Screen channel liquid acquisition device outflow tests in liquid hydrogen

This paper presents experimental design and test results of the recently concluded 1-g inverted vertical outflow testing of two 325 × 2300 full scale liquid acquisition device (LAD) channels in liquid hydrogen (LH₂). One of the channels had a perforated plate and internal cooling from a thermodynamic vent system (TVS) to enhance performance. The LADs were mounted in a tank to simulate 1-g outflow over a wide range of LH₂ temperatures (20.3–24.2 K), pressures (100–350 kPa), and flow rates (0.010–0.055 kg/s). Results indicate that the breakdown point is dominated by liquid temperature, with a second order dependence on mass flow rate through the LAD. The best performance is always achieved in the coldest liquid states for both channels, consistent with bubble point theory. Higher flow rates cause the standard channel to break down relatively earlier than the TVS cooled channel. Both the internal TVS heat exchanger and subcooling the liquid in the propellant tank are shown to significantly improve LAD performance.     

Design and experimental investigation of a cryogenic system for environmental test applications

This paper is concerned with the design, development and performance testing of a cryogenic system for use in high cooling power instruments for ground-based environmental testing. The system provides a powerful tool for a combined environmental test that consists of high pressure and cryogenic temperatures. Typical cryogenic conditions are liquid hydrogen (LH2) and liquid oxygen (LO2), which are used in many fields. The cooling energy of liquid nitrogen (LN2) and liquid helium (LHe) is transferred to the specimen by a closed loop of helium cycle. In order to minimize the consumption of the LHe, the optimal design of heat recovery exchangers has been used in the system. The behavior of the system is discussed based on experimental data of temperature and pressure. The results show that the temperature range from room temperature to LN2 temperature can be achieved by using LN2, the pressurization process is stable and the high test pressure is maintained. Lower temperatures, below 77 K, can also be obtained with LHe cooling, the typical cooling time is 40 min from 90 K to 22 K. Stable temperatures of 22 K at the inlet of the specimen have been observed, and the system in this work can deliver to the load a cooling power of several hundred watts at a pressure of 0.58 MPa.     

Thermal vacuum integrated system test at B-2

The National Aeronautics and Space Administration (NASA) Glenn Research Center (GRC) Plum Brook Station (PBS) Space Propulsion Research Facility, commonly referred to as B-2, is NASA’s third largest thermal vacuum facility. It is the largest designed to store and transfer large quantities of liquid hydrogen and liquid oxygen, and is perfectly suited to support developmental testing of chemical propulsion systems as well as fully integrated stages. The facility is also capable of providing thermal-vacuum simulation services to support testing of large lightweight structures, Cryogenic Fluid Management (CFM) systems, electric propulsion test programs, and other In-Space propulsion programs.A recently completed integrated system test demonstrated the refurbished thermal vacuum capabilities of the facility. The test used the modernized data acquisition and control system to monitor the facility during pump down of the vacuum chamber, operation of the liquid nitrogen heat sink (or cold wall) and the infrared lamp array. A vacuum level of 1.3 × 10^?4 Pa (1 × 10^?6 torr) was achieved. The heat sink provided a uniform temperature environment of approximately 77 K (139°R) along the entire inner surface of the vacuum chamber. The recently rebuilt and modernized infrared lamp array produced a nominal heat flux of 1.4 kW/m² at a chamber diameter of 6.7 m (22 ft) and along 11 m (36 ft) of the chamber’s cylindrical vertical interior. With the lamp array and heat sink operating simultaneously, the thermal systems produced a heat flux pattern simulating radiation to space on one surface and solar exposure on the other surface. The data acquired matched pretest predictions and demonstrated system functionality.     

