Experimental investigation on the performance of a neon cryogenic oscillating heat pipe

An experimental investigation is conducted to study the performance of a cryogenic oscillating heat pipe (OHP) using neon as the working fluid. The stainless steel OHP with an inner diameter of 0.9 mm has 4 turns, and the lengths of the evaporator, condenser section and adiabatic section are 35 mm, 35 mm and 95 mm, respectively. The temperature of the evaporator and condenser and the pressure of the OHP are measured. The results show that the cooling down process of the OHP from room temperature to the working temperature can be significantly accelerated by charging with neon. During the pseudo steady-state operation process, the temperature of evaporator and the pressure of the OHP increase with increasing heat input. When the dry out appears, the temperature of evaporator rises quickly, and the pressure of the OHP drops sharply. In addition, the effective thermal conductivity of the OHP at the different heat inputs and the different filling ratios is calculated. It increases with increasing heat input, and there exists an optimum filling ratio which makes the maximum effective thermal conductivity. For this OHP, the optimum filling ratio is 24.5%, at which the effective thermal conductivity is 6100–22,180 W/m K.     

Cryogenic turning of the Ti–6Al–4V alloy with modified cutting tool inserts

Productivity in the machining of titanium alloys is adversely affected by rapid tool wear as a consequence of high cutting zone temperature. Conventional cutting fluids are ineffective in controlling the cutting temperature in the cutting zone. In this research work, an attempt has been made to investigate the effect of liquid nitrogen when it is applied to the rake surface, and the main and auxiliary flank surfaces through holes made in the cutting tool insert during the turning of the Ti–6Al–4V alloy. The cryogenic results of the cutting temperature, cutting forces, surface roughness and tool wear of the modified cutting tool insert have been compared with those of wet machining. It has been observed that in the cryogenic cooling method, the cutting temperature was reduced by 61–66% and the surface roughness was reduced to a maximum of 36% over wet machining. The cutting force was decreased by 35–42% and the flank wear was reduced by 27–39% in cryogenic cooling over that of wet machining. Cryogenic cooling enabled a substantial reduction in the geometry of tool wear through the control of the tool wear mechanisms. The application of liquid nitrogen to the heat generation zones through holes made in the cutting tool insert was considered to be more effective over conventional machining.     

Cold storage characteristics of mobile HTS magnet

A cold storage system specialized in mobile high-temperature superconducting (HTS) magnets (e.g. for magnetically levitated (maglev) vehicles) has been proposed. In this system, a cooling source is detachable and a HTS coil is capable of maintaining superconducting state with its heat capacity. This system allows a considerably lightweight HTS magnet.An apparatus was constructed to evaluate the possibility of using cold storage systems in maglev vehicles. The thermal characteristic of this apparatus was based on a magnet for previous maglev test vehicles [1]. The operational temperature range of the magnet was assumed from 20 K to 50 K. Some experiments indicated that heat conduction by residual gas was not negligible. Especially over 30 K, gas conduction took a large part of heat input. This phenomenon is attributable to reduction of cryopumping effect. However, activated carbon in the apparatus compensates cryopumping effect. A unique heat capacitor was also used to enhance the cold storage effect. Water ice was chosen as a heat capacitor because water ice has a higher heat capacity than metallic materials at cryogenic temperatures. A small amount of water ice also prolonged cryogenic temperature condition. These results indicate 1 day of cold storage is probable in a magnet for maglev vehicles.     

Numerical analysis on pressure drop and heat transfer performance of mesh regenerators used in cryocoolers

An anisotropic porous media model for mesh regenerator used in pulse tube refrigerator (PTR) is established. Formulas for permeability and Forchheimer coefficient are derived which include the effects of regenerator configuration and geometric parameters, oscillating flow, operating frequency, cryogenic temperature. Then, the fluid flow and heat transfer performances of mesh regenerator are numerically investigated under different mesh geometric parameters and material properties. The results indicate that the cooling power of the PTR increases with the increases of specific heat capacity and density of the regenerator mesh material, and decreases with the increases of penetration depth and thermal conductivity ratio (a). The cooling power at a = 0.1 is 0.5-2.0 W higher than that at a = 1. Optimizing the filling scale of different mesh configurations (such as 75% #200 twill and 25% #250 twill) and adopting multi segments regenerator with stainless steel meshes at the cold end can enhance the regenerator’s efficiency and achieve better heat transfer performance.     

