Experimental investigation of surface roughness effects on the flow boiling of R134a in microchannels

Rahim Jafari, Tuba Okutucu-Özyurt*, Hakkı Özgür Ünver, Özgür Bayer

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

20 Citations (Scopus)


This study experimentally investigates the effect of surface roughness on the hydrodynamic and thermal performance of microchannel evaporators. Three micro-evaporators of the same dimensions and different surface roughness have been fabricated by micro-WEDM. Each micro-evaporator consists of forty rectangular microchannels of 700 μm height, 250 μm width, and 19 mm length. A microscale vapor compression refrigeration cycle has been constructed to carry out the experiments. R134a is used as the refrigerant. Heat transfer coefficient, pressure drop and COP results are presented at variously imposed heat fluxes, and at mass fluxes of 85 and 200 kg/(m2 s). The results demonstrate up to 45% enhancement in the two-phase heat transfer coefficient at low to moderate heat flux values as the surface roughness increases. Considering the surface roughness effect of the microchannel walls, a new correlation is developed to predict the heat transfer coefficient of R134a boiling in microchannels.

Original languageEnglish
Pages (from-to)222-230
Number of pages9
JournalExperimental Thermal and Fluid Science
Publication statusPublished - 1 Dec 2016
Externally publishedYes

Bibliographical note

Publisher Copyright:
© 2016 Elsevier Inc.


This study has been financially supported by the Scientific and Technological Research Council of Turkey (TÜBİTAK) under grant number 112M168 . The micro-evaporators of different roughness have been fabricated at the Micro System Design and Manufacturing Center of Bilkent University, Ankara, Turkey. The authors would like to thank Mr. Mustafa Yalçın for his contribution to construct the test setup.

FundersFunder number
Türkiye Bilimsel ve Teknolojik Araştirma Kurumu


    • Boiling
    • Micro-evaporator
    • Microscale two-phase flow
    • Surface roughness
    • Vapor compression refrigeration cycle


    Dive into the research topics of 'Experimental investigation of surface roughness effects on the flow boiling of R134a in microchannels'. Together they form a unique fingerprint.

    Cite this