Low Rotational Speed Research Articles

PIV and CFD investigation of paddle flocculation hydrodynamics at low rotational speeds

In this study, flocculation hydrodynamics were evaluated by investigating the velocity field of turbulent flow experimentally and numerically, in a laboratory scale paddle flocculator. Turbulence that either promotes the particle aggregation or the breakage of flocs is complicated and has been considered and compared in this work using two turbulence models; namely, the SST k–ω and the IDDES. Results showed that IDDES provided very slight improvement as compared to SST k–ω, yielding the latter sufficient in accurately simulating the flow inside the paddle flocculator. A Goodness-of-Fit evaluation was adopted to study the convergence between PIV and CFD results, and to compare the results of the used CFD turbulence models. The study focused, as well, on the quantification of the slippage factor k, as 0.18 at low rotational speeds of 3 rpm and 4 rpm, and compared to conventional typical value of 0.25. This reduction of k from 0.25 to 0.18 yields around 27–30% increase in the power imparted to the fluid, and about 14% increase in velocity gradient (G). This implies that more mixing is provided than expected, and therefore, less energy is input and thus the electric consumption for the flocculation unit at a drinking water treatment plant could be potentially decreased.

Demulsification of phosphoric acid/ tri-n‑butyl phosphate (W/O) emulsion by a novel rotor-stator spinning disc device

The demulsification process of phosphoric acid/tri-n‑butyl phosphate (W/O) emulsion is investigated by a novel rotor-stator spinning disc device (RSSDD). Emulsion properties varied with emulsification rotor speed and phase ratio, and operating parameters such as flow rate and disc speed have been studied for their effects on demulsification efficiency D, relative volume of separated oil phase λ, dispersed phase fraction of creamed emulsion ɸc and change in the average droplet size of emulsion Δdc. The results show that D is primarily due to emulsion stability. Low emulsification rotor speed and phase ratio reduce the emulsion stability, resulting in an increase in D. The shear and centrifugal forces from rotation and the residence time, influenced by operating parameters, play a major role in D and Δdc. Operating at higher disc speed and lower flow rate is not supposed. D decreases with increasing flow rate and decreasing disc speed, while Δdc behaves in the opposite way. λ disperses within 1.52%-2.94%, resulting in a linear relationship between D and ɸc. The optimal operating parameters are determined with D of 41.12% for one cycle in RSSDD. A model is proposed for the prediction of D and ɸc, showing an acceptable agreement with the experimental results.

Spontaneous crystallization of chiral active colloidal particles

The crystallization dynamics of chiral active colloids are explored numerically. It is found that chiral colloids with large angular velocity could be localized by self-trapping, which promotes the formation of hexagonal crystal structures. The competition between chirality and coupling strength leads to the transition between liquid and solid regimes. Comparing to the achiral particles, the transition points shift towards the weak coupling region greatly with the increasing degree of chirality. The hexagonal structure seems more tenacious and more difficult to melt. Therefore, the solid–liquid coexistence region shrinks in the phase diagram. In the low rotational speed region, active particles swap neighbors rapidly, the system becomes globally ordered but undergoes a nonnegligible diffusion, leading to the structural ordering occurrence before dynamical freezing.

Nonlinear Dynamic Analysis of Gas Bearing-Rotor System by the Hybrid Method Which Combines Finite Difference Method and Differential Transform Method

