Longer Mixing Times Research Articles

Elemental mapping by micro X-ray fluorescence to assess binder distribution of improved soils

This paper explores micro X-ray fluorescence (µXRF) as a novel technique in geotechnical engineering to investigate the binder distribution in a cement-improved clay. The technique scans a 2D surface of a specimen providing continuous heatmaps of an element of interest such as calcium, a major component in cement. A soft and sensitive natural clay was improved with cement using different mixing times ranging between 30 s and 10 min. The subsequent µXRF tests revealed a poor binder distribution with considerable binder accumulations for short mixing times. Longer mixing times, however, resulted in a well distributed binder. The unconfined compressive strength after around four weeks of curing ranged from 100 to 200 kPa for the shortest mixing times to 400–450 kPa for the longest mixing time as a direct result of the varying binder distributions. The paper demonstrates that the µXRF technique can be a useful technique to characterise the binder distribution in improved soils.

Influence of mixing time and coarse aggregate content on the flowability, setting time, and mechanical properties of cemented backfill

Ensuring the even mixing of filling slurry is crucial for the performance of cemented backfill, and mixing time is a key factor in this process. This study comprehensively investigates the effects of mixing time and coarse aggregate content on the fluidity, setting time, and mechanical properties of coarse aggregate backfill through extensive experiments. The results indicate no significant regularity in the vibration diffusion of the filling slurry at different regions of the mixing shaft, and positional variations do not impact the slurry's fluidity. Vibration diffusion initially increases and then decreases with prolonged mixing time, suggesting an optimal mixing time of within 9 minutes. The setting time of the filling slurry shows no significant variation across different regions of the mixing shaft. However, the setting time decreases with longer mixing times and increases with higher coarse aggregate content. The uniaxial compressive strength (UCS) of the backfill improves with extended mixing time, particularly benefiting early UCS. Incorporating an optimal amount of coarse aggregate, around 60 %, also enhances the UCS. Both extending the mixing time and adding an appropriate amount of coarse aggregate help suppress the expansion of destructive cracks and reduce internal void structures, thereby improving the overall mechanical properties of the backfill.

Electrospun PLLA/PEI nanofibers for controlled drug release behaviors and antibacterial efficiency

This study focused on the poly(L-lactic acid) (PLLA) polymer matrices by adding branched polyethyleneimine (PEI) as an aminolysis agent. Electrospun nanofibers were made by blending PLLA and PEI at various weight ratios (85-15, 75-15, and 65-35) and mixing times (0.5 h, 1 h, and 2 h). Amine groups were introduced into the nanofiber matrices, as confirmed by Fourier-transform infrared (FTIR) spectroscopy. The PLLA-PEI reaction was affected by mixing time, as shown by rheological measurements of absolute viscosity and surface tension. As a result, the nanofiber diameters decreased up to 42% and 89% with longer mixing time and higher PEI content, respectively. The aminolysis reaction rate increased up to 6.6 times with more PEI. Furthermore, the nanofibers had improved host-guest interactions, as demonstrated by contact angle, drug release, dye adsorption and water adsorption tests. The drug-loading capacity of the nanofibers was enhanced by PEI modification, as indicated by the release profile of tetracycline hydrochloride. The nanofibers also revealed more than 99.99% antibacterial activity due to the presence of the amine groups in PEI. Optimum mixing time and polymer ratio were proved to be substantial parameters to reach appropriate nanofiber and improve spinnability for further biomedical applications.

Influence of Water Content and Mixing Conditions on the Properties of Lime-Based Materials

This paper evaluates the influence of water content and mixing conditions (mixing time and sequence of addition of the constituents) on the fresh state properties of lime-based materials and their impact on the hardened state properties. Higher water contents allowed an increased fluidity and lower torque, yield stress and plastic viscosity values. In turn, a longer mixing time with the aggregate caused a progressively stiffer mortar and a substantial increase in the torque, yield stress and plastic viscosity values due to the breakdown of lime agglomerates that consume part of the free water available to lubricate the mix. A longer mixing time without the aggregate caused similar trends, albeit to a much lesser extent. The water content and mixing conditions also had a major impact on the resulting porous structure of lime mortars and, thus, on their mechanical strength.

