m3] and viscosity μ[Pa.s] of the fluid, and the typical length ℓ[m] and typical speed u[m/sec] of the system into consideration:μμlii4ρ·u·ℓraehs ,erusserPnoitom cduF圧力・剪断流体運動An impeller is a generic term for rotational mixing blades. Mixing itself is a common operation in many industries, but systematic R&D efforts about mixing started only a few years ago. The impeller shape and diameter are studied carefully, along with the rate of rotation, according to the purpose of mixing and working conditions. This profess is important as the fluidic condition in the mixing tank is affected by Reynolds number which, in turn, is determined by various factors.The Reynolds number is an index that represents the fluidic condition of a fluid. It is usually expressed by the following equation taking density ρ[kg/撹拌翼形状による撹拌作用の割合の変化The blade is one of the critical elements of the mixer. It receives mechanical energy of rotational motion from power drive and serves two purposes: (1) Cause the entire liquid in the mixing tank to move (fluid circulation) and (2) Cause local mixing by velocity gradient (shearing). The propeller type impeller takes its origin in the propeller of a ship and the wing of an airplane. It is designed carefully to minimize or prevent a flow separation occurring in the back of the blade, thereby centralizing the discharge flow efficiently and creating an axial flow.The flat paddle type impeller and the flat turbine type impeller characteristically have higher pressure and shear ratios due to the separated swirls occurring at the blade edge or separated flow in the back of the blade.Recent studies, however, have led to the development of the high-shear, low-drive turbine type impeller based on the flow field. Thus, it is very important that the impellers are chosen carefully according to the flow condition of material and the specific purpose of mixing. The diagram below is intended to give a very rough measure for selecting the impeller shape. Please keep in mind that it does not offer absolute criteria as the purposes of mixing and physical properties of the material need to be considered.Methods of selecting impellersBlade shapes and mixing高剪断の低動力型タービンも開発されてきており、流動状態と撹拌目的に合った作用を的確に与えることが重要です。下に示す図は、インペラ形状を選定するときの一般的な目安にはなりますが、撹拌目的や撹拌液の物性などによって異なりますので、絶対的なものではありません。Re=With regard to mixing, the Reynolds number is expressed as shown below using the impeller’s diameter d[m] as the system’s typical length and the impeller’s circumferential speed n(1/sec).d[m] as the typical speed:NRe=ρ·n·d2If the Reynolds number of mixing NRe and the impeller shape are known, you should be able to tell rough conditions of the fluid in the tank. This is to say the density (low or high) is not the only criteria of selection. Impellers must be selected comprehensively taking the impeller speed and diameter, the tank dimensions and various other factors into account.[—][—]（消費動力一定）(a)軸流型(a) Axial flow typeプロペラPropeller(Constant drive)(b)斜流型(b) Mixed flow typeピッチドパドルPitched paddleピッチドタービンPitched turbineフラットタービンFlat turbine(c)輻流型(c) Radial flow typeDSインペラDS impellerBlade shapes vs. mixing ratiosImpellerSeriesellers
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