Tank Geometry Research Articles

RESPONSE OF A FIRST-ORDER SERIES SYSTEM TO THE TRANSFER FUNCTION, THE LIQUID LEVEL OF TWO INTERACTING TANKS

This article presents the experimental and theoretical results of the discharge and filling of water between two torispherical tanks connected in series at different heights, the model that was used was developed with equations reported in the literature for geometries of torispherical tanks and it was necessary to develop two more equations in the laboratory to calculate the discharge and fill volumetric flows for the tanks used. The unloading and filling model was obtained with transitory mass balances resulting in two simultaneous linear differential equations where the unloading and filling heights are related as a function of the operation time. The model was solved numerically, and the experimental results were compared against those of the proposed model, finally the transfer function for this system of interacting tanks was found. KEYWORDS: Transient mass balances in two atmospheric interacting tanks at different heights and equal torispherical geometries. The discharge and fill model of two interacting tanks as a function of time. The volumes of partially filled torispherical tanks. The transfer function of a pulse in the discharge pipe that affects the volumetric flow within the discharge tank.

Fragility assessment of bottom plates in above ground storage tanks during flood events

This study aims to improve the fundamental understanding on the performance of bottom plates in above ground storage tanks (ASTs) during flood events. To this end, fragility models that estimate the probability of material yielding and rupture in the bottom plates were derived. A significant number of ASTs are located in coastal areas and are susceptible to hurricane hazards. Consequently, ASTs have suffered severe damage during past hurricanes resulting in spills with catastrophic environmental and social impacts. Therefore, several failure modes such as flotation, buckling, and sliding have been studied in past research. However, the literature lacks studies that consider the failure of bottom plate due to uplift pressure generated during floods and there are no design guidelines to address this issue. To address this gap, fragility functions that provide the probability of failure as a function of tank geometry, material properties, design parameters, and hazard conditions were developed herein. For this purpose, Latin Hypercube Sampling was performed to span the space of these parameters uniformly. For each parameter combination, maximum stresses in bottom plates were determined using analytical formulations for simply supported and clamped boundary conditions and were compared against two different failure thresholds. The results were used to develop a closed form fragility model using step wise logistic regression. Fragility functions were applied to four case study tanks. Sensitivity analysis were performed to understand the impacts of different probability density functions for various variables on the bottom plates’ fragility. The results provided several insights such as ASTs with larger diameter were vulnerable to bottom plate failure. Comparison with other failure modes revealed that the probability of bottom plate failure was higher than flotation failure for anchored ASTs with clamped boundary condition.

A silicon vertex detector with timing for the Upgrade II of LHCb

The LHCb Upgrade II aims at maximizing the potential for heavy flavour physics at high luminosity-LHC. The Vertex Locator (VELO) plays an important role in this task due to its excellent tracking and vertexing abilities. During Run 5 and 6, the detector will undergo through a substantial increase in data rate, pile-up and radiation damage. To achieve the same vertex reconstruction efficiency as the current Upgrade I detector, the introduction of timing and its possible implementations are discussed. Additional requirements for new sensor and ASIC technologies, introduced to cope with increased radiation damage, data rate and timing, are also presented. Finally, possible new detector layouts, adapted to expected conditions, are discussed and their impact on the RF-foil and vacuum tank geometries are treated.

Modelling and Simulation Hydrodynamics Processes in Liquefied Natural Gas Transportation Systems

Global natural gas resources are growing and are increasingly geographically diverse. A Floating Storage and Regasification Unit (FSRU) is one of the most commonly used vessel types in the global ship fleet due to the possibility of storage, reloading to another ship, and regasifying it for re-injection into the natural gas grid. It is important to control system parameters for reliable technological processes such as tank hydrostatic pressure, vapor pressure, LNG density, LNG temperature, and phase changes between liquid and gas states. Additionally, pressure monitoring is important to control during transit in port and bunkering to prevent the pressure in the tanks from exceeding the tank design pressure. In this research study, a comprehensive hydrodynamic model for an LNG storage tank in a real-life regasification terminal (Floating Storage and Regasification Unit, LNG Terminal of Klaipeda City, Lithuania), operating in transportation mode to the regasification unit, was created. For this research, LNG is investigated as a compressible liquid and the speed of sound in LNG is evaluated. A complex mathematical model of the system allows the analysis of high-speed hydrodynamic and dynamic processes at cryogenic temperature (110 K) and evaluates the geometric parameters (tank geometry, electric motors and pumps, pipe geometric parameters, and roughness of internal surfaces) and the characteristics of pumps and electric motors. The complex mathematical model of the system was implemented using Fortran programing language and MATLAB R28a. It determined the parameters (pressure, velocity, liquid level of LNG in the tanks, electric motor angular velocity, torques, hydraulic energy losses, etc.) of the system during its start-up mode (until 5 s). It was found that hydraulic energy losses in all pipes contain 1.7% of the whole system power (the total power of the electric motors is 3132 kW). In case of increasing energy costs, this model could be used to control energy losses during the operation of the FSRU in various technological modes.

