Study On Particulate Materials Flow And Heat And Mass Transfer In Rotary Dryers

The main body of a rotary dryer is revolving round drum with a small slope, is a kind of equipment that is heated by high temperature and can transport matter, and it is widely used. It vary in shell size from 0.5 m diameter by 2 m length to 3 m diameter by 50 m length. Where the solids enter one end of a rotating drum, move down the drum length cascading from peripherally mounted lifting flights, and exit at the other end suitably dried. In the paper. Movement of solid, mass and heat transfer have been analyzed. Mechanism and Experimental study of the rotary dryer is carried out in a systematic way. The works is beneficial to increasing productivity, saving the sources of energy and developing the rotary dryer. The main works in the dissertation were summarized as followings:1. On the basis of a detailed study, the testing equipment of a rotary dryer is designed and made. The slope of the drum, rotational speed of the rotary dryer, wind-force, wind temperature, flights and feed rate all can be adjusted. The equipment runs perfectly well.2. Right angle and extended-circular flights characteristics of rotary dryers is researched. On the basis of the mathematical model, a set of equations has been derived to calculate the solids holdup on right angle and extend-circular flights in such dryers. Ratio of the solids holdup to maximum solids holdup is explored. The testing equipment of the rotary dryer is simulated by VB program language. The result of the simulation is obtained in some kinds of different conditions. Simulated results is satisfactory. The programming is a useful reference for research of the similar problem.3. A particle progresses down the drum length in a succession of cascades. Each cascade is made up of a period in a flight and a period falling through the air, where the distance it moves forward is determined by the height of fall, the slope of the drum, and the gas velocity. On the basis of the mathematical model, the equations has been derived, the position of a particle can be defined at any moment. It is simulated by VB program language. The residence time can be defined according to rotational speed of the rotary dryer, radius of the drum, the slope of the drum, wind-force and the particle quality.4.Using mass balance equation, energy balance equation, heat and mass transfer equation, a mathematical model of heat and mass transfer during the granular materials drying has been presented. The finite element method and Matlab is used. Both the variation of material' temperature and moisture content can be predicted. The model prediction agrees with the experiment data.5. Based on study of the theory, research is done to test and verify the precision of simulation in the rotary dryer. These include variations of hot air temperature of entrance to the rotary dryer, variations of moisture content of materials, variations of rotational speed, and variations of inclination. Experiment is shown that rotational speed interferes with retention period of materials in the rotary dryer. Hot air temperature and moisture content of materials also interfere with dry rate of materials.