Band 19, Heft 12

In this paper we used the examples for four kinetic schemes under substrate and product inhibition of a biochemical reaction occurring in a real CSTR with Cholette’s model to demonstrate the strategy for high conversion and the multiplicity problem. In addition, it is found that the non-ideal mixing indeed influences the necessary and sufficient conditions for input multiplicity and output multiplicity. Meanwhile, for each of four kinetic schemes under substrate and product inhibition of a biochemical reaction, the input multiplicity regions are found inside the output multiplicity regions. This fact reveals that when deriving an operating strategy to obtain a high conversion and to avoid the control problem, only the output multiplicity is needed to consider even in the CSTR with the input and output multiplicity occurring simultaneously.

Liquid–gas ejector as a key component of jet loop reactor (JLR), plays an important role in the continuous production of gas–liquid mixing reaction. In this paper, a formula for estimating the gas induction of the ejector is presented. The effects of nozzle radius and mixing length on gas induction of liquid–gas ejector for gas–liquid mixing are simulated, and the formula is verified. Focusing on the efficiency and gas induction, the geometrical parameters are analyzed for the same cases, so that the performance of the ejector can be thoroughly understood. The results show that the optimum mixing section length to diameter ratio (LDR) is about 5–7, and the decrease of nozzle outlet radius can increase the gas induction, which provides a reference for the evaluation of gas induction for liquid–gas ejector and has crucial guiding significance for the design of nozzle and mixing section of liquid–gas ejector in industry.

The design of control methods for unstable plants is somewhat complex than that of stable plants. This is because unstable process models contain one or more poles lying on the right of the s-plane which yields unbounded closed-loop response. Further, the presence of the dead-time induces more complexity as it decreases the gain and phase margins which in turn deteriorates the closed-loop performance. The design of control strategies become more challenging for plants of unstable nature with positive zeros because they exhibit a phenomenon called inverse response. This paper suggests a method to design a double-loop scheme for unstable plants with/without inverse response. Accordingly, a proportional-derivative (PD)/proportional (P) controllers are used in the inner-loop for stabilizing the plant. A fractional order internal model controller (FOIMC) scheme is used to obtain the outer-loop controller using the stabilized plant model. The P/PD controller settings have been obtained by using the Routh-stability criteria and the maximum sensitivity approach. Procedure for selecting the outer-loop tuning parameter and fractional order is also given. Linear and nonlinear models of unstable plants including bioreactors and isothermal chemical reactors are used to demonstrate the merits of the suggested strategy. Robustness of the design and effect of measurement noise are also studied. Integrated absolute/squared error measures are also calculated. The suggested design is found to be more effective in controlling unstable processes than some reported works.

Digesting scheelite by using H 2 SO 4 –H 3 PO 4 is an environment-friendly and low-cost technology. The key approach to achieving efficient scheelite decomposition involves providing a good environment with uniform material composition for the growth of calcium sulfate. Therefore, numerical simulation of gypsum particle suspensions in a square stirred tank with a frame-type agitator for leaching scheelite was investigated. Simulated optimized results showed that the homogeneity of a multiphase flow system increased with the speed of the agitator. Reducing off-bottom clearance eased the dispersion of gypsum into the liquid. Adding baffles increased turbulence intensity and axial velocity in the tank, which eased solid suspension. The suspension improved, together with increases in the torque and power requirements of the agitator when the speed changed and baffled were added. However, when the solid suspension improved, the stirring torque and power slightly decreased, under a different off-bottom clearance of the agitator. Meanwhile, with residence time distribution as an evaluation criterion, the experimental results verified that the flow characteristics of the solid particles improved after optimization. This study can provide a theoretical basis and guidance for the optimization of the design and enlargement test of the stirred tank for leaching scheelite with sulfuric–phosphorous mixed acid.

The present study identifies the hydraulic efficiency of a novel onsite sanitation system at variable hydraulic shock loading conditions. The system consisted of three chambers, each working as an up-flow anaerobic bioreactor, accommodated within a single unit. The hydraulic characteristics were identified with the help of residence time distribution (RTD) analysis by step feeding of lithium chloride (LiCl) solution into the system. The experiments were run at variable hydraulic loading conditions at different peak flow factors (PFF) of 1, 2, 4 and 6 while maintaining 24-h hydraulic retention time. As revealed in the RTD analysis, the biofilm reactor achieved a very good hydraulic efficiency that varied from 0.76 to 0.81 at PFF 1, 2 and 4. Although in the case of PFF6, it was comparatively low. It was noted that the dispersion number was always below 0.2 at variable hydraulic shock loading conditions under different PFFs, which indicated that the reactor behaved perfectly between mixed-flow and plug-flow reactor. The system was also able to achieve good pollutant removal efficiency for chemical oxygen demand (COD) and total suspended solids (TSS) under all PFFs, which was more than 68 and 75%, respectively.

