ArchiveSpace Name Record
Publication Search Results
Now showing 1 - 6 of 6
ItemExperimental characterization of extreme temperature granular flows for solar thermal energy transport and storage - supplementary data(Georgia Institute of Technology, 2022) Bagepallii, Malavika V. ; Jeong, Shin Young ; Brooks, Joshua ; Zhang, Zhuomin ; Ranjan, Devesh ; Loutzenhiser, Peter G.High-temperature, dense granular flows along an inclined plane were considered for solar thermal energy transport and storage with sintered bauxite particles. A series of experiments was performed for particle inlet temperatures of ~ 200, 400, 600, and 800 °C to understand the mechanisms of granular flows at extreme temperatures. Mass flow rates were measured using a load cell and free-surface velocities were measured and computed using particle image velocimetry. Surface temperatures were measured using infrared cameras. A significant decrease in steady-state particle mass flow rate was observed with increasing temperature due to changing flow properties. A decrease in bulk particle free-surface velocities was observed at higher temperatures. Free-surface velocity measurement error between experiments were within 20% of the average. The particle surface temperatures decreased from inlet to outlet with larger gradients at higher temperatures observed due to increasing convection and radiative heat losses. A decrease in temperature was observed along the side walls due to a decrease in particle velocities.
ItemGeorgia Tech | Gen3 CSP Mechanical and Radiative Property Database(Georgia Institute of Technology, 2022) Loutzenhiser, Peter G. ; Ranjan, Devesh ; Zhang, Zhuomin ; Schrader, Andrew J. ; Pathikonda, Gokul ; Brooks, Joshua ; Bagepali, Malavika ; Chuyang, Chen ; Jeong, Shin Young ; Yarrington, Justin D.The focus of this work is to systematically characterize the heat transfer and flow properties for particulate (granular) flows at elevated temperatures up to 800 °C. This work is intended to address a serious gap within the field related to the understanding and modeling of particulate flow behavior and the related heat transfer at different temperatures, which directly correspond to the operating points of concentrated solar power applications that use particles for heat storage. These objectives will be accomplished using a combination of fundamental experimental measurements, modeling, and simplified flow experimentations over a range of temperatures. Ceramic sintered bauxite proppants will be used as a baseline for comparison with a range of other particles used for various applications. These results will be made available during the project to the research community to provide updated guidance and inputs to current modeling efforts to improve their results.
ItemHigh-Temperature Granular Flow Experiments and Analysis along a Stair Geometry for Solar Particle Receiver Applications Dataset(Georgia Institute of Technology, 2022) Bagepallii, Malavika V. ; Jeong, Shin Young ; Brooks, Joshua ; Zhang, Zhuomin ; Ranjan, Devesh ; Loutzenhiser, Peter G.High-temperature, dense granular flows along a stair geometry were considered for application in concentrated solar receivers. A series of experiments was performed using sintered bauxite particles with inlet temperatures of ~600°C and ~800 °C. Mass flow rates were measured using a load cell. Changes in particle arial fraction was determined using high speed images and free-surface velocities were measured and computed using particle image velocimetry. Particle temperatures were measured using infrared cameras. Mass flow rate was steady during the experiment and did not change with temperature. Areal fraction decreased along the curtain flow direction due to increase in particle velocities. Particle velocities at curtain regions were in good agreement with theory. Average temperature decreased along the flow directions and were repeatable between experiments, with error within 1% deviation from the mean computed using a 95% confidence interval. Particle bed velocities at the stair geometry decreased with depth of layers due to shear forces from stagnant layers. The temperature of particle layers correlated well with velocities wherein inner, slow-moving layers were at lower temperatures compared to upper, fast-moving layers.
