Use of three-dimensional computational fluid dynamics model for a new configuration of circular primary settling tank

Appropriately used, CFD models are powerful tools to design and optimize primary settling tanks (PSTs). This paper uses a Fluent-based 3D model to identify the possible causes for underperformance of the circular PSTs at the Cali WWTP, Colombia, and to propose design modifications to improve performance. A new configuration for the center well (CW) is proposed and evaluated. The influence of a rotational sludge scraper and of continuously sludge removal were considered in the numerical simulation. The new configuration included the modification of the current CW diameter and the location of a second baffle with the CW. The results suggest that the installation of the second baffle allows a more uniform flow distribution within the PST and consequently, the hydrodynamic problems associated with short-circuiting of the influent to the bottom of the tank are reduced. The second baffle suppresses the downward current, effectively dissipates the kinetic energy in the influent and forces the particles to move toward the bottom of the PST. In addition, the second CW baffle allows the formation in the inlet zone of a consistently more concentrated sludge blanket layer and thicker sludge, reducing the risk of solids leaving in the effluent of the PST.

Influence of Hydrophobic Fin Configuration in Thermal System in Relation to Electronic Device Cooling Applications

In this study, heat and flow analysis of the cooling system incorporating fins with hydrophilic and hydrophobic wetting surfaces has been considered in relation to electronic cooling applications. Temperature and velocity fields in the solution domain are simulated for various fin numbers and sizes. A temperature parameter is introduced to assess the thermal performance of the system. Fin count is introduced to formulate the number of fins in the solution domain. The Nusselt number and pressure drop between the inlet and exit ports due to different fin configurations of the cooling system for various fin counts are presented. It is found that the temperature parameter attains high values for large sizes and small fin counts, which is more pronounced for low Reynolds numbers. Increasing number of fins results in almost uniform flow distribution among the fin, which is more pronounced for the hydrophobic fin configuration. The Nusselt number attains larger values for the hydrophilic fin configuration than that corresponding to the hydrophobic fin, and it attains a peak value for certain arrangement of fin count, which differs with the Reynolds number. The pressure drop between the inlet and exit ports reduces for hydrophobic fin; hence the slip velocity introduced for hydrophobic fin improves the pressure drop by 6% to 16% depending on the fin counts in the cooling system.

Modeling of flow uniformity by installing inlet distributor within the inflow part of a pressurized module using computational fluid dynamics

Uniform flow distribution is a significant parameter for designing pressurized membrane modules because non-uniform flow distribution can cause serious local flux and fouling problems within a module. Thus, this study investigated the fluid behavior with regards to the evenness of water distribution using newly designed inlet distributors in the inflow part of a pressurized membrane module. From the results of velocity and pressure at the cross-sectional and outlet planes, we confirmed that a conventional membrane module with no distributor (non-distributor) had fluid that was concentrated at the central part. Case 1, which had a cross-shaped distributor, reduced the central concentration tendency, and Case 2, which had a round-shaped distributor, displayed a relatively uniform flow based on the velocity, pressure, flux, and standard deviation data. Here, the non-uniformity coefficient (<i>N</i>) and energy utilization (<i>η</i>) for Cases 1 and 2 showed a lower non-uniformity coefficient (0.030 and 0.017, respectively) than for the Non-distributor (0.039). The energy utilization of Cases 1 and 2 were higher (1.35e-0.5 and 1.46e-05) than the Non-distributor (1.64e-05). Overall, we confirmed that the inlet distributors led to increased evenness of flow distribution within an inflow part.