Agitation and Mixing for Food and Dairy Technology studentsg.pptx

Agitation and Mixing for Food and Dairy Technology students

1. Case Study: Prepared by: Design of Agitation System

2. Index Introduction Agitation and Mixing of Liquids Reasons for agitation in dairy plant Agitation equipment Types of impellers (Stirrer)based on flow pattern Types of Agitators Methods to avoid formation of vortex

3. Introduction In most of the processing operations in dairy plant, the process fluid may have to be heated or cooled. It would need some kind of agitation. Similarly, mixing various ingredients like that for ice cream mix, is also common. They form very important unit operations in the processing industry. The aim is to achieve the objective with minimum of energy input, and wear and tear.

4. Agitation and Mixing of Liquids Agitation: It is the induced motion of a material in a specified way usually in a circulatory pattern inside some sort of container. e.g. Agitation of milk in a storage tank. Mixing : It is random distribution, into and through one another, of two or more initially separate phases. e.g. Mixing of Ice cream ingredients before freezing. Single homogenous material can be agitated, but can not be mixed until some other material is added. Agitation is for producing turbulence in the material to efficient result in extraction, mixing, absorption, heat transfer, chemical reaction etc.

5. Reasons for agitation in dairy plant Maintenance of a homogenous distribution of raw milk, cream, concentrated milk etc. Adjustment of fat content by adding cream milk (standardization). Cooling and heating of milk and milk products. Preparation of starters cultures. Stirring of curd-whey mixtures. Preparation of a homogenous liquid mass after acidification (starter addition) for yoghurt & cultured milk. Dispersion and dissolving of milk powder, sugar, salt etc.

6. Reasons for agitation in dairy plant Dispersion of air bubbles in the aeration of aerobic fermentation (e.g. lactose fermentation) Preparation of ice-cream mix, processed cheese, fruit yogurt etc. Growing of lactose & ice-crystals Preparation of powders with an increased fat content (e.g. milk replacer for animal feed) Very intensive stirring disadvantageous Power absorbed increase Material stirred adversely affected

7. Agitation equipment Liquids are most often agitated in some kind of a tank or vessel. Vessel: Usually a cylindrical tank with rounded bottom, to eliminate sharp corners where agitation does not penetrate. Liquid depth ~ diameter of tank. Propeller (stirrer): mounted on overhung shaft. Driven by electric motor – directly connected or through reduction gear box. Propeller creates flow pattern causing the liquid to circulate through the vessel and return to impeller.

8. Axial flow impeller: Generates currents Parallel with axis of Impeller shaft. Types of impellers (Stirrer)based on flow pattern

9. Types of impellers (Stirrer)based on flow pattern Radial Flow impeller: Generates currents in a tangential or radial direction

10. Types of Agitators Radial Flow impeller: Generates currents in a tangential or radial direction Paddle Propeller Turbine Open Straight Blade Bladed Disk Vertical Curved blade

11. Methods to avoid formation of vortex Action of agitation sometimes leads to formation of vortex, which can suck air into the fluid being agitated. Methods by which this objective is achieved are. Tilted impeller shaft Mounted on side (eccentrically) of tank Baffles

12. Methods to avoid formation of vortex Vertical strip perpendicular to the wall of tank Four baffles sufficient Side entering, inclined or off-center propellers do not need baffles Draft Tubes:   Draft tubes are used when direction and velocity of flow to the suction of the impeller to be controlled. They are useful when high shear at impeller itself desired. e.g.: emulsions. Also they are used when solid particles tend to float on surface

13. Thankyou