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Calliban

Member

From: Northern England, UK

Registered: 2019-08-18

Posts: 3,433

Re: Current Gasoline/Petrol Price$

I have been giving some thought to kbd512s idea of a vehicle powered by stored heat.  I wonder if a system based on sensible heat could work, using superheated rock?  Lets say we take a 1000kg cube of silica rock, with a density of 3000kg/m3.  It would be a cube some 69cm aside.  If we could heat it to 1000°C, with a heat capacity of 1KJ/kg.K across that range, it would store about 1GJ of heat.  Suppose we use a small, closed cycle heat engine convert that heat into mechanical power.  If we can get 2/3 of carnot efficiency, then average efficiency over the full temperature range would be 40%.  So total work energy available would be 400MJ, or 111kWh.  That is about twice the capacity of a standard 50kWh Tesla 3 battery.

The big sticking points are waste heat removal and thermal insulation requirements.  If our thermal energy store were provided with 12" of rockwool insulation, its side length would increasefrom 2.25' to 4.25' (1.3m).  We would probably need to tow the store behind the car on a trailer.  Putting the heat engine on the trailer would make plumbing hot fluids much easier.  Power can be transmitted from the trailer to the car, by flexible electric cable or flexible hydraulic couplings.  Given resource constraints, I tend to favour the second option.

If the heat store is put on a trailer, fire hazard concerns are reduced, but top speed is limited.  But I think achievable power using stored heat will tend to limit top speed anyway.  A heat store on a detachable trailer could have other uses as a portable energy storage system.  If we have an offgrid wind turbine powering a house or group of houses, the proposed heat engine could absorb 265kWh of electric power, returning 111kWh of electricity and 154kWh of low grade heat for space and water heating.  This is a system that is simple enough for a hobbyist to build a prototype.  If we assume that half of all electric power is stored, the other half is consumed directly.  Overall system electrical efficiency is 70%, ignoring leakage.  Exergy efficiency would be closer to 80%.  Thermal leakage would realustically reduce these values somewhat.

Last edited by Calliban (2023-05-01 12:34:14)

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"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."

kbd512

Administrator

Registered: 2015-01-02

Posts: 7,431

Re: Current Gasoline/Petrol Price$

Calliban,

How about powdered limestone heated to 600C (136.5kWt per metric ton)?

At 2,710kg/m^3, we need 369L / 97.5 US gallons of volume per metric ton.  Cost ranges from $10 to $55 per metric ton, so we can afford to purchase quite a lot of it without significant cost.  We'll coat both sides of the storage tank with thermal barrier CeraKote so we can use ordinary steel without significant oxidation issues.  We're running this tank at the upper end of the range for exhaust manifolds.  That means we'll need decent insulation to keep the heat where it belongs.

Calliban

Member

From: Northern England, UK

Registered: 2019-08-18

Posts: 3,433

Re: Current Gasoline/Petrol Price$

Limestone looks like the best choice.  Between 100°C and 600°C, specific heat averages about 1.1KJ/kg.K.
https://www.zkg.de/en/artikel/zkg_2010- … 27357.html

Thermal decomposition does not begin until temperature exceeds 800°C, so it should be stable long term at 600°C.  A tonne of limestone heated from 100°C to 600°C, gives us 153kWh of stored heat by my estimate.  Which is close to the 136.5kWh which you gave.  The stuff is dirt cheap, which is encouraging.

Insulation might be more of a challenge.  The thermal conductivity of mineral wool is 0.04W/m.K at 27°C, but increases to 0.2W/m.K at 600°C.  At 300°C, it is at 0.1.  I assumed 1' of thermal insulation, which is about 0.3m.  I am going to estimate thermal leakage rate by assuming a cube 0.7m aside, surrounded by a thickness of 0.3m insulation.  So I take effective surface area to be 6m2 for all faces of the cube, which accounts for the cube itself and the half thicknessof insulation.  I further assume a radiating surface temperature of 100°C.  Estimating leakage rate using Fouriers law:

Q = K×A×dT/dX = 0.1×6×500/0.3 =  1000W

In other words, it would take 14 - 15 hours for the heat store to leak 10% of its thermal energy to the environment.  This is exceeds the length of a typical workday, commuting included.  To achieve this, we need 1.8 cubic metres of mineral wool.  This would add about 200kg of weight and ~$500 of cost.

If we can convert 30 - 40% of the stored heat into mechanical power, then the thermal battery rivals a standard Tesla battery in terms of recoverable energy.  The only downside is that we need at least twice as much electricity to charge it.  But one of the many plus sides of this concept is that minimal electronics are needed to build it.  It is charged using heating elements, which coukd be stainless steel or tungsten.  We need a thermostat that stops the charge when temperature reaches 600°C, but that is a simple transistor switch.

The Tesla 3 consumes 1kWh of stored electrical energy for roughly 7km of driving.  If our proposed vehicle achieves only half of that, and we can convert heat into work at 33% efficiency, then we need about 1kWh of heat per km.  Our 150kWh heat battery should be good for 150km, or 93 miles of range.  That is easily enough for the average commute.  In terms of cost, 1kWh of electricity costs $0.1-0.3, depending upon where you live.  So that is $0.1-0.3/km.  A 100km daily commute will set you back $10 - $30.  Not so bad if you are living somewhere with cheap electricity.

Last edited by Calliban (2023-05-02 14:46:15)

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"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."

SpaceNut

Administrator

From: New Hampshire

Registered: 2004-07-22

Posts: 28,884

Re: Current Gasoline/Petrol Price$

Here is some more of what makes todays car the way that they are.

