Extending the wet bulb line to the left shows the enthalpy of a pound of air. The intersection of the 70 ° F dry bulb line and 70 ° F wet bulb line is 100% or saturation.
Examples: The intersection of the 75 ° F dry bulb line and the 65 ° F wet bulb line is the 60% RH line. If one knows the dry and wet bulb temperatures, the RH can be found at the intersection of the two lines. The angled straight lines are wet bulb temperatures, and the curved and dotted lines are relative humidity. Along the bottom of the chart are dry bulb temperatures. For clarity sake, some lines and scales found on the usual psychometric chart have been omitted. A psychometric chart can be used to ascertain enthalpy.įigure 1 is a partial psychometric chart. When vaporizing water, latent heat is added to the air, and when vapor is condensed, latent heat is removed from the air.Įnthalpy is the sum of sensible and latent heat in the air. The heat required to change water to a vapor without changing temperature or pressure. Heat that changes the dry bulb temperature of air without changing the moisture content. No more moisture can be contained in the air. A 35% RH means the air is holding 35% of the moisture it could hold at that temperature and pressure. The ratio of moisture in air compared to the maximum amount of moisture the air could hold at the same temperature and pressure. A sling psychrometer is an example of an instrument that can measure wet and dry bulb temperatures at the same time. When the temperature stops falling and stabilizes, that is the wet bulb temperature. Evaporation of the water from the wick causes the temperature to drop around the bulb. The temperature read on a thermometer whose bulb is encased in a wet wick with air blown over the wick at a minimum of 900 feet per minute. The temperature reading on an ordinary thermometer. In order to understand the term “enthalpy,” the thermodynamics of air must be understood.Ĭommon terms used in studying the properties of air are: Enthalpy controls are not well understood by many service technicians.
0 kommentar(er)
