Design of closed-loop mixed refrigerant Joule-Thomson cryosurgical probe with precooling stage.

Cryosurgery is an effective medical procedure to destruct malignant tissues such as prostate cancer cell, wart or cervical cancer by freezing-induced apoptosis. A cryosurgical probe is a mechanical cooling device to develop extremely low temperature to freeze the target cells in a human body. A high-pressure open-loop Joule-Thomson (J-T) refrigeration technique has been commonly employed for the cryosurgical probe because the required geometry of such a cryosurgical device can be very narrow and thin. As a downside, however, since the open-loop device has to consume high pressure refrigerant gas after its service, the closed-loop J-T cryosurgical probe has drawn great attention to avoid the replenishment problem. In this paper, a closed-loop J-T cryosurgical probe is proposed by designing non-flammable mixed refrigerant (NF-MR) refrigeration cycle combined with a precooling stage. 1-dimensional (1-D) transient heat diffusion model is formulated to find the proper thermodynamic boundary condition of the probe. The cold-end temperature is varied from 100 K to 200 K, and the cooling capacity of the probe is examined between 1 W and 25 W to find the optimum thermal performance factor of the probe. The precooling cycle and the main refrigeration cycle are analysed in detail to be able to define the best operating conditions such as pressure, flow rate and precooling temperature. The coefficient of performance (COP) is calculated and the relevant exergy analysis is also performed to identify the inefficiency of the proposed MR J-T cycle.