A review of phase change materials and heat enhancement methodologies

AbstractPhase change materials (PCMs) are an efficient alternative to store and release heat at a specific range of temperature. Here PCMs and heat enhancement methodologies for PCM storage are reviewed. A short overview of PCMs and their applications is presented in addition to the progress during the last 10 years. Heat enhancement techniques, that is, extended surfaces, multiple and composite PCMs, and encapsulation techniques, are presented along with a statistical overview of studies during 2016–2021. The importance of various fin and storage tank geometries (extended surfaces) is discussed in detail. Advancement in the latest heat enhancement techniques such as use of nano‐enhanced PCMs is presented. Recommendations for future research are provided.This article is categorized under: Emerging Technologies > Energy Storage Sustainable Energy > Energy Efficiency

Machine learning model for the optimization and kinetics of petroleum industry effluent treatment using aluminum sulfate

Small-scale preliminary studies are necessary to determine the feasibility of the machine learning (ML) algorithm and time-evolution kinetics to meet the design specification of the treatment unit. The train and test datasets were obtained from jar test experimentation on the petroleum industry effluent (PIE) sample using aluminum sulfate (AS) as the coagulant. The ML algorithm from scikit-learn was employed to determine the optimum operating condition for the removal of colloidal particles, causing turbidity in the PIE. The predictive capacity of four ML models was compared based on their statistical metrics for clean discharge. The predicted optimum condition corresponds to pH (10), dosage (0.1 g/L), and settling time (30 min) which transcends to residual turbidity ≤ 10 NTU and translates to 95% removal efficiency. The second-order AS-sweep flocculation kinetic showed that at the predicted optimum conditions, modeled rate constant of 1.33 × 10−3 L/g.min and flocculation period of 1.2 min reduced the combination of the monomer, dimmer, and trimmer class colloids from an initial 570 mg/L concentration to the residual counts of 24 mg/L corresponding to residual turbidity ≤ 10 NTU under the mixing regime 14 s−1 ≤ G ≤ 164 s−1 satisfied the EPA standard for clean effluent discharge. It incorporated the selected ML output with time-evolution and aggregation kinetics to define sedimentation tank geometry for cleaner discharge. The findings from the design-driven optimization recommended a flow rate (1000 m3s−1), coefficient of kinematic viscosity (0.841 mm/s), and the required detention time (30–60 min) to define the sedimentation tank geometry.

Numerical simulation of the inlet channel geometry influence in the torque generated at the gravitation water vortex turbine

The gravitational water vortex turbine is presented as an alternative for electric power generation for both low head and water flow conditions, additionally it is easy and low cost to implement and maintenance. However, the experimentally reported efficiencies motivate the scientific community to develop new geometries in order to improve its performance. First, it is not clear how the efficiency of the turbine is obtained and second, not all studies report it. The turbine is mainly made up of a tank, the rotor and the electric generator. The geometry of the tank is important because it stabilizes the fluid and in this component that the generation of the vortex is induced, which determines, added to other factors like tank geometry and runner, the global efficiency of the turbine. The primary purpose of this study is to compare numerically the torque generated at six (6) geometrical configurations of the basin inlet channel for Gravitational Vortex Turbine (GVT) with a Savonius rotor. The study was developed in ANSYS® CFX, where a transient state VOF model was configured with a BSL K − ω turbulence model and a discretization a discretization of the control volume made in the ICEM module. The highest torque was 0.553 Nm at 25 rpm for the trapezoidal curved inlet channel geometry, increasing the efficiency respect to the conventional Square inlet channel of the 2.73 %. The increase of tangential velocity contributes positively to the vortex generation, and consequently, an increase in torque is obtained. On the other hand, the design of the rotor considerably affects the performance of the GVT, where it may or may not take advantage of the kinetic energy of the vortex

