Thermal Flow Model Research Articles

Coupled electromagnetic acoustic and thermal-flow modeling of an induction motor of railway traction

In order to optimize the design of an enclosed induction machine of railway traction, a multi-physical model is developed taking into account electromagnetic, mechanical and thermal-flow phenomena. The electromagnetic model is based on analytical formulations and allows calculating the losses. The thermal-flow modeling is based on an equivalent thermal circuit which has the feature to consider the flow structure inside the machine. In this way, a numerical study has been carried out to evaluate this internal flow structure depending on the rotational speed. The results of the multi-physical model are confronted with experimental results.

Mesoscale Analysis of Thermal Flow of Magnetic Fluids

With respect to the magnetic interactions and other nonmagnetic interactions among the suspended magnetic nanoparticles and the ambient carrier liquid molecules as well as the effect of an external magnetic field, a two-phase thermal flow model is developed based on the lattice Boltzmann method to investigate energy transport and flow dynamics of the magnetic fluid at the mesoscale level. By means of this model, the microscopic morphology of the magnetic fluid and flow behavior in a channel are simulated and the effect of the external magnetic field is studied.

Thermal Behaviour for InGaAsP/InP Multi-Quantum-WellSuperluminescent Diodes

Using a two-dimensional thermal flow model, we calculate the thermalresistance and the temperature distribution of InGaAsP/InPmulti-quantum-well superluminescent diodes. The influence of lateralchip size and composition are evaluated. The results reveal that whenthe injection power reaches 1 W, temperatures in the active region risesup to almost 50 K. The width and length of the chip also have stronginfluence on the thermal resistance that can reach two orders ofmagnitude. The thermal resistance will change from 290 K/W to 68 K/W whenthe chip width increases from 500 μm to 2500 μm, and a similarresult exists for the length. There is small effect on thermalresistance for active width. In view of the characteristics of outputpower versus the input current under pulsed and continues currents, thefitted experimental thermal resistance matches well with the measuredresults.

Electromagnetic and thermal-flow modeling of a cold-wall crucible induction melter

An approach for modeling cold-wall crucible induction melters is described. Materials in the melt and melter are nonferromagnetic. In contrast to other modeling studies reported in the literature, the numerical models use commercial codes. The ANSYS finite-element code[1] is employed for electromagnetic field simulations and the STAR-CD finite-volume code[2] for thermal-flow calculations. Results from the electromagnetic calculations in the form of local Joule heat and Lorentz force distributions are included as source terms in the thermal-flow analysis. This loosely coupled approach is made possible by the small variation in temperature and, consequently, small variation in electrical properties across the melt as well as the quasi-steady-state nature of the thermal-flow calculations. A three-dimensional finite-element grid for electromagnetic calculations is adapted to a similar axisymmetric finite-volume grid for data transfer to the thermal-flow model. Results from the electromagnetic model compare well with operational data from a 175-mm-diameter melter. REsults from the thermal-flow simulation provide insight about molten metal circulation patterns, temperature variations, and velocity magnitudes. Initial results are included for a model that simulates the formation of a solid (skull) layer on the crucible base and wall. Overall, the modeling approach is shown to produce useful results that relate operational parameters to the physics of steady-state melter operation.

Early-age finite element modelling of industrial ground floors

A series of finite element (FE) models of ground floor slab behaviour has been developed and validated against in situ data from site instrumentations. Good agreement was obtained for thermal flow models, and the negative impact of air movement over the top of the slab has been highlighted. Plane stress models of slabs exposed to uniform and differential thermal gradients representing hydration and shrinkage effects demonstrated that the stresses resulting from frictional restraint are significantly less than those caused by warping restraint, even though the latter are currently not considered in design.

