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at 17% relative humidity the dew point is -5.8C at a dry bulb of 20C
for air water system wet bulb equals to dry bulb at 100 % relative humidity for that given temperature of air.
dry bulb temperature simply tells us the temperature of dry air.but the comfort also depends on humidity ie. water vapour presents in the air.Wet bulb temperature measures the humidity in the air.Because the evaporation of water in the bulb wick depends on the relative humidity of surrounding air.
A sling psychrometer (or hygrometer) uses the difference in readings between a wet bulb thermometer and another with a dry bulb to measure the relative humidity. The bulb that is wet will cool by evaporation to the "dew point", which is the temperature at which the current humidity would be the maximum possible. Comparing that to the dry bulb (the general air temperature) on a comparative chart will yield the approximate relative humidity.
answer is
Typically wet bulbs are used to give a heat-index or what it "feels like" outside. Because humans cool themselves by sweating, wet bulbs attempt to factor in humidity and wind speed to approximate the effective temperature while sweating. The wet bulb temperature is also used, together with the dry bulb temperature, to determine the relative humidity. If you know the relative humidity, you can calculate the difference with an equation given at: http:/en.wikipedia.org/wiki/Heat_index
Answeractuall humidity is given as the amount of water. use a table stating how much water the air can hold at the given temp, this is your 100% humidity. now calculate howw much you got and that would be relative humidityAnswer:To calculate relative humidity you need a wet bulb and a dry bulb thermometer and a psychrometric chart (a graph of the physical properties of moist air at a constant pressure). The chart graphically expresses how various properties relate to each other.Using an ordinary thermometer you read the dry bulb temperature(DBT). You will locate this temperature on the x-axis of the chart.Next you will determine the wet bulb temperature (WBT) from a thermometer who's bulb is covered with a wet wad of cotton and typically waved in the air until the temperature goes to its minimum. This works because dry air evaporates water and evaporation cools the wad. The temperature it reaches is related to the air's humidity. This value goes on the curved line at the top of the chart.The relative humidity (RH) is read off the chart from the intersection of the lines from these two points.
51%.... open to the Relative Humidity chart in the reference tables. the wet bulb temperature is -1C and the dry bulb temp. is 2C, making a difference of 3C. On RH chart, go down to 3C column (difference between the Wet bulb and dry bulb) until it intersects the dry bulb 2C. At this intersection is 51%
You would use both to determine the relative humidity.
as the air passes over the wet bulb thermometer the water in the cloth evaporates. as the water evaporates the cloth cools. if the humidity is low the water will evaporate more quickly and the temperature reading on the wet bulb thermometer will drop. if the humidity is high only a little bit of water will evaporate from the cloth of the wet bulb thermometer and the change in temperature will be small.
the relative humidity will decrease.