Thermal Transfer Model Research Articles

Modelling of the gas to fuel droplets radiative exchange

The results of the implementation of the thermal radiation transfer model into the commercial computational fluid dynamics (CFD) code VECTIS of Ricardo Consulting Engineers and its application to modelling the fuel droplets radiative exchange with gas in a Diesel engine cylinder are reported. The P-1 model with Marshak boundary conditions at the droplets’ surfaces is shown to be the most suitable for modelling the thermal radiation transfer in a Diesel engine where the contribution of soot allows the combustible charge to be approximated as an optically thick medium. The results of the implementation of this model were tested for the idealised case where droplet evaporation and burning are ignored, and the gas temperature is kept constant. In this case the equation for droplet heating in gaseous media, taking into account the effects of convection and thermal radiation, is resolved analytically and numerically (based on the VECTIS CFD code). Analytical results are obtained in two limiting cases where the effects of radiation dominate over or are dominated by the effects of convection. Possible time dependence of gas temperature, radiation temperature, and/or convective heat transfer coefficient is accounted for. Solutions obtained for spherical droplets are generalized for the case of droplets having the forms of prolate and oblate spheroids. Good agreement between the analytical and numerical results endorses the approximations on which the analytical solutions are based and the VECTIS numerical results. It is shown that thermal radiation noticeably accelerates the droplet evaporation, which is reflected in a more rapid decrease in the droplet diameter when compared to the case, when thermal radiation is ignored. The asymptotic values of droplet surface temperature are shown to be independent of thermal radiation.

Geometry Modeling and Control by Infrared and Laser Sensing in Thermal Manufacturing with Material Deposition

A lumped-parameter, analytical model of material and thermal transfer is established in this paper for metal deposition by a moving, concentrated source. This is a dynamic description of the distinct width, height, length, and temperature of the ellipsoidal molten puddle, expressed with respect to the torch power, material feed and angle, and the source motion. This is established through scalar mass, momentum and energy balances of the puddle control volume, and thermal conduction in the substrate. The model is validated by GMA welding experiments, through measurements by an infrared camera and a laser profilometry scanner. These sensors are next employed for real-time identification of the model efficiency parameters, and for output feedback in a closed-loop geometry control system. Because of sensor delays, the model is run in-process to provide substitute estimates to the controller in a Smith predictor scheme. Closed-loop testing was conducted for control of the bead cross section profile through the torch velocity, and the applicability of such geometry regulation to solid freeform fabrication is discussed.

Analysis of the load loss by the Monte Carlo Method

We usually use the Finite Element method (FEM) to calculate the load loss at the outer vessel of super conducting coil. There is also a method called the Monte Carlo method (MCM) to analyze thermal transfer models. Methods to use random numbers for calculation are generically called the MCM. For instance, we use the MCM for thermal transfer analysis quickly out put the temperature at one point.In this paper, we use the MCM to calculate the temperature of outer vessel of super conducting coil and linear generator coils for the maglev system. We also measure the temperature of these equipment items at bench tests by a simple wind tunnel. The results of MCM are found to be consistent with those bench tests and analysis.

Heat transfer and oxygen diffusion in Ag-clad BSCCO superconducting tapes

The quality of Ag-clad BSCCO superconducting tapes is a function of their processing conditions. Two important processing parameters are the cooling rate from the annealing condition, and the oxygen partial pressure in the furnace. Although a link between oxygen content and critical current density has been established, apparently no attempts have been made to predict the temperature and oxygen content distributions within a Ag-clad BSSCO tape. This study presents a combined thermal and mass transfer model which enables the calculation of the oxygen content distribution, and the results indicate a slow cooling rate, and relatively high oxygen partial pressure, leading to a greater and more uniform oxygen concentration within the tape, and thus potentially superior superconducting properties.

On derivation of a thermal transfer model of a thermostat housing a heat source with several watts

This article presents a trial for deriving a thermal transfer model of a thermostat housing a heat source generating several watts and achieving high temperature stabilization. It is intended for investigating the open-loop linearity of operational amplifiers labeled as high precision or low noise and their noise characteristics. This thermostat is built up with a double-jacket constructed with a copper plate of 10 mm thickness and an approach of deriving a lumped parameter model to each jacket on the temperature control is presented. The temperature stability of the order of 3×10−5°C per 1°C temperature change in the air outside in 1 h is realized in the inner jacket. The linearity is measurable and it is clarified that amplifiers are classified into three groups.

