FLOW IN AGITATED THIN FILM HORIZONTAL EVAPORATOR

We made a theoretical analysis for an axial flow of a working liquid of low viscosity without concern for the thermal effects. Variables studied were rotational speed of wiping blades, volumetric flow rate and viscosity.

When the viscosity is low, theoretical values are in proper accord with experimental ones. As a result, we can say that the residence time and the effective area for heat transfer are able to be controlled (when the viscosity is low) by selecting the rotational speed.     

SNIPPET ON DRYING

ABSTRACT

When regarding the atmospheric contact drying of granular beds wetted with a liquid mixture, both the drying rate and the selectivity of the process, i.e. the change of moisture composition, are of interest. The batch drying of a free flowing ceramic substance, wetted with a 2-propanol-water mixture, is investigated in a rotary dryer with heated wall and air flow.

The theoretical analysis is based on physical models for heat and mass transfer, moisture migration and particle transport, which are presented in examples.

The experimental and theoretical results show that higher selectivities can be achieved by reducing the particle size because of the lower liquid-phase mass-transfer resistance. An increase of the rotational speed leads to a higher drying rate with slightly decreased selectivity if the particles are sufficiently small, since contact heat transfer is enhanced.     

Separation and Recovery of Nickel and Molybdenum Using Continuous Rotating Annular Chromatography

ABSTRACT

A continuous rotating annular chromatograph was developed for preparative separation of nickel and molybdenum. Dowex 50W-8X cation resin (hydrogen form) was packed in a 505-mm long and 10-mm wide stationary annular column. The feed solution was continuously introduced at the top of the bed by a rotating feed nozzle and was carried down through the annular column with an eluent of 10% sulfuric acid. The products were collected by a rotational tray rotating at the same speed as the feed nozzle. To evaluate the performance of this device, the effect of feed flow rate and rotational speed of feed nozzle were measured. Experimental results were compared with results calculated using model-plate theory. It was found that the optimum feed flow rate, at a constant eluent flow rate of 48.8 mL/min and a rotational speed of 4.5 degree/min, was 3.5 mL/min.     

Effect of process variables on melt velocity profiles in extrusion process using single screw plastics extruder

Abstract

Single screw extruders are used to generate a continuous flow of molten polymer in many industrial polymer processes. The melt velocity profile as extruded is important in determining the properties of the final product and influences process related phenomena such as die swell and the onset of sharkskin. The factors that influence the velocity profile would be expected to be the melt temperature (this affecting the viscosity of the melt), the screw and die geometry, and the output rate from the extruder. In the present work a thermocouple mesh sensor coupled with a cooled stainless tube has been used to determine velocity profiles in melts exiting from the screw of a single screw extruder. The results show that the technique can be used successfully to determine velocity profiles in the extrusion process.

It was found that the main influence on the magnitude of the melt velocity was the extruder screw speed. Melt temperature, and hence melt viscosity, were found to have little effect on the velocity profiles measured. The flow in the centre of the duct was retarded slightly owing to the flow across the screw tip and no rotational component of flow was observed. The velocity profiles measured seemed to be reasonably stable, only small changes being observed in the velocity profiles as the melt flowed along a duct of uniform cross-section, although these changes were limited in nature. Die diameter and length had a limited effect on the velocity profiles generated, although the die entry angle did have a significant effect on the shape of the velocity profile at higher screw speeds.     

Development of reactive rotational moulding process

Abstract

A recent revival of industrial interest in rotational moulding of reactive liquid polymers has led to renewed research efforts in this area of polymer processing. This paper describes the design and construction of a reactive liquid polymer feed system for use in reactive rotational moulding. This feed system allows multiple material shots to be added to the mould without the need to stop mould rotation. The paper also describes work to develop a control technique that explores the exploitation of changes in ultrasound signal properties to monitor viscosity during cure in reactive rotational moulding (RRM). Tests have been conducted on dicyclopentadiene (DCPD) in a static off-line rig, to simulate the conditions that are expected during rotational moulding. The signals propagated through the DCPD indicate a rise in ultrasonic velocity during cure, associated with mechanical property changes owing to increased crosslinking. This technique is non-intrusive, and measurements can be obtained real-time for the duration of cure.     

