Equipment Geometry Research Articles

Cleanability study of complex geometries: Interaction between B. cereus spores and the different flow eddies scales

Wall shear stress measurements and the distribution size of turbulent structures at the confined zone near the wall were used in order to investigate the cleanability of a part of a dairy processing line consisting in a manometer and a two-way valve. Geometry of equipment was discerned as an important factor governing the flow behavior and thereafter the initial contamination and the cleanability of the installation. Interactions between suspended spores and coherent turbulent structures of different sizes were used to explain the eventual re-adhesion of spores in confined zones of the loop. These interactions also helped to explain the role of the bursting phenomenon in the increase of the wall shear stress which induces spores detachment.

Minimising oil droplet size using ultrasonic emulsification

The efficient production of nanoemulsions, with oil droplet sizes of less than 100 nm would facilitate the inclusion of oil soluble bio-active agents into a range of water based foods. Small droplet sizes lead to transparent emulsions so that product appearance is not altered by the addition of an oil phase. In this paper, we demonstrate that it is possible to create remarkably small transparent O/W nanoemulsions with average diameters as low as 40 nm from sunflower oil. This is achieved using ultrasound or high shear homogenization and a surfactant/co-surfactant/oil system that is well optimised. The minimum droplet size of 40 nm, was only obtained when both droplet deformability (surfactant design) and the applied shear (equipment geometry) were optimal. The time required to achieve the minimum droplet size was also clearly affected by the equipment configuration. Results at atmospheric pressure fitted an expected exponential relationship with the total energy density. However, we found that this relationship changes when an overpressure of up to 400 kPa is applied to the sonication vessel, leading to more efficient emulsion production. Oil stability is unaffected by the sonication process.

The rainbow as interactive art: modeling the Elaisson Beauty installation at SFMOMA

The rainbow has had an important role in religion, art, and science. Recently, artists have attempted to create indoor rainbow displays as interactive exhibitions of art, but based, nonetheless, on the principles of the scattering behavior of raindrops and the experience of experiment. Motivated by recently viewing the Beauty, 1993, installation at the San Francisco Museum of Modern Art (SFMOMA), we describe here a modeling program to explain the diversity of rainbow phenomena one can see visually in the gallery. The most significant impression gleaned in the museum is the acute spatial dependence of rainbow form on the viewing position in the presence of a local divergent light source (i.e., a floodlamp), in stark contrast to the unchangeable natural rainbow produced by an unimaginably distant Sun. This represents a case of the local (divergent) versus solar (parallel) light ray source distinction in atmospheric optical displays, which is one of a handful of anthropogenic versus natural situations responsible for optics displays that have been so far described. Through geometrical optics and Airy's theory simulations we show a rich relationship between the locally produced rainbow phenomena and the chamber equipment geometry and viewing position.

Computational Fluid Dynamics for the Prediction of Temperature Profiles and Hygienic Design in the Food Industry

Many factors need to be considered to ensure that food process lines consistently deliver microbiologically safe products. These factors include process and equipment design, and in particular the interaction between the product and the equipment geometry. Computational fluid dynamics (CFD) has recently been used within the food industry in a number of applications. In this work a commercial finite volume CFD code, FLUENT, has been used to predict those parameters critical to the prediction of velocity and temperature profiles for low viscosity fluids in typical, complex equipment geometries and compared these with experimental data. A comparison of the temperature distribution using predictive modelling and experiments is encouraging, and qualitatively satisfactory and reliable for laminar and turbulent flows. Application of this approach will enable the interaction between food products and equipment geometries to be predicted, and provide an improved method of assessing the implications for the microbiological safety of foods.

A hybrid CFD—reaction engineering framework for multiphase reactor modelling: basic concept and application to bubble column reactors

The coupling of turbulent mixing and chemical phenomena lies at the heart of multiphase reaction engineering, but direct CFD approaches are usually confronted with excessive computational demands. In this hybrid approach, the quantification of mixing is accomplished through averaging the flow and concentration profiles resulting from a CFD flow field calculation and a computational (“virtual”) tracer experiment. Based on these results, we construct a mapping of the CFD grid into a generalised compartmental model where the chemistry calculations can be efficiently carried out. In contrast to the empirical models used in the residence time distribution (RTD) approach, the compartmental model in this methodology, owning to its CFD origins, retains the essential features of the equipment geometry and flow field. A procedure for extracting the mixing information from k– ε based CFD codes is outlined, but the main concept of the approach is not restricted to any particular type of turbulence modelling, and will therefore benefit from future developments. A phenomenological model of mass transfer and chemical reaction, based on the penetration theory, is employed to simulate the interfacial phenomena in gas–liquid reactors, and a study of CO 2 absorption into alkali solution is presented to demonstrate the method.

