Liquid nitrogen has shown excellent performances as a good fracturing medium in the extraction of unconventional natural gas,and its application in coalbed methane extraction is currently a research hotspot.This study...Liquid nitrogen has shown excellent performances as a good fracturing medium in the extraction of unconventional natural gas,and its application in coalbed methane extraction is currently a research hotspot.This study focuses on the acoustic emission properties of coal specimens treated utilizing liquid nitrogen with varying initial temperatures in a three-point bending environment.Through examination of the load-displacement curves of the considered coal samples,their mechanical properties are also revealed for different initial temperatures and cycling frequencies.The findings demonstrate a gradual decline in the maximum load capacity of coal rock as the temperature rises.Similarly,when subjected to the same temperature,an escalation in the cycling frequency leads to a reduction in the peak load of coal rock.This suggests that both temperature and cycling frequency exert a notable impact on the fracturing efficacy of liquid nitrogen.Freeze-thaw cycling treatments and exposure to high-temperature conditions can activate preexisting damage in the coal rock,and,accordingly,influence its mechanical properties.In particular,throughout the progressive loading of coal rock samples,the failure mechanisms are predominantly characterized by the occurrence of tensile cracks,succeeded by the development,spread,and fracture of shear fissures.展开更多
This article discusses and analyzes the law of nitrogen increase in liquid steel and the main factors affect-ing the nitrogen increasing of molten steel,through the way of adding nitrogen to molten steel by bottom blo...This article discusses and analyzes the law of nitrogen increase in liquid steel and the main factors affect-ing the nitrogen increasing of molten steel,through the way of adding nitrogen to molten steel by bottom blowing nitrogen gas in LF refining process.It is considered that the main factors affecting the nitrogen increasing instability of molten steel are the initial temperature of LF refining,nitrogen relative element,surface active elements[O]and[S]of steel liquid,and bottom blowing rate of ladle.The large-scale production practice shows that T[O]not more than 50×10-6 and[S]is not more than 0.020 in LF refining at the initial temperature of not less than 1570.The liquid steel nitrogen enrichment test is carried out by ladle bottom blowing nitrogen gas after 20 min of refining,the flow rate is set as(6.0~7.0)NL/min per ton,and it is turned to 2 NL/min at 6 min before the end of refining,the nitrogen increasing rate of liquid steel is basically stable at(5~6)×10-6 per minute.展开更多
Producing complex fracture networks in a safe way plays a critical role in the hot dry rock (HDR) geothermal energy exploitation. However, conventional hydraulic fracturing (HF) generally produces high breakdown press...Producing complex fracture networks in a safe way plays a critical role in the hot dry rock (HDR) geothermal energy exploitation. However, conventional hydraulic fracturing (HF) generally produces high breakdown pressure and results only in single main fracture morphology. Furthermore, HF has also other problems such as the increased risk of seismic events and consuption of large amount of water. In this work, a new stimulation method based on cyclic soft stimulation (CSS) and liquid nitrogen (LN2) fracturing, known as cyclic LN2 fracturing is explored, which we believe has the potential to solve the above issues related to HF. The fracturing performances including breakdown pressure and fracture morphology on granites under true-triaxial stresses are investigated and compared with cyclic water fracturing. Cryo-scanning electron microscopy (Cryo-SEM) tests and X-ray computed tomography (CT) scanning tests were used for quantitative characterization of fracture parameters and to evaluate the cyclic LN2 fracturing performances. The results demonstrate that the cyclic LN2 fracturing results in reduced breakdown pressure, with between 21% and 67% lower pressure compared with using cyclic water fracturing. Cyclic LN2 fracturing tends to produce more complex and branched fractures, whereas cyclic water fracturing usually produces a single main fracture under a low number of cycles and pressure levels. Thermally-induced fractures mostly occur around the interfaces of different particles. This study shows the potential benefits of cyclic LN2 fracturing on HDR. It is expected to provide theoretical guidance for the cyclic LN2 fracturing application in HDR reservoirs.展开更多
The fracturing process of sandstone is inherently complex due to its loose internal structure and deformation adaptability.Liquid nitrogen pre-injection has emerged as a promising approach to damage reservoir rocks,ef...The fracturing process of sandstone is inherently complex due to its loose internal structure and deformation adaptability.Liquid nitrogen pre-injection has emerged as a promising approach to damage reservoir rocks,effectively reducing fracture pressure and establishing intricate fracture networks,thus offering a potential solution for reservoir reconstruction.To unravel the fundamental mechanisms governing sandstone fracturing behaviors following liquid nitrogen pre-injection,sandstone fracturing experiments were conducted under varying durations of liquid nitrogen injection,rock temperature,and in-situ stress conditions.The experiments showcased the evolution of injection pressure and fracture characteristics under different testing conditions,complemented by electron microscope analysis to elucidate the factors driving the complex fracture characteristics of sandstone.The findings revealed a significant decrease in fracture pressure after liquid nitrogen pre-injection,accompanied by a notable increase in the complexity of the fracture network and the roughness of the fracture surface.Moreover,prolonging the duration of liquid nitrogen injection and elevating reservoir temperature further contributed to reducing fracture pressure,consequently enhancing fracture complexity and surface roughness.Conversely,the application of confining pressure amplified fracture pressure while intensifying the degree of fracturing.Notably,the investigation highlighted the increased presence of microcracks in sandstone resulting from liquid nitrogen preinjection,facilitating fluid diffusion during fracturing and yielding lower fracture pressures,thereby enhancing the effectiveness of sandstone reservoir reformation.The research results can provide theoretical guidance for geothermal reservoir reconstruction.展开更多
