Temperature profiles, modeling melt

Measured and calculated temperature profiles under melting lake ice, illustrates that large amounts of heat can be stored in the water beneath the ice before break-up. Fig. 2. This indicates that the molecular sub-layers below the ice interface are important, a fact that implies that wall functions need to be introduced in the turbulence modelling. 

Figure 8. X-Z direction temperature profile (model with melt rotation apparatus)...

It is instructive to examine predictions of the Bunimovich et al. model. The temperature profiles in Fig. 16a at times within a half cycle are about the same as the profiles for 6 vol% S02 predicted by Xiao and Yuan (1996) and shown in Fig. 14a. Note that curves 1 and 5 in Fig. 16 are those at the switching time and show the inversion when the flow direction changes. The remarkable prediction of the Table XI model is the sharp variation of the S03 concentration in the melt with position in the bed that develops about 1 min after the direction changes and persists for about 13 min. Curves (c) to (f) show there is a substantial change in the complexes present in the melt with position in the bed and that the complex concentrations... 

Power law model fluid with temperature dependent viscosity m0 = e( a(-T Tm The rate of melting is strongly dependent on the shear thinning behavior and the temperature dependent viscosity of the polymer melt. However, we can simplify the problem significantly by assuming that the viscous dissipation is low enough that the temperature profile used to compute the viscosity is linear, i.e.,... 

Fig. 9.32 A differential volume element perpendicular to the melt film-solid bed interface. Schematic view of temperature profile in the film and solid bed shown at right. Schematic views of velocity profiles (isothermal model) in the x and z directions are also shown.

Fig. 10.48 Numerical simulation results of nonisothermal flow of HDPE, Melt Flow Index MFI = 0.1 melt obeying the Carreau-Yagoda model for a typical FCM model wedge of e/h — 3 and =15. (a) Velocity (b) shear rate and (c) temperature profiles [Reprinted by permission from E. L. Canedo and L. N. Valsamis, Non Newtonian and Non-isothermal Flow between Non-parallel Plate - Applications to Mixer Design, SPE ANTEC Tech. Papers, 36, 164 (1990).]...

Ice surfaces at temperatures close to melting are often said to have a liquidlike layer at the contact with a vacuum [14]. (Fig. 4 above shows that for the SPC/E model at least, this is an over-simplification thee are several different non-ice-like layers at the vacuum.) Therefore it is interesting to study how the Na+ and Cl- ions behave at the ice/vacuum interface. The ions were initially placed at z = 15 A in the MD box, i. e., approximately at the distance of 2 A from the surface. We then allowed the ions to approach the interface over a period of 20 ps, and only after that started the production runs. In order to characterize the location of solute ions with respect to the surface, we introduced a single-ion density profile accumulated over a certain time window. We have found that such single-ion density profiles for cases such as our system, being accumulated over the time of 60 ps, have the width of ss 2 A... 

The simplest way to derive thermodynamic parameters from UV melting data is to apply a van t Hoff analysis of the data by assuming a two-state model (i.e. native and denatured states) and that the difference in heat capacities of the native and denatured states, ACp°, is zero (13-16) (more complex models are described in Section 5). At each temperature the absorbance can be used to calculate the fraction of strands in the native and denatured states, thereby allowing the calculation of an equilibrium constant (10). Thus, the absorbance versus temperature profile is used to determine the temperature dependence of... 

Fig. 8. Comparison of model calculations of diameter attentuation, birefringence, and temperature profiles with pilot plant data for melt spinning of 0.65 IV poly(ethylene ter-phthalate) at a take-up speed of 5947 m/min. Reproduced from Ref. 33. Courtesy of the Society of Rheology.

The heart of any melter simulation will be an engineering model (Figure 21.1). This focuses on the fluid dynamics behavior of a vitrification melt. Simulations of the thermal and mass transport within the melter present a quantitative picture of the dynamic temperature profile of the glass. The boundary conditions arising in these computational fluid dynamics (CFD) simulations act as an input to finite element (FE) simulations of material stresses developed within the melter material— which in turn can be used to advise on how to input heat to the melt and melter to reduce the thermal gradients that cause stress. 

Our purpose in this paper is to develop an integrated model of intermeshing counter-rotating twin screw extruders which includes solid conveying, melting, and melt metering. We seek to predict positions and extent of fill, pressure and temperature profiles as well as... 

This paper presents a simplified model for calculating the flow and temperature in laser transmission welding. The model was compiled on the basis of finite element analysis (FEA) and permits the comprehensive simulation of the process variants of contour welding, quasi-simultaneous welding and simultaneous welding. The model makes allowance for both the influence of the mechanical and thermal loading on the residual melt layer thickness and the temperature profiles in the joining seam. 

One of the common problems associated with underwater pelletizers is the tendency of the die holes to freeze off. This results in nonuniform polymer melt flow, increased pressure drop, and irregular extrudate shape. A detailed engineering analysis of pelletizers is performed which accounts for the complex interaction between the fluid mechanics and heat transfer processes in a single die hole. The pelletizer model is solved numerically to obtain velocity, temperature, and pressure profiles. Effect of operating conditions, and polymer rheology on die performance is evaluated and discussed. 

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