ON THE DYNAMICS OF PERIODICALLY FORCED CHEMICAL REACTORS†

A method for studying the dynamics of periodically forced chemical reactors is presented along with the appropriate numerical techniques for its implementation. The method is capable of routinely treating many characteristics of forced oscillatory systems such as subharmonic and related bifurcations, bifurcations to invariant tori and frequency locking. It involves direct solution for the fixed points of the stroboscopic map. This procedure is particularly suitable for detecting certain routes to deterministic chaos such as the Feigenbaum period doubling cascade. Some illustrative examples from a homogeneous catalytic reactor model are included.     

THE INFLUENCE OF POROUS MEDIA ON THE FLOW OF POLYMER MELTS IN CAPILLARIES†

Porous media placed in the entrance of capillaries were found to reduce the pressure drop across the capillaries (?P_c) by a factor of two or three for polystyrene. The reduction in ?P_c was found to be a function of the distance of the porous media from the capillary entrance, the type of porous media, the length of the capillary, and the rheological properties of the polymer melt. No significant reduction in ?P_c was observed for a polymer melt such as polyethyleneterephthalate (PET) which is nearly devoid of memory. The apparent shear rate for the onset of melt fracture was extended by a factor of three when polystyrene passed through the porous media before entering the capillary. No significant difference in die swell values was observed with the use of porous media in the entrance of the capillaries. The mechanism which accounts for these phenomena is believed to be associated with the break up of the entanglement network in the porous medium which temporarily changes the rheological properties of the polymer melt.     

INFLUENCE OF CATALYST DEACTIVATION ON THE NATURE OF THE STEADY STATE SOLUTIONS FOR REACTIONS ON CATALYTIC SURFACES†

Densities of solutions of CaCl₂ in the mixtures of water and methanol have been measured at 25°C and the apparent molar volume of solute, φ_v, was calculated. Experimental concentration dependence of φ _v was compared with the coefficient S_v derived from the Debye-Hückel theory. The relation between φ_v — S_vc^1/2 and c is linear but the slopes changed from horizontal to gradually negative with increase of the methanol content in the solvents, showing that in addition to interionic interactions expressed by the D-H theory, some types of solute-solute interactions are working in the solutions. V _2? of CaCl₂ decreased remarkably in the methanol-rich regions. This is ascribable to the strong electrostricion effect of Ca²⁺ ion in solutions.     

STUDY ON THE GRAFT REACTION OF MALEIC ANHYDRIDE ONTO METALLOCENE-BASED POLYETHYLENE–OCTENE ELASTOMER

Grafting of maleic anhydride (MAH) onto metallocene based polyethylene–octene elastomer (POE) was studied in this article. By the results of Fourier transform infrared spectroscopy, proton nuclear magnetic resonance spectroscopy, and differential scanning calorimetry (DSC), it was confirmed that POE was grafted with MAH but the crosslinking reaction was accompanied by the predominant graft reaction due to a competition of POE macro-radical and excited MAH. Effects of various parameters such as monomer loading, initiator loading, and reaction time on grafting percentage and gel yield were also investigated. It was also found that the grafting percentage and the gel yield, at equilibrium, were both higher for POE containing lower degree of comonomer content. From the result of DSC characterization, it was shown that the change of crystallinity is slight for POE-g-MAH copolymer when the gel was removed from the copolymer. So one thought that the effect of gel formation on the properties of POE-g-MAH can be neglected due to the low gel yield. It was also proved that strength and elongation at break are both decreased while the grafting percentage was increased. Finally, the method proposed in this research can produce POE-g-MAH copolymer with low gel.     

AN ANALYSIS OF CELLULAR FLOW OBSERVED ON THE INTERFACE OF A PARTIALLY FORMED DROPLET†

In [16], during an experiment designed to model the internal circulation of a forming droplet, secondary surface flows were observed on the droplet interface.

After summarizing the experimental results of [16], we present one possible mechanism, based on the surface surfactant mass transport equation of Levich and the surface stress-strain boundary conditions at a free surface, that provides a good qualitative explanation of the origins and the nature of the secondary motion observed in [16]. The critical hypotheses in this mechanism are that the normal component of ihe vorticity at the free surface is determined primarily by the components of the velocity field tangential to the level lines of the surface surfactant density, near the maxima and minima of that density function and that the normal component of the fluid stress does not vanish at such points.

The consequent analysis of the mass transport equation in the interface shows that the resulting surface motion may be viewed as arising from a resonance phenomenon analogous to the forced vibrations of a spring at resonance.

The effects of adsorbtion-desorbtion and surface dilational viscosity may be incorporated in this mechanism. A method for the experimental measurement of surface dilational viscosities is proposed.     