プリント基板用ＧＦＲＰのレーザ加工面の品質に関する研究 穴あけ加工時の被削材内部の温度分布と損傷

This paper describes the relation between the temperature and the damage at the hole wall of GFRP for printed wiring board in laser drilling. First, the temperature is measured by a thermocouple at various positions on the drilled hole wall in laser drilling. Secondly, the width of damage is observed by an optical microscope and SEM after laser drilling. The temperature at thermal damage is clarified by comparing these results. Finally, the thermal transfer model paying attention to the thermal properties of glass fiber is proposed for the laser drilling. From these experimental and calculated results, the practical formula is derived in order to predict the damage width.

Simplified analytical model for thermal transfer in vertical hollow brick

A modern building envelope has a lot of little cavities. Most of them are vertical with a high height to thickness ratio. We present here the conception of a software to determine heat transfer through terra-cotta bricks full of large vertical cavities. After a bibliographic study on convective heat transfer in such cavities, we made an analytical model based on Karman-Polhausen's method for convection and on the radiosity method for radiative heat transfer. We used a test apparatus of a single cavity to determine the temperature field inside the cavity. Using these experimental results, we showed that the exchange was two-dimensional. We also realised heat flux measurements. Then we expose our theoretical study: we propose relations between central core temperatures and active face temperatures, then between outside and inside active face temperatures. We calculate convective superficial heat transfer because we noticed we have boundary layers along the active faces. We realise a heat flux balance between convective plus radiative heat transfer and conductive heat transfer, so we propose an algorithm to calculate global heat transfer through a single cavity. Finally, we extend our model to a whole hollow brick with lined-up cavities and propose an algorithm to calculate heat flux and thermal resistance with a good accuracy (≈ 7.5%) compared to previous experimental results.

The P-1 model for thermal radiation transfer: advantages and limitations

The P-1 model for thermal radiation transfer: advantages and limitations

The P-1 model for thermal radiation transfer: advantages and limitations

The P-1 model for thermal radiation transfer is re-examined in view of its potential applications to industrial problems as part of a computational fluid dynamics (CFD) analysis. The concept of radiation temperature adopted is shown to be particularly useful when this model is used in a general curvilinear coordinate system. An explanation is given as to why the P-1 model gives reliable predictions in the case of 1D plane geometry in both optically thin and optically thick media, while it overestimates the radiation heat fluxes from localized heat sources in optically thin media. It is pointed out that the P-1 model is particularly useful for accounting for the radiative exchange between gas and particles. The results of modelling of coal combustion processes in an industrial furnace based on the P-1 model are shown to be consistent with experimental observations.

Dye Diffusion Thermal Transfer Model Including Partition Coefficients in Dye Diffusion Thermal Transfer Printing.

A two-dimensional finite-element model for dye diffusion thermal transfer printing has been developed, in which partition coefficients are included. Experimental data of the partition coefficients and the dye diffusion coefficients are used in the model. Dye concentration after printing is not always continuous at the interface between the dye-coated layer and receiver-coated layer in the model. The stability of the computer calculation has been checked from various points of view. The optical density prediction shows good agreement with the experiments. The model has been applied to the calculation of the amount of transferred dye when the physical parameters of the medium are varied. It is concluded that the most important factors for increasing the amount are the dye diffusion coefficients and the partition coefficients.

Effect of inclination on the performance of CPC solar energy collectors

A theoretical numerical model of thermal transfer in a line-axis, symmetric, compound parabolic concentrating solar energy collector (CPC) is presented. The effect of the angle of axial inclination of an east-west aligned CPC and hence the effect of the latitudinal and tracking configuration of the CPC system on performance is investigated. The angle of inclination is taken into consideration in the determination of both internal and external convective heat transfer. The convective, radiative, conductive and overall heat transfer coefficients and system efficiency for various angles of inclination, concentration ratios and insolations was determined, and are presented as graphs of heat transfer variation and Hottel-Whillier-Bliss characteristic curves respectively.

