1st Year: May exam Flashcards
Learning the important equations
First Law of Thermodynamics:
Q − W = ∆U + ∆KE + ∆P E + ∆SE
First Law of Thermodynamics for a cyclic process
∑Q = ∑W
Equation of state for a perfect gas
P V = mRT
or
P = ρRT
Change in internal energy:
∆U = mCv∆T
Change in enthalpy:
∆H = mCp∆T
Isothermal Process
Constant Temperature
Process Path: P V = C
Work: W = mRTln(V2/V1)
Adiabatic Process
No Heat Transfer
Q=0
Process Path: P V ^γ = C
Work: W =(P1V1 − P2V2)/γ − 1
Polytropic Process
Process Path: P V ^n = C
Work: W =(P1V1 − P2V2)/n-1
Relating ratios of T, V, and P…
T2/T1 = (V1/V2)^γ−1 = (P2/P1)^y-1/y
change γ to n for polytropic processes
y =
Cp/Cv
normally equals 1.4
R =
Cp - Cv
Cv =
R / y-1
Cp =
R*y / y-1
Constant Pressure Process: Q=
mCp∆T
Mass flow rate
m* = VAρ
Volume flow rate
Q = AV
Bernoulli’s equation
P1/ρ + V1^2/2 + gZ1 = P2/ρ + V2^2/2 + gZ2
First Law of Thermodynamics for a Closed process
Q-W=∆U
more specifically:
Q-(Wshaft +Wdisp)=∆U
Units of Volume flow rate:
m^3/s
Units of Mass flow rate
Kg/s
Effect of nozzle on tube opening
Are decreases so velocity increases as flow rate constant.
What does a steady flow process mean?
Flow RATE constant. ie Q or M
Not necessarily velocity constant
What is Guage pressure?
The amount the pressure is over atmospheric.
What is Vacuum pressure
The amount the pressure is under atmospheric.
