外文翻译-搅拌器设计的一般程序.doc

南华大学机械工程学院毕业设计 外文翻译A General Procedure for Mixer DesignAbstract :This paper introduced the procedure of chemical mixer design as a rule. For a simplest liquid-liquidmixing project , the procedure contains 5 steps to fit the demands of user , such as the determination of type ,dimensions , speed and power of the mixer. This can give reference for designer.Key words :chemical engineering ; design procedure ; mixerStirring can accelerate the chemical process of heat transfer and mass transfer in the petrochemical，Extensive use of work equipment.Stir the object can be liquids, solids and gases, including liquidMajority. The most common liquid is water, its viscosity is very low. But the liquid also may be very thick, such as butter at room temperature for up to 1 000 000 cP (viscosity degrees, 1 cP = 10 - 3 Pa s, the same below). If added too much liquid-solids, such as sand, will lose mobility, a mud pie. This material can also be stirred, not within the scope described in this article. Gas is not too much lead to loss of mobility, but from the foam. The simplest is to mix the two issues could be mixing miscible liquids. The requirements of users is often the extent of mixing time and mixing. Successful design should be able to meet these requirements, and that they are more to spend on maintenance. We always pursue the goal is technology, machinery and the cost of the balance among the three. Miscible liquid mixing can not be much more complex, according to the requirements of users, sometimes high-power, high-speed, high shear emulsification equipment. The second common issue is the suspension of solid particles, which can be can be dissolved, it can be a valuable solid material in the leaching. Can have a chemical reaction, can only store the mix. The third is a liquid 2 gas mixing, commonly used in wastewater treatment aeration equipment.Usually agitator (mixer) by the motors as the prime mover (motor, electric, pneumatic or hydraulic), Reducer (reducer, gearbox), and the reducer output shaft connected to the shaft and the shaft of the impeller installed in the mixing composition. Slowing the body through a bracket or base plate is connected with the mixing container. When the pressure inside the container, the stirring shaft through the floor into the container should have a seal, often packing seal or mechanical seal. Both the motor and the seal is usually purchased, the study focused on the impeller. Impeller stirring performance of the material of the pumpingand create vortex(Turbulence), which produces the fluid velocity and fluid shear. The former leads to the return of all containers, media translocation, preventing the precipitation of solids and produce on the Tube bundle (if any) owashed, cut a large return in the micro-mixing, you can break the liquid bubbles or insoluble Drops, resulting in uniform. For the double role of different types of impellers have different emphases. Pitched blade turbines and hydrofoil impeller (long thin blade propeller) low energy consumption, mainly the axial flow. Its advantage lies in access speed of the fluid, commonly used in batch (batch) production mixing and solid suspension, there is a world is even more important. Radial wheel high energy consumption (such as curved leaves, trunk upright 6 - Rushton turbine), resulting in a high percentage of shear. Axial energy round 1 / 3 Cut, 2 / 3 speed; Rushton turbine on the contrary, 2 / 3 consumed in the shear, commonly used in the gas dispersion and immiscible liquid emulsion.The major impact of mixing on heat transfer and the nature of the material, mixing power and transfer film coefficienthc relationship can be expressed qualitatively the following formula:( hc DT) / k = K( D2 N / ) ( C / k) b (o / ) cWhere: DT is the tank diameter, D is impeller diameter, N is speed; C, k, and are the material specific heat, thermal conductivity, density and viscosity; o is the viscosity on the wall; K, a, b and c are experimental coefficients.