Optimization Of Hot Air Circulation Program For Brick Tea Drying Chamber Based On Numerical Simulation

Abstract:"Blossoming" and drying is of great importance in the brick tea production process, the performance of "blossoming" and drying in the drying chamber is of great influence to the quality and cost of production of brick tea. Currently the design and use of domestic brick tea drying chamber are mainly based on production experience, lacking of theoretical guidance, thus during the production, problems such as the presence of non-uniform temperature in the drying chamber and brick tea easy to mold occur. Optimization of brick tea drying chamber has important implications for energy conservation and improvement of product quality.Taking an enterprise brick tea drying chamber as the object, with the FLUENT software platform, using numerical simulation method, the numerical model of brick tea drying chamber during the "blossoming" was established. The distribution of velocity and temperature field of drying chamber was analyzed. On this basis, optimization of hot air circulation heating scheme was carried out.The main contents and conclusions of this dissertation are as follows:(1) The three-dimensional steady model of brick tea drying chamber during the "blossoming" was established. Standard k-ε two-equation model and SIMPLE algorithm are applied for simulation of natural convection flow field inside the drying chamber. The velocity and temperature distribution of drying chamber was gained, and compared with the production test data, the maximum error is8.46%, verified the reliability of the simulation model.(2) The simulation of basic condition results show that the velocity of flow is slow in the drying chamber, the hot air lift up in the center of the chamber, and spread to both sides when hampered by the platform in the second floor, and then settling down adjacent to the wall to form return flow, eventually form four vortexes in the chamber. The airflow in the top zone is in a state of stagnation; uneven temperature distribution inside the drying chamber, stratification of temperature occurs in the vertical direction(above high and bottom low), while in the horizontal direction the temperature in intermediate is high and ends low. There appears large temperature gradient near heat sources.(3) Since the base condition with heat sink heating cannot meet the temperature-uniform demand of brick tea production,4hot air circulation schemes were proposed. The simulation results show that:hot air circulation drying system has a significant role for improving the uniformity of the temperature field. Through comparative analysis, the unilateral-in and unilateral-out solution was determined. The temperature in the brick tea placed area remains at a constant value in this scheme, it has the best temperature uniformity, can well meet the demand of brick tea production process.(4) For the unilateral-in and unilateral-out scheme, the influence of3factors, flow velocity, flow angle and brick spacing on the drying chamber was investigated, and found that:increased flow velocity can significantly reduce the mean age of air in the chamber, and air flows more smoothly, and can slightly improve the uniformity of the temperature field in the drying chamber as well; downward deflection angle will help improve the velocity field uniformity, though with a straight air angle can obtain the minimum mean age of air; shorten brick spacing can reduce the uneven temperature drying chamber on the left; the mean age of air in the non-working area inside the chamber is not affected by the brick spacing, while in the working area increases as brick spacing reduces, though increases significantly slight.