Inverse problem of estimating the heat flux at the roller/workpiece interface during a rolling process

In this study, an inverse algorithm based on the conjugate gradient method and the discrepancy principle is applied to estimate the unknown space-dependent heat flux at the roller/workpiece interface during rolling process from the knowledge of temperature measurements taken within the roller. It is assumed that no prior information is available on the functional form of the unknown heat flux; hence the procedure is classified as the function estimation in inverse calculation. The temperature data obtained from the direct problem are used to simulate the temperature measurements, and the effect of the errors in these measurements upon the precision of the estimated results is also considered. The results show that an excellent estimation on the space-dependent heat flux can be obtained for the test cases considered in this study.     

Molecular dynamics calculation of heat dissipation during sliding friction

A novel method of calculation of heat dissipation during sliding between metals was presented by using molecular dynamics. Temperature distribution in the regions near the contact interface was calculated. The calculation results show that plastic deformation in the near-surface regions accounts for most of the friction heat and the temperature increase. Friction heat was built up in the regions subject to plastic deformation. In the case that no plastic deformation occurred, elastic waves contributed mainly to the energy dissipation so that no large heat buildup could take place in the vicinity of the contact regions.     

Modelling the heat and mass transfer analysis during oil-frying of cylindrical sausages

An analytical and experimental study was performed on the analysis of the heat and mass transfer within cylindrically shaped sausages during deep-oil frying. Experiments were conducted to determine temperature distribution at the centre of an individual sample and the changes in the weight, moisture and oil contents of the samples. The proposed approach was used to estimate these parameters theoretically. Good agreement was found between the experimental and theoretical results. The results of this study indicates that the proposed approach is capable of analysing the heat and mass transfer during frying of the cylindrical sample.     

In-situ determination of the heat flux density at the glass/mould interface during a glass pressing production cycle

The glass pressing process involves heat transfer between the glass gob and the forming tool which are among the most important parameters influencing the thermo-mechanical stresses in the moulds. The present paper presents the development of the instrumentation of a mould for the measurement of temperatures during the production cycle. These measurements are exploited with an inverse method to evaluate the heat flux densities at the working surface of the mould. The influence of each process stage and of the location at the surface of the mould on the thermal loadings are described. The evaluated heat flux densities are used as boundary conditions in a finite element calculation. The validity of these results are discussed taking into account the differences between experiment and calculation, the hypothesis of the inverse method and the time response of the thermocouples.     

蒸汽直接加热冷水的汽液界面压力振荡特性仿真研究

为探究蒸汽直接加热冷水过程中汽液界面瞬态压力振荡及两相流动特性,选用基于热平衡原理的凝结模型、大涡模拟湍流模型和流体体积分数多相流模型,对管道内蒸汽直接加热冷水过程进行了数值模拟,并将数值模拟获取的压力振荡与实验值进行了对比分析。结果表明,数值模拟获取的压力振荡时域特征与实验测量值吻合较好,汽液界面呈现显著的瞬态压力梯度波动,界面压力波动导致附近冷水流场结构发生瞬态剧烈变化。     

Radiative heat transfer during turbulent combustion process

We investigate the radiative heat transfer in a co-flowing turbulent nonpremixed propane-air flame inside a three-dimensional cylindrical combustion chamber. The radiation from the luminous flame, which is due to the appearance of soot particles in the flame, is studied here, through the balance equation of radiative transfer which is solved by the Discrete Ordinates Method (DOM) coupling with a Large Eddy Simulation (LES) of the flow, temperature, combustion species and soot formation. The effect of scattering is ignored as it is found that the absorption dominates the radiating medium. Assessments of the various orders of DOM are also made and we find that the results of the incident radiation predicted by the higher order approximations of the DOM are in good agreement.     

