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Effect of Ambient Pressure on Leidenfrost Temperature Edinburgh Research Explorer Effect of ambient pressure on Leidenfrost temperature Citation for published version: Orejon, D, Sefiane, K & Takata, Y 2014, 'Effect of ambient pressure on Leidenfrost temperature', Physical Review E - Statistical, Nonlinear and Soft Matter Physics, vol. 90, no. 5, 053012. https://doi.org/10.1103/PhysRevE.90.053012 Digital Object Identifier (DOI): 10.1103/PhysRevE.90.053012 Link: Link to publication record in Edinburgh Research Explorer Document Version: Publisher's PDF, also known as Version of record Published In: Physical Review E - Statistical, Nonlinear and Soft Matter Physics Publisher Rights Statement: Publisher's Version/PDF:green tick author can archive publisher's version/PDF General rights Copyright for the publications made accessible via the Edinburgh Research Explorer is retained by the author(s) and / or other copyright owners and it is a condition of accessing these publications that users recognise and abide by the legal requirements associated with these rights. Take down policy The University of Edinburgh has made every reasonable effort to ensure that Edinburgh Research Explorer content complies with UK legislation. If you believe that the public display of this file breaches copyright please contact [email protected] providing details, and we will remove access to the work immediately and investigate your claim. Download date: 07. Oct. 2021 PHYSICAL REVIEW E 90, 053012 (2014) Effect of ambient pressure on Leidenfrost temperature Daniel Orejon,1,2,3,* Khellil Sefiane,1,3 and Yasuyuki Takata1,2 1International Institute for Carbon-Neutral Energy Research (WPI-I2CNER), Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan 2Department of Mechanical Engineering, Thermofluid Physics Laboratory, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan 3School of Engineering, The University of Edinburgh King’s Buildings, Mayfield Road, Edinburgh EH9 3JL, United Kingdom (Received 16 July 2014; revised manuscript received 29 September 2014; published 21 November 2014) The accurate prediction and control of the interaction of liquids with hot surfaces is paramount in numerous areas, including cooling applications. We present results illustrating the effect of ambient pressure on the temperature required for a droplet to levitate over a hot surface, i.e., the Leidenfrost temperature. In the present study the dependence of wetting and levitating temperatures on ambient pressure in a range of subatmospheric pressures is reported. Experimental data indicate that the Leidenfrost temperature decreases with decreasing pressure at subatmospheric pressures. A physical approach for the dependence of Leidenfrost temperature on ambient pressure, based on an analogy with saturation pressure dependence, is proposed. Furthermore, previous literature data for pressures above atmospheric are also included in the analysis to support and validate the proposed approach. In addition, the effect of substrate material, substrate roughness, and type of fluid on the Leidenfrost temperature is discussed. DOI: 10.1103/PhysRevE.90.053012 PACS number(s): 47.55.D−, 47.85.mf, 68.03.−g For centuries scientists and engineers have devoted sus- and Mudawar [6] addressed, experimentally, the effect of tained efforts to further our understanding of the ubiquitous substrate finish on Leidenfrost temperature. An increase in interactions between solid surfaces and liquids [1]. Hydropho- levitating temperature was reported when increasing substrate bicity and roughness of the substrate, the nature of the liquid, roughness; however no quantitative evaluation was carried out. or the substrate temperature are some of the factors reported to More recently, Kwon et al. [4] exploited the interplay between strongly influence the interaction between solids and liquids. surface structures (pillars) and the Leidenfrost phenomenon. Particularly, when increasing the temperature of the substrate The authors achieved a shift in Leidenfrost temperature of in contact with a liquid, a layer of vapor sandwiched between more than 100 °C on the same substrate material, when the liquid and the solid is formed. In this region, the liquid modifying the distance between these structures. Another is prevented from physically contacting the surface. For the impressive achievement is the more stable vapor layer re- case of levitating droplets this phenomenon is known as the ported by Vakarelski et al. when immersing a heated metal Leidenfrost effect [1]. This can have undesirable effects in sphere in a liquid [7]. The absence of nucleate boiling cooling due to the insulating features of the vapor phase. on these textured spheres was achieved by a combination The dramatic reduction in cooling efficiency