The influence of micro coolers on the physical-mechanical characteristics of the steels used in making railway monoblock wheels
Original scientific paper The paper introduces the possibilities of improving mechanical characteristics of the steels used in making railway monoblock wheels, by using micro coolers on steel casting. The laboratory experiments are aimed at studying the control of round cross-section steel ingot solidification by adding crystallization germs in their central area, in order to influence the internal structure and the mechanical characteristics of the steel. The stimulation of heterogeneous germination on the surfaces generated by the particles introduced in the center of the ingot, while it was in a liquid state, leads to the formation of a second solidification front and heat absorption in this area. The data we obtained during the research have been processed in Excel, in order to obtain the correlation equations that express the variation of the steel mechanical characteristics as a function of the chemical structure both for the experimental samples and for the reference ones.
BUOYANCY-INDUCED FLOW AND HEAT TRANSFER OF POWER LAW FLUIDS IN A SIDE HEATED SQUARE CAVITY
This paper details the numerical study of laminar natural convection in a square enclosure filled with a non-Newtonian fluid. Thermal boundary conditions of the Dirichlet type are applied on the vertical walls of the enclosure while the horizontal ones are assumed adiabatic. A Power-law model is used to characterize the viscous behaviour of the purely viscous non-Newtonian fluids. The governing differential equations have been solved by the standard finite volume method and the hydrodynamic and thermal fields were coupled together using the Boussinesq approximation. The effects of Power-law index (n) in the range 0.50 ≤ n ≤ 1.50 on the heat and momentum transport are investigated for the values of Rayleigh number (Ra) in the range 10 ≤ Ra ≤ 10 and a Prandtl number of Pr = 10. We report accurate results of a systematic study with a focus on the most important buoyancyinduced flow and heat transfer characteristics. It is shown that the mean Nusselt number values increases with the increasing values of Rayleigh number for Newtonian as well as Power-law fluids. However, shear-thickening fluids (n > 1) are characterised with smaller Nu ̅̅ ̅̅ values. Finally, the onset of convection dominated heat transfer mechanism is shifted towards lower values of Ra for the shearthinning fluids (n < 1). (Received in April 2014, accepted in January 2015. This paper was with the authors 4 months for 2 revisions.)
General expression for the density effect for the ionization loss of charged particles
The equations for the density-effect correction $\ensuremath{\delta}(X)$ for the ionization loss as given in a previous paper have been extended to the case where $\ensuremath{\delta}({X}_{0})\ensuremath{\equiv}{\ensuremath{\delta}}_{0}g0$. Here ${X}_{0}$ is the lower limit of the range ${X}_{0}lXl{X}_{1}$, where a particularly simple expression for $\ensuremath{\delta}(X)$ applies; $X={log}_{10}(\frac{p}{{m}_{0}c})$, where $p$ is the momentum and ${m}_{0}$ is the mass of the incident particle. The case ${\ensuremath{\delta}}_{0}g0$ applies directly to the calculation of $\ensuremath{\delta}(X)$ for conductors (metals).