ENTC 303 Announcements

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# ENTC 303 Announcements - PowerPoint PPT Presentation

ENTC 303 Announcements. A lab manual is available for this course PDF version is available on line through eCampus We will have labs starting next week: 8-12 September We will meet at Thompson 008 (DXP Pump Lab). Key Concepts/Properties. Pressure :

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ENTC 303 Announcements
• A lab manual is available for this course
• PDF version is available on line through eCampus
• We will have labs starting next week: 8-12 September
• We will meet at Thompson 008 (DXP Pump Lab)
Key Concepts/Properties
• Pressure:
• Amount of Force exerted on a unit area
• P = Force/Area
• Pressure acts uniformly in all directions and perpendicular to the boundaries in the container
• Example: Piston

Force

Area= p/4*D2

P

Pressure=Force/Area

Unit: Psi or Pa (SI)

Example
• A container holding a liquid supports a loaded movable piston. Determine the magnitude of the pressure in the liquid under the piston if the total weight of the piston and load is 500 N, and the area of the piston is 2500 mm2.

Key Concepts

• Density, r:
• Amount of mass per unit volume
• r = mass/volume
• Density is a fluid property and slightly dependent on temperature
• Units: kg/m3, g/cm3, lb/ft3
• Specific Volume, n:
• Inverse of density
• n = 1/r, m3/kg
Key Concepts
• Specific Gravity, SG:
• Is the ratio of density of fluid to the density of reference fluid (usually water) at the same temperature
• SG=r/rwater
• SG of seawater in the death sea (SG = 1.24):
• SG of men: 0.96
• SG for women: 0.91
• http://jap.physiology.org/content/19/5/955

Specific Weight

• Specific Weight (g) = Weight/Volume

g = w/V

• Examples
• Calculate the weight of a reservoir of oil if it has a mass of 825 kg
• If the volume is 0.917 m3, compute density, specific weight, specific gravity

Equations for Property Calculations

• Circular Area:
• Weight: w = m*g
• Density: r = m/V
• Specific Weight: g = w/V
• Specific gravity: SG=r/rwater

Area = p/4*D2

Examples

• Glycerine at 20° C has a specific gravity of 1.263. Compute its density and specific weight.
Surface Tension
• Property by which droplets of water (or water molecules) adhere to each other and other surfaces
• When water molecules stick to each other: cohesion
• When they stick to other substance: adhesion
• Surface tension varies with temperature; decreases with increase in temperature.
Examples of Surface Tension

Surface tension helps the spider walk on water. The force

of surface tension balances the spider’s weight, helping it

to walk on water. Surface tension affects the top layer of

water, causing it to behave like a stretched elastic sheet.

http://udel.edu/~inamdar/EGTE215/Introduction.pdf

Wetting

glv

Hydrophobic

Hydrophillic

gsl

gsv

Young equation (1805)

qeq

qeq = contact angle

Viscosity
• Dynamic Viscosity
• = Shear Stress/Slope of velocity profile
• =

n

v

F

Slope = v/y

y

Units: cP (centipoise), mPa-sec

Newtonian and Non-Newtonian Fluids
• Rheology: Study of the deformation and flow characteristics of fluids
• Two types of fluids: Newtonian and Non-Newtonian:

Shear Rate or Velocity Gradient

Viscosity
• Kinematic Viscosity
• Units: cS (centistokes) mm2/s
• 0.10 mm2/s to 70,000 mm2/s
Newtonian and Non-Newtonian Fluids

Bingham

Pseudoplastic

Newtonian

Shear

Stress

Dilatant

Newtonian Fluids
• Water
• Oil
• Gasoline
• Alcohol
• Kerosene
• Benzene
• Glycerine
Non-Newtonian Fluids
• Time-independent Fluids
• Pseudoplastic (Blood Plasma, syrups, inks)
• Dilatant (Starch in water)
• Bingham (catsup, mustard, toothpaste)
• Carbon nanotube-based nanofluids
• Time-dependent Fluids
• Electrorheological (behavior changes due to electric field, particles are present)
• Magnetorheological (iron powders in fluid)
• http://en.wikipedia.org/wiki/Power-law_fluid
Viscosity MeasurementRotating Drum Viscometer

Drum

--Velocity at cup wall is zero

--Fluid near drum moves with velocity of drum

--du/dy is known

Cup

dy

Viscosity MeasurementCapillary Tube Viscometer
• Capillary Tube
• Makes use of pressure drop to determine viscosity

Equation 2-5:

Viscosity MeasurementCapillary Tube Viscometer

Upper timing mark

Filled with test fluid

Suction draws fluid through

bulb and above timing mark

Suction removed and fluid

flows by gravity

Time is recorded between

upper and lower marks

Bulb

Lower timing mark

Viscosity MeasurementFalling Ball Viscometer
• Viscosity is determined by noting the amount of time a ball takes to travel between two lines
Viscosity MeasurementSaybolt Universal Viscometer
• Ease of fluid flow through orifice is an indication of viscosity
• Measurement is not based on definition of viscosity
• Results are relative, so a standard sample is used for calibration
• Fast and easy
Saybolt Viscosity
• Saybolt Equations:
• (cS) = 0.226t - 195/t, t< 100 SUS
• (cS) = 0.220t – 135/t, t> 100 SUS

t, amount of time (seconds, SUS, Saybolt Universal Seconds) it takes for 60 cm3 to flow through orifice (Saybolt viscometer)

• Example:
• An oil has a viscosity of 230 SUS at 150° F. Compute the viscosity in cS and cP. Specific gravity is 0.9.

http://www.liquidcontrol.com/etoolbox/viscosity.aspx

Viscosity Chart

m Force

Temp. ° F

http://webbook.nist.gov/chemistry/fluid/

Temp. C

http://www.klassenhydraulics.com/Reference/viscositychart.htm

Hydraulics Fluids for Fluid Power Systems
• Fluid Power
• Pneumatics: air-type systems
• Hydraulics: liquid-type systems
• Hydraulic Fluids:
• Petroleum oils
• Water-glycol fluids
• High water based fluids (HWBF)
• Silicone fluids
• Synthetic oils

http://en.wikipedia.org/wiki/Hydraulic_fluid

Characteristics of Hydraulic Fluids
• Lubricating capability
• Cleanliness
• Chemical stability
• Non-corrosiveness
• Ability to resist growth of bacteria
• Ecologically acceptable
• Low compressibility

http://www.castrol.com/castrol/sectiongenericarticle.do?categoryId=9045295&contentId=7080615

Hydraulic Fluids
• HWBF
• Fire resistant
• ~40% oil in water
• Water-glycol fluids
• Fire resistant
• 35 to 50% water

https://engineering.purdue.edu/Maha/index.html

Hydraulic Fluids
• Petroleum Oils
• SAE 10 W, SAE 20-20W (W means rated at maximum viscosity and cold temperatures)
• Engine oils
• Additives are required to avoid growth of bacteria
• Silicone Fluids
• For high temperature applications