Saw dust can be used to slow down the melting process of ice.




What happens when ice is stores in saw dust?



Saw dust occupies a larger volume as compared to wood. The extra space entraps air within it. Air as well as wood is bad conductors of heat. As a result, the heat transfer that takes place between ice and the atmosphere is inhibited to a much larger extent as compared to what happens when ice is exposed to open atmosphere. This helps in preserving the ice in solid state for longer duration of time.



Why saw dust is so effective in storing ice?



Apart from acting as heat insulator, saw dust is also hydrophobic (water repellant). When the initial layer of ice melts in to water it forms a layer over the ice. The saw dust doesn’t absorb this water. Instead it floats on this layer of water. As this layer is surrounded by air and saw dust which are themselves heat insulators, heat transfer is reduced significantly.



When ice is exposed to the atmosphere directly, whatever ice is converted in to liquid water flows away from the surface. But when ice is stored in saw dust, the water layer doesn’t flow away so easily. However, it may try to evaporate. But since water has a large heat of evaporation, a lot of heat needs to be absorbed. Since ice is at a lower temperature than the water, the heat absorption takes place from surrounding saw dust. This prevents heat transfer to the ice, and helps ice to stay as solid for longer duration of time.

http://edu.thinkingpal.com/air-conditioning/storing-ice-using-saw-dust/