Cheonkyu Lee

Investigation on Cryogenic Refrigerator and Cooling Schemes for Long Distance HTS Cable

High-temperature superconducting (HTS) cable is one of the most prospective superconducting technologies for its low electric power transmission loss and high power density. One difficulty of practicing this technology is maintaining the HTS cable at a cryogenic temperature approximately at 70 K. The types of cryogenic refrigerators are briefly reviewed to apply in long-distance HTS cables. Recuperative-type refrigerators, such as Brayton and Joule-Thomson (JT) refrigerators, are more appropriate to satisfy the required high cooling power. The theoretical reliability of the newly proposed dual mixed refrigerant (DMR) JT refrigerator is analyzed. The cycle configuration of the DMR JT refrigerator is more complex than that of a Brayton refrigerator; however, the degradation of reliability was not significant. Furthermore, a remote operation apart from the compressor is possible in the JT refrigerator without moving components inside the cold box. This is the most desirable characteristic for long-distance HTS cable cooling. Finally, the advantage of using an oxygen and nitrogen mixture as the circulating coolant is discussed. The number of cooling stations can be reduced in a long-distance HTS cable by lowering the coolant feeding temperature.

Development of a closed-loop J–T cryoablation device with a long cooling area and multiple expansion parts

Cryoablation is a surgical procedure used to freeze defective cells by inserting a low temperature probe into a human body to destroy malignant tissues. Miniaturized Joule-Thomson (J-T) refrigerators are often used to minimize the volume of the cooling device and reduce the destruction zone of normal tissue. The cooling effects of the existing probes are not uniformly generated along the longitudinal direction of the probe, which makes their applications less effective in surgeries of incompetent great saphenous veins (GSVs), where the target cells are distributed over a broad range. Long uniform refrigeration is required across the entire area of the probe to apply the same cooling effects. In this paper, a closed-loop J-T cryoablation probe was designed and fabricated to provide uniform refrigeration over a large area, with multiple expansion parts. Using flow boiling heat transfer, uniform cooling of a 200 mm-long and 0.3 mm thickness piece of target tissue was possible and simulated in a gelatin solution. The developed probe produced a greater than 53 K min(-1) cooling rate and the cooling temperature was below 253 K to satisfy the required cell death conditions.

Joule-Thomson cryocooler with neon and nitrogen mixture using commercial air-conditioning compressors

A 2-stage mixed refrigerant (MR) Joule-Thomson (JT) cryocooler was designed for cooling high temperature superconducting cable below 70 K. The low temperature cycle was to operate with neon-nitrogen mixture, and the required compression ratio was approximately 24 when the suction pressure was 100 kPa. The high compression ratio of 24, the low pressure of 100 kPa at compressor suction, and the working fluid with high heat of compression were challenging issues to existing typical compression systems. We developed an innovative compression system with commercial oil-lubricated air-conditioning compressors. They were 2-stage rotary compressors originally designed for R410Aand connected in series. The compressors were modified to accommodate effective intercooling at every stage to alleviate compressor overheating problem. Additionally, fine-grade three-stage oil filters, an adsorber, and driers were installed at the discharge line to avoid a potential clogging problem from oil mist and moisture at low temper...

Experimental investigation of CO{sub 2} condensation process using cryogen

Carbon dioxide ( CO 2 ) is one of the dominant gas molecules that causes greenhouse effect, i.e. global warming. Numerous studies have been carried out to regulate the emission of CO 2 to reduce greenhouse gas. The liquid CO 2 is a convenient form of transportation compared to high-pressurized gaseous CO 2 . Therefore, the direct liquefaction mechanism of CO 2 at low temperature draws technical attention recently. In particular, cold thermal energy of Liquefied Natural Gas (LNG) could be a candidate to condense gaseous CO 2 , especially in the LNG powered ship. In this paper, the detailed direct condensation process of CO 2 using LN 2 with intermittent solidification is investigated. Pressurized CO 2 at 600 kPa is directly liquefied in a vessel by liquid nitrogen which is supplied into the coiled tube heat exchanger inside the CO 2 vessel. The heat exchanger temperature is controlled from 130 K to 205 K to regulate the solidification and sublimation of CO 2 by duty control with cryogenic solenoid valve. The characteristics of CO 2 condensation process with cryogen are analyzed from the measurement results. The results show that the solidification causes the significant degradation of CO 2 condensation heat transfer. Finally, the condensation rate with and without solidification is compared.

