Acta Polytechnica https://doi.org/10.14311/AP.2022.62.0488 Acta Polytechnica 62(4):488–497, 2022 © 2022 The Author(s). Licensed under a CC-BY 4.0 licence Published by the Czech Technical University in Prague A COMPARATIVE STUDY OF FERROFLUID LUBRICATION ON DOUBLE-LAYER POROUS SQUEEZE CURVED ANNULAR PLATES WITH SLIP VELOCITY Niru C. Patela, Jimit R. Patela, ∗, Gunamani M. Deherib a Charotar University of Science and Technology (CHARUSAT), P. D. Patel Institute of Applied Sciences, Department of Mathematical Sciences, CHARUSAT campus, Changa 388 421, Gujarat, India b Sardar Patel University, Department of Mathematics, V. V. Nagar 388 120, Anand, Gujarat, India ∗ corresponding author: patel.jimitphdmarch2013@gmail.com Abstract. This article makes an effort to present a comparative study on the performance of a Shliomis model-based ferrofluid (FF) lubrication of a porous squeeze film in curved annular plates taking slip velocity into account. The modified Darcy’s law has been adopted to find the impact of the double- layered porosity, while the slip velocity effect has been calculated according to Beavers and Joseph’s slip conditions. The modified Reynolds equation for the double-layered bearing system is solved to compute a dimensionless pressure profile and load-bearing capacity (LBC). The graphical results of the study reveal that the LBC increases in the case of magnetization, volume concentration and upper plate’s curvature parameter while it decreases with other parameters for both the film thickness profile. A comparative study suggests that the exponential film thickness profile is more suitable to enhance LBC for the annular plates lubricated by ferrofluid, including the presence of a slip. The study shows that the slip model performed quite well and there is a potential for improving the performance efficiency. Besides, multiple methods have been presented to enhance the performance of the above mentioned bearing system by selecting various combinations of parameters governing the system. Keywords: Shliomis model, curved annular plates, double-layered porous, slip velocity, exponential and hyperbolic film profile, ferrofluid. 1. Introduction Porous materials seem to be ubiquitous and play a notable role in many aspects of day-to-day life. They are extensively used in various areas, such as energy management, vibration automotive, heat insulation, processes of sound, turbine industries and fluid filtra- tion. Due to the phenomenon known as self-lubrication, the porous bearing has a porous film filled with some amount of lubricants so that it does not require more lubrication throughout the life period of the bearing. The lubricant comes out of the porous layer and is deposited between the annular plates to inhibit fric- tion and wear, as well as withstanding the original load applied to the annular plates. Therefore, the impact of lubrication due to the double porous layer is better than that of the single porous layer. Due to the remarkable mechanical properties and wide appli- cations of the annular plates, many researchers have been focused on analysing annular bearing systems, such as Lin [1], Shah and Bhat [2], Bujurke et al. [3], Deheri et al. [4], Fatima et al. [5] and Hanumangowda et al. [6]. Also, numerous studies (Ting [7], Gupta et al. [8], Bhat and Deheri [9], Shah et al. [10], Shimpi and De- heri [11], Patel and Deheri [12], Rao and Agarwal [13], Vasanth et al. [14] and Shah et al. [15]) have been carried out to examine the impact of porosity on the effectivity of annular plates. A synthetic fluid, namely “ferrofluid”, is a mixture of colloidal dispersions containing ferromagnetic par- ticles in a liquid carrier. Besides being used in elastic dampers to reduce noise, FFs are used in cooling and heating cycles, long-term sealing of rotating shafts, and reducing unwanted resonances in loudspeakers. In the last four decades, several investigators (Kumar et al. [16], Sinha et al. [17], Shah and Bhat [18], Patel and Deheri [19], Shah and Shah [20] and Munshi et al. [21]) have worked on a FF lubrication theory to examine the behaviour of various bearing systems. Alternative physical boundary conditions were proposed in the advanced study of Beavers and Joseph [22] that allowed a non-zero tangential velocity (called slip velocity) at the surfaces and uncovered that slip velocity had a broad effect on the bearing per- formance. Several studies have been documented in the literature about slip velocities for different condi- tions in bearing systems (Chattopadhyay and Majum- dar [23], Shah and Parsania [24], Shah and Patel [25], Venkata et al. [26], Deheri and Patel [27], Patel and Deheri [28], Shah et al. [29], and