The efficiency of a new cryoprotectant,GP,for the preservation of Acidithiobacillus ferrooxidans（A.ferrooxidans） strain DC in liquid nitrogen was investigated.The optimal concentration of this new cryoprotectant for...The efficiency of a new cryoprotectant,GP,for the preservation of Acidithiobacillus ferrooxidans（A.ferrooxidans） strain DC in liquid nitrogen was investigated.The optimal concentration of this new cryoprotectant for the maximal viable cell recovery and the highest ferrous ion oxidation activity was determined.The results show that 30%（volume fraction） GP is optimal for the cryopreservation with 84.4% of cells surviving,completely oxidizing ferrous ions within 120 h,and growing to a final density of 5.8×107 cell/mL after 6 d in the culture.Furthermore,the optimal residual GP concentration for viable cell recovery after culture of thawed cells in 9K medium for 6 d is 0.6%（volume fraction）.At this concentration,strain DC completely oxidizes ferrous ions within 108 h and grows to a final cell density of 6.8×107 mL-1.Thus,GP is a simple,effective cryoprotectant for the preservation of A.ferrooxidans strain DC in liquid nitrogen.展开更多
AIM To evaluate the efficacy and safety of liquid nitrogen cryotherapy as a primary or rescue treatment for BE,with and without dysplasia,or intramucosal adenocarcinoma (IMC).METHODS This was a retrospective,single-ce...AIM To evaluate the efficacy and safety of liquid nitrogen cryotherapy as a primary or rescue treatment for BE,with and without dysplasia,or intramucosal adenocarcinoma (IMC).METHODS This was a retrospective,single-center study carried out in a tertiary care center including 45 patients with BE who was treatment-na?ve or who had persistent intestinal metaplasia(IM),dysplasia,or IMC despite prior therapy.Barrett's mucosa was resected via EMR when clinically appropriate,then patients underwent cryotherapy until eradication or until deemed to have failed treatment.Surveillance biopsies were taken at standard intervals.RESULTS From 2010 through 2014,33 patients were studied regarding the efficacy of cryotherapy.Overall,29 patients (88%) responded to cryotherapy,with 84% having complete regression of all dysplasia and cancer.Complete eradication of cancer and dysplasia was seen in 75% of subjects with IMC; the remaining two subjects did not respond to cryotherapy.Following cryotherapy,15 patients with high-grade dysplasia (HGD) had 30% complete regression,50% IM,and 7% low-grade dysplasia (LGD); one subject had persistent HGD.Complete eradication of dysplasia occurred in all 5 patients with LGD.In 5 patients with IM,complete regression occurred in 4,and IM persisted in one.In 136 cryotherapy sessions amongst 45 patients,adverse events included chest pain (1%),stricture (4%),and one gastrointestinal bleed in a patient on dual antiplatelet therapy who had previously undergone EMR.CONCLUSION Cryotherapy is an efficacious and safe treatment modality for Barrett's esophagus with and without dysplasia or intramucosal adenocarcinoma.展开更多
A liquid-nitrogen-cooling friction stir spot welding(C-FSSW) technology was developed for welding AZ31 magnesium alloy sheets. The liquid-nitrogen cooling degraded the deformability of the welded materials such that t...A liquid-nitrogen-cooling friction stir spot welding(C-FSSW) technology was developed for welding AZ31 magnesium alloy sheets. The liquid-nitrogen cooling degraded the deformability of the welded materials such that the width of interfacial cracks increased with increasing cooling time. The grain size of the stirred zone(SZ) and the heat-affected zone(HAZ) of the C-FSSW-welded joints decreased, whereas that of the thermomechanically affected zone(TMAZ) increased with increasing cooling time. The maximum tensile shear load of the C-FSSW-welded joints welded with a cooling time of 5 or 7 s was larger than that of the friction stir spot welding(FSSW)-welded joint, and the tensile shear load decreased with increasing cooling time. The microhardness of the C-FSSW-welded joints was greater than that of the FSSW-welded joint. Moreover, the microhardness of the SZ and the HAZ of the C-FSSW-welded joints increased, whereas that of the TMAZ decreased, with increasing cooling time.展开更多
This article described the characteristics of the liquid nitrogen engine's ideal open cycle.Using two interconnecting strokes to achieve the power output can mitigate the trade-off between high efficiency and the ...This article described the characteristics of the liquid nitrogen engine's ideal open cycle.Using two interconnecting strokes to achieve the power output can mitigate the trade-off between high efficiency and the potential mechanical complexity of multiple-cylinder engines. The total specific energy of the binary media (methane-nitrogen) cycle system could be much higher than the unitary medium (liquid nitrogen) cycle system. By theoretical analysis, the reasonably acceptable driving range proved the feasibility of the liquid nitrogen engine used for supplying power for a lightweight car.展开更多
Multiple size group （MUSIG） model combined with a threedimensional twofluid model were em ployed to predict subcooled boiling flow of liquid nitrogen in a vertical upward tube. Based on the mechanism of boiling heat...Multiple size group （MUSIG） model combined with a threedimensional twofluid model were em ployed to predict subcooled boiling flow of liquid nitrogen in a vertical upward tube. Based on the mechanism of boiling heat transfer, some important bubble model parameters were amended to be applicable to the modeling of liquid nitrogen. The distribution of different discrete bubble classes was demonstrated numerically and the distribu tion patterns of void fraction in the wallheated tube were analyzed. It was found that the average void fraction in creases nonlinearly along the axial direction with wall heat flux and it decreases with inlet mass flow rate and sub cooled temperature. The local void fraction exhibited a Ushape distribution in the radial direction. The partition of the wall heat flux along the tube was obtained. The results showed that heat flux consumed on evaporation is the leading part of surface heat transfer at the rear region of subcooled boiling. The turning point in the pressure drop curve reflects the instability of bubbly flow. Good agreement was achieved on the local heat transfer coefficient aalnst experimental measurements, which demonstrated the accuracy of the numerical model.展开更多
