Combination Of Process Variables Research Articles

CHARACTERISTICS OF MICROMETER AND SUBMICROMETER SIZE O/W EMULSIONS PRODUCED BY RAMOND SUPERMIXER®

A novel motionless mixer named the Ramond Supermixer® (RSM®) was employed to produce O/W emulsions composed of micrometer and submicrometer-size droplets. Liquid paraffin as dispersed phase, aqueous sucrose solution as continuous phase, and anionic sodium dodecyl sulfate as emulsifying agent were used as the model emulsification system. Pressure drop, droplet size distribution, Sauter mean diameter (d 32), and geometric standard deviation of the droplet size distribution (σg) were investigated under the various combinations of process variables; superficial liquid velocity, number of mixing units, number of passages through RSM®, dispersed phase viscosity (ηd), continuous phase viscosity (ηc), and dispersed phase volume fraction. Different modes of droplet size variations with process variables were obtained, with respect to micrometer- and submicrometer-size ranges, and theoretical explanations are forwarded. For the micrometer-size range, maximum droplet diameter (d max) was proportional to d 32. For the submicrometer-size range, d max varied with d 32 in the range of 1.53–2.19-fold, and a correlation is proposed with K (=ηd/ηc); d 32 and σg were well correlated with the process variables. Furthermore, a semi-empirical mechanistic model was developed for the formation of droplets obtained under inertial sub-range to interpret the effect of process variables.

Crystal Transformation and Development of Tensile Properties upon Drawing of Poly(L‐lactic acid) by Solid‐State Coextrusion: Effects of Molecular Weight

AbstractMelt‐crystallized films of poly(L‐lactic acid) (PLLA) with Mv in the range of 3.8 ∼ 46 × 104 consisting of α‐form crystals were uniaxially drawn by solid‐state coextrusion. The effects of Mv, extrusion draw ratio (EDR), and extrusion temperature (Text) on the crystal/crystal transformation from α‐ to β‐form crystals and the resultant tensile properties of drawn products were studied. The crystal transformation proceeded with EDR and more rapidly for the higher Mv's. Furthermore, the crystal transformation proceeded most rapidly with EDR at a Text around 130 °C, independently of the Mv's. As a result of the optimum combination of processing variables influencing the the crystal transformation (Mv, Text, and drawability), highly oriented films consisting of β‐form crystals alone were obtained by coextrusion of higher Mv samples at Text's slightly below the melting temperature (150 ∼ 170 °C) and at higher EDR's > 11. Both the tensile modulus and strength increased rapidly with EDR. The modulus at a given EDR was slightly higher for the samples with higher Mv's. In contrast, the strength at a given EDR was remarkably higher for the higher M v's. The highest tensile modulus of 8.0 GPa and strength of 500 MPa were obtained with the sample of the highest Mv of 46 × 104 coextruded at 170 °C to the highest EDR of 14.

The optimization of the extrusion process when using maize flour with a modified amino acid profile for making tortillas

SummaryMaize with a modified amino acid profile, i.e. greater amounts of lysine and tryptophan than normal, is known as ‘quality protein maize’ (QPM). The objective of this work was to find the best combination of extrusion process variables to produce QPM flour for making tortillas. QPM grits were mixed with lime and water and had a moisture content of 28%. The single screw extruder operation conditions were selected from factorial combination of three process variables: extrusion temperature (ET, 70–100 °C), lime concentration (LC, 0.1–0.3% of the maize weight) and screw velocity (SV, 80–250 rpm). Response surface methodology was used as an optimization technique. In vitro protein digestibility (PD); total colour difference (ΔE) of the flours, and tortilla puffing (TP) were chosen as response variables. A graphical method was used to obtain maximum PD, TP and minimum ΔE. The optimum combination of process variables was: ET = 85 °C/LC = 0.21%(w/w)/SV = 240 rpm. Tortillas from QPM flour had similar chemical composition, physicochemical and sensory properties to tortillas from commercial nixtamalized maize flour; however, the former had the highest (P ≤ 0.05) available lysine content and were therefore better nutritionally.

