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ÖZDEMİR, MEHMED RAFET

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ÖZDEMİR

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MEHMED RAFET

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2016 - 201912020 - 20212
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Author: ÖZDEMİR, MEHMED RAFET × Subject: 2-PHASE FLOW ×

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Now showing 1 - 3 of 3
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    PublicationOpen Access
    Flow Boiling of Water in a Rectangular Metallic Microchannel
    (TAYLOR & FRANCIS INC, 2021-03-26) ÖZDEMİR, MEHMED RAFET; Ozdemir, Mehmed Rafet; Mahmoud, Mohamed M.; Karayiannis, Tassos G.
    The article presents the experimental results of flow boiling of water in single rectangular microchannels. Three rectangular copper microchannels having the same hydraulic diameter (0.56 mm) and length (62 mm) but different aspect ratios (width/height, 0.5, 2.56, and 4.94) were investigated using de-ionized water as the working fluid. The experiments were conducted over the experimental range of mass flux 200-800 kg/(m(2)s), heat flux 4-1350 kW/m(2) and inlet subcooling of similar to 14 K. The results showed that the channel with smaller aspect ratio exhibited better heat transfer performance up to certain heat fluxes (similar to 480-500 kW/m(2)), whilst the effect of channel aspect ratio became insignificant for higher heat fluxes. The flow boiling patterns were observed and the main flow regimes were bubbly, slug, churn, and annular flow. Flow reversal was also observed that caused a periodic flow in the two microchannels having smaller aspect ratio. A comparison of the experimental results with widely used macro and micro-scale heat transfer correlations is presented. The macro-scale correlations failed to predict the experimental data while some micro-scale correlations could predict the data reasonably well.
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    Design and implementation of minichannel evaporator for electronics cooling
    (SPRINGER, 2021) ÖZDEMİR, MEHMED RAFET; Sokucu, Mehmet Harun; Ozdemir, Mehmed Rafet
    The present study elucidates the design and experimentation of a minichannel evaporator in an R134a vapour compression refrigeration system for electronics cooling applications. In the current study, a calculation module was developed to design a minichannel evaporator to keep the surface temperature of the chip below a certain value for reliable operation conditions in electronic cooling applications. In the calculation module, the conventional-scale heat transfer correlation was used to predict the surface temperature of the chip. On the other hand, the conventional-scale and microscale pressure drop correlations were tested to assess the pressure drop in the minichannel evaporator. The proposed calculation module was verified using experimental tests for different heat loads. It was found that the proposed calculation model predicted very well the experimental data of the surface temperature of the chip for all heat input. The calculation module with micro-scale pressure drop correlation predicted well the experimental pressure drop data in the minichannel evaporator for all heat loads. Moreover, the effects of the degree of subcooling, superheating degree and condensation temperature on the surface temperature of the chip and pressure drop in the minichannel evaporator were investigated to determine optimum operating conditions at different cooling capacities using the calculation module. The results showed that the increase in the degree of subcooling enhances the performance of the minichannel evaporator. On the other hand, the lower degree of superheating and condensation temperature yielded better performance for the minichannel evaporator. The feasibility of the results for electronic cooling applications is discussed based on the findings.
  • Thumbnail Image
    PublicationOpen Access
    FLOW BOILING HEAT TRANSFER IN A RECTANGULAR COPPER MICROCHANNEL
    (YILDIZ TECHNICAL UNIV, 2016) ÖZDEMİR, MEHMED RAFET; Ozdemir, Mehmed R.; Mahmoud, Mohamed M.; Karayiannis, Tassos G.
    Flow boiling characteristics of de-ionized water were tested experimentally in a rectangular copper single microchannel of 1 mm width, 0.39 mm height and 62 mm length. De-ionized water was supplied to the microchannel at constant inlet temperature (89 degrees C) and constant inlet pressure (115 kPa). The mass flux ranged from 200 to 800 kg/m(2)s and the heat flux from 56 to 865 kW/m(2). The heat transfer rate data are presented as plots of local heat transfer coefficient versus vapour quality and distance along the channel. Flow visualization was also conducted using a high-speed, high-resolution camera. The results indicate that unstable flow boiling occurred starting at boiling incipience for all mass flux values. The local heat transfer coefficient depends on heat flux only at very low heat and mass fluxes. At high mass flux, there is no heat flux effect with little dependence on vapour quality after the entry region. The mass flux effect was more complex.