朗读显示对应的拉丁字符的拼音The mixer has a series of his usual vendors, so the performance (as its power coefficient, flow coefficient) is also known impeller. The problem is how to combine the selection of impeller actual conditions to determine the geometry, parameters such as speed and torque. Single-layer arrangement of the impeller can also be multi-layer combination of impeller pumping downward direction can also be up.In technology design, people often refer to an existing plant or laboratory data were similar to zoom in or out. 2 for liquid-liquid mixing and solid suspension may wish to assume that TQ (equivalent volume of the required units of torque, TQPVol. eq) as a constant value, as the basic parameters. Correction factor required for its small, and therefore more accurate, and can thus directly the size of the selected gear (for gas dispersion issues, more often amplify the power demand as the basic parameters). Figure 1 is a pitched blade turbines, the material is 1 000 cP viscosity when the torque between the volume of two schematic diagram of the equivalent volume Vol. eq equal to the actual volume of material than the density multiplied by Sg (material density and water density Ratio, dimensionless), in units of US gal, 1US gal = 31785 L, torque TQ to lb in as a unit, 1 lb= 01113 N m.This linear relationship can also be a list, as shown in Table 1.Because of different speeds made by different choices, actually introduced the concept of power. In theory, the torque and power by the two methods the results obtained should be the same.Mixing power consumption of the following formula:P = Np Sg N3 D5 / (6. 12 107 )Where: P is power (in horsepower hp, 1 hp = 0. 745 7 kW), NP is the power factor (dimensionless), Sg is the specific density (dimensionless), N is impeller speed (rPmin) and D Impeller Diameter (in feet ft, 1 ft = 0. 304 8 m).Np with the impeller changes, for a given impeller type, low viscosity, a baffle of the container to a constant. Baffles to prevent vortex (swirl), located almost all of the mixing baffle. Small Tip Angle of the hydrofoil impeller (long thin blade propeller), Np = 013; and the high blade Rushton impeller, Np up to Power equation can be resolved into two parts:P = K N3 D5 = ( K1 N D3 ) ( K2 N2 D2 )Where: (N D3) reflects the pumping energy; (N2 D2) reflecting the cut. Tip tangential velocity Tip speed = D N, and shear related.General design procedure General design procedure shown in Figure 2. Figure 5 steps are:1) The user equipment according to the existing D / DT (wheel diameter / tank diameter) values, and the mixing time, mixing degree requirements, several different speeds selected torque or power requirements.Among them, the mixing is affected by material viscosity difference, the proportion of poor, if non-Newtonian fluid and other factors. We can give a classification method (such as: mild, moderate, severe, strong; or 2,3,4 Etc.), which is a fuzzy concept.2) selected to install a reasonable height of the impeller, combining equipment, it is estimated the approximate shaft length.朗读显示对应的拉丁字符的拼音3) a reasonable estimate of the motor power.4) Refer to Factory for performance, such as the impeller power consumption, speed reducer, the output shaft, frame, etc., selected to meet the requirements of the former three blender.5) and then tip tangential speed in accordance with the conditions, determine the most appropriate speed, to optimize the design, according to the identified conditions to computer program for power and strength of the shaft such factors as checking and analysis.Design Examples2.1 Calculation of basic parameters For a pitched blade turbines, can be calculated with following: Step One: Select the impeller speed N, such as 45,56 rPmin; the second step: Calculate the Reynolds number of the container.朗读显示对应的拉丁字符的拼音 NRE = 50V2P3 NSg /, Where: V is the volume batches of materials,US gals; Sg is the specific density; is the viscosity, cP.Step Three: If NRE 15 000, the following calculation, TQ = 01084 V Sg, where: TQ to the required torque, lb in. If NRE 15 000 ,进行以下计算, TQ =01084VSg ,其中: TQ 为所要求的扭矩,lbin。如NRE 15 000 , TQ = 0. 78 Sg0. 61 V0. 74 0. 39PN0. 39第四步:按不同的N 重复计算,将计算结果列表。混合时间计算:先算雷诺数NRE为1 550ND2Sg / ,其中: N 为叶轮转速,rPmin ; D 为叶轮直径,ft ;Sg 为比密度;为动力粘度,cP。混合雷诺数NB 和容器雷诺数关系如图3 所示。混合雷诺数NB 定义如下NB = B T ( TQ/ Vol . eq) 1P2 / V1P3其中: BT 为混合时间,min ;V 为批次物料容积,gals ;( TQ/ Vol . eq) 为当量容积扭矩,1 bin/ gal