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I was boiling the water for some pasta the other day, with the extraction hood switched on. It was clear to me that this was a hugely inefficient system, with considerable energy lost in heating the air in the kitchen.
I came to a proposal.
Firstly, the rising steam from the boiling water
could be used to semi-power the extraction process ie. as the steam rises, it could power a small turbine which in turn could power extraction. It wouldn't completely power it, but it would go some way towards it.
Secondly, the Ideal Gas equation (link) says that as you reduce pressure, energy required for boiling is less. So, if my new extraction hood was powerful enough to lower the pressure above the pan of water, it would take less energy to boil it.
The temperature of the boiling water would also be lower and potentially safer.
Ideal Gas Equation
http://www.pmel.org/HandBook/HBpage20.htm
... hope this might explain it [jonthegeologist, Oct 04 2004]
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By reducing the pressure, not only will you reduce the boiling point of your water, you will increase the time it takes to cook your food. This will lead to soggy vegetables and pasty pasta. |
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... fine for boiling milk, warming babies bottles.... |
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If you get this thing working efficiently enough, will you even need the stove? |
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The simplest way to increase the efficiency of your system is to put a lid on the pan, then turn the heat down to avoid boiling over. It helps if you have a glass lid so you can monitor the boiling. |
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As for milk, if the goal is to make condensed milk, sure, lowering the presure is a good way to extract the water. If you actually want to cook anything, you need to raise the temperature. |
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If you want to boil pasta really efficiently, you should use an insulated pressure cooker with a temperature/pressure controled heating element inside of the insulated chamber. When the water reaches boiling temperature, the pressure will have increased, so it won't actually boil, but the pasta will cook. Since it is insulated, very little heat will need to be added to keep it at boiling temperature for the specified cooking time. Then of course you'd want a stirring mechanism to avoid sticking and a pressure lock for extracting single noodles to make sure they are done before letting all the pressure out. And since you've got to have a valve to safely release the pressure, have that directly vented outside to avoid heating the house in the summer. |
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Some thoughts about boiling: The reason we boil food is that boiling water acts as a very simple to use temperature regulator, so we can hold the food at 100 degees C for the required cooking time. When you add salt to the water, you are fine tuning the boiling point and increasing the regulated cooking temperature. This method of temperature regulation is inefficient because it keeps the temperature down by throwing away any water molecules that are hotter than 100 C, wasting that heat. Decreasing the pressure reduces the boiling temperature, but it is still just as inneficient becasue all the hot molecules are leaving the pot. As you point out, you can recover some of the energy from the steam, but heat engines are not very eficient, especially with a fairly small temperature difference between low pressure steam and room temperature. |
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This idea could be useful for baby bottles if you could lower the pressure enough that it boiled at the ideal temperature of a baby bottle. Then you'd be using the reduced boiling point for temperature regulation. That would prevent overheating the milk. Unfortunately, it would still be inefficient, and it would heat the bottle more slowly than using hotter boiling water or a microwave. |
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