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Chemistry > Solutions > What is Psychrometer and How does it Work?

What is Psychrometer and How does it Work?

What is Psychrometer and How Does it Work?                         

First of all, relative humidity refers to the ratio of the partial pressure of water vapour to the water’s equilibrium vapour pressure at a particular temperature. The relative humidity is the ratio of how much water vapour is present in the air in comparison to how much water the air can actually contain. Most noteworthy, we can measure it with the help of psychrometer.

Moreover, relative humidity depends on various factors like temperature, dew point, and air saturation. Also, relative humidity changes continuously. Irrespective of any such factor, a psychrometer can certainly measure relative humidity.


Design of Psychrometer

We can say it is a simple hygrometer – which is a device measuring humidity. It has two bulbs both connected with a thermometer.

One bulb is wet while the other is dry. We expose the dry bulb to the air so as to measure the temperature. We cover the wet-bulb with a cloth wick and dip it in water until it is ready to use.

Working of Psychrometer

In order to measure the temperature of a room, we first remove the wet-bulb from the water. As the water evaporates, the wet-bulb will start cooling eventually. Furthermore, we can measure the cooling of the wet bulb and can estimate how much water is evaporating.

Consequently, it will give us the data on how humid the air is. Moreover, moist air will undergo only a little water evaporation, and the wet bulb will barely change its temperature.

In comparison, dry air absorbs a lot of moisture, which cools the wet bulb quite a bit. The more the air is dry, the more evaporation takes place from the wet bulb, which will drop the temperature of the thermometer.

Reading of a Psychrometer

A Psychrometer works on the assumption that evaporation is a cooling process. After we have finished swinging the psychrometer in the room for about a minute, we must note down the temperature of the dry and wet bulb.

We must note here that wet bulb temperature is never greater than the dry bulb. If it is happening, then the water we are using is too hot.

Now record the difference of temperature between wet and dry bulb. For example – let us assume that dry bulb = 35°C and wet bulb = 30°C. Difference between the two is of 5°C. Now we need to make a graph. Mark the dry bulb temperature on the y-axis and the difference of temperature on x-axis.

The temperature where these two will meet is the dew point temperature. From here we can find the relative humidity. The number where two-point meet in the graph is the relative humidity, which we can express in percentage.

Uses of Psychrometer

The major uses of a psychrometer are as follows:

  • We can see the use of electric psychrometer in some ships as the primary wet bulb temperature measuring device. They use it as a backup for automatic air temperature and dew point sensors.
  • Psychrometers are attached with musical instruments like pianos, guitars, violin, which get damaged by improper humid conditions.
  • Coating industry uses it as paints are sensitive to humidity.

Solved Question For You

QHow temperature and humidity are related to our health and comfort?

Ans – High humidity and temperature will mean more water in the air, which carry more odour molecules. This lead to the foul smell of garbage in summer.

Furthermore, if the air is both hot and humid, then the sweat will not evaporate properly, which lead to dehydration and overheating. Moreover, temperature and humidity directly causes influenza virus transmission.

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