•Coal isothermal adsorption/desorption deformation experiments with liquid nitrogen quenching were carried out.•The variation of coal gas adsorption capacity and volumetric strain under liquid ...nitrogen cold leaching were investigated.•The relationship between coal adsorption capacity and volumetric strain under liquid nitrogen cold leaching was discussed.
The research on gas adsorption deformation characteristics of coal under liquid nitrogen cold soaking deserves investigation, as most of the investigation efforts in this field are in a preliminary stage. In this article, the experiments of coal adsorption deformation under different times of liquid nitrogen cold soaking (0, 1, 3, 5, 7 and 9) were carried out. The variation of coal gas adsorption capacity and volumetric strain under different times of liquid nitrogen cold soaking were investigated. Based on thermodynamics, the adsorption strain model of coal was developed, and the relationship between coal adsorption capacity and volumetric strain was discussed. The research results show that: (i) the coal adsorption capacity and volumetric strain both gradually decrease with the increase of the number of liquid nitrogen cold soaking; (ii) the saturated gas adsorption capacity and limit volume strain of coal both show a decreasing trend with the increase of liquid nitrogen cold soaking times; (iii) the volumetric strain of coal under the different times of liquid nitrogen cold soaking first accelerates and then slowly rises with the increase of adsorption capacity. After liquid nitrogen cold soaking, the volumetric strain growth rate of coal gradually decreases; (iv) the coal under different cold soaking times reaches the limit volumetric strain at a pressure (P) that is higher than the pressure (p) required to reach the saturation adsorption capacity, and the values of p and P both show a decreasing trend with the increase of liquid nitrogen cold soaking times; (v) the model results have good predictive effect.
The Doppler broadened R (0) and R (1) lines of the (2–0) vibrational band of HD have been measured at liquid nitrogen temperature and at pressures of 2 Pa, with a comb referenced continuous-wave ...cavity ring-down spectrometer set-up. Transition frequencies of 214905335185 kHz and 217105181898 kHz were derived from 33 and 83 recordings, with corresponding root mean squared deviation of 53 and 33 kHz for the R (0) and R (1) transition, respectively. This is the first sub-MHz frequency determination of the R (0) transition frequency and represents a three order of magnitude accuracy improvement compared to literature. The R (1) transition frequency is in very good agreement with previous determinations in saturation regime reported with similar accuracy. To achieve such accuracy, the transition frequency of the (101)–(000) 2 11 –3 12 line of H 2 16 O interfering with the R (0) line had to be precisely determined and is reported with a standard error of 100 Hz at 214904329826.49(10) kHz (relative uncertainty of 5 × 10 −13 ). These measurement sets provide stringent reference values for validating future advances in the theoretical description of the hydrogen (and water) molecule.
•The critical temperature threshold of fracture toughness of CSTBD granite after heating and LN2 cooling treatment is 400 °C.•Under mode-I loading, near the peak load, a high Evm band appears along ...the loading direction.•High temperature causes thermal damage to the rock, and the rapid cooling by LN2 intensifies this damage.•Exceeds 400 °C, the trace of fracture gradually deviates from the straight line, secondary cracks extend.
Liquid nitrogen (LN2) ultra-low temperature fracturing technology has broad application prospects in the storage and transformation of geothermal wells. Therefore, it is of great significance to investigate the fracture toughness of granite samples after elevated temperature treatment and LN2 cooling. In this paper, the Cracked Straight Through Brazilian Disc (CSTBD) granite specimen was heat-treated at different temperatures to study the mode-I fracture toughness of granite after rapid cooling by LN2. Meanwhile, acoustic emission (AE) and digital image correlation (DIC) techniques were used to monitor the deformation and failure process of granite. Our results show that when the heating temperature is more than 400 °C, after LN2 cooling, the internal thermal damage of granite is intensified, the plastic characteristics are gradually enhanced, and the fracture toughness decreases significantly. The DIC results show that, with increasing stress, cracks start to form at the two ends of the pre-crack and propagate to the contact point between the press and rock sample along the loading direction under mode-I loading. Near the peak load, the Von-Mises equivalent strain (Evm) gradually increases, and a high strain band appears along the loading direction. When the heating temperature exceeds 400 °C, the density and width of thermally induced cracks in granite gradually increase after LN2 cooling, the fracture track gradually deviates from the straight line, secondary cracks extend, and the plastic characteristics are enhanced. High temperatures cause thermal damage to the rock, and rapid cooling exacerbates this damage. It can be considered that 400 °C is the critical temperature threshold at which the physical–mechanical behavior and fracture characteristics of CSTBD granite change significantly under the condition of rapid LN2 cooling.
