Is it faster to cool hot water by adding ice immediately or waiting a few minutes before adding?

Question

You are heating a quart of boiling water. After taking it off of the burner, you have the task of getting the water to the lowest temperature possible at the 15 minute mark. You MUST add 50 ml of ice water in order to do so (can't omit it).

Should you add the ice water immediately after taking the boiling water off of the burner, or wait add the ice water at the 14-minute mark? It is either or; no times in between. Or does it matter at all?

Please expand on your reasoning and explain why the other options would be wrong if you can!

Answer 1

I suggest adding the water at the 14 minute mark because when the water is in boiling state steam escapes from it absorbing latent heat of vapourisation which only helps in the change of state from water to steam thereby decreasing the temperature of the water..If we add the ice cold water at the beginning the temp of the mixture would not cool quickly as the water will not evaporate and the latent heat of vapourisation that would have been lost will now be used to offset the temp. decrease brought about by the addition of ice.So if we add ice after 14 mins the mass of water will also be less and there will be lesser heat in that mass and so the temperature will fall rapidly.

Answer 2

I believe it is right at the 14 minute mark. Initially, the heat transfer is to the environment. Allow the greater differential between the boiled water and local environment to allow the greatest rate of heat transfer.

Then, once 14 minutes have passed, that temp differential is less. Adding the ice at this point will again increase that temperature differential, allowing a greater rate of heat transfer.

If allowed, I would suggest stirring throughout the process. This would allow the warmer center of the hot fluid to reach the outer edges, adding to the ability to transfer the heat either to the environment (or to the ice).

This reasoning does not apply if the ambient environment is at the same temp as the ice. I am not sure which time to add the ice if this is the case.

Answer 3

Try to draw a cooling curve to test the options. It may be that waiting a few minutes will give the fastest result.

My reasoning is as follows: Initially there is a large temperature gradient between the hot water and the ambient air. So the hot water will cool quickly without the ice (especially if stirring is allowed). After a brief period, the temperature curve will flatten as the water temperature gets closer to the ambient air. This would be a good time to add the ice and get another large temperature gradient to kick the curve downwards again.

Answer 4

It doesn't matter because there isn't enough ice to make a difference. If there was more you would want to add it at the begining because there is where it requires the ice the most. The ice would absorb the energy, the energy causes it to change phases, therefore you would want it added in the begining to absorb the energy but since there is an insufficient amount of ice for this it doesn't matter. Hope this helps!

Answer 5

the temp of the boiling water will drop eventually so therefore i would wait when adding the ice water. the 14 min mark would sound about right becuz u are shocking the water in its already cooling state.

Answer 6

Chocolate Eclair 1/2 (8 ounce) box graham crackers 2 (3 1/2 ounce) packages cheesecake flavor instant pudding and pie filling mix 3 1/2 cups milk 1 (8 ounce) carton french whipped topping 2 (1 ounce) semi-sweet chocolate baking squares 2 tablespoons butter or margarine 1 teaspoon light corn syrup 3 tablespoons milk 1 teaspoon vanilla extract 1 1/2 cups sifted confectioners' sugar Cover the bottom of a 13 X 9 baking pan with whole graham crackers, set aside. Combine pudding mixes and milk, fold in whipped topping. Spread over graham crackers. Top with another layer of crackers. In a saucepan, melt chocolate and butter. Remove from heat and add remaining ingredients. Spread over top of graham cracker layer. Cover and refrigerate. Best made at least a day ahead of time, to let it soften and blend flavors. I've also used 1 package of french vanilla pudding mix and one cheesecake pudding mix.

Answer 7

I would think it doesn't make a difference at all. Think of it this way:
What could make you get to the destination faster, Running the first 2 minutes or the last 2 minutes?

Answer 8

right away start the cool down quicker