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This new topic is inspired by the recent travails of some members of the forum who have experienced cold temperatures in recent weeks.
It is also inspired by news of recently published research drawing upon thousands of recordings of earthquakes on Earth, which offers hints that there may be an "inner inner" core at the center of the Earth.
In reading the article, I ran across a reference to a temperature in the core estimated to (possibly) be as high as 9000 degrees. I didn't note the scale, but at that temperature, there is very little difference between the scales.
Elsewhere in the forum, the archive contains discussion of generation of electricity due to temperature differences.
Thermoelectric effect - Wikipedia
en.wikipedia.org › wiki › Thermoelectric_effect
The Seebeck effect is the electromotive force (emf) that develops across two points of an electrically conducting material when there is a temperature difference between them. ... This potential difference is proportional to the temperature difference between the hot and cold ends. Thomas Johann Seebeck · Seebeck coefficient · Thermocouple
Google kindly refreshed my memory of the effect I'm thinking of for the present topic.
I'm hoping that one or more members of the forum may be willing to invest some thought in computing the potential for developing a reliable source of home electricity by dropping a shaft down far enough from the surface to reach a region of the crust where temperatures are high enough to be enlisted for this project.
The "traditional" way of enlisting thermal energy from the Earth is by sinking thermal energy from the surface into the water under the surface when surface temperatures are high, and by pulling thermal energy from the under-surface when surface temperatures are low.
The means by which heat energy is transferred from surface to below, or the reverse, has traditionally been use use of a gas or a liquid, or a combination of the two with phase change.
I am proposing for this topic an approach I have not seen published before.
That doesn't mean it hasn't been published somewhere. Surely it has. It just means ** I ** haven't seen it.
The proposal of this topic then, is that if a home owner living somewhere on Earth, such as New Hampshire, or in Texas, or perhaps even in latitudes further North, such as Canada or Alaska, it might be possible to establish a constant, reliable flow of electric current from a hot region far below the surface, to the constant cold region just below the surface.
A shaft dug from the surface to a hot region would NOT be carrying fluid of any kind. It would instead by carrying current flowing from a hot region to a cold one.
For those who may not be familiar with the technology involved, I hasten to caution that what I am proposing may not in fact be possible.
The Seebeck effect works (as I understand it) when there is a temperature difference between the two sides of a metal junction.
However, if a shaft is sunk to a distance well under the surface of the Earth (or any planet with a hot core) there would be NO temperature difference available at the bottom of the shaft. The temperature difference would be between the bottom of the shaft and the top.
That is why liquids are traditionally used to carry heat from one end of a shaft to the other.
However, if there ** is ** a way to implement the Seebeck effect without moving fluids, I am hoping a member of the forum will be able to suggest it.
(th)
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For Tahanson:
https://www1.eere.energy.gov/ba/pba/pdf … y_rock.pdf
However, if there ** is ** a way to implement the Seebeck effect without moving fluids, I am hoping a member of the forum will be able to suggest it.
The short answer is 'no'. The only other heat transfer mechanism that is applicable (other than forced convection) is conduction. Given that the well needs to be 4km deep on Earth and probably 12km on Mars (1/3rd the geothermal gradient of Earth), the rate of conduction through a solid bar would be miniscule.
One problem with geothermal power on Earth and Mars is that pumping losses through the shafts and fractured rock are generally high. And you need to go down much further on Mars to reach the temperatures needed to generate steam. On the plus side, we may have access to abundant liquid CO2 on Mars. The critical temperature of CO2 is 31°C. So you may not need high temperatures to generate power.
On a small scale, it may be possible to generate power from diurnal temperature fluctuations. These can be as high as 100°C on Mars. If you can sink shafts into the ground and store night time cold in the ground beneath solar collectors and daytime heat in an insulated tank, then a heat engine could run between them 24/7. Whilst this is not something that would scale to power a city, a research base that needs perhaps 10kwe could be powered by something like this. The hot source would be a water tank, containing a mixture of water and ice. During the day, solar heat would be used to melt the ice. When the sun is down, the power plant would withdraw heat that is stored in the heat of fusion of the ice, which is about 400KJ/kg. A 10kWe powerplant, with a 10% efficiency, would need a tank of 11m3 to store enough energy to keep generating over a 12 hour Martian night. The bigger the tank is, the more stored energy it can provide, but the more it costs to install.
Last edited by Calliban (2021-03-12 09:55:09)
"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."
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For Calliban re #2
Thanks for picking up this question ... I hoped you might find it worth a bit of your time.
There is a third option, which you have cited on numerous occasions ... radiation...
Now, I recognize that radiation is happening at a uniform rate in all parts of the subterranean cavity, and there is no place to radiate ** to ** ...
