774. Tribological adhesion of particles in acoustic field

Transcription

1 774. Tribological adhesion o particles in acoustic ield Vladas Vekteris 1 Vytautas Striška Vadim Mokšin 3 Darius Ozarovskis 4 Rolandas Zaremba 5 Vilnius Gediminas Technical University Department o Machine Engineering Lithuania 1 vekteris@vgtu.lt vytautas.striska@vgtu.lt 3 vadim@vgtu.lt 4 darius.o@vilpra.lt 5 roliuxas@gmail.com (Received 1 September 011; accepted 14 May 01) Abstract. This paper investigates interaction between two particles in acoustic ield. It is shown that additional oscillating movements o particles occur as a result o plain acoustic wave action. This suiciently increases the probability o collisions between particles. Micro-displacements in the collision zone help to remove various pollutants oxidation products and adsorbed gas molecules rom suraces o particles. Strong adhesive bonds are ormed in the contact area between the particles. Keywords: acoustic ield particles adhesion aggregation. Introduction Suraces o solid particles dispersed in the atmosphere are ouled by oxidation products and have high moisture content [1]. Chemical bonds (short-range orces) between suraces o particles reach their peak value under the action o these pollutants []. I two particles come into contact with each other only Van Der Waals interaction become suicient or adhesion because chemical bonds reach peak value and total thickness o ouling layer is bigger than action interval o mentioned surace orces. However i the interaction o particles takes place in the presence o acoustic ield additional tangential orce occurs. This orce can break the ouling layer thereby removing pollutants and increasing the contact area between the particles. It is considered that small displacements occur on the separation suraces o particles under the action o tangential orces. This results in several-old increase in adhesion and higher degree o aggregation o particles. When two particles approach one another Van Der Waals attraction orces start to act between them. These orces occur due to luctuations in the charge distribution o atoms and molecules o particles. These charges orm continuously moving dipoles. As a irst solid body approximation it can be considered that Van Der Waals orce acting between atoms or molecules has additive character. Thereore total orce can be calculated by summing pairs o atoms o the both suraces. With this assumption Casimir [3] irst derived the ormula or adhesion orce acting on interace o two mirror polished suraces: F c A 40z0 4 A = ħπ where: ħ = h / π h is the Planck s constant c is the speed o light z 0 is the separation between suraces A>> z 0 is the area. It is established [4] that Van Der Waals adhesion orce acts between all the materials which are brought together at the nanometric distance. I the separation between suraces is less than 1 nm various chemical bonds are ormed between suraces depending on chemical composition o suraces. Fuller and Tabor [5] proposed the adhesive parameter : θ= Ez β β γ where E is the eective Young modulus z is the separation o average lines o two bodies β is the curvature radius o asperities γ is the variation o surace energy. Quantity β γ is related to the 3 / 1/ adhesion orce and quantity Ez β to the surace orce between asperities which appears when suraces are torn apart. I Fuller-Tabor parameter is small the adhesion plays a central role i large asperities dominate adhesion becomes weak. 3 / 1/ VIBROENGINEERING. JOURNAL OF VIBROENGINEERING. JUNE 01. VOLUME 14 ISSUE. ISSN

2 VLADAS VEKTERIS VYTAUTAS STRIŠKA VADIM MOKŠIN DARIUS OZAROVSKIS ROLANDAS ZAREMBA This work investigates the impact o acoustic ield on particle adhesion or large values o θ. Object o investigation The interaction between two general shape SiO particles 1 and (Fig. 1) in the acoustic ield was chosen as object o investigation. Let the radii o the particles be r 1 and r respectively separation between them is denoted by l. Value o interaction angle φ may vary and can be stochastic. Fig. 1. Scheme o particle motion in the acoustic ield: 1 particles l separation between particles φ interaction angle x coordinate Fig.. Approximate composition o surace layer o the particle: 1 ouling layer adsorbed gas layer 3 oxidation products 4 particle material The scheme o the surace layer o particles beore collision can be presented as shown in Fig.. Interaction between particles F p Interaction orce acting between two oscillating particles can be expressed as ollows [6]: r1 r u = ρ π 4 ( 1 3cos φ) (1) l where ρ is the density o the low r 1 and r are the radii o particles u is the velocity o the low l is the separation between particles (Fig. 1) φ is the interaction angle (Fig. 1). Velocity o the low can be obtained rom plain acoustic wave equation [7]: u = πx cos πt () where is the requency o the acoustic ield x is the amplitude o the low t is the time. The orce that makes the particles and low oscillate can be expressed as ollows [8]: 10π r Fs = 3 c 3 s J 4πx sin cs where J is the sound intensity x is the coordinate c s is the speed o sound. Graphical representation o Eq. (1) is presented in Fig. 3. (3) 510 VIBROENGINEERING. JOURNAL OF VIBROENGINEERING. JUNE 01. VOLUME 14 ISSUE. ISSN

