The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Srinivas Garimella - One of the best experts on this subject based on the ideXlab platform.
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investigation of a Microchannel heat and mass exchanger for absorption systems
Applied Thermal Engineering, 2019Co-Authors: Dhruv C Hoysall, Srinivas GarimellaAbstract:Abstract An investigation of a Microchannel heat and mass exchanger for vapor absorption systems is presented. A sheet with 88 Microchannels of depth 0.5 mm and width 0.76 mm is investigated via visual and thermal measurements. The flow in the Microchannels is predominantly in the slug-flow regime, with distinct vapor and liquid regions. High rates of heat transfer were observed in the absorber. However, poor liquid mass transfer rates limit the performance of the Microchannel absorber. The performance of the Microchannel absorber is compared with that of an absorber with serpentine microscale passages containing micro-pin fins. A physics-based model for the absorption of ammonia into a dilute solution of ammonia-water in a Microchannel absorber with mixing sections is developed using insights from flow visualization. The model is validated by comparing its predictions with the data. The potential of surfactants to enhance absorber performance is also investigated.
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measurement and modeling of condensation heat transfer in non circular Microchannels
International Journal of Refrigeration-revue Internationale Du Froid, 2010Co-Authors: Akhil Agarwal, Todd M Bandhauer, Srinivas GarimellaAbstract:Heat transfer coefficients in six non-circular horizontal Microchannels (0.424 < Dh < 0.839 mm) of different shapes during condensation of refrigerant R134a over the mass flux range 150 < G < 750 kg m−2 s−1 were measured in this study. The channels included barrel-shaped, N-shaped, rectangular, square, and triangular extruded tubes, and a channel with a W-shaped corrugated insert that yielded triangular Microchannels. The thermal amplification technique developed and reported in earlier work by the authors is used to measure the heat transfer coefficients across the vapor-liquid dome in small increments of vapor quality. Results from previous work by the authors on condensation flow mechanisms in Microchannel geometries were used to interpret the results based on the applicable flow regimes. The effect of tube shape was also considered in deciding the applicable flow regime. A modified version of the annular-flow-based heat transfer model proposed recently by the authors for circular Microchannels, with the required shear stress being calculated from a non-circular Microchannel pressure drop model also reported earlier was found to best correlate the present data for square, rectangular and barrel-shaped Microchannels. For the other Microchannel shapes with sharp acute-angle corners, a mist-flow-based model from the literature on larger tubes was found to suffice for the prediction of the heat transfer data. These models predict the data significantly better than the other available correlations in the literature.
Suresh V. Garimella - One of the best experts on this subject based on the ideXlab platform.
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a comprehensive flow regime map for Microchannel flow boiling with quantitative transition criteria
International Journal of Heat and Mass Transfer, 2010Co-Authors: Tannaz Harirchian, Suresh V. GarimellaAbstract:Due to the critical role of vapor confinement in establishing distinct flow and heat transfer characteristics in Microchannels (as distinct from those in larger channels), the conditions under which such confinement occurs in Microchannels are of great interest. It is shown in the present work that channel dimensions and flow properties alone, as proposed in past studies, are insufficient for determining confinement effects in Microchannel boiling. Hence, a new criterion for physical confinement in Microchannel flow boiling, termed the convective confinement number, that incorporates the effects of mass flux, as well as channel cross-sectional area and fluid properties, is proposed. This criterion helps determine the conditions under which a channel qualifies as a Microchannel for two-phase flow, needing special treatment, and when a macroscale treatment is adequate. In addition, based on previous work by the authors, a new comprehensive flow regime map is developed for a wide range of experimental parameters and channel dimensions, along with quantitative transition criteria based on nondimensional boiling parameters.