Microchannel heat exchanger for two-phase Mixed Refrigerant Joule Thomson process

Mixed Refrigerant Joule Thomson (MR-JT) refrigerators are widely used in various kinds of cryogenic systems these days. Printed Circuit Heat Exchanger (PCHE) is one of the promising cryogenic compact recuperators for MR-JT refrigerators due to its compactness, high NTU and robustness. However, PCHE composed with microchannel bundles can cause flow mal-distribution, and it can cause the degradation of thermal performance of the system. To mitigate the flow mal-distribution problem, the cross link (or intra-layer bypass) can be adapted to parallel microchannels. Two heat exchangers are fabricated in this study; one has straight channels, and the other one has intra-layer bypass structure between channels to enhance the flow distribution. The MR-JT refrigerators are operated with these two heat exchanger and the no-load temperatures are compared. The lower no load temperature achieved with the intra-layer bypass structured heat exchanger. The results indicate that the flow mal-distribution in the microchanne...

Experimental investigation of CO2condensation process using cryogen

Carbon dioxide ( CO 2 ) is one of the dominant gas molecules that causes greenhouse effect, i.e. global warming. Numerous studies have been carried out to regulate the emission of CO 2 to reduce greenhouse gas. The liquid CO 2 is a convenient form of transportation compared to high-pressurized gaseous CO 2 . Therefore, the direct liquefaction mechanism of CO 2 at low temperature draws technical attention recently. In particular, cold thermal energy of Liquefied Natural Gas (LNG) could be a candidate to condense gaseous CO 2 , especially in the LNG powered ship. In this paper, the detailed direct condensation process of CO 2 using LN 2 with intermittent solidification is investigated. Pressurized CO 2 at 600 kPa is directly liquefied in a vessel by liquid nitrogen which is supplied into the coiled tube heat exchanger inside the CO 2 vessel. The heat exchanger temperature is controlled from 130 K to 205 K to regulate the solidification and sublimation of CO 2 by duty control with cryogenic solenoid valve. The characteristics of CO 2 condensation process with cryogen are analyzed from the measurement results. The results show that the solidification causes the significant degradation of CO 2 condensation heat transfer. Finally, the condensation rate with and without solidification is compared.

Experimental investigation of CO2 condensation process using cryogen

Carbon dioxide ( CO 2 ) is one of the dominant gas molecules that causes greenhouse effect, i.e. global warming. Numerous studies have been carried out to regulate the emission of CO 2 to reduce greenhouse gas. The liquid CO 2 is a convenient form of transportation compared to high-pressurized gaseous CO 2 . Therefore, the direct liquefaction mechanism of CO 2 at low temperature draws technical attention recently. In particular, cold thermal energy of Liquefied Natural Gas (LNG) could be a candidate to condense gaseous CO 2 , especially in the LNG powered ship. In this paper, the detailed direct condensation process of CO 2 using LN 2 with intermittent solidification is investigated. Pressurized CO 2 at 600 kPa is directly liquefied in a vessel by liquid nitrogen which is supplied into the coiled tube heat exchanger inside the CO 2 vessel. The heat exchanger temperature is controlled from 130 K to 205 K to regulate the solidification and sublimation of CO 2 by duty control with cryogenic solenoid valve. The characteristics of CO 2 condensation process with cryogen are analyzed from the measurement results. The results show that the solidification causes the significant degradation of CO 2 condensation heat transfer. Finally, the condensation rate with and without solidification is compared.