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The absorption (equivalent to dielectric loss) is used in microwave ovens to heat food that contains water molecules. A frequency of 2.45 GHz , wavelength 122 mm, is commonly used. Radiocommunication at GHz frequencies is very difficult in fresh waters and even more so in salt waters.
The specific enthalpy of fusion (more commonly known as latent heat) of water is 333.55 kJ/kg at 0 °C: the same amount of energy is required to melt ice as to warm ice from −160 °C up to its melting point or to heat the same amount of water by about 80 °C. Of common substances, only that of ammonia is higher.
An overview of absorption of electromagnetic radiation.This example shows the general principle using visible light as a specific example. A white light source—emitting light of multiple wavelengths—is focused on a sample (the pairs of complementary colors are indicated by the yellow dotted lines).
At the heat source of a system of natural circulation, the heated fluid becomes lighter than the fluid surrounding it, and thus rises. At the heat sink, the nearby fluid becomes denser as it cools, and is drawn downward by gravity. Together, these effects create a flow of fluid from the heat source to the heat sink and back again.
Many natural building materials are hygroscopic, that is they can absorb (water condenses) and release water (water evaporates). The process is thus: Condensation (gas to liquid) ΔH<0; enthalpy decreases (exothermic process) gives off heat. Vaporization (liquid to gas) ΔH>0; enthalpy increases (endothermic process) absorbs heat (or cools).
An endothermic process is a chemical or physical process that absorbs heat from its surroundings. [1] In terms of thermodynamics, it is a thermodynamic process with an increase in the enthalpy H (or internal energy U) of the system. [2] In an endothermic process, the heat that a system absorbs is thermal energy transfer into the
in the condensation of the water-vapour of the air on the cold surface of a glass; in the capillarity of hair, wool, cotton, wood shavings, etc.; in the imbibition of water from the air by gelatine; in the deliquescence of common salt; in the absorption of water from the air by concentrated sulphuric acid; in the behaviour of quicklime". [4]
Ammonia is the refrigerant and water the absorption medium. [1] In the absorber and generator, the absorption or effect of the ammonia aqueous solution is used to radiate heat or absorb heat. In the evaporator and condenser, the phase change of pure ammonia is used to complete the external absorption or heat release. [4]