Heating Of Cylinder Research Articles

Controlling the startup modes of cogeneration steam turbines operating as part of combined-cycle power plants

The results obtained from investigations of combined-cycle power plants produced by the Ural Turbine Works aimed at achieving high maneuverability, reliability and longevity of cogeneration steam turbines taking into consideration the possibilities of modern automated process control systems are presented. The dynamic models for simulating the heating of a steam turbine cylinder’s parts with the use of limited computation capacities are developed.

Melt Electrospinning by Cylinder Heating Method

Melt Electrospinning by Cylinder Heating Method

The onset of oblique vortex shedding behind a heated circular cylinder in laminar wake regime

Oblique vortex shedding (OVS) behind a heated circular cylinder in air was experimentally investigated. Similar to that in the parallel vortex shedding (PVS), the results show that the non-dimensionalized shedding frequency, Strouhal number, decreases under the influence of cylinder heating for oblique shedding mode. Although the onset Reynolds number of OVS increases with the cylinder temperature, the onset effective Reynolds number remains 63.3 ± 1.3 regardless of the cylinder heating. A general Strouhal-Reynolds-number relationship for OVS has been found based on the effective temperature concept in the present study. The ratio of the critical Reynolds numbers for the onsets of OVS and PVS is found to be an invariant with value of 4/3 for both isothermal and non-isothermal cases despite different length/diameter ratios and end conditions.

Thermal analysis of moving induction heating of a hollow cylinder with subsequent spray cooling: Effect of velocity, initial position of coil, and geometry

In this paper, temperature analysis of the complete process of moving induction heat treatment is performed using numerical methods. A non-linear and transient magneto-thermal coupled problem with a moving coil which is considered as moving heat source, is investigated by an efficient finite-element procedure. A vertical hollow circular cylinder is heated by the moving coil at a given velocity along it, and the heated parts then quenched by a moving water–air spray. The effects of natural convection with air on the both inner and outer surfaces of cylinder, and also radiation of outer surface of cylinder with ambient are taken into account. For quenching of work-piece, a specific kind of atomized spray cooling which utilizes a mixture of water and air with different mass fractions is used. This procedure includes moving boundary conditions, temperature-dependent properties, and change in magnetic permeability of specified alloy at the Curie temperature. Obtained numerical results have been verified by comparison with analytical solutions using Green’s function methods. Also, the effect of velocity, initial position of inductor and inner to outer radius ratio on temperature distribution are investigated.

Temperature Created by a Tilted Moving Heat Source: Heating Line and Cylinder

Temperatures created by a moving tilted line and a moving tilted cylinder are considered. Analytical expressions for low Peclet (Pe⪡1) and high Peclet (Pe⪢1) numbers are obtained for the whole range of possible tilt angles. These expressions almost overlap: It is shown that these analytical expressions describe very well the results of numerical calculations at any Peclet numbers except for a very narrow range of Pe close to unity. A method of calculation of the cut shape (variation of the tilt angle inside the cut) is discussed.

Vortex shedding and heat transfer dependence on effective Reynolds number for mixed convection around a cylinder in cross flow

The influence of surface heating of a circular cylinder on the wake structure and heat transfer in the range of Reynolds number ( Re) for which parallel vortex shedding occurs, is investigated numerically for different values of the buoyancy parameter, Gr. The role of buoyancy induced baroclinic vorticity on the wake formation is addressed in the present study. The variation of Strouhal number and Nusselt number with the ’effective Reynolds number’, is analyzed for different values of cylinder to free stream temperature ratio. Both Strouhal number and the rate of heat transfer increases monotonically with the increase of the effective Reynolds number. The validity of the correlations, which have been established by several authors, between the effective Reynolds number and Strouhal/ Nusselt number for forced convection, is examined in the mixed convection regime. The curves between the effective Reynolds number and the computed data for Strouhal number and Nusselt number do not collapse for the range of temperature ratio considered here. The flow field is found to be asymmetric and the cylinder experiences a negative lift. The drag coefficient increases steadily with the rise of surface temperature.

Thermomechanical behavior of polarizable and magnetizable electroconductive solids subjected to induction heating

This paper presents a mathematical and numerical model developed for coupled time-dependent electromagnetic, temperature and mechanical processes, which occur in polarizable and magnetizable electroconductive solids subjected to an electromagnetic field generated by external currents. The electromagnetic field in the solid and in its surroundings is described by Maxwell’s equations. The temperature variation in the solid is governed by the classical heat-transfer equation. To predict the stress–strain state of the solid, a nonisothermal theory for thermoplastic materials is used. The model takes into account the temperature dependence of all material coefficients and the nonlinear dependence of the induction on the strength of both the electrical and the magnetic fields. The problem is solved by a finite-element method and a unified set of single time-step algorithms. As an example, the process of high-temperature induction heating of a finite cylinder is considered.

