The dew point of about 73☏ can be read out using the chart. elationshis of lines of properties on the psychrometric chart. Once the point is located, the values of all other properties can be read (Figure 1 1-2). It can be defined and located by the values of any two properties. Find out where the intersection point is with RH of 70%. 1 1.4.1 State Points Any point on the chart can be a state point. Find the dew point.įollow the vertical line of the DB temperature of the chart at 85☏. Question 2: The DB temperature of a sample of air is 85☏ and relative humidity is 70% RH. Read the humidity line where this point is. Find out the point where these two lines intersect. Similarly, follow the line of the WB temperature at 60☏. Question 1: If the DB (dry bulb temperature) is 80☏ and WB (wet bulb temperature) is 60☏, find the relative humidity.įollow the vertical line of the DB temperature of the chart at 80☏. The SI units are cubic meters per kilogram of dry air other units are cubic feet per pound of dry airĮxamples of using the Psychrometric Chart Specific Volume is the volume of dry air and water vapor occupied by one unit of mass of dry air. The SI unit is joules/kg of air or BTU/pound of dry air. Take note that these lines are not parallel to the wet bulb temperature lines though they may look so. These are oblique diagonal lines that are drawn from left to right and are parallel to one other. Specific Enthalphy is the total energy of the sample of dry air and water vapor. It is measured in grams of water/kg of dry air, or grains of water/pound of air. Humidity Ratio is the weight of water in a sample of air compared to the weight of the same sample of air without any moisture in it. Here, DBT and WBT have measured the properties of moist air, and the remaining properties are. The saturation curve is at 100% RH, while dry air is at 0% RH. The psychrometric chart represents dry bulb temperature T db, wet bulb temperature T wb, dew point temperature T dp, specific humidity or humidity ratio(), relative humidity(), degree of saturation(), specific volume() and specific enthalpy(h). It has no unit and is the hyperbolic lines that are shown in intervals of 10%. Relative Humidity is the ratio of the absolute humidity to the maximum possible density of water vapor in the air at the same pressure and temperature. Here, the moisture began to condense in the form of dew. Other unit used is ☏ahrenheit.ĭew Point Temperature is the temperature of saturation of a given atmospheric pressure. These lines are oblique lines on the chart. Wet Bulb Temperature is the temperature of evaporation of which the air would become saturated if moisture were added to it without the addition or substraction of heat. This temperature is located at the horizontal scale of the chart or abscissa.
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