Refrigerant charge reduction: On a new design optimization criterion for compact heat exchangers

With refrigerant charge reduction concern we introduce a new criterion, the so-called Ecological Cost (EC), and establish its relevance for HEXs design optimization. EC takes into account both entropy generation in the HEX and its refrigerant charge by the special environment cost values c and c’. EC minimization is conducted with given heat flux rate or given temperature difference. Results show that optimal design value depends on device life duration and on c/c’ Leakage effect can also be included in EC. We establish a link between EC and TEWI and show that optimal EC leads to optimal TEWI. We deal in the second part of this paper with volumes optimal allocation of cold and hot heat exchangers under given total volume or total refrigerant fluid mass constraint when assuming reversible cycle.     

Mi?bildungen beim Feldhasen und bei der Wachtel

Ohne Zusammenfassung     

Grain growth of silicon

In this paper we report on 2-D phase-field simulations in order to study the influence of the growth kinetics and the surface energy on the growth behaviour of grains during solidification of silicon. We investigated in detail the growth of two grains.     

An optimum plan of reliability control

The aim of this paper is to use the simulation of some stochastic processes combined with the stochastic approximation technique, to determine the optimum sequence of moments of time for the reliability control. It is shown that the obtained stochastic approximation control plan is adaptive.     

IR and UV laser-assisted deposition from titanium tetrachloride: A comparative study

Laser-induced TiCl₄ decomposition at vapour pressure was performed and comparative study of the composition and structure of thermally (at 10.6 μm) and photolytically (at 248 nm) deposited Ti-based films is presented. Emphasis was given to the less explored titanium deposition process by CO₂ laser pyrolysis of TiCl₄. The detailed structure of films deposited on quartz substrates was examined by scanning electron microscopy and X-ray photoelectron spectroscopy. The influence of the incident laser energy on the chemical content of the films as well as on the film growth rate was demonstrated. The results indicate that in the thermal IR decomposition of TiCl₄ a multilayer structure is formed with unsaturated TiSi_x at the interface and oxidized phases at the surface. The photolytic process leads to films with increased purity and a specific growth morphology.     

Some remarks on the use of isothermal thermogravimetric data for the evaluation of kinetic parameters. Applications for degradation of polymeric materials

A critical analysis of the isoconversional methods for evaluating kinetic parameters of decomposition of solids from isothermal thermogravimetric data is presented. An isoconversional integral method to evaluate the activation energy is suggested. This method allows removing the errors due the correction of the degradation time by subtracting the induction period to onset of the main reaction (also including the time required to heat the sample to the temperature at which the isotherm is recorded). This procedure was used to study the degradation of two series of polymeric materials, (a) poly(vinyl chloride)/acrilonitrile–butadiene–styrene (PVC/ABS) blends and (b) poly(vinyl chloride)/chlorinated poly(ethylene) (PVC/CPE) blends. The values obtained for the activation energy are in fairly good agreement with those obtained from the Prout–Tompkins model in case (a) and from nonisothermal data in case (b). © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 355–360, 2003     

Action of some organophosphonic compounds on a diglycidyl ether-bisphenol-A epoxy resin

The effect of three organophosphonic compounds on the thermooxidative degradation of the uncured diglycidyl ether-bisphenol-A epoxy resin was investigated, using infrared spectroscopy, thermogravimetry, differential thermogravimetry, static pyrolysis, pyrolysis-gas chromatography and elemental analysis. The results obtained indicate that additives with phosphorus and chlorine or nitrogen in molecules exercise an influence upon the degradative process of uncured resin by catalysing its decomposition in the lower temperature region. At the same time, the tested additives promote the formation of highly thermostable and non-flammable structures in the solid residue.     

Fractal image coding - achievements and prospects

Fractal image coding is a relatively new technique of lossy image compression which exploits the piecewise self-similarity existing in an image. In this paper we present a survey of the achievements in the field. We then focus our attention on a fundamental aspect of fractal coding - that concerning the nature of the transformations used in matching natural patterns. Through the analysis of a few models we try to suggest both the difficulties and the potential of this line of research.     

Freeze-drying of some strains of biotechnological interest (Aureobasidium pullulans)

Optimal freeze-drying conditions for Aureobasidium pullulans were investigated. Protective substances were used to compensate for the stress reported during freezing (gelatin, calf serum) and desiccation (saccharose, raffinose, trehalose), used in different combinations.