Thermocapillary lubricant migration on textured surfaces - a review of theoretical and experimental insights

Abstract

Thermocapillary migration in tribological systems such as gearboxes, piston ring-liner assemblies, or bearings can lead to lubricant starvation and, consequently, to severe damages. Due to surface tension gradients induced by local temperature gradients on the frictionally heated surface, lubricant may flow out of the hotter contact zone to colder adjacent regions. In order to manipulate lubricant migration, several approaches exist to create migration barriers or to guide lubricant in a well-defined way back into the contact. These approaches are either based upon surface topography (designed surface textures) and/or surface chemistry (designed chemical patterns). In this review article, the state-ofthe-art regarding thermocapillary migration is summarized from a theoretical and experimental point of view. After a brief introduction, theoretical models are presented to introduce the underlying theory of droplet spreading and thermocapillary migration. Subsequently, the influence of surface textures and chemical patterns on thermocapillary migration and the possibilities to use these approaches to manipulate lubricant migration are discussed. After addressing applied research in this field and potential applications, current challenges and future research directions are presented before closing with general conclusions.

Influence of Groove Dimensions on the Tribological Behavior of Textured Cylindrical Roller Thrust Bearings under Starved Lubrication

“…pillars, pits, grooves or grid, in a geometry or pattern on the target surfaces, LST has proved to be a one-step, fast, economic, accurate and easily-controlled way to tune the tribological performance of mechanical components (e.g. piston rings, seals, roller bearings and gears) (Uddin and Liu, 2016;Saeidi et al, 2017;Gachot et al, 2017;Marian et al, 2018;Marian et al, 2019;Grützmacher et al, 2019a;Grützmacher et al, 2019b;Galda et al, 2019;Wang et al, 2019;Vl adescu et al, 2019;Grützmacher et al, 2021;Kumar and Sharma, 2018). Under oil lubrication, texture units can act as an oil reservoir thus inducing a secondary oil effect, trap wear debris and contribute to an additional hydrodynamic pressure (Rosenkranz et al, 2019a).…”

“…However, most of the papers focus on journal bearings, thrust bearings or sliding tribo-pair (Gropper et al, 2018a;Gropper et al, 2018b). The use of STs in REBs is still scarce compared to other machine elements and the concern is mainly related to rolling contact fatigue life (Grützmacher et al, 2021). This is because the wear behavior of REBs is very complex and the textures with small diameters and depths are difficult to manufacture.…”

“…Therefore, based on previous works (Sun et al, 2017;Sun et al, 2020), a fiber laser marking system (PL100-30W, China) was used to process grooves on the shaft washers of 81107TN bearings (YFB, Changzhou, China) with different groove dimensions. Based on the researches of Grützmacher et al (2019aGrützmacher et al ( , 2019bGrützmacher et al ( , 2021, a vertical universal wear test rig (MMX-1A) was used to obtain their coefficients of friction (COFs) under starved lubrication. An electronic analytical balance (EX225D, Ohaus) with a precision of 0.1 mg (0.01 mg readability) was used to measure their wear losses.…”

Determining the tribological behavior of 316L stainless steel with lubricating micro-channels produced by the selective laser melting (SLM) method

“…In addition, there are many articles in the literature about the lubrication of the surfaces that are in contact with each other due to the thermocapillary effect, capillary effect, gravity effect or microchannel, etc. without external lubrication (Berthier et al, 2016;Dai et al, 2016Dai et al, , 2021Grützmacher et al, 2020).…”

Photothermocapillary Method for the Nondestructive Testing of Solid Materials and Thin Coatings

“…Another report states that the PTC effect is a thermocapillary (TC) flow, since fluid flow can take place at a very low velocity in the absence of deformation [ 1 ]. In general, a temperature change, , on the surface of a liquid can be induced using various heat sources, including focused electromagnetic radiation of any wavelength (ultraviolet, visible, or infrared) [ 12 , 17 , 18 , 19 , 20 , 21 , 22 , 23 ]. In two limiting cases, PTC flow takes place in a liquid, which strongly absorbs the electromagnetic radiation at its surface, and/or in a liquid, which is either transparent or weakly absorbs the radiation of a pumped laser or a halogen lamp [ 13 ].…”