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Efficient and Lightweight Cryogenic Gas Heat Exchanger


OBJECTIVE: Develop a compact, highly efficient, and light-weight cryogenic gas heat-exchanger to maximize heat transfer while maintaining a low pressure drop for use in naval superconducting system applications. DESCRIPTION: The Navy is developing several superconducting systems (such as degaussing, propulsion motors, electrical generators and power distribution systems) for use onboard future ships and submarines to reduce system weight, energy usage and installed volume. These systems rely on the use of cryogenic helium gas for operation. Helium has a low heat capacity at the operational temperatures of 10-150K and significant amounts of heat from 100-4000W need to be removed from these systems during operation. Current commercially available cryogenic heat exchangers utilize a combination of stainless steel and copper helix coils wrapped around a mass of metal (Ref 1). Gaseous helium is then pumped through the coils in order to convectively and conductively transfer cooling power from the cryocooler to the superconducting system. Current heat exchanger designs have a heat exchanger effectiveness of about 70%, weigh approximately 50lbs, and maintain a pressure drop of less than 1 psi. The current equipment package required to transfer the heat (cold box containing the heat exchanger plus a cryocooler) weighs approximately 350 lbs and costs approximately $75K (Ref 2). Given the amount of potential heat to be removed, a 20% increase in effectiveness will provide a significant reduction in the overall weight and cost of the system. Novel materials such as metal foams and matrix materials have been investigated for cryogenic heat exchangers but have not been implemented because of their high cost or limited availability (Ref 3). Recent improvements in material processes and additional applications for metal foams in room temperature heat exchangers have been documented but not at cryogenic temperatures (Ref 4). The Navy seeks to develop a highly effective (>90%), low weight (<50 lbs), low acquisition cost (<$10K), low pressure drop (<2 PSI) heat exchanger for operation with a gaseous helium pressure (up to 20 bar), with temperature ranges from (10 - 150K) for flows from 1 to 20 g/s. It is anticipated that accomplishing these goals will require innovative approaches beyond the current state of the art with the potential application of new materials, methods and/or manufacturing processes in order to develop potentially viable concepts. Proposed concepts should be of sufficient ruggedness to survive a naval, shipboard environment. Aspects such as smaller physical size and lower weight are of particular interest. PHASE I: Demonstrate the feasibility of a novel compact heat exchanger design able to operate with Navy cryogenic systems as defined above. Perform bench top experimentation, where applicable, as a means of demonstrating the identified concepts. Establish validation goals and metrics to analyze the feasibility of the proposed solution. Provide a Phase II development approach and schedule that contains discrete milestones and provides risk reduction for product development. PHASE II: Develop, demonstrate and fabricate a prototype as identified in Phase I. In a laboratory environment, demonstrate that the prototype meets the performance goals established in Phase I. Verify final prototype operation in a representative laboratory environment and provide results. Develop a cost benefit analysis and a Phase III development, installation, testing, and validation plan for the transition of the technology to Navy use. PHASE III: Upon successful Phase II completion, the company will support the Navy in transitioning the technology to military and commercial cryogenic or superconducting applications. Working with government and industry partners, as applicable, the company will install the cryogenic gas heat exchanger onboard a selected Navy ship and conduct extended shipboard testing. The company will support the Navy for test and validation to certify and qualify the system for Navy use. PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: A more compact heat exchanger may be of use in land based High Temperature Superconducting (HTS) power cables and power delivery applications. As land based HTS power cables transition from R&D projects to commercial installations, these heat exchangers will save on weight and promote higher cooling capability, which would promote overall higher efficiencies in the power system itself.
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