On the effective temperature concept in the problem of laminar vortex shedding behind a heated circular cylinder

Prediction of the nonisothermal vortex shedding based on the effective temperature Teff=T∞+c(TW−T∞) is always linked with the specific material properties of the working fluid, while a desirable universal prediction is unknown. Here we show that the thermal effect in diluted gases, where cylinder heating stabilizes wake flow (thus delaying the onset of vortex shedding), can be quantified in the extraordinary compact form of the proportionality between the critical Reynolds number ReC,∞ and the dimensionless film temperature Tf*. The theoretically derived c value for any dilute gas is related to an exponent n of the kinematic viscosity-temperature power law by a simple formula c=(2n)−1. The universal character of the proportionality has been proven; the linear increase of the critical Reynolds number is independent of the specific material properties for all diluted gases.

A mathematical simulation of high temperature induction heating of electroconductive solids

The mathematical model of non-stationary coupled electromagnetic and thermal processes in polarizable and magnetizable axisymmetric electroconductive solids subjected to electromagnetic field generated by external currents is proposed. The processes parameters are connected through heat sources and temperature dependence of material characteristics. The problem is solved by finite element method. The process of induction heating of a finite steel cylinder is considered.

The influence of temperature gradient on the Strouhal–Reynolds number relationship for water and air

This paper focuses on the wake flow behind a heated circular cylinder in the laminar vortex shedding regime. The phenomenon of vortex shedding from a bluff body is an interesting scientific and engineering problem. Acquisition of reliable experimental data is considered an indispensable step toward a deeper physical understanding of the topic. An experimental study of the wake flow behind a heated cylinder in the forced convection regime is performed using water as the working fluid. Firstly, qualitative visualization experiments were performed and the parallel vortex shedding mode was adjusted. Next, hot-wire anemometry was used for St–Re data acquisition. Data analysis confirmed the so-called thermal effect in water: cylinder heating increases the vortex shedding frequency and destabilizes the wake flow. The effective temperature concept was used and the St–Re data were successfully transformed to the St–Re eff curve. Furthermore, a comparison with air as the working fluid was discussed (cylinder heating decreases the vortex shedding frequency in air, thus stabilizing the wake flow). The formula to determine the effective temperature in water was experimentally derived from the present data, while the data and formula for air is already known. The relationship between the Strouhal number and the effective Reynolds number for water and air is represented by the same, universal formula: St = 0.2660 - 1.0160 Re eff - 0.5 , where Re eff is calculated at the effective temperature. Finally, the measurement results were compared to the thermodynamic St–Re equation derived by Maršík et al. [F. Maršík, Z. Trávníček, R.H. Yen., A.-B. Wang, Fluid dynamics concept for the critical Reynolds number of a heated/cooled cylinder in laminar crossflow, in preparation]. A satisfactory agreement between the derived equation and experimental data for both fluids (water and air) was achieved.

A Transient Technique for Measuring the Effective Thermal Conductivity of Saturated Porous Media With a Constant Boundary Heat Flux

An experimental technique for measuring the effective thermal conductivity of saturated porous media is presented. The experimental method is based on the transient heating of a semi-infinite cylinder by a constant heat flux at the boundary. The data reduction technique is unique because it avoids determining the effective thermal diffusivity and quantifying the boundary heat flux. The technique is used to measure the effective thermal conductivity of glass-water, glass-air, and steel-air systems. These systems yield solid-fluid conductivity ratios of 1.08, 25.7, and 2400, respectively. The solid phases consist of 3.96mm glass spheres and 14mm steel ball bearings, which give mean porosities of 0.365 and 0.403. In addition, particular attention is paid to assessing experimental uncertainty. Consequently, this study provides data with a degree of precision not typically found the literature.