Heat transfer characteristics of oscillating flow regenerators in cryogenic temperature range below 20 K

Linearized thermoacoustic model considering temperature oscillation in the solid wall is applied to analyze the heat transfer characteristics of compressible oscillating flow in parallel-plate and circular-tube regenerators. In particular, the study focus results of heat transfer analysis are applicable in lower cryogenic temperature ranges (<20 K). Complete expression for Nusselt number is derived and it is shown to be the function of six nondimensional parameters when the shape of the regenerator is fixed. These parameters are discussed, respectively. Simplified expressions of the Nusselt numbers for both parallel plates and circular tubes structured regenerators are derived. Heat transfer characteristics can be evaluated via these simple expressions. Possible approaches of enhancing heat transfer in a thermoacoustic regenerator are discussed.     

Experimental investigations of a closed-loop oscillating heat pipe

Results are given of experimental investigations of an oscillating heat pipe (OHP) made in the form of a closed-loop coil of a copper capillary tube with an inside diameter of 2 mm, 4.5 m long, and filled with water in an amount of 50% of internal volume. The starting characteristics of OHP are studied in the range of heat loads from 30 to 100 W under conditions of cooling by way of natural and forced air convection. The pattern of temperature pulsations in the zones of heating, heat transport, and cooling is investigated. It is found that temperature pulsations exhibit a chaotic pattern. In cooling of an OHP by way of natural convection, the increase in heat load is accompanied by an increase in the maximal temperature of the heating zone with a simultaneous decrease in the nonuniformity of the temperature field. When an OHP is cooled by way of forced convection, a decrease in the maximal temperature of the heating zone is observed; however, this is accompanied by an increase in the amplitude of temperature pulsations and in the nonuniformity of the temperature field.     

Effects of filling ratio and condenser temperature on the thermal performance of a neon cryogenic oscillating heat pipe

A cryogenic oscillating heat pipe (OHP) made of a bended copper capillary tube is manufactured. The lengths of the condenser section, adiabatic section and evaporator section are 100, 280 and 100 mm, respectively. Neon is used as the working fluid. Effects of liquid filling ratio and condenser temperature on the thermal performance of the OHP are studied. A correlation based on the available experimental data sets is proposed to predict the thermal performance of the neon cryogenic OHP with different filling ratios and condenser temperature. Compared with the experimental data, the average standard deviation of the correlation is about 15.0%, and approximately 92.4% of deviations are within ±30%.     

A vibration free cryostat using pulse tube cryocooler

This paper introduces a new vibration free cryostat cooled by liquid helium and a 4 K pulse tube cryocooler. The cryogenic device mounts on the sample cooling station which is cooled by liquid helium. The boil off helium is recondensed by the pulse tube cryocooler, thus the cryostat maintains zero boil off. There is no mechanical contact between the cryogenic part of the cryocooler and the sample cooling station. A bellows is used to isolate the vibration which could transfer from the cryocooler flange to the cryostat flange at the room temperature. Any vibrations generated by the operation of the cryocooler are almost entirely isolated from the cryogenic device. The cryostat provides a cooling capacity of 0.65 W at 4.21 K on the sample cooling station while maintaining a vapor pressure of 102 kPa. The sample cooling station has a very stable temperature with oscillations of less than ±3 mK during all the operations. A cryogenic microwave oscillator has been successfully cooled and operated with the cryostat.     

Localisation of deposited filling gases (CO2) in cryogenic thermal insulation materials using neutron radiography

The local distribution of deposited filling gases (CO₂) within a sample consisting of a packed bed of ∼1 μm-sized solid glass spheres exposed to a temperature gradient at cryogenic temperatures was investigated by neutron radiography measurements. This local distribution is useful for the understanding of the degradation of the thermal conductivity in cryogenic thermal insulations and the technique of deposition–evacuation (cryoevacuation). As neutron radiography is expected to be sensitive to the CO₂-distribution, a special sample cell was designed which allows establishing a typical cryogenic temperature gradient (77–293 K). The two-dimensionally resolved transmission of the neutron flux by the cell reveals that all CO₂ is deposited preferentially at and close to the cold wall. The form of the spatial CO₂-distribution is not affected by the total amount of CO₂ injected into the sample.     

Influence of condensed water on heat radiation absorptivity at cryogenic temperatures

Influence of water deposit on heat radiation absorptivity of a metallic surface was measured in a device designed for investigation of thermal radiative properties of materials at cryogenic temperatures. In this device heat transfer between planparallel surfaces of radiator and absorber is measured. An aluminium sample of 40 mm in diameter was used as absorber. A radiator consisting of an organic composite on a copper disk was used in two experiment stages. At temperature of 298 K, water outgassed from the organic layer formed the deposit on the absorber. Then the heat emitted from the radiator at temperatures from 45 K up to 250 K was used for the absorptivity measurement. Substantial influence of deposit of 85 mg/m² on the sample absorptivity was found.     

