Abstract: Heat transfer to boiling liquid flowing through narrow minichannels has become a modern solution to heat transfer enhancement in small, mainly electronic devices. The paper discusses the method for simultaneous measurement of the flow boiling void fraction and heating surface temperature distribution, which aims at determining local values of the vapor quality and heat transfer coefficients. The studies were conducted for boiling FC-72 in a rectangular, vertical and asymmetrically heated minichannel. Employing a high-speed camera on the measurement stand constructed by the author helped to determine, for the set sections, the void and liquid fractions as a function of variable thermal and flow parameters such as channel hydraulic diameter, heat flux, pressure, mass flux and temperature of liquid subcooling at the minichannel inlet. Measurements of the heating surface temperature distribution and photographic observations of the two-phase flows, when conducted simultaneously, allow deter-mining the dependence of the recorded local void fraction on the local temperature. The liquid crystal thermography technique helped to perform the repetitious measurements of the temperature on the heating surface. One of the advantages of this technique is a possibility of observing the instantaneous temperature field of the heating surface. There were observed the following flow patterns: bubbly flow, bubbly-slug flow, slug flow, slug-wispy flow and wispy flow.
B I B L I O G R A F I A[1] Saisorn S., Kaew-On J., Wongwises S.: Flow pattern and heat transfer characteristics of R-134a refrigerant during flow boiling in a horizontal circular mini-channel, Int. J. Heat Mass Transfer, vol. 53, pp. 4023-4038, 2010.
[2] Piasecka M., Maciejewska B.: The study of boiling heat transfer in vertically and horizontally oriented rectangular minichannels and the solution to the inverse heat transfer problem with the use of the Beck method and Trefftz functions. Experimental Thermal and Fluid Science, vol. 38, pp. 19-32, 2012.
[3] Kandlikar S. G.: Scale effects on flow boiling heat transfer in microchannels: A fundamental perspective, Int. J. Thermal Sciences, vol. 49, pp. 1073-1085, 2010.
[4] Ong C. L., Thome J. R.: Macro-to-microchannel transition in two-phase flow: Part 1 -Two-phase flow patterns and film thickness measurements, Experimental Thermal Fluid Science, vol. 35, pp. 37-47, 2011.
[5] Bohdal T.: Przyczyny niestabilności przemian fazowych czynników energetycznych, Wydawnictwo Uczelniane Politechniki Koszalińskiej, Monografia Wydziału Mechanicznego PK, nr 130, Koszalin, 2006.
[6] Thorncroft G. E., Klausner J. F., Mei R.: An experimental investigation of bubble growth and datachment in vertical upflow and downflow boiling, Int. J. Heat Mass Transfer, vol. 41, pp. 3857-3871, 1998.
[7] Thome J. R.: Engineering data book III, Wolverine Tube Inc., 2004.
[8] Dupont V., Thome J. R.: Evaporation in microchannels
influence of the channel diameter on heat transfer, Proc. 2nd Int. Conf. on Micro- and Minichannels, Rochester, NY, USA, pp. 461-468, 2004.
[9] Kaniowski R., Poniewski M. E.: Two-phase flow patterns and boiling heat transfer in asymmetrically heated minichannels, Proc. ECI 8th Int. Conf. on Boiling and Condensation Heat Transfer, CD - paper - o_s1_1509, pp. 10, 2012.
[10] Kaniowski R., Poniewski M. E.: Measurement of void fraction distribution and heating surface local temperature in a rectangular, vertical minichannel heated asymmetrically, The Six International Conferece on Transport Phenomena in Multiphase System, Heat 2011, pp. 263-270, 2011. 
Pełny tekst 
YADDA/CEON