Search results for "Heat Transfer"
showing 10 items of 442 documents
Modelling of phase boundaries for large industrial FZ silicon crystal growth with the needle-eye technique
2003
In order to facilitate the numerical calculations of the phase boundaries in large industrial floating zone silicon crystal growth with the needle-eye technique, the chain of improved mathematical models is developed. The phase boundaries are solved in a partly transient way and the modelling improvements cover the open melting front, the inner triple point and the free melt surface. The view factors model is applied for the radiative heat transfer. The electromagnetic field is calculated with account of a multiple-slit inductor.
Analytical RF Pulse Heating Analysis for High Gradient Accelerating Structures
2021
The main aim of this work is to present a simple method, based on analytical expressions, for obtaining the temperature increase due to the Joule effect inside the metallic walls of an RF accelerating component. This technique relies on solving the 1-D heat-transfer equation for a thick wall, considering that the heat sources inside the wall are the ohmic losses produced by the RF electromagnetic fields penetrating the metal with finite electrical conductivity. Furthermore, it is discussed how the theoretical expressions of this method can be applied to obtain an approximation to the temperature increase in realistic 3-D RF accelerating structures, taking as an example the cavity of an RF e…
Influence of combined electromagnetic fields on the heat/mass transfer in the Bridgman process
2002
The influence of combined magnetic fields (travelling and rotating) on the characteristics of heat/mass transfer with an aim to obtain the needed profile of the interface is considered, that is a necessary condition, which insures the homogeneity of single crystal content. The crystallization process of a cylindrical sample is considered. It was presumed that the sample moves with a permanent velocity towards the cold part of the heater and a partial-linear temperature distribution characteristic to the Bridgman method was set in along the heater's length. Permanent temperature values were set in on the top and bottom edges of the calculation mesh. It has been shown that combinations of dif…
Numerical 2D modelling of turbulent melt flow in CZ system with dynamic magnetic fields
2004
Abstract The paper presents results of 2D axisymmetric mathematical modelling of laboratory CZ model facility that corresponds well to a large industrial silicon CZ growth system. The purpose of the investigation is to examine turbulent melt flow features that develop in the model crucible, when various dynamic magnetic fields (travelling, alternating) are applied, and to test the applicability of the modified low Re k–e turbulence model for the calculation of flows in these cases by extensive comparisons between calculated and measured data. The electromagnetic field is calculated with a self-developed program, and the calculations of the melt motion are carried out with the user modified …
K-ϵ-L model in turbulent superfluid helium
2020
We generalize the K−ϵ model of classical turbulence to superfluid helium. In a classical viscous fluid the phenomenological eddy viscosity characterizing the effects of turbulence depends on the turbulent kinetic energy K and the dissipation function ϵ, which are mainly related to the fluctuations of the velocity field and of its gradient. In superfluid helium, instead, we consider the necessary coefficients for describing the effects of classical and quantum turbulence, involving fluctuations of the velocity, the heat flux, and the vortex line density of the quantized vortex lines. By splitting the several fields into a time-average part and a fluctuating part, some expressions involving t…
Thermophysical-Property-Based Selection of Tool Protective Coatings for Dry Machining of Steels
2003
A method is proposed for determining the optimum cutting conditions in dry turning of carbon and stainless steels using multilayer coated tools for physical criteria such as the maximum temperature of a cutting tool or maximum heat flux. The modified thermal number describing the tool-chip behavior, is introduced. The correlation between the thermal number and the average tool-chip interface temperature and frictional heat flux is examined for both flat-faced and grooved rake configurations. Although not shown here directly, the thermal barrier effect observed for multilayer coatings with an intermediate Al2O3 layer increases the heat partition to the chip at substantially reduced cutting t…
Prediction of friction and heat flow in machining incorporating thermophysical properties of the coating–chip interface
2004
Abstract This paper deals with an experimental and analytical investigation into the thermodynamically activated effects influencing the behaviour of the multi-layered coated tool rake face during orthogonal cutting of ferromagnetic and paramagnetic steels. Temperature measurements on the tool rake face using a thermocouple-based technique and identification of the contact zone by means of computer image processing were carried out. New methodology for assessing friction and the amount of thermal energy generated when machining with a coated tool insert with natural and restricted contact coupled with a metallic chip, using thermophysical properties of the sliding materials is developed in …
Vegetation and soil – related parameters for computing solar radiation exchanges within green roofs: Are the available values adequate for an easy mo…
2016
Several studies analyze the thermal performance of vegetated roofs, presenting either mathematical models or experimental quantifications of heat transfer process through them, also showing the effect of vegetation and soil parameters on the thermal and energy performance of this type of roofing system. However, presently the level of availability of these parameters, has not been enough considered. This work intends to investigate this underestimated issue of the green roofs’ thermal modeling, through the consideration of the availability of parameters pertinent to the shortwave radiation exchange, which are adopted by models based on leaf area index (LAI) and on the fractional vegetation …
ALE Simulation of Orthogonal Cutting: a New Approach to Model Heat Transfer Phenomena at the Tool-Chip Interface
2007
This paper presents a new procedure to evaluate the global heat transfer coefficient in orthogonal cutting. The knowledge of the actual heat transfer conditions is a fundamental issue as far as the life, tool wear and tool substitution interval are regarded. More in detail, an Arbitrary Lagrangian-Eulerian approach was utilised to model orthogonal cutting process and the numerical simulations were validated by making experimental tests for identifying cutting forces and internal tool temperatures. A mild steel was cut utilising both an uncoated (WC) and a coated (TiN) tool. On the basis of both experimental and simulative data, a consistent model of the global heat transfer coefficient as f…
Numerical Modelling of Room Thermal Comfort Conditions
2006
Particular heat transfer coefficients of building elements gives quantitative notion only about heat losses through this building element. Analysis of the overall heat balance and heat losses of complete building and study of particular contribution of building elements in overall balance allows one to figure out the state of the building and find the building elements of bounding construction with most significant heat losses. Project variants of the buildings (or rebuilding in case of renovation), which ensure the desirable economy of energy and proportions of investments can be find varying the proportions of the surface area of building elements (e.g., windows and doors). A lot of facto…