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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, 2015 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
    – Frames Catherine White
    May 16, 2015 at 9:48

4 Answers 4

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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

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  • Started working with it... Cheers!!!
    – mustangDC
    May 16, 2015 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, 2015 at 13:20
  • Completely agree
    – mustangDC
    May 16, 2015 at 19:38
  • @mustangDC Salt lowers the freezing / melting point... Thereby accelerating melting because it would have to be even colder to remain frozen than if there were no salt. This is why we dump salt on the roads in Canada.
    – Luke Sawczak
    Jul 30, 2021 at 12:59
  • @LukeSawczak I think the answer is working the logic the other way. By freezing salted water, the intention is to start with ice at sub-zero degrees. You’d get the benefit of the additional temperature differential when it melts in the room.
    – Lawrence
    Aug 1, 2021 at 15:51
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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.

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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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Also you want the air to skim across the cold Ice/water So I agree with most of the comments I will make it clear that if you are trying to cool off anything bigger than a approx. 10' x 12' room you are definitely going to need it to be insulated so if it 108°F outside and your garage is 115-120°F YOU BETTER GO FROM LITTLE TO HUGE! So what you need to do is get a good fan one that pushes some air. More like a blower is best. Anyway channel the air down and force it directly at the ice/water. Leaving only 2-3 inches between the cooling source and the bottom of the air funnel. But be sure that you have enough airflow to let the fans motor do its job at optimal efficiency. So go with 4x1.5" or 2" if needed or you will burn the motor out quick as shit. The blowback from the air not being able to escape freely is a lot of the problem that people don't even realize. That said once you do this it will drop a 12'x12' insulated room 10-20°F really easy and quiet quickly. Crack a window just about ¹/²" and let the hot air be pushed out of the room also for about 5-10 min. Mix sugar with the water ( Sugar? Yes sugar ) and freeze it. If you have a block of ice put it in the bucket cover the top with about 1/2-3/4 of a cup of sugar. Sugar will make it melt more slowly than hot water, cold water, and salt. I know most people never heard of putting sugar on it just salt. You always can look it up and make sure if you want to. But I have been doing a lot of homework lately and I've been impressed with how much colder the temp dropped and for how much longer. 1st test temp coming from the 2x 1¹/4" ports was 55-62. Then i added the funnel and 2 more x 1¹/4" holes= 4x1¹/4 and it dropped the temp coming out to 36-44°F. When I added the sugar onto the Ice alone it dropped the temp down to 24-28°F consistently and lasted 1¹/2 longer than just ice or ice with salt.

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