Mishra et al. [30]). In their studies, Fragassa et al. [31], Janevski et al. [32] and Geike [33] analysed the theory of static- dynamic load and lubricated contacts, respectively. These investigations confirm that the load profile re- 488 https://doi.org/10.14311/AP.2022.62.0488 https://creativecommons.org/licenses/by/4.0/ https://www.cvut.cz/en vol. 62 no. 4/2022 A comparative study of ferrofluid lubrication . . . mains crucial for the bearing design. Patel and De- heri [34] examined the influence of variations of viscos- ity of the ferrofluid on long bearings. It was noticed that the viscosity variation does not help to increase the LBC in the case of long bearings. Patel and Deheri [35] presented a comparison of a porous struc- ture on shliomis-model-based ferrofluid lubrication of a squeeze film between rotating rough-curved circu- lar plates. It has been ascertained that the Kozeny- Carman model has an edge over the Irmay’s model in improving the LBC. A study of thin film lubrication at nanoscale appears in Patel and Deheri [36], where a ferrofluid-based infinitely long rough porous slider bearing has been considered. It has been found that the magnetic fluid induced a higher load and showed a further improvement when the thin film lubrication at nanoscale took place. Very few studies have been made regarding the fer- rofluid lubrication in multi-layered porous plates in the presence of slip velocity. And even lesser amount of studies has been done concerning the comparative studies on the performance of ferrofluid lubricated porous squeeze film in the multi-layered bearing sys- tem considering slip velocity. Thus, it was thought proper to put forward a comparative study regard- ing the performance of a ferrofluid-based squeeze film in two-layered porous annular plates when the slip velocity is taken into account. To what extent can the ferrofluid lubrication counter the adverse effect of porosity and slip velocity? This fundamental question has been addressed while presenting the comparison. 2. Analysis Figure 1 involves two annular disks (inner and outer radius b and a, respectively (b < a)) with curved (exponential and hyperbolic film) upper surface and flat lower surface. Figure 1. Diagram of the porous annular bearing In view of Murti [37], Shah and Bhat [2] and Patel and Deheri [38], the thickness profile h of the film is assumed as h(r) = h0e−βr 2 , b ≤ r ≤ a for the exponential and h(r) = h0 1 + βr , b ≤ r ≤ a (1) for the hyperbolic profile. As per the discussions of Shliomis [39] and Ku- mar [40], and neglecting the assumptions of Shukla and Kumar [41], the governing equations for the flow of FF as suggested by Shliomis [39] are −∇p+η∇2q+µ0(M ·∇)H + 1 2τs ∇×(S−IΩ) = 0 (2) S = IΩ + µ0τs(M × H), (3) M = M0 H H + τB I (S × M), (4) with the continuity equation (∇ · q = 0), equations of Maxwell ∇ ×H = 0, ∇ · (H +M) = 0 and Ω = 12 ∇ ×q (Bhat [42]). Above mentioned equation(2) reduces to −∇p+η∇2q+µ0(M ·∇)H+ 1 2 µ0∇×(M ×H) = 0 (5) and M = M0 H [ H + τ(Ω × H) ] , where τ = τB 1 + µ0τBτs I M0H with the help of equations (3) and (4), as given in Shliomis [39]. Equation(5) takes the following form, as discussed in Bhat [42] and Patel and Patel [43] with u, H = (0, 0,H0) and an axially symmetric flow, ∂2u ∂x2 = 1 η(1 + τ) dp dr (6) where τ = 3 2 ϕ ξ − tan hξ ξ + tan hξ . Because of Beavers and Joseph’s [22] slip boundary conditions u(z = 0) = 0, u(z = h) = − 1 s ∂u ∂z , ηa = η(1 + τ), the solution of equation (6) can be transformed to u = − 1 ηa z2 − zsh(z − h) 2(1 + sh) dp dr . (7) 489 N. C. Patel, J. R. Patel, G. M. Deheri Acta Polytechnica With the help of the above expression (7), one can find the continuity equation (1 r d dr ∫ h 0 rudz +wh −w0 = 0 ) , as 1 r d dr ( h3r(2 + sh) 1 + sh dp dr ) = 12ηa(wh − w0). (8) Assuming the upper surface having a double layered porous facing and the lower flat surface being solid in the annular plate bearing. In the present study, P1 and P2 of the porous region satisfy the following equations, respectively (Bhat [42]), 1 r ∂ ∂r ( ∂P1 ∂r ) + ∂2P1 ∂z2 = 0 and 1 r ∂ ∂r ( ∂P2 ∂r ) + ∂2P2 ∂z2 = 0. (9) Using the Morgan-Cameron approximation, one gets( ∂P1 ∂z ) z=h1 = H1 r d dr ( r dp dr ) ,( ∂P2 ∂z ) z=h2 = H2 r d dr ( r dp dr ) . (10) Since the lower surface is solid and the upper sur- face has a double layer porous facing, the velocity component along z-direction is w0 = 0 wh = ḣ0 − [ k1 ηa ( ∂P1 ∂z ) z=h1 + k2 ηa ( ∂P2 ∂z ) z=h2 ] . (11) Incorporating equation (9) and (10), equation (11) turns into w0 = 0 wh = ḣ0 − [ k1 ηa ( H1 r d dr ( r dp dr )) + k2 ηa ( H2 r d dr ( r dp dr ))] . (12) Using equation (12), and ηa = η0 ( 1 + 52ϕ ) (1 + τ), equation (8) yields 1 r d dr ({ h3(2 + sh) 1 + sh + 12k1H1 + 12k2H2 } r dp dr ) = 12η0 ( 1 + 5 2 ϕ ) (1 + τ)ḣ0. (13) Upon introduction of the non-dimensional measures: R = r b , h = h h0 , β = βb2 (exponential), β = βb (hyperbolic), P = − h0 3p η0b2ḣ0 , s = sh0, ψ1 = k1H1 h0 3 , ψ2 = k2H2 h0 3 , (14) and using above equation (14), equation (13) trans- forms to 1 R d dR {[ h 3 (2 + sh) 1 + sh + 12(ψ1 + ψ2) ] R dP dR } = −12 ( 1 + 5 2 ϕ ) (1 + τ). (15) Considering boundary conditions of annular plates, P(1) = P(k) = 0, (16) one can find the dimensionless P as P = ∫ R 1 ( − 6ER G ) dR + C1 ∫ R 1 ( 1 GR ) dR, (17) where C1 = ∫ k 1 (6ER G ) dR∫ k 1 ( 1 GR ) dR , G = h 3 (2 + sh) 1 + sh + 12(ψ1 + ψ2), E = ( 1 + 5 2 ϕ ) (1 + τ), while the non-dimensional LBC of the annular plates can be found as, W = − h0 3W 2πη0b4ḣ0 = ∫ k 1 RP dR = − 1 2 (∫ k 1 − 6ER3 G dR + C1 ∫ k 1 R G dR ) (18) 3. Result and discussion The results for the double-layered porous medium and slip velocity on exponential and hyperbolic film profiles of the annular bearing are discussed in this sec- tion. Equation (17) establishes the non-dimensional 490 vol. 62 no. 4/2022 A comparative study of ferrofluid lubrication . . . pressure, while equation (18) represents a dimension- less LBC. In addition, expression (18) is linear in terms of the magnetization parameter, which indi- cates an improvement of the LBC of annular plates mathematically. As far as LBC is concerned, a comparison of the film profile is exhibited graphically in Figures 2–13 with double-porous facing in the occurrence of a slip. The first figure demonstrates the exponential film shape and the second figure depicts the impact of the hyperbolic profile. The performance of appearance of the Shliomis’ FF lubricated double porous medium annular plates is based on the foundation of several non-dimensional parameters like magnetization, upper plate’s curvature, porosity, volume concentration and slip velocity. It can be observed that the exponential film fares better. It is noticed that equation (18) suggests the LBC of a single layer porous medium when ψ2 → 0. With ψ1 → 0 and ψ2 → 0, this investigation transfers to the non-porous FF based annular bearing system with the slip velocity. Also, this study reduces to a study of a traditional annular bearing by removing the effect of magnetization in the absence of the slip. For the range of the parameters, one can refer below: τ: 0.1–0.5, ϕ: 0.01–0.05, β: 1.5–1.9, 1/s: 0.02–0.1, ψ1: 0.001–0.005 and ψ2: 0.001–0.005. The dispensation of LBC about the τ, for numerous values of ϕ, β, ψ1, ψ2 and 1/s shown in Figures 2–5, recommends that the LBC rises strictly due to the FF lubricant. A closer examination of the figures emphasizes that the functionality of bearing systems as well as the increase in load is connected with all the parameters for both the film profiles. Exponential film profile registers a higher load as compared to the hyperbolic shape in Figures 2–5. The behaviour of the volume concentration parame- ter concerning various parameters of LBC is illustrated in Figures 6–8, respectively. Due to the rise of the volume concentration parameter, the effect of LBC de- creases with porosity (in Figure 7) and slip velocity (in Figure 8), while the effect of β (in Figure 6) increases the LBC. Moreover, Figure 8 suggests a marginally improved effect of the slip velocity in an exponen- tial film bearing, which indicates an enhancement of the overall annular bearing’s performance up to some extent. The profile of a non-dimensional LBC with respect to the β is described in Figures 9–11. If we increase the β, then the capacity of the load is growing sharply in the case of the hyperbolic function, while a re- verse behaviour is observed with porosity and slip velocity. However, the LBC increases slightly for the exponential profile and follows the same trends for the parameters mentioned above. One can visualize an identical scenario for the curvature of exponential and hyperbolic functions, which is shown in Figures 9–11. The effect of the porosity on the load distribution of the bearing is shown in Figures 12 and 13. In Fig- ure 12, the effect of slip velocity is negligible for the exponential profile. However, Figure 13 suggests that the trends of both the porosity parameters are almost the same. Both layers help to improve the lifespan of the system by creating a film layer between the surfaces. The graphical representation makes it clear that the following takes place. (1.) The nature of both porous facings is almost the same with the same values (ψ1 = ψ2), however, that does not apply when the porosity values differ. (meaning ψ1 > ψ2 or ψ1 < ψ2 ). (2.) Figure 13 displays the maximum load among all the figures, which means the double porous layer improves the LBC in annular plates bearing sys- tems. (3.) Higher values of curvature parameter have a negli- gible effect on the LBC in the case of the exponential profile, but it does reflect on the LBC in the case of the hyperbolic film profile. (4.) The effect of slip velocity is satisfactory for the exponential surface profile as compared to the hy- perbolic surface. (5.) Finally, this study helps to improve the LBC by considering the proper selection of all parameters and film shapes while designing the bearing system of annular plates. 