Read the following text and fill in the words from the list below.

Date: 2015-10-07; view: 399.

Meteorological offices and aviation textbooks use the following figures:

The weight of 1) _____ air (no moisture content) at 0 deg C and under a normal atmospheric 2) _____ of 1013 mbar is 1.293 Kg/cu metre.

The weight of dry air (no moisture content) at 0 deg C and at a pressure of 1000 mbar (1 Bara) is 1.275 Kg/cu metre.

The amount of water vapour contained in air can be 3) _____ in one of several ways:

The Dewpoint Method

Air is cooled down and the 4) _____ at which condensation begins is measured. The actual water 5) _____ of the air is then obtained from a set of steam tables.

Hygrometers

These air direct reading 6) _____ which usually measure the change in dimensions of a material due to the amount of moisture it contains. Older hygrometers used wood or paper and the changes in dimensions due to 7) _____ would take ages to stabilise. Modern probes use metal oxides such as aluminium and these hygrometers only take a few minutes to get within 5% of the final reading. However, depending upon the size of the system it may take another day to finally stabilise.

Psychrometry

These measure the wet bulb and dry bulb temperature across thermometers, thermocouples or resistance thermometers. Still air humidity is measured using Sling Psychrometers or Aspiration Psychrometers. In any event, a correction to the wet bulb temperature is required if the air 8) _____ past the wet bulb is not between 800-900 ft per min.

Chemical Analysis

This is obtained by exposing a known chemically dry 9) _____ to the air and then measuring the increase in moisture content over a fixed time interval