Suresh V. Garimella

Purdue University, ウェストラファイエット, Indiana, United States

Are you Suresh V. Garimella?

Claim your profile

Publications (350)499.62 Total impact

  • Ravi S. Patel, Justin A. Weibel, Suresh V. Garimella
    [Show abstract] [Hide abstract]
    ABSTRACT: A new measurement technique is developed for quantitatively mapping the liquid–gas interface profiles of air bubbles in an adiabatic microchannel slug flow environment. Water seeded with 0.5 μm-diameter fluorescent polystyrene particles is pumped through a single acrylic microchannel of 500 μm × 500 μm square cross section. A periodic slug flow is achieved by the controlled injection of air into the channel. Particles are constrained to the liquid phase, and their distribution in the flow is visualized through an optical microscope in an epifluorescent configuration with pulsed laser illumination to resolve the instantaneous liquid–gas interface profile to within ±2.8 μm in the focal plane.
    International Journal of Heat and Mass Transfer 07/2015; 86. DOI:10.1016/j.ijheatmasstransfer.2015.02.067 · 2.52 Impact Factor
  • Journal of Solar Energy Engineering 06/2015; 137(3):031012. DOI:10.1115/1.4029453 · 1.13 Impact Factor
  • Xuemei Chen, Justin A. Weibel, Suresh V. Garimella
    Advanced Materials Interfaces 02/2015; 2(3). DOI:10.1002/admi.201400480
  • Suchismita Sarangi, Justin A. Weibel, Suresh V. Garimella
    [Show abstract] [Hide abstract]
    ABSTRACT: The enhancement of pool boiling heat transfer by copper-particle surface coatings is experimentally investigated, using the wetting dielectric fluid FC-72. In one technique, loose copper particles are placed on a heated copper surface to provide additional vapor nucleation sites in the cavities formed at particle-surface and particle–particle contact points, thereby enhancing boiling performance over a polished surface. This ‘free-particle’ technique is benchmarked against the more traditional technique of sintering a fixed layer of copper particles to the surface to enhance boiling heat transfer performance. The effect of particle size on the heat transfer performance is studied for particle diameters ranging from 45 μm to 1000 μm at a constant coating layer thickness-to-particle diameter ratio of approximately 4. The parametric trends in the boiling curve and the critical heat flux are compared between the two techniques, and the dominant boiling mechanisms influencing these trends are compared and contrasted. High-speed visualizations are performed to qualitatively assess the boiling patterns and bubble departure size/distribution, and thus corroborate the trends observed in the boiling curves. The measured wall superheat is significantly lower with a sintered coating compared to the free-particle layer for any given particle size and heat flux. Performance trends with respect to particle size, however, are remarkably similar for both enhancement techniques, and an optimum particle size of ∼100 μm is identified for both free particles and sintered coatings. The free-particle technique is shown to offer a straightforward method to screen the boiling enhancement trends expected from different particulate layer compositions that are intended to be subsequently fabricated by sintering.
    International Journal of Heat and Mass Transfer 02/2015; 81. DOI:10.1016/j.ijheatmasstransfer.2014.09.052 · 2.52 Impact Factor
  • S H Taylor, S V Garimella
    [Show abstract] [Hide abstract]
    ABSTRACT: A sensor concept is developed and analyzed for in situ characterization of a thin dielectric layer. An array of long, planar electrodes is flush-mounted into opposing faces of two substrates on either side of the dielectric layer. The substrates are oriented such that the lengthwise dimensions of the opposing electrodes are orthogonal. Capacitance is measured between single electrode pairs on opposite substrates while all other electrodes are grounded. The electric field between the active electrodes is sharply focused at their crossing point, resulting in high sensitivity to void content in a square detection zone of the dielectric layer. For a fixed interfacial gap size, direct proportionality of the capacitance with void fraction within the detection zone is poor for high electrode-to-electrode spacing on the substrates, but improves dramatically as this spacing is reduced. Three methods of deriving a simulation-based sensitivity response of measured capacitance to any arbitrary two-dimensional void geometry are investigated. The best method requires data from simulations of an empty air gap and a TIM-filled gap, and uses a reduced-order superposition technique to predict the normalized capacitance value obtained for any void geometry to within 10% of that predicted by a high-fidelity direct simulation. The sensing technique is demonstrated using manually introduced voids of 250 µm–2000 µm diameter in a 254 µm thick interface material layer with a dielectric constant of 4.7. The relationship of the capacitance to the void fraction is shown to fall within the predicted bounds.