3 VLADAS VEKTERIS VYTAUTAS STRIŠKA VADIM MOKŠIN DARIUS OZAROVSKIS ROLANDAS ZAREMBA a) b) Fig. 3. Interaction orce F p as unction o size o particles and interaction angle φ: a) = 10 khz x = 0.5 mm t = s l = r 1 + r ; b) = 0 khz x = 0.5 mm t = s l = r 1 + r Experimental investigations Special setup (Fig. 4) was designed and manuactured or experimental investigations. The scheme o the setup is presented in Fig. 4a. It consists o pipes 1 with integrated analyzers acoustic chamber with tone generator throttle 3 dispenser 5 an 4 and HEPA ilter 6. Lasair II particle detecting and counting system was used. Particle shape and size analysis was perormed using optical microscopy. Microscope images o particles are shown in Figs. 5 and 6. Particles have irregular shapes as is evident rom the igures. Aggregates o particles can be clearly observed in Fig. 6. VIBROENGINEERING. JOURNAL OF VIBROENGINEERING. JUNE 01. VOLUME 14 ISSUE. ISSN

4 VLADAS VEKTERIS VYTAUTAS STRIŠKA VADIM MOKŠIN DARIUS OZAROVSKIS ROLANDAS ZAREMBA a) b) Fig. 4. Experimental setup: a) scheme; b) photography; 1 pipe with analyzer acoustic chamber 3 throttle 4 an 5 dispenser 6 HEPA ilter 7 aerosol diluter Ati TDA-D100 8 particle detecting and counting system Lasair II 9 sound level in acoustic chamber Fig. 5. Quartz sand particles ater the action o acoustic ield (photo rom the optical microscope magniication 0) 51 VIBROENGINEERING. JOURNAL OF VIBROENGINEERING. JUNE 01. VOLUME 14 ISSUE. ISSN

5 VLADAS VEKTERIS VYTAUTAS STRIŠKA VADIM MOKŠIN DARIUS OZAROVSKIS ROLANDAS ZAREMBA Fig. 6. Quartz sand particles aggregation caused by the action o acoustic ield (photo rom the optical microscope magniication 00): 1 two-particle aggregate three-particle aggregate Conclusions 1. Theoretical investigations show that interaction between particles occurs only i the value o interaction angle φ exceeds 50º. Interaction orce increases as requency o acoustic ield decreases.. Theoretical and experimental investigations demonstrate that the rate o particle aggregation depends on requency o acoustic ield and value o interaction angle. When interaction angle increases the orce created by surace roughness occurs i.e. the riction actor increases. 3. Microscopic analysis o aggregated particles reveals that their suraces have an irregular shape and approximately coincide with the suraces shown in Fig. 6. Reerences [1] Schmaltz G. Technische Oberlächenkunde. Berlin: Springer-Verlag [] Czichos H. A Systems Approach to the Tribology. Moscow: Mir 198. [3] Casimir H. B. G. On the attraction between two perectly conducting plates. Proceedings o the Royal Netherlands Academy o Arts and Sciences Vol p [4] Briscoe B. J. Tabor D. Surace orces in riction and adhesion. Faraday Special Discussions o the Chemical Society Issue 197 p [5] Fuller K. N. G. Tabor D. The eect o surace roughness on the adhesion o elastic solids. Proceedings o the Royal Society A Vol. 345 No p [6] Bergman L. Ultrasound and its Application in Science and Technique. Moscow: Publishing House o Foreign Literature [7] Vekteris V. Zaremba R. Striška V. Tribology and adhesion o particles in acoustic ield. Proceedings o 13 th International Research/Expert Conerence Trends in the Development o Machinery and Associated Technology TMT009 Hammamet Tunisia 16 1 October 009 p [8] King L. V. On the acoustic radiation pressure on circular discs: Inertia and diraction corrections. Proceedings o the Royal Society A Vol. 153 No p VIBROENGINEERING. JOURNAL OF VIBROENGINEERING. JUNE 01. VOLUME 14 ISSUE. ISSN