Parametric investigation of particulate matter emissions in a gasoline direct injection engine using computational fluid dynamics modelling

ABSTRACT The effects of start of injection (SOI) timing, spark ignition (SI) timing and exhaust gas recirculation (EGR) rate on particulate matter (PM) emissions in a gasoline direct injection engine are examined through computational fluid dynamics modelling. Varying SOI timing entails compromising between longer mixing time and lower fuel impingement. Delaying the optimal SOI timing by 20 crank angle degree (CAD) results in a 78% increase in number density and a threefold-increase in mass density. PM control benefits from retarding SI timing which prolongs mixing time and shortens soot residence time. A 10 CAD delay from the SI timing at 25 CAD before top dead centre reduces number density and mass density by 65% and 57%, respectively. EGR renders the in-cylinder condition unfavourable for PM formation despite the overall increase in equivalence ratio. For 10% EGR rate, a drop of 547 K in peak temperature decreases number density by 24%. However, mass density increases by a 1.7 factor due to high particle growth species availability.

Effect of isomaltodextrin on dough rheology and bread quality

SummaryIsomaltodextrin (IMD) is a novel highly branched α‐glucan ingredient that has potential applications in foods as a promising source of dietary fibre. In this study, we assessed the incorporation of IMD in baked products and its effect on dough rheology and physico‐textural characteristics of wheat breads. IMD was added to wheat flour to reach the US FDA level of ‘good’ source of fibre (10% IMD). Use of the straight‐dough method with IMD and regular dough mixing time (8 min) resulted in less elastic doughs and resulting breads displayed lower cohesiveness, springiness and chewiness compared to the control bread. A modified straight‐dough method, with longer mixing time (36 min) and adjusted water level (70%), and a sponge‐and‐dough method were used to allow gluten structure to more fully hydrate and develop. With IMD addition, the modified straight‐dough (36 min dough mixing time) and sponge‐and‐dough methods yielded enhanced dough elasticity compared to the original straight‐dough method. Breadmaking methods were identified (improved straight‐dough and sponge‐and‐dough) whereby IMD could be added at a 'good source' of fibre level with loaf appearance and texture similar to breads without IMD.

Optimisation Of Nano-ZnO And Nano-SiO2 Mixing Time For Bitumen Modification

Nanotechnologies have gradually penetrated to the field of bitumen modification especially where durable asphalt mixtures have to be designed. Longer mixing time, higher temperatures or/and higher rotation (shearing) speeds are needed to increase the dispersion of nanoparticles in bitumen. However, this is not necessarily beneficial to the physical and mechanical properties of the final material. As a result, in this study nano-zinc oxide (nano-ZnO) and nano-silica (nano-SiO2) mixing time for bitumen modification was optimized considering the physical and mechanical properties of the final bitumen. For this purpose bitumen PMB 25/55-60 was modified with nanoparticles at 180 °C using a laboratory high-shear mixer at a rotation speed of 4000 rpm for different modification time selected on the basis of literature review (60 and 90 minutes). Penetration, softening point, viscosity at 135 °C, recovery and non-recoverable creep compliance (multiple stress creep and recovery test) at 60 °C were measured in order to determine the optimal mixing time. The results showed that 60 minutes ensures the dispersion of nano-ZnO and nano-SiO2 in the bitumen PMB 25/55-60 and longer mixing time do not have a significant effect on the properties of nano-ZnO and nano-SiO2 modified bitumen (the difference was less than 7%).

Influence of the mixing procedure on the fresh state behaviour of recycled mortars

The effect of two different mixing protocols on the fresh-state behaviour of self-compacting mortars with and without recycled sand was compared. For this purpose, the mortar mixes were designed considering three solid volume fractions, while maintaining the water to cement ratio and superplasticiser dosage constant. The results conclude that the inclusion of recycled sand harmfully affects the rheological behaviour of the mortars and this effect can be mitigated using mixing protocols with longer mixing times and delayed admixture addition times. Finally, a rheograph was developed to explain the expectable changes in a conventional mix when recycled sand is incorporated, the solid volume fraction is varied and changes are applied to the mixing procedure.

