Independent and collective roles of surface structures at different length scales on pool boiling heat transfer.

Calvin H Li,Russell P Rioux

doi:10.1038/srep37044

Abstract

Spherical Cu nanocavity surfaces are synthesized to examine the individual role of contact angles in connecting lateral Rayleigh-Taylor wavelength to vertical Kevin-Helmholtz wavelength on hydrodynamic instability for the onset of pool boiling Critical Heat Flux (CHF). Solid and porous Cu pillar surfaces are sintered to investigate the individual role of pillar structure pitch at millimeter scale, named as module wavelength, on hydrodynamic instability at CHF. Last, spherical Cu nanocavities are coated on the porous Cu pillars to create a multiscale Cu structure, which is studied to examine the collective role and relative significance of contact angles and module wavelength on hydrodynamic instability at CHF, and the results indicate that module wavelength plays the dominant role on hydrodynamic instability at CHF when the height of surface structures is equal or above ¼ Kelvin-Helmholtz wavelength. Pool boiling Heat Transfer Coefficient (HTC) enhancements on spherical Cu nanocavity surfaces, solid and porous Cu pillar surfaces, and the integrated multiscale structure have been investigated, too. The experimental results reveal that the nanostructures and porous pillar structures can be combined together to achieve even higher enhancement of HTC than that of individual structures.

Highlights

Spherical Cu nanocavity surfaces are synthesized to examine the individual role of contact angles in connecting lateral Rayleigh-Taylor wavelength to vertical Kevin-Helmholtz wavelength on hydrodynamic instability for the onset of pool boiling Critical Heat Flux (CHF)
In order to investigate the individual role of contact angles on controlling hydrodynamic instability wavelength, uniform 200 nm and 500 nm diameter spherical Cu nanocavity surfaces have been synthesized (Fig. 1) to create different contact angles from that on a plain Cu surface, which enables to examine the magnitude of CHF enhancements due to the hydrodynamic instability wavelengths changed by contact angles
Based on the comparisons among experimental data of this study and previous reportes by other research groups, and predictions of theoretical models developed in this study and previously reported, it demonstrates that different physics of the liquid/solid/vapor interaction at different spatial scales exist on spherical Cu nanocavity surfaces and porous Cu pillar surfaces

Summary

Introduction

Spherical Cu nanocavity surfaces are synthesized to examine the individual role of contact angles in connecting lateral Rayleigh-Taylor wavelength to vertical Kevin-Helmholtz wavelength on hydrodynamic instability for the onset of pool boiling Critical Heat Flux (CHF). The hydrodynamic instability model investigated by Kutateladze[11], Zuber[12], and Lienhard and Dhir[13] hypothesizes that when the velocity of vapor in escaping columns reaches a critical value, the interface wave on vapor columns will reach a Kevin-Helmholtz (K-H) wavelength, λK−H, and cause a collapse of neighboring vapor columns The weakness of this model is the failure to take into consideration of heating surface effects on hydrodynamic instability. We will investigate the control mechanisms of hydrodynamic instability wavelength at different surface structure characteristic length scales, and will answer the following questions as (1) What are the www.nature.com/scientificreports/

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Conclusion