Wyniki wyszukiwania - BazTech

1

Experimental and numerical investigation of axialand tangential forces in a stirred tank with yield-stress fluids

Story Anna, Story Grzegorz, Jaworski Zdzisław

Chemical and Process Engineering

|

2021

|

Vol. 42, nr 2

173–-190

EN

Complex rheological properties of yield-stress materials may lead to the generation of an intensive mixing zone near a rotating impeller. From the practical point of view, the zone should cover most of the stirred liquid. According to the literature review, several parameters may affect the size of the mixing zone, in particular forces exerted on the liquid. This paper presents both experimental and numerical investigation of axial and tangential forces generated during mechanical mixing of yield-stress fluids in a stirred tank. The tested fluids were aqueous solutions of Carbopol Ultrez 30 of concentration either 0.2 or 0.6 wt% and pH = 5.0. The study was performed for three types of impeller, pitched blade turbine, Prochem Maxflo T and Rushton turbine, in a broad range of their rotational speed, 𝑁 = 60 − 900 rpm. The axial and tangential forces were calculated from the apparent mass of the stirred tank and torque, respectively. The experimental results were compared with CFD predictions, revealing their good agreement. Analysis of the generated forces showed that they are dependent on the rheological characteristic of liquid and the impeller type. It was also found that although axial force was smaller than tangential force, it significantly increased the resultant force.

2

The impact of the energy state of the surface of friction pairs on the friction and wear in internal combustion engines

Borkowska J., Kaźmierczak A., Krakowian K., Cienciała M., Skorupa P., Łoza Ł.

Journal of KONES

|

2015

|

Vol. 22, No. 4

37--41

EN

The elements creating a friction pairs are described to be very difficult in terms of defining all optimal parameters in an unequivocal way. The research on stability of friction pairs is focused on the surface and the top layer of surface in the parts concerned. The main goal is to find new design solutions and materials, thereby achieving one million kilometers of mileage to main repair in the case of internal combustion engines. The biggest structural difficulties are noticeable in friction pairs where it can be observed sliding and returning motion, which is also connected with sealing function. A typical example of such pair is piston ring – cylinder sleeve in piston – rings - cylinder unit in an internal combustion engine. Engineers are currently seeking an additional factor, which would enable gaining the reduction of tangential force by reducing the friction coefficient in elements of friction pair during operations. The surface free energy may be such factor - it results from molecular structure and nature of the bonds between the molecules present in the material. Components of surface free energy determine the tribological properties of the material, which is reflected in the stability of the units. Energy state of the surface, which is connected with chemistry and characteristics in the material, is the first step to consider about the impact on wearing in internal combustion engine. This is the main topic of this article.

3

Pomiar składowej stycznej i normalnej siły oddziaływania między powierzchniami w procesie tarcia z uwzględnieniem adhezji

Kusiak Cz.

Tribologia

|

2005

|

nr 3

147-153

PL

Tematem referatu jest zależność między adhezją a tarciem ślizgowym ciał metalicznych. Adhezję powodują siły oddziaływania między powierzchniami, zagadnienie tych sił było analizowane we wcześniejszych publikacjach autora. Dla weryfikacji uzyskanych wówczas wyników za planowano eksperyment, polegający na zmierzeniu sił, działających między czołowymi powierzchniami próbek cylindrycznych, wykonanych ze stali, polerowanych dla uzyskania adhezji. W tym celu zaprojektowano i wykonano stanowisko badawcze omówione w referacie. Badając zależność między tarciem a adhezją wykonano pomiary momentu skręcającego, powodującego zerwanie połączenia adhezyjnego, oraz pomiary siły oderwania próbek. Na podstawie uzyskanych danych wyliczono, stosując odpowiednie procedury, umowną wartość siły oraz współczynnika tarcia. Rejestrowane podczas eksperymentu wykresy momentu skręcającego oraz siły adhezji dostarczają informacji o zmianie tych parametrów w funkcji czasu. Uzyskane wyniki potwierdziły, zdaniem autora, przydatność urządzenia i zastosowanej metody pomiaru oraz rejestracji wyników do badań związków między tarciem a adhezją.

EN

In the paper the role of adhesion in the process of friction has been discussed. It was noted that adhesion may constitute an important source of the resistance to motion, especially under dry friction condition. It was confirmed that for the benefit of the process uniformity it would be good to control friction and adhesion forces using the same friction pair. The layout of a test stand for a simultaneous measurement of these two values together with some preliminary results was presented.

4

Wyznaczenie składowej stycznej i normalnej siły oddziaływania między powierzchniami w procesie tarcia

Kusiak C.

Tribologia

|

2004

|

nr 3

227-235

PL

Omówiono podstawowe oddziaływania między dwiema cząsteczkami oraz siły działające między powierzchniami ciał stałych. Zakładając, że siła tarcia wynika z przyciągania między atomami na zetkniętych powierzchniach, na potrzeby analizy procesu tarcia przyjęto zależność siły oddziaływania od odległości wyrażoną w jednostkach umownych oraz przypomniano przedstawiony we wcześniejszej publikacji model tarcia ślizgowego. Kontynuując te rozważania, wyznaczono zależność siły stycznej i normalnej od odległości między powierzchniami tworzącymi skojarzenie cierne.

