John G. Brisson

Design of an Integrated Loop Heat Pipe Air-Cooled Heat Exchanger for High Performance Electronics

The continually increasing heat generation rates in high performance electronics, radar systems and data centers require development of efficient heat exchangers that can transfer large heat loads. In this paper, we present the design of a new high-performance heat exchanger capable of transferring 1000 W while consuming less than 33 W of input electrical power and having an overall thermal resistance of 0.05 K/W. The low thermal resistance is achieved by using a loop heat pipe with a single evaporator and multiple condenser plates that constitute the array of fins. Impellers between the fins are driven by a custom permanent magnet synchronous motor in a compact volume of 0.1 × 0.1 × 0.1 m to maximize the heat transfer area and reduce the required airflow rate and electrical power. The design of the heat exchanger is developed using analytical and numerical methods to determine the important parameters of each component. The results form the basis for the fabrication and experimental characterization that is currently under development.

The thermal conductivity of Kapton HN between 0.5 and 5 K

Abstract The thermal conductivity of Kapton HN is measured for temperatures between 0.5 and 5 K. The temperature rise across two different Kapton–Stycast 1266 stacks is measured for a known heat transfer rate. These two measurements, combined with the geometry of the stacks, are then used to infer the bulk thermal conductivity of the Kapton. The measured conductivity was found to fit to a power law of the form k =4.638×10 −5 T 0.5678 W/cm K, where T is in Kelvins.

Design, construction, and performance of plastic heat exchangers for sub-Kelvin use

Abstract The ultimate temperature and cooling power of both the superfluid Stirling refrigerator (SSR) and the 3 He– 4 He dilution refrigerator depend largely on the efficiency of their counterflow heat exchangers. This efficiency is limited mainly by the Kapitza boundary resistance at low temperatures. The usual method of overcoming this problem has been to increase the surface area of the heat exchangers. A different approach is to make the heat exchangers out of materials that have low Kapitza boundary resistance such as plastics. This article describes the design, construction, and performance of plastic heat exchangers that have been successfully used in our SSRs. Specifically, the paper includes a detailed description of our heat exchangers, step-by-step instructions on the construction of a plastic heat exchanger, and simple calculations of the performance of the heat exchanger under typical SSR operating conditions.

A simple method for the analysis of sub-Kelvin refrigerators that use a dilute superfluid 3He–4He mixture as a working fluid

Abstract The recent development of new types of sub-Kelvin refrigerators that use dilute superfluid 3 He– 4 He mixtures has made it apparent that a simple method of cycle analysis is needed. General control volume forms of the first and second laws of thermodynamics appropriate to this working fluid are presented. Simple analytic constitutive relations for the internal energy, entropy, enthalpy, osmotic enthalpy and 4 He chemical potential are presented. Several examples are worked out using these relations.

Development of a low-dissipation valve for use in a cold-cycle dilution refrigerator

A low-dissipation valve for use at helium temperatures, which uses a polished stainless steel valve head and a PCTFE seat for the sealing surfaces, has been developed and tested. The leak rate with a closing force of 10 kgf and a differential pressure of 8000 Pa across the valve was experimentally determined to be approximately 0.2 μmol/s of gaseous helium at 4.2 K. Estimates of dissipation obtained using finite element analysis and experimental results from bellows tests suggest that this valve has energy dissipation on the order of 2 μJ per cycle. The valve is found to be suitable as a compressor valve for a previously proposed cold-cycle dilution refrigerator (CCDR) as well as other refrigeration cycles that require low temperature valves.

Design and analysis of high-performance air-cooled heat exchanger with an integrated capillary-pumped loop heat pipe

We report the design and analysis of a high-power air-cooled heat exchanger capable of dissipating over 1000 W with 33 W of input electrical power and an overall thermal resistance of less than 0.05 K/W. The novelty of the design combines the blower and heat sink into an integrated compact unit (4″ × 4″ × 4″) to maximize the heat transfer area and reduce the required airflow rates and power. The device consists of multiple impeller blades interdigitated with parallel-plate condensers of a capillary-pumped loop heat pipe. The impellers are supported on a common shaft and powered with a low-profile permanent magnet synchronous motor, while a single flat-plate evaporator is connected to the heat load.

