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This lecture focuses on essential definitions related to air and water vapor mixtures, addressing key concepts such as dry bulb temperature, wet bulb temperature, dew point temperature, humidity ratio, vapor pressure, relative humidity, enthalpy, and volume. By exploring these definitions, we can better understand moisture issues in both the air and grains, enhancing our grasp of psychrometry. The lecture also introduces the psychometric chart, a valuable tool for visualizing relationships among these properties.
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Definitions • Air –Water Vapor Mixture • Two moisture issues * moisture in the air * moisture in the grain • Dry Bulb Temp • Temp of ambient air • Wet Bulb Temp • Similar to dry bulb measure, except that the bulb is covered with a water moistened wick, and placed in moving air stream, where the thermometer is cooled by the water evaporation
Definitions Cont. • Dew point Temp • Point at which the air vapor is cooled without adding or removing moisture, the RH will increase until it reached 100%. Basically temp at which dew occurs. • Humidity Ratio • Wt of water/unit of dry air • Vapor Pressure • Pressure Exerted by water vapor in a given sample • Relative Humditity • Ratio of vapor pressure of the water vapor contained in an air-vapor mixture to the vapor pressure of an air-vapor mixture that is completely saturated
Definitions • Enthalpy • Amount of heat energy contained in an air-vapor mixture per unit wt of dry air. Expressed as Btu/Lbs dry air • Volume • Two terms are needed * humid volume-volume occupied by an air vapor mixture per pound of dry air @ a given temp • Psychometric Chart • Graph of all above relationships, where if two properties are know can solve for an unknown