A state-of-the-art review of experimental and numerical studies on BLEVE overpressure prediction

Accidents of Boiling Liquid Expanding Vapour Explosions (BLEVEs), which have been often reported worldwide, can bring about significant economic and environmental damages as well as injuries and loss of lives. Studies of BLEVE overpressure prediction and its effect on surrounding structures are, however, relatively limited. Current practice in BLEVE loads predictions for analysis and design of structures against BLEVE effects are based primarily on theoretical-based TNT equivalence empirical methods, which do not necessarily give accurate explosion load predictions. Some experimental tests and numerical simulations have also been carried out to predict BLEVE loads. This paper presents a systematic review of the experimental and numerical studies on BLEVE overpressure prediction. First, the experimental studies on critical parameters of tank rupture pressure, rupture temperature, liquid fill ratio, and tank's volume that affect the BLEVE overpressure generation are reviewed and discussed. The theoretical-based empirical models are also compared. Subsequently, the commonly-used Computational Fluid Dynamics (CFD) models, the recently developed Artificial Neural Network (ANN) models and numerical-based empirical methods for BLEVE overpressure predictions are reviewed and discussed. It is concluded that the BLEVE overpressure prediction using CFD models is more accurate than theoretical-based TNT equivalence empirical methods since complex BLEVE conditions such as tank geometries and surrounding environments can be considered in the CFD model, but it is time consuming and requires relatively large computer power. A properly trained ANN model and numerical-based empirical models could also reliably predict BLEVE overpressures with significantly improved efficiency than CFD simulation. The advantages and disadvantages of the different prediction methods are summarized and discussed in detail.

Efficacious slosh suppression technique in road tankers to enhance the effectiveness of drinking water distribution

During summer months, many parts of the world experience the water crisis and water tankers transport fresh drinking water from rivers and other reservoirs and distribute to communities often located at far off places. Effectiveness of this distribution is adversely affected by the instability of tankers due to the phenomenon called liquid sloshing, the oscillation of free liquid surface subjected to external excitation. The liquid within the tank moves along the side walls back and forth creating an oscillation which becomes dangerously worse at certain situations. Sloshing makes the tanker unstable when the operating frequency and the tanker frequency coincides which may even cause the tanker to roll over. Hence, quite often, the tankers have to be operated on roads only at its maximum capacity and the water left in the tank may have to be spilled and wasted if the storage facility at the destination is less than the tanker capacity. In this work we are proposing an optimum design of water tankers to minimize the effect of sloshing and thereby enabling trouble-free operation of the tankers even in partially filled conditions. Sloshing parameters such as slosh height and dynamic wall pressures are experimentally and numerically analyzed for various tank geometries with and without baffles. A numerical model for analyzing slosh parameters is also developed and validated using experimental results. Based on the study an optimized tanker configuration is proposed.

A Preliminary CFD and Tritium Transport Analysis for ARC Blanket

The Affordable, Robust, Compact (ARC) fusion reactor is a preconceptual design proposed by the Plasma Science and Fusion Center at the Massachusetts Institute of Technology that will be developed by Commonwealth Fusion Systems. ARC features a Li2BeF4 (FLiBe) molten salt liquid blanket that provides reactor cooling, neutron shielding, and tritium breeding. This work aims to develop a preliminary coupled computational fluid dynamics (CFD) and tritium transport model to describe FLiBe flow inside the tank and to assess ARC tritium inventory in the vacuum vessel and blanket. Both models are built by taking advantage of COMSOL® Multiphysics. FLiBe velocity and temperature fields are evaluated by the CFD models, and they are passed as input to the tritium transport model. The tritium transport model computes tritium concentration inside solid materials and FLiBe. An auxiliary FLiBe inlet has been moved from the original position in the ARC preconceptual design to improve blanket cooling and to reduce the size of flow eddies. Results show that many recirculation zones generate inside the tank for the chosen tank geometry, size, and inlet-outlet conditions. Larger FLiBe temperature and tritium concentration are found in these zones. The high FLiBe temperature in recirculation areas may not allow for effective cooling, and Inconel 718 reaches critical temperatures. The largest tritium concentration for a steady-state model with continuity of tritium partial pressure at the interfaces is found in Inconel 718 while the second-highest concentration is reached in FLiBe. The total tritium inventory in the ARC blanket with the assumed model is quantified as 3.16 g.

