lecture 3.1.5 (9).ppt
- 1. DISCOVER . LEARN . EMPOWER University Institute of Agriculture Sciences B.sc Agriculture Sciences BLOCK-9 Subject Name and Code Protected cultivation and Post harvest management AGT-352
- 2. 1 University Institute of Agriculture sciences
- 3. University Institute of Agricultural Sciences Harvinder Singh/Dr.Ambika Name of Topic:Types of drying Chapter 3.2 Lecture 2 DISCOVER . LEARN . EMPOWER
- 4. 4 Objectives To strengthen the understanding of basics of protected cultivation. To focus on Planning and design of greenhouses • To acquaint students with principles of green house technology • To provide basic knowledge of planning and design of greenhouses Course Outcome
- 5. INTRODUCTION 5 • Drying is the universe method of conditioning grain by removing moisture. • It is the oldest most common method of grain drying in agriculture. • It is a essential process for conditioning the grains for safe storage. • Correct drying method preserves the quality, nutritive value and viability of grain. • Drying involves both heat and mass transfer operations. • Drying and Evaporation are the major moisture removal methods.
- 6. Methods of Drying • There are many methods to develop water-vapour pressure difference between product and atmosphere. • For increasing of water vapour pressure of grain, the methods are: 1. Solar or sun drying 2. Conduction drying 3. Infra-red drying • The methods usually employed to lower the water vapour pressure of air are: 1. Heated air drying 2. Desiccated air drying 3. Refrigerated air drying 6
- 7. Natural Drying • Natural drying is the method of drying, in which we are using the natural source (viz. Sun) for drying of food products. • It is also known as sun/solar drying. • Sun drying is cheaper method due to natural source of drying. While it is slow process, very prone to contaminants as well as weather dependent. That is why it is not most common in commercial scale. Types of sun drying: Drying of standing crops, Drying of grains on stalks,Drying of threshed grains
- 8. Advantages: • Free • No added cost for equipment • No added cost for electricity or gas Disadvantages: • Contaminations from the environment. • Product losses and contaminations by insects and birds. • Floor space requirements. • Difficulty in controlling the process. • Inconsistent sensory quality.
- 9. Mechanical Drying • Mechanical drying is the method of drying of foods by means of mechanical systems. • Hot air is produced by the system which is used for the drying of food material. • Several mechanical dryers are developed by the researcher in the field of food technology. • Various types of mechanical drying system available in the market which are hot air convective drying, freeze drying, vacuum drying, fluidized bed drying, spray drying, microwave drying, vacuum assisted microwave drying, microwave assisted fluidized bed drying.
- 10. Advantages • Quick method • Perfect drying is possible even under unfavorable weather condition. • Seed loss is minimized • Small no of unskilled labors • Required little space Disadvantages • Requires specialized equipment and machine, which is costly. • Care should be taken while drying the seed using hot air, as it causes damage to the seed. • Tempering is to be followed while drying the seed in this method.
- 11. Mechanical Drying Methods 1. Contact drying • In this methods, heat is supplied to wet products by conduction. • Heat is transferred through a heated surface like plate, dryer wall etc. • Thermal efficiency is higher, but product quality may be affected. 2. Hot air convective drying • The principle of hot air convective drying is based on conventional heat transfer from heated air to the material being dried. • Hot air is forced through the material and does the moisture diffusion process that result in the drying • This method has been widely used in industries. • Different types of dryers have been developed and employed in commercial production. • Heated air is blown through the material by cross flow or by fan generated flow.
- 12. 3. Freeze drying • Freeze drying is the technique of removing the moisture content from the liquid food, by freezing and removing the water portion of the food materials. • Some pharmaceuticals are heat sensitive. • Some fruits and vegetables lose their aroma and flavor if they remain in high temperature for significant figure of time. • For such cases freeze-drying is an alternative. • Freeze drying requires several successive steps, as pre- freezing, primary drying, secondary drying, conditioning and dehydration. • It is expensive and requires sophistication. • Hence, it is difficult to apply to all commercial drying needs.
- 13. 4. Vacuum drying • The basic principle of vacuum drying is to remove the water by means of vacuum. • There are four essential elements in a vacuum drying system: a vacuum chamber, vacuum generating device, system for collecting water vapor and means for supplying heat required for vaporization of water. • For reasons similar to freeze-drying vacuum drying is also an expensive drying method. • It is used only for costly products.
- 14. 5. Fluidized bed drying • Fluidized bed drying is the drying technique in which fluidization is take place. • Fluidization provide better surface area of heat and mass transfer. • Fluidized bed dryer are found throughout all industries, from heavy mining through food, fine chemicals and pharmaceuticals. • They provide an effective method of drying relatively free flowing particles with a reasonable narrow particles size distribution. • Fluidized bed dryers can process a wide variation of feed rates from pounds to several hundred tons per hour. • Two principle types of fluidized bed dryers exist- 1 static fluid bed, 2. vibrating fluidized bed.
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