Subcooled flow boiling of R-134a in vertical channels of small diameter
2007 (English)In: International Journal of Multiphase Flow, ISSN 0301-9322, Vol. 33, no 8, 822-832 p.Article in journal (Refereed) Published
Subcooled flow boiling heat transfer for refrigerant R- 134a in vertical cylindrical tubes with 0.83, 1.22 and 1.70 turn internal diameter was experimentally investigated. The effects of the heat flux, q = 1-26 kW/m 2, mass flux, G = 300-700 kg /m(2) s, inlet subcooling, Delta T-sub,T-i = 5-15 degrees C, system pressure, P = 7.70-10.17 bar, and channel diameter, D, on the subcooled boiling heat transfer were explored in detail. The results are presented in the form of boiling curves and heat transfer coefficients. The boiling curves evidenced the existence of hysteresis when increasing the heat flux until the onset of nucleate boiling, ONB. The wall superheat at ONB was found to be essentially higher than that predicted with correlations for larger tubes. An increase of the mass flux leads, for early subcooled boiling, to an increase in the heat transfer coefficient. However, for fully developed subcooled boiling, increases of the mass flux only result in a slight improvement of the heat transfer. Higher inlet subcooling, higher system pressure and smaller channel diameter lead to better boiling heat transfer. Experimental heat transfer coefficients are compared to predictions from classical correlations available in the literature. None of them predicts the experimental data for all tested conditions.
Place, publisher, year, edition, pages
2007. Vol. 33, no 8, 822-832 p.
heat transfer, R-134a, subcooled boiling, onset of nucleate boiling, heat-transfer, circular microchannels, general correlation, annuli, tubes
IdentifiersURN: urn:nbn:se:kth:diva-16858DOI: 10.1016/j.ijmultiphaseflow.2007.02.002ISI: 000248634500002ScopusID: 2-s2.0-34250868303OAI: oai:DiVA.org:kth-16858DiVA: diva2:334901
QC 201005252010-08-052010-08-05Bibliographically approved