Ethanol Water Heat Exchange

Hello.

We are assigned to do this for our final exam:

We should heat 1 liter of water using 100 ml ethanol. We are only allowed to use a mechanical stirrer. Absolutely no other forms of energy should be added...except on igniting the ethanol.

The ethanol and water are in one container.

The one with the highest final temperature of water will get the highest possible grade...(i think if the water goes up to 100 Celsius.. your grade will be 100...if 50 Celsius..then you get 50)

Please help me on this. Any suggestion will be very much appreciated...thanks...

Are you supposed to heat the water by burning the ethanol? If so, I don't understand how they can be in the same container, because the ethanol and water will mix giving a ~9% ethanol solution, which you won't burn especially if you are stirring at the same time.

You could add heat by increasing the speed of the agitator, and also by increasing agitator diameter. Fitting baffles to the inside of the pot you're heating in will improve turbulence, and thus heat transfer.

Insulating the pot externally (except for the area of heat input!) will reduce heat loss, as will covering the pot's opening.. Make sure the insulation won't burn. I'd make the inside of the lid reflective (e.g. with foil) to help minimise losses by reflecting heat into the pot.

You may me able to use a spirit burner (with a wick) to burn the ethanol in a controlled way. If you put the burner under the water pot, then you could put something reflective (like foil) under the burner to reflect heat upwards (look at the reflective coating surrounding the bulb in a flashlight), although this may not help appreciably.

If you do manage to boil the water, you will lose heat through steam. If you are receiving marks for how high the water temperature is, then you don't want to lose steam, because your heat input will be used for latent heating, which sees no temperature increase. If you are trying to sustain your boiling temperature as long as possible, then it would be better to put out the burner when you reach 100 degC, and relight it when the temperature starts to drop, to make most use of your available heat.

Does the water have to be pure water? If you are allowed to add salt (for example), this will elevate the boiling point, so you stand less chance of losing heat through steam, and more chance of reaching the highest temperature. Check if you are allowed to do this.