Keeping Things Cold

Aside for the normal gas or electric refrigerator, there are other ways to keep drinks and food cool while you are out on the river. This page looks at a few alternatives that may be useful.

Coolgardie Safe / Water Bag

The Coolgardie Safe and the water bag work on evaporation. In the Coolgardie safe, hessian flags are kept moist using water in a reservoir on the top of the safe, while the fabric of water bag allows water to seep put, keeping the surface moist. The safe and the bag work because water absorbs heat as it evaporates. This means that heat is drawn from the moist Hessian flaps on the safe or the surface of the bag. The movement of air around the safe and the bag are important as it prevents the air surrounds the wet surfaces from becoming saturated and reducing the cooling effect. The movement of air through the safe also moves the cooler air over the items to be cooled.

The effectiveness of these devices depends on the relative humidity and the amount of air movement. The lower the relative humidity, the more effective the cooling will be. The units are also more effective if there is a breeze rather than still air. Once the air flow is enough to remove all of the additional moisture in the air caused by the evaporation of the water, there is little to be gained with higher wind speeds.

Evaporative air conditioners work on the same principle as the Coolgardie Safe and the water bag. As a result, the best cooling you can expect with these devices is similar to what you can expect with evaporative air conditioners. In practice you can expect that the cooling will not be as effective as proper evaporative air conditioning unit.

Water Ice

Ice made from water is the most commonly used coolant for ice boxes and has a number of advantages, not the least of which is that it is relatively cheap and readily available. It is generally available from most hotels and bottle shops, many garages as well as bait and tackle shops. Generally ice in Australia is made from potable water so it can be used in drinks provided it has been kept in sanitary conditions.

Ice straight the supplier is likely to be around -20 degrees Celsius. Fresh ice is normally provided in a bag of some kind, so the risk of your hand freezing to the ice is relatively low and generally considered safe. Ice melts at 0 degrees Celsius under normal atmospheric conditions and this should be considered the storage temperature of items in an ice box with an adequate supply of ice.

Ice in a solid block will tend to last longer before it completely melts. Ice cubes or other granulated ice, such as crushed ice, will cools the contents faster, but melt faster as more surface area of the ice is exposed.

To get the most out of your ice, it is recommended that all items to be placed in the ice chest are first cooled as much as possible. This means that the ice does not have to cool the items down to the melting point of the ice. The higher the volume of ice being used to the volume of the products being cooled will also influence how long the ice will last. The more ice there is the more heat it can absorb before it all completely melts.

One of the disadvantages of ice is that as it melts, it leave behind water. This water can soak into the produce being stored and possible reduce its quality. In these cases, it is best to place the items to be cooled into waterproof bags or containers to keep the melt water away. Some water in the ice chest does allow items such as drink cans to be cooled quicker as the water allows the heat from the cans to be drawn away faster. This down side is the ice ends up melting faster.

Dry Ice

Unlike water ice, dry ice is frozen Carbon Dioxide. At normal atmospheric pressure, dry ice sublimated as it warms. That is, the Carbon Dioxide goes straight from a solid to a gas. Hence the name "dry ice". Carbon dioxide melts at a -81 degrees Celsius, which is much lower than water. As a result, touching dry ice can result in serious frost bite and care should be taken when handling dry ice. It is normal practice to wrap dry ice in some sort of covering to protect people. A few sheets of newspaper wrapped around the dry ice is a cheap and effective way to protect yourself, although you should always use gloves when handling dry ice.

Because dry ice is much colder than water ice, it is possible to fully freeze items when they are packed in dry ice. This means that it is possible to keep items such as meat and frozen vegetables frozen solid. 

Although dry ice does not produce water, it does produce carbon dioxide which can cause suffocation by excluding oxygen in the ice chest. This is not likely to be a hazard to adults, but depending on the size of the chest, it may be a hazard to children as the Carbon Dioxide may linger even after the dry ice has fully evaporated. Because the dry ice excludes the oxygen in the ice chest, it does tend to slightly preserve the contents because aerobic bacteria cannot grow as well without the normal level of oxygen.

Like water ice, dry ice can come in granules or blocks and like water ice, the blocks tend to last longer, but the granules tend to cool faster as they have a greater surface area that can come in contact with the air.

Dry ice can have a disastrous effect on your drinks. The temperature of dry ice is low enough to freeze even alcoholic drinks and the resulting expansion will burst the bottles and cans.

Dry ice can be used to produce bubbling fog in drinks at parties and pellet dry ice is best for this purpose. However care must be taken to ensure that dry ice does not end up in drinks as it can cause internal frost bite if swallowed.

The River

The river itself is a good way to cool things down. Drinks and other items can be cooled simply lowering it into the water which is quite cool. To ensure that the items are not affected by the water, they should be placed in a sealed plastic bag before immersion. This will prevent the water affecting food and stop the labels on bottles from coming off.

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