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Thermodynamics > Thermoelectric Effects > Flashcards

Thermoelectric Effects Flashcards

1
Q

conditional current

A

Goes from high to low, but elections flow in the opposite direction

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2
Q

Since V+>V-, then

A

There is always a loss of energy

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3
Q

The drop in electrical potential energy as current passes through a material due to a voltage difference will create heat that will leave the material

A

Joule heating, homie resistance heating

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4
Q

What factors affect heat generation?

A

High voltage difference, high currents

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5
Q

If we have high voltage, then _____ is best

A

Low resistance

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6
Q

Resistance of a given piece of material depends on its…

A

Geometry and its material properties

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7
Q

Thermoelectric Power Generator

A

If there is a temperature difference between the two junctions, then a current flows through the circuit

If we break the circuit, current cannot flow, but a voltage difference is generated

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8
Q

______ describes the voltage potential generation due to a temperature difference across two junctions of two conjoined different metals

A

Seekbeck effect

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9
Q

Seebeck Effect origins

A

Named after Thomas Seebeck for his discovery in 1821

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10
Q

There are two major applications of the Seebeck effect

A

Temperature measurement

Power generation

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11
Q

A ______ device is any device that operates using a thermoelectric circuit which incorporates thermal and electrical effects

A

Thermoelectric device

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12
Q

The working principle behind thermocouples

A

If we break the circuit we create a voltage difference that is proportional to the temperature difference

If we measure the voltage difference, we can determine the temperatures

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13
Q

There are many different types of thermocouples

A

K-type (chromed-alumel) most common with a sensitivity of 41uV/C

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14
Q

Thermocouples generate…

A

Small voltages per degree change in temperature

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15
Q

We put a bunch of thermocouple devices in series to produce a _____

A

Thermopile

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16
Q

Thermopile

A

To measure a very small temperature difference

Commonly used in applications where heats of reaction are being measured (e.g. concentrations of dilute species)

17
Q

Changing the sensitivity of a thermocouple device

A

Pairing up specific metals

18
Q

_______ is a material property that represents the induced voltage in response to a temperature difference across the material

A

Seebeck coefficient

19
Q

When we combine two different materials…

A

We can identify the expected voltage difference or temperature difference

20
Q

The voltage gradient will point in the….

A

Opposite direction of the temperature gradient

21
Q

The Seebeck Coefficient is relative value (since measuring it will create additional thermoelectric effects) and material values are compared to _____

A

Platinum (0uV/K)

22
Q

______ absorbs heat from a high-temperature source and rejects heat to a low-temperature sink; the difference is the produced electrical work

A

Thermoelectric generator

23
Q

Thermoelectric generator - working fluid

A

Electrons

24
Q

The efficiency of a thermoelectric generator

A

Limited by the temperatures of the source and sink

The presence of an irreversibility (resistance) keeps the actual efficiency below the Carnot efficiency

25
Q

Thermoelectric generator - applications

A

Low power applications

Limited fuel source applications (e.g. space exploration)

Waste heat recovery

26
Q

What if we powered a thermoelectric generator by means of an external voltage?

A

We could drive the heat transfer in the opposite direction (like a refrigerator or heat pump)

27
Q

Thermoelectric refrigerators are driven by the _____

A

Peltier Effect

28
Q

Compared to vapor-compression refrigeration cycles, Peltier coolers are…

A

Smaller
Quieter
More reliable
Low COPs

29
Q

Peltier Coolers

A

2 column-pairs (one n-type, the other p-type)

These alternating columns are arranged in series

When a current passes through, it draws heat away from the cold side and rejects it to the warm side

30
Q

N-type

A

Heavily doped with extra electrons

31
Q

P-type

A

Doped to create extra vacancies

Thermodynamics (11 decks)

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