First Law of Thermodynamics Flashcards
(20 cards)
What does the first law state?
the total quantity of energy is constant, but energy may change forms
deltaE = Ein - Eout = deltaU + deltaEexternal
Definition of closed system.
deltaU = Q + W
Define W > 0
work done on system, compression
Define W < 0
work done by system, expansion
Q > 0
Heat in, adsorption
Q < 0
Heat out, release
What is enthalpy?
H, term used for characterizing then energy of a mechanically reversible, closed system process and is equivalent to the total heat content of the system
H = U + (deltaPV)
Define isochoric equations.
deltaV = 0 W = 0 deltaU = Cv(deltaT) = Q
Define isobaric equations.
deltaP = 0 Q = H = deltaH +P(deltaV) deltaH = Cp(deltaT)
Define isothermal equations.
deltaT = 0 deltaU = 0 Q = -W
Define adiabatic equations.
Q = 0 deltaU = W
Describe mass balance for open systems
the control volume is separated from the surroundings by the control surface. the rate of change within the control volume equals the net rate of mass flow into the control volume
Define the continuity equation.
m(dot) = uA/V
Define the energy balance equation for open systems.
accumulation term = specific enthalpy + .5velocity^2 + zg all multiplied by mass flow rate) in - out + Q(dot) + W(dot)
Describe the Single Inlet case.
there is a controlled volume in but no volume out
Describe the Single Outlet case.
there is a controlled volume out but no volume in
Describe the Steady Flow case.
No mass/volume accumulation anywhere in the system (fluid in pipes and rigid in container)
Describe the Steady Flow and Steady State case.
other properties besides mass or volume can change with time.
Ex: cold water in and hot water out with control
Describe the Adiabatic Case.
The system is insulated, no heat exchange with the surroundings, Q = 0
Describe the No Work Case.
System volume changes through the movement of the piston