4. Conclusion The effect of the double-porous layered on MF lubri- cated curved annular bearing is investigated theoreti- cally with the theory of Shliomis’ flow model of FF, modified Darcy’s law for double layer, and Beavers and Joseph’s more realistic slip conditions. In view of the bearing’s life period, it is evident that some of the parameters appear to have an opposite effect on the performance of the bearing system. Hence, this investigation clarifies that while designing the bearing system, the porosity in two layers, and the slip velocity must be considered. Interestingly, numerous factors (like porosity and slip velocity) disturb the system adversely even though the bearing can support a load without flow, this does not apply in the case of tradi- tional lubricants. Even the upper plate’s curvature, either exponential or hyperbolic, may significantly impact the performance of this bearing system, con- sidering the moderate values of volume concentration, slip velocity, and porosity. Lastly, the exponential film profile exhibits a higher load-bearing capacity, in the case of the double-layered porosity with Shliomis’ magnetic fluid flow when slip is in place. A pertinent question is to elevate this analysis by incorporating the effect of surface roughness and deformation. An immediate concern is to carry out this analysis for some other types of bearing systems including the circular ones with slip velocity. 491 N. C. Patel, J. R. Patel, G. M. Deheri Acta Polytechnica Figure 2. Variation of LBC as regards of τ and ϕ. Figure 3. Variation of LBC as regards of τ and β. Figure 4. Variation of LBC as regards of τ and ψ1. Figure 5. Variation of LBC as regards of τ and 1/s. 492 vol. 62 no. 4/2022 A comparative study of ferrofluid lubrication . . . Figure 6. Variation of LBC as regards of ϕ and β. Figure 7. Variation of LBC as regards of ϕ and ψ2. Figure 8. Variation of LBC as regards of ϕ and 1/s. Figure 9. Variation of LBC as regards of β and ψ1. 493 N. C. Patel, J. R. Patel, G. M. Deheri Acta Polytechnica Figure 10. Variation of LBC as regards of β and ψ2. Figure 11. Variation of LBC as regards of β and 1/s. Figure 12. Variation of LBC as regards of ψ1 and 1/s. Figure 13. Variation of LBC as regards of ψ1 and ψ2. 494 vol. 62 no. 4/2022 A comparative study of ferrofluid lubrication . . . List of symbols a Outer radius of annular plates b Inner radius of annular plates h Film thickness r Radial coordinates p Pressure of fluid u x – component of q w z – component of q H Magnitude of H I A sum of moments of inertia of the particles per unit volume s Slip velocity q Fluid velocity in the film region M Magnetization vector H An identical magnetic field S Internal angular momentum h0 Central film thickness w0, wh Values of w at z = 0, h respectively h1 Thickness of lubricant in the inner layer h2 Thickness of lubricant in the outer layer k1 Permeability of inner layer of the porous region k2 Permeability of outer layer of the porous region M0 Equilibrium magnetization H0 Constant magnetic field H1 Thickness of the inner layer adjacent to lubricant layer H2 Thickness of the outer layer adjacent to solid wall P1 Pressure of inside layer in the porous region P2 Pressure of outside layer in the porous region η Viscosity of suspension β Curvature of the upper plate ξ Langevin’s parameter τ Magnetization parameter ϕ Volume concentration τB Brownian relaxation time parameter τS Relaxation time parameter µ0 Permeability of free space η0 Carrier fluid viscosity ψ1 Inner layer porous structure parameter ψ2 Outer layer porous structure parameter References [1] J. 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Magnetic fluid-based squeeze film between curved porous annular plates considering the rotation of magnetic particles and slip velocity. Journal of Serbian Society for Computational Mechanics 14(2):69–82, 2020. https://doi.org/10.24874/jsscm.2020.14.02.05. 497 https://doi.org/10.24874/jsscm.2020.14.02.05 Acta Polytechnica 62(4):488–497, 2022 1 Introduction 2 Analysis 3 Result and discussion 4 Conclusion List of symbols References