The Mandatory 4 Years Desludging Frequency of Underground Septic Tanks in Residential Areas: A Case Study in Sibu Sarawak, East Malaysia

Underground septic tanks are the most common and conventional primary black water treatment adopted by local households in Sarawak. To ensure its usefulness, periodic mandatory desludging or emptying of the various types of rateable holdings was enforced from 1998. The current mandatory desludging frequency is 4 years for residential households, although its effectiveness is still not clear, substantial annual finance and subsidies are being allocated by the Sarawak State Government. In this study, the underground septic tanks in Sibu located in residential areas in Sarawak, East Malaysia, were evaluated quantitatively based on the measured faecal sludge with a known retention time in respect to the regulated desludging frequency. Furthermore, various problems were encountered during the initial measurement carried out by sludge judge which typically used by the wastewater treatment and chemical plants. A modified PVC pipe was proposed to overcome these observed problems. This has greatly improved the measurement time and substantially reduced unwanted impediments for the contractor during desludging. The back analysis results showed that the recommended desludging frequency based on the ratio of total sludge and scum to the effective working volume in 30% and 50% thresholds for residential areas were 3.82 and 6.36 years, respectively. Furthermore, it was discovered that there was a potential to adjust the existing mandatory 4 years desludging frequency to a longer period for cost-effective consideration. This study is strictly on the physical quantity measurement of sludge and scum volumes for the known retention times. The complex influences of microbiological activities, micro-environmental factors and sizes or geometries of septic tanks for faecal sludge production were not considered.

Prediction of buckling capacity of liquid-filled steel conical tanks considering field-measured imperfections

Geometric imperfections caused by fabrication and welding reduce the buckling capacity of steel conical tanks. Few studies have considered field-measured geometric imperfections in such type of shell structures. This study carries out elastoplastic finite element analyses (FEA) to evaluate the buckling capacity of a full-scale stiffened conical steel water tank by considering its imperfections extracted from high-resolution laser scan data. Both global and local imperfections are obtained by comparing the laser scan data with the nominal tank geometry. The global imperfection involves deviation of the actual central axis of the tank from its nominal axis and ovalization of the tank circumference, whereas the local imperfection involves local fluctuations of the tank geometry around the circumference at a given elevation. The FEA is conducted using the commercial package ANSYS where both geometric and material nonlinearities are considered in the analysis. A four-node shell element with a six degrees of freedom per node is utilized in the model. The analysis results shed light on the shapes and magnitudes of global and local imperfections in an existing stiffened steel conical tank and their impact on the buckling capacity of the tank. Furthermore, the adequacy of imperfection tolerances recommended in widely used design standards for steel tanks are examined and compared with those extracted from the field measurements. The analysis results suggest that the local imperfections can be more critical than the combination of global and local imperfections in terms of the buckling capacity of the conical steel tank.

Equivalent linear roll damping of a FPSO coupled with liquid sloshing in a pair of two-row tanks

The increased risk of reduced transverse stability by free surfaces in cargo tanks in floating vessels such as Floating Production Storage and Offloading (FPSO) units, is well known. Roll decay testing remains the most common method for determining roll damping characteristics. Few works evaluating roll characteristics coupled with the effect of liquid motion exist. In this paper, a series of roll decay tests are carried out for a FPSO model with a pair of two-row prismatic tanks. The four compartment tanks are filled to different levels, and the equivalent linear damping is obtained using the Quasilinear (Logarithmic Decrement) method and the Froude Energy method. The effect of draft change for each loading condition is analyzed based on the average equivalent linear damping coefficient and the effect of the liquid cargo sloshing is also discussed. The results show that an increase in liquid cargo, the location of cargo load, and the geometry of the cargo tank affect the damping of the vessel.

Experimental investigation of the impact of fluid distribution on thermocline storage performance

The influence of fluid distribution on packed bed thermocline storage is studied experimentally on a 107 kWh prototype-scale setup. Three distributors are placed at the top of the tank, comparing uniform, central and peripheral geometries. A reference case is first considered and consists in a charge between 100 °C and 140 °C with an interstitial fluid velocity of 1.25 mm·s−1. Local analysis reveals a short-term influence of the distributor at the top of the packed bed. Radial temperature is most homogeneous when using uniform distribution, then central, then peripheral. However, the packed bed quickly homogenises radial temperature: the differences observed between distributors are erased in less than 6% of the total tank height. As a consequence, the longitudinal temperature profiles are unaffected by the distributor and the same utilisation rate of 81% is obtained for the three geometries. The coupling between fluid distribution and velocity is then studied: five charges are performed at velocities varying between 0.5 mm·s−1 and 1.5 mm·s−1 for each distributor. The influence of velocity is visible over the range studied: the utilisation rate decreases by about 2% due to advection, in agreement with numerical simulations. Fluid distribution, on the other hand, has no influence on global storage performance, showing the robustness of packed bed thermocline systems.