can lead to of surface heterogeneities and chemical modification of the mechanical failure or even to burnout of the heating surface. substrate. This is of paramount importance to applications such as the In addition to these recent studies, other factors such as nuclear industry. On the other hand, and for other purposes, the ambient pressure have attracted the attention of researchers levitation of the liquid can be desirable as the cushion of vapor much earlier [8,9]. Emmerson analyzed, experimentally, the allows for almost frictionless motion of a droplet over a heated effect of high pressure on the temperature required for a water substrate, which is of great importance for liquid manipulation droplet to levitate. The author predicted that Leidenfrost tem- [2,3]. perature would vary with saturation temperature and found that Since the pioneering observations of Leidenfrost [1], the higher substrate temperatures were required when increasing phenomenon has been sparsely investigated, until very recently the ambient pressure although no empirical correlation was where a growing interest in the control of the Leidenfrost proposed [8]. Also Testa and Nicotra observed a decrease in phenomenon is driven by the ability to fine-tune substrate substrate temperature when reducing the pressure of the system properties and hence control the phenomenon. Geometry and below atmospheric [9]. shape of the substrate, size and height of the pillars, or the Besides experimental studies on the Leidenfrost phe- layout and distance between these artificial structures are some nomenon it is noted that limited theoretical models are avail- of the factors studied [3,4]. able to predict Leidenfrost dependence on ambient pressure. Liu and Craig studied the effect of hydrophobicity on Baumeister and Simon proposed an empirical correlation Leidenfrost temperature for smooth and flat substrates [5]. It between the Leidenfrost temperature, thermal conductivity, was found that lower substrate temperatures were required for density, and specific heat of the substrate. However, the the levitation of a droplet on hydrophobic substrates. Bernardin effect of pressure or substrate roughness was not taken into account [10]. A few years later, Lienhard proposed a simpler correlation, for system pressures above atmospheric (superatmospheric). The correlation proposed by Lienhard is a *Corresponding author: [email protected] function of the critical temperature and saturation temperature 1539-3755/2014/90(5)/053012(6) 053012-1 ©2014 American Physical Society DANIEL OREJON, KHELLIL SEFIANE, AND YASUYUKI TAKATA PHYSICAL REVIEW E 90, 053012 (2014) FIG. 1. (Color online) (a) Sketch of the experimental apparatus used in this study and (b) sketch of the heating substrate placed inside the chamber. [11]. However, this correlation does not indicate any change To rule out any inertial effects during droplet deposition, the 2 in Leidenfrost temperature when substituting saturation tem- Weber number (We = ρf v d/γlg where ρf is the density of perature at subatmospheric pressures. the fluid, v the impact velocity, d the droplet diameter, and γlg Despite the effort of researchers over the last decades, the liquid-gas surface tension) was estimated. It was concluded studies and correlations addressing the effect of pressure on that inertial effects can be neglected for droplet deposition the Leidenfrost phenomenon remain rather scarce. The very below 0.1m/s (this is approximately two orders of magnitude few existing investigations are only suitable for high pressures greater than values calculated in the present experiments). or for specific substrate materials. Surface finishes such as The behavior of a water droplet when deposited on a heated hydrophobicity and patterned structures are not taken into aluminum surface at various ambient pressures is presented. account as these effects were only revealed recently [4,7]. Figure 2 includes a representative depiction of droplet typical Lowering the Leidenfrost temperature is proving attractive in behavior, employing single snapshots, of the experiments the light of recent developments on the use of this phenomenon carried out at the same substrate temperature (T = 105 °C) for liquids and solids manipulation [2,3,12]. Indeed, being able and at different subatmospheric pressures. to induce Leidenfrost levitation at lower temperature can make From Fig. 2, it is clear that varying ambient (subatmo- the exploitation of the phenomenon more practical as higher spheric) pressure resulted in noticeably different physical temperatures can be an issue. interactions between the droplet and substrate. For a given A stainless steel low pressure environmental chamber using temperature, three main distinctive regimes can be identified. borosilicate
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