Research On Mechanism And Process Parameters Optimization For Superheated Steam Drying Of The Rice Plant Bowl-seeding Tray

Rice seedling growth modes is the key to realize the rice planting mechanization of ricebreeding, rice bowl brood planting technology is very suitable for China’s northern boreal riceplanting and welcomed by the majority of rice farmers for its resistance to low temperature andyield advantage. Therefore, low carbon and high efficient agricultural characteristics of rice plantbowl-seeding tray and related transplanting machine have been developed independently in ourschool. Plant bowl-seeding tray is rice seedlings carrier by taken rice straw as raw material andadopted trays molding process, the technology has a large range of rice yield and high-qualityrice. The technology can realize the returning straw to soil fertility and two saving and twoincreasing, that is to save soil and seeds, to increase production and efficiency, tray is made ofstraw, when straw is decay which will become fertilizer, so the technology has greatdevelopment potential, and application prospects to develop high yield of rice machine mode andsolve the problem of rice stable and high yield.Plant bowl-seeding tray is a core link of rice breeding planting technology, but in theprocess of using tray to seed, the seedling tray is broken easily, the mechanical strength is notenough, in order to overcome these problems, it is need to dry plant bowl-seeding tray, by usingthe superheated steam drying technology to study seedling tray deeply, in order to improve theperformance quality of seedling tray.In order to make use of superheated steam drying to improve performance quality of theplant seedling-growing tray, achieve the research of superheated steam drying technology andverify the simulation analysis, the plant bowl-seeding tray of superheated steam drying testbench is developed. The test bench is low cost, simple structure, reliable performance, easyoperation, high precision control system, visual display, easy to collect and read the test data.It is draw a conclusion that hot air drying of the dry and wet strength value is smaller thanthe value of the superheated steam drying, indicating that superheated steam drying is superior tohot air drying; the seedling tray appearance is not neat after hot air drying, can appear warping,crack phenomenon, the seedling tray edge is rough, even have burr appear; the seedling trayexternal shape is better after the superheated steam drying, is not has shrinkage and deformation,warping, crack edge and burr phenomenon.The effect of the dry influence factors on the rate of the seedling tray drying, the study showthat: the drying rate increased significantly with the increase of temperature, to enhance thetemperature of the superheated steam drying can enhance the rate of drying; drying rate increaseswith the increase of superheated steam mass flow, the results show that increase superheated steam mass flow can improve the drying efficiency.The effect of the effects of various factors on mechanical strength of the seedling tray isstudied, the results show that: the dry and wet strength with the rise of temperature increase firstand then decrease gradually, the seedling tray strength reach to maximum when dryingtemperature is about145℃, when temperature is too high, the seedling tray is become friable,mechanical strength weakened. The seedling tray along with the growth of the drying time, dryand wet strength increase first and then decrease gradually, with the increase of superheatedsteam mass flow, the seedling tray dry and wet strength gradually increase, with the increase ofthe seedling tray initial moisture content, the seedling tray dry and wet strength value will dropslightly, but not obvious; contrast dry and wet of the seedling tray mechanical strength, it isknown that the value in wet condition is smaller than in dry condition, the strength declined, thisis due to the seedling tray in water and soil in the long-term soaking.The effect of all the key influence factors on the plant bowl-seeding tray strengthperformance of comprehensive is considered, the orthogonal tests are studied, through theanalysis of the model, the dry and wet strength effect size order is as followed: drying time>drying temperature> mass flow; Through the optimization of the regression equation whichestablish by the seedling tray mechanical strength performance, the best superheated steamdrying parameter combination scheme is acquired, the results are as followed: drying time was15.4min, drying temperature is145.11℃, mass flow rate is2.2Kg·m-2·s-1; Through theverification test, strength performance is got which close to the theoretical value, indicating thatthe regression model is reliable. Actual strength is greater than the weight simulation strengthvalue, indicating that strength can meet the requirements of the seedling tray doesn’t break.In order to study the heat and mass transfer law during drying of plant bowl-seeding tray,taking the sheet structural plant bowl-seeding tray materials as the subjects, the heat and masstransfer of plant bowl-seeding tray are analyzed theoretically, according to the energyconservation law and mass conservation law, heat and mass transfer mathematical model isestablished during drying of sheet structural material, parameters are determined in two models,differential equations are discretized by the finite difference method, mathematical models aresolved by numerical methods in MATLAB programming, the prediction results of heat and masstransfer model during drying of plant bowl-seeding tray are obtained. The sheet structuralmaterial of plant bowl-seeding tray is tested under the conditions of the drying chambertemperatures of120℃,140℃,160℃, the test datas of the temperature and moisture contentvariation with time through the test are obtained, variation of temperature and moisture on sheetstructural material of plant bowl-seeding tray in the drying process a re analyzed and discussed. we found that theoretical modeling values are consistent with the experimental values bycomparing theoretical analog values and experimental values. This indicates that the model hasgood accuracy, which can provide a mathematical method for practical application and will be agreat significance for the regulation and development of the scientific basis of the dryingprocess.Dimensional stability of plant bowl-seeding tray was studied, research showed that: as thedrying temperature is increased, the shrinkage rate of the sheet material is also increased,swelling rate is gradually decreased, absorption rate is decreased, and therefore, improve thedrying temperature is conducive to improve the dimensional stability and water resistance.