Pool boiling heat transfer of tandem tubes provided with the novel microstructures

• Published in: The International journal of heat and fluid flow 2011-08, Vol.32 (4), p.777-784
• Main Authors: Ustinov, Alexander, Ustinov, Victor, Mitrovic, Jovan
• Format: Article
• Language: English
• Subjects: Applied sciences; Boiling; Density; Energy; Energy. Thermal use of fuels; Exact sciences and technology; Heat transfer; Heat transfer enhancement; Inclination; Microstructure; Pools; Refrigerants; Tandem; Theoretical studies. Data and constants. Metering; Three phase line; Tube; Tubes
• ISSN: 0142-727X; 1879-2278
• DOI: 10.1016/j.ijheatfluidflow.2011.04.001

► Tandem of microstructured tubes was investigated with pool boiling of R134a at pressures 5-9 bar and FC-3284 at 0.5-1.5 bar. ► Superheat of microstructured surfaces is independent on heat flux due to huge number of nucleation sites and very long TPL. ► Influence of bubbly flow from lower tube was investigated and upper tube maximum superheat was found at moderate heat fluxes. ► Microstructures show higher HTCs at lower pressures: critical bubble diameter becomes comparable with distance between pins. ► Microstructured surfaces with larger number of pins are more efficient, as they provide longer TPL. The paper presents experimental data on pool boiling heat transfer of tandem tubes, arranged one above the other in the same vertical plane. The outer surface of the tubes is provided with the novel microstructures. The structure elements are micropins created by electrolytic deposition of copper upon the tube, using a specially treated polycarbonate foil. By this technique the pins diameter can be varied from 0.1 μm up to 25 μm, the pins height goes up to 100 μm at densities up to 1 × 10 9 pins/cm 2 and pins inclination almost up to 180° regarding the base surface. Micropins with several different inclinations can be created simultaneously on the same surface. Experiments were conducted with two different microstructures using the refrigerant R134a and the highly wetting Fluorinert liquid FC-3284 at pressures of 5–9 bar and 0.5–1.5 bar, respectively. The advantages of the novel microstructure regarding the boiling heat transfer for tandem tubes turned out to be practically the same as for a single tube arrangement. Microstructured tubes have the superheat independent on the heat flux, they show a very low boiling inception superheats (below 2 K), are highly effective in comparison with a technically smooth tubes, and operate stable over the long periods of time.