Gas bearings have been widely applied to high-speed rotating machines due to their low friction and high rotational speed advantages. Nevertheless, gas lubrication is low viscosity and compressible. It causes the gas bearing-rotor system easy to produce self-excited vibration, which leads to instability of the rotor system and hinders the increase of rotor system speed. It is necessary to study the nonlinear behaviors of the aerostatic bearing-rotor system and the nonlinear vibration of the gas bearing-rotor system, especially considering the distribution mass and flexible and gyroscopic effects of the real rotor. In this paper, the nonlinear behavior of the gas bearing-rotor system is investigated from the viewpoint of nonlinear dynamics. Firstly, the dynamics model of a gas bearing rotor is established by combining the transient Reynolds equation and rotor dynamic equation obtained by finite element method (FEM). The transient Reynolds equation is solved using a hybrid method combining the differential transform method (DTM) and finite difference method (FDM). Then the transient gas force is substituted into the FEM rotor dynamic equation. In the end, based on the bifurcation diagram, the orbit of the rotor center, the frequency spectrum diagram and Poincaré map, the rotor system’s nonlinear behaviors are studied using a solution for the rotor dynamic equation with the Newmark method. Results show that there exists a limited cycle motion in the autonomous rotor system and half-speed whirl in the nonautonomous rotor system.

Numerical Investigation of Near-Tip Modifications for a Highly Loaded Low-Speed Rotor Under the Influence of Double Leakage

Abstract This paper numerically investigates the flow field in the tip region of a highly loaded axial low-speed compressor rotor. The rotor in focus is of a hybrid blade configuration, featuring a tandem profile in the mid-span region and single blade profiles near the endwalls. The simulated 1.5-stage configuration also consists of a single row inlet guide vane (IGV) and a tandem stator. Due to high loading coefficients (Ψ = 0.58) in combination with moderate flow coefficients (ϕ = 0.58), double leakage of the tip leakage vortex plays a major role at all operating conditions. As already shown in the past, double leakage is a stability influencing dominant flow phenomenon in compressor rotors and influencing that can be the key to an efficient working range enhancement on compressor stages. This work introduces a simple and powerful method of enhancing the working range for low-speed rotors under the influence of double leakage. It is shown, that modifications to the pressure side (ps) shape of rotor tip profiles can influence the interaction of the tip leakage vortex with the adjacent blade, comparable to the effects of casing treatments. These unconventional blade shapes result from the transformations from tandem blade configurations to hybrid blades near the endwalls. The resulting single blade profile close to the tip features a convex profile element (an increase in local thickness, called the “belly”), which significantly influences the local static pressure gradients. This unusual pressure-side profiling can change mass flow over the tip and, by correct positioning, may reduce the amount of double leakage and, consequently, increase the rotor’s efficient working range. This work presents the geometry definitions for the hybrid blade single-segments, a detailed analysis of the impact on design and off-design operating conditions together with their underlying flow phenomena, and finally proposes design guidelines for the blade-tip geometries of highly loaded rotors under the influence of double leakage.

A CFD Validation Effect of YP/PV from Laboratory-Formulated SBMDIF for Productive Transport Load to the Surface

Several technical factors contribute to the flow of cuttings from the wellbore to the surface of the well, some of which are fundamentally due to the speed and inclination of the drill pipe at different positions (concentric and eccentric), the efficacy of the drilling mud considers plastic viscosity (PV) and yield point (YP), the weight of the cuttings, and the deviation of the well. Moreover, these overlaying cutting beds breed destruction in the drilling operation, some of which cause stuck pipes, reducing the rate of rotation and penetration. This current study, while it addresses the apropos of artificial intelligence (AI) with symmetry, employs a three-dimensional computational fluid dynamic (CFD) simulation model to validate an effective synthetic-based mud-drilling and to investigate the potency of the muds’ flow behaviours for transporting cuttings. Furthermore, the study examines the ratio effects of YP/PV to attain the safe transport of cuttings based on the turbulence of solid-particle suspension from the drilling fluid and the cuttings, and its velocity–pressure influence in a vertical well under a concentric and eccentric position of the drilling pipe. The resulting CFD analysis explains that the YP/PV of SBM and OBM, which generated the required capacity to suspend the cuttings to the surface, are symmetric to the experimental results and hence, the position of the drill pipe at the concentric position in vertical wells required a lower rotational speed. A computational study of the synthetic-based mud and its potency of not damaging the wellbore under an eccentric drill pipe position can be further examined.

