Use pressure to increase temperature of solar oven?

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Discussion Overview

The discussion revolves around the feasibility of using pressure to increase the temperature in a solar oven setup for generating electricity from a thermoelectric circuit. Participants explore the implications of using a pressure cooker concept in conjunction with a solar oven, the role of water in the system, and alternative methods for achieving higher temperatures.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant proposes using a solar oven to heat a copper/iron junction while employing evaporation to cool another section, aiming to maximize the temperature difference.
  • Another participant warns that increasing pressure to raise temperature could lead to thermal runaway, arguing that pressure cookers function by preventing water from boiling and do not provide additional temperature without added energy.
  • A different participant suggests that increasing the temperature of water used for cooling would be counterproductive and recommends lowering pressure instead, although this may require more energy than the temperature difference can provide.
  • One participant acknowledges the confusion in their reasoning regarding pressure and temperature and indicates a shift to using a single piece of metal instead of water.
  • Another participant questions the use of water for the hot part, suggesting that a black-painted metal surface could achieve higher temperatures.
  • One participant contemplates the idea of controlled thermal runaway with water pressure but later decides to simplify their approach to using just metal.
  • Another participant mentions that more temperature results in more energy in a given area and suggests using a magnification system to achieve high temperatures, mentioning the use of a glass lens for concentration.
  • One participant expresses budget constraints and a lack of access to optimal materials, indicating a preference for using a parabolic solar oven.
  • Another participant notes the limited voltage output of the Seebeck effect and emphasizes the need for maximizing temperature differences.

Areas of Agreement / Disagreement

Participants exhibit disagreement regarding the effectiveness and implications of using pressure to increase temperature in the proposed setup. There is no consensus on the best approach, with multiple competing views on the use of water, pressure, and materials.

Contextual Notes

Participants express uncertainty about the interactions between pressure and temperature in their proposed systems, highlighting the complexity of thermodynamic principles involved. There are unresolved assumptions regarding energy requirements and the efficiency of different materials and methods.

Sravoff
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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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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.
 
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.
 
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!
 
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.
 
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.
 
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.
 
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.
 

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