Cryogenic Heat Pipe Research Articles

Development of a Flat-plate Cryogenic Oscillating Heat Pipe for Improving HTS Magnet Cooling

Abstract A new method of including cryogenic oscillating heat pipes (OHPs) in the HTS coil windings as a thermal transport device has been studied. In this work, two type of OHPs are tested in low temperature. Employed working fluids are H2, Ne, N2. We have attained high performance thermal property using a bent-pipe cryogenic OHP as a prototype. Obtained effective conductivities have reached to 46000 W/m K. Then a flat-plate cryogenic OHP has been developed, that is suitable for imbedding in magnet windings. Preliminary experiments have been conducted and the result has been promising.

Development of Cryogenic Oscillating Heat Pipe as a New Device for Indirect/Conduction Cooled Superconducting Magnets

Cryogenic oscillating heat pipes (OHPs) have been proposed as a new heat transfer device for conduction/indirect cooling of high-temperature superconducting (HTS) magnets. OHP is a highly effective two-phase heat transfer device which can transport several orders of magnitude greater heat flux than the heat conduction of solids. The performance of cryogenic OHPs has been intensively examined and the results indicate the ability of dramatically improving the performance of HTS magnets. Semi-empirical correlations stating thermo-physical properties of cryogenic OHPs are introduced based on those of room temperature OHPs. The modeling with non-dimensional quantities is useful for the design of cryogenic OHPs.

Demonstration of liquid nitrogen wicking using a multi-layer metallic wire cloth laminate

Cryogenic heat transport devices are the most basic and critical component for the thermal integration between the cryogenic component and its cooling source. In space environments, containment of heat transfer fluid inside a capillary structure is critical due to the absence of gravity. Cryogenic heat pipes using the capillary force for circulation may provide a solution for heat transfer in space applications due to its independence of gravity and transport distance. To achieve a high effective capillary performance, several options of wicking structures have been investigated. An efficient wicking flow of liquid nitrogen is demonstrated with a sintered, multi-layer, porous lamination of metal wire (pore size as low as 5μm) in an open cryogenic chamber. The test data are presented in this paper. This technology has potential for use in development of improved cryogenic heat transfer devices and containment of cryogenic propellants under micro-gravity environment.

激光二极管泵浦的重复频率大能量低温Yb:YAG激光器设计

At cryogenic temperature, Yb:YAG medium has both good thermal property and high laser performance. Considering that, a 12 kW laser dioder pumped V-shaped cryogenic Yb:YAG laser design has been demonstrated in order to get rep-rated high energy output. Based on the ray tracing method and finite element analysis, the coupling system and cooling scheme were investigated, respectively. In addition, wedge-shaped vacuum window and cryogenic heat pipe schemes have been proposed. The simulation results show that the thermal effect of laser medium is much lower compared with room temperature operated laser, and the design can realize rep-rated high energy output.

Cryogenic Heat Pipe for Cooling High-Temperature Superconducting Coils

An emerging method of propellantless formation flight is the use of electromagnets coupled with reaction wheels called electromagnetic formation flight. To create a large magnetic field necessary for actuating formation-flying spacecraft, electromagnetic formation flight uses high-temperature superconducting wire. To achieve superconductivity, the high-temperature superconducting wire requires a consumable-free cryogenic thermal control system to maintain the wire temperature below the critical temperature throughout the entire electromagnetic formation-flight coil, which could be as large as 2 m in diameter. The research in this paper investigates a consumable-free method of maintaining isothermalization for a large-scale high-temperature superconducting coil. The high-temperature superconducting coil resides inside a thermally conductive jacket that is used for isothermalization. Both a solid conductor and a heat pipe were investigated for use as the thermally conductive jacket. In this paper, a proof-of-concept circular cryogenic heat pipe was tested in a 2-m-diam toroidal vacuum chamber. This system showed the potential for high-temperature superconducting cooling. The experiments in this paper demonstrate the feasibility of operating large high-temperature superconducting coils for future formation-flying missions.

Cryogenic heat pipe for cooling high temperature superconductors

The research in this paper investigates a consumable-free method of operating a high temperature superconducting (HTS) coil in space. The HTS wire resides inside a cryogenic heat pipe which is used for isothermalization. This paper presents the design, implementation, and testing of a cryogenic heat pipe for cooling high temperature superconductors. As a proof-of-concept, an 86 cm long straight heat pipe was constructed and enclosed two straight lengths of HTS wire. The working fluid, at saturation condition, maintains a constant temperature below the HTS wire critical temperature. Testing of the heat pipe in a vacuum chamber was conducted to verify the drop in HTS resistance correlating to the wire operating in a superconducting state.