EN

The fundamental interactions between two particles of a solid with the focus at those phenomena which are of importance in the process of friction were discussed in the first paragraph. In the next paragraph the forces acting between surfaces of solids were discussed. A generally accepted assumption is that the friction force results from the forces of adhesion of the two sliding surfaces. For the purpose of the friction process analysis it was assumed that the relationship between the adhesion force and distance was expressed in conventional units. In the next paragraph the previously presented model of sliding friction, which took into account force interactions between atoms, was summarised. Continuing the previous considerations, a relationship between the tangential force and the normal force and the distance between the surfaces of the friction pair was derived in the body of the paper. The results show that the tangential component of the force of interaction decreases considerable with the increase of the distance to a value of 1.2 of the crystal lattice parameter. Farther increase of the distance does not affect the value of this force. The relationship between the normal component and the distance features a slight initial increase and then a linear decline.

5

Metodyka analizy nacisków i tarcia w łożyskach wałeczkowych w aspekcie korekcji styku

Raczyński A.

Tribologia

|

1999

|

nr 2

151-169

PL

W artykule jest opisany model zastosowany przy obliczaniu nacisków kontaktowych i momentu tarcia w łożysku wałeczkowym dowolnego rodzaju. W modelu tym uwzględnia się zmienność ciśnienia i poślizgu w obszarze styku wałeczków z bieżniami oraz zmienność współczynnika tarcia w zależności od poślizgu i ciśnienia, a także odchylenie wałeczków od nominalnego kierunku toczenia. Obciążenia wałeczka są obliczane przez całkowanie jednostkowych sił normalnych i stycznych. W wyniku rozwiązania równań równowagi wałeczka wyznacz się moment tarcia łożyska .Program komputerowy umożliwia obliczanie maksymalnych nacisków kontaktowych i momentu tarcia w zależności od dowolnie przyjętej korekcji.

EN

In the previous article (Purposes and Possibilities of the Use of Correction in Roller Bearings) the author has demonstrated that the use of correction can serve the purpose of reducing friction work, and as a result can lead to an increase in the mechanical efficiency of a bearing. To theoretically develop appropriate correction, one needs a calculation method allowing the moment of friction of a bearing to be determined depending on the correction. A mathematical-physical model is always the basis of a calculation method. The model assumed for the present analysis is as follows. The bearing rollers are subjected to the action of normal and tangent forces. Normal forces manifest themselves in the form of certain pressure fields in the contact with the roller races, while tangent forces - in the form of fields of unit forces. The pressure distribution I is calculated according to Boussinesq problem, by the finite element I method, taking into consideration the differences between the nomi- I nal and the actual position of the roller. (In reality, forces acting on the rollers cause their skew and tilt). Unit tangent forces are calcu- I lated on the basis of local unit pressures (related to pressure) and a ! local coefficient of friction. The local coefficient of friction depends on the pressure and slide, ace. to the literature data. Characteristics I of the coefficient of friction appropriate for the races (where small I slide occurs) and for the flanges (characterised by great slide). It is I slightly more difficult to calculate the coefficient of friction on the I flange when the area of contact starts on the edge of the roller end, since mixed friction occurs of a different proportion of fluid friction at different points of the contact area. The author has presented his own proposal of a solution to this problem, relating the contribution of fluid friction to the distance from the edge of the roller end. Lost motion at the contact of the roller with the ring is calculated basing on the differences in their tangential velocities. This difference results from the curved profile of these elements, from the skew of the roll- ' ers, and from the fact that the geometrical vertex of the cone of the roller does not lie on the bearing axis (which is a deliberate geometrical discrepancy). After the discussion of the mathematical model, a model of action of the rings on the roller of the cone bearing is presented in the article. This is the most complicated case (asymmetrical structure of the bearing, loads acting on the roller from three sides, greatly diversified lost motion on the races and on the flange, and considerable tendency of the roller to skew). First, the interaction of the race of the inner ring (FIG. 7) has been illustrated. Unit normal and tangent forces are integrated and then represented by concentrated normal and tangent forces and the moment of tangent forces. Next, the interaction of the flange has been illustrated, where the determination of concentrated resultant forces has also been presented. FIG. 8a shows a complete juxtaposition of normal forces and moments acting on the roller of the cone bearing. This juxtaposition is the basis of formulation of equations of balance of the roller (expressions 29-34). Moreover, equations of balance of the outer ring are used (expressions 35-40, FIG. 8b). In these equations there are certain geometrical and kinetic parameters which are functions of the following groups of quantities: a) the dimensions of the bearing imposed by the constructor, b) the normal loads on three races, Qi,Q0, Qf, c) the roller shift parameters: the skew angle Q and the tilt angle r\, as well as the angles of the roller cones j3<(, fito- The parameters enumerated under points b and c are unknowns of the system of equations of equilibrium. The system of equations cannot be solved analytically, since the unknowns are involved in most variables occurring in the equations. Thus, a numerical solution using approximate methods must be used. After solving the equations of equilibrium, the moment of friction from the lost motion on the surfaces of contact of the rollers and rings and the contact pressures occurring in the bearing in the state of equilibrium are calculated. In this manner information is obtained about the parameters of operation of the bearing under consideration, having a given set of dimensions and correction and the load imposed. By repeating such calculations for successive variants of correction, an image of the effect of correction upon the parameters of operation is obtained, which allows one to choose the most advantageous correction.