Analysis Of Coupled Heat And Moisture Transfer Front In Stored Grains During The Vertical And Horizontal Ventilation

Foodstuff problem is a worldwide problem, and it has been solved in China and has made remarkable achievements, especially after the reform and opening up of our country. Food security is facing a new challenge in new situation, especially since the beginning of the 21st century, China’s grain output has achieved a "12 increase". It is really significant to make the stored grain safe, keep the grain quality, and reduce grain loss. Temperature and moisture play an important role for the quality of grain, and study on the transfer front during ventilation can be help to analyze the rules of temperature and moisture front. Meanwhile the reasonable ventilation time and the storage cost can be predicted via the analysis of front, so as to realize the economic security of stored grain.Based on the theory of grain storage ventilation and heat and mass transfer in porous media, numerical simulation can be conducted for the front of temperature and moisture changes by means of CFD numerical simulation method, and combined with a field test of vertical and horizontal ventilation. The main research work are as follows:Firstly, grain storage ventilation and numerical simulation theory was introduced and heat and mass transfer mechanism in the ventilation process was analyzed, the interaction between each other is discussed.Furthermore, based on the heat balance and the theory of heat and mass transfer in porous media, some mathematical models are established to describe the internal air flow, moisture migration, temperature changes during the vertical and horizontal ventilation process in bulk grain, combined with mass, momentum and energy conservation law. Then the ventilation process of heat and moisture coupling is described.Finally, after setting the measurement points, horizontal ventilation test was conducted in a grain bin, using the grain condition monitoring system to record the temperature changes in grain bulks. According to the local climate data, numerical simulation analysis was carried out under three typical ventilation conditions.The results of the study illustrate that:the changes of temperature and moisture in test is similar with numerical simulation data which shows that the numerical simulation is accurate; in the same ventilation condition, the speed of temperature front is faster than moisture front; in the same ventilation conditions but with different ventilation modes, there have the same cooling effect but the moving speed of horizontal ventilation is faster than that of vertical ventilation; the front speed is proportional to ventilation rate, and the distribution of temperature and moisture in different ventilation conditions has a certain delamination.The correlation about heat and moisture front migration can be established as φx= 0.14·V-1.58(x/L)1.6 and φx= 0.121·v-1.722(x/L)1.1, and it also provides a theoretical basis for predicting ventilation time and controlling cost.The result of this research have important theoretical and guiding significance for improving the quality and security of grain storage, and it also can improve the economic benefit of grain enterprises and ensure the sustainable development of national food strategy.