Preliminary Study On Mechanism And Greenhouse Application Experiment Of Wind Stirring Heating Technology

The blade of the stirring rotor stirs the working fluid mechanically.The mechanical energy is converted into thermal energy through the collision and friction between the working fluid and the blade,the vessel wall and the interaction of the working fluid.Stirring heating technology is not only high heating efficiency,but also clean and environmentally friendly,compared with the traditional way of heating by using fossil fuels.This technology is specially designed and used in distributed energy utilization and off-grid application mode,because the heat energy is easy to be stored,it has a good application prospect in the scene of direct heating by new energy such as wind.Based on the distribution of wind energy resources in China,and the distribution of greenhouse construction area,it is concluded that stirring heating technology has high application potential in greenhouse agriculture in Northwest China.The design goal of the stirring heating device is diametrically opposed to that of the stirring mixer,the stirring heating device needs to achieve very high power consumption at low rotational speed.At present,the research on the design method of stirring heating device is still very limited.This greatly limits the practicality and achievement transformation of stirring heating technology.In this study,an existing stirring heating device is used as the prototype to carry out experimental research and CFD simulation on the effects of working fluid factors and structural factors on the stirring heating effect.The stirring heating experiments of various types of working fluids were carried out on the prototype machine;a comprehensive evaluation dimensionless index CEIH for evaluating the heating effect of stirring is established;A multiple linear regression model about CEIH was established.On the basis of the prototype machine,the layout of the rotor,the height of the liquid level,the number of spoilers under the full baffle condition and the structural variables of the embedded spoiler depth variable control experiment are designed,according to the comparison and analysis of functional requirements and design elements of the stirring heating device and the mixing agitator.Transient simulation is carried out by establishing CFD model for rotational speed,working fluid and structure experiment,the experiment data and simulation data are compared and analyzed when the rotational speed,working fluid type,rotor arrangement,liquid level,the number of spoilers under the condition of full baffle and the embedded depth of embedded spoilers;the phase,speed rate cloud image and velocity vector image of the simulation results are analyzed.Based on the experiments of working fluids and structural factors,the optimization scheme of the prototype of stirring heating device is put forward,and a 2 kW stirring heating device is designed.A 6 kW air energy storage and release system are connected in parallel to form a stirring-air energy combined heat storage and release system,and the operation performance of each subsystem is compared and studied.The main research work and conclusions show that:Ⅰ、The multiple linear regression model has a high explanation to the original experimental data and can describe most of the changes of CEIH scores;among the thermophysical factors of working fluid,the degree of influence on the heating effect is in the following order:specific heat capacity,viscosity and density.The specific heat capacity and viscosity are inversely correlated with the heating effect,and the density is positively correlated;according to the CEIH score,the potassium chloride solution with the concentration of 30 g/100g is the best working medium for stirring heating.Ⅱ、The experiment results of structure elements show that the heating effect of the stirring rotor with double layer and wide spacing is the best one;the heating effect of the heating device increases with the increase of liquid level;when the number of spoilers is increased and the width is decreased under the condition of full baffle,the heating effect is not decreased,but also improved to a certain extent;the heating effect of embedded spoiler increases at first and then decreases with the increase of embedded depth.Ⅲ、The fitting power of the simulation data is consistent with the experiment value in the analysis of CFD simulation,and the determination coefficient of the simulation data to the experiment data is more than 0.7,the CFD simulation is very reliable in analyzing the heating problems of stirring heating;at the same time,it shows that turbulent viscous dissipation is the main heating way of stirring heating technology;rotational speed,working fluid and rotor arrangement mainly affect the intensity of turbulent motion,while other structural factors mainly affect the discharge of liquid in the rotor area,which are the main indicators of turbulent dissipation and the work done by the rotor to the liquid working medium,respectively.Ⅳ、The power of the optimized stirring heating device is nearly twice as much as that of the prototype,and the energy efficiency of the air energy storage and release system is very low in continuous rainy and snowy weather in winter.The stirring heating device can make use of the strong wind conditions during the bad weather to make up for this disadvantage and achieve the purpose of emergency heating.The COP of the 2 kW stirring heating device is 0.84,the rated wind energy input of 6 hours per day can meet the daily heat demand of the solar greenhouse with 300 m3 space volume in Guanzhong area of Shaanxi Province.