chapter_8_hydrtherm

# chapter_8_hydrtherm - ME 375 System Modeling and Analysis...

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ME 375 System Modeling and Analysis Section 8 – Hydraulic and Thermal Systems Spring 2009 School of Mechanical Engineering Douglas E. Adams Associate Professor = !

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Key Points to Remember Three primary elements of interest in hydraulics Inertia ( fluid inertia ) Stiffness ( fluid capacitance ) Dissipation ( flow resistance ) When fluid is incompressible, lumped models can be used We use Laws of Thermodynamics (1st law and continuity) Only two primary elements in thermal systems Stiffness ( thermal capacitance ) Dissipation ( thermal resistance ) The rate of heat flow is analogous to current/velocity and heat is analogous to displacement/charge © 2009 D. E. Adams ME 375 – Hydraulic and thermal systems 8.1
Hydraulic Element Laws (linear) Each lumped (linear) element has its own characteristic Hydraulic capacitance is analogous to the inverse of stiffness just as in the electrical domain V P I w C R I Think EFFORT and FLOW V P R V P 1/C Note that these are straight lines with constant slopes © 2009 D. E. Adams ME 375 – Hydraulic and thermal systems 8.2

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Hydraulic Resistance/Capacitance/Inertia Important analogies Hydraulic capacitance/resistance C R © 2009 D. E. Adams ME 375 – Hydraulic and thermal systems 8.3
Hydraulic Resistance/Capacitance/Inertia Important analogies Hydraulic inertia I P 1 P 2 © 2009 D. E. Adams ME 375 – Hydraulic and thermal systems 8.4

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Hydraulic EOMs for Incompressible Fluids We need two laws to derive hydraulic EOMs: Conservation of mass (~ Kirchoff’s Current Law) Newton’s 2 nd law (~Kirchoff’s Voltage law) Hydraulic EOMs are found using mass / volume balance and appear naturally in state variable form.
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