Drying and Dehydration.pptx

Drying and dehydration are two important processes used to remove moisture from food, agricultural products, and industrial materials. While often used interchangeably, there are subtle distinctions between the two. Understanding these differences and the underlying mechanisms is crucial for effective preservation and quality control.

1. DRYING AND DEHYDRATION Presented by  Shaswat Tiwari Ph.D. ( PHP & FE) Submitted to Dr. Mohan Singh Professor and Head Department of Post Harvest Process and Food Engineering College of Agricultural Engineering  Jawahar Lal Nehru Krishi Vishwavidyalaya Jabalpur MP

2. Contents Introduction Moisture Migration During Drying Process Drying Rate Curve Difference Between Drying and Dehydration Importance of Drying Process Drying Methods Mechanical Dryer Methods Types of Dryer

3. Introduction Drying refers to the removal of small amount of moisture from a solid or semi solid material by the evaporation (change of phase from liquid to vapors /gas). Dehydration means removal of moisture to a very low level usually up to bone dry condition. It involves both heat and mass transfer operations together.

4. Moisture Migration During Drying Process

5. Drying Rate Curve

6. Drying It is natural process It does not have control over any climatic condition. It takes more time. Do not have good quality. Dehydration It is an artificial process It has control over climatic condition. It takes less time Dehydrated food have good quality.

7. Importance of Drying Process

8. Drying Methods The agricultural product drying methods can be broadly grouped into two- Sun/Solar drying Artificial drying with mechanical means

9. Mechanical Drying Methods

10. Contact Drying In this method of drying heat is supplied to wet products by conduction. The commonly used heating medium in conduction drying are steam, organic liquids, metals and other materials with high value of heat transfer coefficient.

11. Convective Drying In this method sensible heat of heated air is transferred to the wet products by convection. Heated gaseous medium usually air is used.

12. Freeze Drying

13. Radiation Drying Heat energy is supplied through the electromagnetic waves. The wavelength of the electromagnetic radiation lies between 0.76 to 400 micron. The moisture migration inside the materials and diffusion of vapor follow the same laws as in convection or contact drying

14. Super Heated steam drying Superheated steam drying (SSD) uses steam heated beyond its boiling point to remove moisture from materials. This creates a unique drying environment with several advantages over traditional hot air drying. Advantage Faster drying Higher quality Energy efficiency Sanitization

15. Fluidized Bed drying

16. Types of dryer-

17. Deep Bed Dryers A deep bed dryer is a type of industrial dryer that's used to remove moisture from large volumes of material. The most common shapes are round or rectangular.

18. Flat bed dryer The Flat Bed batch type dryer is similar to deep bed dryer except that the surface area of the dryer is more and the depth of the drying layer is less. These dryers are usually of 1-2 tones capacity.

19. Recirculating Dryer In a re-circulating dryer the same quantity of grain is recycled through the dryer until final moisture content is reached. Recirculatory batch dryer is a continuous flow non mixing type of grain dryer.

20. LSU Dryer Developed at Louisiana state university (LSU) Continuous mixing type dryer Developed specifically for rice to ensure gentle treatment, good mixing & good air to grain contact

21. Rotary Dryer The foodstuff is contained in a horizontal inclined cylinder through which it travels, being heated either by air flow through the cylinder, or by conduction of heat from the cylinder walls. In some cases, the cylinder rotates and in others the cylinder is stationary and a paddle or screw rotates within the cylinder conveying the material through.

22. Tray Dryer Also known as cabinet dryer. It is a rectangular chamber made up of steel which is insulated. Trays are placed one above the other and products are spread on the tray uniformly to a height of 0.1-1 cm. It consists of a fan, a heater and thermostatic control to heat air to desired temperature

23. Tunnel Dryer Tunnel dryers consist of long tunnels through which trucks carrying stacks of trays travel with or against a stream of drying air. The material to be dried is evenly spread on the trays.

24. Spray Dryer Spray drying is a method of producing a dry powder from a liquid or slurry by rapidly drying with a hot gas. Spray Dryer is widely used industrial process for transforming liquid feeds into dried particles

25. Vacuum Dryer A Vacuum Dryer is used dry the materials by the application of vacuum. Hence, water evaporates faster. The heat transfer becomes efficient for example; the rate of drying enhances substantially

26. Thank You