皮膚／木質材料界面における熱挙動のシミュレーション

This paper deals with the simulation of thermal behavior at a boundary between skin and woody materials when the woody materials laid over a cement mortar block are in contact with a man's palm. Plywoods, MDF (medium density fiberboards), and cork boards with different thickness were used as the overlays. Changes in temperature at the skin-overlay-underlayment interfaces were measured with thermo-couples at 10 to 30sec intervals. Furthermore, a thermal transfer model based on a numerical method with finite differences was proposed to analyze the changes in temperature and rate of heat transfer at the interfaces. Thermal constants for the model were obtained by fitting them with the experimental values. Then the changes in temperature and rate of heat transfer were simulated by this model for various overlay materials having different thickness. Not only the model is able to obtain the thermal behavior at the interfaces in good agreement with the experimental results on the samples of various woody materials, but also it is valuable to estimate the sensory warmth felt by man's palm in contact with the surface of the overlays, since both the temperature at the skin surface and the heat transfer across the boundary are highly related with the sensory warmth.

A Model of Thermal Transfer in Czochralski Silicon Molten

Simultaneous multipoint measurement has been performed to determine the temperature of silicon molten of a Czochralski (CZ) system during the growth of a monocrystalline ingot. A high magnitude of temperature fluctuation was found to be totally random without correlation among temperatures of various points in the molten, a phenomenon which could not be explained by models based on a lamina flow. The magnituge of the fluctuation, however, was observed to be related with effective thermal transfer of the molten. A model which took account of thermal transfer induced by local dynamical random motion, a kind of turbulence, of the molten was proposed. The time-averaged temperature distribution taken from the solution of a static diffusion equation with the effective thermal diffusivity agreed very well with the experimental results.

Three-dimensional numerical modelling of thermal transfer through the vittel aquifer (Vosges, France), including approximated topographical effects : Danis, M; Quintard, M Geophys JV96, N2, Feb 1989, P343–351

Three-dimensional numerical modelling of thermal transfer through the vittel aquifer (Vosges, France), including approximated topographical effects : Danis, M; Quintard, M Geophys JV96, N2, Feb 1989, P343–351

Three-dimensional numerical modelling of thermal transfer through the Vittel aquifer (Vosges, France), including approximated topographical effects

SUMMARY A geothermal and hydrochemical anomaly was observed in the Lower Triassic sandstone aquifer in the Vittel region (Vosges, France). This anomaly was attributed to a hydrothermal spring under sedimentary cover. In order to localize the hot spring and to quantify more precisely its flow rate and temperature, it is necessary to consider the 3-D thermal problem by taking into account the complex geometry of the domain and the flow rate in the aquifer. A 3-D numerical model of thermal conductive and forced convective transfer, developed for hydrological problems including approximate geometrical and topographical effects, is used which (i) can be directly applied to geologic strata (aquifers) with varying thickness and top and base slope; and (ii) allows calculation of heat flux anomalies associated with fluid flow in such geologically realistic aquifers. The heat transfer equation is formulated in an orthogonal curvilinear coordinate system. As most geometries dealing with geothermal phenomena in sedimentary basins are nearly horizontal, this formulation can be simplified, leading readily to numerical solution with a finite difference method. The application of the 3-D model to the Vittel aquifer gives temperature results in agreement with measurements. These results provide evidence for the importance of associated forced convection and topographical effects for ground temperature distribution, and show clearly that heat flow in many basins is interpretable only if careful hydrological and thermal studies are made.

A Numerical Study of a Marine Subtropical Stratus Cloud Layer and its Stability

A model for numerical simulation of stratus cloud layers is constructed by combining a second-order closure, turbulent transfer model with a thermal radiative transfer model. The turbulent transfer model allows water vapor saturation. The combined turbulence-radiation model is applied to both a horizontally uniform one-dimensional case and a horizontally nonuniform two-dimensional case. In the latter, the dynamics of mesoscale circulations are also incorporated. Results of the two-dimensional simulation show that the layer cloud instability occurs where the sea surface temperature is high and the large-scale subsidence is weak. The simulated instability is analyzed in view of an instability criterion, the eddy kinetic energy budget, and evaporative cooling near the cloud top.