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the critical role of channel cross sectional area in Microchannel flow boiling heat transfer
International Journal of Multiphase Flow, 2009Co-Authors: Tannaz Harirchian, Suresh V. GarimellaAbstract:Abstract Experiments are conducted with a perfluorinated dielectric fluid, Fluorinert FC-77, to identify the critical geometric parameters that affect flow boiling heat transfer and flow patterns in Microchannels. In recent work by the authors (Harirchian and Garimella, 2009), seven different silicon test pieces containing parallel Microchannels of widths ranging from 100 to 5850 μm, all with a depth of 400 μm were tested and it was shown that for a fixed channel depth, the heat transfer coefficient was independent of channel width for Microchannels of widths 400 μm and larger, with the flow regimes in these Microchannels being similar; nucleate boiling was also found to be dominant over a wide range of heat fluxes. In the present study, experiments are performed with five additional Microchannel test pieces with channel depths of 100 and 250 μm and widths ranging from 100 to 1000 μm. Flow visualizations are performed using a high-speed digital video camera to determine the flow regimes, with simultaneous local measurements of the heat transfer coefficient and pressure drop. The aim of the present study is to investigate as independent parameters the channel width and depth as well as the aspect ratio and cross-sectional area on boiling heat transfer in Microchannels, based on an expanded database of experimental results. The flow visualizations and heat transfer results show that the channel cross-sectional area is the important governing parameter determining boiling mechanisms and heat transfer in Microchannels. For channels with cross-sectional area exceeding a specific value, nucleate boiling is the dominant mechanism and the boiling heat transfer coefficient is independent of channel dimensions; below this threshold value of cross-sectional area, vapor confinement is observed in all channels at all heat fluxes, and the heat transfer rate increases as the Microchannel cross-sectional area decreases before premature dryout occurs due to channel confinement.
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saturated flow boiling heat transfer and pressure drop in silicon Microchannel arrays
International Journal of Heat and Mass Transfer, 2008Co-Authors: Poh Seng Lee, Suresh V. GarimellaAbstract:Flow boiling in arrays of parallel Microchannels is investigated using a silicon test piece with imbedded discrete heat sources and integrated local temperature sensors. The Microchannels considered range in width from 102 μm to 997 μm, with the channel depth being nominally 400 μm in each case. Each test piece has a footprint of 1.27 cm by 1.27 cm with parallel Microchannels diced into one surface. Twenty five microsensors integrated into the Microchannel heat sinks allow for accurate local temperature measurements over the entire test piece. The experiments are conducted with deionized water which enters the channels in a purely liquid state. Results are presented in terms of temperatures and pressure drop as a function of imposed heat flux. The experimental results allow a critical assessment of the applicability of existing models and correlations in predicting the heat transfer rates and pressure drops in Microchannel arrays, and lead to the development of models for predicting the two-phase pressure drop and saturated boiling heat transfer coefficient.
Qi Yang - One of the best experts on this subject based on the ideXlab platform.
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a diamond made Microchannel heat sink for high density heat flux dissipation
Applied Thermal Engineering, 2019Co-Authors: Qi Yang, Jingquan Zhao, Yanpei Huang, Xiaowei Zhu, Jianyin MiaoAbstract:Abstract Flow boiling in Microchannels is a promising technique for cooling high power-density electronic devices. In this study, a Microchannel heat sink using ammonia as working fluid is developed, and its cooling efficiency is experimentally investigated under nonuniform high-density heat flux, which well simulates a practical heat dissipation scenario for microthermal systems. Diamond with high thermal conductivity of 1500 W/m·K is selected as the Microchannel heat sink material. A total of 37 parallel triangular Microchannels with aspect ratio of 5, channel length of 45 mm and hydraulic diameter of 280 μm are uniformly engineered on the diamond film by laser ablation processing. The significance of diamond substrate as a heat spreader to minimize the nonuniformity of heat flux imposed by a central hotspot is verified. The influences of heat flux and mass flux on the cooling efficiency are experimentally investigated. An optimal range of outlet vapor quality from 0.10 to 0.13 is found, within which the minimum heat source temperature can be achieved. Notably, the Microchannel heat sink is capable of managing a central hotspot with heat flux of 267 W/cm2 while maintaining the heat source temperature at 53.3 °C for a mass flux of 320 kg/m2s.
Satish G Kandlikar - One of the best experts on this subject based on the ideXlab platform.
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pool boiling heat transfer enhancement over cylindrical tubes with water at atmospheric pressure part ii experimental results and bubble dynamics for circumferential v groove and axial rectangular open Microchannels
International Journal of Heat and Mass Transfer, 2013Co-Authors: Jeet S Mehta, Satish G KandlikarAbstract:Abstract A two-part experimental study is conducted on pool boiling heat transfer over enhanced cylindrical Microchannel test surfaces with water at atmospheric pressure. In this Part II of the study, the effects of circumferential V-groove Microchannels and axial rectangular Microchannels are reported. These experiments were performed in the horizontal as well as vertical orientations. The heat transfer performances of the modified surfaces are compared with that of a plain surface. At a heat flux of 1070 kW/m2 a maximum heat transfer coefficient of 96 kW/m2 K was achieved with an axial rectangular Microchannel test section in the vertical orientation. Videos captured using a high speed camera were analyzed and the boiling heat transfer mechanisms seen at low and medium heat flux conditions were discussed. The enhancement in the heat transfer performance, and the improvement of the critical heat flux observed with these modified test sections have been attributed to the liquid rewetting phenomenon of the heated surfaces through the Microchannels.
