Basic principle
By cooling at constant pressure if the air temperature is reduced, the water vapour in the air begins to condense at a given temperature. This temperature is called dew point.
Description
The main parts of arrangement are
Surface glossy 1.A (mirror) is fixed with a thermocouple.
Nozzle 2.A provides a jet of air on the mirror.
3.A constantly focused on the mirror light source.
4.A photo cell to detect the amount of light reflected from the mirror.
Operation
1. The mirror is constantly cooled by cooling medium. The cooling medium is maintained at a constant temperature.
2. This mirror is attached a thermocouple leads is connected to a millivoltmeter.
3 Constantly light is falling at an angle on the mirror and the amount of reflected light is perceived by a photo cell.
4. Now a jet of air is falling at an angle on the mirror and the vapour of water (moisture) contained in the air starting condensation on the mirror and they appear as small drops (EDW) on the mirror.
5. This (dews) moisture formed on the mirror reduces the amount of light reflected from the mirror and detected by photocell. When for the first time, there is a change in the amount of light transmitted; It is an indication of the formation of dew.
6. In this instance (i.e. where due formation is detected first), the temperature indicated by the thermocouple attached to the mirror becomes the dew point temperature.
7 So this arrangement is used to determine when the dew appears for the first time temperature and dew point.
Application
1. This instrument is used on ships to protect cargo condensation in now the dew point of air in the holds below the temperature of the cargo.
2. Used in industries for determining dewpoint.
Limitations
1. There are limitations of cooling fluid and light metering.
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