Liquid Nitrogen Injection Research Articles

Influence of substrate cooling on ion conductivity of tantalum oxide thin films prepared by reactive sputtering using water vapor injection

We studied a reactive sputtering technique that involves substrate cooling with liquid nitrogen and water vapor injection into the substrate surface to deposit Ta2O5 solid electrolyte thin films. The ion conductivities of the tantalum oxide films increased upon substrate cooling, and the maximum conductivities of approximately 10−3 S/m were obtained at substrate temperatures of −120°C and −80°C. The deposition rate increased by substrate cooling and high deposition rates of 30–50 nm/min were obtained at substrate temperatures of −80 °C to −170 °C. According to these results, this sputtering technique is highly effective for improving ion conductivity and the deposition rate of Ta2O5 films.

Applicability of liquid nitrogen fire extinguishing in urban underground utility tunnel

This paper built the experimental platform in the shrinkage-sized circular utility tunnel. A series of experiments were conducted by changing the parameters of liquid nitrogen injection. The feasibility of liquid nitrogen fire extinguishing in utility tunnel was studied. It is found that the main mechanism of liquid nitrogen fire extinguishing is cooling and asphyxiation. Cooling during vaporization can suppress fire rapidly, and the asphyxiation completely extinguishes the flame. During the liquid nitrogen fire extinguishing process, the temperature and the heat flux showed a decreasing trend of fast first and then slow. By increasing the injection rate and time of liquid nitrogen, the process of fire extinguishing can be accelerated and the extinguishing time would be shortened significantly. In addition, it is also found that the critical temperature at the flame of liquid nitrogen fire extinguishing is 230.0 °C, and the critical heat flux at 0.2 m from the flame is 0.20 kW/m2. Not considering oxygen consumption and nitrogen leakage, the critical oxygen volume fraction of liquid nitrogen extinguishing cable fire in utility tunnel is about 15–16%.

Nonlinear L1 adaptive control of stagnation pressure in a cryogenic wind tunnel

Cryogenic wind tunnel is a sophisticated aerodynamics ground test facility, which operates in cryogenic temperature with injection of liquid nitrogen. The multi-variable, nonlinear and coupled dynamics existing between the temperature, pressure and Mach number in the tunnel, poses great challenges for the effective control of the tunnel. L1 adaptive control is a new control methodology developed in recent years with good robustness properties, which has good potentials to address these challenges. But this control method does not provide full adaptive feedforward control in its generic structure. In the paper, adaptive feedforward control action is introduced into the standard L1 adaptive control architecture for nonlinear systems in the presence of matched un-modeled dynamics. This new control structure is applied to the stagnation pressure control in a cryogenic wind tunnel, which could also be used for the control of temperature and Mach number in the tunnel. This new method could effectively compensate known disturbances with linear gain uncertainty, which occur in the nonlinear systems, while retaining the closed-loop control performance of L1 adaptive control. After the proof and discussions on the stability of this method, simulations of the stagnation pressure control in the wind tunnel are presented. The results and analysis demonstrate the effectiveness of the proposed control architecture.

Tribological Effect of Lubricated Liquid Carbon Dioxide on TiAl6V4 and AISI1045 under Extreme Contact Conditions

One of the trends in machining is to reduce the consumption of conventional cutting fluids via the use of alternative cooling-lubrication techniques such as Minimum Quantity Lubrication (MQL) or even move to dry cutting. High friction during machining leads to heat generation, which adversely affects the tool life, workpiece surface quality and energy consumption. Reducing the cooling potential with such options can thus have detrimental effects, especially when difficult-to-machine materials are considered, pushing the end-users to limit the cutting conditions. Cryogenic machining based on the injection of liquid nitrogen (LN) or liquid carbon dioxide (LCO2) emerged over the last decade as a promising sustainable assistance in machining. If the cooling capability is definitely enhanced with both, the lubrication capability has not really been proved and is expected to be highly limited. A recent approach to improve both cooling and lubrication is the use of LCO2 in combination with oil, delivered via minimum quantity lubrication (MQL). However, the actual potential of this technique has not really been investigated from a tribological point of view. The proposed work thus aims at assessing the tribological performance of lubricated liquid carbon dioxide when machining TiAl6V4 and AISI1045 with carbide tools. A specially designed open tribometer has been used to characterize the friction coefficient under different sliding velocities. A novel single-channel MQL-delivery system using lubricated LCO2 has especially been applied to perform experiments under LCO2+MQL conditions but also cryogenic LCO2 and dry conditions for a comparison purpose. Whereas a strong influence could be observed on the AISI1045 with a reduction in terms of friction coefficient when applying LCO2+MQL, neither LCO2 nor LCO2+MQL were able to decrease the friction coefficient on TiAl6V4 compared to dry over all the considered sliding velocities, opening the possibility of further research to understand this specific behaviour.