    Measurement Science and Technology 01/2015; 26(1). DOI:10.1088/0957-0233/26/1/015601 · 1.35 Impact Factor
  • Zhenhai Pan, Justin A. Weibel, Suresh V. Garimella
    Numerical Heat Transfer Applications 12/2014; 67(1). DOI:10.1080/10407782.2014.916109 · 1.85 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We investigate hitherto-unexplored flow characteristics inside a sessile droplet evaporating on heated hydrophobic and superhydrophobic surfaces and propose the use of evaporation-induced flow as a means to promote efficient "on-the-spot" mixing in microliter-sized droplets. Evaporative cooling at the droplet interface establishes a temperature gradient that induces buoyancy-driven convection inside the droplet. An asymmetric single-roll flow pattern is observed on the superhydrophobic substrate, in stark contrast with the axisymmetric toroidal flow pattern that develops on the hydrophobic substrate. The difference in flow patterns is attributed to the larger height-to-diameter aspect ratio of the droplet (of the same volume) on the superhydrophobic substrate, which dictates a single asymmetric vortex as the stable buoyancy-induced convection mode. A scaling analysis relates the observed velocities inside the droplet to the Rayleigh number. On account of the difference in flow patterns, Rayleigh numbers, and the reduced solid-liquid contact area, the flow velocity is an order of magnitude higher in droplets evaporating on a superhydrophobic substrate as compared to hydrophobic substrates. Flow velocities in all cases are shown to increase with substrate temperature and droplet size: The characteristic time required for mixing of a dye in an evaporating sessile droplet is reduced by ∼8 times on a superhydrophobic surface when the substrate temperature is increased from 40 to 60 °C. The mixing rate is ∼15 times faster on the superhydrophobic substrate compared to the hydrophobic surface maintained at the same temperature of 60 °C.
  • Matthew J. Rau, Ercan M. Dede, Suresh V. Garimella
    [Show abstract] [Hide abstract]
    ABSTRACT: Local single- and two-phase heat transfer distributions are measured under a confined impinging jet issuing from a cross-shaped orifice. Spatially resolved temperature maps and convection coefficients resulting from the impinging flow are obtained via infrared imaging of a thin-foil heat source. The cooling patterns in single- and two-phase operation are explained by an accompanying numerical investigation of the fluid flow issuing from the orifice; computed velocity magnitudes and turbulence intensities are presented. In single-phase operation, the coolest surface temperatures correspond to areas with high liquid velocities. High velocities and developing turbulence are also shown to increase convective heat transfer along the diagonal outflow directions from the impinging jet. During two-phase transport, boiling preferentially begins in regions of low velocity, providing enhanced heat transfer in the areas least affected by the impingement. The cross-shaped orifice achieves local heat transfer coefficients that exceed the stagnation-point value of a circular jet of equivalent open orifice area by up to 1.5 times, while resulting in an increased pressure drop only 1.1 times higher than that of the circular jet.