Flexural and Shear Properties of CFRP Laminates Reinforced with Functionalized Multiwalled CNTs

The present study focuses on mechanical characterization of CFRP laminates reinforced with non-treated and treated multiwalled CNTs using nitric acid. The CNTs was treated using nitric acid to obtain carboxylic functional group. The epoxy resins are mixed with 0.3%wt of multiwalled CNTs at a constant mixing speed of 2000 rpm and mixing times varied from 24 h to 96 h. Laminates reinforced with treated multiwalled CNTs show an increase in the flexural strength by 17.4% and 15.3% at mixing times of 24 h and 96 h as compared to control laminates. The test results indicated that laminates reinforced with treated multiwalled CNTs have improved interlaminar shear failure stress which are 14% and 7% higher at mixing times of 24 h and 96 h as compared to control specimen. Improvement in behaviour was achieved for functionalized CNTs based laminates which prevents agglomeration. Longer mixing time (96 h) is not beneficial for enhancing the mechanical properties due to the break-up of small aggregates by overcoming the effect of van der Waals forces.

Relationship between microstructure and phase morphology of SBS modified bitumen with processing parameters studied using atomic force microscopy

The aging effects of varying processing parameters, mixing time and shear speed, on the morphology and phase structure of styrene–butadiene-styrene (SBS) modified bitumen were studied used atomic force microscopy (AFM). Both inclusion of SBS and varying processing parameters provide differences in topographic and phase images of the bitumen. The contrast between phases becomes more distinct with increasing mixing time and speed, with the amount of dark phase associated with the asphaltene component of the bitumen also increasing. SBS modification of bitumen results in a decrease in the number of ‘bumble-bee’ like structures and when combined with varying mixing time produced the longest ‘bumble-bee’ structures. At the lowest mixing speeds (1000 rpm), the mixing was not effective for the SBS to absorb the bitumen oily components. Longer mixing times, 45 min, clearly altered the blend morphology and resulted in shorter ‘bumble-bee’ structures.

Dispersion of graphite nanoplates in melt mixed PC/SAN polymer blends and its influence on rheological and electrical properties

The state of dispersion of two types of graphite nanoplates, namely graphene nanoplates (GnPs) and expanded graphite (EG), in polycarbonate (PC)/poly(styrene-acrylonitrile) (SAN) = 60/40 wt.% blends prepared with a two-stage melt-mixing approach is investigated and its influence on the melt rheological and electrical properties is evaluated. By using two different parameter sets in the first mixing step, different states of the filler dispersion are achieved in the PC. After mixing with SAN, the more stringent premixing conditions (higher mixing speed and longer mixing time) resulted in a lower proportion of visible graphitic structures. The EG achieved a better dispersion than the GnPs. The electrical conductivity is lower for each filler type when the samples show a better dispersion. On the other hand, a better dispersion led to a higher reinforcing effect (as observed in melt rheological studies). By determining the shear dilution exponent and applying the Eilers equation to the rheological results, the strengthening effect and the differences in the state of the filler dispersion between the two premixing conditions were evaluated.

Effect of total mixed ration processing time on ration consistency and beef cattle performance during the early fattening period

