Jafari, Rahim

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Citation - WoS: 29
Citation - Scopus: 33
Experimental Investigation of Surface Roughness Effects on the Flow Boiling of R134a in Microchannels
(Elsevier Science inc, 2016) Jafari, Rahim; Okutucu-Ozyurt, Tuba; Unver, Hakki Ozgur; Bayer, Ozgur
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 mu m height, 250 mu m 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/(m(2)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. (C) 2016 Elsevier Inc. All rights reserved.
Citation - WoS: 22
Citation - Scopus: 27
Modeling and Analysis of Surface Roughness of Microchannels Produced by Μ-Wedm Using an Ann and Taguchi Method
(Korean Soc Mechanical Engineers, 2017) Jafari, Rahim; Kahya, Muge; Oliaei, Samad Nadimi Bavil; Unver, Hakki Ozgur; Ozyurt, Tuba Okutucu
Microchannel heat exchangers are used to remove the high heat fluxes generated in compact electronic devices. The roughness of the microchannels has a significant effect on the heat transfer characteristics, especially the nucleate boiling and pumping power. Therefore, development of predictive models of surface texture is of significant importance in controlling heat transfer characteristics of these devices. In this study, micro-Wire electrical discharge machining (mu-WEDM) was employed to fabricate metal-based microchannel heat sinks with different surface textures. First, experiments were conducted to achieve the desired surface roughness values. Oxygen-free copper is a common material in the cooling systems of electronic devices because of its high thermal conductivity and low cost. Design of experiment approach based on the Taguchi technique was used to find the optimum set of process parameters. An analysis of variance is also performed to determine the significance of process parameters on the surface texture. An artificial neural network model is utilized to assess the variation of the surface roughness with process parameters. The predictions are in very good agreement with results yielding a coefficient of determination of 99.5 %. The results enable to determine mu-WEDM parameters which can result in the desired surface roughness, to have a well-controlled flow and heat transfer characteristics for the microchannels.

Journal	Count
Case Studies in Thermal Engineering	1
Energy and Buildings	1
Experimental Thermal and Fluid Science	1
IICETA 2022 - 5th International Conference on Engineering Technology and its Applications -- 5th International Conference on Engineering Technology and its Applications, IICETA 2022 -- 31 May 2022 through 1 June 2022 -- Al-Najaf -- 183264	1
International Advanced Researches and Engineering Journal	1

Jafari, Rahim

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