Study of burr width and height using ANOVA in laser hybrid micro milling of titanium alloy (Ti6Al4V)

Ti6Al4V is regarded as the “workhorse” in aerospace industry for its wide applications at high temperatures. Unique attributes are high strength to density ratio and outstanding material properties at high thermal conditions. This present-day work involves the pre-slotting on Ti6Al4V surface with the help of fibre Laser, followed by the operation of micro-milling on respective Laser engraved slots. Localized melting due to Laser ablation leads to the decrease in the surface contact between milling tool and material surface. Micro-milling in return helps to remove the Heat affected zones (HAZ) created during Laser engraving process. ANOVA helps to point out the contributing factors for burr width and height on both milling sides. Main effect plots generated during process optimization, help to point out optimal combination of input parameters for minimized burr width and height. Higher frequency of Laser helps to generate consistent slots. Lower rotational speeds are responsible for high values of burr width and height. Whereas high rotational speed leads to efficient chip removal, resulting in decreased burr width and height.

Experimental investigations and 3D simulations by the overset grid method on twin-screw machines in both pump and turbine mode

Twin-screw pumps due to their particular capabilities, offer u nique b enefits in comparison to other types of pumps. They can also recover wasted energy from the fluid system when run in a reversed way, i.e., in turbine mode. In this study, the possibility of benefiting twin-screw machines instead of conventional control valves in order to recover energy is investigated. Flow physics and energy recovery are analyzed experimentally and by 3D flow simulations in both, pump and turbine mode. Pump and turbine characteristics under different operating points are experimentally measured for low and high viscous fluids, i.e., water and oil, respectively. It is observed that for higher viscosity the dependency of volume flow rate on the pressure difference imposed on the pump is reduced. This observation indicates the significant effect of viscosity on the gap flow. Based on a simulation method by means of overset grid technique, unsteady 3D flow simulations with a high grid quality and a high spatial resolution particularly in gap regions in terms of y + < 1 are conducted and results are validated against experiments. The profound assessment of gap flow based on the simulation results shows that for highly viscous fluids such a soil, the rotational speed of spindles as well as the direction of rotation have a significant effect on gap flow characteristics and consequently on the pump and turbine performance. From the experiments, it is clarified that with a lower rotational speed of spindles and a higher pressure difference, a higher amount of energy up to about 50% of the fluid energy in the piping system can be recovered instead of being dissipated by a conventional control valve.

Development and creation of a hydrodynamic liquid heating unit

The work is devoted to the study of the parameters of an installation for heating a coolant using liquid forcing through throttle openings. A scheme of a full-size experimental stand has been developed and the principles of operation are described in detail. For visual observation of the state of the liquid at different angular speeds of rotation of the rotor, a transparent drum model is made. The influence of the shape of the rotor skirt and the depth of its immersion in the liquid on the filling capacity of the rotor cavity at an angular velocity from 42 to 314 rad/s has been determined. The optimal parameters of the depth of immersion of the drum skirt with a diameter of 0.5 m in the liquid, at low rotor speeds of 16, 24, 32 rad/s, were obtained. The angle of inclination is calculated and it is experimentally proved that for a conical shape it is 5 degrees. It was found that at angular velocities of the rotor more than 100 rad/s, the shape and depth of immersion of the skirt in the liquid do not affect the filling of the rotor, since the feed is higher than its flow through the throttle openings. It is shown that the use of rotational forces to heat the liquid allows using an electric motor with less power, since it is spent only on unwinding the rotor with the liquid. The calculated dependence of the liquid pressure on the side walls of the rotor, the liquid heating temperature on the angular velocity of rotation of the rotor and on two values of the area of the throttle openings, at 31.4·10-6 m2 and 64.34·10-6 m2, is obtained. When the total area of the throttle openings is doubled, the temperature of the liquid heating at the same angular velocities increases from 35.6 °C to 82.5 °C. The above installation parameters allow you to get hot water when using small shell-and-tube heat exchangers

