Research On The Process Of Droplet Suspension Freezing And Identification Of Freezing State

As a common phenomenon in life,the phase transition of water and ice is accompanied by the absorption and release of energy.Exploring an efficient freezing method has practical engineering significance to alleviate the current world energy shortage and reduce energy consumption.Because of the large contact area and direct contact,the spray suspension freezing has a higher freezing efficiency.The scientific identification of freezing state is conducive to in-depth understanding of the freezing process,and helps to scientifically define the freezing state and promote the development of freezing theory and technology.On the basis of analyzing the force and heat transfer process of droplet in suspension process,combined with the theory of phase change freezing,a mathematical model of single droplet suspension freezing and spray(field)freezing is established by using fluent.The freezing process of single droplet suspension and spray(field)under different conditions is numerically simulated.The results show that:(1)starting from the single droplet suspension freezing,the numerical simulation of single droplet freezing is carried out when the airflow velocity is 8m / s,10 m / s and 12 m / s respectively,and the conclusion is drawn that the completion time of droplet freezing is 11 S,10s and 9.4s respectively under the corresponding conditions;The results show that the freezing time of droplet is 19 S,13s and 10 s respectively under the corresponding conditions.In conclusion,the faster the air flow velocity and the lower the air temperature are,the faster the freezing rate is;(2)Starting from spray(field)freezing and controlling other conditions,numerical simulation of spray suspension freezing is carried out at the flow velocity of 1.414m/s,2.121m/s and 2.828m/s respectively.It is concluded that the droplet temperature of spray outlet center is270.53 K,269.30 K and 267.22 K under corresponding conditions.Controlling the other conditions,numerical simulation of spray suspension freezing at the temperature of248.15 K,253.15 K and 258.15 K is carried out.It is concluded that the droplet temperature at the center of the spray outlet is 263.37 K,267.22 K and 269.44 K under the corresponding conditions.Under the same control conditions,the incident angle of the airflow is 45°,50°And 55°Numerical simulation of spray suspension freezing shows that the droplet temperature at the center of the spray outlet is 267.22 K,267.88 K and 268.13 K respectively under the corresponding conditions.It is clear that airflow velocity,airflow temperature and airflow angle have obvious effects on droplet freezing rate.The greater the airflow velocity,the smaller the incident angle and the lower the air temperature,the better the spray freezing effect is.(3)observed the simulation results of spray(field)freezing under different airflow velocities and airflow angles.The smaller the outlet velocity of the droplets is,which means the better the suspension effect is,the lower the droplet temperature is at the droplet outlet,which indicates that the suspension can effectively improve the freezing efficiency.At the same time,a suspension freezing experiment system was set up to study the spray suspension freezing under the designed condition of airflow temperature,airflow velocity and airflow angle.The experimental results showed that:(1)the freezing state of droplet spray at different positions in the freezing chamber under experiment conditions was observed and compared with the simulation results.The reliability of the theoretical model is verified.(2)through the observation of experiments,it is confirmed that the method of spray suspension freezing can obviously improve the freezing efficiency.In order to get the mathematical description of the freezing state,combined with water freezing state experiment and cusp catastrophe theory,the freezing process is observed from the micro and macro perspectives Through the analysis of the macro and micro structure in the water freezing process and the treatment of the change law of the average diameter of the internal bubble pores,the mathematical model of the state identification of the freezing process is given,and the actual experiment is carried out for verification.The research of this paper will provide theoretical guidance and reference for suspension freezing and identification of freezing state,and promote the engineering application of spray freezing technology.