    International Journal of Heat and Mass Transfer 12/2014; 79:432–436. DOI:10.1016/j.ijheatmasstransfer.2014.08.012 · 2.52 Impact Factor
  • Matthew J. Rau, Suresh V. Garimella
    [Show abstract] [Hide abstract]
    ABSTRACT: Confined jet impingement with boiling offers unique and attractive performance characteristics for thermal management of high heat flux components. Two-phase operation of jet impingement has been shown to provide high heat transfer coefficients while maintaining a uniform temperature over a target surface. This can be achieved with minimal increases in pumping power compared to single-phase operation. To investigate further enhancements in heat transfer coefficients and increases in the maximum heat flux supported by two-phase jet impingement, an experimental study of surface enhancements is performed using the dielectric working fluid HFE-7100. The performance of a single, 3.75 mm-diameter jet orifice is compared across four distinct copper target surfaces of varying enhancement scales: a baseline smooth flat surface, a flat surface coated with a microporous layer, a surface with macroscale area enhancement ( extended square pin fins), and a hybrid surface on which the pin fins are coated with the microporous layer. The heat transfer performance of each surface is compared in single-and two-phase operation at three volumetric flow rates ( 450 ml/min, 900 ml/min, and 1800 ml/min); area-averaged heat transfer parameters and pressure drop are reported. The mechanisms resulting in enhanced performance for the different surfaces are identified, with a special focus on the coated pin fins. This hybrid surface showed the best enhancement of all those tested, and resulted in an extension of critical heat flux (CHF) by a maximum of 2.42 times compared to the smooth flat surface at the lowest flow rate investigated; no increase in the overall pressure drop was measured.
    Journal of Heat Transfer 10/2014; 136(10):101503. DOI:10.1115/1.4027942 · 2.06 Impact Factor
  • Stephen H Taylor, Suresh V Garimella
    [Show abstract] [Hide abstract]
    ABSTRACT: A near-field focusing capacitance sensor consists of an array of long, coplanar electrodes offset by a small interface gap from an identical orthogonal array of electrodes. The sensor may be used to characterize permittivity inhomogeneities in thin dielectric layers. The sensor capacitance measurements represent a tessellated matrix of integral-averaged values describing void content in a series of zones corresponding to the electrode crossing points (junctions) of the sensor. The sensor does not lend itself to computed tomography because the individual capacitance measurements do not represent overlapping regions of sensitivity. An evolving level-set algorithm is proposed to reconstruct a binary permittivity distribution. A mathematical construct, based on the physics of inverse-square fields, is used to approximately reconstruct shape features too small to be captured by the raw measurements. The method accommodates the non-uniform area-sensitivity of the junction capacitance measurement. Effective use of the algorithm requires active management of the convergence criterion and evolution rate. The algorithm is demonstrated on a series of phantoms as well as measurements of a voided dielectric thermal interface material using a near-field focusing sensor.
    Measurement Science and Technology 08/2014; 25(10):105602. DOI:10.1088/0957-0233/25/10/105602 · 1.35 Impact Factor
  • Zhenhai Pan, Justin A Weibel, Suresh V Garimella
    [Show abstract] [Hide abstract]
    ABSTRACT: Prediction and manipulation of the evaporation of small droplets is a fundamental problem with importance in a variety of microfluidic, microfabrication, and biomedical applications. A vapor-diffusion-based model has been widely employed to predict the interfacial evaporation rate; however, its scope of applicability is limited due to incorporation of a number of simplifying assumptions of the physical behavior. Two key transport mechanisms besides vapor diffusion-evaporative cooling and natural convection in the surrounding gas-are investigated here as a function of the substrate wettability using an augmented droplet evaporation model. Three regimes are distinguished by the instantaneous contact angle (CA). In Regime I (CA ≲ 60°), the flat droplet shape results in a small thermal resistance between the liquid-vapor interface and substrate, which mitigates the effect of evaporative cooling; upward gas-phase natural convection enhances evaporation. In Regime II (60 ≲ CA ≲ 90°), evaporative cooling at the interface suppresses evaporation with increasing contact angle and counterbalances the gas-phase convection enhancement. Because effects of the evaporative cooling and gas-phase convection mechanisms largely neutralize each other, the vapor-diffusion-based model can predict the overall evaporation rates in this regime. In Regime III (CA ≳ 90°), evaporative cooling suppresses the evaporation rate significantly and reverses entirely the direction of natural convection induced by vapor concentration gradients in the gas phase. Delineation of these counteracting mechanisms reconciles previous debate (founded on single-surface experiments or models that consider only a subset of the governing transport mechanisms) regarding the applicability of the classic vapor-diffusion model. The vapor diffusion-based model cannot predict the local evaporation flux along the interface for high contact angle (CA ≥ 90°) when evaporative cooling is strong and the temperature gradient along the interface determines the peak local evaporation flux.