Dissipative heating of a viscoelastic cylinder steadily rolling over a rigid foundation

A dissipative-heating problem for an incompressible viscoelastic cylinder rolling over a rigid foundation is solved. The effect of tangential stresses on the dissipative-heating temperature is examined

Resonant Vibrations and Dissipative Heating of an Infinite Piezoceramic Cylinder

The monoharmonic radial vibrations and dissipative heating of an infinite hollow piezoceramic cylinder are studied in dynamic formulation, taking into account the temperature dependence of the complex electromechanical characteristics over a wide range of temperatures, including depolarization temperatures. The influence of the heat exchange conditions, the level of electric load, and geometry on the thermoelectromechanical characteristics is studied in the case of forced vibrations at the first resonance

Dissipative Heating of a Viscoelastic Cylinder under a Load Steadily Moving over Its Surface

The Fourier method is used to find the analytical solutions to two-dimensional quasistatic problems of stationary polyharmonic vibrations and dissipative heating of a linearly viscoelastic cylinder. The influence of the cylinder thickness and the width of the loading area on the thermomechanical state of the cylinder is studied based on numerical data

G211 射出成形における加熱シリンダ内現象の計測と実験解析(基調講演,OS-13 材料加工における熱工学関連技術I)

Resin pellets are plasticated inside the heating cylinder not only by heat transfer from outer heaters but also by shear heating of a rotating screw. This paper introduces, from the viewpoint of heat transfer, the following important phenomena dominating the plasticating process of resins; (1) temperature distribution inside flowing melts at the nozzle and screw channels, (2) heat flux changes at the inner surface of the cylinder, (3) torque axial distributions along the inner surface of the cylinder. The break-up phenomenon of the solid-bed (solid unmelted resin pellets) is also described based on visualization results and correlation with the above-mentioned measurement results.

Heating effect on steady and unsteady horizontal laminar flow of air past a circular cylinder

Extensive numerical experiments were carried out to study the effect of cylinder heating on the characteristics of the flow and heat transfer in a two-dimensional horizontal laminar flow of air past a heated circular cylinder for the range of Reynolds numbers 0.001⩽Re⩽170. The fluid was treated as incompressible (density is independent of the pressure) while the variation of the fluid properties with temperature was taken into account. By including the transient density term of the continuity equation, which was neglected in a previous study by Lange, Durst, and Breuer [Int. J. Heat Mass Transfer 41, 3409 (1998)], we were able to predict correctly the vortex shedding frequency at various overheat ratios using an incompressible flow solver. The effect of dynamic viscosity and density variations on the flow dynamics occurring with the cylinder heating was analyzed separately. Another emphasis of the work was to investigate the physical mechanism behind the “effective Reynolds number” concept widely applied in engineering correlations. Similarity was discovered for the distribution of the local dimensionless viscous force, the vorticity and the Nusselt number at the cylinder surface and the pressure force in the rear part of the cylinder. Two characteristic temperatures, Teff=T∞+0.28(TW−T∞) for the flow dynamics and Tf=T∞+0.5(TW−T∞) for the heat transfer, were identified.

403 加熱と回転が同時に作用する二重円筒容器内流体の温度場と流れの可視化(応用熱工学(熱移動))

403 加熱と回転が同時に作用する二重円筒容器内流体の温度場と流れの可視化(応用熱工学(熱移動))

Extension of the hot wire method to the characterization of stratified soils with multiple temperature analysis

The aim of this article is to develop a practical device able to estimate a thermal conductivity profile in stratified media such as burned soils in Chile. The classical hot wire method consists of measuring the temperature response of a heat step imposed on a thin cylindrical probe by Joule effect. The main characteristic of the extension of the method consists of analyzing the two-dimensional temperature response of multiple thermocouples equally spaced along the heating cylinder. A semianalytical method (quadrupole method) is then implemented in order to obtain a transfer matrix between the heat flux excitation and the temperature response vectors. Such method is suitable to obtain asymptotic expansions in order to investigate the sensitivity analysis and the estimation strategy. A complete two-dimensional model is used in order to define a time window in which the one-dimensional radial heat transfer assumption is valid. Some experiments and estimation results are presented in a case where the characteristic diffusion times in the radial direction are small compared to the inter-layers diffusion time.

Boiling incipience of highly wetting liquids in horizontal confined space

This study concerns boiling incipience of highly wetting liquids ( n-pentane), in transient conditions, in horizontal confined space between a vertical heating cylinder and a disk. The two controlled parameters were the heat flux, ranging from 50 to 200 kW m −2 and the thickness of the liquid in the confined space, ranging from 0 to 240 μm. Experiments were conducted with both smooth and porous disks. The results suggest that in the porous-disk configuration, boiling could appear on the non-heated wall.

Preliminary validation of a numerical code for heat transfer simulations

A great number of heat transfer problems can be treated as transient heat transport phenomena within a body, often semi-infinite or symmetric in some directions, and in these cases a one-dimensional treatise is enough. Dielectric/microwave heating of cylinder and fast cooling of thin slabs are common examples.