It is void. Vacuum is a space devoid
of matter. It represents something
short or vacant. But, in reality it is
linked to pressure. Vacuum is a pressure
below atmospheric pressure. Atmospheric
pressure is 29.92 inches of Hg.
Consider the following steps to understand vacuum.
(i) Consider a bottle is open to atmosphere. Naturally it contains air and water vapors in it. The pressure is atmospheric pressure.
(ii) Now connect suction pipe of a vacuum pump to the mouth of the bottle. Discharge pipe of the pump is dipped in water in an another container.
(iii) Start the vacuum pump. It will take out air and water vapors from the bottle. Bubbles will be seen in the container containing water.
(iv) Now the pressure in the bottle is decreasing and becoming less than atmospheric. Say the pressure becomes 28 inches of Hg.
(v) Therefore, the vacuum will be =29.92 – 28.00 = 1.92 inches of Hg.
REQUIREMENTS OF VACUUM
Evaporation of any liquid below its boiling point takes place under vacuum.
Data given below is from the steam table
(i0 Firstly water evaporates at 50 C requires vacuum equal to 0.9911 bars
(ii) Secondly water evaporating at 9
0 C requires vacuum equal to 0.9883 bars
(iii) Thirdly water evaporates at 400 C requires vacuum equal to 0.9242 bars
For example Water is to be evaporated at 850 C requires vacuum equal to 0.4106 bars
Water evaporating at 950 C requires vacuum equal to 0.1381 bars
IT MATCHES WITH IMPORTANT FACT ‘ THAT BOILING POINT DECREASES WITH THE DECREASE OF PRESSURE AND VICE VERSA’.
PRACTICAL APPLICATIONS OF VACUUM
1. Firstly water evaporates at 50 C in Water – Lithium Bromide Vapor Absorption Refrigeration System.
2. Secondly water evaporates at 50 C in the flash chamber of Steam Jet Refrigeration System.
3. Thirdly water evaporates in day today life at atmospheric temperatures due to partial pressure of water vapor in air. This partial pressure is less than atmospheric i.e. vacuum.
4. Vacuum causes concentration of juices, drying of milk, coating and freeze drying.
These are equipment’s to create vacuum inside a closed vessel. These extract gas from within a vessel. There is a variety of vacuum pumps. Different applications use different vacuum pumps.
https://www.mesubjects.net/wp-admin/post.php?post=1208&action=edit Steam Jet Refrigeration