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Improved Capacity, High Efficiency Cryogenic Cooling System

Description:

TECHNOLOGY AREA(S): Ground Sea 

OBJECTIVE: Develop innovative cryogenic cooling equipment for high temperature superconducting systems with novel enhancements that increase cryocooler capacity, effective system cooling capacity, and system efficiency while minimizing system cost. 

DESCRIPTION: The Navy is interested in High Temperature Superconducting (HTS) cable technology for High Temperature Superconducting Degaussing (HTS DG) and future shipboard high temperature superconducting power cable applications. These applications require affordable and robust cryogenic cooling solutions that meet the unique requirements for surface ship applications. Navy objectives to reduce manning and maintenance costs demand cryogenic cooling solutions that have minimal maintenance requirements over a 30- or 40-year ship service life. Additionally, overall system level affordability is a key requirement for implementation of superconducting system that leads to objectives of low acquisition costs, higher system level efficiencies, and reduced requirements for ship electrical power and chilled water. For Navy HTS cable applications, gaseous helium is cooled by a cryocooler and cryogenic heat exchanger and circulated using a helium circulation fan through a superconducting cable which consists of HTS conductor housed in a flexible cryostat. These cables can range from 10m-300m with operational temperature requirements of 30 K-70 K at pressures of 10-20 bar. The temperature of the cryogen increases in the flow direction due to heat leakage in the order of 1-3 watts per meter which can be minimized by increasing mass flow rate. However, simply increasing mass flow rate tends to reduce the effectiveness of the cryogenic heat exchanger. Additionally, higher volumetric flow rates lead to higher friction flow losses that contribute additional heat load to the cryogenic system. Improvements in overall cryo-cooling effectiveness can be realized through heat exchanger improvements that couple the cryogen flow to the cryocooler in a novel way. Likewise, novel approaches to cryogen circulation can minimize cryogen heat load associated with higher-pressure drops. Increased effective cryogenic cooling capacity will enable multiple HTS cables to be cooled by a single cooling unit with sufficient thermal budget. Improving capacity of the cryocooler so that multiple loops can be cooled from a single cryogenic system will reduce the number of required cryocoolers in procurement. The Navy desires to eliminate the dependence on chilled water and use salt water cooling with water inlet temperatures in the range of 4ºC to 50ºC, thereby reducing the demand on the chiller system by freeing up 25-40 refrigeration tons of cooling plant margin. Complete cryocooler and circulation system cost target of $200/watt cooling at 50 K or cryocooler only costs target of $100/watt cooling at 50 K with integrated system weight target of 1.5 watts/kg cooling at 50 K. State-of-the-art cryocoolers of the appropriate size scale have Carnot efficiencies of 13-25% of Carnot at 77 K and require maintenance every 6,000 to 10,000 hours. Innovations are needed to efficiently increase the effective cryogenic cooling capacity available for shipboard application and reduce or eliminate routine maintenance. Increasing the Carnot efficiency of the cryocooler reduces the electrical burden of the HTS degaussing system. The Navy is expecting to improve efficiency to greater than 30% of Carnot at 50 K with a heat lift greater than 300 watts. Integrated cryocooler heat exchanger solutions are desired that will yield heat exchanger effectiveness greater than 98% at flow rates of 10 grams/sec with a cryogenic heat lift that exceeds 600 Watts at 50 K measured at the cold finger. The HTS degaussing system is predicted to reduce the acquisition cost of a traditional LPD-17 class system degaussing system by nearly $10m per ship. All solutions must consider the objective of low-maintenance requirements and induce no acoustic emission penalty while achieving a 30-year effective service life. System should be designed to pass shipboard qualification testing including shock (MIL-S-901D) and vibration (MIL-STD-167-1A). 

PHASE I: Develop a design concept for an improved capacity and high-efficiency cryogenic cooling system meeting the requirements identified in the description while considering the cryogenic and vacuum compatibility of selected materials and safety aspects in handling the intended working pressure of the cryogen. Demonstrate technical feasibility through modeling, analysis, and bench-top experimentation. The Phase I Option, if awarded, will include the initial design specifications and capabilities description to build a prototype solution in Phase II. Develop a Phase II plan. 

PHASE II: Develop, fabricate, and deliver a prototype system based on the Phase I work and Phase II Statement of Work (SOW) for demonstration and characterization of key parameters and objectives. Deliver the Phase II prototype to the Navy for further performance testing. Based on lessons learned in Phase II through the prototype demonstration, construct a complete advanced prototype to include updated drawings that will pass Navy qualification testing. 

PHASE III: Support the Navy in transitioning the technology for Navy use, including initial production level manufacturing capabilities and providing a fully qualified cryocooler system. If successful, the cryocooler system will transition to the LX(R) Amphibious Ship Program. The company shall develop manufacturing plans to facilitate transition to the Navy. All superconducting cable systems require cryogenic cooling. The cryogenic system being developed under this topic will be appropriately sized for many applications requiring cryogenic cooling for the Navy and the commercial world. In addition to HTS cables, military and commercial motors and generators are also applications that will benefit from a high-efficiency, low-cost, cryogenic system. 

REFERENCES: 

1: Kephart J., Fitzpatrick B., Ferrara P., Pyryt M., Pienkos J., and Golda E.M. "High Temperature Superconducting Degaussing From Feasibility Study to Fleet Adoption." IEEE Transactions on Applied Superconductivity, Vol. 21, Issue 3, pg 2229-2232, June 2011. http://ieeexplore.ieee.org/document/5672800

2:  H. Rodrigo, F. Salmhofer, D.S. Kwag, S. Pamidi, L. Graber, D.G. Crook, S.L. Ranner, S.J. Dale, and D. Knoll. "Electrical and thermal characterization of a novel high pressure gas cooled DC power cable." Cryogenics 52 (2012) 310. http://www.sciencedirect.com/science/article/pii/S0011227512000501

3:  Chul Han Kim, Jin-Geun Kim, and Sastry V. Pamidi. "Cryogenic Thermal Studies on Cryocooler-Based Helium Circulation System for Gas Cooled Superconducting Power Devices." Cryocoolers 18, International Cryocooler Conference, Inc., Boulder, CO, 2014. http://cryocooler.org/proceedings/paper-flies/C18papers/067.pdf

KEYWORDS: Cryocoolers; Superconducting Degaussing Cables; Superconducting Power Cables; High Temperature Superconductor; Helium Circulation Fan; Cryogenic Heat Exchanger 

CONTACT(S): 

Jacob Kephart 

(215) 897-8474 

jacob.kephart@navy.mil 

Avi Friedman 

(215) 897-2150 

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