Matter & Energy


Matter is composed of atoms or groups of atoms called molecules. The arrangement of particles in a material depends on the physical state of the substance. In a solid, particles form a compact structure that resists flow. Particles in a liquid have more energy than those in a solid. They can flow past one another, but they remain close. Particles in a gas have the most energy. They move rapidly and are separated from one another by relatively large distances.

Solar Cooling

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Solar energy can also be used for cooling. An absorption air conditioner or refrigerator uses a large solar collector to provide the heat that drives the cooling process (see Refrigeration). Solar heat is applied to the refrigerant and absorbent mixture, which is combined under pressure in a container called a generator or boiler. The Sun’s heat brings the mixture to a boil. The refrigerant (often ammonia) vaporizes, rises as a gas, and reaches the condenser. There it gives off heat and returns to liquid form. As the drops of pure refrigerant fall, they trickle into the evaporator (freezing unit) where they evaporate vigorously. Evaporation requires heat energy, which comes from the surroundings, and results in cooling: The refrigerant absorbs heat from the unit and cools the space. The refrigerant, now a gas again, rejoins the mixture in the boiler to restart the process.

Absorption coolers must be adapted to operate at the normal working temperatures for flatbed solar collectors—between 82° and 121°C (180° and 250°F) Alternatively, concentrating collectors may be used.