N25A-T028 TITLE: Rapid Cryogenic Cooling of Superconducting Systems

OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Advanced Materials;Directed Energy (DE);Renewable Energy Generation and Storage

OBJECTIVE: Develop a novel process, technique, or material for rapidly cooling a large thermal mass or distributed thermal load from room temperatures down to cryogenic temperatures to enable operation of a superconducting system within roughly 24 hours as compared to several days.

DESCRIPTION: High-temperature superconducting (HTS) magnet systems are being developed by the Navy for the minesweeping mission. These large-diameter magnets (on the order of 2 m) utilize standard heat exchanger technology with circulating cryogenic helium to distribute cooling throughout the magnet and may take several days to achieve operational temperatures. The Navy is also pursuing HTS degaussing systems which have a more distributed load and use circulating cryogenic helium in a cryostat. It is desired to reduce the time to cool down the system to operational temperatures so that the Navy’s mission can be completed with reduced operational timelines. Future potential applications of HTS technologies include motors, generators, cables, etc., and the issue of cool down can be an important consideration in the viability of these concepts.

Heat pipes, often used for cooling electronics, utilize the phase change of a working fluid to dramatically boost the heat transfer across the length of the pipe. Unfortunately, this working fluid must be "tuned" to a particular temperature range as once the fluid freezes, the heat exchange benefit is lost. For cryogenic temperatures, Nitrogen has been explored; however, this limits the cold side temperature to 63 K. Many HTS Systems utilize colder temperatures to increase the ampacity of the wire or compensate for lost ampacity due to magnetic interaction with the material. In these situations, 55 K or below is a relatively common target temperature.

This STTR topic seeks to develop a cryogenic cooling method, and/or heat exchanger technology, capable of dramatically reducing the cooling time to improve operational readiness of Naval HTS systems. The proposed solution should be applicable to rapidly cool down a superconducting magnet that has a large thermal mass on the order of 2,000 lbs from room temperature to around 40-50 K by either direct conduction, or convection with a heat exchanger and circulating helium cryogenic gas. Additionally, there will be further consideration given to proposed solutions that can provide rapid cooling to a more distributed heat load as in a long length cryostat on the order of 600 ft containing HTS wires (HTS cable) with helium gas flowing within the cryostat at roughly 10-15 g/s.

The desire is to apply the rapid cooling method to either application to reduce the temperature from 300 K to below 50 K in as short of a time as possible. Ideally the time to cool will be within a 24 hr period. During this time, it is expected that there will be power available. The use of alternate cryogens such as liquid nitrogen may be considered but it should be noted that liquid nitrogen alone will not achieve the desired temperatures below 50 K. The use of toxic or flammable cryogens or cryogenic materials will most likely not be considered due to safety issues with using or handling these materials. Finally, the proposed solution should also include any auxiliary hardware that would be necessary such as helium circulators, heat exchangers, and cryorefrigerators.

PHASE I: Define and develop concepts for rapid cryogenic cooling. Determine the technical feasibility of the concepts meeting the desired performance specifications. Perform an analysis via modeling, experimentation, etc. Identify characteristics of the technology and nominal performance. Upon identification of a feasible solution, perform a cost estimate, for both prototype development and full-scale production. The Phase I Option, if exercised, includes a detailed design and specifications to build a prototype during a Phase II effort.

PHASE II: Develop, demonstrate, and validate a functional prototype of a rapid cryogenic cooling method and/or heat exchanger with characterization of key performance metrics at the proposer’s facility or other suitable test center identified by the awardee. Establish cool down curves for various cryogenic temperature gradients with a representative thermal mass. Deliver the Phase II prototype to the Navy for further testing, or integration into a larger system.

PHASE III DUAL USE APPLICATIONS: Integrate the Phase II developed cryogenic cooling method and/or heat exchanger into a military or commercial superconducting system to achieve lower operational employment timelines and demonstrate ability to transition the technology. If successful demonstration of the technology is achieved, the transition of the development will lead to lower operational employment timelines for superconducting systems. This will enhance Fleet readiness when deploying superconducting systems in the field. There are several superconducting systems that are currently being transitioned to the Fleet and this technology may be implemented in future upgrades.

Applications in the commercial sector may include superconducting systems being developed for the wind power generation market, resilient power grid, superconducting propulsions for aviation, or existing medical devices such as MRIs.

REFERENCES:

1. Green, Michael. "Methods of speeding up the cool-down of superconducting magnets that are cooled using Small coolers at temperatures below 30 K." OP Conference Series: Materials Science and Engineering, Volume 1240, Advances in Cryogenic Engineering: Proceedings of the Cryogenic Engineering Conference (CEC) 2021, 19-23 July 2021, Virtual Conference, USA.

10.1088/1757-899X/1240/1/012139

2. Kwon, Daniel and Sedwick, Raymond. "Cryogenic Heat Pipe for Cooling High-Temperature Superconducting Coils." Cryogenics, 23, 2009, pp. 514-523. 10.1016/j.cryogenics.2009.07.005

3. Bai, Lizhan; Zhang, Lianpei; Lin, Guiping; He, Jiang and Wen, Dong-sheng. "Development of cryogenic loop heat pipes: A review and comparative analysis." Applied Thermal Engineering, 89, 2015, pp.180-191. 10.1016/j.applthermaleng.2015.06.010

4."Magnetic and Acoustic Generation Next Unmanned Superconducting Sweep (MAGNUSS)." ONR Special Notice N00014-21-S-SN12, 2021. https://sam.gov/opp/ddd803b6d03e42e9b6dbcde611800317/view

5. "High Temperature Superconducting Degaussing System." US Patent Number US 7,451,719 B1, November 2008.

KEYWORDS: Cryogenic Temperature; Heat Exchanger; Rapid Cool Down; Cryogenic Cooling; Superconducting Systems; Cryogenic Thermal Mass; Heat Removal

TPOC 1: Harold Coombe
Email: [email protected]

TPOC 2: Peter Ferrara
Email: [email protected]

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