Critical heat flux triggering mechanism on micro-structured surfaces: Coalesced bubble departure frequency and liquid furnishing capability

Effect of nanostructures on heat transfer coefficient of an evaporating meniscus

“…This enhancement in CHF can be attributed to a variety of mechanisms, including increased nucleation site densities [1,5,15], elongated contact line [7,16], enhanced micro-convection around nucleated bubbles [4,17,18], increased bubble departure frequency [19], and enhanced microlayer evaporation via a strong wicking effect [3,9,13,14,[20][21][22]. Among these possible mechanisms, the enhanced microlayer evaporation through wicking has been widely accepted as the dominant mechanism, where correlations [3,21] and theoretical predictions [22] have been established between the CHF and the wicking rate.…”

A coupled wicking and evaporation model for prediction of pool boiling critical heat flux on structured surfaces

“…In the present work, the Dhir-Liaw model [25] that accounts for the effect of the contact angle on CHF is used to calculate CHF,f q . The apparent contact angle on structured surfaces is calculated using the equilibrium contact angle at room temperature [26], and is substituted into q as a function of the characteristic wicking rate w,ch  for experimental data from the literature on pool boiling on square micropillar arrays [2,3,7,11]. The wetting properties and geometric dimensions of the surfaces used in these references are summarized in Section S2 of the Supplementary Material.…”

“…The predictions from the CHF model developed above are compared with experimental data in the literature for water boiling on square micropillar arrays [2,3,7,11] in Figure 8. The modelpredicted CHF is calculated using the micropillar geometry, wettability, and material properties reported in [2,3,7,11], as listed in Section S2 of the Supplementary Material. A roughness factor of s 2 r  = is used to account for the roughness on the side wall of the micropillars fabricated with deep reaction ion etching (DRIE) [16].…”

“…Over a half-century ago, Zuber [1] derived a hydrodynamics-based model that accurately captures the pool boiling CHF on flat surfaces [2][3][4]. Recent experimental studies [2,3,[5][6][7][8][9][10][11][12][13][14][15][16][17][18] have shown that using micro-/nano-structured surfaces can enhance CHF well above Zuber's limit.…”

“…Recent experimental studies [2,3,[5][6][7][8][9][10][11][12][13][14][15][16][17][18] have shown that using micro-/nano-structured surfaces can enhance CHF well above Zuber's limit. A variety of mechanisms have been proposed to explain the structure-induced CHF enhancement, including increased three-phase contact line length [11,16], microconvection around the bubble [19], increased departure frequency of coalesced bubbles [3], and liquid rewetting via capillary wicking [2,3,5,7,8,11,13,14]. Among these mechanisms, capillary wicking has been the most widely agreed upon, with strong support from experimental data [2,5,10,17].…”