Pore Structure Characteristics of Taiyuan Formation Shale in Qinshui Basin

Qinshui Basin is located in the southeast of Shanxi Province, China. Taking the shale of Taiyuan Formation in Qinshui Basin as the research object, the study analyzed the pore size of the shale of Taiyuan formation in detail from micropore to macropore by the methods of mercury injection, liquid nitrogen analysis and combination of liquid nitrogen and mercury injection. The results show that: 1) the visible pores and macropores are poorly developed and distributed unevenly in the shale of Taiyuan formation, and the micropores are well developed in the shale, and there are more open pores in the pore diameter range, and the pore connectivity is good; 2) the liquid nitrogen experiment shows that the pores of Taiyuan Shale are relatively developed between 15 nm and 20 nm, and the formation of hysteresis loop may be caused by some narrow slit pores with similar layered structure; 3) the comprehensive analysis of liquid nitrogen and mercury injection experiments shows that the shale of the Taiyuan formation mainly develops micropores, the Mesopores is not developed, the pore volume at 10 - 100 nm is more developed than other parts, and the specific surface is mainly contributed by micropores, which can improve the efficiency of shale gas resolution; at the same time, it provides a channel for Shale gas migration, which is beneficial to the development of shale gas.

Freezing method for rock cross-cut coal uncovering I: Mechanical properties of a frozen coal seam for preventing outburst

A comprehensive technology is proposed to realize fast and safe rock cross-cut coal uncovering (RCCCU) based on artificial freezing engineering method. This comprehensive technology includes four steps, namely, drilling a borehole, wetting the coal body by water injection, gas drainage and freezing the coal seam by liquid nitrogen injection. In this paper, the compressive strength, tensile strength and shear strength of frozen coal specimens are tested to obtain the mechanical parameters of the specimen. Then, for RCCCU under freezing temperatures, the outburst prevention effects are calculated and quantitatively analysed with regard to three aspects, namely, the enhancement of coal the mechanical properties, the reduction in the coefficient of outburst hazard (COH) in the distressed zone and the reduction in the interfacial elastic energy ratio (IEER) between the coal seam and the roof/floor. The results show that a considerable improvement in the mechanical properties of frozen coal and that the coal mechanical parameters, such as the compressive strength and the tensile strength, increase linearly with decreasing temperature. The coefficient of outburst hazard in the distressed zone decreases rapidly and drops from above 0.8 to below 0.3. The interfacial elastic energy ratio is greatly reduced from dozens of times of that of the roof/floor before freezing to several times of that of the roof/floor after freezing, which effectively weakens the sudden change of the elastic energy at the coal-rock interface.

Numerical simulation of liquid nitrogen injection in a container with controlled atmosphere

The effects of recirculation velocity on the volume fraction of oxygen and the temperature distribution in a container with a controlled atmosphere (CA) by liquid nitrogen injection were investigated. A three-dimensional (3-D) model was developed, and the airflow, heat, and mass transfer in the process of liquid nitrogen injection were simulated. A validation test was conducted to verify the accuracy of the model. The results indicate that improving the recirculation velocity will extend the time of liquid nitrogen injection but will reduce the temperature difference in the container and on the surfaces of fruits and vegetables. Different recirculation velocities have little effect on the distribution uniformity of the oxygen volume fraction. The temperature at the holes on the division plate were all above 0 °C when the recirculation velocity was 8 m/s. The results of this study provide a detailed understanding of air transport in a container, which will be useful for the design and optimisation of transportation containers for fruits and vegetables in a CA.