Stiffness requirements for wind girders in open-top cylindrical steel tanks

Aboveground cylindrical storage tanks are very thin shell structures which are prone to buckling when subjected to wind pressure. Both external and internal pressures are developed due to wind action, and the magnitudes of the pressures generally vary around the circumference. A wind girder is generally used in open-top cylindrical tanks to increase their resistance against buckling. The wind girder must have adequate strength and stiffness in order to fulfill its function properly. Widely used design specifications provide recommendations for the design of the wind girder. Strength requirements are given in terms of stress resultants, while a minimum second moment of area is provided as a stiffness requirement. The recommendations for the stiffness requirement were developed by conducting Linear Elastic Bifurcation Analysis (LBA) of cylindrical shells subjected to uniform external pressure. This paper explores stiffness requirements for the wind girder in open-top cylindrical steel tanks. The relationship between the buckling strength and the second moment of area of the wind girder was explored through a finite element parametric study. Tank shells with different radius-to-thickness and height-to-diameter ratios and having different wind girder sizes were investigated by means of LBA. A buckling strength curve was developed based on the LBA results where the strengths can be predicted with 90% accuracy. In addition, a new second moment of area requirement was proposed. The parametric study was extended to investigate the behavior using Geometrically Nonlinear Analysis including Imperfections (GNIA). The same tank geometries were studied using GNIA and considering different imperfection amplitudes. A buckling strength curve, which takes into account imperfection amplitudes, was developed to be used in design.

Numerical study for solidification of water inside a storage tank considering copper oxide nanoparticles

In this study, for improving the rate of freezing nano-sized material with different diameter has been dispersed in to water. The geometry of tank has two cold surfaces with circular and wavy shapes and two insulated walls were applied. Also, two inclined fins were connected to circular surface which helps the expedition of freezing. Finite element approach based on Galerkin discretization was applied for solving the energy equation and concentration of solid PCM. The velocity equations were not involved in model because of low impact of gravity force. With start of process, ice front moves from two sides to middle regions. The solidification rate improves around 38.42% with adding nanoparticles. Augmenting the fraction of nano-powders makes the period to decline about 12.04%. With increase of size of powders at first needed time declines around 11.4% then it augments around 25.23%.

Mathematical Modeling & Engineering Design of Wastewater Treatment Unit for Al-Kut Gas Filling Company

New talented treatment method without chemicals and with minimum operational cost was performed to treat industrial waste water discharged by a hydrostatic test performed on the gas bottles maintenance workshops to reuse it. A common method by Tarleton and Wakeman was used to select the general treatment philosophy, The implementation of this study was carried out on three stages, water sample analysis, simulates the proposed preliminary design and detailed engineering designing for the first stage, a sample of waste water was brought from Al-Kut Gas Filling Company - maintenance section and tested for settling, aeration, and filtration. The experiments showed that the most of sediments were insoluble but rather than suspended in water and can be removed by settling. Furthermore, aeration test showed that concentrated Thiophene odor in water was removed at 50 C of water with diffused air bubbling. On the other hand, filtration of using 10 Micron filter paper was achieved to eliminate the rest of tiny sedimentation. Secondly, general dimension of equipment was calculated by engineering design equation according to qualitative and quantitative analyses of waste water. Accordingly, a set of experiments of simulation using ANSYS V19.0 and Eulerian – Eulerian as mathematical model were performed for the 3D two phase flow sedimentation tank with capacity of 5 m3/hr to find the optimum sedimentation performance by testing of the modifications on the tank geometry (baffle depth, distance between baffle and inlet, hooper). Simulation results showed that the optimum tank geometry (0.86 m Baffle depth with inclined part, 2.5m distance between baffle and inlet, hooper within V type geometry W=1.67m/0.29 m, D=1.03 m and tank dimension (L=10m, W=2.5, H=2.5 with slope angle = 2o) with 49.5 volume % in sediment layer with a minimum sediment layer height. 
 The third stage included an accomplishment of the Preliminary and detailed engineering design of the entire unit by SOLIDWORKS software to be ready for prototyping.