Cryogenic fracturing with liquid nitrogen(LN_(2))offers the benefits of reducing the water consumption and adverse environmental impacts induced by water-based fracturing,as well as potentially enhancing the fracture ...Cryogenic fracturing with liquid nitrogen(LN_(2))offers the benefits of reducing the water consumption and adverse environmental impacts induced by water-based fracturing,as well as potentially enhancing the fracture complexity.We performed a series of laboratory experiments to explore the key mechanisms governing the breakdown pressures of shale during cryogenic fracturing.In this study,cylindrical shale samples were pre-conditioned by exposing a borehole to low-temperature LN_(2) for a certain time period,and then,the samples were fractured using gaseous N_(2) under triaxial stress and a high reservoir temperature.The effects of various key parameters on the breakdown pressure were investigated,including the duration of the low-temperature LN_(2) treatment,the confining pressure,the reservoir temperature,and the direction of the shale bedding relative to the borehole axis.The results demonstrate that the injection of low-temperature LN_(2) as a pre-fracturing fluid into a borehole can significantly reduce the breakdown pressure of the shale during subsequent nitrogen fracturing.This reduction in breakdown pressure can be further intensified by increasing the duration of the LN_(2) pre-conditioning.Without LN_(2) pre-conditioning,the breakdown pressure initially increases and then decreases with increasing reservoir temperature.When LN_(2) pre-conditioning is applied,the breakdown pressure keeps decreasing with increasing reservoir temperature.As the confining pressure increased,the breakdown pressure increased linearly in the tests with and without LN_(2) pre-conditioning.The experimental results demonstrate that LN_(2) preconditioning before N_(2) fracturing is a promising waterless fracturing technique that reduces the breakdown pressure and enhances the fracture complexity.展开更多
Thermal shocking effect occurs when the coalbed methane(CBM)reservoirs meet liquid nitrogen(LN2)of extremely low temperature.In this study,3D via X-ray microcomputer tomography(μCT)and scanning electron microscope(SE...Thermal shocking effect occurs when the coalbed methane(CBM)reservoirs meet liquid nitrogen(LN2)of extremely low temperature.In this study,3D via X-ray microcomputer tomography(μCT)and scanning electron microscope(SEM)are employed to visualize and quantify morphological evolution characteristics of fractures in coal after LN2 thermal shocking treatments.LN2 thermal shocking leads to a denser fracture network than its original state with coal porosity growth rate increasing up to 183.3%.The surface porosity of theμCT scanned layers inside the coal specimen is influenced by LN2 thermal shocking which rises from 18.76%to 215.11%,illustrating the deformation heterogeneity of coal after LN2 thermal shocking.The cracking effect of LN2 thermal shocking on the surface of low porosity is generally more effective than that of high surface porosity,indicating the applicability of LN2 thermal shocking on low-permeability CBM reservoir stimulation.The characteristics of SEM scanned coal matrix in the coal powder and the coal block after the LN2 thermal shocking presented a large amount of deep and shallow progressive scratch layers,fracture variation diversity(i.e.extension,propagation,connectivity,irregularity)on the surface of the coal block and these were the main reasons leading to the decrease of the uniaxial compressive strength of the coal specimen.展开更多
The eutectic ionic liquid （EIL） tetraethyl ammonium bromide-malonic acid （TEAB-Mal） was synthesized, with its structure characterized by the FT-IR spectroscopy and the 1H NMR spectrometry. The performance for remo...The eutectic ionic liquid （EIL） tetraethyl ammonium bromide-malonic acid （TEAB-Mal） was synthesized, with its structure characterized by the FT-IR spectroscopy and the 1H NMR spectrometry. The performance for removal of basic nitrogen compounds by EIL was studied using coker diesel as the feedstock. Experimental results showed that the EIL （TEAB-Mal） exhibited a good denitrogenation performance, leading to a 93.6% of basic N-removal efficiency under reaction conditions covering： a temperature of 30 ℃, an EIL to oil mass ratio of 1：1, an extraction time of 30 min, and a settling time of 120 min, while the basic nitrogen content in diesel dropped from 580 μg/g to 37 gg/g. In addition, the efficiency for extraction of basic N-compounds could still reach 62.9% at am EIL/oil mass ratio of 1：7 after four recycles of the EIL.展开更多
Many kinds of high temperature superconductor （HTS） power machines such as HTS cable, HTS fault current limitcr and HTS magnet are cooled by liquid nitrogen. The level of liquid nitrogen should be monitored and cont...Many kinds of high temperature superconductor （HTS） power machines such as HTS cable, HTS fault current limitcr and HTS magnet are cooled by liquid nitrogen. The level of liquid nitrogen should be monitored and controlled to ensure the thermal stability and the dielectric strength as well. To measure the level, capacitance method and differential pressure method are usually used. However, each method has installation difficulties and measurement errors for unsteady state operation with varying system pressure. A new liquid level meter using a 2G HTS conductor is described, which has similar structure with the liquid helium level meter with NbTi filament. The level meter is fabricated with a parallel connected heater, which helps the separation of the superconducting region and normal region, considering the critical temperature, large heat capacity of conductor and cooling characteristics. The level of liquid nitrogen can be obtained from the measured voltage signal along the 2G HTS conductor. Design, fabrication and test results of the new liquid nitrogen level meter are presented.展开更多
To address the high rock strength and low drilling rate issues in deep oil/gas and geothermal exploitation, we performed mechanical property tests on three kinds of rock samples(granite, shale and sandstone) subjected...To address the high rock strength and low drilling rate issues in deep oil/gas and geothermal exploitation, we performed mechanical property tests on three kinds of rock samples(granite, shale and sandstone) subjected to liquid nitrogen(LN2) cooling and conducted rock-breaking experiments using LN2 jet. Rock-breaking characteristics and mechanisms of LN2 jet, heat transfer features between LN2 and rock and thermal stress evolution in rock were analyzed. A novel high-pressure LN2 jet assisted drilling method was proposed accordingly. The study results show that LN2 thermal shock can significantly reduce uniaxial compression strength and elastic modulus of rock. Rock damage and corresponding mechanical deterioration become more pronounced with increasing rock temperature. The LN2 jet has merits of high rock-breaking efficiency and low threshold rock-breaking pressure. Rock failure under LN2 jet impact is characterized by large volume breakage and the rock-breaking performance becomes more significant with increase of rock temperature. Under the impact of LN2 jet, the damage of granite is the most remarkable among the three rock samples. Thus, this method works better for high temperature granite formations. It has a good application prospect in speeding up drilling rate in deep hot dry rock geothermal reservoirs.展开更多
