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Engineering physics Flashcards

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1
Q

Rotational dynamics

What effects the flywheel KE

[4]

A
  1. mass
  2. angular velocity
  3. friction
  4. spoked - mass spread out to the side
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2
Q

Rotational dynamics

three uses of flywheel

A
  1. regenerative breaking
  2. wind turbine
  3. smoothing out torque/ angular v.
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3
Q

how to convert any
quantity
angular -> linear

A

multiply by radius

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4
Q

Thermodynamics

What does +ve Q means

A

energy transfered into the system

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5
Q

Thermodynamics

What does +U mean

A

increased avg. KE of particles

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6
Q

Thermodynamics

What does +WD mean

A

work done by the particles

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7
Q

Thermodynamics

what is the area underneath p-v graph

A

Work done by gas

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8
Q

Thermodynamics

What is constant in isothermal process

A

internal energy / temp.

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9
Q

Thermodynamics

What is constant in adiabatic processes ?

A

heat energy of system

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10
Q

Thermodynamics

Describle the 4 steps to ideal engine cycle

A

Induction - constant Pa expansion
Expansion - adiabatic
Compression - adiabatic
exhaust - constant Pa compression

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11
Q

Thermodynamics

describle the induction step of ideal engine

A
  1. fuel mixture in
  2. volume increases at constant Pa
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12
Q

Thermodynamics

describle expansion stroke of ideal engine

A
  1. valves closed
  2. piston push down to compress gas
  3. spark generated
  4. heat transfered to system
  5. Inc. U => Inc. T and Inc. Pa
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13
Q

Thermodynamics

Describle power stroke

A
  1. net WD by gas to push piston
  2. volume increases
  3. Temp decreases
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14
Q

Thermodynamics

Differences between
real and ideal
engine cycle

A
  1. need induction and exhaust stroke
  2. rounded corners - valve takes time
  3. heating/cooling cannot occur at constant vol.
  4. not ideal gas
  5. fuel may not completely combust
  6. mas pressure is lower
  7. compression/expansion not completely adiabatic
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15
Q

Thermodynamics

Difference between
petrol and diesel
engine

A
  1. only draws air in induction stroke
  2. fuel introduced during expansion stroke
  3. no spark needed
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16
Q

Thermodynamics

Why is there less
work output
in real engine

A
  1. smaller area of loop
  2. area of pumping loop needed subtraction
  3. friction between surfaces
  4. energy used in pumping gas + valve op.
17
Q

Thermodynamics

define 2nd law of thermodynamics

A

the need for engine to operate between a source and a sink

18
Q

Thermodynamics

How to maximise Qh and WD

2nd law of thermodynamcis

A
  1. CHP - combine heat and power
  2. reduce friction
19
Q

Thermodynamics

What is the purpose of refridgerator

A
  • abstract as much heat as possible from cold place
  • maximise Qc
20
Q

Thermodynamic

what is the purpose of heat pump

A
  • deliver as much as heat to hot place
  • maximise Qh
21
Q

Thermodynamics

Eq. of thermal efficiency

A

indicated / Qh

22
Q

Thermodynamics

Eq. of mechanical efficiency

A

brake / indicated

23
Q

Thermodynamics

Eq. of overall efficiency

A

mechanical x thermal

brake / Qh

24
Q

Define input power

A

indicated power (WD) +
output power to sink (Qh)

25
Q

Thermodynamics

How to cal. Indicated power

A

A(loop) * no. of piston * frq of cycle

26
Q

Thermodynamics

Indicated power eq.

A

brake power + frictional power

27
Q

how many rotations per cycle

A

2

28
Q

Describle thermal efficiency

A

how well the calorific value of fuel is converted into work inside engine

29
Q

Describle mechanical efficiency

A

work/power used to overcome friction/viscocity inside engine and operate valves, water and oil pumps.

30
Q

Thermodynamics

why is it not advised to operate above optimal speed

A
  1. thermal efficiency decreases
  2. friction increases at higher speed
  3. work against greater viscosity
31
Q

Thermodynamics

Why is there less WD isothermally than adiabatic

A
  1. adiabatic curve is steeper to reach the same volume
  2. greater area under the curve
  3. so more WD

Physics (3 decks)

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