Electromagnetic and Electromechanical Compatibility Improvement of a Multi-Winding Switch Control-Based Induction Motor—Theoretical Description and Mathematical Modeling

The main advantages of multi-winding (multiphase) induction machines include reducing torque ripple, decreasing rotor harmonics losses, reducing the current per phase without increasing the voltage per phase, reducing the current harmonics of the DC voltage source, and high fault tolerance. The authors propose a theoretical description for the harmonic content of the DC-link current, magnetomotive force, and electromagnetic torque of a multi-winding induction machine (IM), and an account of the interaction of the time harmonics for the power supply and the spatial harmonics for winding functions is presented. The proposed theoretical analysis has made it possible to substantiate supply-winding schemes for the compensation of higher harmonics (6th and 12th in the DC-link current and the IM’s electromagnetic torque) and the improvement of the electromagnetic and electromechanical compatibility of the multi-winding machine, which are justified according to the proposed theoretical description. Further, a schematic solution for the multi-winding induction motor with electronic changing of the pole number is proposed to provide a reduction in speed ripples at low rotation speeds. This decrease is ensured by increasing the number of pole pairs and increasing the frequency of the supply voltage. Mathematical models of multi-winding switch control-based induction machines are developed using the method of average voltages in the integration step for an investigation of electromagnetic and electromechanical processes. It is shown that the developed models are distinguished by high speed of response and accuracy. This is confirmed by the comparative analysis using known methods and models in the Matlab environment, as well as a comparison of the simulation results with the known results of physical experiments. The results of mathematical modeling show that the use of a multi-winding IM with appropriate supply-winding schemes stands to significantly reduce the ripples of the IM’s electromagnetic torque and DC-link current in the case of using six-step voltage source inverters. This makes this type of inverter suitable for use in a frequency-controlled electric drive as an alternative to using a PWM inverter, which has a negative influence on the IM’s state.

Preparation of polyethylene glycol brush grafted from the surface of nitrile butadiene rubber with excellent tribological performance under aqueous lubrication

The water-lubricated bearing will be in a state of poor lubrication when marine stern shafts operate under low speed and heavy load conditions, which could cause severe wear and vibration, endangering the stealth performance of underwater vehicles. In this study, the grafting of polyethylene glycol brush was carried out on the surface of nitrile butadiene rubber (PEG-g-sNBR) by “grafting from” method. Fourier-transform-infrared-spectroscopy, nuclear-magnetic-resonance, and scanning-electron- microscope results demonstrated that the PEG-g-sNBR brush was successfully synthesized, and the reactive site was found. Using a tribological test machine with a high-precision vibration acceleration sensor, the tribological behaviors of PEG-g-sNBR were studied under aqueous lubrication. The results showed that the coefficient of friction of PEG-g-sNBR was reduced by 73.4% at 100 rpm compared to pure NBR, its microscopic wear and vibrational energy were also lower than pure NBR. Moreover, the lubrication states were revealed by friction, wear, together with the complexity of friction-induced vibration signal time series, and a lubricating film was formed on the friction surface of PEG-g-sNBR at lower rotational speed. In addition, the PEG-g-sNBR could work stably for 12 h at 300 rpm, and still maintain good tribological performance.

Analysis of circulating tumour cells separation in a curved microchannel under a high gravitational field

