جستجوی مقالات مرتبط با کلیدواژه « drag coefficient » در نشریات گروه « شیمی »

Semi-circular cylinders provide better space economy than circular and other non-circular cylinders. The cylinders are frequently used in a tandem arrangement in heat transfer equipment. The present study aims to obtain the flow and heat transfer characteristics for the tandem arrangement of semi-circular cylinders. The cylinders are placed in a vertical channel with a blockage (β) of 0.2. The upward flow under the reverse gravity is considered here. The influence of various parameters such as Reynolds number (Re), Prandtl number (Pr), Richardson number (Ri), and spacing between cylinders (YC) is observed. The governing parameters are varied in a range of 1 ≤ YC ≤ 6, 1 ≤ Re ≤ 50, 0.7 ≤ Pr ≤ 50, and 0 ≤ Ri ≤ 2. The numerical results are obtained by solving governing equations using FVM (Finite volume method). The velocity field, thermal field, drag coefficient (CD), pressure coefficient (Cp), and average Nusselt number (Nuavg) are presented. The increase in Re and Pr has enhanced the Nuavg and CD, whereas Ri and YC have shown complex dependency. The obtained results show that the mutual interaction of upstream and downstream cylinders has vanished for YC > 4. The upstream and downstream cylinders have shown different behavior at identical operating conditions. The drag coefficient for the upstream cylinder varies with YC for 1 ≤ Re ≤ 10, whereas for 10 ≤ Re ≤ 50, it shows negligible change except for the case of Pr = 0.7 and Ri = 2. The drag on the downstream cylinder increases monotonically with an increase in YC. The average Nusselt number for both cylinders increased with an increase in YC except for the downstream cylinder at Re = 1 and Pr = 0.7. Overall, the complex interplay of governing parameters has been observed in the flow and thermal characteristics.

The motion of a single droplet rising in quiescent yield stress fluids was investigated experimentally. By using a high-speed camera to follow the rising droplet, the images of the recorded frames were digitized and analyzed using MATLAB, and the aspect ratio and terminal velocity of the droplets were obtained. The results show that the droplet aspect ratio decreases with the increase of dimensionless numbers such as Eötvös number and Tadaki number, and the droplet gradually changes from spherical to ellipsoidal. The larger the yield stress, the larger the Bingham number, which limits the lateral stretching of the droplet, and the droplet shows a spherical shape. The experimental drag coefficient and aspect ratio were compared with correlations in literature, and the comparison showed that these correlations do not give fully satisfactory results in predicting the drag coefficient and aspect ratio of droplet rising in yield stress fluid, showing a big relative error. Therefore, two new empirical correlations were proposed to predict the aspect ratio and the drag coefficient, respectively. It was found that the calculated results by the present correlation agree well with the experimental data.

The performance of surfactants especially in two-phase systems, depends on their type, Hydrophile-Lipophile Balance (HLB) number, concentration, and whether the surfactant is ionic or non-ionic. The current work was conducted to study the effect of the presence of Cetyltrimethylammonium Bromide (CTAB), a cationic surfactant, in air-water systems. Thus, the behavior of a single air bubble rising in aqueous CTAB solutions was studied experimentally. The independent test variables are solution concentration (0.4-1.6mM) and bubble diameter (3.5-4.6mm). The effect of these variables on rising velocity, bubble shape, and drag coefficient has been studied. Due to the importance of the drag coefficient in two-phase fluid, the effect of Reynolds number, Eötvös number, and aspect ratio on it has also been evaluated. Experiments have been performed at high Reynolds numbers (850<Re<1000), which are obtained by increasing the surfactant concentration. The results showed that the selected ionic surfactant had a more tangible effect on bubble behavior than nonionic surfactants. Moreover, there is no noticeable difference in the behavior of the bubble rising at concentrations above and below of Critical Micelle Concentration (CMC) of CTAB, which can be attributed to its high aggregation number compared to other surfactants.

Drag coefficient independent on bubble diameter is required to ease design sieve trays or bubble column, through simulation of computational fluid dynamic. In this paper, the drag coefficients, independent or dependent on the diameter, are reviewed for gas-liquid system. A number of drag coefficients are used for Computational Fluid Dynamics (CFD). Different forces are entered to the liquid-bubble separation surface in diverse directions. Forces are investigated with mathematical proving for Newtonian fluids and Eulerian coordinate. Finally, the external force as a new force, enter to the drag coefficient equations. Drag coefficient is included force coefficient. Drag force is entered in momentum equations. Drag coefficient is used in two-phase systems which bubbles and liquid are activated as dispersed and continuous phase, respectively. Bubbles and liquid are in contact with each other in separation surface on bubble. Drag force is created slip on separation surface. The drag coefficients are investigated depended on the size and configuration of bubbles. The drag coefficient of Krishna et al is used dependent on bubble diameter. Schiller - Nauman model drag coefficient is estimated with 9% error and dependence on bubble diameter. In this article, the modern drag coefficients are studied independent on the diameter and shape of the bubble. The Drag coefficients are resulted theoretical, mathematical and experimental independent and dependent of diameter bubble. The new Drag coefficient is presented dependent on surface tension and diameter of the tower hole with 6.3 of error approximately.