fpcs 5.pdf
TRANSCRIPT
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Class #4
Hydraulic Fluid Properties
ME 4232:
FLUID POWER CONTROLS LAB
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Notes
Lab 2 Regrades
Regrading Policy Undergraduate Research Position:
Compressed Air Energy Storage Testbed
Upcoming Labs:
Lab 7: Bleed Off Circuit
Lab 8: Check Valves: Direct & Pilot Operated
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Agenda
Feedback: Interesting / Challenging
Check Valves Roles of Hydraulic Fluid
Fluid Properties
Viscosity
Viscous Friction
Leakage
Bulk Modulus
Inertia
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FeedbackInteresting
Ingenious Component
Designs
Freedom in Lab = Learning
Understandable Labs
Practical Applications Power of Hydraulics
Variety of Configurations
Matlab for Data Analysis
In Class Activities
Analogies to Electrical
Confusing/Challenging
Learning Matlab
Circuit Diagrams
Understanding Circuit
Operation
Frequency of Labs &Reports
Lab Handout Wording
Cavitation TA Language Challenges
Want Lecture Schedule
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Check Valves
Allows flow only one direction
Main uses are: by-pass components
cylinder locking
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Pilot Operated (open) Check Valve
Allows reverse flow when
pilot pressure is turned on
Enables cylinder locking
Consider force balance to
calculate what pressures
needed to open the check
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Cartridge Valves
Assemble Components
into Circuits in a
Manifold Manifold = metal block
with internal passages
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Cartridge Valves (screw in)
Check Valve Pilot Operated Check Valve
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Cartridge Valve (Screw In)
Relief Valve Pilot Operated Relief Valve
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Roles of Hydraulic Fluid
Primary:
Transmit Power
Secondary:
Lubrication
Sealing
Heat Transfer / Cooling
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Hydraulic Fluid Properties
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Viscosity Index
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Pipe Resistance
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Friction Factor Moody Diagram
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Example: 3 MW Wind Turbine, 35 MPaHydraulic Fluid: ISO 46
= 46 cSt
= 870 kg/m3
Pipe: 100 m long, 20 cm diameter, perfectly smooth
Find:
1. Determine the flow rate and average fluidvelocity.
2. Calculate the Reynolds number. Laminar or
Turbulent?
3. Find the friction factor.
4. Calculate the viscous pressure drop.
5. How does this compare to the pressure
difference due to gravity?
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Hydraulic Connectors
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Example
Q1: Assuming the leakage past the spool is small, find the pressureP
Q2: How long does L need to be for the leakage to be < 0.01% of the
pump flow?
Fluid Properties:
= 870 kg/m3
= 46 x 10-6 m2/s
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Efficiency vs Viscosity vs Temperature
For hydraulic components (e.g. pumps,
motors, actuators) with moving parts,there is always a trade-off between
Volumetric efficiency [leakage]
Mechanical Efficiency [friction]
Total efficiencies for pumps and motorsgiven by:
Optimal viscosity exists for a givencomponent (and system)
Optimal viscosity
However, viscosity changes dramaticallyby temperature!
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Bulk Modulus
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Research Topic:
Fluid Compressibility in Digital Hydraulics Major Form of Energy Loss
Widely Varying Bulk Modulus Models
Goal: Understand the Role of Fluid Compressibility on the
Performance and Efficiency of Switch-Mode Circuits
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Bulk Modulus Models
Bulk Modulus:
Many Models Available in Literature
dPV
dV
Basic: Akers et al.1 1 1 1 1
T a a a
e T T a T a
V V V V
V V V
e
P
R P
o
e
o
PR
P
R PP P
11
1 1111
e
o o
P
P P R c P P P
Merritt
Hayward
Cho et al.0 5 10 15 20 25 30 35
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
Pressure (MPa)
BulkModulus
(GPa)
Bulk Modulus vs. Pressure for R = 0.020
Yu et al.
Cho et al.
Hayward
Merritt
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Experimental
Validation
Vary: Entrained Air, Pressure, Vswitched
Measure: Density, Bulk Modulus, Efficiency
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Bulk Modulus Calculation
Based on Sonic Velocity:
Cross-correlation of Pressure Waves
2
2
e c
T