Cancer cells can detach from their original place and travel through tiny blood vessels or lymphatic capillaries in nearby tissues, forming a new tumour in other places of the body. While these circulating tumour cells (CTCs) are usually few in relation to the native blood cells, they provide crucial information about the characteristics of the primary tumour. Therefore, detecting and separating such cells from the bloodstream is an essential step in terms of diagnosis, treatment and prognosis of cancer patients. Perhaps, one of the well-known methods of separating CTCs is inertial focusing using a curved microchannel. This approach leaves CTCs separation strongly dependant on the channel design and Reynolds number for a given sample’s properties. Thus, the design suitable for a certain sample does not necessarily suit others. Here, a novel micro-analytical device is proposed and analysed. The device is based on using a spiral microchannel spinning around its axis at low rotation speed. The rotation generates Corilois secondary motions, focusing the separation of CTCs. The strength and structure of these Corilois motions can be adjusted easily by changing the rotation rate, which is under external control. This opens up the possibility of handling samples with different properties, achieving both higher throughput and complete separation of CTCs. The present work demonstrates the separation of human breast cancer cells using this approach over a wide range of volume flow rates (100–1000 ml/h) at different rotation rates (0–200 rpm), operating at relatively moderate Reynolds number. A model is developed, giving a quantitative prediction of flow and cells separation. It is shown that, for a single design, the cancer cells can be sorted completely with 100 % purity over a wide range of flow rates (400–700 ml/h) with a small adjustment of the rotation rate.

Effects of inclined state and rolling motion on gas–liquid effective interfacial area in a rotating packed bed

Confined space and floating environment present high challenges for gas–liquid separation and purification processes on offshore platforms. Rotating packed beds (RPBs) have shown great potential in onshore application, but its performance under offshore conditions remains unclear. This study first investigates the effective interfacial area (ae) within an RPB under inclined and rolling conditions by using the CO2 chemisorption method. The inclined state and rolling motion significantly affect ae, which is determined jointly by the secondary axial distribution and gas flow direction. The adverse effects occur at low rotational speed (N) due to the liquid collection driven by the gravity component, and increasing N was found to effectively against the collection and improve ae. Furthermore, ae under different motion periods and operating conditions were also investigated, and its relative rates of change and fluctuation can reach up to 17.4% and 10.7%, respectively. These results suggest that RPBs are somewhat resistant to marine conditions, providing the basis for offshore applications.

Unsteady Investigation of the Effect of Purge Air on the Flow Field Inside a Turbine Vane Frame Using Particle Image Velocimetry

Abstract Reducing greenhouse gas emissions and high fuel expenses motivates manufacturers to design more efficient aircraft engines. For directly driven jet engines, this is possible through increased by-pass ratios for high propulsive efficiencies. This implies a change in the operating condition of the low-pressure turbine (LPT) toward lower rotational speeds at larger diameters. Turbine vane frames (TVFs) guide the airflow from the high-pressure turbine (HPT) to the LPT in radial and circumferential direction. The TVF setup integrates turning vanes and thus removes the need for a vane blade row in the first LPT stage. Consequently, the TVF yields a benefit for overall engine weight and length, resulting in overall efficiency gains. Experimental measurements have been conducted at the two-spool test rig at the Graz University of Technology, consisting of a single-stage HPT, the TVF, and the first LPT rotor. Engine-relevant flow conditions are achieved at the TVF inlet, including HPT tip clearance and purge air effects. Particle image velocimetry (PIV) was used to capture the flow field in between two struts of the TVF upstream of the splitter vanes. Flow data in the area of strong transient interactions between the HPT and the TVF are recorded and discussed in terms of aerodynamic performance. To reveal the unsteady behavior of the fluid, the flow field has been recorded at six serial stator–rotor positions. Two data sets of varying HPT purge flows were obtained to characterize the effect of purge air inside the measurement domain.

Experimental Investigation into the Friction Coefficient of Ball-on-Disc in Dry Sliding Contact Considering the Effects of Surface Roughness, Low Rotation Speed, and Light Normal Load

The friction coefficient is one of the key parameters in the tribological performance of mechanical systems. In the condition of light normal load and low rotation speed, the friction coefficients of ball-on-disc with rough surface in dry sliding contact are experimentally investigated. Friction tests are carried out under normal load 2–9 N, rotation speed 20–48 rpm at room temperature, and surface roughness 0.245–1.010 μm produced by grinding, milling, and turning. Results show that the friction coefficient increases first and then becomes stable, in which the running-in and steady-state periods are included. With the growth of normal load and rotation speed, or the decline of surface roughness, the duration and fluctuation of the running-in period verge to reduce. The whole rising slope of the friction coefficient in the running-in period goes up more quickly with the increment of rotation speed, and it ascends more slowly as normal load enlarges. In terms of the steady-state period, the deviation of the friction coefficient shows a dwindling trend when normal load or rotation speed grows, or surface roughness descends. As normal load or rotation speed rises, the value of the friction coefficient rises first and then drops. Additionally, the mean value of the friction coefficient in steady-state is approximately independent of surface roughness.