Control of Earing in Deep Drawing of Roll-Cast AA3003 Aluminium Sheets

The effect of different parameters during thermo-mechanical processing on the earing behavior of AA3003 aluminum sheets has been investigated. These were homogenization of the cast strip, cold rolling, intermediate and final annealing of the sheets at different gauges. The amount of 0/90° earing formed on annealing decreased with cold rolling prior to annealing. Nevertheless, annealing after partial deformation gave rise to large amounts of 0 to 90° ears to balance subsequent ±45° earing. Homogenization prior to cold rolling resulted in a fine dispersoid distribution which, in turn, increased the tendency for 0/90° earing. All of these observations were consistent with textural studies in which cube and rolling textures were competing to produce positive and negative earing, respectively. It is concluded that the "non-earing" quality in the present material could be obtained by proper combination of processing variables such as; homogenization, cold reduction, and annealing cycles.

PRODUCTION OF SUB-MICROMETER SIZE O/W EMULSIONS USING A HIGH-PRESSURE WET-TYPE JET MILL

ABSTRACT Emulsions composed of sub-micrometer size droplets were obtained by a high-pressure wet-type jet mill. Liquid paraffin as dispersed phase, aqueous sucrose solution as continuous phase, and anionic sodium dodecyl sulfate as emulsifying agent were used as the model emulsification system. Droplet size distribution, Sauter mean diameter (d 32), geometric standard deviation of the droplet size distribution (σg), and emulsion viscosity (ηe) were investigated under the various combinations of process variables: dispersed phase volume fraction (Φ), dispersed phase viscosity (ηd), continuous phase viscosity (ηc), processing pressure, and number of passages through the wet-type jet mil. d 32 and σg were correlated with the process variables. For the entire experimental range, maximum droplet diameter was varied with d 32 in the range of 1.7–1.9-fold, and a correlation was proposed with K (=ηd/ηc) as a variable. Above a marginal value of d 32, at Φ ≥ 0.1, emulsions exhibited Newtonian behavior and could be described well by the Yaron and Gal-Or model. Below the marginal values, emulsions strongly depended on d 32 and exhibited a shear-thinning behavior. The relation between ηe and d 32 for such emulsions was modeled by use of particle Reynolds number.

RETRACTED: Fractals and superstructures in gadolinia thin film morphology: Influence of process variables on their characteristic parameters

Characteristic topographic parameters like fractals and superstructures contribute substantially to the thin film morphology, which directly or indirectly influences the physical, optical and mechanical properties. Fractal geometry and scaling concepts can concisely as well as more effectively describe the complex rough surface morphology. In the present study, such microstructural analysis has been carried out for gadolinia thin films, a most promising candidate to develop multilayer optical coatings in the deep ultraviolet spectral region. Extended power spectral density (PSD) spectra for these films acquired through atomic force measurements have been modeled and analyzed using several thin film morphological functions appropriately modified to suit the present requirements. Analysis results of the PSD functions have distinctly indicated the presence of Brownian fractals and uniformly distributed superstructures in the most experimental films deposited through reactive electron beam deposition technique. Process variables such as the rate of deposition and the oxygen partial pressure have affected the microstructural and related morphological evolutions very differently. The rate parameter strongly influenced the intrinsic microroughness, whereas the oxygen pressure influenced the grain sizes of the gadolinia films. One can advantageously use such information in tailoring a desired surface morphology in thin films by choosing appropriate combinations of process variables.

CONTINUOUS PRODUCTION OF DISSOLVED OXYGEN-FREE WATER USING RAMOND SUPERMIXER®

ABSTRACT The process of continuous production of dissolved oxygen free water was investigated by means of desorption of dissolved oxygen into fine nitrogen bubbles generated in a novel motionless mixer named Ramond Supermixer® (RSM). The pressure drop across the mixer (ΔPSM) and the volumetric mass transfer coefficient (kL a) during the desorption of oxygen from water were measured for various combinations of process variables; liquid and gas velocities and number of mixing units. The kL a during absorption was smaller by less than approximately 6% than that during desorption. Specific gas-liquid interfacial areas (a) were measured by the chemical absorption method for a CO2-aqueous sodium hydroxide solution system. Such process characteristics as ΔPSM, kL a, and a were correlated with the process variables and compared with those available in the literature. To further confirm the mass transfer characteristics in RSM, the desorption of oxygen from aqueous electrolyte solutions was also investigated. All the correlations obtained for kL a during the desorption of oxygen from water and aqueous electrolyte solutions were compatible to a great higher extent.

