تكول.pdfDrying Drying is defined of drying
- 2. Drying is defined as the removal of a liquid from a material by the application of heat It is accomplished by the transfer of a liquid into an unsaturated vapour phase. Drying is commonly the last stage in a manufacture process. Drying
- 3. Drying Drying involves both heat and mass transfer: o Heat must be transferred to the materials to be dried to supply the latent heat required for the vaporization of the moisture. o Mass transfer is involved in the diffusion of water through the material to the evaporating surface in the subsequent evaporation of the water from the surface and the diffusion of the resultant vapour into the passing air stream.
- 4. Drying Passing air stream (air-water system) should have low moisture content. This vapour carrying capacity is very critical in drying operation because, this capacity determine the rate and extent of drying. Also the rate and extent of drying directly proportional to the surface area subjected to the heat.
- 5. Pharmaceutical importance of drying .1 To avoid or eliminate moisture which may lead to corrosion and decrease the product or drug stability. .2 To improve or keep the good properties of a material, e.g. flowability, compressibility. .3 To reduce the cost of transportation of large volume materials (liquids).
- 6. Pharmaceutical importance of drying .4 To make the material easy or more suitable for handling. .5 It is important process in preparation of granules, which can be dispensed in bulk or converted into tablet or capsule. .6 Many products are more stable in drying form (aspirin, antibiotics powders for reconstitution).
- 7. Difference between drying & evaporation Drying Evaporation In drying processes, the main operation usually carried out on solid materials, e.g., powders, or products In evaporation processes, the main operation usually carried out on liquid materials, e.g., solution, or products Drying in most of the cases means the removal of relatively small amounts of water from solids Evaporation include the removal of large amounts of water from solutions In most cases, drying involves the removal of water at temperatures below its boiling point Evaporation means the removal of water/other solvents by boiling a solution In drying , water is usually removed by circulating air over the material in order to carry away the water vapor In evaporation , water is removed from the material as pure water vapor mixed with other gases
- 8. .1 Static bed dryer Types of dryers • In which there is no relative movement among the solid particles being dried. • Only a fraction of the total number of particles is directly exposed to heat sources A/ Oven dryer A drying oven is a device for applying low heat over a long time to a variety of objects for a variety of purposes
- 9. Types of dryers B/Tray dryer • Air flows in direction of the arrows over each shelf in turn. • The wet material is spread on trays resting on the shelves. • Electrical elements or steam-heated pipes are positioned, so that the air is periodically reheated after it has been cooled by passage over the wet material on one shelf before it passes on the next.
- 10. 2. Moving bed dryer (turbo tray dryer) Types of dryers • The drying particles are partially separated so that they flow over each other.
- 11. Types of dryers • Turbo-tray dryers , suitable for granular feeds, operate with rotating shelves and forced convection of the air above the shelves. After about seven to eights of revolution, the material being dried is pushed onto the tray below where it again spread and leveled.
- 12. Types of dryers • The same procedure continues throughout the dryer until the dried material is discharged at the bottom.
- 13. Types of dryers .3 Fluidized bed dryers
- 15. Types of dryers • ‘Fluidized’ means something that behaves like liquid. • In the fluidized bed dryer, the mixture of solids and gas behave like a liquid and solid are called fluidized. • It provides good contact between hot air and particles to obtain efficient drying. • The hot air is passed through a mesh, which supports the conical vessel with a porous base. • This vessel is filled with powder to be dried.
- 16. Types of dryers Advantages of fluidized bed drying • Efficient heat and mass transfer give high drying rates, so that drying times are shorter than with static-bed convection driers. Economic, heat challenge to thermolabile materials is minimized. • The fluidized state of the bed ensures that drying occurs from the surface of all the individual particles and not just from the surface of the bed. Hence, most of the drying will be at constant rate. • The temperature of a fluidized bed is uniform and can be controlled precisely.
- 17. Types of dryers Disadvantages of fluidized bed drying • The turbulence of the fluidized state may cause excessive attrition of some materials, with damage to some granules and the production of too much dust. • Fine particles may become entrained in the fluidizing air and must be collected by bag filters, leading to segregation and loss of fines. • The vigorous movement of particles in hot dry air can lead to the generation of static electricity charges.
- 18. Types of dryers .4 Specialized dryers (freeze dryer)
- 19. Expression of drying efficiency in drying of solid .1 Loss on drying .2 Moisture content
- 20. Experimental work 1. Prepare granules using gelatin solution as a binder. 2. Dry the powder using two different dryers for certain time to show the efficiency of the dryer used. You can also compare the time of drying for the same dryer if you dry the sample for different time intervals 3. Calculate the MC and LOD.
- 21. Experimental work According to Leon Lachman’s industrial pharmacy textbook: “The MC is a far more realistic value than LOD in the determination of dryer load capacity, but due to weight loss in the sample when was dried in a fluidized bed dryer, the application of dry sample weight in the equation of MC will not give true value even if it is high value so that we will depend on LOD in practical work to determine the drying efficiency. At the same time, the high value of MC means a large amount of water was evaporated