With its high latent heat of phase change and suitable phase change temperature, hydrates are emerging cooling medium cold storage. A 4000 L experimental system was firstly developed to investigate ...the mechanism of nucleation and growth, accumulation regularity, and time-varying heat transfer characteristics during the formation and decomposition processes of TBAB hydrates. A novel hydrate bulk phase uniform nucleation and growth characteristics has been discovered. Experiments demonstrated that TBAB hydrate undergoes immediate uniform nucleation, without induction time, once phase equilibrium conditions are reached. Stable formation of TBAB hydrate at approximately 9–10 °C is achievable with subcooling of only 2–3 °C. Moreover, it was clarified that the delamination caused by diffusive deposition of TBAB molecules disappears when the concentration of TBAB reaches 37 wt%. Simultaneously, even after 100 cycles, the stability of hydrate formation is preserved, displaying no signs of decay, while achieving a conversion rate surpassing 90 %. Otherwise, through the analysis of heat transfer characteristics, it was proved that during the hydrate growth process, the heat transfer coefficient decreases by 56 %, and the growth rate decreases by 73 % due to the attachment of hydrates to the heat exchange tubes. This first study provides crucial theoretical for the application of hydrate-based cold storage technology.
•TBAB hydrate is formed stably at 11 °C with a subcooling degree of 1.35 °C.•Hydrate conversion rate is above 90 % and cold storage density at 65 kW·h/m3.•Uniform bulk phase nucleation of hydrates without induction time with no decay•Disappearance of delamination at concentrations above 37 wt%•The heat transfer coefficient decreased by 56 % and heat storage ratio by 73 %.
The exploitation of natural gas hydrate is always hindered by the migration of water and sands due to gas production. Depressurization combined with thermal stimulation is an effective method for ...hydrate dissociation. This paper reported the influence of gas–liquid–solid migration on morphological change of hydrate sediments in natural gas production using visualization method. Different backpressures combined with thermal stimulation methods were applied to simulate natural gas hydrate exploitation. Pressure compensation was first employed to study sediment recovery features. The expansion rate of a porous medium layer under combined dissociation and different backpressure (4.5, 3.5, 2.5, 1.5, and 0.1 MPa) was discussed. A 176% hydrate sediment expansion rate was found after the combined dissociation at 0.1 MPa. In addition, it was observed that the height of the water layer above the porous media after pressure compensation was gradually reduced with a decrease in backpressure and eventually disappeared at 0.1 MPa. It was also found that the disappearing water layer caused an anomalous memory effect phenomenon. Expansion and subsidence of sediments provide a better reference for hydrate exploitation and geological safety.
The study of formation and dissociation of CO
2
hydrate in porous media was characterized by magnetic resonance imaging (MRI) system in
in situ
conditions. This work simulated porous media by using ...glass beads of uniform size. The growth and dissociation habit of CO
2
hydrate was observed under different temperature and pressure conditions. The induction time and the hydrate saturation during the growth and dissociation process in different sizes of porous media were obtained by using the MRI signal intensity. The results indicate that hydrate growth rate and the induction time are affected by the size of porous media, pressure, and degree of supercooling. There are three hydrate growth stages, i.e., initial growth stage, rapid growth stage and steady stage. In this study, the CO
2
hydrate forms preferentially at the surface of vessel and then gradually grows inward. The hydrate tends to cement the glass beads together and occupies the pore gradually. As the hydrate decomposes gradually, the dissociation rate increases to the maximum and then decreases to zero.
The transport properties and differential conductance of the heterostructures constructed by (5,5) single wall carbon nanotube (SWCNT) and (5,5) single wall boron nitride nanotube (SWBNNT) are ...investigated using density functional theory in combination with non-equilibrium Green’s functions. We find that the transmission conductance of (5,5) BN/C nanotube heterostructure is not only continually depressed as the BNNT region increases but also the drop of the conductance is uniform in the energy window (−1.43 eV, 1 eV), which leads to linear I–V dependence for the systems when the bias is within this energy range. Moreover, the differential conductance linearly decreases when
n
≤ 3 but exponentially decreases when
n
≥ 3 for (5,5)(BN)
n
/C heterostructure. Such tunable differential conductance of (5,5) BN/C nanotube heterostructure mainly derives from the blockage of the transport channels induced by the semiconductive BN segment.
Figure
The transmission conductance and differential conductance of (5,5) BN/C nanotube heterostructure is continually depressed as the BNNT region increases.
