Use pressure to increase temperature of solar oven?

In summary: So I would use a parabolic mirror to focus the sun on the junction.In summary, the person is thinking of creating an electrical circuit that is powered by a temperature difference between two unlike materials. They plan to use a pressure cooker to heat up the junction and increase the temperature more than just linearly. They are also thinking of using a parabolic mirror to focus the sun on the junction.
  • #1
Sravoff
15
0
Hello, I want to build an electrical circuit powered by a temperature diffence between two unlike couple, such as copper and iron. I know a good thermocouple would be better, but I don't think I'll be able to get a hold of those materials as easily.

My current plan is to use a solar oven to heat up the iron/copper junction, and use evaporation too cool down another section of the circuit in order to maximize the energy difference.

I started thinking about a pressure cooker and thought if I sealed the junction in a metal container full of water, as the temperature increased, so would the pressure, which would also increase the temperature. In this way would the temperature increase more than just linearly? T=at^2 instead of T=at, where T is temp, a is some constant, t is time--time in focus of the paraboloid I am using to focus the sun.

My reasoning was also influenced by this thread, but it doesn't address my question specifically:
https://www.physicsforums.com/archive/index.php/t-39446.html

In order for my reasoning to be sound, in the Ideal Gas Law PV=nRT; P must be a function of T, and T a function of P, which seems very wonky.

However, back to the pressure cooker, they use pressure to increase heat, or at least retain more heat (as opposed to losing heat out the top of a pot with no lid) so there could be a benefit to pressurizing the junction.

What am I looking at here, and what kind of strange made-up alleys am I finding myself in?

Thank you
 
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  • #2
as the temperature increased, so would the pressure, which would also increase the temperature

If that were possible you would have thermal run away and BOOM.

It doesn't work like that. Pressure cookers work by preventing water from boiling. That way you can raise the temperature of the water above 100C. In an ordinary pan the water turns to steam and dissapears leaving only 100C water behind. However there is no free lunch. You don't get the extra temperature without adding more energy.
 
  • #3
As you use water for cooling, it would be a bad idea to increase its temperature. If you want to play with pressure, lower the pressure. However, this requires more energy than you will get by the better temperature difference in the metal.
 
  • #4
Thanks CWatters, I thought there was something strange going on with that reasoning and now I see exactly what is.

Mfb, I was going to use two reservoirs of water, one sealed for the pressure, and another for the evaporation, which would have to be refilled.

Thanks all!
 
  • #5
Why do you plan to use water for the hot part? A metal surface, painted black, should work fine and you can get a higher temperature - especially as the colder part is quite hot with ~100°C.
 
  • #6
I was thinking the pressure with the water could create a sort of controlled thermal run away, which is not the case. So I will be just using one piece of metal.
 
  • #7
Solar oven?

More temperature = more energy in a given area / volume.

Use a magnification system to heat the junction to very high temperatures.

A simple 120mm glass lense will be more than concentrated enough to "burn" (oxidise) a small thermocouple. Place it in argon in a long small corked test tube, that will stop it from oxidising, but only up to the melting temperature.

I thought the junction really only needed to be a few hundred *C anyway.
 
  • #8
I don't have much of a budget, no means to gather the best, possibly necessary, materials, soi am sticking to what I have. I would love to use a fresnel lens, but I don't have access to one, so parabolic solar oven it is.

Because the seebeck effect only produces tens of microvolts per degree of Kelvin difference, I want as many degrees as I can get.
 

1. How does increasing pressure affect the temperature of a solar oven?

Increasing pressure in a solar oven compresses the air inside, causing it to heat up. This increase in temperature is due to the fact that compressed air molecules have less space to move around, which results in more collisions and an increase in kinetic energy, leading to higher temperatures.

2. How much pressure is needed to increase the temperature in a solar oven?

The amount of pressure needed to increase the temperature in a solar oven varies depending on the size and design of the oven. Generally, a pressure of 1-2 atmospheres is enough to see a noticeable increase in temperature.

3. Can increasing pressure in a solar oven be dangerous?

Yes, increasing pressure in a solar oven can be dangerous if not done properly. It is important to follow safety precautions and use a pressure release valve to prevent the oven from exploding. It is also important to monitor the pressure levels and not exceed the recommended limit.

4. Are there any other factors besides pressure that can increase the temperature in a solar oven?

Yes, besides pressure, the reflectivity of the oven's surface and the intensity of sunlight can also affect the temperature in a solar oven. A highly reflective surface and direct sunlight can help increase the temperature even without added pressure.

5. How can I measure the temperature in a solar oven when using pressure?

To measure the temperature in a solar oven when using pressure, you can use a thermometer placed inside the oven. It is important to make sure the thermometer is not in direct contact with the heated surfaces to get an accurate reading. You can also use an infrared thermometer to measure the temperature without making direct contact with the oven.

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