I am making a cool air equipment on a bucket with a fan above the closed bucket lid. The problem is that the ice on the bottom of the bucket (kept in a packet/bottle) melts faster. I tried using salt with the water, but it does not seem to have much of an effect.

So is there a "best" ratio of salt to water?

Is there any other way to slow the melting of ice?

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    It sounds like you might be trying to break the laws of physics. The only way that ice can take heat out of the room is by the ice absorbing the heat and ultimately melting. If you want to achive X amount of cooling, you'll necessarily need Y amount of melting. You can have less intense cooling over a longer period of time but you can't have your cake and eat it. – David Richerby May 16 '15 at 9:15
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    Further more, it cools the most when it is melting. Like an order of magnitude more energy is expended melting the ice, vs raising the water from 0C to 25C – Lyndon White May 16 '15 at 9:48

You can improve your bucket by:

  • insulating with aluminum foil and/or using a cooler insulated with Styrofoam.
  • draining the ice as soon as water has accumulated.

And if you make your own ice make sure to:

  • boil your water before freezing it to remove air bubbles and make it denser.
  • add 1 tsp. (6 g) or more of salt to a gallon (3,78 l) of boiled water before making ice. Salt changes the freezing temperature of ice. It will freeze and melt more slowly.
  • use as big ice cube trays as possible (muffin tins as alternative). The bigger the ice block the slower it melts

Source: WikiHow

  • Started working with it... Cheers!!! – mustangDC May 16 '15 at 6:02
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    According to this page from the physics department of the University of Illinois, adding 6g of salt to 3.78l of water will suppress the freezing point by around 0.1 Celsius (0.06F). Adding that little salt is a total waste of time. – David Richerby May 16 '15 at 13:20
  • Completely agree – mustangDC May 16 '15 at 19:38

A simple solution is more ice with less surface area. The less surface exposed surface area, the slower the ice will melt. Ideally, use a single ice ball (sphere) instead of multiple small ice cubes.


The point is to have cool air, using a large block of ice might prolong the life of the block but perhaps a smaller block can reach the same cooling results. Therefor, break the block into the sizes that get the job done, and the rest leave in the freezer.Every time the block melts, replace it with what you have in your freezer. Its easier to freeze smaller blocks of ice. In addition , packing the ice box with dry ice around the ice block will prolong the life of the block. But check if its ok to breath that stuff.

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