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Year 3 > Thermofluids > Flashcards

Thermofluids Flashcards

1
Q

What is Drag Force?

A
  • force that flowing liquid exerts on a body in flow direction
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2
Q

What is Lift Force?

A

Force acting perpendicular to the flow direction.
- acts against gravity to support the weight of the object in fluid.
- change in flow direction creates lift force in opposite direction.

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3
Q

What is the Drag Coefficient equation?
- what do the V and A stand for.

A

Cd = Fd / 1/2 p V^2 A
V = Speed of the object moving through the fluid.
A = Reference Area / Frontal Area - area perpendicular to the flow.

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4
Q

What is the Lift Coefficient Equation?
What do V & A stand for?

A

CL = FL / 1/2 p V^2 A
V = velocity of object moving through the fluid
A = Planform area - Area that would be seen if looking down

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5
Q

(Q13) What are the assumption for: Navier Stokes Questions?

A
  • steady flow (d() / dt = 0)
  • incompressible fluid ( p = constant)
  • fluid flows in x-direction ( v = 0, w = 0)
  • no variation in velocity in x- direction ( u = constant)
  • gravity working in -y (gx = 0, gy = -g, gz = 0)
  • viscous fluid (backwards y = 0)
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6
Q

(Q13) What are the steps needed to complete a: Navier Stokes Question?

A
  1. Sketch diagram.
  2. List all assumptions.
  3. Apply continuity equitation.
  4. Apply momentum equation.
  5. Solve resulting differential equation by double integration.
  6. Apply boundary conditions to obtain constants.
  7. Substitute in constants.
  8. Calculate for required parameters.
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7
Q

What is a Heat Engine cycle?

A
  • system that converts heat of thermal energy to mechanical energy
  • mechanical energy then used to do mechanical work
  • bring substance from high temp to low temp
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8
Q

What is the 4 stages of a Heat Engine Cycle

A

1 - Recieves Heat
2 - Converts part of the heat to work
3 - rejects remaining waste to low temp sink
4 - cycles

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9
Q

Explain the 4 main parts of a heat engine:
1. Heat Source
2. Working Substance
3. Thermodynamic Process
4. Efficiency

A
  1. Heat Source - heat engine works between hot and cold reservoirs
  2. Working Substance - engine using working substance with finite heat capacity that abroad’s heat from hot tank,
  3. Thermodynamic Process - 1: working substance expands and contracts. 2: heat absorbed from hot and rejected to cold. 3: supplied heat converted to work.
  4. Efficiency: determines how much useful work it does for given heat.
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10
Q

What are the 4 reversible processes in: carnot cycle

A

1-2: isothermal heat addition
2-3: isentropic expansion
3-4: isothermal heat rejection
4-1: isentropic compression (repeat)

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11
Q

(Q4) What are the steps to answer a carnot cycle question if given Qh & QL

A
  1. calculate thermal eff. n = 1- (Qout/Qin)
  2. calculate power output. Went,out = n * Qin
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12
Q

(Q5) What are the steps to answer a carnot cycle question if given Th & TL & Qh?

A
  1. calculate therm eff. n = 1 - (Qout/Qin)
  2. calculate heat reject. Qh / QL = Th / TL => QL = Qh / (Th / TL)
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13
Q

what are the 4 stages of a 4-stroke reciprocating engine?

A
  1. Intake - Fuel enters, expands, piston moves down
  2. Compression - Piston moves up, compresses fuel.
  3. Ignition - Spark ignites fuel, piston moves down, provides useful work.
    4- Exhaust - Waste exits, cycle repeats.
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14
Q

Reciprocating Engine Components: What is Intake and Exhaust?

A

Intake: Draws air-fuel mix in.
Exhaust: Expels waste.

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15
Q

Reciprocating Engine Components: What is TDC and BDC?

A

TDC - Top Dead Centre: Position of piston that forms smallest volume.
BDC - Bottom Dead Centre: Forms largest volume.

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16
Q

Reciprocating Engine Components: What is Stroke and Bore?

A

Stroke: Largest distance piston can travel.
Bore: Diameter of piston.

17
Q

(Q7) Steps to solve Otto Cycle Question.
Max temp and pressure of cycle.

