The key difference between drying and dehydration is that the drying refers to the removal of solvent from a solid, semi-solid or a liquid whereas dehydration refers to the removal of water from the water-containing compound.
Both terms drying and dehydration refers to the removal of solvent from a solution, thereby leaving only the solute. Therefore, both these processes are mass transfer processes. Moreover, these processes will leave a solid residue at the end.
1. Overview and Key Difference
2. What is Drying
3. What is Dehydration
4. Side by Side Comparison – Drying vs Dehydration in Tabular Form
What is Drying?
Drying is the process of removal of solvent from a solid, semi-solid or a liquid. Hence, it is a mass transfer process because the solvent mass in the solution moves from the solution to the atmosphere via drying. Here, the solvent can be water or any other solvent such as organic solvents. Also, this mass transfer occurs via evaporation. Often, we use this process as the final step before the packaging of some products. The final product of the drying process is always solid. It can be in continuous sheet form, in long pieces, particles or as a powder.
Usually, we use heat energy for the evaporation and for drying, we need an agent that can remove the solvent vapour produced from the evaporation. Desiccation, on the other hand, is a synonym for drying, but sometimes we consider it as an extreme of drying.
Figure 01: Fish Drying in Sri Lanka
Some methods we use for drying are as follows:
- Application of hot air
- Indirect or contact drying (g., drum drying, vacuum drying)
- Dielectric drying (g., microwaves)
- Freeze drying
- Supercritical drying
- Use of natural air
Moreover, the applications of drying process are in the food industry, the pharmaceutical industry, etc. we can dry food items in order to inhibit microbial growth and thereby to preserve the food. Other than that, it also reduces the volume and the mass of the item. In addition to that, we dry non-food items such as wood, paper, washing powder, etc.
What is Dehydration?
Dehydration is the removal of water from the water-containing compound. This compound can be an aqueous solution, solid, etc. At the end of the dehydration process, water forms as an essential byproduct. The end product of the process is always solid. Moreover, unlike the drying process, we use specific processes with controlled temperature and humidity conditions. In contrast, hydration is the addition of water molecules to a compound.
What is the Difference Between Drying and Dehydration?
Drying is the process of removal of solvent from a solid, semi-solid or a liquid whereas dehydration is the removal of water from the water-containing compound. Therefore, this is the fundamental difference between drying and dehydration. Another important difference between drying and dehydration is that drying process produces water or any other solvent as the byproduct while dehydration produces water as an essential byproduct. Apart from that, we can use mild conditions without any control for drying purposes. But we have to control the conditions such as humidity and temperature for the dehydration purpose.
The below infographic presents full details of the difference between drying and dehydration in tabular form.
Summary – Drying vs Dehydration
Both drying and dehydration processes are mass transfer processes. They involve in the removal of a solvent from a compound. They differ from each other according to “what” they are going to remove. Therefore, the key difference between drying and dehydration is that drying refers to the removal of solvent from a solid, semi-solid or a liquid whereas dehydration refers to the removal of water from the water-containing compound.
1. “Drying.” Wikipedia, Wikimedia Foundation, 14 Sept. 2018. Available here
1.”Negombo beach, drying fish (001)”By Honza or Markéta – Own work, (CC BY-SA 3.0) via Commons Wikimedia
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