A Quick Measurement Method For The Thermal Physical Property And Water Content Of Raw Grain

To improve the precision and efficiency in the process of collection and storage of grain water content detection,this paper explores indirect measuring method,which uses the thermal effusivity represents water content.Based on the relationship between the thermal effusivity and water content,the water content of grain is indirectly obtained by measuring the thermal effusivity of grain.Wheat was chosen as the main research object and millet as the reference object.The thermal physical property of wheat and millet with different water content are measured by quasi steady state cylinder method,the relationship between the water content and thermal conductivity,specific heat capacity,thermal diffusivity,thermal effusivity of wheat and millet are calculated.The results show that when the water content of wheat rises from 6.913% to 12.366%,The thermal conductivity increases by 175.3%,the thermal effusivity increases by 118.2%.When the water content of wheat rises from 8.392% to 12.366%,the specific heat capacity increases by 77.4%;Using the linear fitting method,the relationship between the thermal physical property and the water content are obtained.The results show that the the correlation coefficient of thermal conductivity,thermal effusivity and specific heat capacity of wheat with water content change are 0.907,0.922,0.876.It means that the water content of wheat has the highest correlation coefficient with the change of thermal effusivity,and the linearity is the best.The data of millet show that when the water content of millet rises from 6.875% to 15.179%,thermal conductivity increases by 95.8%,the thermal effusivity increases by 82.7%.Using the linear fitting method,the relationship between the thermal physical property and the water content are obtained.The results show that the the correlation coefficient of thermal conductivity and thermal effusivity of millet with water content change are 0.81,0.94.It means that the water content of millet has the highest correlation coefficient with the change of thermal effusivity,and the linearity is the best.In order to meet the need of rapid detection in the field,the thermal wire probe measuring device of thermal effusivity is made.The thermal wire probe adopts the improved hot-wire method to change the line heat source model to the surface heat source model,and reduces the principle error caused by the probe size.The wheat and millet is measured by the thermal wire probe measuring device made by myself.The law of the change of the excess temperature of the grain on the wall of the probe with time is analyzed,and the linear equation of the excess temperature and the square root of the time is calculated,and then the thermal effusivity is obtained by the slope.It is found that the thermal effusivity of wheat increases linearly with the water content in a certain range,but the range of the increase and the range of the numerical variation are not in accordance with the calibrated value.The measurement data of millet show that the thermal effusivity of millet does increase with the increase of water content,and the linear relation of the probe measurement is basically consistent with the relation of calibration.This indicates that it is feasible to measure water content of grain by using the thermal effusivity,and the thermal wire probe measuring device can be applied and measured for grain water content.