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Aerodynamic separation of rice husks from brown rice grains after paddy husking is one of the important processes in rice processing. So far, the realisation of complete separation of rice husks from brown rice is still a challenging task. In this study, computational fluid dynamics (CFD) and discrete element method (DEM) were used to simulate the process, and the simulation results were verified by experiment. Based on this, the process of the separation of rice husks from the mixture was clarified. The mechanisms of brown rice loss and the rice husk retention were explored by analysing the collision process of the husks and rice in the separation duct. The interaction between mixture particles and airflow was explored. The results show that feeding of the mixture particles led to the decrease in the airflow velocity; however, it did not disturb the airflow stability or produce obvious turbulence. Adjustment of airflow velocity significantly influences the separation; nonetheless, incomplete separation of rice husks and brown rice still remains. The mechanism of brown rice loss and rice husk retention in the separation process occurred simultaneously to some extent in the separation region. As a result, brown rice and rice husk entered the opposite regions and collided with each other in their opposite region, respectively. • The separation process of mixture particles was studied by DEM-CFD simulation method. • Feeding mixture doesn't disturb the airflow stability and produce turbulence. • Adjusting the airflow can not solve the problem of incomplete separation. • Brown rice losing is caused by rice husk collision. • The rice husk remaining is caused by brown rice coercion and collision. [ABSTRACT FROM AUTHOR]

Rice hulling is the process of separating rice husks from the grain. Impact hulling is the norm for paddy grain processing because it produces higher quality hulled brown rice. However, high breakage fractions and low one-time hulling percentages can directly affect the quality of subsequent rice processing and restrict the development of paddy grain processing. Understanding the mechanism of paddy grain impact hulling is key to improving the performance of centrifugal rice hullers. In this paper, a single-seed impact test and the discrete element method (DEM) were used to simulate the paddy grain impact hulling. The effects of impact speed and angle on hulling percentage, breakage percentage and hulling pattern were investigated. The results showed that the effectiveness of paddy grain hulling after impact was due to the relative motion between rice husk and its kernel. The combined effect of impact and friction produces a relative motion between the husk and the kernel and increasing the relative motion improves hulling. Optimal impact parameters were obtained using a weighting method. The results of the study could improve the hulling performance of centrifugal rice hulling providing the basis improving the design. • Impact hulling relies on the relative motion between rice husk and brown rice. • The effect of impact velocity and angle on hulling performance was investigated. • The combined effect of impact and friction is key to the relative motion. • The combined weighted scoring method was used to evaluate the hulling performance. • Impact velocity of 35–40 m s−1, impact angle of 60°, are the optimum. [ABSTRACT FROM AUTHOR]

The uniformity of rice milling is of vital significance in the rice processing industry. Unfortunately, the reasons for non-uniform milling of grains in friction rice mills still remain poorly understood. In this paper, the motion of rice in the mill is numerically simulated based on the discrete element method. The removal mechanism for the bran layer in the friction mill is discussed and verified by experiment. A method of quantifying milling uniformity was introduced. The results showed that for successful milling, the intact bran layer must experience abrasion caused by sieve-rice contact then be completely removed by rice–rice friction. Non-uniform milling occurs due to the existence of "milling blind zones", where the bran layer cannot be removed. Milling uniformity is closely related to the ability of rice to move from blind zones to the outer ring of the mill. The use of alternating rate to quantify this ability is proposed. The higher alternating rate the better milling uniformity. Alternation rate is affected by the tumbling movement of rice in the milling cavity. The research helps clarify the milling process of rice and provides guidance for the design of rice friction mills. [Display omitted] • Removal of bran layer mainly depends on the abrasion effect by sieve. • Non-uniform milling is due to existence of milling blind zones. • Higher alternating rate between zones is beneficial for milling uniformity. • Stronger tumbling ability of rice grains can lead to higher alternating rates. [ABSTRACT FROM AUTHOR]

Paddy usually requires a series of processing techniques to become edible polished rice. Among them, rice milling is a necessary processing connection closely related to the nutrition content and economic value of rice. How to accurately control rice milling on demand has always been a frontier topic. In this work, the milling process of rice grains in friction milling cavity with different parameter configurations was simulated numerically. The feasibility of the established simulation model was verified through experiments. Kinematic and dynamic similarity of rice grains in milling cavity were analyzed. The main contribution mechanism affecting the energy loss of rice grains was explored. The scale-up rule that can predict the milling degree of rice was proposed for the first time. The results showed that when the structural or operating parameters change, the flow structure of the particle bed will change significantly, which directly determines rice force characteristics. Besides, the energy dissipation between rice depends more on the configurational temperature dominated by the compactness of particle bed than on the granular temperature. The fluctuation of displacement field of particles will be more intense with the decrease of local space porosity and the increase of external input energy. Finally, a parameter scale-up rule – Relative compaction volume (RCV) suitable for friction rice mill is established. The average dissipated energy of rice grains can be characterized as a linear function of RCV. The characteristic parameter RCV is determined by the geometric characteristics and operating conditions of the rice mill. The research results can provide analytical ideas and theoretical direction for the design and parameter selection of rice mill and similar equipment. [ABSTRACT FROM AUTHOR]

