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Marine Engineering stage 1 > Dr Murphy > Flashcards

Dr Murphy Flashcards

1
Q

Approx how may kPa and how many bar are in 1 atmos?

A

100kPa

1bar

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2
Q

Give gauge pressure in terms of absolute and atmospheric pressure

A

Absolute pressure minus atmospheric pressure

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3
Q

What is meant by a reversible process?

A

Both the fluid and the surroundings can always be restored to initial conditions

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4
Q

On a diagram how is a reversible and how is an irreversible reaction shown?

A

Reversible solid line

Irreversible dotted line

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5
Q

Give the first law of thermodynamics in an equation

A

Qin - Wout =ΔU

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6
Q

Give the non flow energy equation

A

Qin- Wout = ΔU

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7
Q

Give the steady flow energy equation (simplified)

A

Q’in - W’out = ΔKE’ + ΔPE’ + ΔH’

Where ‘ represents dot {first differential wrt time}

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8
Q

Give the equation for m dot

A

=CAρ

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9
Q

Give an equation for h

A

h=Pv+u

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10
Q

Describe a perfect gas

A

Theoretically, ideally behaved gas.

Temp vastly in excess of evaporation point.

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11
Q

Give boyles law and describe what happens to the graph as temp increases.

A

At constant temp: Pv=constant.

As temp increases curve moves further from origin

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12
Q

Give Charles’s laws and the combination if the 2. What is the constant in the combination?

A

At constant P: v/T=constant.
At constant v: P/t=constant.
Therefore Pv/t=constant=R=gas constant

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13
Q

Give the equation of state

A

PV=mRT

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14
Q

Give the equation for specific heat capacity.

A

Q=mCΔT

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15
Q

Give the equations for the 2 specific heat capacities multiplied by the change in temp.

A

Cv(T2-T1)=u2-u1

Cp(T2-T1)=h2-h1

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16
Q

What does Cp equal in terms of Cv?

A

Cp=R+Cv

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17
Q

What does isochoric mean?

A

Constant volume

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18
Q

What does isobaric mean?

A

Constant pressure

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19
Q

What does isothermal mean?

A

Constant temp

20
Q

What does adiabtaic or isentropic mean?

A

No heat loss

21
Q

What is work done equal to?

A

Area under Pv curve. So W=integral of Pdv

22
Q

Give the efficiency of a heat engine.

A

1-Qout/Qin

23
Q

What is a heat engine?

A

A thermodynamic system to which net heat is transferred and from which net work is produced.

24
Q

What is a heat pump?

A

A system that removes heat from a low temperature body and delivers heat to a high temp body and receives external energy as work or heat from surroundings

25
Q

Give the general equation for coefficient of performance

A

COP=desired product/required input

26
Q

What is Q on a temperature entropy diagram?

A

Area under curve. Q=integral of Tds

27
Q

Give a condition for ΔS

A

ΔS greater than or equal to 0

28
Q

On a Ts graph which is steeper: constant vol or constant pres? Why?

A

Constant vol is steeper. Q=CvΔT, Q=CpΔT. Cp>Cv. For const pres there will be a volume change so work done so more heat required for same ΔT. So for the same ΔT more work is done for constant pressure process so must have greater Δs so curve shallower so goes further along graph.

29
Q

What is the significance of the Carnot efficiency?

A

The max poss efficiency for any heat engine operating between 2 thermal energy reservoirs

30
Q

What does the Carnot cycle look like on a Ts graph?

A

Rectangle

31
Q

What are the four stages in the Carnot cycle?

A

1-2) isothermal heat addition
2-3) isentropic exampansion
3-4) isothermal heat rejection
4-1) isentropic compression

32
Q

Give the Carnot efficiency

A

η=1-Tl/Th=Wout/Qin

33
Q

Give some assumptions of the Otto cycle.

A

-closed system so use NFEE
-perfect gas
Assume compression and expansion are adiabatic

34
Q

Give the 4 stages of an Otto cycle.

A

1-2) isentropic compression
2-3) const vol heating
3-4) isentropic expansion
4-1) const vol cooling

35
Q

Which diagram do we use to represent the Otto cycle? Why?

A

Pv. Can measure P. Know where piston is so know volume

36
Q

What is the compression ratio?

A

Realationship between 2 volumes. V1/V2

37
Q

Give the four stages of a diesel cycle.

A

1-2) isentropic compression
2-3) const pres heating
3-4) isentropic expansion
4-1) const vol cooling

38
Q

What is the dual cycle?

A

Combination of Otto and diesel to give a cycle most similar to that in real life.

39
Q

Give the five stages of the dual cycle.

A 
1-2) isentropic compression
2-3) const vol heating
3-4) const pres heating
4-5) isentropic expansion
5-1) const vol cooling
40
Q

Give the efficiency of the dual cycle.

A

η=1-Qout/Qin=1-Cv(T5-T1)/(Cv(T3-T2)+Cp(T4-T3))

41
Q

Give the efficiency of the joule/brayton cycle.

A

η=Wnet/Qin=(T4-T5)/(T3-T2)

42
Q

What is the latent heat of vaporisation?

A

The heat required to turn saturated water completely into saturated vapour

43
Q

Which diagram do we use for joule/brayton? And how may stages are there?

A

Ts. Five stages

44
Q

Giv ethe first law of thermodynamics.

A

Conservation of energy. Energy cannot be created to destroyed.

45
Q

Give the second law of thermodynamics

A

Heat will naturally migrate from a high temp to a low temp

Marine Engineering stage 1 (2 decks)

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