A

1-2:
- interpolation to find T2, U2.
- table to find vr1.
- vr2 = v1 = v1 / r
P1v1 / T1 = P2v2 / T2 => P2=P1 (T2/T1)(v1/v2)
v1/v2 = r
2-3:
- qin = U3 - U2
-interpolation to fine T3, v3.
-P3v3/T3 = P2v2/T2 => P3=P2(T3/T2)(v2/v3).
v2/v3 = 1

18
Q

(Q7) Steps to solve Otto Cycle Question.
Net work output. (4-1)

A

net work = net heat @ cycle 4.
- v4/v3 = r => v4 = r * v3
- interpolate for T4, U4.
- qout = u4 - u1
-wnet = qnet => qin- qout

19
Q

(Q7) Steps to solve Otto Cycle Question.
Thermal Efficiency

A

nth = wnet / qin

20
Q

(Q7)Steps to solve Otto Cycle Question.
MEP

A

v1 = R * T1 / P1
MEP = wnet / v1 (1 - (1/r))

21
Q

(Q8) Steps to solve Diesel Cycle Question (Cold air assumptions).
Temp and pressure at end of each cycle.

A

1-2:
- use table
- v2 = v1 / r
- T2 = T1 (v1 / v2)^k-1. - v1/v2 = r
- P2 =P1 (v1 / v2)^k. - v1/v2 = r

2-3:
- P3 = P2
- P3v3 /T3 = P2v2 / T2 => T3 = T2 ( v3 / v2). - v3/v2 = rc

3-4:
T4 = T3(v3 / v4)^k-1. - v3 = rc * v2, v4 = v1.
P4 = P3 (v3/ v4)^k

22
Q

(Q8) Steps to solve Diesel Cycle Question (Cold air assumptions).
net work output

A

net work = net heat transfer
mass of air = m1 - P1 * v1 / R * T1
2-3:
- Qin = m(h3-h2) = m(cp)(T3 - T2)
4-1:
-Qout = m(u4 - u1) = m(cv)(T4 - T1)

wnet = Qin - Qout

23
Q

(Q8) Steps to solve Diesel Cycle Question (Cold air assumptions).
thermal efficiency

A

nth = wnet / Qin

24
Q

(Q8) Steps to solve Diesel Cycle Question (Cold air assumptions).
Mean effective pressure.

A

MEP = wnet,out / v(max) - v(min)
=> wnet,out / v1 - v2

25
Q

(Q16) How to solve LMTD counter flow question.
- length of heat exchanger required

A
  1. Q = [m * c(p) ( Tout - Tin)] - for water
  2. Q = [m * c(p) (Tin - Tout)] - for thermal
    => Tout = Tin - (Q / m * c(p))
  3. change T(Lm) = change T1 - change T2 / Ln ( change T1 / change T2)

=> change T1 = Th,in - Tc,out
=> change T2 = Th,out - Tc, in

  1. Q = U* A(s) * change T (Lm)
    => A(s) = Q / U * change T (Lm)
    ==> A = piDL
    ===> L = A(s) / pi * D
26
Q

(Q17) How to solve LMTD counter flow question.
- max heat transfer rate
- outlet temp of cold and hot water

A
  1. Ch = mh * cp(h)
    Cc = mc * cp(c)
    Qmax = Cmin (Th,in - Tc,in)
  2. change T(max) = Th,in - Tc,in
    - Q = Cc (Tc,out - Tc,in)
    => Tc,out = Tc,in + Q / Cc
    - Q = Ch (Th,in - Th,out)
    => Th,out = Th,in - Q / Ch
27
Q

What is Fouling?

A
  • build up of deposits on heat exchanger surfaces
  • performance deteriorates with build up
  • effected by velocity and ???
28
Q

Fouling:
What is Precipitation Fouling.
How do you prevent it?

A

-build up of solid deposits
- occurs when solubility of compounds is exceed and they crystallise
Prevention:
- process water to remove solids
- treat water to remove solids

29
Q

Fouling:
What is Corrosion Fouling.
How do you prevent it?

A
  • fouling caused by chemical reactions
    — such as oxidation, decomposition, corrosive fluids
    Presentation:
  • fluid treatment
    -coating HE pipes
    -material selection (plastic pipe instead of metal)
    -regular cleaning
    -optimise operating conditions - minimise fouling
30
Q

Fouling:
What is Algae Fouling.
How do you prevent it?

A
  • build up of algae growth
  • biological fouling
    Presentation:
  • chemical treatment
  • regular cleaning
    -filtration
    -material selection (anti-microbial properties)
  • uv sterilisation
31
Q

Do an Interpolation example!
Q1, Q2 Interpolation, Q3

A

Q1) a - use table to find vf, b - v=mv
Q2) a - use table to find P, b - x = mg / m(total) ==> v = vf + x(vg - vf) ==> v = m*v
Q3) interpolation equation i cba typing it
Q4) interpolation equation, again cba typing

Year 3 (9 decks)

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