The aim of this study was to assess the effect of processing time of the total mixed ration (TMR) on its physical and chemical characteristics, consistency over time, dry matter intake (DMI), rumination, activity, feed conversion ratio (FCR) and performance of beef cattle. The trial was conducted on 98 charolais bulls (476 ± 36 kg) which were randomly assigned to two groups (1:54 animals in 6 pens; 2:44 animals in 5 pens). The two groups were fed rations with the same composition, but that were mixed for a short (20 min) mixing time (SMT) or for a 10 min longer mixing time (LMT). The trial lasted 60 days and was divided into 2 periods (P1 and P2). After P1 the diets were exchanged between groups according to a cross-over design. Animals were assessed for average daily weight gain (ADG), DMI, FCR, rumination and activity. All data were submitted to a mixed ANOVA model using the pen as random effect and period, mixing time and their interaction as fixed effects. The differences on TMR composition between pens and consecutive days within each diet, were tested through a GLM model using pen and day as fixed effects. A One-way ANOVA model was used to test the significance of the differences in activity and rumination between pens, within each diet, using the pen as fixed effect.The LMT ration had a lower particle geometric mean length (GML) compared with SMT (4.12 vs. 5.08 mm; P < 0.001). Bulls raised with the LMT showed a significantly higher ADG (1.96 vs. 1.87 kg/day; P = 0.035) and a lower conversion ratio (4.97 vs. 5.39; P = 0.036) compared with animals raised with SMT. Average daily rumination time and activity level did not differ between mixing time and were 381 min and 494 binary digits, respectively, but LMT bulls showed a lower (0.083 vs. 0.095; P = 0.012) index of dishomogeneity in activity (DA) and a lower sorting activity against long particles (99.8 vs. 96.3 %; P = 0.005). The variation of TMR composition between one day and another was significant (P < 0.001) for both neutral detergent fibre (aNDF) and starch in SMT, whereas in LMT it showed a tendency to significance (P = 0.056) only for neutral detergent fibre.These results indicate that LMT improved consistency of TMR over time, ADG, FCR and reduced feed sorting.

Mixing time influence on fatigue crack growth in a carbon black-filled natural rubber vulcanizate

Various processing parameters affect the dispersion of carbon black (CB) in a rubber matrix, of which mixing time plays a major role. The physical properties of a green compound namely bound rubber and Mooney viscosity along with mechanical and fatigue crack growth (FCG) are affected by the dispersion of filler particles. To determine the effect of mastication on dispersion, the mixing time was varied from 120 s to 600 s where it was gauged that an optimum range of mixing times display better dispersion. The difference in dispersion between the green and the cured compounds was also stark due to the flocculation mechanism. Longer mixing times do not show much decrease in agglomerate size on curing, that is, approximately 2%, whereas shorter time has led to a decrease of 20%. The FCG properties were studied using a tear and fatigue analyser, where the FCG rate displays a similar trend with the dispersion of CB.

The effects of sodium reduction on the gas phase of bread doughs using synchrotron X-ray microtomography.

Globally, the bakery industry has a target of reducing sodium content in bread products. However, removing salt results in changes in the quality of bread through effects on dough's gas phase during the breadmaking process. Using synchrotron X-ray microtomography, the objective of this study was to investigate how sodium reduction induced changes in the gas phase parameters (i.e., gas volume fraction, bubble size distribution (BSD) and its time evolution) of non-yeasted doughs made from a wide range of formulations (i.e., wheat cultivar and water content) prepared with different mixing times. As salt content was reduced, a lower gas volume was retained in the dough by the end of mixing. Less gas bubbles were also retained if doughs were prepared from a stronger wheat cultivar, higher water content, and/or mixed for a shorter time. Rates of change in the median (R0) and the width (ε) of the fitted lognormal radius dependence of bubble volume fraction [BVF(R)] indicated that reduced sodium content permitted disproportionation to proceed more rapidly. Higher water content or longer mixing time also resulted in faster disproportionation, indicating that water content and mixing time can be manipulated as a means of increasing bubble stability against disproportionation during low-sodium breadmaking. An examination of relative changes in dough's gas phase parameters arising from sodium reduction demonstrated that wheat cultivar, water content and mixing time all affected dough's tolerance to sodium reduction. Therefore, attainment of good bread crumb cell structure in low-sodium bread formulas is a function of salt's effects on dough rheology in addition to its effect on yeast activity, so that dough formulation and mixing conditions also need to be considered.

