Browsing by Subject "Naphthalene sublimation"

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    Experimental verification of heat/Mass transfer analogy in turbulent separated flow behind a backward facing step.
    (2010-12) Mittal, Rajat
    Heat and mass transfer from a surface to a stream of fluid are governed by Fourier’s law and Fick’s law respectively. These are mathematical manifestations of the process of diffusion. In the realm of transport processes, the mathematical equations describing the two phenomena can become analogous under certain assumptions and boundary conditions. From an engineering perspective, it is difficult to measure heat transfer coefficients in separated flows because of high spatial thermal gradients and the intrusive nature of the various techniques. The analogous mass transfer measurement using the naphthalene sublimation technique, on the other hand, overcomes these challenges and presents significant advantages of speed, economy, better resolution and accuracy over its thermal counter-part. However, the diffusion rates of napthalene and heat into a stream of air are different. So, the physical and mathematical similarity between the two processes can be utlized effectively only when the analogy factor (F=Nu/Sh) is determined. This study investigates the heat/mass transfer analogy in a turbulent separated flow behind a backward facing step. The heat (Nu) and mass (Sh) transfer measurements were made using the thermal boundary layer technique and the naphthalene sublimation technique respectively under identical flow conditions. Analogous boundary conditions of constant temperature and constant concentration were imposed on the active surface in the study which is the recirculation-reattachment region behind the backward facing step.
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    Local Variation of Heat and Mass Transfer for Flow Over a Cavity and on a Flat Plate
    (2017-09) Taliaferro, Matthew
    Boundary layer theory for flat plates is fundamental to our understanding of fluid flow and heat transfer. However, most of the experimental and analytical work for thermal boundary layers focus on streamwise effects. Lateral changes of heat and mass transfer near a lateral singularity in the surface boundary conditions have not been as extensively studied. Lateral heat transfer is studied using OpenFOAM to run numerical simulations for heated strips of varying width, fluids with varying thermal properties, separation lengths, and unheated starting lengths. Turbulent mass transfer is studied using the naphthalene sublimation technique for heated strips of varying depths, widths, and freestream velocities. The lateral edge effect is found to scale with the conduction thickness for both turbulent and laminar boundary layer flows. For laminar boundary layer flow the lateral edge effect extends approximately three conduction thicknesses into the flow, while for turbulent boundary layer flow it extends approximately ten conduction thicknesses into the flow. The results are useful for modeling heat transfer from discrete electronic components. In addition, the results should serve as useful benchmarks for numerical fluid models and computations where lateral transport is important.