https://northumbria-test.eprints-hosting.org/id/document/264686

An introduction to superhydrophobicity

We report that liquids perform self-propelled motion when they are placed in contact with hot surfaces with asymmetric (ratchetlike) topology. The pumping effect is observed when the liquid is in the Leidenfrost regime (the film-boiling regime), for many liquids and over a wide temperature range. We propose that liquid motion is driven by a viscous force exerted by vapor flow between the solid and the liquid.

Self-propelled Leidenfrost droplets.

Advances and challenges in explaining fuel spray impingement: How much of single droplet impact research is useful?

A computer model was used to study the impingement of sprays on walls. The spray model accounts for the effects of drop breakup, drop collision and coalescence, and the effect of drops on the gas turbulence. A new submodel was developed to describe the spray/wall interaction process. Predictions of the effect of engine swirl, ambient gas pressure (density), wall inclination angle and the distance from the nozzle to the wall, were in good qualitative agreement with the experiments

Modeling Engine Spray/Wall Impingement

Recent demands for superior material properties and more efficient use of materials and production time are forcing manufacturers to develop intelligent processing techniques for enhanced process control in order to better dictate the end product. In the heat treatment and processing of metallic alloys, the desire to obtain parts of enhanced and uniform mechanical properties is requiring increased control over heat removal rates and enhanced temperature control. In particular, spray quenching has been shown to be an effective means to control and enhance the cooling rates of heat treatable aluminum alloys. This study presents a detailed and thorough parametric study of the Leidenfrost point (LFP), which serves as the temperature boundary between the transition and film boiling regimes. Sessile drop evaporation experiments were conducted with acetone, benzene, FC-72, and water on heated aluminum surfaces with either polished, particle blasted, or rough sanded finishes to observe the influential effects of fluid properties, surface roughness, and surface contamination on the LFP. A weak relationship between surface energies and the LFP was observed by performing droplet evaporation experiments with water on polished copper, nickel, and silver surfaces. Additional parameters which were investigated and found to have negligible influence on the LFP included liquidmore » subcooling, liquid degassing, surface roughness on the polished level, and the presence of polishing paste residues. The accumulated LFP data of this study were used to assess several existing models which attempt to identify the mechanisms which govern the LFP. The disagreement between the experimental LFP values and those predicted by the various models suggests that an accurate and robust theoretical model which effectively captures the LFP mechanisms is currently unavailable.« less

The Leidenfrost point : Experimental study and assessment of existing models

The leidenfrost phenomenon: film boiling of liquid droplets on a flat plate

Forced convection boiling inside helically-coiled tubes

The design process for heat exchangers in the process industries and for similar applications in the power and large-scale environmental control industries is described. Because of the variety of substances (frequently multicomponent, of variable and uncertain composition, and changing phase) to be processed under wide ranges of temperatures, pressures, flow rates, chemical compatibility, and fouling propensity, these exchangers are almost always custom-designed and constructed. Many different exchanger configurations are commercially available to meet special conditions, with design procedures of varying degrees of reliability. A general design logic can be applied, with detailed procedures specific to the type of exchanger. The basis of the design process is first a careful and comprehensive specification of the range of conditions to be satisfied, and second, organized use of a fundamentally valid and extrapolatable rating method. The emphasis in choosing a design method is upon rational representation of the physical processes, rather than upon high accuracy. Finally, the resultant design must be vetted in detail by the designer and the process engineer for operability, flexibility, maintainability, and safety

Heat Exchanger Design for the Process Industries

The design process for heat exchangers in the process industries and for similar applications in the power and large-scale environmental control industries is described. Because of the variety of substances (frequently multicomponent, of variable and uncertain composition, and changing phase) to be processed under wide ranges of temperatures, pressures, flow rates, chemical compatibility, and fouling propensity, these exchangers are almost always custom-designed and constructed. Many different exchanger configurations are commercially available to meet special conditions, with design procedures of varying degrees of reliability. A general design logic can be applied, with detailed procedures specific to the type of exchanger. The basis of the design process is first a careful and comprehensive specification of the range of conditions to be satisfied, and second, organized use of a fundamentally valid and extrapolatable rating method. The emphasis in choosing a design method is upon rational representation of the physical processes, rather than upon high accuracy. Finally, the resultant design must be vetted in detail by the designer and the process engineer for operability, flexibility, maintainability, and safety.Copyright © 2004 by ASME

This analysis considers isothermal flow and gravity-controlled condensation on a vertical fluted surface. In the initial part of the analysis, isothermal flow (drainage), which mainly occurs in the trough region of the flute, is considered, and velocity profiles, parametric dependences, etc. are studied. The simplified form of the equation of motion is solved by using the orthogonal collocation technique, which is particularly suitable for this kind of problem. In the second part, the condensation of a vapor on the fluted surface is studied with the basic assumptions required in Nusselt's analysis. The average Nusselt number for a given length of the tube is computed by solving the surface tension-governed equation of motion, while the Reynolds number is calculated by the method mentioned earlier. As a result, the Nusselt number as a function of Reynolds number can be computed for a given set of other parameters.

Kenneth J. Bell

Papers

The leidenfrost phenomenon: film boiling of liquid droplets on a flat plate

Forced convection boiling inside helically-coiled tubes

Heat Exchanger Design for the Process Industries

Heat Exchanger Design for the Process Industries

Analysis of Nusselt-type condensation on a vertical fluted surface