Comprehensive

Question 1

What is the definition of humidity ratio (ω)?

Answer 1

ω = lb_water / lb_dry_air. EXAM TRAP: Do not confuse with relative humidity; ω comes from Pv, not RH directly.

Question 2

How do you find mass of water vapor in a volume of air?

Answer 2

m_water = ω × ρ_air × V. EXAM TRAP: Density must be dry air density, not moist air density.

Question 3

What psychrometric properties are read directly from the chart?

Answer 3

ω, h, v, RH, WB. EXAM TRAP: Do not calculate if chart is explicitly allowed.

Question 4

Steady-flow energy equation for heat exchangers (no work/loss)?

Answer 4

ṁ1(h1i − h1e) = ṁ2(h2e − h2i). EXAM TRAP: No shaft work term.

Question 5

Carnot efficiency for a heat engine?

Answer 5

η = 1 − TL/TH (absolute). EXAM TRAP: Must use Rankine or Kelvin.

Question 6

COP definition for refrigerator?

Answer 6

COP_ref = Q_L / W_in. EXAM TRAP: Refrigerators use heat removed, not rejected.

Question 7

COP definition for heat pump?

Answer 7

COP_HP = Q_H / W_in. EXAM TRAP: Heating mode ≠ cooling mode.

Question 8

Maximum COP (reversed Carnot)?

Answer 8

COP_ref = TL/(TH−TL), COP_HP = TH/(TH−TL). EXAM TRAP: Absolute temps only.

Question 9

What does 1 ton of refrigeration equal?

Answer 9

12,000 Btu/hr = 3.516 kW. EXAM TRAP: Tons ≠ mass.

Question 10

What is an isentropic process?

Answer 10

Δs = 0 (reversible adiabatic). EXAM TRAP: Adiabatic alone ≠ isentropic.

Question 11

What is an isenthalpic process?

Answer 11

Δh = 0 (throttling valve). EXAM TRAP: Temperature may change.

Question 12

What happens across an expansion valve?

Answer 12

Pressure drops at constant h → two-phase mixture. EXAM TRAP: Not isentropic.

Question 13

How do you find refrigerant quality after throttling?

Answer 13

x = (h − hf)/hfg. EXAM TRAP: Use downstream pressure properties.

Question 14

Isentropic temperature relation (ideal gas)?

Answer 14

T2/T1 = (P2/P1)^((k−1)/k). EXAM TRAP: Only valid for ideal gas.

Question 15

Isentropic efficiency of compressor?

Answer 15

η = W_isentropic / W_actual. EXAM TRAP: Compressor uses MORE actual work.

Question 16

Newton’s Law of Cooling?

Answer 16

Q = hA(Ts − T∞). EXAM TRAP: Sign convention.

Question 17

Lumped capacitance time constant?

Answer 17

τ = (ρVc_p)/(hA). EXAM TRAP: Valid only when Bi < 0.1.

Question 18

Fin heat transfer equation (straight fin)?

Answer 18

Q = √(hPkAc)(Tb − T∞)tanh(mL). EXAM TRAP: Corrected length Lc often used.

Question 19

Nusselt number definition?

Answer 19

Nu = hL/k. EXAM TRAP: Characteristic length matters.

Question 20

Grashof number meaning?

Answer 20

Buoyancy / viscous forces. EXAM TRAP: Only for free convection.

Question 21

Pitot tube velocity equation?

Answer 21

V = C√(ΔP/ρ). EXAM TRAP: Convert inches of water correctly.

Question 22

Manometer pressure difference equation?

Answer 22

ΔP = (ρ2 − ρ1)gh. EXAM TRAP: Use density difference.

Question 23

When is incompressible flow valid?

Answer 23

Mach ≤ 0.3. EXAM TRAP: Air above this is compressible.

Question 24

Darcy–Weisbach equation?

Answer 24

hf = f(L/D)(V²/2g). EXAM TRAP: hf is head loss, not pressure.

Question 25

Pump horsepower equation?

Answer 25

HP = (QΔP)/(3960η). EXAM TRAP: Use pressure in psi.

Question 26

Sensible heat ratio (SHR)?

Answer 26

SHR = sensible / total heat. EXAM TRAP: Total includes latent.

Question 27

Moist air enthalpy equation?

Answer 27

h = 0.24T + ω(1061 + 0.444T). EXAM TRAP: T in °F.

Question 28

Henry’s Law?

Answer 28

Pi = hxi. EXAM TRAP: Valid only at low concentrations.

Question 29

Gibbs Phase Rule?

Answer 29

F = C − P + 2. EXAM TRAP: Non-reacting systems only.

Question 30

Kelvin–Planck statement?

Answer 30

No engine converts all heat to work. EXAM TRAP: Efficiency < 100%.

Question 31

Clausius statement?

Answer 31

Heat won’t flow cold → hot without work. EXAM TRAP: Defines refrigeration need.

Question 32

Why does mass flow cancel in COP?

Answer 32

Same ṁ through cycle. EXAM TRAP: Don’t overthink units.