Study On Food Freezing Numerical Simulation And Technique Of Quick Freezing Crayfish In Ultra-low Temperature Water

China is the world's large producer and exporter of crayfish(scientific name: Procambarus clarkii)and the current export products are all frozen crayfish.The traditional method of freezing is mainly based on air cooling while there are prevalent problems including huge refrigeration energy consumption,poor freezing effect and low freezing efficiency in the refrigeration enterprise.In this paper,an ultra-low temperature water medium freezing method is proposed targeting the characteristics and freezing requirements of crayfish.The method can keep the temperature below 0 ? without freezing after using water under negative pressure or adding NaCl solution,and put forward the theory of ultra-low temperature water circulation quick freezing.According to the theory of heat transfer,the freezing process and law of food were studied and the method of reducing pressure and adding Na CL was studied for the effect of it on the freezing effect of food and the replication experiment was carried out in the laboratory.In this paper,a negative pressure water circulation freezing experiment device was designed and manufactured.The experiment verification was carried out in the industrial cold storage with crayfish as the frozen object to come up with the temperature change law of the freezing process.The traditional freezing method and the new negative pressure water circulation freezing method were respectively applied for freezing comparison experiment on the same frozen object.The experimental results show that:(1)In the negative pressure environment or by adding a certain concentration NaCL,the refrigerating fluid can keep the flow state without being frozen,revealing the rule of food icing and influencing factors.(2)The experimental device can put the frozen body into the-8 ? circulating frozen medium under ultra-low temperature environment at the beginning of freezing,proving the feasibility of the freezing method.(3)The new negative pressure water circulation freezing method,compared with the traditional air freezing method,requires less freezing time to reach-8 ? of frozen body center and enjoys more reasonable distribution rule of frozen surface and the center temperature after the same freezing time and makes more obvious improvement in the quality of frozen products.In this paper,a new type of negative pressure water circulation freezing method was proposed and the freezing experiment device was designed and manufactured.Through the comparison experiment with the traditional freezing method,it's proved that the freezing efficiency and the freezing quality are improved greatly,which provides a theoretical basis and technical support for crayfish freezing technique and provides a reference for same type of freezing technique research.