However, I'm wondering if you have a reference that explains how a radiator in deep space is able to release heat into the cosmos.
Perhaps the answer is simply that the radiation from a body (black body radiation is the familiar concept) is able to escape because it is NOT reflected back to the sending body by the surroundings.
The most recent discussion of this phenomenon was with respect to a space craft inside a hollow asteroid..
I had proposed that the radiation from a spacecraft inside such a cavity would be able to keep the craft cool, but I was left with the impression you were not convinced.
Is it because you expect is that the material inside the wall of the cavity would heat up (due to poor conductivity in the material of the asteroid) and radiate right back to the space craft?
It would seem to me that if the interior of such an asteroid is near absolute zero, the radiation from the spacecraft should not be reflected back for a considerable time.
(th)
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Not sure if this relates directly to what has been discussed so far, but don't we also have the opportunity on Mars of using CO2 as the equivalent of a steam engine with condenser without having to deploy additional energy. It can be fine tuned with use of solar reflectors during the day. If placed near or within a settlement you might be able to run it at night off the ambient heat of the settlement.
Let's Go to Mars...Google on: Fast Track to Mars blogspot.com
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For Louis re #4
Thank for contributing what comes across to me as a nicely packaged summary of the concept of using CO2 as a working fluid in the special circumstances of the surface of Mars. I'm hoping Calliban will confirm (or perhaps correct) my impression, because (of course) his explanation is quite detailed.
I ** am ** hoping Calliban will be willing to consider/think-about the mechanism by which radiation allows objects to cool down in free space. That is a concept worth understanding, it seems to me, whether a person is in a spacecraft far from home, or in a nice snug bungalow on Terra Firma.
(th)
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The quotes below are a first attempt to explore the question of how radiation cools an object ...
Radiative cooling is the process by which a body loses heat by thermal radiation. As Planck's law describes, every physical body spontaneously and continuously emits electromagnetic radiation.
Radiative cooling - Wikipedia
en.wikipedia.org › wiki › Radiative_cooling
http://hyperphysics.phy-astr.gsu.edu/hb … otime.html
The rate of radiative energy emission from a hot surface is given by the Stefan-Boltzmann law .
Here P is the power emitted from the area, and E is the energy contained by the object. For very hot objects, the role of the ambient temperature can be neglected. If the hot temperature is more than 3.16 times the ambient, then the contribution of ambient terms is less than 1%. For example, for 300K ambient on the earth, an object of temperature higher than 1000K can be treated like a pure radiator into space. If the heat loss is purely radiative and not limited by heat transfer to the radiating surface, then the cooling time can be modeled for a hot object.
It is my understanding that radiation (a photon) occurs any time a charged particle is accelerated.
If a charged particle is circling another charged particle, it is undergoing acceleration.
When an atom is accelerated due to electrostatic collision with another atom, I would expect it to generate a photon, although I would imagine the photon involved is NOT identical to one produced when an electron drops from an outer shell to an inner one.
In any case, the advice from Calliban, that a solid iron bar would NOT perform well as a conductor of heat from 1 kilometer below the surface of the Earth to the surface, leads me to imagine that there is a pipe from the 1 kilometer location that extends to free space.
In that case, radiation emanating from the bottom of the shaft should be able to travel unhindered to the end of the Universe, if it does not encounter an obstacle on the way.
If there is no radiation heading ** down ** the pipe, I would expect the radiator to function as well as does a radiator on a spacecraft carrying a RTG.
Google found this:
http://www.esa.int/esapub/bulletin/bull … roli87.htm
Heat rejection
Radiators
A radiator is simply a (highly) conductive panel exposed to deep space and (normally) coated with a high-emissivity coating. Depending on the spacecraft's size and configuration, there can be central radiators to which all the heat dissipated on board is transferred, or multiple radiators each dedicated to a payload unit or group of payloads and/or subsystems.The dissipating equipment can either be mounted directly on the radiator or connected to it via heat pipes or fluid loops. In the latter case, the heat pipes or fluid lines can either be fixed to the external faces of the radiator or directly embedded into its structure. The second solution is more efficient from the structural (mass-saving) and thermal viewpoints, but can also be less reliable due to the probability of micro-meteoroids impacting the radiator, and is more critical with regard to spacecraft integration activities.
The radiator's size depends on the power to be dissipated, the temperature of rejection (defined by the items to be controlled) and the temperature of the surrounding environment (Fig. 8). In most cases, the radiator is mounted on a spacecraft panel and therefore only radiates on one side. In the case of high and/or varying powers or changing environmental conditions, this configuration is not very efficient. A better solution is to use both faces of the radiator, but this implies the need for radiator deployment.
