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Degree

MS, University of Cincinnati, Engineering and Applied Science: Mechanical Engineering, 2012.

Abstract

Saturated, nucleate pool boiling on a horizontal, cylindrical heater in aqueous solutions of a zwitterionic fluorosurfactant (FS-50) has been experimentally investigated. FS-50 is a long chain molecule of fluorinated carbon atoms, and it produces very low dynamic surface tension in aqueous solutions (varying from 75 x 10-3 N/m to 16.8 x 10-3; N/m, depending upon both surface age and concentration). The time scale or surface age for complete interfacial relaxation ranges from 10e-2 seconds < τ < 8 seconds. Boiling curves (given by the variation of wall heat flux with wall superheat) and photographic records of the ebullient behavior are presented, along with a detailed characterization of the interfacial behavior of the aqueous solutions and its interplay with boiling. It is seen that nucleate pool boiling behavior of water is significantly altered by the addition of FS-50, and the heat transfer is increased considerably. The enhancement in boiling is seen to stem from the dynamic changes in the interfacial tension and its overlapping timescale with that of boiling. A rather complex interplay of dynamic interfacial tension and surface wetting changes due to varying surfactant concentrations is seen to affect the phase change ebullient dynamics and associated heat transfer. In order to develop a scaling modal for predicting heat transfer for nucleate pool boiling in aqueous reagent solutions an attempt has been made to scale them with the interfacial properties. To do this, apart from the present results, data for few other (SDS (anionic), CTAB (cationic), TRITON X-100 (non-ionic)) are considered along with heat transfer results from previously published studies. It may be noted that FS-50 is a zwitterionic reagent. This scaling has been based upon modeling of the adsorption-desorption mechanisms of the reagent, and their influence on bubble dynamics associated with boiling. The proposed scaling method is derived using the existing theoretical deductions in the literature. A scaling parameter based on the most relevant dynamic interfacial property is developed and used to predict the heat transfer in aqueous solution of reagents. The proposed method works within 95 % agreement with the experimental values.

Subject Headings

Mechanical Engineering

Keywords

Boiling; Reagents; Surfactants

Committee / Advisors

Raj Manglik, PhD (Committee Chair)
Milind Jog, PhD (Committee Member)
Yuen Kao, PhD (Committee Member)

Pages

101p.

Document number: ucin1343085793
Permalink: http://rave.ohiolink.edu/etdc/view?acc_num=ucin1343085793

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