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ISSN Online: 2377-424X

ISBN Print: 978-1-56700-474-8

ISBN Online: 978-1-56700-473-1

International Heat Transfer Conference 16
August, 10-15, 2018, Beijing, China

EXPERIMENTAL INVESTIGATION ON REVERSIBLE CHARACTERISTICS OF HEAT TRANSFER AND FLUID FLOW USING WAVELENGTH-DEPENDENT PHOTORESPONSE OF AQUEOUS SURFACTANT SOLUTION

Get access (open in a dialog) DOI: 10.1615/IHTC16.hte.023287
pages 5049-5055

Abstract

The present study experimentally investigated the thermal flow characteristics of an aqueous surfactant solution whose rheological properties can be reversibly altered by irradiation of ultraviolet (UV)/visible (Vis) light. The solution composed of CTAB (cetyltrimethylammonium bromide) and ADCA (azobenzene-3,3'-dicarboxylic acid) was used as a working fluid. The mixture of CTAB/ADCA self-assembles into wormlike micelles, and their lengths are closely related to the molecular geometry of ADCA. The degree of elongation and entanglement of micelles change reversibly as ADCA undergoes trans (anti)-cis (syn) photoisomerization, which results in a reversible light-triggered switching of viscoelasticity of the aqueous surfactant solution. To examine the possibility of a heat transfer control by utilizing this photo-rheological fluid as a heat transfer medium, measurements of rheological properties, heat transfer coefficient, and pressure loss penalty were carried out for the CTAB/ADCA solution of different light irradiation conditions. After 15 h/L UV light irradiation, the relaxation time of the solution diminished from 3.9 s to 2.2 s. Both the mean Nusselt number and friction factor of the solution flowing in a serpentine milli-channel at low Reynolds number condition (Re ~ O(1)) decreased compared to their initial values before the irradiation. After the consecutive 5 h/L Vis light irradiation, they recovered almost to the levels before the irradiation, with the increase of the relaxation time up to 4.6 s. These results imply the future application of photo-sensitive micellar solutions to the reversible and spatio-temporal control of thermal-fluid transport in a miniaturized heat exchanger by light irradiation.