Heat and fluid flow in a scraped-surface heat exchanger containing a fluid with temperature-dependent viscosity

Scraped-surface heat exchangers (SSHEs) are extensively used in a wide variety of industrial settings where the continuous processing of fluids and fluid-like materials is involved. The steady non-isothermal flow of a Newtonian fluid with temperature-dependent viscosity in a narrow-gap SSHE when a constant temperature difference is imposed across the gap between the rotor and the stator is investigated. The mathematical model is formulated and the exact analytical solutions for the heat and fluid flow of a fluid with a general dependence of viscosity on temperature for a general blade shape are obtained. These solutions are then presented for the specific case of an exponential dependence of viscosity on temperature. Asymptotic methods are employed to investigate the behaviour of the solutions in several special limiting geometries and in the limits of weak and strong thermoviscosity. In particular, in the limit of strong thermoviscosity (i.e., strong heating or cooling and/or strong dependence of viscosity on temperature) the transverse and axial velocities become uniform in the bulk of the flow with boundary layers forming either just below the blade and just below the stationary upper wall or just above the blade and just above the moving lower wall. Results are presented for the most realistic case of a linear blade which illustrate the effect of varying the thermoviscosity of the fluid and the geometry of the SSHE on the flow

Modelling credit spreads with time volatility, skewness, and kurtosis

This paper seeks to identify the macroeconomic and financial factors that drive credit spreads on bond indices in the US credit market. To overcome the idiosyncratic nature of credit spread data reflected in time varying volatility, skewness and thick tails, it proposes asymmetric GARCH models with alternative probability density functions. The results show that credit spread changes are mainly explained by the interest rate and interest rate volatility, the slope of the yield curve, stock market returns and volatility, the state of liquidity in the corporate bond market and, a heretofore overlooked variable, the foreign exchange rate. They also confirm that the asymmetric GARCH models and Student-t distributions are systematically superior to the conventional GARCH model and the normal distribution in in-sample and out-of-sample testing

Inversion formulas for Riemann-Liouville transform and its dual associated with singular partial differential operators

We define Riemann-Liouville transform ℛα and its dual tℛα associated with two singular partial differential operators. We establish some results of harmonic analysis for the Fourier transform connected with ℛα. Next, we prove inversion formulas for the operators ℛα, tℛα and a Plancherel theorem for tℛα

Inversion of the Riemann-Liouville operator and its dual using wavelets

We define and study the generalized continuous wavelet transform associated with the Riemann-Liouville operator that we use to express the new inversion formulas of the Riemann-Liouville operator and its dual

Influence of the Aminated Conditions on the pH Sensitivity of Silica and Amorphous Silicon Film

International audienceSilicon nitride has been widely used as a pH sensitive membrane of the ion sensitive field e#ect transistor (ISFET) thanks to the high reactivity of the SiNH2 sites to the H f ions. In this paper, we report experimental results on the H+ sensitivity of silica and amorphous silicon aminated films, obtained by the photo-CVD. We have studied the dependence of their response to pH as a function of the time and the temperature of amination of thejIm. The response of the aminatedjilms (silica and amorphous silicon) is quasi-Nernstian for amination exposure time higher than 1 min, deposited at temperature lower than 200°C. A theoretical model of deposition is presented. It can explain the influence of the deposition conditions. Published by Elsevier Science Limited

Epitaxial and polycrystalline growth of AlN by high temperature CVD: Experimental results and simulation

International audienc