Three-dimensional Monte Carlo simulation of sputtered atom transport in the process of ion-plasma sputter deposition of multicomponent thin films

An algorithm for Monte Carlo simulation of sputtered atom transport during ion-plasma sputtering was developed. The experimentally determined initial energy distribution of sputtered atoms, the influence of the background gas mixture and the real equipment geometry of the magnetron sputtering system were taken into account. To describe the collision between sputtered atoms and background gas atoms, the Firsov interatomic potential with Nikulin screen function was used. In simulations, the equipment geometry and deposition conditions were chosen corresponding to those of DC magnetron deposition of Cu and YBa 2Cu 3O 7- x thin films. The spatial, energetic and angular distribution of sputtered atoms on the substrate surface, target and chamber’s walls were calculated. The obtained results are in good agreement with experimental ones. The presented simulation procedure is useful in daily research work to choose the optimal deposition conditions for both on- and off-axis magnetron deposition systems.

Erosion de cavitation : méthodes pratiques de prédiction au stade du projet

Click to increase image sizeClick to decrease image sizeCavitation erosion is the final consequence of a number of highly complex physical phenomena.The geometry of the hydraulic equipment, its operating conditions including the flow velocity and cavitation as well as the nature and history of the fluid are the key parameters which govern the size and type of vapor cavities. These cavities are entrained by the flow and collapse against the neighboring solid boundaries. When strong enough, each of these collapses may create a small pit in the material. This pit formation is called the incubation period. The cumulative effect of these numerous impacts is responsible of fatigue at the surface of materials and this finally causes material removal. It is practically imposssible to simulate all these phenomena by available computer models or correlations. The only possible way to forecast cavitation damage is to use reduced scale models and apply proven scaling laws. The most complex part of the scaling concerns the hydrodynomic phenomena. It has been shown that they were satisfactorily represented on models provided the scaling parameters are within a reasonable range and the test fluid is correctly prepared. This may imply nuclei injection. This hypothesis has been used to derive scaling laws on the flow geometry, the rate of occurence of vapor cavities and their capability to produce pits on solid materials during the so-called incubation period. The histogram of the pits produced can be a measure of the damage capability of the flow. Finally, it has been shown experimentally that this histogram of pits, or at least part of it could be transposed to other operating conditions of a similar flow.

Low-resolution gamma-ray measurements of process hold-up

This tool, consisting of software with a compact detector, an M3CA, and an Intermec datalogger: 1. 1. acquires and manages several hundred spectra in an hour; 2. 2. produces prompt and reliable quantitative analyses; 3. 3. is self-powered, easily carried and operated by a single user; 4. 4. accomodates varying degrees of user expertise; 5. 5. corrects for the effects of equipment geometry; 6. 6. corrects for the effects of equipment attenuation; 7. 7. tolerates facility variables such as temperature fluctuations and equipment accessibility; 8. 8. has been subjected to quality testing under field conditions; and 9. 9. does not require extensive specialized training for the operators.

Effect of cross-polar coupling on open area test site measurement correlation and repeatability

Radiated emission measurements taken on open area test sites (OATSs) show repeatability problems when comparing measurements of the same equipment under test (EUT) on different sites. Significant levels of cross-polar coupling have been observed in the authors' measurements of insertion loss on an OATS. It is demonstrated that cross-polar coupling is a source of repeatability problems when emissions measurements are performed on an arbitrarily polarised EUT. Cross-polar coupling also leads to problems when trying to correlate measurements taken on different OATSs. Simple OATS modelling, using the method of moments code NEC, is presented. From the results, the authors isolate some mechanisms which cause the cross-polar coupling observed in their measurements and assess their relative importance. It is shown that small disruptions to the geometry of OATS equipment can cause cross-polar coupling of the same size as that observed in measurements, and that it is very hard to remove cross-polar coupling effects from any OATS measurement.

Improved design of magnetizer for magnetic powder flaw detection with AC nonlinear analysis

Some problems owing to the magnetic field distribution often occur in magnetic powder flaw detection. For example, magnetic flux density concentrates locally because of geometry and configuration of magnetization equipment, and hence incorrect detection is caused. To overcome the problem two different techniques have been applied to a model of a square steel billet. The solution was obtained by using an AC nonlinear FEM analysis.

Simulation of the Fluidized‐bed Crystallizers (I) Influence of Parameters

AbstractA computer programme for the simulation of an ammonium sulphate producing fluidized‐bed crystallizer was elaborated. The results pointed out the strong influence of the equipment geometry and also a very intensive self‐regulation of the system.

