Purandare, Abhishek

Vanapalli, S.

Wennemars, Gerjan

English

Heat and mass transport in the case of an evaporating liquid droplet or a sublimating solid is driven by the strong temperature and concentration gradients that appear at the phase-changing interface in a medium with a discontinuous temperature and vapor concentration. Obtaining fundamental data regarding the factors that influence the rates of the transport phenomena is essential for applications such as spray cooling, machining, and food freezing. In this work, we employ the Schlieren imaging technique to visualize the density gradients that arise due to temperature and concentration changes at the interface of a dry ice sphere and the surrounding gas medium, while simultaneously tracking the movement of the sublimating dry ice boundary. A qualitative comparison between experimental results and numerical results predicted using the commercial COMSOL Multiphysics software is presented

University of Twente Research Information

Sublimation of a dry ice sphere in a controlled ambientVisualization of density gradients at the phase-changing interfaceAbhishek Purandare, Gerjan Wennemars, Srinivas VanapalliTemperature and concentration gradient at phase-changing interface a.s.purandare@utwente.nlHeat and mass transport in the case of an evaporating liquid droplet or a sublimating solid is driven by the strong temperature and concentrationgradients that appear at the phase-changing interface in a medium with a discontinuous temperature and vapor concentration. Obtaining fundamentaldata regarding the factors that influence the rates of the transport phenomena is essential for applications such as spray cooling, machining, and foodfreezing. In this work, we employ the Schlieren imaging [1] technique to visualize the density gradients that arise due to temperature and concentrationchanges at the interface of a dry ice sphere and the surrounding gas medium, while simultaneously tracking the movement of the sublimating dry iceboundary. A qualitative comparison between experimental results and numerical results predicted using the commercial COMSOL Multiphysicssoftware is presented.[1] Settles G S,  Schlieren and shadowgraph techniques: Visualizing phenomena in transparent  media, Springer-Verlag GmbH (2001)[2] Schroeder D V An Introduction to Thermal Physics, Addison Wesley (2000)[3] Purandare A, Verbruggen W, and Vanapalli S 2023 Experimental and theoretical investigation of the dry ice sublimation temperature for varying far-field pressure and CO2 concentration Preprint 10.2139/ssrn.4462700Test-section with ambient control [3]Schlieren systemTransient problem of coupled heat,momentum and mass transport from thedry ice surface to the surrounding gasmedium is computed assuming:f3f2Cameraf1 Knife edgeRefracted angle (𝜀)LEDxyzy𝜕𝜌𝜕𝑥As seen by human eyeAs captured by SchlierenAfter image processingzxzxzx5 mm5 mm5 mmN2-CO2 gas inletN2-CO2 gas outlet• Axial symmetry of the problem.• Negligible radiative heat transfer in gasdomain.• Velocity of dry ice surface depends on thelocal mass flux – 𝑗𝑠𝑢𝑏/𝜌𝑠.• Inlet CO2 concentration, Ci is determinedby the ideal gas law.• Saturation concentration at the dry iceinterface is obtained from Clausius-Clapeyron relation[2].• Laminar flow for the given geometry andflow conditions 80 < Re < 150.Dry iceDry iceDry ice0.20.150.100.0505 mm0.180.140.100.060.025 mm• Model results and Schlieren images reveal alike density gradients around the dry ice sphere featuring distinct side gradients and elongated bottomgradient.• Model's qualitative alignment with experiments is evident; however, further investigation, especially in quantifying Schlieren image density gradients,is necessary.• Gas velocity accelerates and intensifiessublimation near sphere's lower part.• Gradually adopting elliptical shape over time.• Bright region in Schlieren image ~ Large refractive index gradient.• Refractive index gradient ~ Density gradient due to temperature and concentration variations.•∆𝐼𝐼~𝜕𝜌𝜕𝑥~𝜕𝑇𝜕𝑥and/or𝜕𝐶𝜕𝑥5 mm5 mmt ~ 1000 st ~ 0 sCi ~ 100% vol5 mmDensity gradientLight intensity gradientModel Schlieren Imagex1x1x2 x2Dry iceCi ~ 0% volLight intensity gradient and density gradient along x1 - x2Exp. t ~ 200 sExp. t ~ 400 sModel t = 400 sModel t = 200 s0 5 10 15-800-600-400-200-0605040302010070Distance x1-x2 (mm)∆𝐼/𝐼(A.U.)𝜕𝜌𝜕𝑥(kg/m4)• Desired initial condition: Flush (1 liter/min) test-section with N2-CO2 gasmixture.• Dry ice sphere (~ 3.5 g) is introduced in the test-section.• Schlieren images captured for varying inlet CO2 concentrations –0:20:100 Vol %.• Pressure is maintained constant at ~ 1.01 bar.Applied Thermal Sciences, University of Twente, The NetherlandsDry iceDry iceSchlieren SystemPhenomenological ModelConclusion and OutlookCO2 concentration and density gradientDry ice morphologyCO2Concentration Light intensityDry ice5 mm

Sublimation of a dry ice sphere in a controlled ambient:: Visualization of density gradients at the phase-changing interface

https://ris.utwente.nl/ws/files/329942999/Poster_IHTC_final.pdf

Sublimation of a dry ice sphere in a controlled ambient:: Visualization of density gradients at the phase-changing interface

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