MECH 213 - 8.31.2007

MECH 213 - 8.31.2007 - • Fourier’s Law – heat...

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MECH 213 – August 31, 2007 Internal Energy – (U) Energy reactions that are microscopic o When divided by mass u Kinetic Energy (KE) (ke) Potential Energy (PE) (pe) E = U + KE + PE o Specific total energy e = u + ke + pe Closed System Open System (bold m and V have dots) m = ρV Mass flow rate ( m = ρ V ) where V is volumetric flow rate Conservation of Mass m 2 = m 1 Steady state Σ m in – Σ m out = 0 General: Σ m in – Σ m out = d/dt (m sys ) Heat Transfer (Q) o Any energy crossing the system boundary due to a temperature change or temperature gradient o Adiabatic – no heat transfer involved in a system or process o Adiabatic + Quasi-static (Q-S) Isentropic process o Any Q into system is positive o Q-dot = rate of heat transfer o Q = integral of Q-dot from 0 to t If Q-dot is constant Q = Q-dot Δt o Path function δQ = infinitesimal amount of heat transfer integral of small delta Q from state 1 to 2 is defined as Q o Q/m = q and Q-dot/m-dot = q o MODES OF HEAT TRANSFER Conduction – Q with two things in direct contact
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Unformatted text preview: • Fourier’s Law – heat transfer is Q-dot = k t A(ΔT/Δx) where k t is thermal conductivity • k t A(dT/dx) Convection – mostly in liquids, relies on the fact that particles could move • Q-dot = hA(T s- T ∞ ) where h is a huge function, A is surface Area Radiation – • Q-dot = ΕσA(T s- T ∞ ) Work – any energy crossing a system boundary that is not heat transfer o Forms of Work Flow work/flow energy • How much energy it takes to push it into the control volume o Pressure/density Mechanical energy – energy that can be converted to work if using a perfect turbine • e mech ≡ pressure/ρ + ke + pe o W = work W = W/m o W-dot = power = rate of work o Δw => integral of delta w from 1 to 2 is work o W = FΔx = integral Fdx from x1 to x2 w = integral F/A x Adx from x1 to x2 = integral of pdV from V to V Δx F p 1 p 2 2 t...
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MECH 213 - 8.31.2007 - • Fourier’s Law – heat...

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