Energy balance of droplets impinging onto a wall heated above the Leidenfrost temperature

This work is an experimental study aiming at characterizing the heat transfers induced by the impingement of water droplets (diameter 80–180 μm) on a thin nickel plate heated by electromagnetic induction. The temperature of the rear face of the nickel sample is measured by means of an infrared camera and the heat removed from the wall due to the presence of the droplets is estimated using a semi-analytical inverse heat conduction model. In parallel, the temperature of the droplets is measured using the two-color Laser-Induced Fluorescence thermometry (2cLIF) which has been extended to imagery for the purpose of these experiments. The measurements of the variation in the droplet temperature occurring during an impact allow determining the sensible heat removed by the liquid. Measurements are performed at wall conditions well above the Leidenfrost temperature. Different values of the Weber numbers corresponding to the bouncing and splashing regimes are tested. Comparisons between the heat flux removed from the wall and the sensible heat gained by the liquid allows estimating the heat flux related to liquid evaporation. Results reveal that the respective level of the droplet sensible heat and the heat lost due to liquid vaporization can vary significantly with the droplet sizes and the Weber number.

[1]  Bharat Bhushan,et al.  Wetting, adhesion and friction of superhydrophobic and hydrophilic leaves and fabricated micro/nanopatterned surfaces , 2008 .

[2]  C. Tropea,et al.  Abstract of "ANALYSIS OF IMPACT OF DROPLETS ON HORIZONTAL SURFACES" , 2000 .

[3]  D. Maillet,et al.  Thermal Quadrupoles: Solving the Heat Equation through Integral Transforms , 2000 .

[4]  M. Rein,et al.  Drop-surface interactions , 2002 .

[5]  Inverse Conduction Technique in Hankel Domain Using Infrared Thermography: Application to Droplet Stream Quenching a Metal Disk , 2010 .

[6]  G. Castanet,et al.  Dynamics and temperature of droplets impacting onto a heated wall , 2009 .

[7]  G. Castanet,et al.  A two-color planar LIF technique to map the temperature of droplets impinging onto a heated wall , 2012 .

[8]  John D. Bernardin,et al.  The Leidenfrost point : Experimental study and assessment of existing models , 1999 .

[9]  Shi-Chune Yao,et al.  The dynamics and leidenfrost temperature of drops impacting on a hot surface at small angles , 1988 .

[10]  K. Baumeister,et al.  Leidenfrost temperature - Its correlation for liquid metals, cryogens, hydrocarbons, and water. , 1973 .

[11]  G. Castanet,et al.  Heat and mass transfer in evaporating droplets in interaction: Influence of the fuel , 2010 .

[12]  R. Schmehl,et al.  CFD Analysis of Spray Propagation and Evaporation Including Wall Film Formation and Spray/Film Interactions , 1999 .

[13]  M. Lebouché,et al.  Measurement of the temperature distribution within monodisperse combusting droplets in linear streams using two-color laser-induced fluorescence , 2003 .

[14]  Jungho Kim.  Spray cooling heat transfer: The state of the art , 2007 .

[15]  I. Mudawar,et al.  TED-AJ03-538 A LEIDENFROST POINT MODEL FOR IMPINGING DROPLETS AND SPRAYS , 2004 .

[16]  G. Castanet,et al.  New insight into two-color LIF thermometry applied to temperature measurements of droplets , 2010 .

[17]  John D. Bernardin,et al.  Mapping of impact and heat transfer regimes of water drops impinging on a polished surface , 1997 .

[18]  B. W. Webb,et al.  Single-Phase Liquid Jet Impingement Heat Transfer , 1995 .

[19]  António L. N. Moreira,et al.  Advances and challenges in explaining fuel spray impingement: How much of single droplet impact research is useful? , 2010 .

[20]  L. Wachters,et al.  The heat transfer from a hot wall to impinging water drops in the spheroidal state , 1966 .

[21]  C. Tropea,et al.  Outcomes from a drop impact on solid surfaces , 2001 .

[22]  C. Tropea,et al.  Droplet-wall collisions: Experimental studies of the deformation and breakup process , 1995 .

[23]  M. Lebouché,et al.  Evaporating and combusting droplet temperature measurements using two-color laser-induced fluorescence , 2001 .

[24]  C. Tropea,et al.  Drop impact, spreading, splashing, and penetration into electrospun nanofiber mats. , 2010, Langmuir : the ACS journal of surfaces and colloids.