Linear Stability Theory of Non‐Isothermal Flow Between Two Rotating Disks

AbstractThe objective of the present study is to investigate the flow stability of mixed convection in non‐isothermal rotating fluids between a rotating disk and a stationary one. The buoyancy effects stemmed from the rotational forces, including centrifugal and Coriolis, are taken into account. A similarity model of thermal flow with the assumption of Boussinesq fluids is formulated for generating axially symmetric solutions of the basic state. Disturbance equations are derived by using the concept of small perturbation of normal mode expressions, and then solved by the Chebyshev collocation spectral method. The influences of the rotation‐induced buoyancy effects and the rotational conditions on the flow stability characteristics of the two‐disk rotating fluid motion are explored. The present results disclose the mechanisms and the significance of the rotation‐induced buoyancy on flow stability characteristics of the non‐isothermal fluids in the rotor‐stator disk systems.

Lattice-Boltzmann algorithm for simulating thermal two-phase flow

An algorithm is described for incorporating thermal effects into lattice-Boltzmann simulations of two-phase flow. This algorithm is a combination of a two-distribution model for simulating single-phase thermal flow recently proposed by the authors and the thermodynamically-based model for isothermal two-phase flow of Swift et al. [Phys. Rev. E 54, 5041 (1996)]. The algorithm also corrects a problem with the original single-phase thermal flow model, which described the thermal energy flux as proportional to a gradient of the internal energy instead of being proportional to the gradient of the temperature. For ideal-gas systems, these two descriptions are equivalent but for nonideal systems there is a systematic discrepancy between the original thermal model and classical hydrodynamics. The algorithm is tested on several simple problems. These include formation of a free-standing isothermal thin liquid film, evaporation of a thin liquid film from a heated plate, evaporation of an isolated droplet, and condensation of liquid in a channel. Where possible, the simulations are compared against known analytic results.

Investigation Of Buoyancy Effects in Non-Isothermal Rotating Flows by Scaling Analysis and a Novel Similarity Model

ABSTRACTThe objective of the present study is to investigate the buoyancy effects induced by various body forces in non-isothermal rotating fluids. The buoyancy effects stemmed from the gravity, the centrifugal and Coriolis forces generated by system rotation, and the curvilinear motion of the fluids are all taken into account. Mixed convection between two disks rotating at different rates is employed as the physical model. The present work is the first study for detailed investigation of the various buoyancy forces in the class of non-isothermal flows. Complete system of axially-symmetric thermal flow model with assumption of Boussinesq fluids is formulated. By a scaling analysis and the solutions of a novel similarity model developed in this work, the relative importance of the buoyancy effects induced by various body forces is explored. The present work discloses the significance of the rotation-induced buoyancy effects under various conditions and is useful in understanding the mechanisms as well as modeling the mixed convection heat transfer in the class of rotating thermal flows.

THERMAL ANALYSIS OF ASPHALT PAVEMENT USING METEOROLOGICAL DATA

Temperature profile in asphalt pavement manifests nonlinear distribution which varies with time. In the past researches, there exist two major approaches; one uses a correlation between air temperature and temperature measured in pavement, and the other considers the effect of solar radiation. However, asphalt which has a strong characteristics of absorbing and storing heat, also emit the heat to the atmosphere. Dust and waterdrop in the atmosphere also radiate heat to pavement This paper presents a general thermal flow model between pavement and its surroundings and the effect of factors involved in the model on the temperature distribution in pavement using meteorological data

INTEGRATED FINITE ELEMENT MODEL FOR TRANSIENT FLUID FLOW AND THERMAL STRESSES DURING CONTINUOUS CASTING

A finite element computational methodology is presented for predicting the temperature distribution, fluid flow, and thermal stresses evolving in a solidifying ingot, which itself is growing in length, during the start-up phase of a continuous casting process, with a particular reference to aluminum casting. The approach is based on the coupling of a thermal and flow model with a stress model, The thermal flow model is developed using a deforming finite element method with an Eulerian-Lagrangian transformation to account for the fact that the ingot itself is also growing at a prescribed casting speed. The stress model is developed also by the finite element method, with mechanical deformations in the solidifying materials described by a hypoelastic-viscoplastic constitutive relation. The integrated model has been applied to study the dynamic development of temperature, flow, and stresses in the solidifying ingot during the start-up phase for continuous casting of aluminum. The results show that the fluid ...

