Flow Boiling Heat Transfer Of Refrigerants R134a And R245fa In A Horizontal Micro-Channel
2012 (English)In: Experimental heat transfer, ISSN 0891-6152, E-ISSN 1521-0480, Vol. 25, no 3, 181-196 p.Article in journal (Refereed) Published
Micro-channel-based evaporators are a promising option for high heat flux cooling applications. Micro-channels offer several advantages, including a smaller coolant inventory, superior heat transfer performance, compactness, lightness of weigh. Despite being attractive, the governing phenomena in micro-channels, especially during phase change, are less understood. This article reports the experimental flow boiling heat transfer results of refrigerants R134a and R245fa in a horizontal micro-channel. A series of experiments was conducted to measure the heat transfer coefficients in a circular micro-channel made of fused silica having an internal diameter of 781 mu m and a uniformly heated length of 191 mm. The outer surface of the test tube was coated with a thin, electrically conductive layer of indium-tin-oxide. The surface coating with the electrically conductive layer of indium-tin-oxide made it possible to visualize the flow boiling process simultaneously with uniform heating of the test section. R134a and R245fa were used as working fluids and experiments were performed at a system pressure of 7.7 bar for R134a and at 1.8 bar for R245fa, corresponding to saturation temperature of 30 degrees C. Mass flux was varied from 175 kg/m(2)s to 500 kg/m(2)s, and heat flux ranged from 5 kW/m(2) to 60 kW/m(2). A high-speed camera was used to capture the images in the case of flow boiling of R134a. The experimental results indicated that the heat transfer coefficient increased with heat flux while the mass flux proved to have a negligible effect on heat transfer coefficient.
Place, publisher, year, edition, pages
2012. Vol. 25, no 3, 181-196 p.
two-phase, visualization, heat transfer, micro-evaporator
IdentifiersURN: urn:nbn:se:kth:diva-100181DOI: 10.1080/08916152.2011.609962ISI: 000306089700004ScopusID: 2-s2.0-84863482970OAI: oai:DiVA.org:kth-100181DiVA: diva2:542927
2nd European Conference on Microfluidics, DEC, 2010, Toulouse, France
QC 201208062012-08-062012-08-062012-08-06Bibliographically approved