    Langmuir 08/2014; 30(32). DOI:10.1021/la501931x · 4.38 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: A non-intrusive electrical impedance-based sensor is developed for measurement of local void fraction in air–water adiabatic flow through rectangular microchannels. Measurement of the void fraction in microchannels is essential for the formulation of two-phase flow heat transfer and pressure drop correlations, and may enable real-time flow regime control and performance prediction in the thermal regulation of high-heat-flux devices. The impedance response of the sensor to a range of flow regimes is investigated for a configuration with two aligned electrodes flush-mounted on opposing microchannel walls. Numerical simulations performed on a multi-phase domain constructed from three-dimensional reconstruction of experimentally observed phase boundaries along with the corresponding experimental results serve to establish the relationship between void fraction and dimensionless impedance for this geometric configuration. A reduced-order analytical model developed based on an assumption of stratified gas–liquid flow allows ready extension of these calibration results to different working fluids of interest.
    Measurement Science and Technology 07/2014; 25(9):095301. DOI:10.1088/0957-0233/25/9/095301 · 1.35 Impact Factor
  • Karthik K. Bodla, Suresh V. Garimella
    Journal of Heat Transfer 07/2014; 136(7):072601. DOI:10.1115/1.4026969 · 2.06 Impact Factor
  • Karthik K. Bodla, Suresh V. Garimella, Jayathi Y. Murthy
    [Show abstract] [Hide abstract]
    ABSTRACT: Characterization and design of fluid–thermal transport through random porous sintered beds is critical for improving the performance of two-phase heat transport devices such as heat pipes. Two-dimensional imaging techniques are quite well developed and commonly employed for microstructure and material characterization. In this study, we employ 2D image data (thin sections) for measuring critical microstructural features of commercial wicks for use in correlation-based prediction of transport properties. We employ a stochastic characterization methodology based on the two-point autocorrelation function, and compare the predicted properties such as particle and pore diameters and permeability with those from our previously published studies, in which 3D X-ray microtomography data was employed for reconstruction. Further, we implement a reconstruction technique for reconstructing a three-dimensional stochastic equivalent structure from the thin sections. These reconstructed domains are employed for predicting effective thermal conductivity, permeability and interfacial heat transfer coefficient in single-phase flow. The current computations are found to compare well with models and correlations from the literature, as well as our previous numerical studies. Finally, we propose a new parametrized model for the design of porous materials based on the nature of the two-point autocorrelation functions. Using this model, we reconstruct sample three-dimensional microstructures, and analyze the influence of various parameters on fluid–thermal properties of interest. With advances in additive manufacturing techniques, such an approach may eventually be employed to design intricate porous structures with properties tailored to specific applications.
    International Journal of Heat and Mass Transfer 06/2014; 73:250–264. DOI:10.1016/j.ijheatmasstransfer.2014.02.006 · 2.52 Impact Factor
  • Ravi S. Patel, Suresh V. Garimella
    [Show abstract] [Hide abstract]
    ABSTRACT: A diagnostic technique capable of characterizing interfaces between transparent, immiscible fluids is developed and demonstrated by investigating the morphology of liquid-gas interfaces in an adiabatic two-phase flow through a microchannel of 500 μm × 500 μm square cross section. Water seeded with 0.5 μm-diameter fluorescent polystyrene particles is pumped through the channel, and the desired adiabatic two-phase flow regime is achieved through controlled air injection. The diagnostic technique relies on obtaining particle position data through epifluorescent imaging of the flow at excitation and emission wavelengths of 532 nm and 620 nm, respectively. The particle position data are then used to resolve interface locations to within ±1 μm in the focal plane. By mapping the interface within individual focal planes at various depths within the channel, it is possible to determine the complete liquid-gas interface geometry across the channel cross section in a dynamic flow environment. Utilizing this approach, the liquid-gas phase boundaries of annular flows within a microchannel have been successfully characterized.
