Experimental Study on Throttling and Cooling Characteristics of CO₂ in Cryoprobes

By comparing the cooling characteristics of four types of cryoprobes under different inlet pressures, the effects of the inlet pressure, J-T slot inner diameter, and backflow channel size on the cooling of cryoprobes are analyzed, and the size of ice hockey balls formed in gelatin are tested. The results show that the temperatures of 1.8-0.42 mm, 1.8-0.30 mm, 1.8-0.12 mm, and 1.1 mm cryoprobes are the fastest under the inlet pressure of 4.5 MPa, 4.0 MPa, 5.5 MPa, and 5.5 MPa, respectively. When the pressure is low, the cooling rate is positively correlated with the inlet pressure. When the inlet pressure is greater than the optimal pressure, the ice blockage increases with increasing pressure. Among the cryoprobes, a smaller inner diameter of the J-T slot improves the cooling rate of the cryoprobes and lowers the temperature of the tip, and a larger backflow channel can reduce ice blockage in the pipe and improve the cooling rate; 1.8-0.42, 1.8-0.30, 1.8-0.12 mm, and 1.1 mm cryoprobes have the largest ice hockey ball diameters under air supply pressures of 4.5, 4.5, 6.0, and 6.0 MPa, respectively. When the inner diameter of the J-T slot decreases, its optimal air supply pressure increases.