Our Cooler

There is a little bit of science, and a LOT of trial and error that we went through to get to where we are now.  I once saw a video on salt water vs regular water ice blocks, and it was enough to convince me to do my own tests, which supported what I found in the video.   The end result is that I have salt water ice blocks in reusable containers that we use in our Cabela's cooler, and refreeze when we get home.  The picture to the right is one of our salt water ice blocks after about 48 hours in the cooler. The fresh water ice block in this test was about 1/6 ice to water in comparison.

Here are some facts (Ok, you math wizzes out there, someone check my calculations on this, because I went to skool in Kentucky):

• Blocks of ice have less surface area than tiny ice cubes, and therefore melt at a slower rate.  For example a 10" x 10" x 10" ice block has  600 square inches of surface area.  An individual ice cube of 1" x 1" x 1/4" has ~3 square inches of surface area.  This means that the block of ice has the equivalent surface area of only ~200 pieces of ice!  Now, to make up the same volume of cubed ice (.25 cubed inches) as we have in the block (1000 cubed inches), it would take  4000 ice cubes!  Now I haven't taken the downtime to count the number of ice cubes that come in a 10 or 20 lb bag, but seems to me a  block would take up a LOT less space in my cooler!  

• Cubed ice cools more quickly because of the larger amount of surface area in which heat can be absorbed.

Pure water freezes at 32 degrees; salt water freezes a t a lower temperature, depending on how much salt is in the water.  Here are some examples:

• Seawater freezes at 28.4 degrees Fahrenheit
• A 10-percent salt solution freezes at 20 degrees Fahrenheit 
• A 20-percent solution freezes at 2 degrees Fahrenheit

The thermal conductivity of water is much higher than air, meaning that air is a better insulator at keeping the outside temperature where it needs to be.  Outside my cooler.  My thought process is that if having water in contact with the inside of the box would increase the flow/transfer of heat through the walls of the box into the interior contents, it would therefore be conducive to not have any water in the cooler, which would further slow the thermal transfer of heat into the cooler, prolonging the desired cooling effect of the contents.  I don't like soggy anything in my cooler, but I don't like salty soggy anything in my cooler either.  So, that's one of the reasons why we use containers for our salt blocks.

So, here's what we found that works for us.  On the outside:

• We use a well insulated cooler.  
• We picked a WHITE cooler to reduce heat absorption.
• We keep our cooler out of the sun
• We keep our cooler wrapped in a reflective windshield sun shade.  They are ~$3 in the automotive section of the local-but-well-known-round-the-world-retail chain.

And on the inside:

• We pre-chill the cooler using whatever we have available, dry ice, gel freezer packs, regular ice blocks, etc.
• We freeze or pre-chill anything that goes in our cooler.  
• We reduce the surface area and increase the volume of ice by using ice blocks.
• We increase the efficiency of the ice blocks by adding salt to reduce the temperature at which the blocks melt.
• We contain the cold water so it doesn't soggy our food (Hey, that water is still cold too!)
• We reuse our salt water ice block containers over and over again.

One last thing.  We use POPCORN salt because it also turns the water yellow, so that we can tell them apart!

UPDATE: We used these salt water Ice Blocks on our Grand Canyon Trip. I packed the pre-chilled cooler on Sunday at 2PM. On FRIDAY the bacon still had ice crystals on it, but it wasn’t  completely frozen. We expected it to thaw, but we did not expect Ice crystals!  All in all our system worked very well on our trip, although we had one block that melted quicker than the other. We were very pleased with the outcome!