Application of genetic algorithm for optimization of vegetable oil hydrogenation process

Finding optimal reaction conditions leading to minimal total trans isomer and maximal cis-oleic acid formation during vegetable oil hydrogenation is very crucial. An Artificial Neural Network was developed and used to predict the amount of total trans isomer and cis-oleic acid during the hydrogenation process. Using a large number of experimental data from a pilot plant reactor, the Neural Network was trained and then validated with a validation subset. Having a reasonably accurate Neural Network model of the hydrogenation process, Genetic Algorithm was then used to search for a combination of process variables resulting in minimal total trans isomer and maximal cis-oleic acid formation during the hydrogenation process. The outputs of Genetic Algorithm (i.e. predicted process variables) were used in actual settings of the hydrogenation process to evaluate the effectiveness of the scheme. The results indicated that the scheme could be effectively used to identify the optimal hydrogenation conditions resulting in minimal trans isomer and maximal cis-oleic acid formation during vegetable oil hydrogenation process.

EXPERIMENTAL OPTIMIZATION OF A CONTINUOUS-FLOW REACTIVE DISTILLATION REACTOR FOR BIODIESEL PRODUCTION

A comprehensive study of biodiesel preparation from canola oil was performed on a continuous-flow reactivedistillation (RD) reactor system. Optimization of six process variables was studied experimentally and analyzed statisticallyon the overall performance of the RD reactor system. These variables include the feed methanol to triglycerides molar ratio,reaction time, reboiler temperature, catalyst concentration, methanol circulation mode, and catalyst formulation. Anexperimental design was used in the experiments, and statistical multiple response regression models were employed forprocess optimization. Under the operating conditions explored, product yields ranged from 41.5% to 94.9%, productivityranged from 16 to 55.8 kmol/m3h (5.6 to 19.5 m3/m3h), and soap formation varied from 4.44 to 29.1 mol/100 mol (0.19 to1.27%wt.). For different optimization criteria, the following optimum variable ranges were found: feed molar ratio from3.65:1 to 4.50:1, reaction time from 3.76 to 5.56 min, reboiler temperature from 100C to 130C, and catalyst concentrationfrom 0.13 to 0.24 mol/mol. Although the process variables individually affected the system performance to a certain extent,the interactive effect of the process variable combinations affected the system efficiency more significantly. When maximized,the product yields and productivity were 98.8% and 55.6 kmol/m3h (18.5 m3/m3h), respectively. However, when soapformation was minimized, the yield and productivity were 72% and 9.3 kmol/m3h (3.1 m3/m3h), respectively. It isrecommended that the optimization of the RD reactor system be based on the maximization of product yield and reactorproductivity.

Robustness studies on coal gasification process variables

Optimisation of the Sasol-Lurgi gasification process was carried out by utilising the method of Factorial Experimental Design on the process variables of interest from a specifically equipped full-scale test gasifier. The process variables that govern gasification are not always fully controllable during normal operation. This paper discusses the application of statistical robustness studies as a method for determining the most efficient combination of process variables that might be hard-to-control during normal operation. Response surface models were developed in the process variables for each of the performance variables. It will be shown how statistical robustness studies provided the optimal conditions for sustainable gasifier operability and throughput. In particular, the optimum operability region is significantly expanded towards higher oxygen loads by changing and controlling the particle size distribution of the coal.

