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Study On The Separation Characteristics Of White Rice In An Indented Cylinder Separator

Posted on:2020-12-15Degree:MasterType:Thesis
Country:ChinaCandidate:X Y MengFull Text:PDF
GTID:2393330575988074Subject:Agricultural mechanization project
Abstract/Summary:PDF Full Text Request
The precision separation of whole and broken rice is of vital importance for the rice processing.The price of head rice is almost more than two or three times than that of the broken rice.The precision separation of rice can not only satisfy the requirement of accustoms,but also brings benefits for the factory.However,nowadays,the design of indented cylinder separator is mainly based on the rule of thumb,which can not thoroughly improve the separation efficiency.This paper aims at providing a novel method for determining the best parameters for the indented cylinder separator based on the understanding of motion of rice and separation characteristics.This study was based on the understanding of the separation process in an indented cylinder separator at a particle scale.Firstly,the effect of rotational speed ratio and broken content on the motion of rice in the mixing area of the indented cylinder separator was investigated by DEM.Secondly,distribution of escape angle of whole and broken rice was investigated for various rotational speed ratios and indent numbers.Based on the difference of distributions,a novel optimization method for the design of indented cylinder separator was proposed.Finally,the effect of parameters including rotational speed ratio,broken rice content and trough angle on the separation efficiency and losses was investigated by experiments.The best combination of parameters was obtained.The result of the experiment was compared with the simulation to verify the reasonability of the novel method.The key conclusions of the investigation are as follows.(1)The motion of rice in the mixing area and their influence on the separation was clarified.The velocity difference of rice in adjacent layers increases with the increase in the rotational speed ratios alongside the direction of center chord,showing as the relative motion becoming stronger.It leads to a uniform mixing,which provides more opportunity for the broken rice move into the indents.While the broken rice content has a negligible influence on the mixing of rice.The undesired phenomenon of broken rice gathering in the center of the mixing area and surrounded by the whole rice can not be broken up by adjusting the broken rice content.(2)A novel optimization method for the design of indented cylinder separator was proposed.Hellinger distance which can be used to quantify the difference between two probability distributions,was adopted to measure the separation ability.After obtaining the optimal operating condition for the best separation,the position of the trough was decided based on the algorithm of Alphashape by searching the boundary of parabolic trajectories of whole rice after leaving indents.With the increase in the rotational speed ratio,no matter whole or broken rice,the escape angle increases.Meanwhile,the distribution of escape angle became wide.The Hellinger distance appears to initially increases to a maximum and then decreases.The maximum value is achieved at rotational speed of 55% of the critical speed which corresponding to the best separation ability.With the increase in the indent number,no matter whole or broken rice,the escape angle decreases.The Hellinger distance increases with indent number until a maximum value then keeps stable.It shows that the Hellinger distance increases with indent number until a maximum value reached when indent number is 72.With further increase of indent number,the Hellinger distance keeps stable.(3)The best combination of parameters was obtained with the aim of maximum separation efficiency and minimum losses.Through the experiments,it was found that the rotational speed ratio was the most important factor to influence the separation efficiency,followed by trough angle and broken rice content was the least important.All the factors have a significant effect on the separation efficiency except for linear term of broken rice content,interaction term of rotational speed ratio and trough angle.It was also found that the trough angle was the most important factor to influence the losses,followed by rotational speed ratio and broken rice content was the least important.All the factors have a significant effect on the losses except for linear term of broken rice content,interaction term of rotational speed ratio and broken rice content.
Keywords/Search Tags:White rice separation, Indented cylinder separator, Discrete element method, Parameter optimization
PDF Full Text Request
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