New experimental results on flow boiling of R-134a in a vertical microchannel
2007 (English)In: Proc. 10th UK Heat Transfer, Academic Conferences Publishing, 2007Conference paper (Refereed)
With the rapid development of micro electronic devices and micro manufacturing technology, heat transfer in microchannels has become increasingly important. However, the governing phenomena are not yet well understood.This paper presents new experimental results on flow boiling of R-134a in a vertical microchannel. Local heat transfer coefficients are measured along a single metal tube with internal diameter of 640 μm and a uniformly heated length of 213 mm, for three different mass fluxes, 250, 400 and 600 kg/m2s, two system pressures, 7.70 and 8.87 bar at the inlet (corresponding to saturation temperatures of 30 and 35 ºC), heat fluxes ranging from 5 to 70 kW/m2, and vapour qualities up to 0.89.From the experimental results it is clear that the heat transfer coefficient increases with heat flux and system pressure and does not change with vapour quality or mass flux when the quality is less than 0.45–0.50. For higher vapour qualities, the heat transfer coefficient decreases with vapour quality and the effect of the heat flux on the heat transfer coefficient seems to diminish. This deterioration of the heat transfer coefficient is believed to be caused by the occurrence of intermittent dry out in this vapour quality range.The experimental heat transfer coefficients are compared against predictions from three generalized models, two developed specifically for microscale geometries and one for conventional channels, showing unsatisfactory agreement, especially for the high vapour quality range.
Place, publisher, year, edition, pages
Academic Conferences Publishing, 2007.
IdentifiersURN: urn:nbn:se:kth:diva-89524OAI: oai:DiVA.org:kth-89524DiVA: diva2:503097
10th UK National Heat Transfer Conference, Edinburgh, Scotland, September 10-11, 2007
QC 201205152012-02-142012-02-142012-05-15Bibliographically approved