Enhanced pool-boiling heat transfer and critical heat flux on femtosecond laser processed stainless steel surfaces

Abstract

In this paper, we present an experimental investigation of pool boiling heat transfer on multiscale (micro/nano) functionalized metallic surfaces. Heat transfer enhancement in metallic surfaces is very important for large scale high heat flux applications like in the nuclear power industry. The multiscale structures were fabricated via a femtosecond laser surface process (FLSP) technique, which forms self-organized mound-like microstructures covered by layers of nanoparticles. Using a pool boiling experimental setup with deionized water as the working fluid, both the heat transfer coefficients and critical heat flux were investigated. A polished reference sample was found to have a critical heat flux of 91 W/cm 2 at 40 °C of superheat and a maximum heat transfer coefficient of 23,000 W/m 2 K. The processed samples were found to have a maximum critical heat flux of 142 W/cm 2 at 29 °C and a maximum heat transfer coefficient of 67,400 W/m 2 K. It was found that the enhancement of the critical heat flux was directly related to the wetting and wicking ability of the surface which acts to replenish the evaporating liquid and delay critical heat flux. The heat transfer coefficients were also found to increase when the surface area ratio was increased as well as the microstructure peak-to-valley height. Enhanced nucleate boiling is the main heat transfer mechanism, and is attributed to an increase in surface area and nucleation site density.

Secondary pool boiling effects

“…Throughout the literature, only a few examples of secondary boiling effects can be found. 6,21,24,25 Secondary boiling effects can be seen on 10 lm silicon nanowire surfaces, stainless steel surfaces with 200 lm aluminum porous coatings, 21 35 lm tall stainless steel mound structures with a nanoporous layer, 24 and 400 lm tall copper microchannels with a porous coating. 25 An attempt to explain secondary boiling effects has been given by Chen et al 6 and Patil et al 25 In the work conducted by Chen et al, secondary boiling effects were seen on 10 lm tall silicon nanowires.…”

“…Heat flux is measured via embedded thermocouples and surface temperature is calculated. A more in depth description of the FLSP technique and the pool boiling experimental setup is given by Kruse et al 24,26 Five unique surfaces are analyzed in this work, two Inconel, two stainless steel, and one copper. Their surface characteristics have been obtained using a Keyence Laser Confocal Microscope and are tabulated in Table I.…”

Creation of micro/nano surface structures on silver using collinear double femtosecond laser pulses with different pulse separation

“…As an alternative explanation, when using the dual-pulse technique the second pulse may reheat the plasma from the first pulse, resulting in a hotter plasma than when using single-pulse FLSP (Zhao and Shin 2015). The hotter plasma may be needed to drive (Groeneveld et al 1995) None Nickel 8 (Beaurepaire et al 1996) Yes (Zuhlke et al 2013) Titanium 18.5 (Ahmmed et al 2015) Yes (Vorobyev and Guo 2007) 304 Stainless steel 14.4 (Winter et al 2016) Yes (Kruse et al 2015) the self-organization processes for the structures to form on silver.…”

“…Femtosecond laser surface processing (FLSP) is a developing technique for creating micro/nanoscale surfaces with a wide range of applications including improved heat transfer (Kruse et al 2013(Kruse et al , 2015(Kruse et al , 2016, medical implants (Vorobyev and Guo 2007), improving efficiency of electrolysis cells , and controlling material wetting properties (Zuhlke et al 2013). In most of these applications, the greatest enhancements result from a surface with a combination of micro and nanoscale surface features.…”

Leidenfrost transition temperature for stainless steel meshes

“…This reduction in solid-liquid contact area means that the heat flux required to generate the supporting vapour layer required for a Leidenfrost state has to be transferred through the reduced contact area between the liquid and the solid wires. This would mean that a higher temperature is needed for the required heat flux to generate a continuous vapour and so produce a Leidenfrost state [21][22][23][24]. Figure 2(b), degrades the fit, suggesting that this area is not a significant factor.…”