Experimental investigation of cryogenic oscillating heat pipes

A novel cryogenic heat pipe, oscillating heat pipe (OHP), which consists of an 4 × 18.5 cm evaporator, a 6 × 18.5 cm condenser, and 10 cm length of adiabatic section, has been developed and experimental characterization conducted. Experimental results show that the maximum heat transport capability of the OHP reached 380 W with average temperature difference of 49 °C between the evaporator and condenser when the cryogenic OHP was charged with liquid nitrogen at 48% (v/v) and operated in a horizontal direction. The thermal resistance decreased from 0.256 to 0.112 while the heat load increased from 22.5 to 321.8 W. When the OHP was operated at a steady state and an incremental heat load was added to it, the OHP operation changed from a steady state to an unsteady state until a new steady state was reached. This process can be divided into three regions: (I) unsteady state; (II) transient state; and (III) new steady state. In the steady state, the amplitude of temperature change in the evaporator is smaller than that of the condenser while the temperature response keeps the same frequency both in the evaporator and the condenser. The experimental results also showed that the amplitude of temperature difference between the evaporator and the condenser decreased when the heat load increased.

Experimental Analysis of Supercritical Startup of Nitrogen/Stainless Steel Cryogenic Heat Pipe

An experimental investigation of the supercritical startup of a nitrogen/stainless steel cryogenic heat pipe is presented. A detailed description of the experimental setup used for this investigation is presented, and several data sets for the transient axial temperature distribution of the heat pipe are shown. A transient, one-dimensional model developed for microgravity environment available in the literature is used to obtain the internal pressure and working fluid axial distribution. The results showed that cryogenic heat pipes are very sensitive to parasitic heat loads (e.g., heat convection), even in rarefied atmospheres, and the parasitic heat loads can significantly change the operational temperature of the cryogenic heat pipe. The effects of parasitic heat loads must be accurately considered during the design stages. Also, the fluid charge plays an important role in the determination of the initial thermodynamic state of the cryogenic heat pipe. An excess of fluid charge may prevent a successful startup due to an increased vapor pressure, whereas a deficiency may prevent the startup due to lack of working fluid to sufficiently prime the heat pipe.

Analysis of Supercritical Startup of Cryogenic Heat Pipes With Parasitic Heat Loads

A mathematical model to predict the transient temperature profile of a cryogenic heat pipe during startup is presented. The improved model accounts for a known time-variable temperature boundary condition at the condenser region, while the boundary condition in the remaining length of the heat pipe is a radiative parasitic heat flux. The vapor pressure is modeled to determine the mass distribution of the saturated liquid inside the heat pipe. An axially grooved aluminum/oxygen cryogenic heat pipe is considered. Theoretical results for the axial temperature profile of the heat pipe for the startup period are compared to experimental μ-g flight data to validate the new model. Following the validation, the effects of some operational parameters over the axial temperature profile for the startup period are investigated to determine under what conditions the cryogenic heat pipe will start properly.

Optimal cooling of HPGe spectrometers for space-born experiments

We present current results on the theoretical and experimental studies of optimal cryogenic cooling of gamma-ray spectrometers based on high-purity germanium (HPGe) detectors. We show that the technology of cryogenic heat pipe diodes (HPDs) usually allows one to meet cooling requirements with minimal weight, power consumption and cost. Results of computer modeling and laboratory tests of HPDs, Stirling cooler and complete cooling solutions are presented.

High temperature superconducting current lead test facility with heat pipe intercepts

A high temperature superconducting (HTS) current lead test facility using heat pipe thermal intercepts is under development at the Superconductivity Technology Center at Los Alamos National Laboratory. The facility can be configured for tests at currents up to 1000 A. Mechanical cryocoolers provide refrigeration to the leads. Electrical isolation is maintained by intercepting thermal energy from the leads through cryogenic heat pipes. HTS lead warm end temperature is variable from 65 K to over 90 K by controlling heat pipe evaporator temperature. Cold end temperature is variable up to 30 K. Performance predictions in terms of heat pipe evaporator temperature as a function of lead current are presented for the initial facility configuration, which supports testing up to 200 A. Measurements are to include temperature and voltage gradient in the conventional and HTS lead sections, temperature distribution and heat transfer rate in the heat pipes, as well as optimum and off-optimum performance of the conventional lead sections.

