| The dryer equipment has been widely used in chemical industry,pharmaceutical,food,light industry,agriculture,forestrylocal,products and other fields.Drying is a process with high energy consumption.In developed countries,about 10% of the fuel is used for drying.It is also a complex heat and mass transfer process.Material characteristics,drying medium parameters and drying process will have an impact on the drying process.Therefore,in order to reduce the energy consumption of material drying process,it is necessary to take measures to improve the energy efficiency of drying equipment.This paper presents a powder flow heat pump dryer,which can improve the drying quality and reduce the energy consumption in the drying process.In this paper,we study the powder flow heat pump dryer is the heat pump system with the special structure of vertical powder dryer,the combination of vertical powder dryer partition and powder materials refrigerant in heat exchange,and by a small amount of cold wind will wet discharge air dryer,heating and dehumidification of separation,compared with the traditional hot air drying method,the powder flow efficiency of the heat pump dryer is higher.The flow process of the powder material in the vertical powder dryer determines the drying effect of the final material,and the residence time of the powder material in the dryer can be equal to ensure the uniformity of the drying material.In this paper,the drier of the powder flow heat pump dryer is taken as the research object,and the discrete element method is introduced into the study of the flow process of the powder material in the drier,and the flow of the powder material in the drier is simulated.In the simulation without shunt cone condition,it is found that the flow process of particles in the dryer presents convergent flow,and the flow trajectory of particles located in the center of the dryer is basically coincident with the axis of the dryer,and it flows out of the dryer first.In the process of falling,the particles on both sides of the dryer will continue to get close to the axis and stay in the dryer for a long time.The residence time of the particles on both sides in the dryer is about 1.3 times that of the particles at the center.The residence time of the particles in the dryer is quite different,which may lead to uneven drying.In order to improve the flow of particles in the dryer,a shunt cone with a certain Angle was added to the dryer to simulate the flow of particles in the dryer after the shunt cone was installed at 40°,50°,60° and 70°,and the flow analysis was carried out.The analysis mainly includes the change of the shape of the flow field,the change of the trajectory of typical particles,the change of the particle position with time,the distribution of the velocity field and the discharge rate.Through simulation,it is found that the shape of flow field is obviously improved after the placement of 40° and 50° divergent cones,but it is still convergent flow.The shape of the flow field basically realized the horizontal thrust flow after the 60° shunt cone was installed.The shape of the flow field becomes "convex in the middle" after placing the 70° shunt cone.Through comprehensive analysis,find a place for 60 ° after the shunting cone,realize the basic horizontal pushing flow shape of flow field,a typical particle residence time within the dryer is evener,falling fastest and the slowest particle position and randomized,particles and wall in granular basic equal falling,in short,placed within 60 ° diversion cone can make dryer particles flow state to reach the expected results.To test and verify the accuracy of simulation results,the establishment of dryer experimental prototype(sample size is consistent with the 3 d model employed in the simulation process size),the experimental materials,select the urea particles from Texas a fertilizer into two)(white and yellow,the experimental process in the first place in the dryer white grain filling a certain height,the top dryer 40 mm space filling yellow grain,It is convenient to watch the flow state of the particles.After the particles are filled with the dryer,the discharge flow experiment is started.The flow process of the particles in the dryer is recorded with a digital camera,and the discharge rate is weighed and calculated.The experimental results are in good agreement with the simulation results.The comprehensive analysis shows that under the working condition of 60° shunt cone,the flow field shape of particles can realize the horizontal push flow,and the residence time of particles in the dryer is more equal,which is the prerequisite to achieve uniform drying. |
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