2.3 Thermodynamics Flashcards

1
Q

Name the 3 types of thermometers

A
  • Bulb thermometer
  • Bimetallic thermometer
  • Thermistor
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2
Q

What are thermocouples used for

A

Measure high temperatures

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3
Q

Where would a Bimetallic Thermometer be used

A

Fire detection system & OAT

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4
Q

What is a Thermistor

A

A device to measure temperature that changes its electrical resistance with changes in temperature. Most common device

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5
Q

3 scales of tempeature

A

Deg Celcius (C)
Kelvin (K)
Deg Farenheit (F)

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6
Q

Formula to convert Deg F to Deg C

A

deg C = 5 / 9 (F - 32)

(50 - 32) x 5 / 9 = 10 deg C

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7
Q

Formula to convert Deg C to Deg F

A

deg F = 9 / 5 C + 32

9 / 5 x 50 + 32 = 122 deg F

9/5 = 1.8

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8
Q

Temperature at which deg C & deg F are the same

A

-40 deg

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9
Q

Formula to convert Kelvin to deg C

A

K = deg C + 273.15

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10
Q

What is zero Kelvin otherwise known as

A

Absolute Zero. Whare all molecular movement would stop

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11
Q

Formula for Specific Heat

A

c = Q / m x /\T or Heat added Q = m x c x /\T

  • c = specific heat {j/kg K}
  • Q = heat energy added {J}
  • m = mass {kg}
  • /\T = change in temp {K}
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12
Q

Formula for Heat Capacity

A

C = Q / /\T or Haet added Q = C x /\T
* C = heat capacity (J/K)
* Q = heat energy added (J)
* /\T = change in temp (K)

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13
Q

Name the 3 types of Heat transfer

A

Conduction, Radiation, Convection

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14
Q

The only method of heat transfer in solids is

A

Conduction, however it also occurs in liquids

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15
Q

Heat transfer from one part of the fluid to another, is called?

A

Convection

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16
Q

Formula for Linear Expansion

A

/\L = aLo/\T
* /\L = change in length (m)
* a = coefficient of linear expansion
* Lo = original length
* /\T = change in temperature

17
Q

Formula for Area Expansion

A

/\A = 2aAo/\T
* Ao = original area of body (m^2)
* a = coefficient of linear thermal expansion
* /\A - change in area of the body (m^2)
* /\T = change in temperature (deg C)

18
Q

Formula for Volumetric Expansion

A

/\V = 3aVo/\T
* Vo = original volume of the body (m^3)
* a = coefficient of linear thermal expansion
* /\V = change in volume of the body(m^3)
* /\T = change in Temperature (deg C)

19
Q

Describe the first law of thermodynamics?

A

Energy can neither be created nor destroyed but can only be transformed from one form to another. In simple terms: Energy in = Energy out

20
Q

Formula for Thermodynamics first law

A

Q = /\U + W or W = Q - /\U or /\U = Q - W
* Q = heat energy added (J)
* W = work done by the gas (J)
* /\U = change in internal energy (J)

21
Q

2nd Law of Themodynamics

A

The second law of thermodynamics states that the total energy output (as produced by a machine) is equal to the amount of heat supplied.

22
Q

Formula for change in Entropy

A

/\S = Q / T
* /\S = change in entropy (J/K)
* Q = heat energy absorbed (J)
* T = temperature (K)

23
Q

There are two types of thermodynamic cycles: open and closed. Each cycle has the same five basic elements. What are they?

A

Working substance – a medium that receives, stores and transports the energy.
Heat source – supplies thermal energy to the working fluid.
Heat receiver – absorbs the heat (or thermal energy) from the working substance.
Pump – moves the working substance from the low-pressure side to the high-pressure side of the cycle.
Engine – converts the thermal energy to work in mechanical energy.

24
Q

There are three main processes in the engine working cycle during which changes in temperature, pressure, or density occur:

A
  • Compression
  • Combustion
  • Expansion
25
Boyle's Law formula - (Isothermal)
**PV = k** or **P1V1 = P2V2** **(Temp remains Constant)** * P = pressure (N/m^2) * V = volume (m^3) * * k = a constant (pa-m^3) or * P1 = initial pressue (N/m^2) * V1 = initial volume (m^3) * P2 = final pressure * V2 = final volume
26
When real gases are compressed at a constant temperature, what happens?
changes in the relationship between pressure and volume occur. ie. Volume increase, Pressure decreases and vice versa
27
Charles’s Law (Isobaric Process)
At constant pressure, **the volume of a given mass of an ideal gas increases or decreases by the same factor as its temperature increases or decreases.** This is called an isobaric process. **V / T = k** * V = volume (m^3) * T = temp (K) * k = a conctant (m^3 / K)
28
Gay-Lussac’s Law (Isochoric Process)
**At constant volume,** the pressure of a given mass of gas varies directly with the absolute temperature of the gas. **i.e Temp increases, Pressure increases.** This is called an isochoric process. **P / T =k** * P = pressure (Pa) * T = temp (K) * k = a constant (Pa/K)
29
An isothermal process is one in which?
the temperature remains constant. Boyles Law
30
Specific Heat at constant volume
**cv = Q / m x /\T** or **Q = m x cv x /\T** **cv** of air is given as **718 J/KgK** ***Specific heat at Constant Pressue = Cp*** **Cp** for air is given as **1005 J/KgK**
31
An adiabatic process is one in which?
no heat is transferred to or from the system.
32
What is used to remove heat during expansion & compression
A heat sink
33
Expansion and Compression, name the different types of processes
* **Isochoric**: - Constant volume - **Guy Lussacs** * **Isobaric**: - Constant pressure - **Charles** * **Isothermal**: - Constant temperature - **Boyles** * **Adiabatic**: - No heat transfer between system and surroundings
34
Name the two main types of thermodynamic processes:
**Reverisble & Irreversible**
35
What is an Otto cycle
The Otto cycle is an idealised thermodynamic cycle **Piston Engine**
36
There are four thermodynamic processes making up a complete Otto cycle:
**Process 1–2 Adiabatic compression:** Piston moves from bottom dead centre (BDC) to top dead centre (TDC). No heat transfer takes place, temperature and pressure increase and the volume decreases. **Process 2–3 Reversible isochoric heating:** Piston is at TDC, ignition of the fuel-air mixture takes place. Temperature and pressure increase, volume is constant. **Process 3–4 Adiabatic expansion:** The increased pressure exerts a force on the piston and pushes it towards BDC. Air expands and does work on the piston. Pressure and temperature decrease. No heat transfer takes place during the process. **Process 4–1 Reversible isochoric rejection (cooling):** The piston is at BDC. Pressure and temperature decrease to original value.
37
What is a Brayton Cycle
The Brayton cycle is a thermodynamic cycle describing the processes in a constant‑pressure heat engine. Three compunants Gas Compressor, Combustion Chamber & Expansion Turbine
38
There are four thermodynamic processes making up a complete Brayton cycle in gas turbines:
**Process 1–2 Adiabatic compression:** Fresh air is drawn into the compressor, pressurising it. No heat transfer takes place, temperature and pressure increase and the volume decreases. **Process 2–3 Isobaric heating:** The compressed air runs through a combustion chamber, where fuel is burned, heating the air. Pressure is constant, volume and temperature increase. **Process 3–4 Adiabatic expansion:** The heated, pressurised air gives up energy when it expands through a turbine. Some of the work extracted by the turbine is used to drive the compressor. Pressure and temperature decrease. No heat transfer takes place during the process. **Process 4–1 Isobaric cooling:** The air cools down in the atmosphere. Volume and temperature decrease to their original values.