Nixtamalized Flour From Quality Protein Maize (Zea mays L). Optimization of Alkaline Processing

Quality of maize proteins is poor, they are deficient in the essential amino acids lysine and tryptophan. Recently, in Mexico were successfully developed nutritionally improved 26 new hybrids and cultivars called quality protein maize (QPM) which contain greater amounts of lysine and tryptophan. Alkaline cooking of maize with lime (nixtamalization) is the first step for producing several maize products (masa, tortillas, flours, snacks). Processors adjust nixtamalization variables based on experience. The objective of this work was to determine the best combination of nixtamalization process variables for producing nixtamalized maize flour (NMF) from QPM V-537 variety. Nixtamalization conditions were selected from factorial combinations of process variables: nixtamalization time (NT, 20-85 min), lime concentration (LC, 3.3-6.7 g Ca(OH)2/l, in distilled water), and steep time (ST, 8-16 hours). Nixtamalization temperature and ratio of grain to cooking medium were 85 degrees C and 1:3 (w/v), respectively. At the end of each cooking treatment the steeping started for the required time. Steeping was finished by draining the cooking liquor (nejayote). Nixtamal (alkaline-cooked maize kernels) was washed with running tap water. Wet nixtamal was dried (24 hours, 55 degrees C) and milled to pass through 80-US mesh screen to obtain NMF. Response surface methodology (RSM) was applied as optimization technique, over four response variables: In vitro protein digestibility (PD), total color difference (deltaE), water absorption index (WAI), and pH. Predictive models for response variables were developed as a function of process variables. Conventional graphical method was applied to obtain maximum PD, WAI and minimum deltaE, pH. Contour plots of each of the response variables were utilized applying superposition surface methodology, to obtain three contour plots for observation and selection of best combination of NT (31 min), LC (5.4 g Ca(OH)2/l), and ST (8.1 hours) for producing optimized NMF from QPM.

Instant flour from quality protein maize ( Zea mays L). Optimization of extrusion process

Traditional nixtamalization process for producing instant flours is highly time and energy consuming; in addition, it presents problems of high liquid waste discharges (3–10 L H 2O/kg maize). Extrusion represents an alternative technological for producing instant flours and does not generate effluents. The objective of this work was to determine the best combination of extrusion process variables for the production of instant flour from quality protein maize (QPM) ( Zea mays L) V537 variety. Prior to extrusion, the maize kernels were broken to obtain grits (1−2 mm) which were mixed with lime and water to reach a moisture content of 28 g/100 g. The single screw extruder operation conditions were selected from a factorial combination of process variables: extrusion temperature ( ET, 70–100°C), lime concentration ( LC, 0.1–0.3 g/100 g maize) and screw velocity ( SV, 30–80 rpm). A central composite experimental design with five variation levels was chosen. Response surface methodology was applied as optimization technique, over four response variables: in vitro protein digestibility ( PD), total color difference (Δ E), water absorption index ( WAI) and pH. Predictive models for response variables were developed as a function of process variables. The conventional graphical method was applied to obtain maximum PD, WAI, pH and minimum Δ E. Contour plots of each of the response variables were utilized applying superposition surface methodology, to obtain three contour plots for observation and selection of a superior (optimum) combination of ET (79.4°C), LC (0.24 g/100 g maize) and SV (73.5 rpm) to obtain optimized extruded maize flour (EMF) from QPM with a single screw extruder. Optimized EMF had similar physico-chemical and functional characteristics than commercial nixtamalized maize flours (NMF).

Experimental design and statistical evaluation of a full-scale gasification project

Sasol in South Africa gasifies approximately 30 million tons of bituminous coal per year to synthesis gas, which is converted to fuels and chemicals via the Fischer–Tropsch process. Three years ago, Sasol embarked upon a unique project to optimise the gas production of the Sasol–Lurgi fixed bed dry bottom coal gasification process. Optimisation of the gasification process was carried out by utilising the method of factorial experimental design on the process variables of interest obtained from a specifically equipped full-scale test gasifier. A response surface model in the process variables was fitted for each of the performance variables. The models developed were validated and proved to be valid when considering different data sets. This paper discusses the application of factorial experimental design and the combination of process variables and mixture components in optimising a production process.