To simulate the fracture of the coal under impact load, uniaxial pressure test of coal which retrieved from KongZhuang coal mine-DaTun coal and electricity Company of China coal group was done in the ...manner of strain control which rest with a function of uniform variable acceleration. Through researches on the stress-strain relationships and acoustic emission characteristics, the relationship between ring count rate and time series was founded, and the process before failure of coal was divided into four stages: low-level ringing count rate, higher level, highest level and peaceful period. Through the comparison and analysis, it is founded that acoustic emission characteristics in the stage of higher level of ringing count rate can be regarded as a basis for the prediction of coal fracture. According to three obvious rise stages of acoustic emission signal in the process before failure of coal, growth factor of climbing speed is introduced and the values are calculated between 2 to 4, and it is conferred that the value of is proportional to compressive strength of coal and loading rate. It is of great significance for the prediction of coal fracture by acoustic emission characteristics in the stage of new cracks.
Heat treatment was carried out to the 1420 Al-Li alloy electron beam welding (EBW) joints after welding, and the microstructures of welded joints are analyzed systematically before and after ...post-weld heat treatment (PWHT). The observation of joint microstructure demonstrates that the grain morphology of weldment changes from equiaxed dendrites in as-welded (AW) condition into equiaxed grains after PWHT, and that the fine strengthening phases precipitate within the grain. The XRD analysis of phase constituent and TEM observation of weldment indicate that the main strengthening phases in 1420 Al-Li alloy weldment are spheroidal δ′(Al3Li), β′(Al3Zr) and rod-like T(Al2MgLi) after PWHT. Furthermore, the δ′ phase precipitate free zone (PFZ) is found along the grain boundary. The scanning observation of joint fracture shows that Al-Li alloy EBW joint presents the characteristic of transgranular ductile fracture in AW condition. After PWHT, the Al-Li alloy welded joint presents the pattern of intergranular fracture. The variation of fracture mode is related to dispersed precipitation of δ′ phase and the formation of PFZ at the grain boundary in weldment after heat treatment.
The ultimate fracture of rock depends on flows which rock contains, and the process of fracture is nonlinear and unbalanced. Materials like rocks are inhomogeneous, and geometric shapes of crack are ...usually complicated and irregular. The macroscopic fracture of limestone is studied by using SWA-2000 Electro-hydraulic Servo-controlled Rock Mechanics Testing System and fractal geometric methods. The results indicate that the magnitude of confining pressure is related to the fractal dimension, and macroscopic fracture can be described quantitatively by using fractal geometric methods.
Based on general instantaneous strength test and uniaxial creep tests under devastating or integrated states, strain characteristics of mudstone in different stages have been determined. Analyzing ...strain features of mudstone developing in every stage of different tests, evolving creep law of mudstone under uniaxial devastating state may be validated, which axial limited creep strain under the decided loading standard is equal to that value at uniaxial complete strain-stress curve rearwards ultimate strength. Relationship between designed loading stress and its corresponding creep strain can be linear in uniaxial creep test of mudstone under integrated state, while must not be a determinate secant of uniaxial complete strain-stress curve. Studying results present that terminal creep strain of rock with certain loading levels and under devastating state can be only corresponded with an exclusive point of traditional uniaxial complete strain-stress curve rearwards the ultimate strength, and the extended limited creep courses of mudstone will answer for Boltzmann function.
This study analyzes population structure and linkage disequilibrium (LD) among 187 commonly used Chinese maize inbred lines, representing the genetic diversity among public, commercial and ...historically important lines for corn breeding. Seventy SSR loci, evenly distributed over 10 chromosomes, were assayed for polymorphism. The identified 290 alleles served to estimate population structure and analyze the genome-wide LD. The population of lines was highly structured, showing 6 subpopulations: BSSS (American BSSS including Reid), PA (group A germplasm derived from modern U.S. hybrids in China), PB (group B germplasm derived from modern U.S. hybrid in China), Lan (Lancaster Surecrop), LRC (derivative lines from Lvda Reb Cob, a Chinese landrace) and SPT (derivative lines from Si-ping-tou, a Chinese landrace). Forty lines, which formerly had an unknown and/or miscellaneous origin and pedigree record, were assigned to the appropriate group. Relationship estimates based on SSR marker data were quantified in a Q matrix, and this information will inform breeder’s decisions regarding crosses. Extensive inter- and intra-chromosomal LD was detected between 70 microsatellite loci for the investigated maize lines (2109 loci pairs in LD with
D′
> 0.1 and 93 out of them at
P
< 0.01).This suggests that rapidly evolving microsatellites may track recent population structure. Interlocus LD decay among the diverse maize germplasm indicated that association studies in QTLs and/or candidate genes might avoid nonfunctional and spurious associations since most of the LD blocks were broken between diverse germplasm. The defined population structure and the LD analysis present the basis for future association mapping.
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