The precise separation of whole and broken rice is an issue of great significance in rice processing industry. This paper presents a numerical study on the rice separation in an indented cylinder separator based on the discrete element method. The probability density function of escape angle of whole and broken rice was investigated at 10% filling level for various rotational speeds and indent numbers. Hellinger distance, a statistical estimate used to quantify the difference between two probability distributions, was adopted to measure the separation ability. It was found that the Hellinger distance appears to initially increase to a maximum and then decrease with the increase in rotational speed. While the Hellinger distance increases to a maximum value then keeps stable with the increase in indent number. After obtaining the optimal operating condition for the best separation, the position of trough was decided based on the boundary of parabolic trajectories of whole rice after leaving indents. The aim of this work is to determine the best parameters for the indented cylinder separator based on the understanding of separation progress at a particle scale, providing a foundation for the numerical investigation of indented cylinder separator. Unlabelled Image • Separation of rice by indented cylinder was simulated using discrete element method. • Effect of rotation speed and indent number on escape angle distribution was analyzed. • Hellinger distance was used to quantify the difference of escape angles. • The position of trough was decided based on the boundary of whole rice trajectory. • Rotation speed ratio of 55%, indent number of 72, trough angle of 60 is the optimum. [ABSTRACT FROM AUTHOR]

Rice milling is a key step that decides nutritional quality and economic benefits of rice in rice processing. Because of diverse requirements for the bran removal degree and rice handling capacity, rice milling effect must be accurately controlled. In this study, the milling process of rice in milling cavity was simulated through discrete element method, and simulation effectiveness was verified by experiments. Dynamic response characteristics of rice particles to different parameters were clarified. The more energy input and the larger particle volume fraction in shear zone, the higher milling degree of rice. A scale-up mathematical model involving structural and operating parameters was established for the first time. There is a linear relationship between the model and the energy loss. Experimental results showed that the model can accurately predict the milling degree of rice. This study can provide theoretical guidance for the design of rice mill or similar equipment. • DEM can accurately simulate the rice milling process in milling cavity. • Mechanics response characteristics of rice under different parameters are analyzed. • Dissipated energy of rice is related to energy input and particle volume fraction. • A scale-up model involving structural and operating parameters is proposed. • Study can give theoretical direction for design of rice mill or similar equipment. [ABSTRACT FROM AUTHOR]

Rice milling, as a critical process in rice processing, determines the subsequent storage, nutritional quality and economic value of rice. Unfortunately, due to the complex milling mechanism and few quantitative methods to predict the milling effect of rice, the improvement of the key components of rice mill has become one of the issues restricting the development of rice milling industry. In this work, rice milling performance in rice mill with different convex rib helix angle α was studied through the combination of simulation and experiment. Modified actual milling time distribution can accurately quantify the uniformity of rice milling. Milling uniformity of rice gradually deteriorated with α. Compared with traditional evaluation methods, the regional energy algorithm can reflect the rice milling degree more accurately. Besides, the friction effect between rice become more intense with increased α. These results can provide theoretical guidance for the parameter optimization of rice mill. • Simulating the movement of rice in rice mill by DEM is effective and accurate. • Kinematic characteristics of rice in radial and axial directions are analyzed. • Modified actual milling time distribution can quantify the rice milling uniformity. • Regional energy algorithm can accurately reflect rice milling degree in rice mill. • The results can provide theoretical support for design and optimization of mill. [ABSTRACT FROM AUTHOR]

• DEM can accurately simulate the movement of particles in vertical rice mill. • The rice in milling chamber is transported dispersedly rather than layer by layer. • The particle transport mechanism is revealed from the perspective of kinematics. • A method that can establish link between mill parameters and uniformity is proposed. • This study can provide guidance of the parameter design for similar equipment. Rice milling is a crucial step to determine the final rice quality in rice processing. The uniformity of rice transportation in milling chamber is the key factor affecting the milling uniformity. Unfortunately, the cause of the uneven transport of rice in milling chamber is still poorly understood, which constrains the development of rice milling industry. In this study, the movement process of rice in vertical friction rice mill was numerically simulated by discrete element method. The macroscopic motion law of rice was obtained first and then quantified by residence time distribution (RTD). Then, the transport mechanism of rice in the milling chamber was analyzed from the kinematic perspective. Finally, a mathematical model involving the relationship between the mill parameters and the rice transport uniformity was established. The results showed that the axial dispersion of rice occurs during the transport process in milling chamber. The RTD curve indicates that the residence time of most particles in the milling chamber is short while that of a few particles is long. Besides, with the increase of rotational speed, the axial motion consistency of the particles becomes worse. The particle bulk density distribution shows that particle flow is affected by both axial backflow and radial centrifugation. There are complex convection and local vortices flow in particle vector field. In addition, the trough value and peak value of the axial velocity of the particle flow layer decrease and increase respectively with rotational speed. The swept volume method containing the structural and operating parameters of the rice mill is established. There is a strong corresponding relationship between swept volume and the uniformity of flow layer. Specifically, the larger the swept volume, the stronger the axial convective mixing, the more uneven the rice transportation. Finally, it is verified by experiments that the milling uniformity of rice mainly depends on the swept volume. The research result is of guiding significance for the design of relevant parameters of similar equipment. [ABSTRACT FROM AUTHOR]