This quote is from an overview of spacecraft design considerations. The paper dates to 1995.
(th)
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Overnight, additional ideas for this topic started to gel ...
Experimental apparatus to Simulate Deep Space Heat Sink
Hypothesis: Phonons can be transmitted via waveguide (**)
Background: It is known that a temperature of 1000 degrees Fahrenheit (537 Celsius) can be found at a depth on the order of 1 kilometer below the surface of the Earth. Meanwhile, soil below the surface can be expected to have a temperature of (about) 55 degrees Fahrenheit (about 13 degrees Celsius)
Soil can hold heat better than air does. It is also insulated by soil above it, vegetation, and snow. In fact, the deeper you go, the more insulation and the higher the average temperature, to a point. From about 30 to 200 feet below the surface, the soil temperature is relatively constant (about 55 degrees F.).
The difference of (about) 950 degrees Fahrenheit (512 Celsius) could be used in a Seebeck device to produce a flow of current.
[PDF] Low-Power Energy Harvesting with a Thermoelectric Generator ...
www.asee.org › file_server › papers › attachment › file › Low_Power...
Thermoelectric generators (TEG) are devices that convert temperature differences into ... The Seebeck effect occurs when a temperature difference ... cold side is rated to a maximum of 180 degree Celsius continues (356 degrees Fahrenheit).
From the paper above (from 2014) we have:
First graph in Figure 2 shows power output based on temperature differences on both sides of
TEG unit. The tested temperature for cold side is from 25C to 100C and hot side temperature
from 50C to 300C. The larger the temperature difference is the more output power is available
from TEC unit. For example, TEG generates about 20W power having cold side 25C and hot
side 300C which is about 275C temperature differences.
Second graph in Figure 2 shows voltage output based on same temperature conditions for power
output. The maximum voltage generated is 4 Volts at 275C temperature difference between hot
and cold plates. The ambient temperature should be considered when there is very low or hot
ambient temperature is available.
The purpose of the quote above is to provide a sense of what is practical using existing Thermoelectric Generator devices.
An experimental apparatus to investigate the possibility of transferring phonons from a place of high temperature to a place of low temperature using radiation via waveguide would include:
1) Waveguide chosen to optimize the flow of electromagnetic waves at the frequency of phonons (whatever that may be)
2) Radiator at the hot end to generate electromagnetic waves to carry energy away from the hot end
3) Radiator at the cold end to absorb radiation received via the waveguide and transfer it to the heat sink via conduction/convection
4) Equipment to measure current flows at both ends
Expected result: The cold end of the waveguide will "look" like deep space to the hot end. There will be no traffic back toward hot end from the cold end (*).
(*) this may not be possible to achieve in practice.
(**) Per Google:
pho·non
noun
a quantum of energy or a quasiparticle associated with a compressional wave such as sound or a vibration of a crystal lattice.
I deduce from the definition above that a radiator has the function of converting phonons to photons. Accordingly, it would be photons that are conveyed along a waveguide.
(th)
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In Post #7, I described an experimental apparatus to investigate transmission of heat energy through a waveguide, by converting phonons to photons.
The concept of transferring energy via a wave guide has been studied extensively for military and civilian applications:
Google came up with this:
In a microwave oven a waveguide transfers power from the magnetron, where waves are formed, to the cooking chamber. In a radar, a waveguide transfers radio frequency energy to and from the antenna, where the impedance needs to be matched for efficient power transmission (see below).
Waveguide - Wikipedia
en.wikipedia.org › wiki › Waveguide
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I note the requirement for impedance matching, and wonder what that implies for the proposed experimental apparatus.
The field of Solar Power Satellites depends upon the efficient transfer of power via microwaves, although that application is done in the open air.
(th)
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Heat gradient power in solar is called thermal syphon and its from warming back to cooling that it happens to flow. That energy creation is caused by the working fluid flow that currents in a turbine which cause it to create power.
There are a great number of working fluids which can be used and its dependent on the temperatures that the system would see.
Wave guides are a channel that restricts the flow or spread of the energy as transmitted out of from a magnetron. It takes the place of wired connections to the antenna.
Photons while they have energy are tiny and its going to take alot of them to concentrate to produce any amount there in for temperature change from absorption as already seen from solar sails.
RTG's are both a thermal creation as well as electrical in nature and are well known for applications. The current mars rovers are examples of these in use. What is not said is radiation exposure range if people are in proximity to them.
In the first post I was thinking that we are going to take about heat pumps and or making use of geo thermal energies and its going to be dependent on depth and size of the entry hole to which we are using to capture that heat.
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