An Experimental Study on the Heat and Mass Transfer of Liquid Nitrogen in a Loose Medium

Liquid nitrogen is a vital medium during the extinguishing and chilldown process of coal spontaneous combustion in coal mine goafs. In this paper, the heat and mass transfer of liquid nitrogen in a loose medium was investigated. A laboratory system including a temperature sensing system was designed and built to explore the effects of different nitrogen injection positions and angles on the chilldown effect. The results indicate that after liquid nitrogen injection, the temperatures in the liquid nitrogen flow area and the bottom of the model can be quickly reduced to −196 °C, which was the best chilldown effect zone. With the vaporization of the liquid nitrogen, the cryogenic nitrogen gradually diffused. At 20,000 s, the bottom temperature was about –63 °C, the middle was –30 °C, and the upper was 0 °C. When the model angle was 0°, the effective chilldown zone was the largest. As the angle increased, the effective chilldown volume and holding time decreased significantly. The model angle had a greater impact on the chilldown. For the position of nitrogen injection, the inlet was set slightly farther from the gas outlet’s position, leading to a larger coverage for the liquid nitrogen and cryogenic nitrogen chilldown. This study can provide a theoretical basis for the flow and chilldown of nitrogen injection in goafs.

Modeling temperature distribution upon liquid-nitrogen injection into a self heating coal mine goaf

Liquid N2 could be injected into goaf to decrease temperature and prevent spontaneous combustion during mining. A working face at Liangbaosi coal mine was adopted for study. Firstly, a mathematical model for calculating the temperature field in goaf was developed and field tests without injection of liquid N2 were conducted to validate the model. Comparable development trends and hot zones between the simulation and field measurements were found. The hot zones were located about 35–45 m behind the workface on the air-return and air-intake sides in the goaf. Then the model was employed to simulate the time development of temperature distribution in the goaf with injection of liquid N2 from different locations. It was observed that a low-temperature cooling zone (<300K) due to injection of liquid N2 gradually grew and became relatively stable 90 min after continuous injection. The size of the cooling zone depends on the injection location and flow rate. The cooling zone was smaller when the N2 was injected from the air-intake side than from the air-return side. The largest cooling zone was found when the N2 was injected 35m behind the workface from the air-return side. The cooling zone increases with increasing N2 perfusion rate. This study provides a quantitative assessment for preventing coal oxidation and spontaneous combustion using the liquid N2 technology.

Forming an ice plug inside a high diameter pipeline in stationary water using a nitrogen vapour exhaust restriction

The ice plug isolation technology is used for repair or maintenance activities conducted on large diameter horizontal pipelines without shutting down the entire thermal-hydraulic installation or its water supply. The amount of information useful in dimensioning the ice plug devices as well as on the operating techniques themselves is extremely scarce. The nitrogen vapour exhaust nozzle diameter is arbitrarily chosen; reducing it by 24 % has an important influence on the ice plugging process. Its influence is more or less dependent on the liquid nitrogen injection technique inside the device. The article contains a brief presentation of the experimental technological facilities used, followed by a series of two experiments performed on a 200 mm diameter testing section using stationary demineralized water under similar temperature and liquid nitrogen supply conditions. At the end of the article, there is a brief result analysis and a few conclusions. The paper is dedicated to specialists working in research and technological engineering.

Mechanical response of ultra-high strength (Grade 1200) steel under extreme cooling conditions

Ultra-high strength steels (UHSS) with nominal yield strength of up to 1200 MPa have many potential applications in engineering fields. However, due to inadequate knowledge on the mechanical behaviour of these materials under extreme loading conditions (e.g. severe temperature changes), their extent of application in civil construction has remained restricted. This paper characterises the mechanical properties of Grade 1200 UHSS under extreme cooling conditions, which is defined as cooling from fire temperatures with an extreme cooling rate or cooling from ambient state to sub-zero temperatures. In order to simulate the extreme cooling rate, UHSS standard dog-bone specimens are heated up to different fire temperatures and cooled to room temperature using water-quenching (WQ) technique. To evaluate the effect of extreme cooling rate on the post-fire mechanical response of the tested materials, the residual mechanical properties of water-quenched specimens are compared to the air-cooled (AC) ones for different fire temperature exposures. For simulation of extreme cooling temperatures, the test specimens are cooled to sub-zero temperatures using Liquid Nitrogen (LN) injection. The changes in the mechanical properties of the tested specimens are then quantified and discussed. In both set of experiments, the mechanical behaviour of UHSS under extreme cooling conditions is compared to the common structural steels. Microstructural evaluation of UHSS tested specimens are also presented using optical and scanning electron microscopy (SEM) techniques.