A STUDY ON THERMAL PROPERTIES FOR ZrO2 COATINGS BY ARC PHOTOTHERMAL TECHNIQUE AND FINITE-DIFFERENCE THERMAL FLOW MODEL

The thermal conductivity and thermal diffusivity of ZrO2 coatings were studied using arc-photothermal evaluation technique in which the sample was heated at front surface and detected at back surface, and finite-difference thermal flow model was applied. The values of thermal conductivity and thermal diffusivity of ZrO2 are ｋ＝０．００６９Ｊ／ｃｍ·Ｋ·ｓ and α＝０．００２８ｃｍ2／ｓ, respectively. It is shown that, first, the finite-difference thermal flow model is an available and useful method for the multilayer coating system, and, second, the arc photothermal evaluation technique has low cost of equipment, and more simple and convenient measurement.

Physics and modeling of thermal flow in unconsolidated porous media : Settari, A SPE Prod EngngV7, N1, Feb 1992, P47–55

Physics and modeling of thermal flow in unconsolidated porous media : Settari, A SPE Prod EngngV7, N1, Feb 1992, P47–55

Physics and Modeling of Thermal Flow and Soil Mechanics in Unconsolidated Porous Media

Summary This paper describes a new formulation of nonlinear soil mechanics and multiphase thermal flow. The nonlinearities of the soil behavior and their interactions with fluid flow causing shear failure of the soil are the dominant features of the process. The numerical formulation of the coupled flow/stress solution model includes nonlinear compressibility and flow properties as functions of pressure, stress, and temperature; nonlinear, incremental, thermal poroelastic stress analysis; and shear or tensile failure and its effects on transport properties, porosity, and stress. An efficient sequential numerical scheme was developed. It is mass conservative and applicable to external coupling of existing simulators. The 1D examples show some startling new features of reservoir mechanics in unconsolidated media.

Temperature evolution of plasma-sprayed niobium particles impacting on a substrate

A fast two-color pyrometer is used to monitor the temperature evolution of individual plasma- sprayed niobium particles after their impact on a substrate. The experimental setup permits rejection of thermal events corresponding to in-flight particles intersecting the pyrometer field of view, ensuring that only particles impacting on the substrate surface are examined. Cooling rates as high as 10 8Ks -1 are measured when particles are sprayed on steel and alumina substrates. An interruption of the rapid cooling process and a transient temperature increase are observed near the niobium melting point. Experimental results are interpreted with the help of a numerical thermal flow model taking into account undercooling and the recalescence effects.

Cerebral blood flow and the thermal properties of the brain: a preliminary analysis.

Safe and effective use of hyperthermia for the treatment of brain tumors requires precise control of the distribution of temperatures (that is, the thermal field) within the tumor and within the adjacent brain. Major influences upon the distribution of temperatures include the passive thermal properties of the brain, such as its specific heat (Cb), and the contribution of cerebral blood flow (CBF). Recently, an electrical-mechanical analog model of heat flow within the brain has been developed from which an expression for CBF has been derived: CBF = Cb/(tau rho c) where tau is the thermal decay constant, rho is the density of blood, and c is its specific heat. To test this model a series of experiments was carried out in adult dogs in which stereotaxically implanted microwave antennas operating at 2450 MHz, fluoro-optical thermometry probes, and platinum electrodes were used to simultaneously measure CBF by thermal washout and hydrogen clearance techniques. The correlation coefficient for estimates of CBF derived by the two methods in 52 paired observations was 0.89. Measurements of CBF were more reliable at increased distances from the microwave antenna, since CBF is sensitive to the degree of temperature elevation (delta T). The ratio of post-heating CBF to pre-heating CBF varies linearly with delta T and has a correlation coefficient of 0.86. When values of CBF determined by the hydrogen clearance method were employed in the above equation, it was possible to derive Cb as 0.70 +/- 0.08 cal/gm-degrees C. Use of this value for Cb in this equation produces estimates of CBF by thermal clearance that are within 10% of the values for CBF as measured by the hydrogen clearance method. It is concluded that this model of thermal flow within the brain may have heuristic value for treatment planning and that microwave antennas and fluoro-optical probes may represent a new methodology for the clinical estimation of CBF. These methods have recently been employed in patients undergoing combined hyperthermia and chemotherapy.