EFFECT OF OPERATING TEMPERATURE AND PRESSURE ON THE TRANSITION FROM BUBBLING TO TURBULENT FLUIDIZATION

Experiments have been carried out to investigate the effects of operating temperature(50 to 500℃)andpressure(1×10~5 to 8×10~5 Pa)on the transition from bubbling to turbulent fluidization by computer analysisof the pressure fluctuation in dense phase.In order to reveal the influence of particle properties on the tran-sition process,eight kinds of particles were employed.A empirical correlaton which takes into accountthe effects of temperature and pressure is recommended for the prediction of transition velocity     

THE THROMBORESISTANCE OF A HEPARIN-POLYVINYL ALCOHOL HYDROGEL†

Heparin immobilized onto polyvinyl alcohol (PVA) by action of glutaraldehyde has been shown to be biologically active in a novel parallel flow arteriovenous shunt in dogs. The hepann-PVA hydrogel originally devised by Merrill and his collaborators was applied as a coaling to chromic acid etched polyethylene lubing. A pair of Y-connectors was used to divert < 2% of the flow in the AV shunt through the heparinized tube, which remained patent for longer Ihan two hours while a control tube without heparin was occluded within 30 minutes at a main shunt flow rate of ～l50mL/min. This enhanced patency was achieved without significant release from the surface, consistent with earlier experiments attributing the thromboresistance of the heparin-PVA hydrogel to the formation of a surface bound inactive thrombin-antithrombin III complex. Radiolabelled thrombin adsorbed onto beads made from the gel was readily displaced by arvinized plasma, indicating that the inactive complex was not itself permanently bound to the surface.

These results demonstrate the utility of Merrill's hydrogel for preparing materials with potential long lerm thromboresistance and for testing the validity of the hypothesized limitations to the long term use of immobilized heparin.     

A MONTE-CARLO APPROACH TO THE INTERPRETATION OF BUBBLE PROBE SIGNALS IN FREELY BUBBLING FLUID BEDS†

The interpretation of the signals generated by a double probe may be done by the three characteristic times method:

t₁ the time duration of the pulses;

t₂ the time shift between the signals of the two probes;

t₃ the time interval between two pulses on one channel.

Each of these times is largely dispersed and the corresponding histograms may be constructed.

The present work is a trial to go over from the time histograms to physical properties of the bubbles combining a Monte-Carlo simulation and a flexible simplex optimisation procedure.

As a result, the percentage of oblique bubbles cutting just one level, the bubble size distribution, the average velocity-size relation, and the individual dispersion around it may be defined.

The procedure is finally applied to experimental results obtained with a light probe in a fluid bed of glass beads.     

THE INFLUENCE OF PROCESS PARAMETERS ON THE INTERFACIAL CHEMISTRY OF γ-GPS ON ALUMINIUM: A REVIEW

Within the “International Collaborative Programme on Organosilane Adhesion Promoters” (ICOSAP), scientists from the U.S. and Europe contributed to the understanding of an organosilane primer process, based on an aqueous solution of γ-glycidoxypropyl trimethoxysilane (γ-GPS), used currently for aerospace repair purposes. Parameters such as temperature of cure, ageing time, and concentration of the aqueous solution have been investigated, and this work reviews the effect that each variable has on the process, and the resulting integrity of the GPS/aluminium interface. The aim of the work was to provide a more environmentally friendly replacement for pretreatments containing Cr(VI) that are currently used, such as chromic acid anodising and acid etching employed for the structural adhesive bonding of aluminium.

The formation of covalent interfacial bonding is shown to be a function of the hydrolysis and condensation of the silane molecules in solution as well as the type of solvent used. The curing temperature of the aqueous film on the aluminium is also shown to have an effect on the chemistry of the resulting primer film and its efficacy as an adhesion promoter. All these parameters must be optimised to obtain durability that matches that obtained by a phosphoric acid anodising pretreatment. This work reports on the various studies performed towards this aim carried out within the remit of the ICOSAP initiative, with a particular emphasis on the interfacial chemistry between γ-GPS and the aluminium substrate, and indicates the manner in which the results point the way towards a viable, environmentally friendly pretreatment for the adhesive bonding of aluminium for aerospaceapplications.     

STUDY ON THE SCALE-UP EFFECT OF CYCLONES

The scale-up effect, which is a key factor controlling the performance of industrial cyclones, is conventionally estimated through grade efficienty curves. A new principle based on the centrifugal separation factor (CSF) is proposed to improve the scale-up procedure in designing industrial cyclones.     