The kinetics of denitrogenation from liquid steel was studied by using an oxygen-nitrogen analysis system(LECO TC-436) under 1600 degreesC similar to 2813 degreesC conditions. The results show that when [S]=0.005%, ni...The kinetics of denitrogenation from liquid steel was studied by using an oxygen-nitrogen analysis system(LECO TC-436) under 1600 degreesC similar to 2813 degreesC conditions. The results show that when [S]=0.005%, nitrogen removal was controlled by nitrogen transfer in liquid diffusion layer, when [S]=0.012% and 0.140%, it was controlled by both nitrogen transfer in liquid diffusion layer and the chemical reaction at the liquid-gas interface below 2250 degreesC, and by nitrogen transfer in liquid diffusion layer under 2250 degreesC similar to 2813 degreesC conditions. The activation energy E-a was 57 kJ/mol for 0.0050%[S], 95 kJ/mol for 0.012%[S], 165 kJ/mol for 0.140%[S]. The resistance of sulphur on nitrogen removal decreased with the temperature rose, and disappeared at 2630 degreesC. Based on the results obtained, it has been answered why the nitrogen in liquid steel can be decreased rapidly by carbon-oxygen reaction under very high oxygen and sulphur content conditions during the BOF, EAF, VOD and AOD steelmaking processes.展开更多
Removal of air pollutants, such as nitrogen and sulphur containing compounds from a model oil (dodecane) was studied. An ionic liquid (1-ethyl-3-methylimidazolium chloride [C2mim] [Cl]) was used as an extractant. Liqu...Removal of air pollutants, such as nitrogen and sulphur containing compounds from a model oil (dodecane) was studied. An ionic liquid (1-ethyl-3-methylimidazolium chloride [C2mim] [Cl]) was used as an extractant. Liquid-liquid extraction by using 1-ethyl-3-methylimidazolium chloride [C2mim] [Cl] was found to be a very promising method for the removal of N- and S-compounds. This was evaluated by using a model oil (dodecane) with indole as a neutral nitrogen compound and pyridine as a basic nitrogen compound. Dibenzothiophene (DBT) was used as a sulphur compound. An extraction capacity of up to 90 wt% was achieved for the model oil containing pyridine, while only 76 wt% of indole in the oil was extracted. The extraction capacity of a model sulphur compound DBT was found to be up to 99 wt%. Regeneration of the spent ionic liquid was carried out with toluene back-extraction. A 1:1 toluene-to-IL wt ratio was performed at room temperature. It was observed that, for the spent ionic liquid containing DBT as a model compound more than 85 wt% (corresponding 3852 mg/kg) could be removed from the oil. After the second regeneration cycle, 86 wt% of the DBT was recovered from the ionic liquid to toluene. In the case of indole as the nitrogen containing species, more than 99 wt%, (corresponding to 2993 mg/kg) of the original indole was transferred from the model oil to the ionic liquid. After the first-regeneration cycle of the spent ionic liquid, 54 wt% of the indole–in-IL was transferred to toluene. Thus, both extractions of nitrogen and sulphur model compounds were successfully carried out from model oil and the back-extraction of these compounds from the ionic liquids to toluene demonstrated the proved the concept of the regeneration point of view.展开更多
Three kinds of autotrophic bioleaching bacteria strains,including mesophilic and acidophilic ferrous ion-oxidizing bacteria Acidithiobacillus ferrooxidans(A.ferrooxidans),mesophilic and acidophilic sulfur-oxidizing ba...Three kinds of autotrophic bioleaching bacteria strains,including mesophilic and acidophilic ferrous ion-oxidizing bacteria Acidithiobacillus ferrooxidans(A.ferrooxidans),mesophilic and acidophilic sulfur-oxidizing bacteria Acidithiobacillus thiooxidans(A.thiooxidans),and moderately thermophilic sulfur-oxidizing bacteria.4cidianus brierleyi,were cryopreserved in liquid nitrogen and their ferrous ion-or sulfur-oxidizing activities were investigated and compared with the original ones.The results revealed that ferrous ion/sulfur oxidation activities of the strains were almost equal before and after cryopreservation.Glycerin was used as cryoprotective agent.In conclusion,liquid-nitrogen cryopreservation is a simple and effective method for autotrophic bioleaching microorganisms.展开更多
The equations, used in this paper to calculate the surface tension of the liquid nitrogen film formed by the physical adsorption on many different model solids (e.g. spherical partiele, plane particle and spherical ca...The equations, used in this paper to calculate the surface tension of the liquid nitrogen film formed by the physical adsorption on many different model solids (e.g. spherical partiele, plane particle and spherical cavity pores or cylindrical pores at the openings of both ends in solid bodies), have been derived on the thermodynamie principle. The calculated results have shown that the surface tension (γ) of the adsorbed liquid nitrogen film on most of non-porous solid surfaces diminishes with the rise of the nitrogen gas pressure (p) or of the adsorbed layers (n) at 77.3K; when p reaches the vapour pressure (p_s) of the bulk liquid nitrogen, y turns into the surface tension (γ_o) of the bulk liquid nitrogen; whgn p /p, 【0.98, there is an obvious difference between γ and γ_O.展开更多
To illustrate the effect of liquid nitrogen preservation on antigenicity of human homograft aortic valve (HAV), human aortic valve tissue were cocultured together with peripheral blood mononuclear cells (PBMCs). Follo...To illustrate the effect of liquid nitrogen preservation on antigenicity of human homograft aortic valve (HAV), human aortic valve tissue were cocultured together with peripheral blood mononuclear cells (PBMCs). Following detections were done to show the difference of antigenicity of HAV indirectly at different period after being preserved in liquid nitrogen: ① 3H TdR incorporation (cpm) was observed after tissue cell cocultured and stimulation index (SI) was calculated;② Density of IL 2 in medium was measured by MTT means. The results indicated that antigenicity of fresh HAV was the strongest; with the prolong of being preserved, antigenicity decreased gradually. It decreased significantly within first 48 h preserved at 4℃, then decreased significantly after preserved in liquid nitrogen for 24 h. 2 weeks later, antigenicity decreased to the lowest level.展开更多
基金the National Natural Science Foundation(52004285)Fundamental Research Funds for the Central Universities from China University of Mining and Technology-Beijing(JCCXXNY06)the Open Fund of State Key Laboratory Cultivation Base for Gas Geology and Gas Control(Henan Polytechnic University)(WS2021A03).
