真空探针冷冻和复温性能实验测试及数值模拟

Test and numerical simulation of freezing and rewarming performance of vacuum probe

针对现有的冷热复合治疗探针中存在的问题,设计了直径3 mm的真空探针,用电阻加热和真空层相结合的方法解决探针非工作段的低温问题,以液氮冷冻和电阻加热的方式实现探针的冷热交替过程。分别在空气、蒸馏水和离体猪肝中进行探针的性能测试实验。发现电加热与真空层结合可以提高探针非工作段的温度;在蒸馏水中探针形成轴向长度为3.6 cm,径向长度为1.8 cm的冰球;在离体猪肝中形成轴向冻结直径约为3.6 cm,化冻直径为1.2 cm的区域。使用数值计算的方法计算探针的有效治疗范围,形象直观地展示组织在冷冻和复温过程中的温度场分布,为临床手术提供数据支持。从整体效果看,探针有良好的冷冻和复温性能,促进冷热复合治疗的进一步发展。

A 3-mm-diameter vacuum cryoprobe was designed. Low temperature problem in non-working section of probe was solved by resistance heating and vacuum layer. The freezing and rewarming process of the vacuum cryoprobe was realized through liquid nitrogen and resistance heating, and the freezing and rewarming properties of the vacuum cryoprobe were studied in air, distilled water and isolated porcine liver. According to the temperature variation data of the vacuum probe’ s working section in the isolated pig liver, set the corresponding boundary conditions in the numerical simulation, and use the classical bio-heat transfer equation to calculate the temperature distribution of the vacuum probe during freezing and rewarming process in human tissues, which can better understand the performance of the designed vacuum probe. In air, firstly, the vacuum probe has same temperature that working section is-190℃ and non-working section is-100℃ at 0.2 MPa,0.25 MPa,0.3 MPa, but the cooling rate will increase with increasing pressure. Secondly, the vacuum layer outside the probe’s non-working section can prevent heat transfer. Thirdly, the resistance heating method can increase the temperature of the vacuum cryoprobe.Resistance heating can make the temperature of the probe’s non-working section within the acceptable range of the human body, and without damaging the human normal tissues. In distilled water, the probe’s working section can form ice hockey with an axial length of 3.6 cm and a radial length of 1.8 cm at 600 s, and volume of ice hockey is 6.11 cm3. In vitro porcine liver, the freezing phenomenon can be clearly seen. The freezing temperature reaches-192.9℃ and rewarming temperature reaches-55℃ in working section, and average cooling rate is 128℃/min. At the end of the experiment, the axial frozen diameter and axial thawed diameter are 3.6 cm and 1.2 cm, respectively.In simulation, the influence heat sources on the temperature field of human tissues was analyzed. From the nephogram, the tissues form ice hockey and melt gradually. Without heat source, freezing effective area is ellipse which long axis is 12.4 mm at 600 s, while rewarming effective area is ellipse which long axis is 10.4 mm at 1400 s.If heat source is considered, whole tissue’s temperature will increase during the freezing and rewarming process, and it has a great influence on rewarming process. From the overall effect, the probe has good freezing and rewarming properties, which promotes the further development of cold-heat compound therapy.