APPLICATION OF “VAPOR-PHASE RESISTANCE METHOD” TO THE STUDY ON CONDENSATION IN HORIZONTAL TUBES

A physical model and a mathematical model were established in order to describe and improve the“vapor-phase resistance method” of Bell and Ghaly.Considering the effect of ripples at the interface onvapor-phase resistance,a correction factor v_ι was proposed.Another factor (θ/π)β which correctsthe influence of the liquid pool along the bottom of the horizontal tube on the liquid-phase heat transfercoefficient was derived and the relationship of θ and β was correlated.The heat transfer coefficient pre-dicted by Bell's method are approximately 10—15% lower than the experimental values if the effect ofripples on vapor-phase resistance has not been taken into account.The comparison of the predicted valuesof h_c from the modified vapor-phase resistance method with the experimental data showed a deviation of±10%.     

A FURTHER INVESTIGATION ON THE PARAMETERS OF THE VDW TYPE EQUATION OF STATE

1 INTRODUCTIONSince the days when Soave [1] and Peng and Robinson [2] disclosed their modifiedvan der Waals(vdW)equations of state(EOS),a large number of papers on the samesubject have been published.All vdW type EOS are similar in structure,as they are de-rived from a generalized equation [3].Therefore,studies on vdW EOS are essentially fo-cused on the searching of the most rational parameters and the most appropriaterepresentation of these parameters.Although a lot of efforts were paid on this subject in     

THE EFFECT OF A FINITE PROPAGATION VELOCITY ON TURBULENT MASS TRANSFER NEAR A RIGID INTERFACE†

Because or the close coupling between the mean and fluctuating fields, the turbulent flux of a passive additive will exhibit a relaxation phenomenon over a space-time domain which affects the mean field. For fully developed turbulent flow near a rigid interface at large Schmidt numbers, the theory developed here yields

The memory length l₁₁ (x₁) and the turbulent diffusivity D₁₁(x₁) are related to the velocity space-time correlation and the molecular diffusion coefficient. The existence of a finite propagation velocity u_p(=D₁₁/l₁₁) causes a retardation of the turbulent flux and a decrease in the mean mass transfer coefficient compared with the case u_p=∞ The Stanton numbers predicted for u_p<∞ are in better agreement with experimental data than previous calculations which assumed l₁₁=0.     

THE APPLICATIONS OF A GENERALIZED EQUATION OF STATE TO THE CORRELATION AND PREDICTION OF PHASE EQUILIBRIA∗

Two methods of generalizing an equation of state are demonstrated and their limitations are outlined. One method involves the correlation of the equation of state constants and the second method involves a recently proposed Generalized Corresponding States Principle based on the properties of two (nonspherical) reference fluids. The PVT properties of pure fluids are represented by a new cubic equation of slate with four parameters which are obtained from vapor pressure and saturated liquid density data. It is demonstrated how a limited amount of data on key components may be used to obtain phase equilibria in mixtures.     

THE EFFECT OF INCLUSION COMPOUNDS ON THE PHOTOPHYSICS AND PHOTOCHEMISTRY OF SCHIFF’s BASES

通过形成希夫碱分子与环糊精或脱氧胆酸的包合化合物的方法，不仅可以使一些固态时具有热致变色性质的希夫碱表现出光致变色的性质，延长光产物的寿命，而且也可以在室温下检测到具有光致变色性质的包合化合物的荧光．     

STUDIES ON CYANATION OF O-HALOGENATED AZO DYES(Ⅰ)IDENTIFICATION OF THE PRODUCTS OF THE CYANATION

The molecular structures of the products of the cyanation of 2,6-bromo-4-nitro-4′-(N,N-diethy1)-azo dye withCuCN were analyzed and identified.Mechanism of the formation of the by-products was also discussed.     

THE EFFECT OF FREE STREAM CONCENTRATION ON HEAT AND BINARY MASS TRANSFER WITH THERMODYNAMIC COUPLING IN CONVECTION ON A ROTATING DISC†

Simultaneous heat and mass transfer, which arises from injecting a gas (helium or hydrogen) from or through the solid surface into a flowing external stream, has been studied for a rotating disc geometry. The effects of concentration levels of the injected gas in the external stream on the thermodynamic coupling in the presence of centrifugal force have been investigated over a wide range of T_w/T_e.

Boundary layer equations for heat and mass transfer were solved numerically. Exact and linearized approximate solutions were obtained. The results have shown that the thermal diffusion effect on mass transfer becomes increasingly important as the free stream concentration increases and as T_w/T_e departs from unity. The diffusion thermo effect on heat transfer was found to be the most important when the free stream concentration is zero and as T_w/T_e approaches unity.