查看更多>>摘要：As an important issue of the quench simulation in large-scale applications， the effect of time step control is discussed on the well-known thermo-hydraulic model of superconducting magnets。 Through our approach of model reduction， the reason of numerical anomaly is identified in terms of the time stepping around dynamical events， and just leads an effective countermeasure against the observed issue。 Apart from the practical means out of such an investigation， a novel idea of non-iterative time step adaptation is introduced as a breakthrough not only being applied to the quench propagation model itself， but also to be extended to the common pitfalls of linearization scheme in general transient PDE (partial differential equation) problems。
查看更多>>摘要：The nitrogen-charged cryogenic loop heat pipe (CLHP) was utilized as an effective cryogenic heat switch operating at around 100 K by thermally connecting or blocking a cryogenic heat source and a cryogenic heat sink。 The switching-off function of the CLHP heat switch was achieved by eliminating heat load on the secondary evaporator without any dedicated support of additional components or mechanisms during a normal operation。 The removal of heat load on the secondary evaporator leads to the dry-out of the primary evaporator， which causes the thermal switching-off ultimately。 The on/off thermal conductance ratios of the CLHP heat switch were obtained in various operational conditions such as different heat loads on the primary and secondary evaporators and different initial charging-pressures of nitrogen。 The switching-off process divided into the on-state， transient state， and off-state was investigated experimentally， and the characteristics in the unsteady off-state were specially analyzed in detail。 The obtained on/off thermal conductance ratios of the CLHP heat switch were in the range from 400 to 3900 in the experiments which are exceedingly larger than those of the conventional heat switches。 The ratio becomes larger when the initial charging-pressure of working fluid is low but the heat loads on the primary evaporator and/or the secondary evaporator are large because the effective thermal conductance in the on-state is dominantly affected by the mass flow rate of working fluid。 Between the heat loads on the primary and secondary evaporators， the on/off thermal conductance ratio of the CLHP heat switch is more sensitively affected by the heat load on the PE。
查看更多>>摘要：Carbon capture and sequestration / utilization using cryogenic conditions have found attention due to lower energy penalty compared to other separation methods。 In cryogenic processes， carbon dioxide is likely to desublimate from a vapor phase or freezes out from a liquid phase。 This study deals with phase equilibrium calculations where solid carbon dioxide forms in the presence of vapor phase (SLV)， liquid phase (SLE)， or both (SLVE)。 Two of the successful solid fugacity models are used with predictive cubic equations of state (EOSs) in calculating the phase equilibrium of carbon dioxide mixtures。 The advantages and limitations of the models are discussed。 In addition， a new fugacity model which describes solid carbon dioxide along solid-liquid coexistence curve is developed。 This model remedies the previous models and is used from low to very high pressure。 This model reduces to an analytical expression for describing carbon dioxide melting curve。 When coupled with the predictive cubic EOSs， this model satisfactorily describes the SVE， SLE， and SVLE of carbon dioxide mixtures。
查看更多>>摘要：The applications of high-Tc superconducting magnets comprising REBa2Cu3O7-x (REBCO)-coated conductors， such as nuclear magnetic resonance instruments， high-field magnets， high-energy particle accelerators， and industrial apparatuses， are being actively developed worldwide。 A few of them are conduction-cooled magnets and are operated at temperatures above the critical temperature of low-Tc superconductors。 To reduce the heat loads of cryocoolers and improve their energy efficiency， low resistance and handy joint technologies for REBCOcoated conductors are required。 We evaluated the resistances of soldered joints of commercial REBCO-coated conductors in liquid helium。 We soldered REBCO-coated conductors manufactured by Fujikura Ltd。 and SuperPower Inc。 over a silver protective layer using superconducting Pb0。45Bi0。45In0。1 solder。 The joint resistance was dominated by the interfacial resistance between REBCO and the silver protective layers and was estimated to be 3 x 10-12 omega m2。 Further， a drastic reduction in the joint resistances could be realized by improving the electrical connectivity between REBCO and the silver layers。 Assuming a conduction-cooled high-Tc superconducting magnet， we demonstrated quasipersistent operation of a loop specimen of REBCO-coated conductors with a soldered joint using two Gifford-McMahon cryocoolers。 The exponential decay of induced current in the loop specimen was observed with a decay time constant that was dependent on the joint resistance。
de Vera, Francesca Isabel N.Singidas, Bess G.Sarmago, Roland, V
8页
查看更多>>摘要：The interplay between intrinsic grain and inter-grain effects at the superconducting state defines the behavior of bulk high-temperature superconductors。 In this work， we use DC resistivity and AC magnetic susceptibility measurements to show how the intrinsic and inter-grain properties influence the intergrain phase coherence and flux dynamics of Bi2Sr2-xInxCaCu2O8+d。 High In-doped samples， x >= 0。4， have broad resistive and diamagnetic superconducting transitions due to weak intergrain coupling caused by segregated impurities。 Low doping levels， x <= 0。3， have sharp superconducting resistive and diamagnetic transitions， with higher transition temperature T-C attributed to an increase superconducting pair density。 This results to enhanced intergrain coupling and strong diamagnetic screening of intergrain void networks。 An applied AC field of 0。77 mT amplitude deteriorates the intergrain diamagnetic screening at x = 0。2 through AC flux slip between grains。
Esposito, C.Peveroni, L.Gouriet, J. B.Steelant, J....
