THERMODYNAMICS

# THERMODYNAMICS - Glossary to accompany Thermodynamics An...

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Glossary to accompany Thermodynamics: An Engineering Approach, 5 th edition by Yunus A. Çengel and Michael A. Boles Absolute entropy is entropy calculated relative to the absolute reference point determined by the third law of thermodynamics. Absolute humidity (specific humidity or humidity ratio) is the mass of water vapor present in a unit mass of dry air; that is, it is the ratio of the mass of water vapor to the mass of dry air in atmospheric air. Absolute pressure is the actual pressure at a given position and it is measured relative to absolute vacuum (i.e., absolute zero pressure). Throughout this text, the pressure P will denote absolute pressure unless specified otherwise. Absolute temperatures are temperatures measured on the Kelvin scale or Rankine scale, and these temperatures vary between zero and infinity. Absorption chillers are air-conditioning systems based on absorption refrigeration, and they perform best when the heat source can supply heat at a high temperature with little temperature drop. Absorption refrigeration systems involve the absorption of a refrigerant by a transport medium. The most widely used absorption refrigeration system is the ammonia–water system, where ammonia (NH 3 ) serves as the refrigerant and water (H 2 O) as the transport medium. Absorption refrigeration systems are economically attractive when there is a source of inexpensive heat energy at a temperature of 100 to 200 ° C. Some examples of inexpensive heat energy sources include geothermal energy, solar energy, and waste heat from cogeneration or process steam plants, and even natural gas when it is available at a relatively low price. Absorptivity is the fraction of the radiation energy incident on a surface that is absorbed by the surface. Acid rain is defined as rain or snow that washes acid-laden droplets from the air on to the soil. Adiabatic combustion temperature (see adiabatic flame temperature) Adiabatic flame temperature is the maximum temperature the products of combustion will reach in the limiting case of no heat loss to the surroundings during the combustion process. The adiabatic flame temperature attains its maximum value when complete combustion occurs with the theoretical amount of air. Adiabatic process is a process during which there is no heat transfer. The word adiabatic comes from the Greek word adiabatos , which means not to be passed. 1

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Glossary to accompany Thermodynamics: An Engineering Approach, 5 th edition by Yunus A. Çengel and Michael A. Boles Adiabatic saturation process is the process in which a steady stream of unsaturated air of unknown specific humidity is passed through a long insulated channel that contains a pool of water. As the air flows over the water, some water will evaporate and mix with the airstream. The moisture content of air will increase during this process, and its temperature will decrease, since part of the latent heat of vaporization of the water that evaporates will come from the air. If the channel is long enough, the airstream will exit as saturated air (100 percent relative humidity) at the exit temperature.
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