# Tag Info

47

The efficiency of a thermoelectric generator is around 5 - 8%. The efficiency of a large steam turbine power plant aproaches 40%. In fact the thermodynamic efficiency of a large steam turbine power plant is over 90%, so it's about as efficient as anything could be. The maximum possible efficiency of a steam driven engine is given by the idealised model ...

18

my question is about whether it's possible in principle The answer is yes. and whether anyone tried it. The answer is by all chances, no. So, how come? The effect The thermoelectric effect for electricity generation (called the Seebeck effect) is the phenomenon that a voltage is generated at a temperature different across the ends of a ...

11

In principle, the drop in the Gibbs energy when the uranium gets converted to the fission products is available for doing useful work. While a steam engine will not come close to the maximum possible efficiency attainable (which is very close to 100%), a thermoelectric device will have much worse performance, as pointed out in detail in the other answers. ...

4

There are two main reasons As temperature is decreased the voltage of a car battery decreases and it's internal resistance increases. This means the battery can supply less current. As temperature is decreased the viscosity of oil in the engine increases so the engine is harder to turn over. In the days before fuel injection there was a third factor ...

4

Good conductors are materials providing a lot of efficient electric charge transporters. electrons and ions are two kinds of them. But electron are light and in stable phase in metal, while ions in fluids are heavy, slow, and need the fluid to be there, contained, not changed too much in partial densities of components, and this for a very long time if it's ...

3

In a metal the Fermi energy is somewhere in an unfilled band. At any temperature above absolute zero (which you can never reach) there are states available for electrons to get to and result in conduction at the Fermi surface. This will occur in any metal. Superconductivity is a separate phenomena that I won't touch on here.

3

The drift velocity of electrons in a metal is given by the equation $I=enAv_D$ where $I$ is the electric current in the metal wire, $n$ is the number of electron density, $A$ is the cross sectional area of the metal wire and $v_D$ is the drift velocity. From this we get $v_D= \frac{I}{enA}$ The thermal velocity is given by ...

3

In order to have the hot side remain hot, and the cold remain cold, while transmitting the electricity, ideally a substance is desired that conducts electricity well, but heat poorly. No. The two ends are assumed to be connected to heat sources or sinks that maintain a constant temperature at those nodes. Heat does flow well from one end to the other, ...

3

When the metal is heated, all inter-atomic distances increase by the same factor. This drawing may help understand why the hole also increases in size. Here, I increased all distances by a factor a two. Replace the atoms with galaxies, and you have a model of the expanding Universe, which may help understand why an observer in any galaxy will see herself ...

2

Current as low as 10mA can paralyze, and 100mA can induce a heart attack. Be careful even when working with "low" currents.

2

The voltage differences you can get from thermocouples are usually in the range of $\mu$V per Kelvin for metals. In other materials this can be a bit higher but there is no material that can create thousands of Volts for a temperature difference between the heating and other parts of the building. For static electricity you need a few conditions coming ...

2

The thermoelectric effect is the direct conversion of temperature differences to electric potential differences (Seebeck effect) and vice-versa (Peltier effect). When considering the electrical currents and heat fluxes involved, there is a size dependency, but such is not the case for the temperature differences and the electric potential differences ...

2

Micro black holes have been hypothesized in some large dimension string phenomenological models and are searched for in the experiments at the CERN LHC. The first approach to the decays was thermodynamic with Hawking radiation diminishing them rapidly. Their lifetimes are very short so there is no way to gather and contain them and experiment with feeding ...

2

H2 + O2 is exothermic. That drives the fuel cell. Platinum adsorbs H2 and O2. This means it "sticks" those atoms to it so that the offering and accepting of electrons is made easier. This presenting of atoms must have an energy cost and so weakens the diatomic bonds otherwise keeping respective H2 and O2 molecules bound. That is why heterogeneous ...

2

The line itself does not change much over years. What changes and therefore needs maintenance on power transmission lines is insulators, connectors and spacers. Insulators get dirty or simply break, connectors work loose due to thermal expansion and contraction, mechanical stresses and oxidation, and spacers can be damaged by wear due to these same ...

