Crisis phenomena in metal hydride hydrogen storage facilities

We present the results of experimental studies of heat and mass transfer processes in a metal hydride reactor under absorption and release of pure hydrogen. The hydrogen absorption/release reaction is shown to proceed in three stages: (I) heating/cooling of the absorbing material bed up to the reaction temperature; (II) equilibrium absorption/release; and (III) reaction completion. The transition from the first stage to the second is accompanied by a sharp decrease in the hydrogen flow rate at the reactor input/output. The crisis is caused by the ineffective pick-up/application of hydrogen absorption/release heat from/to the absorbing material bed. The reactor charging/discharging operation modes balanced against heat transfer make it possible to avoid crisis and to proceed under a constant flow rate of hydrogen.     

Mechanochemical synthesis and hydrogen sorption properties of nanocrystalline TiFe

The equiatomic intermetallic compound TiFe has been prepared by elemental mechanochemical synthesis in a planetary ball mill from Fe and Ti powders. The structural and phase transformations during synthesis were followed using X-ray diffraction. The reaction of the synthesized compound with hydrogen was studied volumetrically. The results demonstrate that the hydrogen capacity of the mechanochemical TiFe is 1.2 wt % at 2.5 MPa. Its absorption isotherm has an extended plateau in the range 1.6–1.7 MPa at room temperature.     

Typical features of measurement of the flow rate of biological fluid in hemodialysis machines

We consider the typical features of application of the laser Doppler method for determination of blood flow rate in hemodialysis machines. We have analyzed the scattering characteristics of blood and blood flow in the blood tubing. We have obtained estimates of the basic parameters of the Doppler signal and we present the optical layout of the flowmeter.     

Processor control in computerized data-acquisition systems

A method is proposed for detecting single and double processor errors during arithmetic and logicaloperations with reduced time consumption.     

Quantification of human error in maintenance using graph theory and matrix approach

Assessment of human error in maintenance requires identification of the contributing factors that lead to human error(s). These factors are called human error inducing factors (HEIFs), which take into consideration both the active and latent error contributing aspects related to man, machine and environment. A systems approach of the Graph Theory is applied in this paper for quantifying human error in maintenance activities that models the identified factors and their interactions/interrelationships in terms of human error digraph. The nodes in the digraph represent the HEIFs and the edges represent their interrelationships. The digraph is converted into an equivalent matrix and an expression based on this is developed, which is characteristic of the human error in maintenance. This expression is used to evaluate a human error index by substituting the numerical value of the factors and their interrelations. The index is a measure of the human error potential involved in the maintenance of systems. A higher value of index indicates that the error likelihood is more for the associated tasks, and more efforts are required to make the system less prone to human error. The proposed methodology is illustrated using a case study. The approach is anticipated to play a significant role in identifying sources of human errors and predicting their impact; and will help to integrate human factors during design stage with the objective of reducing human error in maintenance. Copyright © 2011 John Wiley & Sons, Ltd.     

Electric conductivity of metal-dielectric-metal structures with dielectric layer formed by spherical metal oxide nanoparticles

The electrical properties of metal-dielectric-metal (MDM) structures with the dielectric layer representing a monolayer of spherical Al₂O₃ or ZrO₂ oxide nanoparticles have been studied. It is established that these heterogeneous structures exhibit electric conductivity according to the mechanism for which the differential resistance dU/dI is negative and reversibly approaches zero with increasing current I. The electric conductivity strongly depends on the polarity of the applied voltage U, provided that electrodes are made of basically different metals or the same metal with different surface conditions. The mechanism of the electric conductivity in the given MDM structure depends on the diameter of nanoparticles in the dielectric layer.     

Mathematical simulation of a twisted pseudoplastic fluid flow in a cylindrical channel

The results of investigations of a pseudoplastic fluid twisted flow in a cylindrical channel are presented. With increase in the shear stresses caused by the flow twisting, the effective viscosity decreases. As a result, in the axial part of the channel a zone of lower pressure is formed which, at smaller flow twisting, leads to the formation of the zone of backward flows.