Cryogenic flat-panel gas-gap heat switch

A compact additive manufactured flat-panel gas-gap heat switch operating at cryogenic temperature is reported in this paper. A guarded-hot-plate apparatus has been developed to measure the thermal conductance of the heat switch with the heat sink temperature in the range of 100–180 K. The apparatus is cooled by a two-stage GM cooler and the temperature is controlled with a heater and a braided copper wire connection. A thermal guard is mounted on the hot side of the device to confine the heat flow axially through the sample. A gas handling system allows testing the device with different gas pressures in the heat switch. Experiments are performed at various heat sink temperatures, by varying gas pressure in the gas-gap and with helium, hydrogen and nitrogen gas. The measured off-conductance with a heat sink temperature of 115 K and the hot plate at 120 K is 0.134 W/K, the on-conductance with helium and hydrogen gases at the same temperatures is 4.80 W/K and 4.71 W/K, respectively. This results in an on/off conductance ratio of 37 ± 7 and 35 ± 6 for helium and hydrogen respectively. The experimental results matches fairly well with the predicted heat conductance at cryogenic temperatures.     

Performances of the 50 mK ADR/sorption cooler

CEA/SBT is currently testing a 50 mK cooler developed in the framework of a European Space Agency Technological Research Program targeted for the Advanced Telescope for High Energy Astrophysics space mission. This cooler is composed of a small demagnetization refrigerator pre cooled by a sorption cooler stage. This Engineering Model is able to produce 1 μW of net heat lift at 50 mK and an additional 10 μW at 300 mK provided by the sorption cooler stage. The autonomy of the cooler is 24 h, and once the low temperature phase at 50 mK is over, it can be recycled in about 8 h with 10 μW and 100 μW available at respectively the 2.5 and 15 K heat sinks. These performances are in agreement with the European Space Agency requirements.In this paper, we present the detailed thermal performances of the cooler in nominal conditions as well as sensitivity measurements of the variation of the heat sink and the cold end temperatures.     

Pressure drop reduction and heat transfer deterioration of slush nitrogen in triangular and circular pipe flows

Slush fluids such as slush hydrogen and slush nitrogen are characterized by superior properties as functional thermal fluids due to their density and heat of fusion. In addition to allowing efficient hydrogen transport and storage, slush hydrogen can serve as a refrigerant for high-temperature superconducting (HTS) equipment using MgB₂, with the potential for synergistic effects. In this study, pressure drop reduction and heat transfer deterioration experiments were performed on slush nitrogen flowing in a horizontal triangular pipe with sides of 20 mm under the conditions of three different cross-sectional orientations. Experimental conditions consisted of flow velocity (0.3–4.2 m/s), solid fraction (0–25 wt.%), and heat flux (0, 10, and 20 kW/m²). Pressure drop reduction became apparent at flow velocities exceeding about 1.3–1.8 m/s, representing a maximum amount of reduction of 16–19% in comparison with liquid nitrogen, regardless of heating. Heat transfer deterioration was seen at flow velocities of over 1.2–1.8 m/s, for a maximum amount of deterioration of 13–16%. The authors of the current study compared the results for pressure drop reduction and heat transfer deterioration in triangular pipe with those obtained previously for circular and square pipes, clarifying differences in flow and heat transfer properties. Also, a correlation equation was obtained between the slush Reynolds number and the pipe friction factor, which is important in the estimation of pressure drop in unheated triangular pipe. Furthermore, a second correlation equation was derived between the modified slush Reynolds number and the pipe friction factor, enabling the integrated prediction of pressure drop in both unheated triangular and circular pipes.     

Operating characteristics of a single-stage Stirling cryocooler capable of providing 700 W cooling power at 77 K

High cooling capacity Stirling cryocooler generally has hundreds to thousands watts of cooling power at liquid nitrogen temperature. It is promising in boil-off gas (BOG) recondensation and high temperature superconducting (HTS) applications. A high cooling capacity Stirling cryocooler driven by a crank-rod mechanism was developed and studied systematically. The pressure and frequency characteristics of the cryocooler, the heat rejection from the ambient heat exchanger, and the cooling performance are studied under different charging pressure. Energy conversion and distribution in the cryocooler are analyzed theoretically. With an electric input power of 10.9 kW and a rotating speed of 1450 r/min of the motor, a cooling power of 700 W at 77 K and a relative Carnot efficiency of 18.2% of the cryocooler have been achieved in the present study, and the corresponding pressure ratio in the compression space reaches 2.46.     