Exploration of the dynamic osmotic membrane bioreactor in low-speed rolling motion for membrane fouling mitigation

A specific dynamic osmotic membrane bioreactor (DR-OMBR) in low-speed rolling motion was designed to alleviate membrane fouling. Using a low rotation speed (2 rpm) together with the cross-flow velocity in this designed DR-OMBR, the shear stress (−1.57 × 10−4 N/m2) and the centrifugal force (1.31 × 10−4 N) were generated to reduce the attachment of foulant to the membrane surface and achieve a relatively stable water flux. A parallel experiment indicated that the water flux of the conventional OMBR (without rotation) was 10% lower than that of the DR-OMBR, and total organic carbon and phosphate removals still achieved 99.9 and 97.0%, respectively. The ammonium rejection was slightly lower as a result of the Donna effect. Furthermore, compared to rotation speeds (0–5 rpm), the rotation speed of 2 rpm achieved better water flux (6.4 LMH) and lower reversal salt diffusion (3.7 gMH) because the centrifugal force had a positive effect on the reversal salt flux and a negative impact on the water flux, and a higher rotation speed could generate a considerable centrifugal force to limit the water flux and increase the reverse salt flux. Furthermore, the mitigation of membrane fouling was further confirmed by the relatively low amount of extracellular polymeric substances (EPS) and soluble microbial products (SMP) on the membrane surface of the DR-OMBR.

Antimicrobial photodynamic therapy as an adjunctive treatment to ultrasound for the dentin caries-like lesion removal

ObjectiveTo evaluate in vitro the efficacy of ultrasound device to remove caries-like dentin and the curcumin-mediated antimicrobial photodynamic therapy (aPDT) to decontaminate the affected dentin. MethodsBovine dentin specimens (n = 173) of 4 × 4 × 2 mm were first submitted to Knoop surface microhardness to standardize the specimens (29 ± 3 KHN). Artificial caries lesion was induced by Streptococcus mutans strain by biological model for 7 days. Infected dentin was removed (1 min) with the following techniques: dentin excavator, bur at low-speed rotation and ultrasound device. After that, aPDT application was performed using blue LED under 460 nm. Polarized light microscopy (PLM), removal rate (n = 10), cross-sectional microhardness (n = 10), colony forming units per milliliter (CFU) (n = 9) and confocal laser microscopy (CM) (n = 2) were performed. ANOVA with Welch correction, post-hoc Games-Howell and two-way ANOVA followed by Tukey's post-hoc tests were used. ResultsPLM confirmed the caries lesion formation with a depth of ∼147.9 µm. Groups treated with ultrasound showed lower removal rate (p = 0.001). Regardless of the treatment, the microhardness values increased as function of depth (p ≤ 0.05). Carbide bur showed the highest microhardness value, followed by ultrasound and excavator. CFU and CM showed a significant reduction in S. mutans after aPDT application. ConclusionUltrasound was efficient, since it removed infected dentin, preserving the affected dentin and aPDT can be used as a complementary therapy to decontaminate the affected dentin. Clinical significanceUltrasound device may help the clinician to remove dentin caries-like lesions since it is a conservative technique and provided the removal of infected dentin, preserving the affected dentin. aPDT application may be used as a complimentary technique to promote antibacterial effect and possibly minimize the risk of secondary caries.

