Astronomy lab: Planetsmyslu.stlawu.edu/~aodo/SLU/climate/Assignments/Measuring... · 2018-02-07 ·...
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Envs, Geol, Phys 112: Global Climate Name ____________________ MEASURING HUMIDITY While there are more “modern” ways of measuring humidity, one of the oldest techniques (and still the scientific standard) is the “dry bulb-wet bulb” thermometer. Here is the idea: When the humidity is high, there will be little tendency for water to evaporate. On the other hand, when the humidity is low, water will evaporate rapidly. If one could measure the rate of evaporation for a given air temperature, one could figure out the humidity of the surrounding air. In particular, if one had a piece of wet cloth wrapped around the bulb of a thermometer, evaporation would cool the thermometer – the faster the rate of evaporation, the cooler the thermometer would get. By comparing the temperature of the air (the “dry bulb” temperature) to the temperature of the wet cloth, one can find the relative humidity by using a psychrometric chart. The standard instrument for this is a sling psychrometer. We don’t happen to have any commercial ones, so we’ll make our own using thermometers, wicking, water, and waving our arms. Use a regular thermometer and one with wet wicking on the bulb to record the Dry Bulb and Wet Bulb temperatures (swing the thermometer with the rapidly and record the lowest temperature it shows). Dry-bulb air temperature: T D = °C Wet bulb air temperature: T W = °C Atmospheric Pressure: P = hPa Dry-bulb air temperature: T D = °C Wet bulb air temperature: T W = °C Atmospheric Pressure: P = hPa Dry-bulb air temperature: T D = °C Wet bulb air temperature: T W = °C Atmospheric Pressure: P = hPa Location, Date & Time: ________________________________________ Location, Date & Time: ________________________________________ Location, Date & Time: ________________________________________ Sling Psychrometer BH 2 nd fl. breezeway, 1:25 pm 1/29/18 23 15 1019.3 33.854 hPa 30.10"Hg 1019.3 hPa 1"Hg = 16 11 1022.7 BH 232, 11:30 am 2/7/18 33.854 hPa 30.22"Hg 1023.1 hPa 1"Hg = Examples
Transcript of Astronomy lab: Planetsmyslu.stlawu.edu/~aodo/SLU/climate/Assignments/Measuring... · 2018-02-07 ·...
Envs, Geol, Phys 112: Global Climate Name ____________________
MEASURING HUMIDITY
While there are more “modern” ways of measuring humidity, one of the oldest techniques (and still the scientific standard) is the “dry bulb-wet bulb” thermometer. Here is the idea: When the humidity is high, there will be little tendency for water to evaporate. On the other hand, when the humidity is low, water will evaporate rapidly. If one could measure the rate of evaporation for a given air temperature, one could figure out the humidity of the surrounding air. In particular, if one had a piece of wet cloth wrapped around the bulb of a thermometer, evaporation would cool the thermometer – the faster the rate of
evaporation, the cooler the thermometer would get. By comparing the temperature of the air (the “dry bulb” temperature) to the temperature of the wet cloth, one can find the relative humidity by using a psychrometric chart.
The standard instrument for this is a sling psychrometer. We don’t happen to have any commercial ones, so we’ll make our own using thermometers, wicking, water, and waving our arms.
Use a regular thermometer and one with wet wicking on the bulb to record the Dry Bulb and Wet Bulb temperatures (swing the thermometer with the rapidly and record the lowest temperature it shows).
Dry-bulb air temperature: TD = °C
Wet bulb air temperature: TW = °C
Atmospheric Pressure: P = hPa
Dry-bulb air temperature: TD = °C
Wet bulb air temperature: TW = °C
Atmospheric Pressure: P = hPa
Dry-bulb air temperature: TD = °C
Wet bulb air temperature: TW = °C
Atmospheric Pressure: P = hPa
Location, Date & Time:
________________________________________
Location, Date & Time:
________________________________________
Location, Date & Time:
________________________________________
Sling Psychrometer
BH 2nd fl. breezeway, 1:25 pm 1/29/18
23
15
1019.3 33.854 hPa30.10"Hg 1019.3 hPa1"Hg
=
16
11
1022.7 BH 232, 11:30 am 2/7/18
33.854 hPa30.22"Hg 1023.1 hPa1"Hg
=
Examples
Envs, Geol, Phys 112 Measuring Humidty 2/7/2018
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Use the Psychometric Chart from Trane and the equations below to determine
Relative Humidty: % Moisture Content: (kg H2O)/(kg Dry Air) Specific Humidity: (g H2O)/(kg Dry Air) Air Density: (kg Dry Air)/(m3 Dry Air) Moisture Content: (mℓ H2O)/(m3 Dry Air) Relative Humidty: % Moisture Content: (kg H2O)/(kg Dry Air) Specific Humidity: (g H2O)/(kg Dry Air) Air Density: (kg Dry Air)/(m3 Dry Air) Moisture Content: (mℓ H2O)/(m3 Dry Air) Relative Humidty: % Moisture Content: (kg H2O)/(kg Dry Air) Specific Humidity: (g H2O)/(kg Dry Air) Air Density: (kg Dry Air)/(m3 Dry Air) Moisture Content: (mℓ H2O)/(m3 Dry Air) Using the pressures and dry-bulb temperatures, calculate how many milliliters of water are in a cubic meter (m3) of air in the location you sampled. Comment on your results
Location, Date & Time:
________________________________________
3 3 3
____kg Dry Airkg Dry Air m Dry Air m Dry Air m Dry Air
____ g water g water m water____ ____
× = =
Location, Date & Time:
________________________________________
( )( )dry air 3
p kg_______ Pa ____RT m287 ____ 273
ρ = = =+
Location, Date & Time:
________________________________________
BH 2nd fl. breezeway, 1:25 pm 1/29/18 42
( )( )dry air 3
kg101930 Pa 1.1999m287 23 273
ρ = =+
1.1999
0.00738
7.38
2 2H O H O3 3
7.38 m 8.86 m1.1999 kg Dry Airkg Dry Air m Dry Air m Dry Air
=
8.86
BH 2nd fl. breezeway, 1:25 pm 1/29/18
( )( )dry air 3
kg102307 Pa 1.2335m287 16 273
ρ = =+
2 2H O H O3 3
6.15 m 7.59 m1.2335 kg Dry Airkg Dry Air m Dry Air m Dry Air
=
55
1.2335
0.00615
6.15
7.59
See Figure 2
See Figure 1
Envs, Geol, Phys 112 Measuring Humidty 2/7/2018
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Figure 1: Pschometric chart for example Figure 2: Pschometric chart for classroom
