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EXPERIMENTAL AND COMPUTATIONAL STUDY OF NUCLEATE POOL BOILING HEAT TRANSFER IN AQUEOUS SURFACTANT AND POLYMER SOLUTIONS

ZHANG, JUNTAO
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1077304904

Abstract Details

2004, PhD, University of Cincinnati, Engineering : Mechanical Engineering.
Saturated, nucleate pool boiling on a horizontal, cylindrical heater and the associated bubble dynamics in aqueous surfactant and polymer solutions are experimentally and computationally investigated. Boiling curves for different additive concentrations and photographic records of the salient features of the ebullient behavior are presented, along with a characterization of the interfacial properties (dynamic surface tension and surface wettability) of the aqueous solutions. The surfactant additive significantly alters the nucleate boiling in water and enhances the heat transfer. The enhancement increases with concentration, with an optimum obtained in solutions at or near the critical micelle concentration (CMC) of the surfactant. On the other hand, boiling in aqueous polymer solutions shows contrary results. The enhancement is seen to increase with polymer concentration in the aqueous surface-active HEC solutions, while boiling in shear-thinning Carbopol 934 solutions is seen to decrease continuously with increasing concentrations. In order to develop a theoretical model and understand the associated convective mechanisms, the dynamics of a single growing and departing bubble during nucleate boiling from a horizontal heated surface has been numerically simulated. The results highlight the role of the microlayer in nucleate boiling, as well as the effects of altered surface tension and viscosity, apparent contact angle, and wall superheat on the bubble dynamics and boiling behavior in aqueous surfactant and polymer solutions. In multiphase heat transfer, the nature and dynamics of surface contact often plays a dominant role. In fact, almost all the transport processes in nucleate boiling, from the inception of an embryonic bubble to the subsequent phase change, are intricately connected with this interface. To better characterize the molecular dynamics of the additives at the interfaces, an extensive literature review is presented that delineates the surfactant adsorption process and its electrokinetic effects (zeta potential), and the concomitant surface wetting behavior. This fundamental understanding is supported by the measured interfacial properties of the solutions reported in this study. And as shown by the boiling data, the heat transfer performance is changed dramatically when the interfacial transport process is altered. Finally, as documented by the pool boiling experiments with aqueous surfactant solutions, a markedly different ebullient behavior than not only that of water is observed, but between pre- and post-CMC solutions as well. The characteristic bubble dynamics is found to correlate well with the measured surface wettability and the adsorption isotherm, which in turn correlates with the zeta potential. In essence, the unique structure of a surfactant - a hydrophilic head with a hydrophobic tail - provides the means to control of nucleate boiling by altering surface wettability. The advantage of this very effective method is that there is no need to make any changes to any existing boiling equipment, except for the addition of desired amount of surfactant into the solution. The potential application impact extends to any process that involves phase-change (large-scale as well as micro-scale heat exchange devices). Furthermore, the surfactant physisorption and its electrokinetics are not only basic to a fundamental understanding of nucleate boiling control, but also can provide insights into related natural phenomena in other applications as well. There include chemical and biological sensors, microgravity applications, and microfluidic (or lab-on-chip) devices, among others. Also, some nanofluids or nanoparticles with special surface properties based on the different structures of surfactant micelles can be developed to provide even greater interfacial control in these broad spectrum of emerging applications.
Dr. Raj Manglik (Advisor)
209 p.
Engineering, Mechanical
interfacial phenomena; dynamic surface tension; wettability; bubble dynamics; level set method; enhancement

Recommended Citations

Citations

  • ZHANG, J. (2004). EXPERIMENTAL AND COMPUTATIONAL STUDY OF NUCLEATE POOL BOILING HEAT TRANSFER IN AQUEOUS SURFACTANT AND POLYMER SOLUTIONS [Doctoral dissertation, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1077304904

    APA Style (7th edition)

  • ZHANG, JUNTAO. EXPERIMENTAL AND COMPUTATIONAL STUDY OF NUCLEATE POOL BOILING HEAT TRANSFER IN AQUEOUS SURFACTANT AND POLYMER SOLUTIONS. 2004. University of Cincinnati, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1077304904.

    MLA Style (8th edition)

  • ZHANG, JUNTAO. "EXPERIMENTAL AND COMPUTATIONAL STUDY OF NUCLEATE POOL BOILING HEAT TRANSFER IN AQUEOUS SURFACTANT AND POLYMER SOLUTIONS." Doctoral dissertation, University of Cincinnati, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1077304904

    Chicago Manual of Style (17th edition)

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This open access ETD is published by University of Cincinnati and OhioLINK.