h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Antimatter requires a lot of complicated equipment. What if instead you took a lump of radioactive material and threw it into where the coals should be. The heat from the decay should be able to heat the water and drive your car. And glowing in the dark will mean you get seen in traffic.

Antimatter would not work to heat up water. Antimatter reactions generate energy in the form of gamma rays, which would shoot right through just about anything you held around the antimatter reaction without heating anything up to any appreciable degree.

Theoretically, you could use nuclear fission to generate heat to make steam. For a vehicle, however, the major design barrier would be the shielding necessary to keep from killing everything within 50 feet every time the car started. Nuclear power plant reactors are generally shielded with several feet of concrete. A "safe" nuclear powered car would probably resemble an American M1 battle tank and be too heavy to move.

but it would cerianly have enough energy.

-- DoctorMO --

"You scare me sometimes H"

Aah, I'm a pussycat. Although I'm not a man you'd want to buy a kettle from, obviously...

H.

OK, liquids that boil at around 40 ºC

Ether, dichloromethane, petroleum ether (40-60ºC fraction)

Unfortunately they all suffer from either high toxicity and/or extreme flammability. Also, they lack the one ingredient that is reasonably unique to water as a liquid, a high heat capacity. This means that they are *much* easier to heat up, however - and this is the killer, they are unable to retain this heat when they get it so they would cool down very quickly and lose any advantage you gained.

Having just read the BL since yesterday, I was wondering when someone would mention *why* we use water/steam as opposed to other liquids.

Producing useful work from a *heat* engine is ALL about the heat capacity of the fluid used. Water and steam have a phenomenal capacity to store heat energy, way above most other liquids, plus they stay chemically stable across a wide range of operating temperatures and pressures I mean they don't go bang

Thanks for the geeky bit, H

I am amazed none of you have mentioned the microwave oven which must be the most efective method of heating water (or is it?).

To check your Microwave, pour exactly 1 litre of cold water into a plastic, microwave safe container. Stir the water and measure and record the temperature. For accurate results the water should be about 60°F (20°C).
Place the container on the center of the oven cooking tray (do not leave the thermometer in the container and remove any metal racks). Use a watch, not the oven timer to heat the water (at full power) for 63 seconds.
After the heating time is completed, immediately remove the container, stir the water, re-measure and record the temperature of the heated water.
Subtract the starting water temperature (step 2) from the ending water temperature (step 3) to obtain the temperature rise.
The output power in watts, is the total temperature rise times 38.75(for Fahrenheit); 70(for centigrade).
Try doing the same with an electric kettle.

Blue/Green Alji

Two things:

Way back in Post 2, someone mentioned cost-effectiveness, which sort of blows the antimatter idea out of the air.
Lightning would be my suggestion there. As far as I know, no-one's yet worked out a way of selling it.

Isn't it interesting how people start talking about arguments and hot air just two posts after Hoov turns up.

B

The reason no one has mentioned using a microwave is the reason that the post originator wants to heat water. The need for heated water is to generate steam to drive a steam-powered vehicle. If one were to use a microwave to heat the water for this, one might as well use the electricity required to drive an electric motor.

Wampus, I think you should read the first post again!

<quote from post 1>
Say, for example, boiling water. There are lots of sources of heat, and ways of generating it, but if I wanted to heat something up, say boil a litre or two of water and keep it boiling, what is the most efficient way?



Blue/Green Alji

Its A good Question

Have you tried the cold fusion packs from the galaxy core yet?
They are on sale for over a century now.
Perhaps for steam efficiency it is best to use your local sun:
use a convex mirror as the basis of your vehicle.
Place a container filled whith that liquid filling your oceans.
Wait for the temerature to raise high levels and pull the small plug on what you think to be the rear side of your vehicle.
Clear the sky using bright days and build a reflector on the night side of your planet to travel anywhere.
Ofcourse you can always use the more convenient way of transport of steptiles.

Rev., see post 6. It offers further explanation.

OK from post 6;
However, if you could have an extremely efficient means of heating the water and maintaining the steam then the steam powered vehicle would become much more attractive.

