附件242 国Chopter2 damentl yrnie Fid e◆a 3 Viscosity The sketeh of viscosity is illustrated by Fig 2-1 Cohesion between two mnolecules. have u+du reen the twe fhud t= Where lt is viscosity coefficient,also dynamic Fig.2-1 The sketch of viscosity 国Chopter2 Fandamental历draieFid Mechanie年a There are three methods to describe the viscosity: absolute viscosity,Kinematic viscosity and relative viscosity. (1)Dynamie viscosity or absolute viscosity (Pa.s)or(Nm (2)Kinematic viscosity (mm2/s) =u (2-4) (3)Relative viscosity (conditional viscosity) The relative viscosity E which used in China is tested by the E iscometer,such as Fig.2-2. 9
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附件24.2 图capa2 Pndmontlyr Fid echnic。 Fig.2-2 illustrates the E viscometer principle. 《度 2.8mm E-/ Fig.2-2 Principle of E viscometer Take the noteE describes the viscosity E,=t t2 (2.5 on formula between theE and kinematic visco =(731°E 63 )×106a2/s) (2-6) (4Viscosity-temperature:For the viscosity less than 15E ad the temperature 3150C the viscosty-temperatre formula is desribeas following We also can look up from Fig2-3. (27) (5)Viscosity-pressure 。=v,ep≈y0+0.03p) (2-8) (6)Others performances:physical and chemucal.such as auti-inflammability. anti-oxygenation.anti-concreting,anti-foam and anti-corrosion etc 10
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附件242 图Chapter2 Fndamental Hydranlic Fhnid Nechanies卷 () 101520304050 7080 0 Fig.2-3 The viscosity-temperature of homemade oils 2.1.2 The requests and choice of hydraulic oil 1.Request The oil plays two roles ofronand briction on the sfaces of working interaction The requests for the hydraulic fluids are:appropriate viscosity.the good i stabilities,compatibleith other system materials and so on 2.Choice The hydraulic oil in a hydraulic system atv0)x1m2s is generally. The hydraulic oil should be chosen in according to the request of hydraulic pump e hydraulic oil viscosity adapted for different hydraulic pumps is listed in Tab.2-
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附件24.2 Tab.2-2 The range of viscosity of hydraulic oil adapted to pumps viscosities(106m2/s) Viscosities(106m2/s) Types 540℃ Types 40℃400 P<7MPa 30-50 40-75 Gear 30-7095-165 pumps Vane Radial P≥7P: 50-70 50-90 piston 30-50 65-240 pumps Axial Screw pumps 30-50 40-80 3070 70-150 List 2.2 Hydrostatics(液体静力学) Chapter2 Fundamental Hydraulic Fhuid Mechanics 2.2.1 Characteristics of Hydrostatics 1.The hydrostatics Static pressure:the action force in normal on a unit area.It is ntituled pressure in physics and action force in engineering usually 2.The characteristics of hydrostatics (1)In any homogeneous fluid system at rest,the pressure creases with the depth of the fluid. (2)Pressure at any point in a homogeneous fluid system at rest acts perpendicularly to surfaces in contact with the fluid. 12 Hmpee List Upeards Dorsvcards Retum Eit
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附件242 Chapter2 Fundamental Hydranlic Fluid Mechanics 2.2.2 The basic formula of hydrostatics 1.The basic formula of hydrostatics The acting pressures on the fluid at rest,in a container include the weight,force on the fluid surface,shown in Fig 2-4a The total balance force formula is pA4p,△d+Pgh△429 A mula (2-9)divide by then (2-10 a b p=P。+pgh Fig.2-4 The distribution of forces in a container with rest fluid 国Chapter2 Fundamental历dranlie Fid Mechanies年 The formula (2-10)is the basic equation for hydrostatic.It states that the distribution status of hydrostatics as following: (1)The pressure on a rest fluid coutained involves two parts: P=P。+8h (2-11) (2)The pressure with the depthh (3)Isotonic pressure surface,that is,the pressures are all equal at the surface consisted by all points at given depth h.such as at the line ofA (4)Conservation of energy +h=P+h=constant (2-12) pg Here.the Popg as pressure energy at per uit mass fluid
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