DC Superconducting Cable Using

Tsinghua University, University of Cambridge, and MIT are collaborating to design, construct, and test an MgB2 dc cable for microgrid applications. Two-stage current leads with nitrogen vapor cooled copper and gaseous helium cooled hightemperature superconductor will be used. The two-stage cryostat will be cooled using a single helium fan with a recuperator. The helium gas used to cool the MgB2 to 20-25 K will be cooled with a two-stage GM cryocooler. The cryogenic stability of the cable will be presented. Designs of cryostats are being investigated. Semi-rigid cryostats, with low heat leak, are being designed and will be tested as part of this program. The system will operate up to 1 kV and 1 kA, limited by the present power equipment. However, the MgB2 conductor is being designed for 5 kA, and may be tested at low voltage with upgraded current leads. A 30-m cable will be tested using facilities at Tsinghua University in Beijing.

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Future spacecraft cooling and sensing systems will require advanced multi‐stage cryocoolers capable of providing continuous cooling at multiple temperature levels ranging from 10 K to 95 K. Stirling and pulse‐tube cryocoolers have achieved compactness and reliability by adopting mechanically simple cold head configurations at the expense of thermodynamic efficiency. Large‐scale terrestrial cryogenic refrigerators achieve much higher efficiencies by employing complex designs, but their high efficiency is not retained at the small scale required for spacecraft cryogenic cooling. AMTI, in collaboration with MIT, is developing a multi‐stage 10 K cryocooler that applies modern microelectronic sophistication to achieve high efficiency in a reliable, compact design. The cryocooler is based upon a novel modification of the Collins cycle, a cycle commonly used in many high‐efficiency terrestrial cryogenic machines. Innovations of the design include floating piston expanders and electro‐magnetic smart valves, which...

Wires

The feasibility of a compact, reliable, low-cost, and efficient cryocooler capable of delivering 2W of cooling at 10 K using less than 1 kW of input power has been demonstrated analytically. The technical approach is to apply a high-efficiency thermodynamic cycle to a compact and reliable small-scale system by implementing a modern microprocessor into a mechanically innovative machine. The innovations of the design include “floating” piston expanders and electromagnetic “smart” valves, which eliminate the need for mechanical linkages and reduce the input power, size, and weight of the cryocooler in an affordable modular design. It is predicted that a three-stage cryocooler operating with 15-bar helium could produce 2 W of cooling at 10 K while requiring less than 1 kW of compressor power. A laboratory prototype is currently being designed and built for development testing in the Summer and Fall of 2002.

Floating Piston Expander Development for a Small‐Scale Collins Type 10 K Cryocooler for Space Applications

The Muon-to-Electron Conversion Experiment (MECO) seeks to detect muon to electron conversion, providing evidence that the conservation of muon and electron type lepton number can be violated. Observation of this violation would suggest physics beyond the Standard Model. The experiment is to be installed at Brookhaven National Laboratory (BNL). A high energy proton beam produces pions upon hitting a heavy target inside the 1.5 m diameter by 5 m long Production Solenoid (PS). A fraction of the muons from pion decay are captured in the 0.5 m diameter bore by the 13 m long, S-shaped Transport Solenoid (TS), which contains collimators, providing sign and momentum selection. The muons are stopped in a target inside a 1.9 m bore by 10 m long Detector Solenoid (DS) that houses detectors to measure the energy of the conversion electrons. Magnetic field is controlled to 5 T /spl plusmn/5% at the high-field end of the PS and to 1 T /spl plusmn/0.2% in the detector region of the DS. The conceptual design for the magnets is summarized, including conductor, coil, structure and cryogenic design.