The effect of liquid nitrogen cooling on coal cracking and mechanical properties

Liquid nitrogen is a type of super-cryogenic fluid, which can cause the reservoir temperature to decrease significantly and thereby induce formation rock damage and cracking when it is injected into the wellbore as fracturing fluid. An experimental set-up was designed to monitor the acoustic emission signals of coal during its contact with cryogenic liquid nitrogen. Ultrasonic and tensile strength tests were then performed to investigate the effect of liquid nitrogen cooling on coal cracking and the changes in mechanical properties thereof. The results showed that acoustic emission phenomena occurred immediately as the coal sample came into contact with liquid nitrogen. This indicated that evident damage and cracking were induced by liquid nitrogen cooling. During liquid nitrogen injection, the ring-down count rate was high, and the cumulative ring-down counts also increased rapidly. Both the ring-down count rate and the cumulative ring-down counts during liquid nitrogen injection were much greater than those in the post-injection period. Liquid nitrogen cooling caused the micro-fissures inside the coal to expand, leading to a decrease in wave velocity and the deterioration in mechanical strength. The wave velocity, which was measured as soon as the sample was removed from the liquid nitrogen (i.e. the wave velocity was recorded in the cooling state), decreased by 14.46% on average. As the cryogenic samples recovered to room temperature, this value increased to 18.69%. In tensile strength tests, the tensile strengths of samples in cooling and cool-treated states were (on average) 17.39 and 31.43% less than those in initial state. These indicated that both during the cooling and heating processes, damage and cracking were generated within these coal samples, resulting in the acoustic emission phenomenon as well as the decrease in wave velocity and tensile strength.

Design and development of a direct injection system for cryogenic engines

The cryogenic engine has received increasing attention due to its promising potential as a zero-emission engine. In this study, a new robust liquid nitrogen injection system was commissioned and set up to perform high-pressure injections into an open vessel. The system is used for quasi-steady flow tests used for the characterisation of the direct injection process for cryogenic engines. An electro-hydraulic valve actuator provides intricate control of the valve lift, with a minimum cycle time of 3 ms and a frequency of up to 20 Hz. With additional sub-cooling, liquid phase injections from 14 to 94 bar were achieved. Results showed an increase in the injected mass with the increase in pressure, and decrease in temperature. The injected mass was also observed to increases linearly with the valve lift. Better control of the injection process, minimises the number of variables, providing more comparable and repeatable sets of data. Implications of the results on the engine performance were also discussed.

Integrated Approaches forExtinguishing the Fire of Coal Pillars in Contiguous Coal Seams

The fire of coal pillars caused by spontaneous combustion in contiguous coal seams at the Dongrong2# colliery in China was examined. The reasons of spontaneous combustion of coal pillars in 16# coal seam were investigated. Based on testing results, the scope of high temperature was judged. To deal with the problem of significant air leakage together with a large fire area and the hidden fire source easily re-ignite, a series of key techniques for extinguishing the fire of coal pillars was put into practice. These mainly included plugging air leakage channel, high-flow injection of liquid nitrogen, and infusion of a large quantity of foam inhibitor into flame locations by drillings. The results showed that these integrated measures rapidly extinguish the fire of coal pillars, reduce carbon monoxide (CO) concentration from 1.6% to about 0.001% and temperature in the closed area of 16# coal seam from 81℃ to less than 20℃. In a word, the fire of coal pillars is successfully controlled in contiguous coal seams, which protect the safety of personnel and equipment.