Beta-carotene, a pigment found in plants, is mainly produced by microalgae. Nevertheless, this production has only been investigated in pure cultures. Beta-carotene production through mixed culture eliminates the costly procedure of sterilization and contamination prevention needed for pure cultures. In this study, for the first time, the growth, beta-carotene, and chlorophyll production of a mixed culture of microalgae from Caspian Sea was investiagted under different stress conditions. At the condition of tripled light intensity and nitrogen starvation, beta-carotene content increased from 18.03 to 43.8 and 46.5 mol beta-carotene g −1 protein, respectively. However, the salinity of 4 mol L −1 caused the beta-carotene content to fall to zero. The blank sample reached a constant value of 23 mol beta-carotene g −1 protein. The comparable results with the specific monoculture species exhibit the high potential of a mixed culture of microalgae for beta-carotene production without need of the high sterilization cost. Nevertheless, more research is needed for where it can be a good substitute for pure culture.

In this study, we examined and strengthened the motion and heat transfer characteristics of tire particles in a rotary kiln. To overcome the difficulty of controlling the residence time of tire pellets and poor heat transfer, a study was conducted on heat transfer enhancement owing to lifting flight in a rotary kiln with spiral grooves. We developed a particle mechanics model using the discrete element method, and then simulated tire particle motion and obtained results using the EDEM software platform. The obtained motion results were programmed on a MATLAB platform for performing a heat transfer simulation study on the improvement in heat transfer. The coupling model of motion and heat transfer of waste tire particles was established. Through the analysis of particle movement and heat transfer, the following conclusions are obtained: with the increase of the lifting flight, the particle swarm heats up faster and more uniformly; with the increase of the rotation speed, the temperature of the particles rises faster and more uniformly, which has only the same effect as the lifting flight; to a certain extent, the smaller particle size can also improve the heat transfer effect. The maximum error of the relatively accurate coupling model of tire particle motion and heat transfer in a rotary kiln was only 12%, which provides a certain guiding significance for the improved design of the reactor.

In this study, membrane less double chambered microbial fuel cell has been used for the simultaneous electricity generation and organics removal from glucose and glutamic acid (mole ratio 1:1) based synthetic solution in the presence of municipal wastewater activated sludge-based microbes using graphite as an electrode. A central composite design technique has been employed to optimize the experimental conditions using design expert software for modeling input–output model as surface function of various input parameters like initial COD, anodic pH, and run time for voltage and current density generation. The predicted model suggests that maximum voltage and current density generation of ∼14.8 mV and ∼41.11 μA/m 2 , respectively are obtained at COD: 1500 mg/L, pH: 7, run time: 7 days. Further, methylene blue is used as mediator for voltage and current density production at optimum condition. Experimental result depicts the substantial role of mediator concentration and showing maximum current and voltage production, approximately 10 times higher than that without meditator under similar conditions. In addition to bioenergy production, values of BOD and COD in the wastewater simulant are found to be reduced after each run which exists below the permissible limits. The developed model equations give better prediction on the voltage and current density generation which lies within the error limits of −12 to +12% and −2 to 14%, respectively to their corresponding experimental values. Overall, the process can generate simultaneously bioenergy along with wastewater treatment and the empirical model gives better prediction with experimental values.

In Lab-On-Chip (LOC) applications, micromixing is the most important step to obtain fast analytical response in many biochemical and biological detections. Design and realization of smaller and shorter mixers with higher efficiency has become a necessity more than a recommendation. In this work, a numerical optimization of a passive mixer with a serpentine-shaped channel is proposed. By considering a laminar flow regime, the continuity and momentum equations, along with the advection-diffusion equation, are solved to evaluate the mixing performance. The optimization of the slanted grooves micromixer with a serpentine channel is achieved using computational fluid dynamics (CFD) and response surface methodology (RSM) based on Box-Behnken design. This method is used to find a second-order polynomial regression model and to obtain the optimal groove design. The considered objective function is the mixing index, while the four design variables are: the number of grooves per half cycle (N), the groove angle ( θ ), the groove depth to channel height ratio (d/h) and the ratio of groove width to channel width ( W d /W ). The optimization results indicate that the highest values of each selected interval of the groove depth to channel height ratio (d/h) and the angle between the radius and the groove ( θ ), on the other hand, the ratio of groove width to channel width ( W d /W ) of about 0.45 are desirable to promote faster mixing. The Flow behaviour in optimized “slanted grooves mixer (SGM) with serpentine channel was tested for low Reynolds number Re ranging between 0.3 and 5, and the results have shown that in the range of Re from 0.3 to 0.7 the mixing index is greater than 85%, for large range of Re from 1 to 4.5, the mixing index reaches the value of 93% in the first cycle of the channel and it approaches 100% for channel length of 1.25 mm from the inlet of the channel. Thus the most important result of this work shows that higher efficiency is obtained for short distance and the required pressure drops decreases. This micromixer can be selected as a good candidate in applications that require a high degree of mixing with relatively small length mixing as polymerase chain reaction (PCR) in the analysis and extraction of DNA.