文摘Liquid nitrogen has shown excellent performances as a good fracturing medium in the extraction of unconventional natural gas,and its application in coalbed methane extraction is currently a research hotspot.This study focuses on the acoustic emission properties of coal specimens treated utilizing liquid nitrogen with varying initial temperatures in a three-point bending environment.Through examination of the load-displacement curves of the considered coal samples,their mechanical properties are also revealed for different initial temperatures and cycling frequencies.The findings demonstrate a gradual decline in the maximum load capacity of coal rock as the temperature rises.Similarly,when subjected to the same temperature,an escalation in the cycling frequency leads to a reduction in the peak load of coal rock.This suggests that both temperature and cycling frequency exert a notable impact on the fracturing efficacy of liquid nitrogen.Freeze-thaw cycling treatments and exposure to high-temperature conditions can activate preexisting damage in the coal rock,and,accordingly,influence its mechanical properties.In particular,throughout the progressive loading of coal rock samples,the failure mechanisms are predominantly characterized by the occurrence of tensile cracks,succeeded by the development,spread,and fracture of shear fissures.
文摘This article discusses and analyzes the law of nitrogen increase in liquid steel and the main factors affect-ing the nitrogen increasing of molten steel,through the way of adding nitrogen to molten steel by bottom blowing nitrogen gas in LF refining process.It is considered that the main factors affecting the nitrogen increasing instability of molten steel are the initial temperature of LF refining,nitrogen relative element,surface active elements[O]and[S]of steel liquid,and bottom blowing rate of ladle.The large-scale production practice shows that T[O]not more than 50×10-6 and[S]is not more than 0.020 in LF refining at the initial temperature of not less than 1570.The liquid steel nitrogen enrichment test is carried out by ladle bottom blowing nitrogen gas after 20 min of refining,the flow rate is set as(6.0~7.0)NL/min per ton,and it is turned to 2 NL/min at 6 min before the end of refining,the nitrogen increasing rate of liquid steel is basically stable at(5~6)×10-6 per minute.
基金supported by the Youth Program of the National Natural Science Foundation of China(52004299)Major Project of the National Natural Science Foundation of China(52192621)+2 种基金the National Science Foundation for National R&D Program for Major Research Instruments of China(51827804)Beijing Outstanding Young Scientist Program(BJJWZYJH01201911414038)the National Science Foundation for Distinguished Young Scholars of China(51725404).
文摘Producing complex fracture networks in a safe way plays a critical role in the hot dry rock (HDR) geothermal energy exploitation. However, conventional hydraulic fracturing (HF) generally produces high breakdown pressure and results only in single main fracture morphology. Furthermore, HF has also other problems such as the increased risk of seismic events and consuption of large amount of water. In this work, a new stimulation method based on cyclic soft stimulation (CSS) and liquid nitrogen (LN2) fracturing, known as cyclic LN2 fracturing is explored, which we believe has the potential to solve the above issues related to HF. The fracturing performances including breakdown pressure and fracture morphology on granites under true-triaxial stresses are investigated and compared with cyclic water fracturing. Cryo-scanning electron microscopy (Cryo-SEM) tests and X-ray computed tomography (CT) scanning tests were used for quantitative characterization of fracture parameters and to evaluate the cyclic LN2 fracturing performances. The results demonstrate that the cyclic LN2 fracturing results in reduced breakdown pressure, with between 21% and 67% lower pressure compared with using cyclic water fracturing. Cyclic LN2 fracturing tends to produce more complex and branched fractures, whereas cyclic water fracturing usually produces a single main fracture under a low number of cycles and pressure levels. Thermally-induced fractures mostly occur around the interfaces of different particles. This study shows the potential benefits of cyclic LN2 fracturing on HDR. It is expected to provide theoretical guidance for the cyclic LN2 fracturing application in HDR reservoirs.
基金supported by the National Key R&D Program of China(2022YFE0128300).
文摘The fracturing process of sandstone is inherently complex due to its loose internal structure and deformation adaptability.Liquid nitrogen pre-injection has emerged as a promising approach to damage reservoir rocks,effectively reducing fracture pressure and establishing intricate fracture networks,thus offering a potential solution for reservoir reconstruction.To unravel the fundamental mechanisms governing sandstone fracturing behaviors following liquid nitrogen pre-injection,sandstone fracturing experiments were conducted under varying durations of liquid nitrogen injection,rock temperature,and in-situ stress conditions.The experiments showcased the evolution of injection pressure and fracture characteristics under different testing conditions,complemented by electron microscope analysis to elucidate the factors driving the complex fracture characteristics of sandstone.The findings revealed a significant decrease in fracture pressure after liquid nitrogen pre-injection,accompanied by a notable increase in the complexity of the fracture network and the roughness of the fracture surface.Moreover,prolonging the duration of liquid nitrogen injection and elevating reservoir temperature further contributed to reducing fracture pressure,consequently enhancing fracture complexity and surface roughness.Conversely,the application of confining pressure amplified fracture pressure while intensifying the degree of fracturing.Notably,the investigation highlighted the increased presence of microcracks in sandstone resulting from liquid nitrogen preinjection,facilitating fluid diffusion during fracturing and yielding lower fracture pressures,thereby enhancing the effectiveness of sandstone reservoir reformation.The research results can provide theoretical guidance for geothermal reservoir reconstruction.