Interrogating common clarification models for unit operation systems with dynamic similitude

Surface overflow rate (SOR), plug flow reactor (PFR) and continuously stirred tank reactor (CSTR) are common models for clarification unit operations (UO). With wide deployment in engineering practice and regulation, through tools from spreadsheets to complex numerical codes, these models are formulated based upon conceptualized system geometry (e.g., rectangular channel) and idealized hydrodynamics (plug flow or well-mixed conditions). Yet the hydrodynamics and geometry of actual UO systems can be complex and substantially different from these assumptions. As a result, the applicability and generalizability of these models require critical and systematic interrogation. This study examines the predictive capability and generalizability of these common models for a hydrodynamic separator (HS), tanks, rectangular clarifiers and an urban drainage basin based on physical model data and high-fidelity large-eddy simulation (LES). Moreover, this study presents a novel application of dynamic similitude to developing a more generalized and physically interpretable model based on the hypothesis that PM and PM-partitioned constituent separation in a UO can be approximated solely through the dimensionless settling velocity W (Hazen number). Based on this hypothesis and dynamic similitude, a similarity modified gamma model (SMG) is proposed and tested. With dynamic similitude and W, results show common models are not robust and generalizable for predicting PM separation with error ranging from 30 to 50% and can significantly oversize a clarifier up to 904%. The non-linear characteristics of PM separation are shown to have a critical role in clarifications system design scalability and economics. In contrast, the SMG model is robust and generalizes the PM separation for geometrically similar systems, irrespective of particle density, particle size distribution (PSD), and loading conditions. The developed theory and proposed SMG model also can simplify and reduce the effort as well as expense of physical model testing while serving as an adjuvant for numerical simulations of clarification systems. Results also reveal commercial HS systems do not outperform simple plain tank geometries. The complex turbulence vortical structures pose significant challenges for UO system analysis and design.

FLNG Parametric Design: A Synthesis Modeling Approach

This article deals with the development of a numerical tool based on an integrated synthesis model to carry out the first project cycle of floating liquefied natural gas (FLNG) platforms to produce, process, store, and export liquefied natural gas (LNG). The topside configuration, tank geometry and capacity, production levels, equipment list, environmental and operating conditions, classification society requirements, structure, stability, and seakeeping are considered in a single synthesis model, generating a sufficiently large number of solutions. The case generation and the evaluation process are performed hierarchically, dividing the parameters into groups to better solve the solution space, which cannot be achieved with conventional techniques such as traditional point-based design. This methodology is applied as a case study to design three FLNG platforms with different production levels (2, 3, and 4 million metric tons per year). Performance parameters are defined and evaluated, optimizing downtime, structural mass, and load capacity. The resulting platforms are compared to existing FLNG dimensions. Essential conclusions are drawn about design improvements, such as key dimensions, quantity, and configuration of tanks, freeboard specifications, and operating draft. The developed synthesis framework proved to be a quick and useful tool for the early stages of the FLNG project.

DEM-VOF simulations on the drawdown mechanisms of floating particles at free surface in turbulent stirred tanks

• The drawdown process is divided into three stages. • The force acting on floating particles is one main drawdown mechanism. • Particle collision and turbulence kinetic energy of free surface are also mechanisms. • OED was used to study the effects of particle properties and stirred tank geometries. The drawdown of floating particles in turbulent stirred tanks is widely encountered in industrial processes. However, the data oriented drawdown mechanisms and the dependence of particle dispersion on particle properties and stirred tank structures are lacking. Especially in the simulation works, the effect of the free liquid surface on the drawdown of particles is commonly ignored. In this work, discrete element model coupled with volume of fluid method (DEM-VOF) is used to investigate the influence of particle properties and stirred tank structures on the drawdown processes with an orthogonal experimental design (OED). Both up-pumping and down-pumping of a 45° pitched blade (PBTU and PBTD) in the flat-bottomed stirred tank are studied. The method has been verified and validated with the invasive image-based experiments. Here, it is shown that the drawdown processes of PBTU and PBTD are different. The drawdown process is divided into pull-down stage, dispersion stage and cycle stage. Particle-particle collision, the total force, the coupling force and the turbulent kinetic energy of the free liquid surface are the main drawdown mechanisms. Baffles and the impeller clearance are key factors. The optimal combinations of factors level for the most uniform distribution and the least power consumption are obtained by OED, which provides reference for further industrial applications.