Liquid nitrogen freeze–thaw has been used in oil, shale gas and coalbed methane exploitation as an efficient fracturing technology. This paper aimed to study the effect of different coal ranks and ...liquid nitrogen soaking times on the temperature distribution of coal samples, and to explore the temperature evolution mechanism of different coal ranks during liquid nitrogen soaking. For these objectives, the temperature change process, thermophysical parameters and infrared spectrum of different coal ranks under liquid nitrogen soaking were tested using, respectively, (a) liquid nitrogen soaking temperature measurement, (b) laser thermal instrument and (c) Fourier transform infrared spectrometer. The results showed that the temperature curves of coal samples under liquid nitrogen soaking were divided into an accelerated cooling stage I, a decelerated cooling stage II, and a maintained low-temperature stage III. As the number of liquid nitrogen soaking increased, the time required to reach low-temperature Stage III gradually shortened. During the rise in coal sample temperature, it increased with time in accordance with a logarithmic function. The order of absolute values of maximum heating/cooling speed was lignite > bituminite > anthracite. The higher coal rank is, more oxygen-containing functional groups were removed by coalification. The less content of oxygen-containing functional groups led to closer molecular structure, which resulted in smaller thermal conductivity and ultimately caused slower temperature transfer. The study results are of important guides to understand further the action process and mechanism of liquid nitrogen soaking on coal.
•A new method of high-pressure liquid nitrogen jet for geothermal drilling is proposed.•The conjugate heat transfer method is employed to manage the heat transfer between hot rock and liquid ...nitrogen.•The thermo-physical properties of liquid nitrogen and rocks are considered in detail.•The process of rock breaking coupled with thermal stresses and liquid pressure, is analyzed.•The effect of thermal stresses on rock breaking is validated by a set of experiments.
This paper presents a numerical analysis of heat transfer and thermal stress in bottomhole rocks during geothermal drilling with high-pressure liquid nitrogen jet. The simulation is conducted by a three-dimensional model in transient state. The conjugate heat transfer method is employed to compute heat transfer between solid and liquid. The thermo-physical properties of liquid nitrogen and rocks are considered in detail. The results indicate that high velocity and turbulence kinetic energy of liquid nitrogen jet at impingement surface enhance heat transfer efficiency between cryogenic fluid and hot rock. Huge tensile stress is generated adjacent to the solid-liquid interface, which is favorable for rock breaking on bottomhole. The primitive rock temperature has a significant impact on maximal stress value. A set of experiments is conducted to validate the effects of thermal stresses on rock breakage. The thermal stresses diminish significantly under laboratory conditions without effective constraint on rock boundaries. In our experiments, the coal rather than other types of rock, was selected as working specimen due to its well-developed natural cracks and small tensile strength. Our results would shed light on the geothermal drilling with high-pressure nitrogen jet.
The coupled thermal–mechanical effect in the high-speed machining of hardened steels induces the formation of a surface white layer structure, which adversely affects the mechanical properties and ...service performance of the machined component. However, knowledge about the white layer formation mechanisms is in severe dearth, particularly for high-speed machining under a cryogenic cooling condition. This paper presents an experimental study of the formation mechanisms for surface white layers in high-speed machining of a hardened steel. Both machining with cryogenic liquid nitrogen (LN2) cooling and dry cutting conditions are considered and the characteristics of the white layers formed under the two cooling conditions are compared to reveal the effect of process parameters. It is shown that the hardness of the white layers is increased while their grain size is decreased under the cryogenic LN2 cooling condition as compared to dry cutting. Under both the cooling conditions, no material phase transformation or recrystallization is noticed alongside the white layer formation, but severe plastic deformation is found to be the dominant reason for white layer formation. Tool wear is noticed to increase the white layer thickness. It is shown that during the cutting process, the work material undergoes two stages of intense plastic deformation. In the first stage, the material slips and approaches the first deformation zone, then gradually bulges and produces significant dislocations, and eventually forms a dense dislocation center around the shear plane. In the second stage, part of the material slides toward the tool flank face. The material dislocation slip induced by friction and material shearing further stretches the surface martensite lath bundles to form dislocation tangles and cellular substructures. The highly stretched martensite lath bundles are finally transformed into white layer structure under the interweaving multi-dislocation movement.