Feasibility study of friction spot welding of dissimilar single-lap joint between poly(methyl methacrylate) and poly(methyl methacrylate)-SiO2 nanocomposite

In this work, the feasibility of friction spot welding (FSpW) of a commercial poly(methyl methacrylate) (PMMA) GS grade and a PMMA 6 N/2 wt% silica (SiO₂) nanocomposite was investigated. Single-lap joints welded at rotational speeds of 1000, 2000 and 3000 rpm were produced. The analysis of the joint microstructure and material flow pattern indicated that joints could be produced using all of the tested welding conditions. However, the joint produced at 1000 rpm displayed sharp weld lines (weak links), indicating insufficient heat input, while the welds produced at 3000 rpm displayed excessive plastic deformation (bulging of the bottom plate), volumetric defects and a lack of material mixing in the welded area, associated with higher heat input. The weld produced at a rotational speed of 2000 rpm resulted in improved material mixing, which was indicated by the absence of weld lines and volumetric defects due to the more correct heat input. This welding condition was selected for further mechanical testing. Lap shear testing of PMMA GS/PMMA 6 N/2 wt% SiO₂ nanocomposite single lap joints welded at 2000 rpm resulted in an average ultimate lap shear strength of 3.9 ± 0.05 MPa. These weld strength values are equal to or better than those obtained using state-of-the-art welding techniques for PMMA materials, thereby demonstrating the potential of friction spot welding for thermoplastic nanocomposites.     

Cryogenic capillary screen heat entrapment

Cryogenic liquid acquisition devices (LADs) for space-based propulsion interface directly with the feed system, which can be a significant heat leak source. Further, the accumulation of thermal energy within LAD channels can lead to the loss of subcooled propellant conditions and result in feed system cavitation during propellant outflow. Therefore, the fundamental question addressed by this program was: “To what degree is natural convection in a cryogenic liquid constrained by the capillary screen meshes envisioned for LADs?” Testing was first conducted with water as the test fluid, followed by liquid nitrogen (LN₂) tests. In either case, the basic experimental approach was to heat the bottom of a cylindrical column of test fluid to establish stratification patterns measured by temperature sensors located above and below a horizontal screen barrier position. Experimentation was performed without barriers, with screens, and with a solid barrier. The two screen meshes tested were those typically used by LAD designers, 200 × 1400 and 325 × 2300, both with Twill Dutch Weave. Upon consideration of both the water and LN₂ data, it was concluded that heat transfer across the screen meshes was dependent upon barrier thermal conductivity and that the capillary screen meshes were impervious to natural convection currents.     

Cryogenic design and test results of 30-m flexible hybrid energy transfer line with liquid hydrogen and superconducting MgB2 cable

In this paper we present the development of a new hybrid energy transfer line with 30 m length. The line is essentially a flexible 30 m hydrogen cryostat that has three sections with different types of thermal insulation in each section: simple vacuum superinsulation, vacuum superinsulation with liquid nitrogen precooling and active evaporating cryostatting (AEC) system. We performed thermo-hydraulic tests of the cryostat to compare three thermo-insulating methods. The tests were made at temperatures from 20 to 26 K, hydrogen flow from 70 to 450 g/s and pressure from 0.25 to 0.5 MPa. It was found that AEC thermal insulation was the most effective in reducing heat transfer from room temperature to liquid hydrogen in ∼10 m section of the cryostat, indicating that it can be used for long superconducting power cables. High voltage current leads were developed as well. The current leads and superconducting MgB₂ cable passed high voltage DC test up to 50 kV DC. Critical current of the cable at ∼21 K was 3500 A. It means that the 30 m hybrid energy system developed is able to deliver ∼50–60 MW of chemical power and ∼50–75 MW of electrical power, i.e. up to ∼135 MW in total.     

Experimental study of one-stage VM cryocooler operating below 8 K

The Vuilleumier (VM) refrigerator, known as heat driven refrigerator, is one kind of closed-cycle Stirling type regenerative refrigerator. The VM refrigerator with power being supplied by liquid nitrogen was proposed by Hogen and developed by Zhou, which shows great potential for development below 10 K. This paper describes the experimental development of a VM cryocooler operating below 8 K, which was achieved by using liquid nitrogen as a heat sink of middle cavity. The regenerator was optimized by using a part of metallic magnetic regenerator material Er₃Ni to replace the lead sphere and a no-load temperature of 7.8 K was obtained. Then all the lead spheres were replaced by Er_0.6Pr_0.4 material and a no-load temperature of 7.35 K was obtained, which is the lowest temperature for this kind of refrigerator reported so far. The cooling power at 10 K is about 500 mW with a pressure ratio near 1.6 and a charge pressure of 1.8 MPa. Especially, the magnetic material Er_0.6Pr_0.4 was found to be a potential substitution for the conventional lead.     

