International Journal of Engineering
Volume:17 Issue: 2, Jul 2004

Biological hydrogen production by anaerobic bacterium, Rhodospirillum rubrum was studied in batch and continuous bioreactors using synthesis gas (CO) as substrate. The systems were operated at ambient temperature and pressure. Correlations available in the literature were used to estimate the gas-liquid mass transfer coefficients (KLa) in batch reactor. Based on experimental results for the continuous reactor, new correlation was generated. The results showed that the agitation, gas flow rate and dilution rate were greatly influenced the hydrogen production as well as on KLa. It was found that the KLa of continuous bioreactor was 180 times higher than the mass transfer coefficient reported in batch reactor. It can be considered that the estimation of KLa for the continuous bioreactor may be successful for the large-scale biological hydrogen production.

Texture and color appearance of froth is a discreet qualitative tool for evaluating the performance of flotation process. The structure of a froth developed on the flotation cell has a significant effect on the grade and recovery of copper concentrate. In this work, image analysis and neural networks have been implemented to model and control the performance of such a system. The result reveals that these techniques can be employed to control the performance of flotation cells, improve the recovery of the copper concentrate and finally reduce the dependency of the performance on the solely observation of an operator which can be otherwise subjected to human error.

An artificial neural network can be used as an intelligent controller to control non-linear, dynamic system through learning. It can easily accommodate non-linearities and time dependencies. Most common multi-layer feed-forward neural networks have the drawbacks of large number of neurons and hidden layers required to deal with complex problems and require large training time. To overcome these drawbacks, a generalized neuron based non-linear controller has been developed and illustrated as a power system stabilizer. Studies on a five machine power system show that the proposed controller can significantly improve the dynamic performance and provide good damping of the power system over a wide operating range.

Recently electronic tap-changer has received more attention due to its quick response, better performance and simpler maintenance compared to the mechanical tap-changer. This paper presents the capability of the distribution transformer equipped with an electronic tap-changer for improving power quality. At this end, the analytical computation for determining the compensating limit of electronic tap-changer is given and then this system is simulated in order to show its capabilities for power quality enhancement. Meanwhile, the impact of the electronic tap-changer in power quality parameter improvement is compared with that of other custom power tools.

This paper describes the robust optimal incremental motion control of a current sensorless synchronous reluctance motor (SynRM), which can be specified by any desired speed profile. The control scheme is a combination of conventional linear quadratic (LQ) feedback control method and sliding mode control (SMC). A novel sliding switching surface is employed first, that makes the states of the SynRM follow the nominal trajectories (controlled by any type of nominal controller) when the motor parameter uncertainties and the disturbance load torque exist. The SM controller has no reaching phase and produces small SMC chattering. Then, using the above tracking controller, the well-known torque control schemes, maximum torque (MTC), constant current inductive axis control (CCIAC) and maximum power factor control (MPFC) related to the SynRM are examined below and above the base speed. Finally the validity of our proposed control scheme is verified by computer simulation results.

This investigation deals with the transient analysis of the machine repair system consisting of M-operating units operating under the care of single repairman. To improve the system reliability/availability, Y warm standby and S cold standby units are provided to replace the failed units. In case when all spares are being used, the failure of units occurs in degraded fashion. In such situation there is a facility of one additional repairman to speed up the repair. The lifetime and repair time of units are exponentially distributed. We use matrix method to solve the governing Chapman-Kolmogorov equations. Expressions for the system reliability, availability, mean time to system failure, etc. are established in terms of transient probability. Computational scheme is discussed to facilitate the numerical results. Sensitivity analysis is also carried out to depict the effect of various parameters on the system reliability.

Assessment of creep damage and residual creep life of a cast HP 40 Nb Mod. Reformer tube was performed, wherein the experimental Larson–Miller diagram and area fraction of creep voids were adopted. The state of damage of the tube in service was metallographically analyzed by using light and electron microscopy. Samples from the serviced reformer furnace tube were cut and prepared for void examination and creep test at 940ºC-1000ºC under 20-30 MPa stress. Microstructural examination was carried out with an Scanning electron microscope with secondary and backscattered electron detectors. Inter-granular voids in the microstructure of the worked tube as a result of a creep phenomenon are ranked relating to the remaining life.

Thermodynamics of extraction of Zn2+ from sulfuric acid media contacting to a mixture of DEHPA and MEHPA diluted with 80 wt% aromatic-aliphatic kerosene with a constant DEHPA to MEHPA ratio is investigated at different acidities, concentrations and temperatures. As a result, the extraction reaction is found to be endothermic with a zinc distribution factor that increases with increasing of the temperature, acidity of the solution and the concentration of the extractant. The mechanism of the extraction reaction is shown to be different for pH > 1 with that at pH <1. The pH of the aqueous media has also an important influence on progressing of the extraction reaction.

In this research, a method for producing gum tragacanth (GT) fibers is presented. Ribbon type GT of Astragalus Gummifer species were obtained from local production lands. The gum was treated with alkali to increase its process ability, and allowed to stand for a period of time to reach the proper viscosity and/or to "ripen". Samples with different ripening times were prepared and their viscosities were measured to determine the effect of ageing time on viscosity. They were injected into a coagulation bath. Calcium chloride with different concentrations was applied as the coagulant agent. The consolidated samples were washed under different pH conditions. Finally, the mechanical properties of these premitive fibers were measured and their scanning electron micrographs were taken. The results show that chemically modified GT can be processed into fibers with different qualities.