It's not about using electricity to power a motor, it's about boiling water!

Blue/Green Alji

Okay, then let me tell you how efficient using a microwave to boil water is.

In order to generate electricity, most power plants use a heat cycle to generate steam and turn a turbine. Due to the second law of thermodynamics, the most efficient such a cycle could be is 40%; that is, only 40% of the heat generated in a power plant gets converted to electricity, and the rest gets dumped into the surrounding environment.

Once that electricity leaves your house, it goes over high-voltage transmission lines. Electrical grids are only 50% efficient at moving electricity. If the power plant puts out 2 megawatts of electricity, then one MW of electricity actually gets to consumers and the rest dissipates as heat in the power lines.

So between thermodynamics and transmission loss, using any electricity at your house requires four times that much energy to be dissipated into the environment. And then once it gets to your house, you convert that 20% efficient electricity back into heat to heat up your water in the microwave, which generally runs between 1000 to 1500 watts, which is enough power to light twenty-five 60-watt lightbulbs.

To boil one kg of water that's started at room temperature (25 degC), you'll need about 394 kilojoules of heat energy. If you use electricity, then that 394 kj of heat requires the power plant to release 1970 kj of heat, or the energy in 54 litres of natural gas at standard pressure. Me, I'm going to use a natural gas stove, and use 1/5 that amount of natural gas (9.8 L) to boil my water.

Convenience does not equal efficiency.

A cautionary WARNING to anyone considering microwaving a container of water.

This is seriously dangerous.

It has been known (albeit rarely) for microwaved containers of water to *appear* to be unboiled, however once disturbed and removed from the microwave the contents *can* turn into steam and seriously injure you.

It is the opposite effect to that of cooling pure water to freezing. The water (depending on purity and movement) can appear to remain liquid until an impurity is introduced or the container is adequately disturbed.

This is NOT a joke.

are you really wedded to steam as a power source? there are lots of other "alternate energy" systems which you could use if you are not wedded to steam.

for example a sterling engine might be a better bet. it is a thermal to mechanical converter, which gives you a reciprocating motion which you then usually convert to rotary.

this is also an external combustion engine with a similarly long history. unfortunately, large horse power sterling engines are very big.

having said that, they can be very efficient. some of the ones you can get for home energy systems can return twice the energy you put in.

you would probably use solar collectors on the roof, combined with air cooled radiators to provide the heat difference. you might also use a solar concentrator or a small burner on the roof collectors as a priming stage.

a lot of good technologies got delayed by decades or more due to vested interests.

Madent, this is due to super-heating of de-gassed water. It can happen when you re-boil water or if the water has been left to stand in the container for a long time.

xyroth, a sterling engine is good for producing electricity because it runs at a constant speed but the steam engine can run at low speed without loss of power.

Ictoan, wants to use steam because of its advantages. He wants to know the most effective way of making steam.


Blue/Green Alji

More on super-heating from http://www.phys.unsw.edu.au/~jw/superheating.html
<quote>
Suppose that we heat one kilogram of water from 100 °C (its normal boiling temperature) to 101 °C, i.e. it is now superheated by 1 °C. When it begins to boil, it will very quickly cool to 100 °C, and the heat liberated turns water into steam. Cooling this kg of water by 1 °C gives 4.2 kJ, which is enough to evaporate c/L = 4200/2230000 kg of water. This is only 1.9 millilitres of water, which does not sound very much, but it turns into 3 litres of steam. Those three litres of steam are created insidethe hot water, quite suddenly, so the water is ejected violently from the container.

Blue/Green Alji

Superheating water is quite tricky. Superheating custard, on the other hand, is very easy, as the surface tends to form a film beneath which quite a lot of superheat can build up. There have been a number of horrific injuries of people who have heated custard in a microwave, then stuck a spoon through the film and been covered in sticky, viscous semi-fluid at temperatures well in excess of 100 C.

Custard-powered car anyone?

H.

Hoo, it also works with porridge!!!

Microwaves are very good at superheating water because the molecules are heated directly.

Blue/Green Alji