Momentum and heat transfer characteristics of a rotating elliptical cylinder in vortex shedding flow of power-law fluids

A numerical analysis is carried out to comprehend the fluid flow and heat transfer phenomena of non-Newtonian power-law fluid flow around a rotating elliptic cylinder. The investigations are accomplished for parameters, namely, the aspect ratio of the cylinder, e=0.1; the rotational speed of the cylinder, 0.5≤α≤2.0; the Reynolds number, Re=100; the power-law index, 0.4≤n≤1.6; and the Prandtl number, 1≤Pr≤100. A detailed vorticity and isotherm patterns are presented to demonstrate the vortex shedding and heat transfer phenomenon around the cylinder. The results clearly show the strong dependency of fluid behaviors and rotational speed on flow and heat transfer phenomena. At a low rotational speed (α≤1.0), the standard vortex-shedding patterns appear. The behavior of the fluid mainly affects the size and strength of the vortices. At a higher rotational speed (α &amp;gt; 1.0), a hovering vortex (HV) appears for Newtonian and shear-thinning fluids. The shear-thinning tendency of the fluid encourages the formation of HV; however, the HV is not observed for shear-thickening fluids. Due to the rotational motion of the cylinder, the surface Nusselt number varies in a periodic manner with time/orientation. As expected, the Prandtl number (Pr) and shear-thinning (n&amp;lt;1.0) behavior of the fluid encourage the heat transfer from the cylinder. The rotational motion of the cylinder also favors the heat transfer phenomena. Finally, a correlation is presented for the time average surface Nusselt number (Nuavg) as a function of the Prandtl number (Pr), fluid behavior (n), and rotational speed (α).

Film thickness in miniature ball bearing grease lubricated

In this paper the authors theoretically evaluated the film thickness in a miniature angular contact ball bearing in grease and oil lubricated conditions and correlated with the variation of the electrical resistance experimentally determined by using tribometer CETR UMT-2. For grease the authors determined the film thickness considering base oil viscosity. The rotational speed of the inner race varied between 1 and 500 rpm and the axial load applied on a 7000C angular contact ball bearing was 8.1 N. The IVR and EHD lubrication regimes were analytically evaluated depending on the rotational speed and lubricants for both inner and outer race. Based of the dependence between film thickness and electrical resistance obtained for oil was evaluated the real film thickness obtained by using the grease. In case of oil lubricated condition, the experimental results showed an increase of electrical resistance with the rotational speed caused by increasing of the film thickness according to the theoretical model. For grease lubricated condition, ”a V-shaped pattern” was obtained. High values of electrical resistance at very low rotational speeds were observed. By increasing the rotational speed the electrical resistance for grease decreases until a limit speed and increase continuum over this limit. This behaviour was also reported in literature by ball-disc interferometry that showed at very low speeds that the thickener is dominant and over a speed limit the base oil is dominant in generating the film thickness.

Production of gamma-aminobutyric acid (GABA) by Bacillus subtilis BBEL02 fermentation using nitrogen-rich industrial wastes as crude feedstocks

Industrial-scale fermentation of γ-aminobutyric acid (GABA) is often limited by high cost of the starting raw materials. Increasing commercial applications of GABA in various industries have urged the research on finding the alternative substrates for the GABA production. The effects of concentration of different types of carbon and nitrogen sources; concentration of monosodium glutamate (MSG) in the defined medium for GABA production using the newly isolated Bacillus subtilis BBEL02 were studied. The feasibility of corn steep liquor (CSL) and soybean hydrolysate (SBH) as the replacement of nitrogen sources in the fermentation media for GABA production was also investigated. Highest GABA content (10.9 gL−1) and productivity (3.7 gL−1d−1) were achieved with defined medium containing 1 % (w/v) glucose, 2 % (v/v) SBH and 5 % (w/v) MSG. Dissolved oxygen (DO) of 80 % in 2-L fermenter presented the highest productivity (4.2 gL−1d−1) and GABA concentration (12.5 gL−1), however DO of 50 % was preferred because of the lower rotation speed to prevent cells deterioration.