Change search
ReferencesLink to record
Permanent link

Direct link
Experimental study of bubble characteristics and heat transfer in subcooled flow boiling of R-134a
Norwegian University of Science and Technology, Faculty of Engineering Science and Technology, Department of Energy and Process Engineering.
2013 (English)MasteroppgaveStudent thesis
Abstract [en]

Because of its high heat transfer efficiency, subcooled flow boiling can contribute to the miniaturization of subsea heat exchangers. An experimental investigation was conducted to study the parametric influence on the distribution of bubble sizes and velocities as well as the heat transfer coefficient in the subcooled flow boiling of R-134a in a horizontal conventional annular channel. High-speed visualization was used to capture the flowing bubble behaviors at the end of a heated tube. The association between the heat transfer coefficients and various bubble characteristics, such as bubble size, velocity, population and interfacial area concentration, under different operating conditions were revealed. Most of the bubbles in the experiments slid along the upper part of the heated tube, while only tiny bubbles lifted off the surface. Bubble size distributions have a bimodal shape, composed of two different bubble size groups. The distributions of two bubble size groups follow the type 1 distribution of Pearson?s system and were interpolated using this system in order to to develop a population balance framework for further study. Bubble sliding velocities were based on size indicating that larger bubbles have higher sliding velocities, conversing to the bulk liquid velocity. Through investigating the observed bubble characteristics, coalescence during flowing was identified as the major mechanism of large bubbles formations. The interfacial area concentration shows a close association with the heat transfer coefficient, and they were correlated by a power function. The Jakob number, the ratio of densities and the Boiling numbers have consistent relations with the bubble sizes and velocities. New correlations were proposed for predicting bubble sizes and sliding velocities as functions of these three dimensionless numbers. The suggested correlations agree with the experimental data with deviations of less than 10%.

Place, publisher, year, edition, pages
Institutt for energi- og prosessteknikk , 2013. , 120 p.
URN: urn:nbn:no:ntnu:diva-22103Local ID: ntnudaim:10313OAI: diva2:646841
Available from: 2013-09-09 Created: 2013-09-09 Last updated: 2013-09-09Bibliographically approved

Open Access in DiVA

fulltext(4995 kB)1044 downloads
File information
File name FULLTEXT01.pdfFile size 4995 kBChecksum SHA-512
Type fulltextMimetype application/pdf
cover(234 kB)15 downloads
File information
File name COVER01.pdfFile size 234 kBChecksum SHA-512
Type coverMimetype application/pdf

By organisation
Department of Energy and Process Engineering

Search outside of DiVA

GoogleGoogle Scholar
Total: 1044 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

Total: 84 hits
ReferencesLink to record
Permanent link

Direct link