9页
查看更多>>摘要：Cryogenic cavitation can be easily encountered in rocket liquid propulsion systems at the very initial phase of the launch due to the propellant passing through orifices and valves。 This leads to flow instability， performance degradation， and even damages to the structures。 Hence， the design of the propulsion systems cannot overlook cavitation phenomena。 Despite the relevance of the topic， their accurate prediction is still hampered by the difficulty in modeling the high non-equilibrium phenomena involved。 From an engineering point of view， the main interest is to design such restrictions present in propellant systems and， hence， to predict the maximum flow rate they can reach。 This work questions the possibility to design orifices for cryogenic applications based on purely isothermal testing。 Therefore， we performed cavitation experiments with both water and liquid nitrogen by considering two orifices hydraulically similar。 This implies a geometric similitude in terms of the orifice characteristic ratio (beta) and its dimensionless thickness (th)。 The results show that the hydraulic similitude is not sufficient to predict the orifice behavior for a cryogenic flow correctly。 In particular， the level of liquid subcooling (Delta Tsub) upstream of the orifice plays an important role since it impacts the minimal value of pressure of the flow downstream the orifice and thus its thermodynamic state。
查看更多>>摘要：An aftercooler for a pulse tube cryocooler (PTC) was experimentally investigated。 The aftercooler is the heat exchanger on the high-temperature side and one of the main components of a PTC。 Three types of aftercoolers were studied: a mesh type with complex flow channels， a square hole type and a circular hole type with uniform flow channels。 The mesh type has high heat transfer characteristics but also a large viscous loss， while the latter two types have low heat transfer but also small viscous loss due to their uniform flow channels。 In this study， one mesh type and two circular hole type aftercoolers were constructed， and their heat transfer characteristics in steady flow， and the cooling performance of the PTC were experimentally evaluated。 In the steady flow experiments， the mesh type aftercooler showed higher heat-transfer performance than the circular hole type aftercoolers。 Next， an oscillatory flow experiment was conducted by installing the aftercoolers into a PTC。 The PTC with the circular multi-hole type aftercoolers showed better cooling performance than the PTC with the mesh type aftercooler， contrary to the results of the steady flow experiment。 To investigate the reason for this difference， we evaluated the power loss in the aftercooler and measured the temperature distribution along it in oscillatory flow experiments， and found that the mesh type aftercooler showed characteristics different from those of the other aftercoolers。 Based on these results and the relationship between the flow channel radius and the thermal boundary layer thickness， the issues with the mesh type aftercooler were clarified and necessary information for an improved design was developed。
查看更多>>摘要：With the emerging recognition of open scientific hardware， rapid prototyping technology such as threedimensional (3-D) printing is becoming widely available for fields such as cryobiology， and cryopreservation， where material selection for instruments and hardware has traditionally been problematic due to extreme low temperatures。 A better understanding of the mechanical properties of 3-D printing thermoplastics at cryogenic temperatures is essential to material selection， part design， and printing optimization。 The goal of the present study was to explore the feasibility of development for a 3-D printed device ('CryoTensileDevice') to hold a test specimen in liquid nitrogen and be mounted in standard mechanical testing systems to evaluate 3-D printing material behaviors at cryogenic temperatures。 The CryoTensileDevice was prototyped with flexible filaments with a per-unit material cost of <US$5 and a printing time of 5 h。 The commonly used printing filament polylactic acid (PLA) was selected to evaluate the utility of the CryoTensileDevice。 At room temperature， the CryoTensileDevice did not significantly (P 0。05) affect PLA tensile measurements such as Young's modulus， yield stress， yield strain， stress at break， or strain at break。 With the CryoTensileDevice， specimens 3-D printed with PLA at 50%， 75%， and 100% infill rates had comparable tensile properties when tested at room and liquid nitrogen temperatures。 The PLA showed superior performance in tensile properties in comparison to acrylonitrile butadiene styrene (ABS)。 This device can assist characterization of 3-D printing approaches for cryogenic work， and opens a pathway for future innovations to create a variety of 3-D printed devices to study a wide range of material properties for cryogenic applications。
查看更多>>摘要：A thermodynamic study is carried out for hydrogen liquefaction with cascade Joule-Thomson (JT) systems， which do not require any expansion machines。 Since there is no moving part at cryogenic temperatures， the cascade JT systems have a potential advantage of high reliability and easy scale-up of liquefaction capacity， as demonstrated in the full-scale LNG plants under operation。 A variety of combinations for pre-cooling JT cycles with single-component refrigerants (including neon， nitrogen， argon， oxygen， hydrocarbons， and ammonia) are investigated to estimate the figure of merit (FOM) as a performance index of liquefaction。 In every JT cycle， the pressure levels are optimized to maximize the FOM with a process simulator (Aspen HYSYS) and real properties of working fluids (NIST REFPROP)。 It is rigorously shown that the cascade JT systems can achieve a reasonably high FOM， if the irreversibility below 77 K is effectively reduced。 A few suitable cascade systems for large capacity hydrogen liquefaction are identified， and the details of optimized cycles are presented。
查看更多>>摘要：A Ne-liquefaction system cooled by a G-M cryocooler was developed。 The heat load and liquefied rate of the system were analyzed theoretically。 The neon gas was liquefied over 340 min while the condenser chamber was cooled down to 26。7 K。 The gas pressures of the heat exchanger inlet and condenser are directly proportional to its absolute temperature， which decreased with the reduction of cryostat system temperature。 The pressure of the heat exchanger inlet decreased from 105 kPa to 100。4 kPa with the pressure of the condenser decreased from 101 kPa to 100。1 kPa。 Neon gas with a purity of 99。999% was used in liquefaction and the mass flow is set to 0。173 g/s。 The production rate of liquid neon is determined to be 0。52 L/h。 The liquid neon was collected in a glass vacuum dewar with a transparent window， which allows to observe the liquid level and conduct the optical tests。 The refractive index and transmittance of the 940 nm infrared in liquid neon are 1。103 and 99。85%， respectively。 The parameters will provide a valuable database on infrared equipment with liquid neon as a cryogen。
NSTL
Elsevier