# 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 ...

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

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 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

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

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

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

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

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

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 ...

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

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

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

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

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 ...

1

If you're looking to produce power from a temperature differential, go with a device optimized for the Seebeck effect. Peltier and Seebeck effects are essentially the same thing, or rather flip sides of the same thing, but thermoelectric generators (Seebeck) are optimized differently from thermoelectric coolers (Peltier).

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

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

A Peltier module is not what you want. Some of the specs that I've seen require minimum currents of a few amps (≈2A for a small module), so unless you want to lug around even a small sealed Lead-acid battery with attendant wires, I'd think of something else. In fact, an electrical solution may not even be suitable. However, how about modifying a gas ...

1

As mentioned by Programmer, saying that if the wire temperature is constant then half of the heat will flow in either direction is incorrect. It really depends on the boundary conditions on either end of the wire (since it is of finite length). Assuming that the wire is at a spatially uniform temperature (not constant in time) and has same boundary ...

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

If you only want to heat the bit to help melt off ice from the screw and do not care about cooling the bit, then the Peltier device, which is a heat pump, is unnecessarily complicated and delicate. The most efficient way to heat something is through a resistive load (i.e. like in a toaster). There are a number options for making the heater, but a 100 Ohm, 1 ...

1

In a solid body the energy that we call heat is stored as vibrational motion of the atoms/molecules in the solid. When you place a hot solid in contact with a cold one the vibrating atoms in the hot solid bash into the more slowly vibrating atoms of the cold solid and transfer energy to them. You end up with the atoms in the hot body vibrating a bit less and ...

1

Coiling a light filament has several effects. Because the bulb is not under vacuum, the gas inside cools the filament. The coiling reduces the cooling effect from the gas (substantially). An uncoiled filament with the required surface area will be much longer than an coiled one. A longer filament needs more support (expense) in a commercial bulb. A ...

1

Can you? Yes. Would it make sense to? Probably not. Peltier cells are not very efficient (guess: 10%), so your combination would be perhaps 1% efficient. If the heat's free, and you don't care about the cost of the cells, and you aren't cooling very much, then it might be worth it. Otherwise, not.

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