DEWATERING OF WASTE ACTIVATED SLUDGE VIA CENTRIFUGAL FIELD

ABSTRACT

While conducting centrifugal dewatering tests on waste activated sludge, this work considered how the rotational speed and the application of cationic polyelectrolyte flocculation affected the sludge. Increased rotational speed and/or conditioning the sludge to a charge neutralization point could enhance dewatering efficiency. A model was proposed to estimate the disruption energy exerted on the sludge body using centrifugation. Experimental results indicate that the disruption energy level provided by the centrifuge increases with rotational speed and decreasing water content in the filter cake. Moreover, polyelectrolyte flocculation may significantly reduce the disruption energy level of the water from sludge particles and the residual water contents at the end of the test.     

Fabrication and application of flexible rectangular microtubes

ABSTRACT

Rectangular microchannels are useful in biological and chemical research. However, high-efficient method for producing rectangular microchannels has not been established. Here, flexible rectangular microtubes are produced via a micro-extrusion method. The size of the rectangular channels is controlled by drawing speed, flow rates of the polymer melt and air. A theoretical model is built to predict the size of the channels. To show the capability of the products, they are used as disposable micro-emulsifiers and used for protecting and observing volatile samples. More applications are to be developed for the novel tool which will facilitate research in many fields.     

Macro- and microdispersion of carbon black in liquid silicone rubbers

Abstract

A correlation between the online during mixing measured conductance of carbon black (CB) filled silicone rubber and macrodispersion of CB determined by optical microscopy and microdispersion analysed by AFM has been established. The online conductance is a suitable tool to characterise the effect of technological parameters (e.g. rotor type, speed, mixing temperature) and material parameters (matrix viscosity, CB type and content) on the macro- and microdispersion directly during the mixing process. Thus, a modified method of the online conductance measurement can be used as the in-process method for monitoring the production process of electrical conductive polymer materials with low viscosity, e.g. liquid silicone rubbers.     

CO2 absorption into K2CO3/KHCO3 solution enhanced by organic phase in a rotor–stator reactor

ABSTRACT

This work studied the gas–liquid–liquid (G–L–L) reaction system of CO₂ absorption into K₂CO₃/KHCO₃ buffer solution enhanced by organic phase in a rotor–stator reactor (RSR). The effects of volume fraction of organic phase, type of organic phase, rotational speed of RSR, gas and liquid volumetric flow rate, and temperature on CO₂ absorption percentage were investigated. Results indicate that the addition of the organic phase with a volume fraction of 1.3–1.6% had significant promoting effect on CO₂ absorption. CO₂ absorption percentage increased with increase in the rotational speed of the RSR but decreased with rise in liquid temperature and gas–liquid ratio. This work demonstrates that RSR can significantly enhance liquid–liquid mixing and gas–liquid mass transfer processes in the G–L–L system.     

Effect of temperature and mixing conditions on quality and consistency of poly(methyl methacrylate) bone cement

Abstract

The mixing of poly(methyl methacrylate) (PMMA) bone cement has been studied to develop methods for preparing a consistently high quality cement. A novel droplet test experimental procedure was developed that characterised the wetting characteristics involved in bone cement mixing. Using this technique it was established that increased wetting occurred by mixing bone cement at a lower temperature (-28°C) than normal mixing at room temperature.

The effect of temperature on viscosity of the cement mix was also investigated. An increase in viscosity with mixing time was found for all temperatures (owing to dissolution of PMMA in the monomer). However, the rate of increase in viscosity was a function of the initial temperature of the cement components. Cooling of the components initially to -12·6°C resulted in a better mix than room temperature samples, due to the cooled components having more mixing time at a lower viscosity (less than 1000 cP).