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numerical investigation of heat transfer in rectangular Microchannels under h2 boundary condition during developing and fully developed laminar flow
Journal of Heat Transfer-transactions of The Asme, 2012Co-Authors: V V Dharaiya, Satish G KandlikarAbstract:Study of fluid flow characteristics at microscale is gaining importance with shrinking device sizes. Better understanding of fluid flow and heat transfer in Microchannels will have important implications in electronic chip cooling, heat exchangers, MEMS, and microfluidic devices. Due to short lengths employed in Microchannels, entrance header effects can be significant and need to be investigated. In this work, three dimensional model of Microchannels, with aspect ratios (a ¼a/b) ranging from 0.1 to 10, are numerically simulated using CFD software tool FLUENT. Heat transfer effects in the entrance region of Microchannel are presented by plotting average Nusselt number as a function of nondimensional axial length x*. The numerical simulations with both circumferential and axial uniform heat flux (H2) boundary conditions are validated for existing data set for four wall heat flux case. Large numerical data sets are generated in this work for rectangular cross-sectional Microchannels with heating on three walls, two opposing walls, one wall, and two adjacent walls under H2 boundary condition. This information can provide better understanding and insight into the transport processes in the Microchannels. Although the results are seen as relevant in microscale applications, they are applicable to any sized channels. Based on the numerical results obtained for the whole range, generalized correlations for Nusselt numbers as a function of channel aspect ratio are presented for all the cases. The predicted correlations for Nusselt numbers can be very useful resource for the design and optimization of Microchannel heat sinks and other microfluidic devices. [DOI: 10.1115/1.4004934]
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critical heat flux measurement and model for refrigerant 123 under stabilized flow conditions in Microchannels
ASME 2006 International Mechanical Engineering Congress and Exposition, 2006Co-Authors: Wai Keat Kuan, Satish G KandlikarAbstract:The present work is aimed toward understanding the effect of flow boiling stability on critical heat flux (CHF) with Refrigerant-123 (R-123) in Microchannel passages. Experimental data and theoretical model to predict the CHF are the focus of this work. The experimental test section has six parallel Microchannels with each having a cross sectional area of 1054 × 157 µm 2 . The effect of flow instabilities in Microchannels is investigated using flow restrictors at the inlet of each Microchannel to stabilize the flow boiling process and avoid the backflow phenomena. This technique resulted in successfully stabilizing the flow boiling process as seen through a high-speed camera. The present CHF result is found to correlate to mean absolute error (MAE) of 24.1% with a macroscale empirical equation by Katto [13]. A theoretical analysis of flow boiling phenomena revealed that the ratio of evaporation momentum to surface tension forces is an important parameter. For the first time, a theoretical CHF model is proposed using these underlying forces to represent CHF mechanism in Microchannels, and its correlation agrees with the experimental data with MAE of 2.5%.
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evolution of Microchannel flow passages thermohydraulic performance and fabrication technology
Heat Transfer Engineering, 2003Co-Authors: Satish G Kandlikar, William J GrandeAbstract:This paper provides a roadmap of development in the thermal and fabrication aspects of Microchannels as applied in microelectronics and other high heat-flux cooling applications. Microchannels are defined as flow passages that have hydraulic diameters in the range of 10 to 200 micrometers. The impetus for Microchannel research was provided by the pioneering work of Tuckerman and Pease [1] at Stanford University in the early eighties. Since that time, this technology has received considerable attention in microelectronics and other major application areas, such as fuel cell systems and advanced heat sink designs. After reviewing the advancement in heat transfer technology from a historical perspective, the advantages of using Microchannels in high heat flux cooling applications is discussed, and research done on various aspects of Microchannel heat exchanger performance is reviewed. Single-phase performance for liquids is still expected to be describable by conventional equations; however, the gas flow may...
