S053013 Determination of Drag Coefficient in Polygonal Plates

On the basis of a parametric model of wind stress (drag) coefficient over water surfaces and related experiments, objective procedures to obtain this coefficient under variable wind and wave conditions are outlined and recommended for oceanographic applications and air-sea interaction studies. Methods for both fully and non-fully developed sea conditions are given.

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Determination of Physical Properties, Moisture Absorption Process and Aerodynamic Properties of Grain and Cluster Straw of Two Wheat Cultivars

Acta Universitatis Agriculturae et Silviculturae Mendelianae Brunensis ◽

10.11118/actaun202068050831 ◽

2020 ◽

Vol 68 (5) ◽

pp. 831-840

Author(s):

Mohammad Jafari ◽

Gholam Reza Chegini ◽

Javad Khazaei

Keyword(s):

Physical Properties ◽

Drag Coefficient ◽

Moisture Absorption ◽

Mass Density ◽

Terminal Velocity ◽

Wheat Cultivars ◽

Projected Area ◽

Drag Forces ◽

Aerodynamic Properties

In this study, physical properties of grain and cluster straw including geometric dimensions, moisture absorption and aerodynamic properties of two wheat cultivars were investigated. The effect of cultivar on width, thickness, geometric diameter, spheroid coefficient and mass density was significant at 1% probability level whilst there were no significant effect on grain projected area, length and weight. Moisture absorption of the grains was rapid during the first 30–40 min and then turned to zero. The terminal velocity of wheat grain and straw in three shapes was measured by calculating the projected area in horizontal, lateral and perpendicular directions and then, the drag coefficient was obtained by the equilibrium of the gravity and drag forces at the terminal velocity. Results also showed that increasing moisture content resulted in an increase in the terminal velocity and a decrease in the drag coefficient. Results obtained in this study can be used in designing wheat- cluster straw separation and processing.

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Determination of a Bubble Drag Coefficient during the Formation of Single Gas Bubble in Upward Coflowing Liquid

Processes ◽

10.3390/pr8080999 ◽

2020 ◽

Vol 8 (8) ◽

pp. 999

Author(s):

Przemysław Luty ◽

Mateusz Prończuk

Keyword(s):

Drag Coefficient ◽

Chemical Engineering ◽

Liquid Velocity ◽

Bubble Diameter ◽

Bubble Formation ◽

Hydraulic Drag ◽

Gas Bubble ◽

Flowing Liquid ◽

Engineering Research

Bubble flow is present in many processes that are the subject of chemical engineering research. Many correlations for determination of the equivalent bubble diameter can be found in the scientific literature. However, there are only few describing the formation of gas bubbles in flowing liquid. Such a phenomenon occurs for instance in airlift apparatuses. Liquid flowing around the gas bubble creates a hydraulic drag force that leads to reduction of the formed bubble diameter. Usually the value of the hydraulic drag coefficient, cD, for bubble formation in the flowing liquid is assumed to be equal to the drag coefficient for bubbles rising in the stagnant liquid, which is far from the reality. Therefore, in this study, to determine the value of the drag coefficient of bubbles forming in flowing liquid, the diameter of the bubbles formed at different liquid velocity was measured using the shadowgraphy method. Using the balance of forces affecting the bubble formed in the coflowing liquid, the hydraulic drag coefficient was determined. The obtained values of the drag coefficient differed significantly from those calculated using the correlation for gas bubble rising in stagnant liquid. The proposed correlation allowed the determination of the diameter of the gas bubble with satisfactory accuracy.

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