Contents of the Journal of Mechanical Engineering 51, 5-6 (2000)

M. VARCHOLA, P. TOTH: Radial thrust  in  a centrifugal pump (in Slovak)   263

M. GANCO: Secondary flow at the outlet of an impeller of a mixed-flow 
pump (in Slovak)                                                          279

O. STRYCEK: Flow pump properties in the relation to the liquid 
properties (in Slovak)                                                    294

R. PALKA, K. JELEMENSKY: Heat exchange in scraped surface exchanger 
(in Slovak)                                                               307

K. VAVRO, F. DZIANIK, I. CEVOROVA: Particle movement in  classifying 
space of a centrifugal air classifier (in Slovak)                         316 

A. KACHANAK, R. KRBATA: Robust control of mechanical systems 
with structured uncertainty (in Slovak)                                   329

J. SASIK: Application of methods of expressing measurement
uncertainties using multicomponent sensors (in Slovak)                    346

V. MOLNAR, F. RIDZON, B. CERVENKA, J. HLBOCAN: Theoretical model 
of secondary flow in a curved duct with a low aspect ratio (in Slovak)    359
 

Information about the radial thrust on the impeller of the hydrodynamic pump is necessary for bearing design, estimating the gaps in sealing rings, and for cyclic strain of the shaft. The paper deals with an experimental investigation of the radial thrust by the original method and shows the influence of some construction factors, which affect both direction and size of the radial thrust. The paper suggests the differences of the influence of both impeller and a spiral casing on the change of the size and direction of radial thrust. It shows also that the size of radial forces satisfies the affinity equations when the speed changes.

The paper deals with the secondary flow at the outlet of an impeller of a mixed-flow pump. The basic equations, which enable to calculate the average values of velocity components and the value of pressure at the outlet of an impeller of a mixed-flow pump, are written. The theoretical results are compared with the experimental ones. At the end, a summary on the rise and the nature of a secondary flow at the outlet of an impeller of a mixed-flow pump is given.

This article analyses the conditions for the rise of separation flow in impeller vane channels and influence of this flow on the efficiency and work characteristics of the pumps. Conclusions are based on the analyses of the external integrated power characteristics in the flow control mode and on the internal relative velocity fields in the impeller vane channels. The fields of relative velocities are confronted with the impeller vane angles.

The heat exchanger with a rotating built-in mixer (scraped surface heat exchanger, SSHE) can be ranged into group of heat exchangers with mechanically influenced boundary layer. Criteria influencing the heat transfer coefficient were determined by inspection analysis. Then, dependence among the individual criteria was obtained by experiments and the criterion equations were stated - they are dependences of Nu number on Re_m and Pr numbers and blade amounts. The heat transfer coefficient and turbulent thermal conductivity values were verified by a numerical model. The measurements were performed for two liquids: water and 92 wt.% solution of glycerol in water. At the experimental measurements a significant influence of blade geometry was observed.

In this paper, the momentum equation describing the movement of isometric solid dust particles surrounded by countercurrent flow of air in the louver rotor of a centrifugal air classifier is reported. In the classifier, the dust is separated into fine and coarse fractions. Due to the complex nature of the physical model, the momentum equation was solved numerically and, thereafter, path-lines of dust particles relative to louver rotor channel were established. Results of integrating the dynamic equations are discussed with emphasis to the practical engineering use of data obtained so far. Finally, future work is outlined briefly.

In the paper the theory of so called \mu-synthesis of robust controllers is applied to control lumped parameter mechanical systems in conditions of uncertainty. A structured form of generalized model uncertainty is used leading to less conservative robust controller design. The effectiveness of the approach proposed in comparison with classical methods of controller design of mechanical systems is then illustrated by the design of a robust controller for generalized model of mechanical system with two degrees of freedom using so called D-K iterations. For the solution of the problems presented, software package MATLAB/SIMULINK was used and the obtained results can be generalized for more sophisticated model forms with nonlinearities and distributed parameters, as well.

At the present time uncertainties of measurement are being used to characterize the accuracy of measurement using multicomponent sensors. These uncertainties can be got from estimated source uncertainties using calculation models of measurement. The main scope of the paper presented is focused on the application of methods and means of standard, combined and extended uncertainties of measurement estimation. This procedure is a result of primary data processing.

An analysis method of secondary flow in a curved duct is presented. The method is based on an update of the well known Squire-Winter model. A differential equation for stream function of the secondary flow is derived. The equation is solved with a Fortran code to obtain secondary velocities and a secondary kinetic energy coefficient in the outlet plane of a rectangular duct. The results are presented for a 90^o duct with a defined velocity distribution in the inlet plane. The presented method will be used to support the experimental research of secondary flow in linear turbine cascade of a low aspect ratio.