based on long-term model calculations

We obtained estimates of the correlation between regional characteristics of the climate in Eurasia and the North Atlantic and the Atlantic thermohaline circulation (ATHC) based on the results of calculations using the ocean‐atmosphere global climate model (OAGCM) without external forcing (reference numerical experiment) for the period of 500 yr. The regions of statistically significant correlation between the ATHC variations in a few decades with the anomalies of surface air temperature, pressure at sea level, and precipitation in different seasons were distinguished. The most significant correlation was found in the winter period. A correlation was also found between the ATHC and the intensity of the Iceland minimum of the atmospheric action center (AC) [1], which has a strong influence on the weather conditions in Europe. The Atlantic thermohaline circulation, which shows a large-scale North Atlantic meridional overturning circulation (NAMOC) and represents a part of the global 3D oceanic current (conveyor belt) [2, 3], plays an important role in heat transfer to high latitudes of the Northern Hemisphere. The intensity of the ATHC shows strong long-period fluctuations accompanied by anomalies in the ocean surface temperature (OST) in the North Atlantic [4] and variations in the area of the Arctic ice cover [5]. This fact evidences the existence of

Large eddy simulation on hert transfer enhancement of inclined-cut ellipsoidal vortex generator

The flow and heat transfer characteristics of rectan- gle channel with inclined-cut ellipsoidal vortex generator are obtained with large eddy simulation.The instantaneous proper- ties of velocity,temperature and pressure in channel are gained. The variety process of temperature,pressure and inducted vor- tex are revealed.Meantime,the heat transfer enhancement mechanism of vortex generator and flow structure are discussed. The turbulent model is used for verifying correctness of large eddy simulation in calculation of rectangle channel without vortex generator in the same calculation condition.The calcula- tion result with two methods is consistent.The result of simula- tion indicates that the vortex can be induced by vortex genera- tor.Furthermore,the stream-wise vortex induced by vortex generator pays more important role in heat transfer enhance- ment.Compared with the channel without inclined-cut ellip- soidal vortex generator in the same condition,the local heat transfer coefficient is enhanced from 64%～105%,and the av- erage heat transfer coefficient is enhanced from 17%～36%.The enhancement of local heat transfer coefficient is occurred nearby the vortex generator.There is a consanguineous rela- tionship between the fluid flow structure and status in near wall region with the local heat transfer.

A one-dimensional thermo-fluid model of blood circulation in the human upper limb

Blood circulation is considered to play an important role in heat transfer between living tissues, particularly, in peripheral vessels wherein the temperature is, generally, closely related with blood flow rate. The aim of this paper is to study the influence of blood flow rate on body temperature by means of a one-dimensional thermo-fluid model. This model has been recently developed for the circulation system of the upper limb and involves arteries, capillaries, and veins. Computed results of the blood flow, cross-sectional area, and temperature of each vessel are presented, and are then compared with available experimental data. The influence of the bending stiffness of the vessel walls as well as that of blood viscosity on blood pressure and temperature is analyzed.

Heat transfer of fibre beds in resin transfer moulding: an experimental approach

Resin transfer moulding is a fibre impregnation process which is widely used for manufacturing of lightweight fibre reinforced plastic components for automotive and aircraft industry. For economic manufacturing of larger series of production lower cycle times must be achieved, thus injection strategies which allow a rapid infusion of the resin and impregnation of the fibres must be applied. For process optimisation numerical methods are increasingly applied to reduce time to market, cost and risk. Since temperature has an impact on flow and curing of the injected resin, heat transfer mechanisms between the tool and the uncured composite part is of major importance to achieve reliable numerical results. When fluid flows through stationary fibre beds, hydrodynamic dispersion plays an important role in heat transfer and is found to be a function of Peclet number. To understand the hydrodynamic dispersion phenomena, a test rig was designed to measure heat transfer at steady state conditions. The transverse effective diffusivity was investigated, whereas the influence of cavity thickness, porosity and resin flow velocity on effective thermal diffusivity was evaluated. Based on experimental data a model for heat transfer was developed. Because resin flows through a porous media, thermal diffusion is expected to be a combination of conduction and convection. Therefore the model for transverse diffusion for non-crimped fabrics was found to be a function of the thermal properties of the constituent materials, the fibre volume fraction, the degree of filling and the Peclet number. The model is suitable for all process stages, such as preheating, form filling and curing.

STUDY OF THERMAL BEHAVIOR AND FLUID FLOW DURING LASER SURFACE HEATING OF ALLOYS

Transient and steady state laser melting problems are numerically simulated for steel and Al-4.5% Cu. Enthalpy and apparent capacity methods are used to solve the energy equation, and the momentum equations are solved in the liquid domain and mushy zone with the SOLA-VOF algorithm. Using a laser with a top-hat profile, a wide range of studies are performed by varying the beam power density and the beam radius. The streamline plots show that the flow pattern is dependent on the strength of the rotating cell along with heat flux. It is found that the shape of the pool, the surface velocity, and the surface temperature are quite different from those without convection in the mushy zone. Convection in the mushy zone plays an important role in heat transfer and fluid flow during laser melting.