Numerical simulation of conjugate heat and mass transfer process within cylindrical porous media with cylindrical dielectric cores in microwave freeze-drying

This paper presents a numerical model for the process of microwave freeze-drying within a cylindrical porous media with cylindrical dielectric cores. The set of transient governing equations developed are solved numerically with variable time-step finite volume method. Analysis of numerical results may lead to following main conclusions for the new freeze-drying process: (1) Proper usage of cylindrical dielectric cores could dramatically reduce the drying time. (2) The loss factor ε″ of the cylindrical dielectric core is an important parameter influencing the drying behavior. (3) Two sublimation fronts do exist within the porous media due to the existence of inner dielectric cores. (4) The impact of cylindrical dielectric cores on drying could not be ignored even though the initial saturation is low (S₀ = 0.2).     

Dimensionless temperatures at the wall of an infinitely long,variable-rate,cylindrical heat source

In geothermal applications the thermal conductivity of rocks is needed, for example, to determine terrestrial heat flow, to evaluate heat losses to the surrounding formations in wells and to design borehole heat exchangers. Cylindrical probes (heaters) with a constant heat flow rate are used in boreholes or in the laboratory to obtain the thermal conductivity of formations and of cementing systems in geothermal wells. A new technique to calculate the temperature at the wall of an infinitely long, cylindrical, time-dependent heat source is presented.     

Evaluation of thermal rectification at the interface of dissimilar solids by phonon heat transfer

Many investigations have suggested that the heat transfer coefficient at the interface between two dissimilar solids depends on the direction of heat flow across the interface. Although many factors that affect heat transfer across the interface are reasonably well understood, the directional dependence of the heat transfer coefficient, called thermal rectification, has not yet been completely explained. In this paper, we evaluate the thermal rectification from the results of linear response theory by considering scattering and transmission of phonons across the interface, which expresses the dependence of the temperature at the interface. This model explains the reported behavior of thermal rectification. © 2001 Scripta Technica, Heat Trans Asian Res, 30(2):164–173, 2001     

Analysis of flow and heat transfer at the interface region of a porous medium

Fluid flow and heat transfer at the interface region are analyzed in depth for three general and fundamental classes of problems in porous media. These are the interface region between two different porous media, the interface region between a fluid region and a porous medium, and the interface region between an impermeable medium and a porous medium. These three types of interface zones constitute a complete investigation of the interface interactions in a saturated porous medium. Detailed analytical solutions, for both the velocity and temperature distributions are derived for all of these interface conditions. The analytical temperature distributions are found in terms of confluent hypergeometric functions for two different regimes, which are found to cover almost the entire range of real fluids. The numerical and analytical results are found to be in excellent agreement. The numerical and analytical results are also checked against an empirically based hypothesis for one of the interface conditions, namely the interface between a fluid region and a porous medium, and are found to be in excellent agreement with that experimental hypothesis.     

A high temperature absorption heat pump as topping process for power generation

With a high temperature absorption heat pump as a topping device to the Rankine-water cycle, the efficiency for power generation may be improved by 40–50% above present values. A possible heat-pump process working with water as absorbent and CaO as absorber is discussed by using diagrams which are suited to study the combination of a heat pump with the Rankine cycle.     

Investigation of heat transfer characteristics of hydrogen combustion process in cylindrical combustors from microscale to mesoscale

In the field of micro and mesoscale combustion, the feature of flame-wall thermal coupling is of great significance because of its small scale nature. Thus, this work provides a comprehensive heat transfer analysis in cylindrical combustors from the perspective of numerical simulation. The combustor has a fixed length-to-diameter aspect ratio of 10, and the channel diameter is scaling up from 1 mm to 11 mm to explore the influence of chamber dimension on heat transfer and flame structure. The distribution of convective and radiative heat flux on inner surface, contribution of thermal radiation are given. Moreover, the role of radiation in flame structure is analyzed, and the convective and radiative heat losses are quantitatively analyzed. We find that radiative heat flux is smaller compared to convective heat flux, and the proportion of radiative heat flux becomes larger with an increasing diameter. Thermal radiation does not change the flame structure when the diameter is less than 3 mm. When the diameter is greater than 5 mm, thermal radiation changes the location of flame front. The heat loss becomes larger at a smaller diameter, and heat loss ratio can reach approximately 73.6% in the combustor with diameter of 1 mm.     

