Study On The Preparation Of Straw-containing Floating Aquatic Feed Based On Twin-screw Extrusion Technology

The scale of Aquaculture in China continues to expand in recent years,so the supply of fodder materials is in short supply,and the situation is getting worse.Crop straw is a kind of good fodder material because of its characteristics of large quantity,wide source and low cost,but it contains a large amount of cellulose substances,has poor palatability and is difficult to digest and the like,and can not be directly used for producing the feed.Compared with traditional single screw,twin screw has stronger mixing and shearing effect,which can effectively destroy the fiber microstructure of straw.However,the application of twin screw extruding technology to grain feed containing crop straw is rarely studied.This paper aimed at the current situation of aquatic feed industry and straw feed utilization in China,studied the floating aquatic feed containing straw extruded by twin screw extruding.Theory and reference was provided to alleviate the current situation of the shortage of feed materials in aquaculture industry and solve the problem of crop straw treatment.The extruding principle of co-meshing twin-screw extruding was analyzed,and the extruding process was divided into three parts:mixture conveying,melting and melt conveying.The mixing transport models of the non-meshing zone and the meshing zone were established by using the non-slug particle system,and the corresponding solution was carried out,and the uniform transport rate of the solid mixture was obtained.The melting model of mixed material in non-meshing region was established.The solid mass equilibrium equation,the temperature distribution equation of molten film and the melting heat equilibrium equation were obtained and solved.Then the melting model of the mixture in the meshing region was established,and the specific energy of the total melting deformation of the mixed material in the first meshing region was obtained.By combining the melting theory between the meshing region and the non-meshing zone,the length of the melt segment of the mixture was obtained.The mathematical model of melt section was analyzed by power law fluid,and the continuity equation,motion equation and Bird-Carreau constitutive equation were established.The preparation of flow field analysis during extrusion and expansion of tomato straw mixture was completed.Based on the theoretical analysis results and MATLAB equation calculation,the screw structure design was completed.Then,the corresponding co-meshing twin-screw extrusion model was established by SOLIDWORKS,and the three-dimensional model was imported into the POLYFLOW to generate the fluid.After setting the corresponding parameters and boundary conditions,the flow field was simulated and analyzed.The distributions of pressure,trace line and shear rate of straw mixture in twin-screw extrusion cavity were obtained,which verified the rationality of the design of the twin-screw extrusion model.According to the nutritional requirements of carp feed in China's aquatic industry,tomato straw meal,fish meal and standard meal were used as main raw materials,feed speed,screw speed,melt conveying temperature and water content of mixture as variables,puffing degree,texture characteristics,molding quality,powder content and water stability as the quality requirements,the single factor test and preparation of co-meshing twin-screw extruding carp feed containing tomato straw were carried out,and the corresponding testing platform for carp feed quality was set up.Based on the above five quality requirements,the experimental feed with different feed speed,screw speed,melt conveying section temperature and water content of mixed material was evaluated in an all-round way.The relationship between the carp feed quality and the variables was clearly analyzed by data,charts and SEM electron microscope pictures.The optimized twin-screw extruding feeding rate is 50 r/min,the screw speed is 100 r/min,the melt conveying temperature is 120 ?,and the moisture content of the mixture is 24%.Finally,experiments were carried out to verify that the quality indexes of carp feed under the technological parameters were excellent.