Glicksman’s viscous limit set of dimensionless parameters have been investigated using experimentally verified computational fluid dynamics model. Simulations have been performed for the two bubbling fluidized beds with different particle sizes and densities. Dimensionless average pressure drops across the bed height, dimensionless pressure standard deviations and dimensionless relative pressures have been investigated as a function of dimensionless superficial gas velocities for the two beds. Fluctuation of solid volume fraction and contours of solid volume fraction have also been investigated at different dimensionless gas velocities. Time series data of the pressure fluctuation and solid volume fraction are compared. The results indicate that the fluid dynamic similarity between two beds holds up to particle Reynolds number of 15. After this, the bubble activities in the two beds start to deviate significantly. The results of the work show that the analysis of solid volume fraction fluctuation gives higher accuracy than time-series pressure fluctuation when scaling the bubbling fluidized bed within the viscous limit.

Lattice Boltzmann method (LBM) is used to model the hydrogen production by splitting water by incident sunlight over Si nanorods. The purpose of this study is to investigate the transport and the formation of the hydrogen bubbles by electrochemical reactions with a 2D and a 3D numerical model using LBM. An ordered array of nanorods is created where each rod is 10 μm in high and 10 nm in diameter. The numerical models are simulated using MATLAB and parallel computing with the program Palabos. A reaction–advection–diffusion transport for two components is analyzed with electrochemical reactions. This process is further coupled with the momentum transport. The effect of different bond numbers and contact angels on the simulation results are analyzed. It has here been shown that LBM can be used to evaluate the transport processes at microscale and it is possible to include the effect of electrochemical reactions on the transport processes. An increased Bond number increases the bubble flow through the nanorod domain. A decreased contact angle facilitates the disconnection of the bubble to the nanorod at the top surface. The collection of the hydrogen bubbles at the top surface of the nanorods will be facilitated by an easy disconnection of the bubbles.

Efficiency is becoming more and more a main concern in the design of power transmissions and the demand for high efficiency gearboxes is continuously increasing. Also the more and more restrictive euro standards for the reduction of pollutant emissions from light vehicles impose to improve the efficiency of the engines but also of the gear transmissions. For this reason the resources dedicated to this goal are continuously increasing. The first step to improve efficiency is to have appropriate models to compare different design solutions. Even if the efficiency of transmissions is quit high if compared with the efficiency of the engines and appropriate models to predict the power losses due to gear meshing, to bearings and to seals already exist, in order to have a further improvement, some aspects like the power losses related to the oil churning, oil squeezing and windage are still to be investigated. In previous papers the authors have investigated by means of computational fluid dynamic (CFD) analysis and experimental measurements the churning losses of planetary speed reducers (in which there is a relative motion between the “planets + planet carrier” and the lubricant). Also the windage power losses have been studied by the authors in previous papers. This report is focused on the oil squeezing power losses. This kind of losses is associated with the compression expansion process by the meshing teeth. The contraction of the volume at the gear mesh implies an overpressure that induces a fluid flow primarily in the axial direction and this, for viscous fluids, means additional power losses and a decrease of the efficiency.In this work this phenomena has been studied by means of some CFD simulations. The influence of some operating conditions like the lubricant properties, the rotational speed and the temperature has been studied.

A steel plate is one of the critical components of a scroll expander system that can experience cavitation micro-pitting while in service. The content of the present paper consists of two distinct but interrelated parts. The first part aims to highlight that the use of computational fluid dynamics (CFD) simulations can constitute a potential tool for the prediction of cavitation erosion areas in scroll expander systems. For this purpose, a three-dimensional CFD, steady-state numerical simulation of the refrigerant working fluid is employed. Numerical results revealed the critical areas where cavitation bubbles are formed. These numerical critical areas are in direct qualitative agreement with the actual eroded regions by cavitation, which were found by microscopic observations across the steel plate on an after use, scroll expander system. The second part of the paper aims to further investigate the behaviour and the durability of the steel plate of the studied scroll expander system subjected to cavitation erosion by using an ultrasonic experimental test rig. Scanning electron microscopy and optical interferometer micrographs of the damaged surfaces were observed, showing the nature of the cavitation erosion mechanism and the morphological alterations of the steel plate samples. Experimental results are explained in terms of the cavitation erosion rates, roughness profile, accumulated strain energy, and hardness of the matrix. The experimental study can serve as a valuable input for future development of a CFD numerical model that predicts both cavitation bubbles formation as well as cavitation damage induced by the bubbles that implode on the steels plates.

Municipal solid waste landfills are potential long-term sources of pollution for both humans and the environment and need to be managed properly both during their lifetime and after closure. This paper analyzes the influence of the Râureni-Râmnicu Vâlcea landfill (Romania) on the concentration of pollutant reaching the groundwater and the nearby Olt River. Prediction of contaminant concentration in groundwater is based on a simple mathematical model of solute transport. Model parameters are determined from field data and scale analysis. Despite its recent closure after 32 years of activity, this landfill has the potential to continue to pollute both the Olt River and the groundwater for decades. Sensitivity analyses are performed to determine the impact of varying the dispersivity coefficients on the resulting contaminant transport and distribution in the aquifer. Aquifer pollution is predicted for twenty years beyond the landfill closure. Enhanced landfill monitoring and establishment of a shared data portal for Romanian environmental data is highly recommended.

The inhomogeneous theory of elasticity considers bodies, the mechanical characteristics of which (the modulus of elasticity and Poisson’s ratio) are functions of the coordinates. If indirect problems of the inhomogeneous theory of elasticity are identified, and the stress-strain state of the body has well-known functions of mechanical characteristics, the essence of inverse problems is to determine the functions of the inhomogeneity for a given stress state of the body. One of the first solutions to such an inverse problem was published in the work of Lekhnitskii (“Radial distribution of stresses in the wedge and half-plane with variable modulus of elasticity”. PMM, XXVI(1), pp. 146–151, 1962). In this article, we consider one-dimensional inverse problems for thick-walled cylindrical and spherical shells that are subjected to internal and external pressures in a non-varying temperature field. The aim of this work is to identify the dependence of the elastic modulus on the radial co-ordinate for which the equivalent stress according to a particular theory of strength will be constant at all points of the body (such structures are called equal stress), or the equivalent stress in all points will be equal to the strength of the material (such structures are called equal strength). For example, the author has proven that the limit loads on resulting equal-strength inhomogeneous shells can be significantly increased.