Mechanical behavior and fracture spatial propagation of coal injected with liquid nitrogen under triaxial stress applied for coalbed methane recovery

Fracturing technology through liquid nitrogen (LN2) injection alters the physical properties of coal and rock masses because of the thermal and pressure effects. In order to investigate heat transfer and fracture propagation behaviors under in situ geological condition with LN2 injections, experimental work was conducted to study the LN2 induced rock/coal failures under true triaxial stress conditions. During the experiments, the temperature, ultrasonic waves, and acoustic emission location detection were monitored to determine the intensity and complexity of specimen failure under singular or cyclic LN2 injections. The results show that a single LN2 injection mainly transfers heat through the solid skeleton and only damages areas adjacent to the injection tube. However, cyclic injections formed a propagated fracture network and the heat can sequentially transfer further along the induced fractures. Moreover, plastic deformation occurred in the entire volume of the sample and the main fractures coalesced until the sample failed. Based on the spatial locations of the acoustic emission sources, the dynamic fracturing within the sample progressed after LN2 injection was clarified. The experimental results can provide evidences for the proposed crack propagation model for the coal masses. The research revealed that high-pressure nitrogen gas transferring liquid water to the tips of new fractures is essential for cyclic LN2 injection to form effective frost-heaving forces and fracturing. Therefore, the fracturing efficiency of the cyclic LN2 injection is far higher than that of singular LN2 injections.

Heat and mass transfer of liquid nitrogen in coal porous media

Liquid nitrogen has been working as an important medium in fire extinguishing and prevention, due to its efficiency in oxygen exclusion and heat removal. Such a technique is especially crucial for coal industry in China. We built a tunnel model with a temperature monitor system (with 36 thermocouples installed) to experimentally study heat and mass transfer of liquid nitrogen in non-homogeneous coal porous media (CPM), and expected to optimize parameters of liquid nitrogen injection in engineering applications. Results indicate that injection location and amount of liquid nitrogen, together with air leakage, significantly affect temperature distribution in CPM, and non-equilibrium heat inside and outside of coal particles. The injection position of liquid nitrogen determines locations of the lowest CPM temperature and liquid nitrogen residual. In the deeper coal bed, coal particles take longer time to reach thermal equilibrium between their surface and inside. Air leakage accelerates temperature increase at the bottom of the coal bed, which is a major reason leading to fire prevention inefficiency. Measurement fluctuation of CPM temperature may be caused by incomplete contact of coal particles with liquid nitrogen flowing in the coal bed. Moreover, the secondary temperature drop (STD) happens and grows with the more injection of liquid nitrogen, and the STD phenomenon is explained through temperature distributions at different locations.

Factors controlling the mechanical properties degradation and permeability of coal subjected to liquid nitrogen freeze-thaw

Freeze-thaw induced fracturing coal by liquid nitrogen (LN2) injection exerts a significant positive effect on the fracture permeability enhancement of the coal reservoir. To evaluate the different freeze-thaw variables which modify the mechanical properties of treated coals, the effects of freezing time, number of freeze-thaw cycles, and the moisture content of coal were studied using combined uniaxial compression and acoustic emission testing systems. Freezing the samples with LN2 for increasing amounts of time degraded the strength of coal within a certain limit. Comparison to freezing time, freeze-thaw cycling caused much more damage to the coal strength. The third variable studied, freeze-thaw damage resulting from high moisture content, was restricted by the coal’s moisture saturation limit. Based on the experimental results, equations describing the amount of damage caused by each of the different freeze-thaw variables were empirically regressed. Additionally, by using the ultrasonic wave detection method and fractal dimension analyses, how freeze-thaw induced fractures in the coal was quantitatively analyzed. The results also showed that the velocity of ultrasonic waves had a negative correlation with coal permeability, and the freeze-thaw cycles significantly augment the permeability of frozen-thawed coal masses.

Boundary-Layer Detection at Cryogenic Conditions Using Temperature Sensitive Paint Coupled with a Carbon Nanotube Heating Layer.

Detection of flow transition on aircraft surfaces and models can be vital to the development of future vehicles and computational methods for evaluating vehicle concepts. In testing at ambient conditions, IR thermography is ideal for this measurement. However, for higher Reynolds number testing, cryogenic facilities are often used, in which IR thermography is difficult to employ. In these facilities, temperature sensitive paint is an alternative with a temperature step introduced to enhance the natural temperature change from transition. Traditional methods for inducing the temperature step by changing the liquid nitrogen injection rate often change the tunnel conditions. Recent work has shown that adding a layer consisting of carbon nanotubes to the surface can be used to impart a temperature step on the model surface with little change in the operating conditions. Unfortunately, this system physically degraded at 130 K and lost heating capability. This paper describes a modification of this technique enabling operation down to at least 77 K, well below the temperature reached in cryogenic facilities. This is possible because the CNT layer is in a polyurethane binder. This was tested on a Natural Laminar Flow model in a cryogenic facility and transition detection was successfully visualized at conditions from 200 K to 110 K. Results were also compared with the traditional temperature step method.