    International Journal of Multiphase Flow 06/2014; 62. DOI:10.1115/IPACK2013-73057 · 1.94 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Prediction and active control of the spatial distribution of particulate deposits obtained from sessile droplet evaporation are vital in printing, nanostructure assembly, biotechnology, and other applications that require localized deposits. This Letter presents surface wettability-based localization of evaporation-driven particulate deposition and the effect of superhydrophobic surface morphology on the distribution of deposits. Sessile water droplets containing suspended latex particles are evaporated on non-wetting textured surfaces with varying microstructure geometry at ambient conditions. The droplets are visualized throughout the evaporation process to track the temporal evolution of contact radius and apparent contact angle. The resulting particle deposits on the substrates are quantitatively characterized. The experimental results show that superhydrophobic surfaces suppress contact-line deposition during droplet evaporation, thereby providing an effective means of localizing the deposition of suspended particles. A correlation between deposit size and surface morphology, explained in terms of the interface pressure balance at the transition between wetting states, reveals an optimum surface morphology for minimizing the deposit coverage area.
    Applied Physics Letters 05/2014; 104(20):201604-201604-5. DOI:10.1063/1.4878322 · 3.52 Impact Factor
  • Susan N. Ritchey, Justin A. Weibel, Suresh V. Garimella
    [Show abstract] [Hide abstract]
    ABSTRACT: As electronics packages become increasingly thinner and more compact due to size, weight, and performance demands, the use of large intermediate heat spreaders to mitigate heat generation non-uniformities are no longer a viable option. Instead, non-uniform heat flux profiles produced from chip-scale variations or from multiple discrete devices are experienced directly by the ultimate heat sink. In order to address these thermal packaging trends, a better understanding of the impacts of non-uniform heating on two-phase flow characteristics and thermal performance limits for microchannel heat sinks is needed. An experimental investigation is performed to explore flow boiling phenomena in a microchannel heat sink with hotspots, as well as non-uniform streamwise and transverse peak-heating conditions spanning across the entire heat sink area. The investigation is conducted using a silicon microchannel heat sink with a 5 × 5 array of individually controllable heaters attached to a 12.7 mm × 12.7 mm square base. The channels are 240 μm wide, 370 μm deep, and separated by 110 μm wide fins. The working fluid is the dielectric fluorinert liquid FC-77, flowing at a mass flux of approximately 890 kg/m2 s. High-speed visualizations of the flow are recorded to observe the local flow regimes. Despite the substrate beneath the microchannels being very thin (200 μm), significant lateral conduction occurs and must be accounted for in the calculation of the local heat flux imposed. For non-uniform heat input profiles, with peak heat fluxes along the streamwise and transverse directions, it is found that the local flow regimes, heat transfer coefficients, and wall temperatures deviate significantly from a uniformly heated case. These trends are assessed as a function of an increase in the relative magnitude of the nonuniformity between the peak and background heat fluxes.
    International Journal of Heat and Mass Transfer 04/2014; 71:206–216. DOI:10.1016/j.ijheatmasstransfer.2013.12.012 · 2.52 Impact Factor
  • Susmita Dash, Suresh V Garimella
    [Show abstract] [Hide abstract]
    ABSTRACT: The evaporation characteristics of sessile water droplets on smooth hydrophobic and structured superhydrophobic heated surfaces are experimentally investigated. Droplets placed on the hierarchical superhydrophobic surface subtend a very high contact angle (∼160°) and demonstrate low roll-off angle (∼1°), while the hydrophobic substrate supports corresponding values of 120° and ∼10°. The substrates are heated to different constant temperatures in the range of 40-60 °C, which causes the droplet to evaporate much faster than in the case of natural evaporation without heating. The geometric parameters of the droplet, such as contact angle, contact radius, and volume evolution over time, are experimentally tracked. The droplets are observed to evaporate primarily in a constant-contact-angle mode where the contact line slides along the surface. The measurements are compared with predictions from a model based on diffusion of vapor into the ambient that assumes isothermal conditions. This vapor-diffusion-only model captures the qualitative evaporation characteristics on both test substrates, but reasonable quantitative agreement is achieved only for the hydrophobic surface. The superhydrophobic surface demonstrates significant deviation between the measured evaporation rate and that obtained using the vapor-diffusion-only model, with the difference being amplified as the substrate temperature is increased. A simple model considering thermal diffusion through the droplet is used to highlight the important role of evaporative cooling at the droplet interface in determining the droplet evaporation characteristics on superhydrophobic surfaces.