Hydrodynamics of a solid-suspended bubble column with a draught tube containing low-density particles

Experiments were conducted to discern the relationship between the hydrodynamics of a solid-suspended bubble column with a draught tube containing low-density particles comparable to those of bioparticles used in biological applications and the operating conditions such as the gas velocity, the solids holdup and the equipment geometry. An empirical correlation for gas holdup evaluation in the draught tube is obtained and found to be a function of the fluid velocity, which is the liquid—solid mixture flow velocity, induced by the dispersion of a gas into the draught tube. The gas holdup in the annulus is correlated to be a function of the gas holdup in the draught tube because of the close relation between them. Further, correlations for the pressure drop due to fluid flow reversal at the column top and base are obtained using the fluid flow velocity. An energy balance, which was used by Miyahara (1986) for the conventional bubble column with a draught tube, is employed to predict the fluid circulation velocity using gas holdup and pressure drop correlations. A reasonable agreement is found between the predicted and the measured fluid circulation velocity.

An X-Ray Technique for Determining Three-Dimensional Seed Placement in Soils

ABSTRACT An X-ray technique was developed to provide a reliable and workable procedure for determining three-dimensional seed placement in no-till soils. The technique is based on the principle that seeds coated with a heavy metal powder (red lead oxide, Pb304) and X-rayed appear on an X-ray radiograph as white or gray spots on a dark background in the soil. Solder wires placed on the soil sample as reference markers appeared on the radiograph as white lines. Images on the radiograph were shadow representations of true locations in the sample. Thus, a correction procedure was developed, based on the geometry of the X-ray equipment to establish the correct position, of each image. These corrected seed and reference positions were then used to calculate sowing depth, in-row spacing and width of spread in the row.

A model for the circulating fluidized bed

A model for the hydrodynamics of circulating fluidized beds is proposed. The model combines existing entrainment and bed expansion correlations with a system pressure balance. Starting from a knowledge of the powder size distribution, particle density, gas velocity, equipment geometry and solids inventory, the variation of voidage within the riser is predicted, together with distribution of solids between the riser and supply hopper (or ‘slow’ bed). Qualitative trends with gas velocity and solid circulation flux show good agreement with experiment, but better quantitative agreement must await the development of an improved correlation for entrainment.

Heat transfer phenomena in liquid-liquid spray columns

Heat transfer experiments were carried out concerning the transfer from cylindrical surfaces immersed in liquid-liquid spray columns 100 and 200 mm in diameter. Water, formamide, glycerol, tetrachloroethylene, tetrabromoethane, toluene and 2-ethylhexanol were used to study the influence of physical properties of immiscible liquids over a wide range. Operating conditions (liquid flow rate of the dispersed phase, equipment geometry) affect the heat transfer comparatively to a low degree. Physical properties of the heating surface were varied to examine the influence of wetting phenomena on the heat transfer coefficient. The calculation model presented in this paper is based on equations of the heat transfer in a single phase flow over a flat plate. Heat transfer is described by Reynolds number incorporating the relative velocity between the drops and the continuous phase, the equivalent diameter and the viscosity of the continuous phase.

Diffusiophoretic particle collection under turbulent conditions

Diffusiophoresis, which is the movement of aerosol particles induced by diffusing gases, was studied under conditions of turbulent flow. A novel theory for diffusiophoretic particle removal is presented which depends solely on the non-steady-state forms of the continuity equations for the particles and gas mixture. It is therefore independent of equipment geometry and patterns of mass transfer or gas flow. Collection efficiencies are predicted for particles moving with the Schmitt and Waldmann velocity (or small particle velocity) as well as the local mean mass and local mean molar velocities of the gas mixture. It is shown that, in the latter two cases, the particle collection efficiency equals the fractional mass and molar removal of gas, respectively. Experimental studies were performed by passing a binary gas mixture containing aerosol particles up through a wetted wall column (0.0254 m I.D. and 0.77 m in length), countercurrent to a flow of water. One component was inert, while the other was partially absorbed. The resulting particle removal was determined by measuring the inlet and outlet aerosol number concentrations in the gas. The soluble gases tested were ammonia and trimethylamine, while the insoluble gases were helium, methane, nitrogen, argon and freon 12 (dichlorodifluoromethane). Uniform latex particles of 0.50, 0.79, 1.011, 2.02 and 5.7 μm in dia. were used. The experimental results were in satisfactory agreement with theoretical predictions.

Glare Characteristics of Lenses and Optical Instruments in the Visible Region

An automatic laboratory glare photometer has been constructed and used to measure the glare characteristics of some typical lenses, and a focal systems by the elementary source method. From the glare distributions produced by the instrument, the concept of a glare spread function (g.s.f.) has been developed and it has been shown that the use of g.s.f.'s permits the glare characteristics of an optical system to be expressed in a manner more basic than has hitherto been possible. The numerical values of the g.s.f. depend only on the system under test and not on the geometry of the test equipment. Glare spread functions can be useful in several contexts. They can be used as procurement standards prior to design or manufacture and the measured g.s.f.'s of existing instruments can be used to calculate glare distributions in particular situations, different from the one actually used for the measurement.