On the Role of Marangoni Effects on the Critical Heat Flux for Pool Boiling of Binary Mixtures

The Marangoni effect on the critical heat flux (CHF) condition in pool boiling of binary mixtures has been identified and its effect has been quantitatively estimated with a modified model derived from hydrodynamics. The physical process of CHF in binary mixtures, and models used to describe it, are examined in the light of recent experimental evidence, accurate mixture properties, and phase equilibrium revealing a correlation to surface tension gradients and volatility. A correlation is developed from a heuristic model including the additional liquid restoring force caused by surface tension gradients. The CHF condition was determined experimentally for saturated methanol/water, 2-propanol/water, and ethylene glycol/water mixtures, over the full range of concentrations, and compared to the model. The evidence in this study demonstrates that in a mixture with large differences in surface tension, there is an additional hydrodynamic restoring force affecting the CHF condition.

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Effects of Surface Orientation on the Pool Boiling Heat Transfer in Water/2-Propanol Mixtures

Journal of Heat Transfer ◽

10.1115/1.2825972 ◽

1999 ◽

Vol 121 (1) ◽

pp. 80-88 ◽

Cited By ~ 15

Author(s):

S. Ahmed ◽

V. P. Carey

Keyword(s):

Heat Transfer ◽

Surface Tension ◽

Heat Flux ◽

Binary Mixtures ◽

Critical Heat Flux ◽

Boiling Heat Transfer ◽

Pool Boiling ◽

Bulk Liquid ◽

Heater Surface ◽

Pool Boiling Heat Transfer

To explore the role of Marangoni effects in the pool boiling heat transfer of binary mixtures, experiments have been conducted with water/2-propanol mixtures at three different concentrations under normal gravity with different orientations of the heater surface. The system pressure was subatmospheric (∼5.5 kPa) and the bulk liquid temperature was near the saturation temperature of the fluids tested. The molar concentrations of2-propanol tested were 0.015, 0.025, and 0.1. These concentrations of 2-propanol are selected because their strong variation of surface tension with concentration gives rise to high surface tension gradients near the heater surface during nucleate boiling. Boiling curves were obtained both for an upward-facing and a downward-facing heater surface. For each concentration of 2-propanol, the critical heat flux has been reached in both orientations of the heater surface. Models of pool boiling heat transfer and the critical heat flux condition for binary mixtures are tested to correlate the data. Comparison of boiling curves and CHF obtained at different orientations of the heater surface indicates that there is strong gravity independent mechanism of boiling heat transfer in these mixtures.

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Investigation of Pool Boiling Critical Heat Flux Enhancement on a Modified Surface Through the Dynamic Wetting of Water Droplets

Journal of Heat Transfer ◽

10.1115/1.4006113 ◽

2012 ◽

Vol 134 (7) ◽

Cited By ~ 10

Author(s):

Ho Seon Ahn ◽

Joonwon Kim ◽

Moo Hwan Kim

Keyword(s):

Surface Tension ◽

Heat Flux ◽

Contact Angle ◽

Critical Heat Flux ◽

Pool Boiling ◽

Water Layer ◽

Contact Angles ◽

Water Droplets ◽

Dynamic Wetting ◽

Modified Surface

Dynamic wetting behaviors of water droplet on the modified surface were investigated experimentally. Dynamic contact angles were measured as a characterization method to explain the extraordinary pool boiling critical heat flux (CHF) enhancement on the zirconium surface by anodic oxidation modification. The sample surface is rectangular zirconium alloy plates (20 × 25 × 0.7 mm), and 12 μl of deionized water droplets were fallen from 40 mm of height over the surface. Dynamic wetting movement of water on the surface showed different characteristics depending on static contact angle (49.3 deg–0 deg) and surface temperature (120 °C–280 °C). Compared with bare surface, wettable and spreading surface had no-receding contact angle jump and seemed stable evaporating meniscus of liquid droplet in dynamic wetting condition on hot surface. This phenomenon could be explained by the interaction between the evaporation recoil and the surface tension forces. The surface tension force increased by micro/nanostructure of the modified zirconium surface suppresses the vapor recoil force by evaporation which makes the water layer unstable on the heated surface. Thus, such increased surface force could sustain the water layer stable in pool boiling CHF condition so that the extraordinary CHF enhancement could be possible.

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Effect of Thermophysical Properties of the Heater Substrate on Critical Heat Flux in Pool Boiling

Journal of Heat Transfer ◽

10.1115/1.4036653 ◽

2017 ◽

Vol 139 (11) ◽

Cited By ~ 8

Author(s):

Pruthvik A. Raghupathi ◽

Satish G. Kandlikar

Keyword(s):

Thermal Conductivity ◽

Heat Flux ◽

Critical Heat Flux ◽

Pool Boiling ◽

Temperature Fluctuations ◽

Operating Conditions ◽

Force Balance ◽

Heater Surface ◽

Monel 400

While the role of the liquid properties, surface morphology, and operating conditions on critical heat flux (CHF) in pool boiling is well investigated, the effect of the properties of the heater material is not well understood. Previous studies indicate that the heater thickness plays an important role on the CHF phenomenon. However, beyond a certain thickness, called the asymptotic thickness, the local temperature fluctuations on the heater surface caused by the periodic bubble ebullition cycle are evened out, and the CHF is not influenced by further increasing the thickness. In the present work, data from literature and pool boiling experiments conducted in this study with seven substrates—aluminum, brass, copper, carbon steel, Monel 400, silver, and silicon—are used to determine the effect of the thermophysical property of the material on CHF for thick heaters that are used in industrial pool boiling applications. The results indicate that the product of density (ρ) and specific heat (cp) represents an important substrate property group that affects the CHF, and that the thermal conductivity is not an important parameter. A well-established force-balance-based CHF model (Kandlikar model) is modified to account for the thermal properties of the substrate. The predicted CHF values are within 15% of the experimental results.

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