Optimisation of extrusion process to transform hardened chickpeas (Cicer arietinum L) into a useful product

AbstractThe objective of this work was to determine the optimum conditions for the production of extruded flour from hardened chickpeas (Cicer arietinum L). Hardened chickpeas were produced using accelerated storage at 33–35 °C and 76% relative humidity for 160 days. Hardened chickpeas were broken, dehulled and softened with a salt solution (2.5 g l−1 NaCl + 7.5 g l−1 NaHCO3 in distilled water) prior to extrusion. The single‐screw extruder operation conditions were selected from factorial combinations of process variables: extrusion temperature (ET, 130–160 °C), feed moisture content (FMC, 200–300 g H2O kg−1, wet basis) and screw velocity (SV, 150–200 rpm). Response surface methodology was applied as optimisation technique over four response variables: in vitro protein digestibility (PD), total colour difference (ΔE), water absorption index (WAI) and water solubility index (WSI). Predictive models for response variables were developed as a function of process variables. The conventional graphical method was applied to obtain maximum PD and WAI and minimum ΔE and WSI. Contour plots of each of the response variables were utilised, applying superposition surface methodology to obtain three contour plots for observation and selection of the best (optimum) combination of ET (150.5 °C), FMC (265 g H2O kg−1) and SV (190.5 rpm) for the production of extruded flour from hardened chickpeas with a single‐screw extruder. Extrusion significantly improved the in vitro protein digestibility (21.7%) and protein efficiency ratio (36.9%) of hardened chickpeas.© 2002 Society of Chemical Industry

Radius ratio estimation and fold situation prediction of the deformation profile in forging–extrusion process

Application of the finite element method in conjunction with abductive network is presented to investigate the geometrical shape of the deformation profile and its related fold defect during forging–extrusion process. The geometrical shape of the deformation profile may be characterized by a parameter of radius ratio that is defined as the ratio of the radius at the equatorial plane to that at the end surfaces of the deformed workpiece. Different geometrical conditions combined with various frictional constraints are taken into account as the process variables in this study. During the forging–extrusion process, several barrels with different radius of curvature may be successively formed along the lateral free surface of the workpiece and the extrusions of the free surfaces of the billet into the aperture surfaces within the dies are accompanied. A finite element based code is utilized to investigate the material flow characteristics resulting in different shapes of the deformation profile, and the abductive network is then applied to synthesize the data sets obtained from the numerical simulation. Finally, the prediction models are established for radius ratio estimation of the barrels and fold occurrence situation judgment under various combinations of process variables.

A response surface methodology approach to optimise pretreatments to prevent enzymatic browning in potato (Solanum tuberosum L) cubes

AbstractThe objective of this work was to find the best combinations of ascorbic acid concentration/soaking time (Pretreatment 1), 4‐hexylresorcinol concentration/soaking time (Pretreatment 2) and ascorbic acid concentration–4‐hexylresorcinol concentration/soaking time (Pretreatment 3) to prevent the development of enzymatic browning in raw potato cubes (10 mm × 10 mm × 10 mm). Potato variety Alpha was used as study model because of its low susceptibility to enzymatic browning. Response surface methodology was applied in all pretreatments on two response variables (Hunter L value and total colour difference) to find the best conditions for carrying out the pretreatments. The various pretreatments had variation levels for ascorbic acid (AA) concentration (1 and 3) and 4‐hexylresorcinol (4HR) concentration (2 and 3) of 1–4 and 0.04–0.20 g l−1 respectively; in all pretreatments the variation level for soaking time was 3–6 h. A central composite experimental design with two factors at five levels was used. Predictive models for Hunter L value and total colour difference were developed as a function of process or independent variables. The optimisation technique was applied to obtain maximum Hunter L values and minimum values of total colour difference. Surface superposition of these variables allowed identification of the best combinations of process variables for each pretreatment as (1) 2.9 g l−1 AA/4.8 h, (2) 0.04 g l−1 4HR/2.6 h and (3) 2.42 g l−1 AA–0.15 g l−1 4HR/5.41 h.© 2001 Society of Chemical Industry

Susceptibility testing of pathogenic fungi with itraconazole: a process analysis of test variables.