The objective of this study is to determine the effect of different barrier positions on the DC breakdown characteristics of liquid nitrogen (LN 2 ), with and without bubbles. The DC breakdown ...voltage is measured of a needle-to-plane electrode, with 9 mm gap distance, with and without PTFE barrier insulation of 40 μm thickness. The presence of bubbles lowers the breakdown voltage and the effect of have the barrier at various distances from the tip of the needle electrode is studied. The results show that with and without bubbles, the closer the barrier to the needle electrode, the higher the breakdown voltage. Observations using a high-speed camera show that the presence of the insulation barrier triggers the breakdown of the LN 2 /insulation barrier composite system.
Lanthanides have been investigated extensively for potential applications in quantum information processing and high-density data storage at the molecular and atomic scale. Experimental achievements ...include reading and manipulating single nuclear spins, exploiting atomic clock transitions for robust qubits and, most recently, magnetic data storage in single atoms. Single-molecule magnets exhibit magnetic hysteresis of molecular origin-a magnetic memory effect and a prerequisite of data storage-and so far lanthanide examples have exhibited this phenomenon at the highest temperatures. However, in the nearly 25 years since the discovery of single-molecule magnets, hysteresis temperatures have increased from 4 kelvin to only about 14 kelvin using a consistent magnetic field sweep rate of about 20 oersted per second, although higher temperatures have been achieved by using very fast sweep rates (for example, 30 kelvin with 200 oersted per second). Here we report a hexa-tert-butyldysprosocenium complex-Dy(Cp
)
B(C
F
)
, with Cp
= {C
H
Bu
-1,2,4} and
Bu = C(CH
)
-which exhibits magnetic hysteresis at temperatures of up to 60 kelvin at a sweep rate of 22 oersted per second. We observe a clear change in the relaxation dynamics at this temperature, which persists in magnetically diluted samples, suggesting that the origin of the hysteresis is the localized metal-ligand vibrational modes that are unique to dysprosocenium. Ab initio calculations of spin dynamics demonstrate that magnetic relaxation at high temperatures is due to local molecular vibrations. These results indicate that, with judicious molecular design, magnetic data storage in single molecules at temperatures above liquid nitrogen should be possible.
Nanostructured metals are usually strong because the ultrahigh density of internal boundaries restricts the mean free path of dislocations. Usually, they are also more brittle because of their ...diminished work-hardening ability. Nanotwinned materials, with coherent interfaces of mirror symmetry, can overcome this inherent trade-off. We show a bulk nanostructuring method that produces a multiscale, hierarchical twin architecture in a hexagonal closed-packed, solute-free, and coarse-grained titanium (Ti), with a substantial enhancement of tensile strength and ductility. Pure Ti achieved an ultimate tensile strength of almost 2 gigapascals and a true failure strain close to 100% at 77 kelvin. The multiscale twin structures are thermally stable up to 873 kelvin, which is above the critical temperature for many applications in extreme environments. Our results demonstrate a practical route to achieve attractive mechanical properties in Ti without involving exotic and often expensive alloying elements.
Understanding quantum tunnelling of the magnetisation (QTM) in single-molecule magnets (SMMs) is crucial for improving performance and achieving molecule-based information storage above liquid ...nitrogen temperatures. Here, through a field- and temperature-dependent study of the magnetisation dynamics of Dy(
BuO)Cl(THF)
BPh
·2THF, we elucidate the different relaxation processes: field-independent Orbach and Raman mechanisms dominate at high temperatures, a single-phonon direct process dominates at low temperatures and fields >1 kOe, and a field- and temperature-dependent QTM process operates near zero field. Accounting for the exponential temperature dependence of the phonon collision rate in the QTM process, we model the magnetisation dynamics over 11 orders of magnitude and find a QTM tunnelling gap on the order of 10
to 10
cm
. We show that removal of Dy nuclear spins does not suppress QTM, and argue that while internal dipolar fields and hyperfine coupling support QTM, it is the dynamic crystal field that drives efficient QTM.
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