Модель роста загрязнения на поверхности пластинчатых теплообменников

Представлено соотношение для расчета образования отложений на поверхности теплопередачи пластинчатых теплообменников. Предложенная зависимость учитывает влияние концентрации загрязнителя, скорости движения раствора, температуры стенки, давления и параметров пластин, на интенсивность появления и роста отложений. Применение зависимости позволит прогнозировать время работы аппарата между остановками на чистку.The relation for deposit formed on heat transfer surface of plate heat exchanger calculations is considered. The dependence which accounted of influence of pollutant concentration, rate solution, wall temperature, pressure and plates parameters to intensity of foiling appear and growth is proposed. The dependence used permit to predicted time of unit operation between cleaning

Numerical Simulation of the Fouling on Structured Heat Transfer Surfaces (Fouling)

The objective of this work is to make a contribution to a good and fast prediction of the crystal growth on flat and structured heat transfer surfaces. For the numerical simulation the CFD code Fluent is used. The simulation enables an unsteady calculation of the fouling process and a realistic description of the temporal modification of the flow and temperature fields due to the continuous crystal growth. The numerical simulation of the crystal growth is based on models for the calculation of the deposition (Krause, 1993) and removal (Bohnet, 1990) mass rates. Based on experimental results of Hirsch (Bohnet et. al., 1999), a model was developed which enables the calculation of the density of the fouling layer not only as a function of the local position within the fouling layer, but also as a function of the time-dependent total thickness of the fouling layer. In addition a model was developed, that enables a realistic distribution of the heat flux along the heat transfer surface during the simulation. All models are implemented into the simulation with the help of the programming user interface of the CFD code. During the experimental and numerical investigations the operating parameters like flow rate, surface temperature, concentration of the salt solution and geometry of the flow channel are varied. The induction period and the effects of aging which occur with almost all fouling processes are not considered. Result of the numerical simulation is the prediction of the fouling resistance as function of time. In view of the complexity of the fouling process during the incrustation of heat transfer surfaces and the fact that not all influences from the used models could be considered the agreement between calculated and experimentally obtained data is satisfactory

On the effect of thermodiffusion on solute segregation during the growth of semiconductor materials by the vertical Bridgman method

The effect of thermodiffusion on dopant distribution in the melt and in the grown crystal is investigated numerically for a vertical Bridgman configuration for situations of pure thermal convection corresponding to dilute alloys. The dopant distribution is shown to be significantly affected by the Soret parameter value. The sensitivity of the system to a variety of parameters, including the Grashof number and the so-called furnace residence time, i.e. the time during which the crucible is maintained in the furnace before initiating the solidification process, is assessed by means of parametric simulations. Moreover, the results indicate that variations in the sign of the Soret parameter can lead to diametrically opposite behaviours, while an increase in the intensity of the thermal convection generally leads to a mitigation of the effects induced by thermodiffusion. On the basis of the numerical results some useful criteria are drawn which could help crystal growers to discern the complex interrelations among the various parameters under one’s control (that are not independent of one another) and to elaborate rational guidelines relating to strategies to be used to improve the quality of the resulting crystals

Large-Scale Numerical Modeling of Melt and Solution Crystal Growth

We present an overview of mathematical models and their large-scale numerical solution for simulating different phenomena and scales in melt and solution crystal growth. Samples of both classical analyses and state-of-the-art computations are presented. It is argued that the fundamental multi-scale nature of crystal growth precludes any one approach for modeling, rather successful crystal growth modeling relies on an artful blend of rigor and practicality

Small business innovation research. Abstracts of 1988 phase 1 awards

Non-proprietary proposal abstracts of Phase 1 Small Business Innovation Research (SBIR) projects supported by NASA are presented. Projects in the fields of aeronautical propulsion, aerodynamics, acoustics, aircraft systems, materials and structures, teleoperators and robots, computer sciences, information systems, data processing, spacecraft propulsion, bioastronautics, satellite communication, and space processing are covered

Chemical vapor deposition fluid flow simulation modelling tool

Accurate numerical simulation of chemical vapor deposition (CVD) processes requires a general purpose computational fluid dynamics package combined with specialized capabilities for high temperature chemistry. In this report, we describe the implementation of these specialized capabilities in the spectral element code NEKTON. The thermal expansion of the gases involved is shown to be accurately approximated by the low Mach number perturbation expansion of the incompressible Navier-Stokes equations. The radiative heat transfer between multiple interacting radiating surfaces is shown to be tractable using the method of Gebhart. The disparate rates of reaction and diffusion in CVD processes are calculated via a point-implicit time integration scheme. We demonstrate the use above capabilities on prototypical CVD applications