ItemNumerical Analyses of High Temperature Dense, Granular Flows Coupled to High Temperature Flow Property Measurements for Solar Thermal Energy Storage Dataset(Georgia Institute of Technology, 2020-09-24) Yarrington, Justin D. ; Bagepalli, Malavika V. ; Pathikonda, Gokul ; Schrader, Andrew J. ; Zhang, Zhuomin ; Ranjan, Devesh ; Loutzenhiser, Peter G.High temperature particle flow properties necessary to predict granular flow behavior for solar thermal energy storage applications were measured and calculated for Carbobead CP 30/60 up to 800 °C. The measured properties included elastic and shear moduli, particle-particle coefficients of static sliding and rolling friction, and particle-particle coefficients of restitution. Poisson’s ratio was calculated with elastic and shear moduli. The flow properties were used as inputs for a numerical model using the discrete element method to examine granular flows along an inclined plane at high temperature. The flow behavior was strongly influenced by the coefficients of static friction, which impacted the particle residence time, shear effects from the side walls, and particle flow mass flux. An 8.7%, 15.6%, and 8.5% increase and 37.9% decrease in steady state mass flow rate was observed for 200 °C, 400 °C, 600 °C, and 800 °C, respectively, when compared to room temperature simulations. A 52%, 59%, and 33% decrease in the time to reach steady state was observed for 200 °C, 400 °C, and 600 °C, respectively, while a 53% increase in time was observed for 800 °C. A significant delay in the flow development at 800 °C was observed due to significantly higher frictional forces.
ItemMeasurement of Flow Properties Coupled to Experimental and Numerical Analyses of Dense, Granular Flows for Solar Thermal Energy Storage Dataset(Georgia Institute of Technology, 2020-06-02) Bagepalli, Malavika V. ; Yarrington, Justin D. ; Schrader, Andrew J. ; Zhang, Zhuomin ; Ranjan, Devesh ; Loutzenhiser, Peter G.Granular flows of sintered bauxite proppants were examined along an inclined plane for solar thermal energy storage applications. Granular flow properties needed to drive numeric granular models were measured for improved numerical model predictions for Carbobead CP 50/140, 40/100, and 30/60 particles. Particle shape and size distributions were determined by coupling optical microscopy to an in-house image processing algorithm. The impulse excitation technique was used to measure elastic and shear moduli, and compute Poisson’s ratio. The coefficient of static sliding friction was measured using the slip-stick method, and the static rolling friction was determined from measured shear on particles positioned between two hot-pressed plates. The coefficient of restitution was measured by dropping particles on a surface and determining the kinetic energy before and after impact with the surface using high resolution particle tracking velocimetry. Particle size did not significantly impact the coefficients of restitution and static rolling friction, however, particle shape distribution resulted in a large variation in measurements. An inclined flow experiment was performed to characterize granular flows of Carbobead CP 30/60 particles using particle image velocimetry. Numerical models of the experiment using discrete element method were generated with the measured mechanical properties as inputs for comparison with experimental results. A constant directional torque rolling friction model best predicted bulk granular flow behavior. Good agreement between the model and experiment was achieved at ambient, steady state conditions, with average velocity differences <10%. item_description: Raw measured data of granular flow properties of sintered bauxite at room temperature
ItemHighly specular carbon nanotube absorbers(Georgia Institute of Technology, 2010-10) Wang, X. J. ; Wang, L. P. ; Adewuyi, O. S. ; Cola, Baratunde A. ; Zhang, ZhuominSpecular black materials have important applications, such as in absolute cryogenic radiometers, space-borne spectroradiometers, and some energy conversion devices. While vertically aligned carbon nanotubes (VACNT) can have close-to-unity absorptance, so far the reported reflection has been essentially diffuse. This letter describes a highly specular black absorber made of VACNT. Both the bidirectional reflectance distribution function and specular reflectance were measured at the wavelength λ = 635 nm using a laser scatterometer. The ordinary and extraordinary optical constants were obtained by fitting the specular reflectance, calculated from modified reflectance formulae for light incident from air to a uniaxial medium, considering surface roughness. Furthermore, the absorptance at λ = 635 nm was shown to be 0.994±0.002, based on the measured directional-hemispherical reflectance.