Automated mixing of the cement was also investigated. A high speed ‘figure of eight’ mixing machine (Kerr^® Automix^TM computerised mixing dental amalgamator) was used in a comparison with traditional hand held mixing devices. The effect of initial component cooling was also investigated in the high speed unit and cement samples were analysed for porosity and homogeneity of mix (using scanning electron microscopy). Results indicate that the combined effects of low initial temperature and automated mixing produces a bone cement that is more homogeneous and of lower porosity than hand mixed cement.     

Relationship between gelation and wall slip in unplasticised poly(vinyl chloride) compounds

Abstract

The degree of gelation reached upon processing influences heavily the properties of poly(vinyl chloride) (PVC) made parts. Gelation involves the conversion of the initial PVC particle structure into an increasingly homogeneous melt and therefore the rheological properties of PVC at low temperatures are very different from those at higher ones. Whereas the former involves both wall slip and particle flow, the latter yields a more conventional behaviour.

As a consequence, the nature and origins of the different mechanisms giving rise to wall slip in PVC compounds must be taken into account when trying to understand the relationship(s) between the processing conditions, the physics of the gelation mechanism, and the final product characteristics.

This work involves the study of the rheological properties of PVC compounds for different initial gelation levels and the identification of wall slip mechanisms using rotational rheometry.     

Comparative analysis of residence and diffusion times in rotating bed used for biogas upgrading

Rotating bed can be used in desorption operation of biogas upgrading as a new technology. For enough time to desorb, it is important to study the relationship between the residence time of liquid in rotating bed and the material diffusion time of liquid droplet in desorption process. By theoretical deduction, the exponential relation between residence time and liquid flow rate and rotational speed and kinematic viscosity is obtained. By analyzing the solution of nonlinear partial differential equation, the time law of material diffusion in the droplet is obtained. Moreover, by comparing the residence and diffusion times, the diffusion time can be within or out of residence time range, which has a direct relationship to rotational speed and liquid flow. By experiment, the comparison between residence and diffusion times is more realistic when the rotational speed is higher.     

Modelling of viscoelastic coextrusion flows in multi-manifold flat dies

Abstract

A recently proposed modification of the viscoelastic Leonov model is employed as a stress calculator in FEM analysis with a full u-v-p-t numerical scheme for coextrusion flow in multimanifold flat dies with 30° and 90° entrance angles. It is shown that the predicted stresses, interface location and streamline fields are in good agreement with the measurements. It is also shown that extensional viscosity has to be used in the modelling of the coextrusion flow to confirm experimental data.     

转鼓式生物反应器中液相体系的流动性能

采用粒子示踪测速法在18 L转鼓式生物反应器中考察了转速和挡板数、挡板类型和粘度对转鼓流场的影响. 结果表明,在低粘的自来水介质中,转速为4~12 r/min时,Y向平均分速度由0.029 m/s增加到0.053和0.064 m/s时,挡板重力提升能力不断增强,提高转鼓转速可促进全局混合. 直挡板数由4增加到8时,挡板提升能力增强32.5%,且能获得更均匀的流场分布;与自来水体系相比,高粘度8 g/L黄原胶溶液体系中流场分布更均匀,剪切更温和.     

Centrifugal Contactors: Separation of an Aqueous and an Organic Stream in the Rotor Zone (LA‐UR‐05‐7800)

Abstract

A multi‐phase flow code is used to simulate the separation of an aqueous and an organic stream in the rotor zone of an annular centrifugal contactor. Different values for the mixture viscosity and for the initial volume fractions of the components are considered. A simple model for mass transfer of a species between phases is used. Geometrical effects are found to have significant influence on the separation of the two‐phase mixture.     