Prediction of Transition Boiling Heat Transfer Based on Partial Dryout Model of Liquid Layers.

The transition boiling heat transfer was analyzed by considering the formation, evaporation and dryout processes of liquid layers beneath individual bubbles. In the low-superheating region, the heat flux is mainly due to the evaporation of the microlayer. In the high-superheating region, the evaporations of both the microlayer and macrolayer play important roles in heat transfer. The predicted fraction of wetted area and heat flux of transition boiling showed good agreement with experimental data reported in literature.

Temperature distribution in a cylindrical Al 2O 3-steel joint during the vacuum brazing cycle

This paper deals with the investigations of temperature distribution during vacuum brazing of cylindric Al 2O 3 and steel samples, using the AgCuInTi active filler metal. The thermovision system AGA 680S was used to register the temperature field during brazing cycle. Bonded joints were observed by the infrared scanner unit during heating, brazing and cooling. Two types of joints with different shape of steel element were examined during temperature measurements. Additionally, a 2D finite element code “ADINA-T” was used to solve for the problem of nonlinear transient thermal analysis of temperature distribution in the axisymmetric models of Al 2O 3-steel brazed joints. The experimental results revealed the presence of big transient axial temperature drops in the ceramic part. The change of metal shape resulted in a reduction of the transient temperature drops in the ceramic element. The finite element calculations corresponded well with the results of measurements and showed that the perfect thermal contact between adjacent surfaces plays the important role in heat transfer and can be a factor affecting temperature gradients in ceramic.

Einfluß der Wandwärmeleitung auf die laminare Mischkonvektion in der thermischen Eintrittszone von horizontalen, rechteckigen Kanälen

This paper presents a numerical study of the effect of peripheral wall heat conduction on laminar mixed convection in the thermal entrance region of horizontal rectangular channels. In addition to the Rayleigh numberRa and the channel aspect ratio (width-to-height) γ, the wall heat conduction parameterK=kwt/(kfDe) plays an important role in heat transfer. A numerical method of solution utilizing the vorticity-velocity formulation is developed to solve the system of governing partial differential equations coupled with the boundary condition equation considering peripheral wall heat conduction. Local friction factor ratio and Nusselt number variations are shown forPr=0.7,Ra=104, 3×104, and 105, γ=0.2, 0.5, 1, 2 and 5,K=0.01, 0.1 and 1. The effect of peripheral wall heat conduction on Nusselt number is found to be significant when the value of γ is less than 1. The asymptotic solutions forz→∞ are compared with the existing numerical results and good agreement is indicated.

THE STRING OF CATALYST SPHERES AS A TOOL FOR HEAT AND MASS TRANSFER STUDY IN A THREE-PHASE SYSTEM

A single vertical string of catalyst spheres with liquid film flowing over their surfaces was employed to model a three phase system. Simultaneous heat and mass transfer characteristics within a porous catalyst pellet and across the laminar liquid film was analyzed in terms of different values of reaction and transport parameters. It is shown that the liquid film thickness after the first three pellets reduces less than 10% even though a highly exothermic reaction is taking place within the pellets. It was also found that the mixing in pendular rings plays an important role in heat transfer from the pellets surface.

Effect of Wall Conduction on Combined Free and Forced Laminar Convection in Horizontal Rectangular Channels

This paper presents a numerical study of the effect of peripheral wall conduction on combined free and forced laminar convection in hydrodynamically and thermally fully developed flow in horizontal rectangular channels with uniform heat input axially, In addition to the Prandtl number, the Grashof number Gr+, and the aspect ratio γ, a parameter Kp indicating the significance of wall conduction plays an important role in heat transfer. A finite-difference method utilizing a power-law scheme is employed to solve the system of governing partial differential equations coupled with the equation for wall conduction. The numerical solution covers the parameters: Pr = 7.2 and 0.73, γ = 0.5, 1, and 2, Kp = 10−4–104, and Gr+ = 0–1.37×105. The flow patterns and isotherms, the wall temperature distribution, the friction factor, and the Nusselt number are presented. The results show a significant effect of the conduction parameter Kp.

Radiative heat transfer from a cylindrical cloud of particles.

In this work the Monte Carlo method is applied to investigate thermal radiation to the exterior base region of a finite cylindrical dispersion of absorbing, emitting, and anisotropically scattering particles. The analysis assumes a scattering function characteristic of aluminum oxide dispersions. Searchlight effect, chamber emitted radiation scattered by the particles to the surroundings, is introduced by permitting the radiation to originate from a black circular surface at the base of the cloud, as well as from within the cloud. The results obtained show that anisotropic scattering and searchlight effect play important roles in heat transfer in this geometry.