Ok...what would be the best liquid for a solar heating system? Water or Ethanol?
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What type of solar heating system are you trying to use? Water heater for a pool? Heat collection system for electricity generation? Water heater for household usage (such as a shower)? Since it seems like you are going for a heat exchange system (such as would be used in electricity generation), I'll go over some of this usage. The heat collecting material is generally one that is A) liquid at the temperatures being dealt with, typically hundreds to thousands of degrees; B) has a high capacity for carrying heat. For instance water has a heat capacity of about 4.18J g−1 K−1. That is, it takes 4.18 joules of energy to heat one gram of water by 1 degree kelvin. This contrasts with Ethanol which has a specific heat of 2.44J g−1 K−1. One way to look at it is that water holds nearly twice the energy as ethanol at a given temperature.
Typically the materials used for this are either a non-volatile hydrocarbon (basically one that won't boil), a saturated salt solution, a molten salt solution, or a molten metal such as liquid sodium. Google "solar heat concentration system and see what it gives you. There's Quite a few different research projects goin on that you may find interesting!
SO I guess a short answer to your question, not knowing any details, is that water would be a MUCH better choice than ethanol for solar heating applications.
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