基金Project(2005DKA21208) supported by the R&D Infrastructure and Facility Development Program from the Ministry of Science and Technology of ChinaProject(2010CB630901) supported by the National Basic Research Program of China
文摘The efficiency of a new cryoprotectant,GP,for the preservation of Acidithiobacillus ferrooxidans（A.ferrooxidans） strain DC in liquid nitrogen was investigated.The optimal concentration of this new cryoprotectant for the maximal viable cell recovery and the highest ferrous ion oxidation activity was determined.The results show that 30%（volume fraction） GP is optimal for the cryopreservation with 84.4% of cells surviving,completely oxidizing ferrous ions within 120 h,and growing to a final density of 5.8×107 cell/mL after 6 d in the culture.Furthermore,the optimal residual GP concentration for viable cell recovery after culture of thawed cells in 9K medium for 6 d is 0.6%（volume fraction）.At this concentration,strain DC completely oxidizes ferrous ions within 108 h and grows to a final cell density of 6.8×107 mL-1.Thus,GP is a simple,effective cryoprotectant for the preservation of A.ferrooxidans strain DC in liquid nitrogen.
文摘AIM To evaluate the efficacy and safety of liquid nitrogen cryotherapy as a primary or rescue treatment for BE,with and without dysplasia,or intramucosal adenocarcinoma (IMC).METHODS This was a retrospective,single-center study carried out in a tertiary care center including 45 patients with BE who was treatment-na?ve or who had persistent intestinal metaplasia(IM),dysplasia,or IMC despite prior therapy.Barrett's mucosa was resected via EMR when clinically appropriate,then patients underwent cryotherapy until eradication or until deemed to have failed treatment.Surveillance biopsies were taken at standard intervals.RESULTS From 2010 through 2014,33 patients were studied regarding the efficacy of cryotherapy.Overall,29 patients (88%) responded to cryotherapy,with 84% having complete regression of all dysplasia and cancer.Complete eradication of cancer and dysplasia was seen in 75% of subjects with IMC; the remaining two subjects did not respond to cryotherapy.Following cryotherapy,15 patients with high-grade dysplasia (HGD) had 30% complete regression,50% IM,and 7% low-grade dysplasia (LGD); one subject had persistent HGD.Complete eradication of dysplasia occurred in all 5 patients with LGD.In 5 patients with IM,complete regression occurred in 4,and IM persisted in one.In 136 cryotherapy sessions amongst 45 patients,adverse events included chest pain (1%),stricture (4%),and one gastrointestinal bleed in a patient on dual antiplatelet therapy who had previously undergone EMR.CONCLUSION Cryotherapy is an efficacious and safe treatment modality for Barrett's esophagus with and without dysplasia or intramucosal adenocarcinoma.
基金financially supported by the National Natural Science Foundation of China (No.51375511)the Research Program of Basic Research and Frontier Technology of Chongqing of China (No.cstc2016jcyj A0167)+3 种基金the Science and Technology Project in the Field of Social Development of Shapingba District of Chongqing of China (No.SF201602)the Key Industry Technology Innovation Fund of Science and Technology Development Board of Xiangcheng District of Suzhou of China (No.XJ201608)the Science and Technology Project of Beibei District of Chongqing of China (No.2016-27)the Fundamental and Advanced Technology Research Funds of Chongqing (No.cstc2015jcyjBX0103)
文摘A liquid-nitrogen-cooling friction stir spot welding(C-FSSW) technology was developed for welding AZ31 magnesium alloy sheets. The liquid-nitrogen cooling degraded the deformability of the welded materials such that the width of interfacial cracks increased with increasing cooling time. The grain size of the stirred zone(SZ) and the heat-affected zone(HAZ) of the C-FSSW-welded joints decreased, whereas that of the thermomechanically affected zone(TMAZ) increased with increasing cooling time. The maximum tensile shear load of the C-FSSW-welded joints welded with a cooling time of 5 or 7 s was larger than that of the friction stir spot welding(FSSW)-welded joint, and the tensile shear load decreased with increasing cooling time. The microhardness of the C-FSSW-welded joints was greater than that of the FSSW-welded joint. Moreover, the microhardness of the SZ and the HAZ of the C-FSSW-welded joints increased, whereas that of the TMAZ decreased, with increasing cooling time.
文摘This article described the characteristics of the liquid nitrogen engine's ideal open cycle.Using two interconnecting strokes to achieve the power output can mitigate the trade-off between high efficiency and the potential mechanical complexity of multiple-cylinder engines. The total specific energy of the binary media (methane-nitrogen) cycle system could be much higher than the unitary medium (liquid nitrogen) cycle system. By theoretical analysis, the reasonably acceptable driving range proved the feasibility of the liquid nitrogen engine used for supplying power for a lightweight car.
基金Supported by the National Natural Science Foundation of China （51106119, 81100707）, the Fundamental Research Funds for the Central University of China, Doctoral Fund of Ministry of Education （20110201120052） and the National Science and Technology Sur0orting Item （2012BAA08B03）.
文摘Multiple size group （MUSIG） model combined with a threedimensional twofluid model were em ployed to predict subcooled boiling flow of liquid nitrogen in a vertical upward tube. Based on the mechanism of boiling heat transfer, some important bubble model parameters were amended to be applicable to the modeling of liquid nitrogen. The distribution of different discrete bubble classes was demonstrated numerically and the distribu tion patterns of void fraction in the wallheated tube were analyzed. It was found that the average void fraction in creases nonlinearly along the axial direction with wall heat flux and it decreases with inlet mass flow rate and sub cooled temperature. The local void fraction exhibited a Ushape distribution in the radial direction. The partition of the wall heat flux along the tube was obtained. The results showed that heat flux consumed on evaporation is the leading part of surface heat transfer at the rear region of subcooled boiling. The turning point in the pressure drop curve reflects the instability of bubbly flow. Good agreement was achieved on the local heat transfer coefficient aalnst experimental measurements, which demonstrated the accuracy of the numerical model.
