Simulation On The Process Of Low Temperature Freezing Skin Disease And Study On Automatic Injection System

Cryotherapy is a treatment method which is using ultralow temperature to destroy abnormal organization. Because it is easy and simple to handle, safe and effective, it is widely used in clinic treatment. Liquid nitrogen is widely used in cryotherapy to treat dermatosis. There are some progresses in the study of liquid nitrogen medical cryogenic apparatus, but because of its high cost, poor safety, inconvenient operation, and large amount of liquid nitrogen volatilization, the cryotherapy is use cotton swab with liquid nitrogen to treat the disease. This method is easy to operate, but cross infection is easily to generate, normal tissue injured easily. By using finite element software, temperatures variation characteristics of liquid nitrogen freeze skin tissue are discussed, guideline for clinical treatment is provided. Meanwhile the model of transporting liquid nitrogen in pipeline and jetting through spray nozzle is set up, the flow characteristic of liquid nitrogen and changes of temperature after jetting is analyzed, and then the pipeline and the type of spray nozzle is determined, the safe liquid nitrogen medical cryogenic system is developed.Clinical application of Liquid nitrogen cryotherapy is mostly implemented based on experience, this brings great difficulties for precisely controlling the frozen area. According to anatomical model of skin tissue,3D heat transfer character of skin tissue is set up to describe its freezing process. With the help of fluent software, the 3D heat transfer model is analyzed, and temperature variation is simulated under the condition of the skin tissue in liquid nitrogen freezing. Temperatures variation characteristics are discussed.To make the simulation of liquid nitrogen freezing skin tissue more precisely, the experiment of liquid nitrogen cryotherapy on pork tissue with skin is conducted, and the temperature variation with time is obtained. Meanwhile, FEM of pork tissue with its own thermal physical properties is set up, the result of experiment and simulation is compared. According to the difference in the results of the simulation and experiment, simulation is optimized, the influence of different thermal physical properties on temperature is obtained, and the influence of different thermal physical on freezing velocity and freezing depth is analyzed.Because the temperature of liquid nitrogen is very low and easy to volatilize at room temperature, there are some limitations in the choice of pipeline and the design of spray nozzle. By the model of transporting liquid nitrogen in pipeline is set up and the analysis of simulation on spray nozzle, the difference of pipe pressure due to different angle of spray and difference viscous force due to different nozzle diameter are analyzed. The relationship of temperature and jet distance is analyzed by the simulation.By the simulations, the guideline of cure area in clinic is provided, and the choice of pipeline and the optimal design of spray nozzle are guided. The safe liquid nitrogen medical cryogenic system is developed, there are containers for liquid nitrogen, operating cabinet, transport system with liquid nitrogen in it, technology guarantee for more precise safe liquid nitrogen medical cryogenic system is provided.This work is supported by the Independent Innovation Foundation of Shandong University (No. 2012DX003).