Study and Economic Evaluation on the Process of Calorific Value Adjustment in the LNG Receiving Terminal

In recent years, large quantities of LNG sources have occured in international trade, which have also presented themselves with vary compositions and contain more than 10 mol % light hydrocarbons components (such as ethane and propane).This paper takes a certain typical Chinese liquefied natural gas receiving terminal as an example. For the exchange and economic issues caused by high C2+ components in the feedstock of the above mentioned LNG terminal, an adjustion of the calorific value in products by adopting LH recovery, nitrogen gas injection and liquid nitrogen injection is advised. In order to evaluate profits in LNG receiving terminal, three kinds of processes have been simulated by using of the Aspen HYSYS to realize the consumption analysis. Further more, economic benefits of three schemes are analyzed based on energy measurements. It was shown that the after-tax net profit of the receiving terminal which adds liquid nitrogen to adjust calorific value is 6.17% higher than that which extracts C2+ components under the volume measurement system. Under the system of energy measurement, the after-tax net profit of three processes is respectively increased by 8.96%, 12.51% and 12.47% compared to the original measure modes. The results suggest that the proposed liquid nitrogen injection processes is the most effective one which injects at the exit of high-pressure efflux pump, and an economical way to adjust heat value, which has the highest net profit and the lowest consumption cost and capital cost in the current Chinese LNG industry chain and economic situation.

액체질소를 이용한 강관압입공법의 역학적 수리학적 안정화공법

본 연구에서는 강관압입 공법 적용 시 굴착 선단부에서 수리학적 또는 역학적 불안정으로 인해 발생 가능한 붕괴를 방지하는 목적으로 액체질소를 주입하여 굴착선단부를 안정화하는 공법에 관하여 연구하였다. 강관압입 공법 적용 시 오거 내 중공(中空)에 액체질소 주입관(호스)를 넣어 오거 선단부에 액체질소를 분사하는 방식을 고안하였다. 실내 실험을 위해 직경이 1,000 mm인 강관압입관을 기준으로 1/5축소 모형오거 및 토조를 제작하였다. 화강풍화토로 지반을 조성하여 함수비를 변화시켜가며 액체질소를 주입한 결과 오거 선단부에 동결 구근이 형성되어 강관압입공법 시공 시 발생 가능한 붕괴를 막을 수 있는 것으로 확인되었다. 액체질소를 이용한 동결공법은 지반이 모래일 때 보다는 소성이 있는 화강풍화토일 경우 더 효과적이었으며, 화강풍화토 지반의 경우 함수비가 최적함수비 이상일 경우 동결효율이 증가하는 것을 확인하였다. 액체질소 분사시간이 길어질수록 동결범위가 더 커졌으며 인위적으로 함수비를 급격히 증가시켜 수리학적 불안정을 유발해 보았더니 강관과 오거 전면의 지반이 약 120~300초 이내에 동결 되어 관으로 흙이 유입되지 않았으며, 차수효과가 있는 것으로 분석되었다. 이번 연구에서는 강관압입공법 안정화에 미치는 주요 인자에 대하여 액체질소를 이용하여 강관압입공법 시공 시 역학적 수리학적인 불안정이 발생할 경우, 화강풍화토 지반의 경우 붕괴를 막을 수 있는 효율적인 방법이 될 수 있다는 것을 확인하는데 큰 의의를 둔다. In this study, to prevent possible collapse caused by hydraulic or mechanical instability, liquid nitrogen injection method is developed and implemented at the tip of drilling auger of steel pipe propulsion tunneling. In this study, 1/5-scale model auger and sand chamber were manufactured. The prototype diameter of steel pile (or casing) is assumed about 1,000 mm. For the frictional sandy soils and plastic weathered soils, liquid nitrogen injection methods were tested varying water contents of the soils. For the induced hydraulic instability, the ground near the drilling auger was frozen within approximately 5 minutes preventing mechanical collapse and water infiltration. Securing stability of steel pile propulsion tunneling using liquid nitrogen was much more effective for which the water content of the soil somewhat exceeds the optimum water content.