Analytical and finite element investigations of shear/compression test fixtures

Insulation systems are critical components of the international thermonuclear experimental reactor (ITER). They must meet the super conducting magnets design requirements, including mechanical strength under combined shear and compressive stresses at cryogenic temperatures. Past cryogenic magnet systems often relied on woven glass/epoxy materials for insulation. An important point is to find a reliable shear/compression test method for these materials. The present work investigates a commonly used shear/compression setup and aims at measuring the reliability of the obtained test results. Therefore, the stress and failure analysis is performed analytically and numerically using the finite element method. The model is based on woven glass fiber reinforced materials which are subjected to combined shear and compressive stresses as well as to thermal loading, that results from cooling from 293 K to the test temperature of 77 K. A short analytical section shows the problems of common failure criteria which are used to describe the interaction of the shear and compression stresses. The numerical—finite element—section is based on three-dimensional linear elastic finite element models under thermo-mechanical loading. The locations of high stress gradients are investigated using an average stress criterion. Three different model geometries (15°, 45°, and 70°) are analyzed and finally compared with respect to their reliability.     

Industrialisation of the insulation vacuum barrier for the large hadron collider (LHC) magnet cryostats

The insulation vacuum (<10⁻⁴ Pa) of the large hadron collider magnet cryostats, thermally protecting the superconducting magnets which operate at 1.9 K in superfluid helium, is divided in to 214 m long segments separated by means of insulation vacuum barriers.The insulation vacuum barrier is a leak-tight stainless steel welded structure, composed of two concentric corrugated cylinders and one internal bellows linked together by a 6 mm thick central plate. As the vacuum barrier mechanically links the cryostat vacuum vessel operating at ambient temperature and the 1.9 K superconducting magnets, it is designed to have minimum heat conductivity. Conduction heat in-leak is intercepted at 65 K by a high-purity copper ring brazed onto the stainless steel central plate and thermally linked to a cryogenic line by a copper-aluminium soldering. The thermal performance has been experimentally validated by cryogenic testing.This paper presents the results obtained after industrialisation, manufacture and testing of prototypes and series units. Qualification of leak-tight welds in thin-sheet stainless steel (thickness 0.15-1.3 mm) has been carried out. Ultrasonic testing is performed on all brazing and soldering. Helium leak testing is performed, using dedicated tooling, to ensure a leak-tightness to a rate better than 10⁻⁹ Pa m³ s⁻¹.     

震荡热管应用于玻璃化保存中的数值模拟

介绍了震荡热管应用于玻璃化保存的新方案,建立了生物组织在玻璃化保存过程中的数学模型,通过ANSYS分析软件,对样品在降温过程中的温度场进行了计算分析和数值模拟.得出了生物组织的瞬时温度分布,并通过模拟结果,计算出了生物组织在降温过程中的降温速率可达2×10~4 ℃/s.研究结果表明:极快速的降温速率可使细胞或组织快速通过0 ℃--60 ℃的危险温度区域,从而抑制冰晶的生成和长大, 减轻胞内冰造成的细胞损伤.     

低温热虹吸管的设计

作为一种高性能的传热方式 ,低温热管在低温技术以及超导磁体的冷却方面有广阔的应用。本文着重阐述了热虹吸管的工作原理、基本设计以及各种传热极限对热虹吸管的影响。     

Development of mechanical cryocoolers for Astro-H/SXS

The Soft X-ray Spectrometer (SXS) is a high-resolution spectrometer with an X-ray micro-calorimeter array onboard the Japanese X-ray astronomy satellite Astro-H, planned for launch in 2013. The micro-calorimeter is operated at cryogenic temperature of 50 mK provided by the Adiabatic Demagnetization Refrigerator (ADR) with a heat sink of 1.3 K liquid helium stored in the SXS Dewar. To extend the liquid helium lifetime to over 3 years in orbit, two types of mechanical cryocoolers are installed: 20 K-class double-staged Stirling (2ST) coolers and a 1 K-class Joule-Thomson (JT) cooler. Improvement of mechanical cryocoolers has been investigated and verified for higher reliability and cooling performance. The engineering model (EM) of upgraded mechanical cryocoolers was fabricated for a long lifetime test. The required cooling power of 200 mW at 20 K for the 2ST cooler and 10 mW at 1.7 K for the JT cooler are achieved by EM test.     