A 2(10-5) fractional factorial model was used to investigate the influence of 10 process variables in broth microdilution susceptibility tests with itraconazole against eight isolates of Candida species and six isolates of filamentous fungi in two growth media. An analysis of variance (ANOVA) indicated that glucose concentration and incubation time both significantly influenced control turbidity optical density (OD) values for most of the Candida spp. isolates, while incubation in >10% CO(2) versus ambient air, incubation temperature and inoculum size significantly influenced these OD values for about half of the yeast isolates. Control OD values for the mould isolates were most influenced by incubation time and temperature, and by occlusion of the wells with an adhesive sticker. Three statistical approaches, ANOVA, rank transformation and Mann-Whitney U-test, were used to assess the influence of the variable combinations on MIC, determined with a 50% growth reduction end-point. Incubation temperature and time, glucose concentration and inoculum size were the variables that most often affected susceptibility results to the level of statistical significance; however, the supplier of RPMI 1640 medium, the use of adhesive stickers and the atmosphere of incubation significantly influenced the MIC for some isolates. The medium used to prepare the test inoculum, the solvent used to prepare the stock solution and the shape of the microdilution plate wells significantly affected outcome, but only sporadically. A principal component analysis of the data matrix confirmed this order of relative influence of the test variables on the MIC. Since each fungal isolate responded differently to combinations of process variables in the test, we conclude that any unified method for antifungal susceptibility determination represents a compromise, rather than an idealized system.

Twin Screw Compounding of PE-HD Wood Flour Composites

Abstract The compounding of wood flour filled polyethylene is discussed with reference to co-rotating twin-screw extruders from two manufacturers. An acrylic acid-grafted polyethylene (PE-HD-AA) copolymer was used as the compatibilizer in high density polyethylene wood flour (PE-HD/WF) composite system. Special consideration was given to the compounding of the heat- and shear-sensitive wood flour. The relevant screw configuration was found to consist of short mixing length with low intensity of shearing. A suitable combination of processing variables was necessary for limiting the thermal degradation of the wood filler, however, tensile properties of the composites were not affected much. Furthermore, the allowable range of processing temperature was limited, and there was an upper bound of rotating speed and a lower bound of throughput rate within which the darkening of wood filler in the composites was acceptable. The processing window was also experimentally constructed in terms of the degree of darkening of wood composites.

Feasibility and multiplicity in reaction–distillation processes for systems with competing irreversible reactions

Several important technical reaction systems consist of competing irreversible reactions of the type A+B→C and A+C→D, in which C is the product and D is an undesired byproduct. To produce C from A and B, a conventional process using a reactor coupled with a distillation column to recycle unreacted educts can be used. An alternative is reactive distillation. In the present paper, a simple mathematical model for the conventional reaction + distillation process is developed (second-order reaction kinetics +∞/∞-analysis of the distillation column). This model is used to comprehensively investigate the feasibility and multiplicity of the process, a task which would be too time consuming using rigorous simulators. The entire range of different combinations of process variables which allow a desired selectivity (C/D) to be obtained is explored and it is shown for which combinations of input variables which types of multiple solutions (output) will occur. As all solutions are obtained analytically, it is possible to give a complete picture of the stationary system behavior including all transitions between the different types of solutions. An interpretation of the different kinds of multiplicity observed in the present process is given. The basic features of the solutions presented here should also hold for the reactive distillation process.

Manufacture of CF/PEEK composites from powder/sheath fibre preforms

The relationships between impregnation mechanisms, consolidation quality and processing conditions during manufacture of carbon fibre/polyetheretherketone (CF/PEEK) composites from powder/sheath fibre bundle preforms were investigated. Microscopy of cross-sections and density measurements were used to examine the quality of impregnation and consolidation. The consolidation process of composite laminates made from these material preforms can basically be divided into two steps: compaction and impregnation. Variations of void content in the laminates as a function of both bundle geometry and combinations of processing variables were estimated using an impregnation model. Effects of variations in bundle geometry and shape ratio on impregnation behaviour are discussed. Results of transverse flexure tests were used to correlate mechanical properties with impregnation quality, in particular the void content in the laminates. Finally, the optimum processing windows for the manufacture of laminates from CF/PEEK-3k and -6k preforms are suggested.