Thermodynamics

Question 1

First law of thermodynamics energy balance

Answer 1

H1 + KE1 + PE1 = H2 + KE2 + PE2 + q + W

Total energy in = Total energy out

-q = heat loss
-W = Turbine work
-H = enthalpy

Question 2

What is enthalpy?

Answer 2

-Total heat and heat content of a substance
-Sum of internal energy and flow work

-h = u + Pv

Question 3

Ideal gas formula

Answer 3

PV = mRT

-P = absolute pressure
-V = volume
-m = mass
-R = gas constant
-T = absolute temperature

Question 4

Any process involving ideal gas (PVT)

Answer 4

(P1V1/T1) = (P2V2/T2) = mR

Question 5

Any process involving ideal gas (U)

Answer 5

U2 - U1 = mCv(T2-T1)

Question 6

Any process involving ideal gas (H)

Answer 6

H2 - H1 = mCp(T2-T1)

Question 7

Any process involving ideal gas (S)

Answer 7

S2 - S1 = mCpln(T2/T1) - mRln(P2/P1)

Question 8

Reversible process

Answer 8

No friction loss

Question 9

Adiabatic process

Answer 9

No heat loss, no heat gain, completely insulated system

Question 10

Adiabatic throttling process

Answer 10

-Constant enthalpy or isenthalpic
-h2=h1 and t2=t1

Question 11

Particular value n for isobaric process

Answer 11

n = 0

Question 12

Particular value n for isothermal process

Answer 12

n = 1

Question 13

Particular value n for isentropic (adiabatic) process

Answer 13

n = k

Question 14

Particular value n for polytropic process

Answer 14

n > 1

Question 15

Particular value n for isometric or isochoric process

Answer 15

n = ∞

Question 16

Definition of subcooled liquid

Answer 16

Liquid whose temperature is lower than the sat. temperature at the given pressure

Question 17

Relationship between vf , vg, and vfg

Answer 17

vfg = vg - vf

• where v = specific volume
• applies to u, h, and s

Question 18

Quality or dryness factor x

Answer 18

x = mv/(mv+mL) = mv/mT
-mv=mass of vapor
-mL=mass of liquid
-mT=total mass of mixture

Question 19

Wetness given dryness factor

Answer 19

Wetness = 1-x

Question 20

Properties of a mixture (v,h,u,s)

Answer 20

v = vf + x vfg

Question 21

Formula for specific heat at constant pressure, cp

Answer 21

Rk/ (k-1)
-R = gas constant
-k = specific heat ratio

Question 22

Formula for specific heat at constant volume, cv

Answer 22

R/(k-1)

Question 23

Pressure and temperature relation for ideal gas (all processes)

Answer 23

T2/T1 = (P2/P1) ^ ( n-1 / n )
-n = particular value

Question 24

Temperature and volume relation for ideal gas (all processes)

Answer 24

T2/T1 = (V1/V2) ^ (n-1)

Question 25

Entropy change under constant pressure

Answer 25

mCpln(T2/T1)

Question 26

Entropy change under constant volume

Answer 26

mCvln(T2/T1)

Question 27

Entropy change under constant temperature

Answer 27

mRln(V2/V1)