He gas gap heat switch

Thermal control at 1 K is still demanding for heat switches development.A gas gap heat switch using ³He gas as the heat-transfer fluid was tested and characterized. The switch is actuated by a sorption pump, whose triggering temperatures were also characterized. Switching times were recorded for different thermalizations of the sorption pump.This paper presents the conductance results of such switch. The temperature scanning of the actuator is also presented. The effect of filling pressure is discussed as well as the thermalization of the sorption pump.About 60 μW/K OFF-state conductance and 100 mW/K ON-state conductance were obtained at 1.7 K. The actuation temperature is slightly adjustable upon the charging pressure of the working gas. Thermalization of the sorption pump at about 8–10 K is enough for producing an OFF state – it can be comfortably linked to a 4 K stage. Temperatures of 15–20 K at the sorption pump are required for reaching the viscous range for maximum ON conduction. Switching time dependence on the thermalization of the sorption pump is discarded.     

Development of superconducting and cryogenic technology in the Institute for Technical Physics (ITP) of the Research Center Karlsruhe

Since the early 1970s the Institute for Technical Physics of the Research Center Karlsruhe has been involved in the development of superconductivity for research and industrial applications. A broad program with a focus on the superconducting magnet technology was established to include large magnets for nuclear fusion, high-field magnets for nuclear magnetic resonance spectrometers, ore separation and energy storage magnets. Research and development work was performed in collaborative projects with other national as well as international institutions and industry. The success of these projects has been supported by a broad foundation of engineering science in superconductor development, electrical and cryogenic engineering. Several well known test facilities like TOSKA, STAR, HOMER, MTA along with well equipped laboratories for conductor development, materials at cryogenic temperatures, cryogenic high-voltage engineering have made substantial contributions to in-house, national and international projects. A strong cryogenic infrastructure with two refrigerators and sophisticated cooling circuits from about 4.5 K down to 1.8 K assure the reliable operation of these large facilities. Last but not least, cryogenic research, including vacuum pumps for International Thermonuclear Experimental Reactor, improvements in thermal insulation, cryogenic instrumentation and small on board refrigerators has supported progress in this field. High-temperature superconductivity projects for low AC loss conductors, a 70 kA current lead and a fault current limiter are currently in progress.     

Northrop Grumman Aerospace Systems cryocooler overview

Mechanical long life cryocoolers are an enabling technology used to cool a wide variety of detectors in space applications. These coolers provide cooling over a range of temperatures from 2 K to 200 K, cooling powers from tens of mW to tens of watts. Typical applications are missile warning, Earth and climate sciences, astronomy and cryogenic propellant management. Northrop Grumman Aerospace Systems (NGAS) has delivered many of the US flight cooler systems and has 12 long life pulse tube and Stirling coolers on orbit with two having over 11 years of continuous operation. This paper will provide an overview of the NGAS cryocooler capabilities.     

The reinforcing effect of graphene nanosheets on the cryogenic mechanical properties of epoxy resins

The reinforcing effect of graphene in enhancing the cryogenic tensile and impact properties of epoxy composites is examined at a weight fraction of 0.05–0.50%. The micro-structure and cryogenic mechanical properties of the graphene/epoxy composites are investigated using scanning electron microscopy, transmission electron microscopy, small-angle X-ray scattering and mechanical testing techniques. The results show that the graphene dispersion in the epoxy matrix is good at low contents while its aggregation takes place and becomes severer as its content increases. And the cryogenic tensile and impact strength at liquid nitrogen temperature (77 K) of the composites are effectively improved by the graphene addition at proper contents. The cryogenic Young’s modulus increases almost linearly with increasing the graphene content. Moreover, the results for the mechanical properties at room temperature (298 K) of the graphene/epoxy composites are also presented for the purpose of comparison.     

The relation between heat treatment and corrosion behavior of Mg–Gd–Y–Zr alloy

The corrosion behavior of Mg–7Gd–3Y–0.4Zr (GW73K) was investigated in as-cast (F), solution-treated (T4) and peak-aged (T6) conditions using immersion tests and electrochemical measurements in NaCl solution (5 wt.%). Microstructure analyses were carried out on GW73K after different heat treatments by optical microscope (OM), field emission scanning electron microscope (FE-SEM), transmission electron microscope (TEM) and X-ray diffraction. It is found that GW73K alloy exhibits higher corrosion resistance in T4 than in F and T6 conditions due to the fully dissolution of cathodic coarse (Gd + Y) rich eutectic compound. The corrosion products of GW73K have different morphologies for F, T4 and T6 conditions. The product for F is less uniform and compact than T4 and T6, and it has been founded that GW73K-T6 had two different morphologies owing to the presence of β′. The results of polarization curves also confirm that proper heat treatment is beneficial to improve the corrosion resistance of GW73K alloy by transforming the microstructures.