Engr Thermo Flashcards
This equation represents the change in energy of a system (ΔE) w.r.t the heat added to the system (Q) and the work done by the system (W).
ΔE=Q−W
This equation represents the change in internal energy (ΔU) of a system w.r.t to the heat added to the system (Q) and the work done by the system (W).
ΔU=Q−W
This equation calculates the work done by a system undergoing a change in volume (ΔV) against a pressure (P)
W=PΔV
This equation represents the enthalpy (H) of a system w.r.t. internal energy (U), pressure (P), and volume (V) (P-V WORK)
H=U+PV
h=u+Pv
These equations help to determine heat transfer (Q) using specific heat capacities (Cp for isobaric, Cv for isochoric)).
Q=mCpΔT (for constant pressure)
Q=mCvΔT (for constant volume)
Heat by conduction (Qcond)
Qcond=kA(ΔT/Δx)
Heat by convection (Qconv)
Q=hAΔT
Heat by radiation (Qr)
Qr=εσA (T^4 −T∞^4)
Heat transfer as a function of internal heat (u) and work (W)
Q=m(u2−u1)+W=m(u2+Pv2−u1−Pv1)
Enthalpy for two-phase mixture (h)
h = ((1-x)hf) + (xhg)
Work being done at linearly varying pressure (W)
W=(1/2)(P1+P2)(V2−V1)
Finding quality/mass fraction of vapor (x)
x = (h - hf) / hfg
What does it mean when there is a dot on top of a variable
Divide by Δt (change in time), will be denoted generally as a “rate”
What does it mean when the variable is in a lowercase?
Divide by m (mass), will be noted as “per unit mass,” applicable in situations where mass remains constant
Conservation of mechanical energy between two points in a system
E2-E1 =U2-U1 +1/2m(V2^2-V1^2) +mg(Z2-Z1)
Continuity and Energy eqns. when there are 3 storage spaces, no mass enters/leaves, one Wout term (B), two Win terms (A,C)
mcv = mA+mB+mC = in - out = 0
Ecv = EA + EB + EC = in - out = QA + QC - WB
Continuity and Energy eqns. when steady-state conditions with a singular flow are applied
0 = mi - me , mi = me = m
0 = Q- W + mihi - mehe, q + hi = w + he
Continuity and Energy eqns. when steady-state conditions with multiple flows (A,B) are applied into a mixing chamber (C)
0 = mA+mB -mC, mC = mA+mB
0 = mAhA + mBhB -mC*hC + Q,
q = hC-hA-hB