2

At present, there is a belief (though obviously not verifiable) by solid-state physicists that a metal cannot exist at absolute zero. The Fermi surface of the metal will be unstable to order of some sort such as superconductivity, charge density waves, magnetic ordering, etc. With that said, let us concentrate on your scenario though. If there are no ...

2

I would like to know whether Carnot cycle limits every kind of thermal to kinetic/electric energy like thermocouples? Yes, since any conversion of heat into "work" is limited by Carnot, as you said: I know that heat engines (heat to kinetic) are limited by Carnot cycle . Also what is the highest possible efficiency of Carnot cycle? The ...

2

The drift velocity is the net velocity of electrons in a certain direction under an applied field. The thermal velocity is has no net direction because it is randomly distributed and occurs in any metal at finite temperatures. Since the two velocities are different, it does not make any sense to say they are qualitatively equal, even though you may equate ...

2

You don't. However, if you use a wire to return the current, your efficiency will drop. The efficiency of a thermometric generator increases with: the difference in Seebeck coefficient between your two element types (Note you could even use two N types, or two P types as long as their magnitude is different) the thermal resistance, or insulation value ...

2

I'm not sure I understand what you're asking exactly, but there are two effects you might be seeing: A coiled wire is longer than a straight wire that fits in the same space. Therefore it has higher resistance ($R=\rho\dfrac{l}{A}$) and so produces more heat from the same current flowing through it. A coiled wire can't cool itself as efficiently as a ...

1

Let's talk about semiconductors which are a bit easier to understand for this problem. Let's say we have a metal plate that we want to cool down. We attach an n-type semiconductor and a p-type semiconductor to different places on the metal plate, and then force a current through that goes from the n-type to p-type semiconductor, through the metal. Due to ...

1

Have you heard of superconductivity? This is a phenomenon where a material exhibits zero resistivity near absolute zero: it clearly contradicts your assertion that thermal excitation is needed for conductivity near absolute zero. For a semiconductor, it is true that electrons need to be kicked into the conduction band by thermal fluctuations - but for a ...

1

If you take a length of copper wire at the same temperature, then the average kinetic energy of an electron, and therefore electron density, is the same through out the wire, balancing the metal ion density. The copper wire is electrically neutral at every point on average. Now heat one end. This raises the average kinetic energy of electrons while reducing ...

1

I am not an expert in thermodynamics but I think the following is reasonable: When heat flows from A to B (temperature $T_a$ and $T_b$) then you could theoretically do work - efficiency given by the ratio of temperatures. A Peltier is an inefficient heat engine running in reverse (a heat pump), and I thought the efficiency is the ratio between the work ...

1

The calibration curve you show isn't typical. In fact there is no typical calibration curve because different types of thermocouples can have very different voltage:temperature dependences. There are lots and lots of articles giving different calibration curves - I selected this PDF as being fairly representative, or try this image search for lots of other ...

1

Why does the platinum take an electron from the hydrogen? Remember that this happens in a fuel cell, where the other electrode loses electrons to O2. The platinum is effectively only an intermediary. It's a metal, so there are a lot of electrons which are not bound to one specific atom. O2 can easily steal one of those, which would leave the platinum ...

1

You'd be lucky to even generate 1 Watt. Compare yours to this much larger 10 Watt generator intended to operate off hundreds of degrees of temperature difference: http://www.devilwatt.com/products/17-10-watt-camping-stove-thermoelectric-generator

1

The details of how your particular device will perform is very much a function of how that device was constructed and how it will be used, but in general, the physical effect is called the Seebeck effect -- briefly, the conversion of a temperature difference across a device to a voltage. Efficiency for such devices is actually quite low, with $\eta = 0.02$ ...

1

The Peltier and Seebeck effects are each others opposites so to say. The Seebeck effect is described by the electromotive force or voltage $V$ generated at a temperature difference $\Delta T$ across the ends of a material: $$V=S\Delta T$$ $S$ is the Seebech coefficient and is a material constant that depends on charge carriers, material density and much ...

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