Shear viscosity of carbon black filled polypropylene at very low shear stresses

The shear viscosity of carbon black filled polypropylene with a range of different carbon blacks was investigated. This was accomplished using (a) a constant shear stress creep instrument, (b) a cone-plate rotational rheometer, (c) a capillary extrusion rheometer. It was found that stresses exist for these compounds below which there are only finite deformations and no steady flow, Much attention was given to measurements of creep at low stresses, especially in the neighborhood of yield values. The magnitudes of yield stresses obtained from such creep measurements are significantly lower than those obtained using standard extrapolation to zero shear rate of higher stress data from rotational instruments. The shear viscosity behavior near the yield value differs significantly depending upon the carbon black used. A high viscosity was observed (～10⁹ to 10¹⁰ Pa.s) plateau in some compounds.     

EXPERIMENTAL STUDY ON DRYING OF CHILLI IN A COMBINED MICROWAVE-VACUUM-ROTARY DRUM DRYER

ABSTRACT

This paper presents new data on drying chilli in a microwave-vacuum-rotary drum dryer. This novel technique is designed to combine the advantages of vacuum drying and evenly dispersed microwave energy in a rotary drum. The drying kinetic and the specific energy consumption at particular product moisture content were measured experimentally. Moreover, the effect of pressure inside the chamber and the rotational speed of the drum were also determined.     

Reverse Direction Anion Capillary Electrophoresis: Theory and Application

Abstract

A new mode for operating capillary electrophoresis for separation of anions without using buffer modifiers has been demonstrated. Reverse direction anion capillary electrophoresis, as the new mode is designated, is performed on two anions, nitrate and nitrite, with similar electrophoretic mobilities at various buffer pH values. Since electroosmotic flow increases as buffer pH is increased, it is shown that resolution is poor at low pH and enhanced at neutral to high pH. Model equations are derived for predicting the resolution and number of theoretical plates for reverse direction anion capillary electrophoresis. From these equations, system efficiency (N) and resolution are plotted as a function of electroosmotic mobility to illustrate how performance can be improved by an increase in electroosmotic flow.     

The Use of Hydrocyclones for Small Particle Separation

Abstract

Hydrocyclone operating characteristics have been studied by measuring the capacity for separating haematite, magnetite and silica particles suspended in water. The effects of viscosity (achieved by changing temperature) and throughput have been investigated and are satisfactorily correlated. The measurements demonstrate that under appropriate conditions of high pressure drop and low viscosity, particles below the usually accepted limit of 2 μm can be separated.

Measured particle separation is expressed as a hydrocyclone efficiency, and its variation with particle size is shown. Anomalous results with magnetite and haematite suspensions are suggested to occur because these materials exist as agglomerates with effective density less than half that of the bulk material.     

Modeling the Extraction Rate Coefficient for the Extraction of Yttrium by DEHPA Using Organic-Phase Recycle

ABSTRACT

Extraction of yttrium (Y) from sulfuric acid was studied using di(2-ethylhexyl) phosphate (DEHPA). A portion of the organic phase was recycled back into the mixer after extraction for the mixer to operate at a moderate organic-to-aqueous volumetric phase ratio while processing at a low organic-to-aqueous flow rate ratio. The effective performance of the mixer was evaluated when operating at different organic-phase flow fractions. To model the extraction rate coefficient, a 2-factor designed experiment was performed by conducting both equilibrium and mixer-settler tests. The organic-phase flow fraction was varied over four discrete levels while the extractant concentration was varied over three discrete levels. Increasing the organic-phase flow fraction yielded a continual increase in the extraction rate coefficient. In contrast, increasing the extractant concentration yielded an initial increase followed by a subsequent decrease in the extraction rate coefficient. The decline in the extraction rate coefficient was attributed to a decrease in the yttrium-extractant complex’s diffusion coefficient. High metal loading caused an elevated organic-phase viscosity and thus the low diffusion coefficient. An extraction rate coefficient model is proposed to describe the effects of extractant concentration, viscosity and organic-phase flow fraction. Mass transfer resistance was largely in the organic phase.