Cooling 27L of Water from 100°C to 20°C in 5 Minutes

In summary, this person is trying to figure out how to cool water quickly using heat. They are aware of formulae, but want help with the time restraint.
  • #1
Etude
28
0
Hi!

So this is the scenario.

I have 27 litres of water at 100 degrees Celsius. I have to cool the water to 20 degrees Celsius within 5 minutes. Since the heater power required is too high, I thought this could be done by adding in water at 20 degrees Celsius while draining out the water at 100 degrees Celsius simultaneously. I need to decide on the following: flow rate of cool water in, flow rate of hot water out while making sure the water cools to 20 degrees within the 5 minutes.
I have no idea which formulae can help me out here. Can anyone please advise which formulae can be used? :smile:
 
Physics news on Phys.org
  • #2


Try googling "method of mixtures" to see the sort of approach you need. Basically, it works on the principle of Heat at start = Heat at finish.
Equate the two and you should get an equation with one unknown (if the question has been set correctly).

Total Masses at start times SH times temp drops plus heat added = Total masses at end times SH times temp rises
Think it through and then put in the appropriate values.
Initially, you'd do the sums ignoring heat loss to the surroundings, of course.
 
  • #3


Thanx!
I am aware of those formulae but I do not know how to factor in the time restraint and would like some help there.
Will still tinkle around with those formulae till then!
 
  • #4


Oh and it s not a 'question' to be solved as such. More like a design project. So lots of unknowns present.
 
  • #5


The approach would be to consider the energy transfers in, say, one minute. You are adding so much water in that minute and the heater is supplying so much energy in that time etc. etc. so you are back to a 'static' situation with an initial state and a final state which will give you the rate of heating per minute (for instance).
Does that help? Often, it can be really useful to do this sort of thing on a spreadsheet, in steps of a minute (or whatever's suitable) and then you can plot a graph of temperature rises as time progresses. (Let the computer take the maths load off your shoulders)

I remember doing the Callendar and Barnes experiment, back in about 1961, at School, with tap water flowing through a heated tube, measuring rate of flow by filling beakers and then reading two thermometers for getting the temperature rise. Happy daze.
 
  • #6


OH! Ok ! That does help! Basically, the final state at minute none will become the initial state for minute two and so on, right ? Thanx!
 

What is the best method to cool 27L of water from 100°C to 20°C in 5 minutes?

The most effective method to cool water quickly is by using an ice bath. Place the container of water in a larger container filled with ice and water, and stir the water to promote even cooling.

How long will it take for 27L of water to cool from 100°C to 20°C using an ice bath?

The cooling time will depend on various factors such as the temperature of the ice bath, the initial temperature of the water, and the rate of stirring. In general, it should take around 5 minutes for the water to reach 20°C.

Can I use a refrigerator to cool 27L of water from 100°C to 20°C in 5 minutes?

No, a refrigerator is not a suitable option for quickly cooling a large volume of water. It may take several hours for the water to cool down to 20°C in a refrigerator. An ice bath is a more efficient method for rapid cooling.

What happens if I add ice directly into the hot water to cool it down?

Adding ice directly into hot water may cause the ice to melt too quickly, resulting in a slower cooling process. It is best to use an ice bath to cool the water gradually and evenly.

Is it safe to cool 27L of water from 100°C to 20°C in 5 minutes?

Yes, it is safe to cool water using an ice bath as long as proper precautions are taken. It is important to handle the containers and ice carefully to avoid any accidents. It is also recommended to use heat-resistant containers to prevent cracking or breaking due to the sudden temperature change.

Similar threads

Replies
5
Views
2K
Replies
31
Views
2K
Replies
2
Views
753
  • Mechanical Engineering
Replies
6
Views
880
Replies
6
Views
19K
  • Introductory Physics Homework Help
Replies
8
Views
3K
Replies
4
Views
1K
  • Mechanics
Replies
13
Views
2K
Replies
43
Views
11K
  • Mechanical Engineering
2
Replies
36
Views
4K
Back
Top