Pulsed Nd: YAG Laser Dissimilar Welding of Ti/Al3105 Alloys

Overlapped strips of titanium grade 2 and aluminum 3105-O alloy were welded together by an innovative spot-like pulse laser procedure. The tactile seam tracking on ring paths yielded reliable weld fit-up of 1 and 0.5 mm thickness strips. Since the welding parameters of Ti-Al were narrow, three welding speeds of 4, 5 and 6.67 mm•s-1 were chosen for the pretest conditions. The microstructural investigations showed that intermetallic compound Ti3Al, formed in Ti-rich fusion zone. Cracks formed in the Al-rich fusion zone as a result of TiAl3 precipitation. Dimple fracture occurred at 6.67 mm•s-1 welding speed. Longer mixing time at Ti-Al interface occurred at lower welding speeds of 4 and 5 mm•s-1, which led to the formation of thicker intermetallic compounds and more massive crack generation. It also increases the hardness of the fusion zone and results in brittle fracture type during the tensile test. The highest strength was achieved with a welding speed of 4 mm•s-1 which was a result of more massive weld nugget and lower porosity.

Flow Analysis of the Symmetric Airfoil NACA0015 Blade at Different Angles of Attack and Mixing Velocities in a Continuous Stirred Tank Reactor (CSTR)

Biogas produces from the degradation of organic compounds of garbage and water wastes from various sources such as ranch and agricultural industries, usually by the fermentation process with anaerobic microorganisms. Layers of sediment are often occurred that can block the flow and longer mixing time is required for a more homogenous mixing. The objective of this study is to solve the non-uniform and non-homogenous as well as to save the mixing time in the fermentation process of biogas production using a model-mixing reactor. Flow analysis using an image processing technique of the symmetric airfoil NACA0015 blade at different angles of attack and mixing velocities in a Continuous Stirred Tank Reactor (CSTR) was examined. The CSTR was equipped with two and three airfoil blades at the angles of attack 0, 10, 16(stall angle) and 20° operated at the mixing velocities at 80, 110, 140 and 190 rpm. The mixing efficiency was evaluated from the homogenous appearance of plastic particles (5 mm diameter) dispersed in water by an image processing technique. The results showed that the mixing efficiencies of CSTR with three blades were higher than that of the CSTR with two blades of about 1.3 folds. The mixing efficiency increased with increasing mixing velocities and angles of attack, and was almost constant when the blade angles of attack increased from 16° to 20° and the mixing velocity increased from 140 to 190 rpm. This may be due to the airfoil blade stall and the saturation of the mixing. A new blade design for the CSTR system from this study can give a more efficient stir and mixing flow which will not only be beneficial for biogas production in the laboratory scale, but also a model design for the industrial biogas production as well.

Viscosities, diffusion coefficients, and mixing times of intrinsic fluorescent organic molecules in brown limonene secondary organic aerosol and tests of the Stokes–Einstein equation

Abstract. Viscosities and diffusion rates of organics within secondary organic aerosol (SOA) remain uncertain. Using the bead-mobility technique, we measured viscosities as a function of water activity (aw) of SOA generated by the ozonolysis of limonene followed by browning by exposure to NH3 (referred to as brown limonene SOA or brown LSOA). These measurements together with viscosity measurements reported in the literature show that the viscosity of brown LSOA increases by 3–5 orders of magnitude as the aw decreases from 0.9 to approximately 0.05. In addition, we measured diffusion coefficients of intrinsic fluorescent organic molecules within brown LSOA matrices using rectangular area fluorescence recovery after photobleaching. Based on the diffusion measurements, as the aw decreases from 0.9 to 0.33, the average diffusion coefficient of the intrinsic fluorescent organic molecules decreases from 5.5×10-9 to 7.1×10-13 cm2 s−1 and the mixing times of intrinsic fluorescent organic molecules within 200 nm brown LSOA particles increases from 0.002 to 14 s. These results suggest that the mixing times of large organics in the brown LSOA studied here are short (&lt;1 h) for aw and temperatures often found in the planetary boundary layer (PBL). Since the diffusion coefficients and mixing times reported here correspond to SOA generated using a high mass loading (∼1000 µg m−3), biogenic SOA particles found in the atmosphere with mass loadings ≤10 µg m−3 are likely to have higher viscosities and longer mixing times (possibly 3 orders of magnitude longer). These new measurements of viscosity and diffusion were used to test the accuracy of the Stokes–Einstein relation for predicting diffusion rates of organics within brown LSOA matrices. The results show that the Stokes–Einstein equation gives accurate predictions of diffusion coefficients of large organics within brown LSOA matrices when the viscosity of the matrix is as high as 102 to 104 Pa s. These results have important implications for predicting diffusion and mixing within SOA particles in the atmosphere.