Development and parametric study of the convection-type stationary adiabatic demagnetization refrigerator (ADR) for hydrogen re-condensation

The adiabatic demagnetization refrigerator (ADR) system in this paper is composed of a conduction-cooled current cycling high-temperature superconducting (HTS) magnet system, a magnetic bed assembly, its heat exchange parts and an auxiliary precooling stage (a commercial GM cryocooler and a liquid nitrogen vessel). The whole magnetic refrigeration system including the conduction-cooled HTS magnet is cooled by the precooling stage to absorb the rejection heat of the ADR cycle. The packed bed type magnetic bed consists of tiny irregular powders of Dy_0.9Gd_0.1Ni₂ enclosed in a thin walled stainless steel container (22.2 mm in O.D., 0.3 mm in thickness and 40.0 mm in height). The precooled heat transfer fluid (helium) travels through the magnetic material when heat rejection is required; otherwise the helium stagnates within its pores (pseudo-adiabatic process). Flow of the heat transfer fluid substitutes for the function of a traditional heat switch, creating, essentially, a forced-convection type heat switch. The magnetic bed assembly is periodically magnetized and demagnetized at the center of the conduction-cooled HTS magnet which can stably generate both strong and alternating magnetic field from 0 T to 3.0 T (0–130 A) with an average ramp rate of 0.24 T s⁻¹. The cooling capacities of the ADR system at 20 K which is the normal boiling point (NBP) of hydrogen, are 11.1 J cycle⁻¹, 6.3 J cycle⁻¹ and 1.9 J cycle⁻¹ when the temperature spans are 1 K, 2 K and 3 K, respectively. We describe the detailed construction of the ADR system and discuss the test results with the operational parameters (the entrained helium pressure, the mass flow rate of helium and the operating temperature span) in the 20 K region.     

Low temperature growth of SnO2 nanowires by electron beam evaporation and their application in UV light detection

For the first time, high quality tin oxide (SnO₂) nanowires have been synthesized at a low substrate temperature of 450 °C via vapor–liquid–solid mechanism using an electron beam evaporation technique. The grown nanowires have shown length of 2–4 μm and diameter of 20–60 nm. High resolution transmission electron microscope studies on the grown nanowires have shown the single crystalline nature of the SnO₂ nanowires. We investigated the effect of growth temperature and oxygen partial pressure on SnO₂ nanowires growth. Variation of substrate temperature at a constant oxygen partial pressure of 4 × 10⁻⁴ mbar suggested that a temperature equal to or greater than 450 °C was the best condition for phase pure SnO₂ nanowires growth. The SnO₂ nanowires grown on a SiO₂ substrate were subjected to UV photo detection. The responsivity and quantum efficiency of SnO₂ NWs photo detector (at 10V applied bias) was 12 A/W and 45, respectively, for 12 μW/cm² UV lamp (330 nm) intensity on the photo detector..     

Development of a new magnesium alloy ZW21

A new magnesium alloy named ZW21 has been developed through orthogonal experiment method and the effects of heat treatment on the alloy’s tensile properties have also been investigated. The results indicate that the alloy only has one Mg–Zn–Y(Nd) phase of Mg₃Zn₃(Y, Nd)₂ (named W phase) and has higher mechanical properties, lower cost and lighter weight compared with the other congeneric alloys. Its microstructure is composed of small equiaxed dendrites and interdendritic discontinuous net-like eutectic structures. The eutectic structures appear in divorced W phase laths in the thin regions between the dendrites and in regular W + α-Mg lamellar structures in the triangle regions. The eutectic structures, especially the W phase, with such distribution are harmful to the tensile properties and thus proper heat treatment can improve its properties through changing the W phase distribution. Solution treatment at 525 °C for 4 h (T₄ treatment) increases the elongation from 17.75% to 26.5%. Subsequent ageing treatment at 250 °C for 24 h (T₆ treatment) improves the ultimate tensile strength from 210 MPa to 243 MPa. The fracture modes of the as-cast, T₄- and T₆-treated alloys all obey the quasi-cleavage regime. The fracture of the as-cast alloy belongs to a mixed mode of intergranular and transgranular forms, but those of the T₄- and T₆-treated alloys follow the transgranular mode due to the relatively high bonding strength between the grains.     

