Factors Influencing Evaporation: Evaporation is the process by which liquid water goes directly to the vapor phase due to an increase in temperature. The main objective of evaporation is to get a concentrated product by vaporizing volatile liquid. Evaporators are generally used to carry out the evaporation process. Evaporation is conducted by non-volatile solute and volatile solvent to produce thick liquor. The rate of evaporation is controlled by the rate of heat transfer.
When heat is applied to the solution, the movement of the molecules increases and the molecules present on the surface overcome the surface tension of the liquid and evaporate because the surface molecules have less cohesive force than the others.
Evaporation differs from distillation because in distillation vaporization takes place at the boiling point while evaporation vaporization takes place below the boiling point.
Objectives of Evaporation
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Evaporation is done
- To get concentrated product
- To remove water from an aqueous solution
- To evaporate seawater for developing drinking water
- To get solid-free water which is used in boilers for chemical processes.
Applications of Evaporation
- Evaporation is generally used in pharmaceutical industries, chemical industries for the manufacturing of bulk drugs.
- Evaporation is used in the manufacture of galenical preparations.
- Evaporation is used in the manufacture of biological products (such as insulin)
- Evaporation is used for the preparation of blood products (such as blood plasma and serum).
- Evaporation is used for the preparations of enzymes, hormones, and antibiotics
- Evaporation is used to get demineralized water used for drinking purposes.
- Evaporation is used to prepare liquid extract or soft extracts.
Factors Influencing Evaporation
- Surface area
- Vapour pressure
- Type of product required
- Time of evaporation
- Economic factors
- Moisture content
Factors Influencing Evaporation
The evaporation rate is directly related to the temperature. As the temperature increases, the rate of evaporation also increases. Because the temperature is rising, the water molecules begin to move faster. As the kinetic energy is acquired by the molecules and they escape from the surface to the vapor state. The heat is needed to provide the latent heat of vaporization, and in general, the rate of evaporation is controlled by the heat transfer rate. The rate of heat transfer depends on the temperature gradient.
2. Surface area
The rate of evaporation is directly proportional to the surface area of the vessel exposed to evaporation.
Agitation is necessary for evaporation.
4. Vapour pressure
Liquids with a low boiling point evaporate quickly due to high vapor pressure.
5. Type of product required
The selection of the method and apparatus to be used for evaporation depends upon the type of product required. For example, an open pan produces liquid or dry concentrate while a film evaporator yields liquid concentrate.
As the density increases, the rate of evaporation decreases.
7. Time of evaporation
Exposure to a relatively high temperature for a short time may be less destructive of the active ingredients than a lower temperature with exposure for a longer period. Film evaporators have used a fairly high temperature but the exposure time is very short.
8. Economic factors
When selecting the method and apparatus the economic factors are important. Evaporators are designed to give maximum heat transfer to liquid.
9. Moisture content
Some drug constituents decompose more rapidly in the presence of moisture, especially at the raised temperature. Hence, evaporation should be carried out at a low controlled temperature.
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