Dr. Monika IvantysynovaMAHA Professor Flud Power SystemsDesign and Modeling of Fluid Power SystemsME 597/ABE 591 - Lecture 2MAHA Fluid Power Research CenterPurdue University© Dr. Monika IvantysynovaDesign and Modeling of Fluid PowerSystems, ME 597/ABE 5912Contents1. Introduction and overview of components, circuit and system design methods 2. Fluid properties, modeling of transmission lines, impedance model of lines 3. Displacement machines design principles4. Steady state characteristics, measurement methods and modeling 5. Gap flow models 6. Flow and pressure pulsation© Dr. Monika IvantysynovaDesign and Modeling of Fluid PowerSystems, ME 597/ABE 5913• Choose max operating pressure• Size the hydraulic motor• Calculate flow requirement• Select type of control, in case of valve control select type and size of control valve• Select pump size based on flow requirement and speed of prime mover• Calculate required line diameter• Add additional components like pressure relief valve, logic elements, filter, reservoir, accumulatorsFluid Power System Design© Dr. Monika IvantysynovaDesign and Modeling of Fluid PowerSystems, ME 597/ABE 5914Fluid Power System DesignExamplemaxmax Flightmax Flightφφmaxφmax FlightMlFmax Flight/s/sduringφφ© Dr. Monika IvantysynovaDesign and Modeling of Fluid PowerSystems, ME 597/ABE 5915MAHA Distance LearningFluid PropertiesProperties of FluidsCompressibilityDensityViscosityChange of density with pressureChange of density with temperatureViscosity - temperature behaviorViscosity - pressure behavior•Oxidative, hydrolytic and thermal stability•Foaming (release air without forming emulsions)•Lubricity (boundary lubricating property)•Air/Gas absorption•Pour Point•Flash point/ fire point© Dr. Monika IvantysynovaDesign and Modeling of Fluid PowerSystems, ME 597/ABE 591617Compressibility of a real fluidDensity is defined:Change of fluid volume with pressure and temperature:Isothermal coefficient of compressibilityBulk modulus is defined as reciprocalof compressibility coefficientTherefore we can write:andFluid PropertiesdV = -V ⋅ βp ⋅dp⋅dp© Dr. Monika IvantysynovaDesign and Modeling of Fluid PowerSystems, ME 597/ABE 591718Bulk modulus12Vpp1p2V1V2In practice secant bulk modulus KS is often used!Fluid can be compressed isothermally or isentropically (adiabatic process)Isothermal bulk modulus KAdiabatic bulk modulus KAFluid Properties⋅ dp⋅ (p2 - p1)© Dr. Monika IvantysynovaDesign and Modeling of Fluid PowerSystems, ME 597/ABE 5918Due to entrapped air the compressibility of the fluid (fluid-air mixture) changes.For the bulk modulus of fluid – air mixture K* can be derived: p0 … atmospheric pressureIn a simplified way for the change of volume of thefluid – air mixture dVM we can derive: For isothermal process follows:simplified:and for the change of fluid volume:Change of air volume with pressure:19Influence of entrapped air© Dr. Monika IvantysynovaDesign and Modeling of Fluid PowerSystems, ME 597/ABE 5919Influence of entrapped air Due to VAir << VF we can make the following simplification: VF=Vthen(1) and(2)Substituting Eq. (3) in Eq. (1) and (2) follows:(3)Example: Calculate how the bulk modulus of the fluid – air mixture with 0.5% undissolved air at p = 100 bar=107 Pa is changed. The bulk modulus of the fluid is K=2·109Pa.20© Dr. Monika IvantysynovaDesign and Modeling of Fluid PowerSystems, ME 597/ABE 59110Viscosity of a real fluidxhp1p2p1=p2v0yThe viscosity of a fluid is the measure of its resistance to flow or of its internal friction.According to Newton’s law the shearing stress between adjacent layers of a viscous fluid is proportional to the rate of shear in the direction perpendicular to the fluid motion (flow direction).vµ … dynamic viscosity [Pa·s=N·s/m2] are empirical constants for a given fluid, whereasTypical values for mineral oil:23© Dr. Monika IvantysynovaDesign and Modeling of Fluid PowerSystems, ME 597/ABE 59111Viscosity of a real fluidKinematic viscosityKinematic viscosity: [m2·s-1] or [cSt]ISO Viscosity Grades for mineral oils (ISO 3448)ISO VG 10mean value at 40°C10 mm2·s-1 , (cSt)ISO VG 2222 mm2·s-1ISO VG 32 32 mm2·s-1ISO VG 46 46 mm2·s-1ISO VG 100100 mm2·s-1© Dr. Monika IvantysynovaDesign and Modeling of Fluid PowerSystems, ME 597/ABE 59112Viscosity-TemperatureViscosity-temperature diagram Kinematic viscostiy [mm2/s]ISO viscosity grade reference temperatureOrdinate: lg lg (ν+0.8)Abszissa: lg TSkydrol (Phosphate ester)Temperature [°C]© Dr. Monika IvantysynovaDesign and Modeling of Fluid PowerSystems, ME 597/ABE 59113Types of Hydraulic FluidsPetroleum based fluids (mineral oils) usually with additives to-prevent oxidation and corrosion HL-reduce foaming -improve lubricity HLP-increase viscosity index HVFire resistant fluids - oil – water emulsions (20% H2O) - HFA - water in oil emulsion (about 40% H2O) - HFB- Polymer solutions with H2O - HFC - water free synthetic fluids ( Phosphate ester) - HFDBiodegradable fluids-Vegetable oil base HTG-Polyglycol base HPG-Synthetic ester HEWater© Dr. Monika IvantysynovaDesign and Modeling of Fluid PowerSystems, ME 597/ABE 59114Water versus Mineral OilViscosity 30 lower5 times higher thermal conductivityViscosity-temperature dependency 14 lowerSpecific heat 2.3 higher50% higher bulk modulusAir –release ability 30times betterHigher vapor pressure50% reduction of pressure lossBetter cooling-abilityHigher stiffness but© Dr. Monika IvantysynovaDesign and Modeling of Fluid PowerSystems, ME 597/ABE 59115Vapor Pressure of WaterWaterVaporPressure [bar]Temperature [°C]Vapor Pressure WaterpV H2O=0.1133 bar @ 50°CpV mineral oil= 0.053Pa = 0.53 µbar @ 50°C© Dr. Monika IvantysynovaDesign and Modeling of Fluid PowerSystems, ME 597/ABE 59116Fluid PropertiesThermal propertiesSpecific heat c [ J/kg ·K]Thermal conductivity λ [W/m ·K]Solubility of gasHenry’s