    Physical Review E 04/2014; 89(4-1):042402. · 2.31 Impact Factor
  • Tae Young Kim, Suresh V. Garimella
    [Show abstract] [Hide abstract]
    ABSTRACT: Enhancement of pool boiling heat transfer in water by means of the introduction of free particles on the heated surface is investigated. The layer of loose particles on the heated surface is free to move and deform under the action of bulk liquid convection and vapor nucleation. High-speed visualizations show that bubble nucleation preferentially occurs at the narrow corner cavities formed between the free particles and the heated surface. The effects of the number and size of the free particles are experimentally explored using copper particles over a wide size range from tens of nanometers to 13 mm. Experimental results show that a mixture of free particle diameters of 3 mm and 6 mm provides the greatest improvement in boiling heat transfer, resulting in an average increase in heat transfer coefficient of 115% relative to a baseline polished surface without particles. A numerical heat transfer simulation and an analytical force balance model are developed to predict nucleation incipience and explain the parametric trends in boiling performance observed in the presence of the free particles.
    International Journal of Heat and Mass Transfer 04/2014; 71:818-828. DOI:10.1016/j.ijheatmasstransfer.2013.12.071 · 2.52 Impact Factor
  • Susmita Dash, Suresh V. Garimella
    [Show abstract] [Hide abstract]
    ABSTRACT: The evaporation characteristics of sessile water droplets on smooth hydrophobic and structured superhydrophobic heated surfaces are experimentally investigated. Droplets placed on the hierarchical superhydrophobic surface subtend a very high contact angle (̃160°) and demonstrate low roll-off angle (̃1°), while the hydrophobic substrate supports corresponding values of 120° and ̃10°. The substrates are heated to different constant temperatures in the range of 40-60 °C, which causes the droplet to evaporate much faster than in the case of natural evaporation without heating. The geometric parameters of the droplet, such as contact angle, contact radius, and volume evolution over time, are experimentally tracked. The droplets are observed to evaporate primarily in a constant-contact-angle mode where the contact line slides along the surface. The measurements are compared with predictions from a model based on diffusion of vapor into the ambient that assumes isothermal conditions. This vapor-diffusion-only model captures the qualitative evaporation characteristics on both test substrates, but reasonable quantitative agreement is achieved only for the hydrophobic surface. The superhydrophobic surface demonstrates significant deviation between the measured evaporation rate and that obtained using the vapor-diffusion-only model, with the difference being amplified as the substrate temperature is increased. A simple model considering thermal diffusion through the droplet is used to highlight the important role of evaporative cooling at the droplet interface in determining the droplet evaporation characteristics on superhydrophobic surfaces.
    Physical Review E 03/2014; 89(4). DOI:10.1103/PhysRevE.89.042402 · 2.33 Impact Factor

Publication Stats

6k Citations
499.62 Total Impact Points

Institutions

  • 2000–2015
    • Purdue University
      • • School of Mechanical Engineering
      • • Cooling Technologies Research Center (CTRC)
      ウェストラファイエット, Indiana, United States
  • 2010
    • Sony Corporation
      Edo, Tōkyō, Japan
    • Tsinghua University
      Peping, Beijing, China
  • 2008
    • University of Houston
      • Department of Mechanical Engineering
      Houston, TX, United States
  • 2003
    • Technische Universität Dresden
      Dresden, Saxony, Germany
    • Georgia Institute of Technology
      Atlanta, Georgia, United States
  • 1993–2001
    • University of Wisconsin - Milwaukee
      • Department of Mechanical Engineering
      Milwaukee, Wisconsin, United States