Thermoelectric Effects Flashcards
conditional current
Goes from high to low, but elections flow in the opposite direction
Since V+>V-, then
There is always a loss of energy
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
Joule heating, homie resistance heating
What factors affect heat generation?
High voltage difference, high currents
If we have high voltage, then _____ is best
Low resistance
Resistance of a given piece of material depends on its…
Geometry and its material properties
Thermoelectric Power Generator
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
______ describes the voltage potential generation due to a temperature difference across two junctions of two conjoined different metals
Seekbeck effect
Seebeck Effect origins
Named after Thomas Seebeck for his discovery in 1821
There are two major applications of the Seebeck effect
Temperature measurement
Power generation
A ______ device is any device that operates using a thermoelectric circuit which incorporates thermal and electrical effects
Thermoelectric device
The working principle behind thermocouples
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
There are many different types of thermocouples
K-type (chromed-alumel) most common with a sensitivity of 41uV/C
Thermocouples generate…
Small voltages per degree change in temperature
We put a bunch of thermocouple devices in series to produce a _____
Thermopile
Thermopile
To measure a very small temperature difference
Commonly used in applications where heats of reaction are being measured (e.g. concentrations of dilute species)
Changing the sensitivity of a thermocouple device
Pairing up specific metals
_______ is a material property that represents the induced voltage in response to a temperature difference across the material
Seebeck coefficient
When we combine two different materials…
We can identify the expected voltage difference or temperature difference
The voltage gradient will point in the….
Opposite direction of the temperature gradient
The Seebeck Coefficient is relative value (since measuring it will create additional thermoelectric effects) and material values are compared to _____
Platinum (0uV/K)
______ absorbs heat from a high-temperature source and rejects heat to a low-temperature sink; the difference is the produced electrical work
Thermoelectric generator
Thermoelectric generator - working fluid
Electrons
The efficiency of a thermoelectric generator
Limited by the temperatures of the source and sink
The presence of an irreversibility (resistance) keeps the actual efficiency below the Carnot efficiency
Thermoelectric generator - applications
Low power applications
Limited fuel source applications (e.g. space exploration)
Waste heat recovery
What if we powered a thermoelectric generator by means of an external voltage?
We could drive the heat transfer in the opposite direction (like a refrigerator or heat pump)
Thermoelectric refrigerators are driven by the _____
Peltier Effect
Compared to vapor-compression refrigeration cycles, Peltier coolers are…
Smaller
Quieter
More reliable
Low COPs
Peltier Coolers
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
N-type
Heavily doped with extra electrons
P-type
Doped to create extra vacancies
