2nd Year Closed/Open Systems

Question 1

Closed System:

Work =

Answer 1

Integral (P) dv

Question 2

First Law

Answer 2

Energy Can only be conserved:

Q - W = ΔU + ΔKE + ΔPE

Question 3

ΔU =

Answer 3

Cv m ΔT

Question 4

ΔH =

Answer 4

Cp m ΔT

Question 5

Perfect Gas laws:

Answer 5

PV = mRT
Pv = RT
PV^y = const 
R = Cp - Cv

Question 6

Constant Volume

Closed

Answer 6

ISOMETRIC
W=0
Q=m Cv ΔT

Question 7

Constant Pressure

Closed

Answer 7

ISOBARIC
W = PΔV
Q= m Cp ΔT

Question 8

Constant Temp

Closed

Answer 8

ISOTHERMAL
W = Q
ΔU = 0
W = P2V2Ln(V2/V1) = mRTln(V2/V1)

Question 9

Constant Entorpy

Answer 9

ISENTROPIC
Q=0
W = (P2V2 - P1V1)/1-y

POLYTROPIC is the same but not with gamma.

Question 10

Open System

SFEE

Answer 10

Q - W = ΔH + ΔKE + ΔPE

Question 11

Open System

Work =

Answer 11

-integral (V) dp

Question 12

mas flow rate =

Answer 12

density * Area* Velocity

Question 13

When isothermal, work requirement for compression is…

Answer 13

LOWEST!

Question 14

When isothermal, work output for expansion is…

Answer 14

LARGEST!

Question 15

Nozzles:

Answer 15

Velocity increased

Pressure Decreased

Question 16

Diffusers

Answer 16

Velocity decreases

Pressure Increases

Question 17

Nozzle and diffuser assumptions:

Answer 17

Q= 0
W=O
ΔPE=0
(SFEE = ΔH + ΔEK = 0)

Question 18

Compressors: (work?)

Answer 18

ON fluid

Question 19

Turbines (work?)

Answer 19

BY fluid (on shaft)

Question 20

work and compressor assumptions:

Answer 20

Q=0
ΔKE=0
ΔPE=0
SFEE = -W=ΔH (+ΔKE if given in question)

W=-∫P dv= - (myRT1)/(y-1)*((P2/P1)^((y-1)/y) - 1)

Question 21

Mixing Process:

Answer 21

m(in) = m(out)

SFEE ΔH=0 = m Cp ΔT =0

Question 22

Heat Exchangers

Answer 22

Depending on how system is defined…
SFEE = ΔH=0
or Q= ΔH (if taken across boundries)

Question 23

Throttling Valve

Answer 23

SFEE ΔH=0