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evolution of Microchannel flow passages thermohydraulic performance and fabrication technology
Taylor and Francis, 2003Co-Authors: Satish G Kandlikar, William J GrandeAbstract:This paper provides a roadmap of development in the thermal and fabrication aspects of Microchannels as applied in the microelectronics and other high heat-flux cooling applications. Microchannels are defined as flow passages that have hydraulic diameters in the range of 10 to 200 micrometers. The impetus for Microchannel research was provided by the pioneering work of Tuckerman and Pease [1] at Stanford University in the early eighties. Since that time, this technology has received considerable attention in microelectronics and other major application areas, such as fuel cell systems and advanced heat sink designs. After reviewing the advancement in heat transfer technology from a historical perspective, advantages of using Microchannels in high heat flux cooling applications is discussed, and research done on various aspects of Microchannel heat exchanger performance is reviewed. Single-phase performance for liquids is expected to be still describable by the conventional equations; however the gas flow may be influenced by the rarefaction effects. Two-phase flow is another topic that is still under active research. The evolution of research into Microchannel heat sinks has paralleled the advancements made in microfabrication technology. The earliest Microchannels were built using anisotropic wet chemical etching techniques based on alkali solutions. While this method has been exploited successfully, it does impose certain restrictions on silicon wafer type and geometry. Recently, anisotropic dry etching processes have been developed that circumvent these restrictions. In addition, dry etching methods can be significantly faster and, from a manufacturing standpoint, create fewer contamination and waste treatment problems. Advances in fabrication technology will continue to fuel improvements in Microchannel heat sink performance and cost for the foreseeable future. Some fabrication areas that may spur advances include new materials, high aspect ratio patterning techniques other than dry etching, active fluid flow elements, and micromolding.Copyright © 2002 by ASME
Guodong Xia - One of the best experts on this subject based on the ideXlab platform.
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a comparative study of experimental flow boiling heat transfer and pressure drop characteristics in porous wall Microchannel heat sink
International Journal of Heat and Mass Transfer, 2018Co-Authors: Y.t. Jia, L.x. Zong, Guodong Xia, D D, Yongzhi TangAbstract:Abstract In this work, we proposed a porous-wall (PW) Microchannel heat sink, in which micro pin fin arrays were fabricated on sidewalls of rectangular Microchannels by MEMS (Microelectrical Mechanical System) technique. High speed flow visualizations were performed simultaneously with heat transfer and pressure drop measurements to investigate the flow boiling characteristics of PW Microchannel heat sink. Conventional rectangular (Rec) Microchannel heat sink was also explored together as a comparison. Experiments were carried out with pure acetone liquid at inlet temperature of 30 °C, mass flux from 255 kg/(m2·s) to 843 kg/(m2·s), heat flux from 4 W/cm2 to 110 W/cm2 and the maximum vapor quality at the outlet of the channel was 0.88. Experimental results demonstrated that the PW Microchannels reduce wall superheat of onset of nucleate boiling (ONB) and improve critical heat flux (CHF) compared to the Rec Microchannels. Moreover, the PW Microchannels show significant heat transfer enhancement, pressure drop reduction and mitigation of two-phase flow instability. The porous walls provide numerous nucleation sites and the intensive pin fins arrangements introduce significant wicking effect to maintain the liquid rewetting, which contribute to the above notable flow boiling enhancement.
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two phase flow pattern and pressure drop in silicon multi Microchannel with expansion constriction cross section
Experimental Thermal and Fluid Science, 2015Co-Authors: Liang Wang, Lei Chai, Mingzheng Zhou, Guodong XiaAbstract:Abstract Gas–liquid two-phase intermittent flow pattern and frictional pressure drop in new silicon multi-Microchannel were investigated experimentally by means of the IDT high-speed camera mounted together with a Nikon microscope. Each test section consisted of 10 parallel Microchannels with 0.1 mm wide and 0.2 mm deep in constant cross-section segment and each Microchannel consisted of an array of periodic reentrant cavities. The major two-phase flow pattern observed was intermittent in the test sections, and the intermittent sub regimes in the new Microchannels were different from those displayed in the rectangular straight Microchannel. Using nitrogen and deionized water as working fluids, the intermittent sub regime maps for the new multi-Microchannel were obtained. Meanwhile, the pressure drops were compared with several existing correlations based on the homogeneous or separated mixture assumption. Results show that the homogeneous flow model cannot predict the two-phase pressure drop data well, while the separated flow model is proposed to provide a better prediction of the two-phase frictional pressure drop. Among the separated flow models investigated, the best two correlations of C value can provide mean deviations within less than 16% for all the three Microchannels and all the predictions lie in the bound of ±30%.
