Enhanced surfaces Boiling

R. L. Webb, The Evolution of Enhanced Surface Geometries for Nucleate Boiling, Heat Transfer Eng. (2/3-4) 46-49, 1981. 

FIGURE 15.57 Enhanced surfaces for boiling (from Webb and Haider [137], with permission from ASME). 

FIGURE 15.58 Improvement in boiling heat transfer using various forms of commercial enhanced surfaces (from Bergles [135], with permission). 

There are a number of problems in the application of enhanced surfaces. One of these is that boiling hysteresis (see Fig. 15.43) may have an even more significant role. Hysteresis... 

FIGURE 15.84 Comparison of heat transfer coefficient for boiling refrigerant 113 on smooth and enhanced surfaces in vertical upward flow over a tube bundle (from Jensen et al. [218], with permission from Taylor Francis, Washington DC. All rights reserved). 

C. Pais and R. L. Webb, Literature Survey of Pbol Boiling on Enhanced Surfaces, ASHRAE Transactions (97/1) 1991. 

R. L. Webb and I. Haider, An Analytical Model for Nucleate Boiling on Enhanced Surfaces, in Pool and External Flow Boiling, V. K. Dhir and A. E. Bergles eds., pp. 345-360, ASME, New York, 1992. 

P. J. Marto and V. J. Lepere, Pbol Boiling Heat Transfer From Enhanced Surfaces to Dielectric Liquids, / Heat Transfer (my. 292-299,1982. 

Webb, R. L., "The Evolution Of Enhanced Surface Geometries For Nucleate Boiling",... 

Thus, the enhancement of heat transfer may be connected to the decrease in the surface tension value at low surfactant concentration. In such a system of coordinates, the effect of the surface tension on excess heat transfer (/z — /zw)/ (/ max — w) may be presented as the linear fit of the value C/Cq. On the other hand, the decrease in heat transfer at higher surfactant concentration may be related to the increased viscosity. Unfortunately, we did not find surfactant viscosity data in the other studies. However, we can assume that the effect of viscosity on heat transfer at surfactant boiling becomes negligible at low concentration of surfactant only. The surface tension of a rapidly extending interface in surfactant solution may be different from the static value, because the surfactant component cannot diffuse to the absorber layer promptly. This may result in an interfacial flow driven by the surface tension gradi-... 

Wu WT, Yang YM, Maa JR (1995) Enhancement of nucleate boiling heat transfer and depression of surface tension by surfactant additives. J Heat Transfer 117 526-529... 

The last problem of this series concerns femtosecond laser ablation from gold nanoparticles [87]. In this process, solid material transforms into a volatile phase initiated by rapid deposition of energy. This ablation is nonthermal in nature. Material ejection is induced by the enhancement of the electric field close to the curved nanoparticle surface. This ablation is achievable for laser excitation powers far below the onset of general catastrophic material deterioration, such as plasma formation or laser-induced explosive boiling. Anisotropy in the ablation pattern was observed. It coincides with a reduction of the surface barrier from water vaporization and particle melting. This effect limits any high-power manipulation of nanostructured surfaces such as surface-enhanced Raman measurements or plasmonics with femtosecond pulses. 

PFE is based on the adjustment of known extraction conditions of traditional solvent extraction to higher temperatures and pressures. The main reasons for enhanced extraction performance at elevated temperature and pressure are (i) solubility and mass transfer effects and (ii) disruption of surface equilibria [487]. In PFE, a certain minimum pressure is required to maintain the extraction solvent in the liquid state at a temperature above the atmospheric boiling point. High pressure elevates the boiling point of the solvent and also enhances penetration of the solvent into the sample matrix. This accelerates the desorption of analytes from the sample surface and their dissolution into the solvent. The final result is improved extraction efficiency along with short extraction time and low solvent requirements. While pressures well above the values required to keep the extraction solvent from boiling should be used, no influence on the ASE extraction efficiency is noticeable by variations from 100 to 300 bar [122]. 

---