Dimensionless temperature at the wall of an infinite long cylindrical source with a constant heat flow rate

The differential diffusivity equation for an infinitely long cylindrical source with a constant heat flow rate in a homogeneous and isotropic medium has a solution in complex integral form. This integral cannot be expressed in terms of known functions. At present the temperature at the wall of the cylindrical source is determined by means of numerical integration techniques. However, in many cases the heat flow rate varies with time. In these cases the principle of superposition should be used, thus requiring an analytical solution for the constant heat flow rate case. In this paper we present a semi- analytical equation that can be used to approximate the transient dimensionless wall temperature. The accuracy of the equation proposed is also given.     

Macroscopic cylindrical governing equations: transport process in unsaturated porous media with a line heat source

The paper outlines a formulation of the cylindrical transport equations which describe simultaneous heat and mass transfer in unsaturated porous materials when a line heat resource is embedded in the medium. A macroscopic continuum mechanics approach is adopted to derive the coupled continuity, momentum and energy equations. Hydrodynamic law such as Darcy's law and Darcy–Buckingham theorem are utilized to simplify the continuity and momentum equations of fluid flow. Migration of liquid due to surface tension effects is modeled in the analysis. The effects of phase change on the heat transfer are also included in the energy equation. The constituent equations are expanded in the cylindrical co‐ordinate system. The resulting equations reported in this paper are found to agree with equations reported in this paper are found to agree with equations obtained by other researchers who used volume‐averaging techniques to study similar phenomena in unsaturated porous materials. Copyright © 1999 John Wiley & Sons, Ltd.     

Control of the boundary heat flux during the heating process of a solid material

In this paper we apply the conjugate gradient method to solve the inverse problem of determining a time-dependent boundary heat flux in order to achieve a given temperature distribution at the final time. The derivation of sensitivity and adjoint equations in conjunction with the conjugate gradient algorithm are given in detail. The zeroth-order Tikhonov regularization is introduced to stabilize the inverse solution. Solutions by finite differences are obtained for various heat flux profiles. It is found that the time-dependent heat flux may be predicted only for a non-dimensional time of the order of 0.1 while the control problem can be satisfactorily solved for an arbitrary period of time.     

Simulation of transient heat and mass transfer during hydrogen sorption in cylindrical metal hydride beds

A CFD analysis of heat and mass transfer in cylindrical metal hydride beds is carried out using the commercial code Fluent 6.2. The effect of bulk diffusion is considered for mass transfer in the solid phase. Temporal and spatial variations of temperature and concentration in hydride bed are plotted. Emphasis is given to monitor the motion of hydrogen within the bed and to the influence of the L/D$L/D$ ratio and porosity. It is observed that a concentration variation in the bed is the driving force for hydrogen flow in hydride beds. The gas movement is observed to be from saturated cooler peripheral region towards the unsaturated hotter core region of the bed.     

褐煤干燥过程对流传热特性的数值模拟

以干燥器内对流传热问题为研究对象,建立了褐煤干燥过程气-固对流传热模型。通过流-固界面传热耦合,利用CFD仿真技术进行模拟,对褐煤在不同粒径、风速及温度下的干燥过程进行了数值模拟,得到不同工况下的温度场分布及对流传热系数。根据模拟结果拟合得到气-固传热关联式,结果表明该关联式与褐煤干燥过程较吻合,可为工程实践提供理论指导。     

Transient boiling heat transfer performances of subcooled water during quenching process

Transient boiling of subcooled water on a vertical flat surface during quenching process was visually observed using high-speed photography technology and analyzed by special boiling heat transfer models. After the quenching process began, the nucleation was initiated within a short time, and then followed by the outbreak transition boiling with extremely unstable bubbles and sharp heat flux increment which lasted only for about 1 s. According to the boiling curves, the nucleate boiling should be divided into two stages including the stable nucleate boiling and transition nucleate boiling with the effects of initial conditions. The outbreak transition boiling was first studied by special boiling curve corresponding to the temperature decrement, and was further analyzed using a theoretical model based on the combination of the boiling heat flux evolution and lumped parameter assumption. The results showed that the boiling curve of outbreak transition boiling predicted by the theoretical model had a good agreement with experimental data and the heat flux almost had linear relation with the square root of temperature decrement.