High-speed deposition of dense,dendritic and porous SiO2 films by Nd: YAG laser chemical vapor deposition

Dense, dendritic and porous SiO₂ films were prepared by laser chemical vapor deposition (LCVD) using a high-power continuous-wave mode Nd: YAG laser (206 W) and a TEOS (tetraethyl orthosilicate) precursor. The effects of laser power (P_L) and total chamber pressure (P_tot) on the microstructure and deposition rate (R_dep) were investigated. Amorphous SiO₂ films were obtained independent of P_L and P_tot. Flame formation was observed between the nozzle and the substrate at P_L > 160 W and P_tot > 15 kPa. At P_L = 206 W, dense, dendritic and porous SiO₂ films were obtained at P_tot < 20 kPa, P_tot = 23 kPa and P_tot > 25 kPa, respectively. The R_dep increased thousands of times under flame formation conditions, the highest R_dep being reached at 1200 μm h^?1, 22,000 μm h^?1 and 28,000 μm h^?1 for the dense, dendritic and porous SiO₂ films, respectively.     

Improvement of magnetic properties of nanostructured Ni79Fe16Mo5 alloyed powders by a suitable heat treatment

The supermalloy (Ni₇₉Fe₁₆Mo₅) nanostructured powder with average crystallite size of about 8 nm was prepared by high energy milling. The obtained powders were characterized by X-ray diffraction, scanning electron microscopy, differential scanning calorimetry and vibration sample magnetometer. The results showed that the coercivity and the saturation magnetization reach about 8 Oe and 75 emu/g at 96 h and become approximately 1 Oe and 85 emu/g after a suitable heat treatment, respectively. The magnetic measurements confirmed that the supermalloy soft magnetic nanostructure powder was produced by mechanical alloying followed by a post heat treatment. The results revealed that a small amount of Mo element remain in the system up to 96 h due to (i) high fusion temperature, T_f = 2893 K, (ii) high mechanical hardness, (iii) low solubility of Mo into Ni at low temperatures in mechanical alloying conditions.     

Enhanced sintering ability of biphasic calcium phosphate by polymers used for bone scaffold fabrication

Biphasic calcium phosphate (BCP), which is composed of hydroxyapatite [HAP, Ca₁₀(PO₄)₆(OH)₂] and β-tricalcium phosphate [β-TCP, β-Ca₃(PO₄)₂], is usually difficult to densify into a solid state with selective laser sintering (SLS) due to the short sintering time. In this study, the sintering ability of BCP ceramics was significantly improved by adding a small amount of polymers, by which a liquid phase was introduced during the sintering process. The effects of the polymer content, laser power and HAP/β-TCP ratios on the microstructure, chemical composition and mechanical properties of the BCP scaffolds were investigated. The results showed that the BCP scaffolds became increasingly more compact with the increase of the poly(l-lactic acid) (PLLA) content (0–1 wt.%) and laser power (6–10 W). The fracture toughness and micro-hardness of the sintered scaffolds were also improved. Moreover, PLLA could be gradually decomposed in the late sintering stages and eliminated from the final BCP scaffolds if the PLLA content was below a certain value (approximately 1 wt.% in this case). The added PLLA could not be completely eliminated when its content was further increased to 1.5 wt.% or higher because an unexpected carbon phase was detected in the sintered scaffolds. Furthermore, many pores were observed due to the removal of PLLA. Micro-cracks and micro-pores occurred when the laser power was too high (12 W). These defects resulted in a deterioration of the mechanical properties. The hardness and fracture toughness reached maximum values of 490.3 ± 10 HV and 1.72 ± 0.10 MPa m^1/2, respectively, with a PLLA content of approximately 1 wt.% and laser power of approximately 10 W. Poly(l-lactic-co-glycolic acid) (PLGA) showed similar effects on the sintering process of BCP ceramics. Rectangular, porous BCP scaffolds were fabricated based on the optimum values of the polymer content and laser power. This work may provide an experimental basis for improving the mechanical properties of BCP bone scaffolds fabricated with SLS.     