基金This work was supported by the National Natural Science Foundation of China(No.51674247)the project for Fundamental Research Funds for the Central Universities(China University of Mining and Technology)under No.2015XKZD06.
文摘Cryogenic fracturing with liquid nitrogen(LN_(2))offers the benefits of reducing the water consumption and adverse environmental impacts induced by water-based fracturing,as well as potentially enhancing the fracture complexity.We performed a series of laboratory experiments to explore the key mechanisms governing the breakdown pressures of shale during cryogenic fracturing.In this study,cylindrical shale samples were pre-conditioned by exposing a borehole to low-temperature LN_(2) for a certain time period,and then,the samples were fractured using gaseous N_(2) under triaxial stress and a high reservoir temperature.The effects of various key parameters on the breakdown pressure were investigated,including the duration of the low-temperature LN_(2) treatment,the confining pressure,the reservoir temperature,and the direction of the shale bedding relative to the borehole axis.The results demonstrate that the injection of low-temperature LN_(2) as a pre-fracturing fluid into a borehole can significantly reduce the breakdown pressure of the shale during subsequent nitrogen fracturing.This reduction in breakdown pressure can be further intensified by increasing the duration of the LN_(2) pre-conditioning.Without LN_(2) pre-conditioning,the breakdown pressure initially increases and then decreases with increasing reservoir temperature.When LN_(2) pre-conditioning is applied,the breakdown pressure keeps decreasing with increasing reservoir temperature.As the confining pressure increased,the breakdown pressure increased linearly in the tests with and without LN_(2) pre-conditioning.The experimental results demonstrate that LN_(2) preconditioning before N_(2) fracturing is a promising waterless fracturing technique that reduces the breakdown pressure and enhances the fracture complexity.
基金Project(2017XKQY012)supported by the Fundamental Research Funds for the Central Universities,China。
文摘Thermal shocking effect occurs when the coalbed methane(CBM)reservoirs meet liquid nitrogen(LN2)of extremely low temperature.In this study,3D via X-ray microcomputer tomography(μCT)and scanning electron microscope(SEM)are employed to visualize and quantify morphological evolution characteristics of fractures in coal after LN2 thermal shocking treatments.LN2 thermal shocking leads to a denser fracture network than its original state with coal porosity growth rate increasing up to 183.3%.The surface porosity of theμCT scanned layers inside the coal specimen is influenced by LN2 thermal shocking which rises from 18.76%to 215.11%,illustrating the deformation heterogeneity of coal after LN2 thermal shocking.The cracking effect of LN2 thermal shocking on the surface of low porosity is generally more effective than that of high surface porosity,indicating the applicability of LN2 thermal shocking on low-permeability CBM reservoir stimulation.The characteristics of SEM scanned coal matrix in the coal powder and the coal block after the LN2 thermal shocking presented a large amount of deep and shallow progressive scratch layers,fracture variation diversity(i.e.extension,propagation,connectivity,irregularity)on the surface of the coal block and these were the main reasons leading to the decrease of the uniaxial compressive strength of the coal specimen.
基金the financial support from the Doctoral Funds of Liaoning Provincial Natural Science Foundation(201601323)
文摘The eutectic ionic liquid （EIL） tetraethyl ammonium bromide-malonic acid （TEAB-Mal） was synthesized, with its structure characterized by the FT-IR spectroscopy and the 1H NMR spectrometry. The performance for removal of basic nitrogen compounds by EIL was studied using coker diesel as the feedstock. Experimental results showed that the EIL （TEAB-Mal） exhibited a good denitrogenation performance, leading to a 93.6% of basic N-removal efficiency under reaction conditions covering： a temperature of 30 ℃, an EIL to oil mass ratio of 1：1, an extraction time of 30 min, and a settling time of 120 min, while the basic nitrogen content in diesel dropped from 580 μg/g to 37 gg/g. In addition, the efficiency for extraction of basic N-compounds could still reach 62.9% at am EIL/oil mass ratio of 1：7 after four recycles of the EIL.
基金Project supported by the Second Stage of Brain Korea 21 Projects
文摘Many kinds of high temperature superconductor （HTS） power machines such as HTS cable, HTS fault current limitcr and HTS magnet are cooled by liquid nitrogen. The level of liquid nitrogen should be monitored and controlled to ensure the thermal stability and the dielectric strength as well. To measure the level, capacitance method and differential pressure method are usually used. However, each method has installation difficulties and measurement errors for unsteady state operation with varying system pressure. A new liquid level meter using a 2G HTS conductor is described, which has similar structure with the liquid helium level meter with NbTi filament. The level meter is fabricated with a parallel connected heater, which helps the separation of the superconducting region and normal region, considering the critical temperature, large heat capacity of conductor and cooling characteristics. The level of liquid nitrogen can be obtained from the measured voltage signal along the 2G HTS conductor. Design, fabrication and test results of the new liquid nitrogen level meter are presented.