Where the Energy Goes: Gasoline Vehicles

A car using gasoline will create from 1 gallon or 6.3 lbs of fuel, 20 lbs of co2 from an approximate 14.7 ration to 1 of which if we had to carry the mass of atmosphere to burn the fuel makes for 23.22 lbs of oxygen is required. To which the total 100 lbs of air is just for that 1 gallon. Now fill the tank up for range and you now have something that will be why conversion to other source of energy is a challenge.

kbd512

Administrator

Registered: 2015-01-02

Posts: 7,431

Re: Current Gasoline/Petrol Price$

Calliban,

How about a vacuum bottle to contain the hot material instead of mineral wool?

If we're going to spend $500 and add 200kg of weight, then I'd rather spend that on a steel vacuum jacket around the hot cell.

I'm trying to make this vehicle as simple, cheap, and effective as possible.

Eliminating the rock wool means one less type of specialty material required, and vacuum is more effective anyway.

If we can get away with CeraKote protected A36 over stainless, then we'll use a ceramic thermal barrier coating to reduce the rate of heat loss.

Calliban

Member

From: Northern England, UK

Registered: 2019-08-18

Posts: 3,433

Re: Current Gasoline/Petrol Price$

High oil prices may soon add to inflationary problems.  Investment into new well development in the US has been on a slow decline since 2014.  But 2022 was a new low.
https://www.zerohedge.com/markets/new-p … put-growth

This is a problem, because the US shale patch and Canadian tar sands, have accounted for all of global oil supply growth since the global financial crisis.  These two oil producing regions have taken up all of the slack from declining production in most other oil producing regions since the GFC.  A peak in US production would definitely equate to a peak in global oil production.  OPEC production peaked in 2016.  It is highly unlikely that OPEC will ever surpass its 2016 peak, because all but a few OPEC producers are in long term decline due to depletion.

The world has changed a lot since 2008.  Aside from a handful of mostly Islamic and African countries, populations are ageing and birthrates are beneath replacement.  The worlds trading blocs are decoupling.  The world will run out of demand for oil, as populations age, shrink and get poorer.  It is a matter of debate whether supply or demand will be the dominant limitation.  But as populations age and capital bases shrink, less investment money is going to be available for sustaining oil supply.  Demographic decline may aggrevate supply problems.  The shrinking investment in the shale patch may be the first indication of this.

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"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."

SpaceNut

Administrator

From: New Hampshire

Registered: 2004-07-22

Posts: 28,884

Re: Current Gasoline/Petrol Price$

I hear that the Saudi's are at it again with reducing what is pumped and sent to the US once more.

Remember when gas was under $1? Here's what it cost when you got your driver's license.

SpaceNut

Administrator

From: New Hampshire

Registered: 2004-07-22

Posts: 28,884

Re: Current Gasoline/Petrol Price$

The price of gas has been dropping since its high for the year near $3.60 and it appears to be still dropping as its reached $3.17 a gallon.

Saw an article that indicates How do we solve climate change? America needs to use more electricity, not less.

how can this be true when

The price of electricity in Iceland is 0.134 U.S. Dollar per kWh for households and 0.065 U.S. Dollar for businesses1. This includes all components of the electricity bill such as the cost of power, distribution and taxes. In the first half of 2020, household electricity prices in Iceland using between 2.500 and 5.000 per kilowatt-hour (kWh) averaged 13.41 euro cents per kWh2. Electricity prices in Iceland rose by 38 percent from the first half of 2013 to the second half of 2018

So then I should be doing fine as I am at over 0.22566 us...

SpaceNut

Administrator

From: New Hampshire

Registered: 2004-07-22

Posts: 28,884

Re: Current Gasoline/Petrol Price$

Price at the pump has continued to drop and rests at $3.01 today.

SpaceNut

Administrator

From: New Hampshire

Registered: 2004-07-22

Posts: 28,884

Re: Current Gasoline/Petrol Price$

Price at the pump continues to drop below to $2.97 which should be a means to driving the economy with the extra funds not spent on gas.

Calliban

Member

From: Northern England, UK

Registered: 2019-08-18

Posts: 3,433

Re: Current Gasoline/Petrol Price$

Daily life in Holland, captured on camera in colour before 1930.
https://m.youtube.com/watch?v=vg-1ULNB4fQ

This was an (almost) pre-gasoline society, though certainly not pre-industrial.  I saw a few cars in this video, but if they had disappeared from life back then it wouldn't have made much difference to daily life for most people.  Life looked poorer, but we would still recognise it as a modern society.  Everything was a lot more labour intensive.  There was plenty of electric transportation, in fact it was more important than it is today.  All of it was in the form of rail based trams, powered by sliding contacts with a grid connected cable.  People walked longer distances and used their muscles a lot more.  My general observation when watching old videos like this, is that life was clearly harder for most people.  But places look more alive than they do now.

Last edited by Calliban (2023-12-07 03:43:31)

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"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."

SpaceNut

Administrator

From: New Hampshire

Registered: 2004-07-22

Posts: 28,884

Re: Current Gasoline/Petrol Price$

Bought gas today at $2.88 a gallon which is a good direction rather that mirroring inflation.

SpaceNut

Administrator

From: New Hampshire

Registered: 2004-07-22

Posts: 28,884

Re: Current Gasoline/Petrol Price$

Primary has come and gone and the day after the price jumped to $3.09 but has been holding.

SpaceNut

Administrator

From: New Hampshire

Registered: 2004-07-22

Posts: 28,884

Re: Current Gasoline/Petrol Price$

Its been a while since I posted what the cost for fuel is in my area.

It has been on the usual rise for the holidays of the summer.

Switching from winter fuels to the summer blend ways has this plotted course.

Its current price as of yesterday is $3.65 a gallon.