

June 5, 2023 at 7:05 amFAQParticipant
Section 8.5.3.2 of the CFX Modeling Guide, entitled “Particle Shape Factors”, explains the significance of the Cross Sectional and Surface Area Factors. The Guide mentions that CFX assumes all particles to be spherical by default, and continues this assumption while calculating a particle’s diameter from dividing its mass by its density. The Cross Sectional Area Factor may be included to modify the assumed spherical crosssectional area if the particles are actually nonspherical. This factor is multiplied by the calculated crosssectional area when assuming spherical particles, and affects the calculated drag force. To elaborate, let a cuboid particle’s dimensions be length (L) x width (W) x depth (D), where L>W>D. Then, let the following definitions be: •Crosssectional area, A = W*D •Volume, V = L*W*D •Equivalent spherical radius, Rv = (3/4*V/pi)^(1/3) •Cross Sectional Area Factor, CSAF = A/(pi*Rv^2) CSAF is then multiplied by the crosssectional area of the spherical particle equivalent of the cuboid particle. The Surface Area Factor (SAF) is analogous to the CSAF in that it adjusts the assumed spherical particle shape to enable nonspherical particles. However, this factor is defined as the ratio of the surface area of the nonspherical particle to the surface area of the spherical particle with the equivalent diameter (nonspherical divided by spherical). The SAF affects mass and heat transfer correlations and thus must be figured out based on the surface geometry of the nonspherical particle compared to the surface of a spherical particle of equivalent mass.

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