基金Supported by National Science Fund for Distinguished Young Scholars(NO.51725404)Program of Introducing Talents of Discipline to Chinese Universities(NO.B17045)National Natural Science Foundation of China(NO.51521063)
文摘To address the high rock strength and low drilling rate issues in deep oil/gas and geothermal exploitation, we performed mechanical property tests on three kinds of rock samples(granite, shale and sandstone) subjected to liquid nitrogen(LN2) cooling and conducted rock-breaking experiments using LN2 jet. Rock-breaking characteristics and mechanisms of LN2 jet, heat transfer features between LN2 and rock and thermal stress evolution in rock were analyzed. A novel high-pressure LN2 jet assisted drilling method was proposed accordingly. The study results show that LN2 thermal shock can significantly reduce uniaxial compression strength and elastic modulus of rock. Rock damage and corresponding mechanical deterioration become more pronounced with increasing rock temperature. The LN2 jet has merits of high rock-breaking efficiency and low threshold rock-breaking pressure. Rock failure under LN2 jet impact is characterized by large volume breakage and the rock-breaking performance becomes more significant with increase of rock temperature. Under the impact of LN2 jet, the damage of granite is the most remarkable among the three rock samples. Thus, this method works better for high temperature granite formations. It has a good application prospect in speeding up drilling rate in deep hot dry rock geothermal reservoirs.
文摘The kinetics of denitrogenation from liquid steel was studied by using an oxygen-nitrogen analysis system(LECO TC-436) under 1600 degreesC similar to 2813 degreesC conditions. The results show that when [S]=0.005%, nitrogen removal was controlled by nitrogen transfer in liquid diffusion layer, when [S]=0.012% and 0.140%, it was controlled by both nitrogen transfer in liquid diffusion layer and the chemical reaction at the liquid-gas interface below 2250 degreesC, and by nitrogen transfer in liquid diffusion layer under 2250 degreesC similar to 2813 degreesC conditions. The activation energy E-a was 57 kJ/mol for 0.0050%[S], 95 kJ/mol for 0.012%[S], 165 kJ/mol for 0.140%[S]. The resistance of sulphur on nitrogen removal decreased with the temperature rose, and disappeared at 2630 degreesC. Based on the results obtained, it has been answered why the nitrogen in liquid steel can be decreased rapidly by carbon-oxygen reaction under very high oxygen and sulphur content conditions during the BOF, EAF, VOD and AOD steelmaking processes.
文摘Removal of air pollutants, such as nitrogen and sulphur containing compounds from a model oil (dodecane) was studied. An ionic liquid (1-ethyl-3-methylimidazolium chloride [C2mim] [Cl]) was used as an extractant. Liquid-liquid extraction by using 1-ethyl-3-methylimidazolium chloride [C2mim] [Cl] was found to be a very promising method for the removal of N- and S-compounds. This was evaluated by using a model oil (dodecane) with indole as a neutral nitrogen compound and pyridine as a basic nitrogen compound. Dibenzothiophene (DBT) was used as a sulphur compound. An extraction capacity of up to 90 wt% was achieved for the model oil containing pyridine, while only 76 wt% of indole in the oil was extracted. The extraction capacity of a model sulphur compound DBT was found to be up to 99 wt%. Regeneration of the spent ionic liquid was carried out with toluene back-extraction. A 1:1 toluene-to-IL wt ratio was performed at room temperature. It was observed that, for the spent ionic liquid containing DBT as a model compound more than 85 wt% (corresponding 3852 mg/kg) could be removed from the oil. After the second regeneration cycle, 86 wt% of the DBT was recovered from the ionic liquid to toluene. In the case of indole as the nitrogen containing species, more than 99 wt%, (corresponding to 2993 mg/kg) of the original indole was transferred from the model oil to the ionic liquid. After the first-regeneration cycle of the spent ionic liquid, 54 wt% of the indole–in-IL was transferred to toluene. Thus, both extractions of nitrogen and sulphur model compounds were successfully carried out from model oil and the back-extraction of these compounds from the ionic liquids to toluene demonstrated the proved the concept of the regeneration point of view.
基金Project(50621063)supported by Chinese Science Foundation for Distinguished GroupProject(2004CB619201)supported by the National Basic Research Program of China
文摘Three kinds of autotrophic bioleaching bacteria strains,including mesophilic and acidophilic ferrous ion-oxidizing bacteria Acidithiobacillus ferrooxidans(A.ferrooxidans),mesophilic and acidophilic sulfur-oxidizing bacteria Acidithiobacillus thiooxidans(A.thiooxidans),and moderately thermophilic sulfur-oxidizing bacteria.4cidianus brierleyi,were cryopreserved in liquid nitrogen and their ferrous ion-or sulfur-oxidizing activities were investigated and compared with the original ones.The results revealed that ferrous ion/sulfur oxidation activities of the strains were almost equal before and after cryopreservation.Glycerin was used as cryoprotective agent.In conclusion,liquid-nitrogen cryopreservation is a simple and effective method for autotrophic bioleaching microorganisms.
文摘The equations, used in this paper to calculate the surface tension of the liquid nitrogen film formed by the physical adsorption on many different model solids (e.g. spherical partiele, plane particle and spherical cavity pores or cylindrical pores at the openings of both ends in solid bodies), have been derived on the thermodynamie principle. The calculated results have shown that the surface tension (γ) of the adsorbed liquid nitrogen film on most of non-porous solid surfaces diminishes with the rise of the nitrogen gas pressure (p) or of the adsorbed layers (n) at 77.3K; when p reaches the vapour pressure (p_s) of the bulk liquid nitrogen, y turns into the surface tension (γ_o) of the bulk liquid nitrogen; whgn p /p, 【0.98, there is an obvious difference between γ and γ_O.
文摘To illustrate the effect of liquid nitrogen preservation on antigenicity of human homograft aortic valve (HAV), human aortic valve tissue were cocultured together with peripheral blood mononuclear cells (PBMCs). Following detections were done to show the difference of antigenicity of HAV indirectly at different period after being preserved in liquid nitrogen: ① 3H TdR incorporation (cpm) was observed after tissue cell cocultured and stimulation index (SI) was calculated;② Density of IL 2 in medium was measured by MTT means. The results indicated that antigenicity of fresh HAV was the strongest; with the prolong of being preserved, antigenicity decreased gradually. It decreased significantly within first 48 h preserved at 4℃, then decreased significantly after preserved in liquid nitrogen for 24 h. 2 weeks later, antigenicity decreased to the lowest level.