Analysis of Supercritical Startup Behavior for Cryogenic Heat Pipes

A theoretical analysis was conducted to describe the startup process from the supercritical state for axially grooved cryogenic heat pipes. Using an approximation method, a heat-balance integral solution was developed to predict the rewetting velocity, liquid front position, and transient axial temperature distributions for axially grooved cryogenic heat pipes. The developed model assumes an initially uniform axial temperature distribution and divides the startup process into two characteristic regions, based on whether a liquid column is established in the condenser region. The predicted transient temperature profiles of two cryogenic oxygen heat pipes were in good agreement with previous experimental microgravity flight data. Nomenclature A = coefficient defined in Eq. (12) Af = cross-sectional area of the working fluid AI = cross-sectional area of the liquid channel As = cross-sectional area of the heat-pipe wall B = coefficient defined in Eq. (12) Ce = effective heat capacity c - specific heat D = coefficient defined in Eq. (12) Dh = hydraulic diameter E = thermal energy F = force h = groove thickness hfg = latent heat of liquid-vapor phase change k = thermal conductivity La = length of adiabatic section Lc = length of condenser Le = length of evaporator P = internal pressure Pc = critical pressure Pr = reduced pressure R = gas constant Re = Reynolds number r = capillary radius T = temperature Tc = critical temperature Tcond = condenser temperature Tr = reduced temperature 7*0 = initial temperature t - time U = liquid mean velocity Ur = liquid rewetting velocity v = specific volume of vapor w = groove width z = compressibility factor ae = effective heat diffusivity j8 = coefficient defined in Eq. (3) 8 = penetration depth e = liquid layer length

A high capacity re-entrant groove heat pipe for cryogenic and room temperature space applications

A high capacity heat pipe has been developed for use in both the cryogenic and room temperature range. The configuration consists of 24 re-entrant axial grooves extruded in a 1-in. (25.4 mm) diameter 6063-T6 aluminium pipe. Using methane, the pipe demonstrated transport capacities as high as 6500 W in. (165 W m) in a level orientation at 115 K. This is an order of magnitude higher than state-of-the-art cryogenic heat pipe technology. Being a derivative of conventional rectangular axial groove heat pipes that have had extensive flight experience, the re-entrant design offers the same high reliability and ease of fabrication. Other benefits include: low fluid charge resulting in reduced internal pressure at ambient temperature, tolerance to the presence of non-condensible gas, and the capability to be bent to fit within tight spacecraft envelopes. The extrusion can also be used at other temperatures with appropriate working fluids, having been tested with ammonia to yield a transport capacity of 29 000 W in. at 283 K. The design lends itself to optimization for specific loads and temperatures, within the constraints of the extrusion process.

Review of cryogenic heat pipes in spacecraft applications

Covers advancements in spacecraft and tactical and strategic missile systems, including subsystem design and application, mission design and analysis, materials and structures, developments in space sciences, space processing and manufacturing, space operations, and applications of space technologies to other fields.

A cryogenic heat pipe coupled between infrared detector and cooler

This paper describes a dummy test of a cryogenic heat pipe coupled between the infrared detector and cooler. The cryogenic heat pipe provides efficient thermal conduction for 2 W power over a 87.5 cm length with a maximum temperature difference of 0.91 K at 82 K operating temperature. The test results have useful applications.

Investigation of the thermophysical characteristics of cryogenic heat pipes with a metal-fiber wick

Results are presented of an experimental investigation of the maximum heat-transmission capability and the heat-transfer intensity characteristics in the heat input and heat output of cyrogenic heat pipes.

Thermal resistance of cryogenic heat pipes

Thermal resistance of cryogenic heat pipes

A cryogenic heat pipe with a reservoir in the transport zone

A cryogenic heat pipe with a reservoir in the transport zone

Experimental study of heat and mass transfer in a cryogenic heat pipe

The operational features of a cryogenic heat pipe are discussed. A description of the experimental device is given, and the experimental results are presented and discussed.

Development of Cryogenic Heat Pipes

The operation of a LN2 cryogenic heat pipe has been demonstrated experimentally in the range 78 K to 90 K. This heat pipe involves a totally new wick concept, viz., the “parallel capillary channel” wick, which affords a heat flux capability an order of magnitude higher than possible with the more conventional heat pipe wick structures. The experimental measurements were performed utilizing specially designed cryogenic heat pipe evaluation equipment which permitted heat flux measurements accurate to within 8 percent. The design and optimization of the cryogenic heat pipe is discussed including a description of the BCL generalized heat pipe computer program. A comparison of experimental data with analytical predictions is also provided.