Effect of thermo mechanical treatments and aging parameters on mechanical properties of Al–Mg–Si alloy containing 3 wt.% Li

In the present work, microstructure and mechanical properties of 3 wt.% Li addition in a Al–Mg–Si alloy of target composition 0.5 wt.% Mg and 0.2 wt.% Si in W (solution heat treated), T6 (solution heat treated and artificially aged) and T8 (solution heat treated, cold worked and artificially aged) conditions was studied. The age-hardening response of the alloy was determined after systematic cold reductions from 10%, 20%, 30%, 40%, 50% and 60% in quenched condition followed by aging at 175 °C (448 K) for 2, 4, 6, 8, 10 and 12 h (T8 condition). The results were compared with samples aged in the same conditions with 0% cold reduction (T6 condition). The alloy displayed a strong artificial aging response and maximum hardness value achieved was after 60% cold work and 10 h of aging time. Furthermore, the yield strength and the ultimate tensile strength were increased from 123 MPa to 224 MPa and 356 MPa to 540 MPa respectively with a slight decrease in ductility. Scanning electron microscopy (SEM) based fractography showed a uniform network of bigger and deeper dimples with round morphology in T6 condition while a ductile tearing with few discernable cleavage planes was observed in T8 condition. The interplay of various precipitation hardening mechanisms and relevant phases was established by X-ray diffraction (XRD) and differential scanning calorimetry (DSC). It was concluded that the enhancement in mechanical properties, with the degree of cold work, was attributed due to a possible refinement of δ′ (Al₃Li) precipitates resulted after aging.     

Boiling heat transfer from a horizontal flat plate in a pool of liquid hydrogen

Heat transfer from a flat plate facing upward immersed in a liquid hydrogen pool was measured for the pressures from atmospheric to 1.1 MPa. The flat plate heater used was 10 mm in width, 100 mm in length and 0.1 mm in thickness. Critical heat fluxes (CHFs) in saturated boiling increased with the increase in pressure up to around 0.3 MPa and then decreased with further pressure increase. The CHFs under subcooled condition at each pressure increased with the increase in sub-cooling. Discussions were made on the experimental results by comparing with those of the other cryogenic liquids and also the Kutateladze’s equations under saturated and subcooled conditions. The experimental CHFs were much smaller than the Kutateladze’s equation for higher pressure up to critical. The heater surface temperature was found to reach the critical temperature before the occurrence of hydrodynamic instability and jump to the film boiling regime at the lower heat flux in the higher pressure range. It was suggested that the CHFs are determined not by the heat flux but by the temperature in the higher pressure range.     

In situ fabrication of titanium carbide particulates-reinforced iron matrix composites

Titanium carbide (TiC) particulates-reinforced iron matrix composites were prepared by in situ fabrication method combining an infiltration casting with a subsequent heat treatment. The effects of different heat treatment times (0, 1, 6 and 11 h) at 1138 °C on the phase evolution, microstructural features, and properties of the composites were investigated. The as-prepared composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and microhardness and wear resistance tests. The XRD results showed that the composites consisted of graphite, α-iron and titanium carbide after heat treatment at 1138 °C for 11 h. The SEM observation revealed that the formed TiC particulates were homogenously distributed in the iron matrix. The average microhardness of the composite heat treated at 1138 °C for 6 h increased depending upon the region: 209 HV_0.1 (iron matrix) < 787 HV_0.1 (titanium wire) < 2667 HV_0.1 (composite region). After being heat treated at 1138 °C for 11 h, the composite indicated no considerable change in microhardness value, and the average microhardness of the composite region was about 2354 HV_0.1. The highest microhardness value obtained for the composite region was due to the formation of titanium carbide particulates as reinforcement phase within the iron matrix. Relative wear resistance was determined by a pin-on-disc wear test technique under different loads, and as a result, the composites containing higher volume fraction of hard titanium carbide particulates presented higher wear resistance compared with the unreinforced gray cast iron.