Borax Crystallization Kinetics in a Pitched‐Blade Turbine/Straight‐Blade Turbine Dual‐Impeller Crystallizer

AbstractThe influence of hydrodynamic conditions on crystallization kinetics and properties of borax crystals obtained in a dual‐impeller batch cooling crystallizer was investigated. The two impellers used, i.e., pitched‐ and straight‐blade turbines, were mounted on the same shaft. Hydrodynamics was analyzed by means of the mixing time values and specific fluid flow patterns generated. Results indicate that wider metastable zones were generally observed at impeller positions characterized by longer mixing times. In those cases, the growth rate constants were lower, resulting in a formation of smaller but more regularly shaped crystals. These findings imply that the dual‐impeller position should be taken into account in order to produce crystals of desired characteristics.

The Effects of Ovine Whey Powders on Durum Wheat-Based Doughs

Two types of ovine whey powder, with different protein content, were added at increasing substitution rates to two types of semolina, one with strong and tenacious gluten and the other with weak and sticky gluten. For each dough the optimum mixing time and hydration level were calculated using the consistograph. The whey powder negatively affected the leavening volume of all doughs, at all percentages except the lowest one (5%), mainly because of its effects on the elastic component of gluten as measured with a stress relaxation test. Differences of the secondary structure of gluten proteins among samples were investigated by analyzing the amide I band in the Fourier transform infrared spectra of the dough. Weak and strong semolina showed a different relative percentage of α-helix, random coil, and β-sheet structures. The longer mixing times for dough formation when using semolina with strong gluten led to an increase in α-helices and random coils, which caused a worse leavening performance than the weak-gluten semolina.

Investigating the Effects of Slurry Preparation Protocol on Electrochemical Performance of Carbon Based Flowable Electrodes

In recent years, a new concept of electrode design known as flowable electrodes have been proposed as a novel approach for many stationary applications including grid-scale energy storage and water desalination [1]. To date, variety of chemistries and charge storage mechanisms regarding flowable electrodes have been reported including intercalation [2], double layer/faradic [3], precipitation/dissolution [4], and polymer redox [5]. Though major differences are present in their mechanism for charge storage, all flowable electrodes depend on inter-particle interactions and extent of formed percolation networks to conduct electrons to/from the current collectors. Currently, one major challenge that limits widespread utilization of flowable electrodes is their relatively lower electrical conductivity in comparison to conventional film electrodes. As much of the electrode mixture consists of highly resistive electrolyte phase, well dispersion of particles and the nature of percolation networks formed play a major role in final conductivity and performance of the flowable electrodes. In this study, effects of dispersion time and mixing methodology on electrochemical performance of flowable carbon electrodes have been investigated. Specifically, 20 different cases have been tested by systematically changing mixing time (1.5, 3, 4.5, 8, 15 minutes), mixing methodology (stir-bar vs. high-speed shear mixing), and electrode composition (activated carbon (AC) only and AC plus multi-walled carbon nanotube (MWCNT) slurries) to study a wide variety of cases. Each case was then subjected to direct current (DC) conductivity and cyclic voltammetry (CV) measurements to identify the effects on electrochemical performance. Constant current and particle size measurements were also conducted to support the findings in this study. From the data collected, conductivity differences up to 60% have been observed depending on the mixing time and mixing methodology for the same electrode composition (Fig.1). Additionally, capacity differences as high as 77% percent have been observed for the slurries containing MWCNTs. Also, as mixing time increased, closer performance gap between tested cases have been observed suggesting a common well-dispersed state in flowable electrodes. These observations highlight the significance of the degree of dispersion on the performance of capacitive flowable electrodes and suggest that higher mixing speeds and longer mixing times are necessary for better electrochemical performance in carbon based flowable electrodes.