A new continuous-flow recycle microwave reactor for homogeneous and heterogeneous chemical reactions

A new continuous-flow recycle microwave reactor suitable for organic synthesis has been developed to handle 0.51 quantities of reagents. The apparatus, which is designed for laboratory use, operates at atmospheric pressure in open- or closed-loop mode. It is fitted with a temperature control system. We describe this novel reactor and illustrate its efficiency with examples of organic syntheses carried out using both homogeneous and heterogeneous reactions.     

A Numerical and Experimental Study of Natural Convective Heat and Mass Transfer from a Vertical Porous Plate

A finite difference scheme for solving the problem of natural transport of heat, mass, momentum and species concentration along vertical porous plates is presented. Several drying related problems are numerically solved, by including a gas-injection boundary condition directly into the governing equations. The effect of variable physical properties is investigated by means of direct comparison against experimental data obtained through holographic interferometry. The relative importance of wall diffusive and convective fluxes is examined. Sherwood and Nusselt numbers can be accurately obtained by means of the proposed techniques.     

DEHYDRATION BY DESORPTION AND BY SPRAY DRYING OF DAIRY PROTEINS: INFLUENCE OF THE MINERAL ENVIRONMENT

A drying method by desorption in a water activity meter was used to simulate the conditions of spray drying and to determine the water transfer inside dairy concentrates towards the surface and from the surface to the drying air. The concentrates were also spray dried and solubility index of powders were determined during reconstitution. Whey protein concentrates (WPC) and native phosphocaseinate suspensions (NPCS) were used to study the effect of NaCl (420 mM), CaCl₂ (222 raM), sodium phosphate (173 mM) and sodium citrate (238 mM) on the water transfers. The decrease in water transfer during drying was explained by the high hygroscopicity of added mineral salts to WPC. NaCl addition to NPCS decreased the water transfer during drying, but increased the solubility index. Citrate and phosphate addition to NPCS increased the water transfer during drying and reconstitution. CaCl₂ increased the water transfer during drying but the solubility index was always low. Results are discussed as a function of the aqueous environment, of the nature of mineral salts, of the structure of dairy proteins and of protein solvation.     

Growth and characterization of undoped ZnSe epitaxial layers obtained by organometallic chemical vapour deposition

Epitaxial ZnSe layers have been grown on GaAs substrates by the metal alkyl hydride technique. First we describe the design of the reactor geometry necessary in order to obtain constant thickness layers. Then the influence of the experimental conditions (gas flows, vapour composition, temperature, substrate orientation) on the growth kinetics and on the crystalline and luminescent properties is described. The results obtained from this work allow us to determine the growth conditions, the different growth processes involved and the origin of contamination. After parameter optimization this method provides low temperature undoped ZnSe epilayers with the same luminescent properties as high purity bulk samples.     

Behaviour in reality

An International Energy Agency task-sharing project recorded some 500 separate measurements every 15 minutes over one year at an office building in Glasgow, Scotland, which has a central variable air volume (VAV) system with controlled air volume (CAV) perimeter heating. Air flow rates and supply temperatures to each space of this multizone building were found to vary significantly, primarily from warming of the VAV air supply from free-gains in the ceiling voids. The controllers did not function according to theory and the equipment did not operate within design limits. The implications for dynamic computational simulations are discussed by members of the Building Physics Laboratory, University of Liege, Belgium.     

Studies of column supported towers

As a result of a research and development programme into the civil engineering of cooling towers launched in 1978 by Electricité de France, very high cooling towers were built at Golfech and Chooz, in France, using column supports. This paper discusses the evolution of this new type of support from classical diagonal supports, presents some of the results of design calculations and survey measurements taken during construction of the shell and analyses the behaviour of the structure.     

On a simple triangular reissner/mindlin plate element based on incompatible modes and discrete constraints

In this paper the formulation of a new triangular element based on the Reissner/Mindlin plate theory is presented. The element has three nodes and three d.o.f. per node only. It is based on constant bending modes plus incompatible energy orthogonal higher order bending modes. The transverse shear effects are represented using the moment equilibrium and the constitutive equations. Discrete (collocation) shear constraints are considered on each side to relate the kinematical and the independent shear strains. The element has a proper rank, is completely locking free, passes all constant patch-tests exactly. The detailed numerical evaluation shows that the element, called DST-BK, is a robust and high-performance element for thick and thin plates.