|
An ice pack or gel pack is a portable plastic sac filled with water, or refrigerant gel or liquid. For use the contents are frozen in a freezer. Both ice and other non-toxic refrigerants (mostly water) can absorb a considerable amount of heat before they warm above 0 °C, due to the high latent heat of fusion of water. These packs are commonly used to keep food cool in portable coolers, or as a cold compress to alleviate the pain of minor injuries; or in insulated shipping containers to keep products cool during transport. Ice packs are used in coolers to keep perishable foods (especially meats, dairy products, eggs, etc.) below the danger zone when outside a refrigerator or freezer, and to keep drinks pleasantly cool. The amount of ice needed varies with the amount of food, its initial temperature, the thermal insulation of the cooler, and the ambient temperature and exposure to direct sunlight. Ice initially well below freezing temperature will last a little longer. Water has a much higher latent heat of fusion than most substances, and a melting temperature which is convenient and easily attained with, for example, a household freezer. Additives to improve the properties of water are often used. For example, substances can be added to prevent bacterial growth in the pack, or to prevent the water from solidifying so it remains a thick gel throughout use. Gel packs are often made of non-toxic materials that will remain a slow-flowing gel, and therefore will not spill easily or cause contamination if the container breaks. Gel packs may be made by adding hydroxyethyl cellulose (Cellusize),〔 〕〔 〕 Sodium polyacrylate, or vinyl-coated silica gel. ==Instant ice packs== Instant cold packs use an endothermic reaction to cool down quickly. They are stored at room temperature, without needing to be cooled before use. When the pack is manipulated to break a tube in it, two chemicals mix or react, and cool by absorbing thermal energy. Common types include solid ammonium nitrate dissolving in water and urea dissolving in water.〔(【引用サイトリンク】title= How Refrigerators Work: Cold Packs )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「ice pack」の詳細全文を読む スポンサード リンク
|