Mass Flow Rate Of Nitrogen Research Articles

Factor analysis and GA-BP-ANN prediction of nitrogen diffusion behavior in underground laboratory under ventilation conditions

Nitrogen is widely used in various laboratories as a suppressive gas and a protective gas. Once nitrogen leaks and accumulates in a such confined space, it will bring serious threats to the experimental staff. Especially in underground tunnels or underground laboratories where there is no natural wind, the threat is more intense. In this work, the ventilation design factors and potential leakage factors are identified by taking the leakage and diffusion of a large liquid nitrogen tank in China Jinping Underground Laboratory (CJPL) as an example. Based on computational fluid dynamics (CFD) research, the effects of fresh air inlet position, fresh air velocity, exhaust outlet position, leakage hole position, leakage hole size, and leaked nitrogen mass flow rate on nitrogen diffusion behavior in specific environments are discussed in detail from the perspectives of nitrogen concentration field and nitrogen diffusion characteristics. The influencing factors are parameterized, and the Latin hypercube sampling (LHS) is used to uniformly sample within the specified range of each factor to obtain samples that can represent the whole sample space. The nitrogen concentration is measured by numerical value, and the nitrogen diffusion characteristics are measured by category. The GA-BP-ANN numerical regression and classification regression models for nitrogen concentration prediction and nitrogen diffusion characteristics prediction are established. By using various rating indicators to evaluate the performance of the trained model, it is found that models have high accuracy and recognition rate, indicating that it is effective in predicting and determining the concentration value and diffusion characteristics of nitrogen according to ventilation factors and potential leakage factors. The research results can provide a theoretical reference for the parametric design of the ventilation system.

A micromachined Joule-Thomson cryocooler for ice lithography

A micromachined Joule-Thomson cryocooler has been designed as a cryostage for ice lithography, which allows high-pressure nitrogen throttling to liquefy and fast cool samples with low vibration. The sample can be cooled down to 99.5 K in 30 min and then heated up to room temperature in 10 min. Compared with previous cooling systems based on liquid nitrogen, the Joule-Thomson cryostage has resulted in a significant 90% reduction in cooling time and a decrease in operating temperature by 30 K. Besides, the nitrogen mass-flow rate beneath the sample remains <20 mg/s to minimize vibration. The measured peak-to-peak amplitude at the minimum temperature is about 5.6 nm. As the first cooler integration within an ice lithography system, this Joule-Thomson cryostage not only enables the exploration of a wider range of ice resists, but also can be applied in kinds of microscopes for helping characterize materials at cryogenic temperatures.

LNG 기화열을 이용한 수조 수온 냉각성능에 관한 실험적 연구

In this study, a heat transfer performance experiment was conducted by experimentally testing the vaporization process of liquefied natural gas (LNG) using a seawater vaporizer and the process of supplying cooled seawater to the aquaculture tank. By using liquid nitrogen instead of LNG, we experimentally analyzed changes in tank water temperature according to changes in liquid nitrogen supply mass flow rate, water supply mass flow rate, and injection angle of the aquaculture tank nozzle. When testing was conducted by fixing the water mass flow rate at 0.05 kg/s and changing the liquid nitrogen mass flow rate to 0.0058 kg/s, 0.0075 kg/s, and 0.0092 kg/s, the target temperature of 17°C was reached under the experimental condition of 0.0092 kg/s.&#x0D; When the water supply mass flow rate was set to 0.05 kg/s, 0.07 kg/s, 0.08 kg/s, and 0.10 kg/s at the constant mass flow rate of liquid nitrogen of 0.0092 kg/s, the target temperature of 17°C was reached under the experimental condition of 0.07 kg/s. When the angle of the water nozzle was adjusted to 0°, 30°, and 60°, the fastest way to reach the target temperature of 17°C was the 0° experimental condition in which water was injected tangentially to the water tank.

Investigation of Heat Transfer Regimes in Subsonic Dissociated-Nitrogen Jets of a High-Frequency Induction Plasmatron under Additional Surface Heating by Laser Radiation

The heat transfer to a cylindrical water-cooled copper model was experimentally investigated in an induction VGU-4 high-frequency (HF) plasmatron of the Institute for Problems in Mechanics of the Russian Academy of Sciences. The model, 30 mm in diameter, equipped with a calorimetric transducer with a heat-adsorbing graphite surface, 13.8 mm in diameter, was exposed to the surface heating in the combined regime by nitrogen plasma and laser radiation and in the cases of the heating with only laser radiation or a nitrogen plasma jet. The experiments in the HF-plasmatron jets were performed at the pressure in the setup low-pressure chamber p = 1 × 104 Pa, nitrogen mass flow rate G = 2.4 g/s, and the plasmatron HF-generator anode power Na.p. = 22 kW. It is established that in the chosen experimental regimes the dissociated-nitrogen jet and the high-frequency induction discharge do not produce a considerable effect on the laser beam passing through them. The values of the heat flux density are obtained as functions of the laser radiation power delivered. The subsonic nitrogen plasma flow in the quartz discharge channel and in the low-pressure chamber of the VGU-4 setup is numerically modeled under the experimental conditions basing on the solution of the complete Navier–Stokes equations using the Patankar–Spalding method.

Thermo-economic analysis and multi-objective optimization of solar aided pumped thermal electricity storage system

The concept of solar energy aided pumped thermal electricity storage (Solar-PTES) was proposed to improve the round-trip efficiency, as well as the solar energy utilization efficiency. The thermodynamic model was developed for such Solar-PTES system with the nominal electricity input of 5 MW and the nominal storage capacity of 6 equivalent hours. Taking the round-trip efficiency, energy density and levelized cost of storage as indicators for system performance, the effects of main design parameters were investigated, including that of main components performance parameters and cycle state parameters. The multi-objective optimization algorithm was applied for optimizing three performance metrics and the trade-off analysis was performed. The results indicates that the round-trip efficiency drops with the growing energy density, while the levelized cost of storage firstly decreases as the round-trip efficiency drops and then slightly rises. The minimum case of levelized cost of storage is selected for investigation. In that case, solar heat input is 5.05 MW and solar energy utilization efficiency of Solar-PTES system is 35.7 %. The nitrogen mass flow rate is 27.54 kg/s. The round-trip efficiency, energy density and levelized cost of storage for Solar-PTES system are 68.1 %, 16.63 kWh/m3 and 0.143 ± 0.023 $/kWh, respectively.

Impact of n-butanol substitution in ethylene on soot yields in laminar diffusion flames at pressures 3 to 10 bar

Bioalcohols are perceived to be cleaner burning fuels and generally are assumed to be soot suppressants when blended with hydrocarbon fuels. Butanol isomers display some superior physical and chemical properties as compared to methanol and ethanol, and could be blended with hydrocarbon based transportation fuels without substantial modifications in engine hardware. However, the controversy in the literature about the influence of lower alcohols on soot when blended with hydrocarbons at various proportions has not been resolved yet. Further, there is a lack of information on the dependence of soot production on pressure obtained from tractable flames of butanol-hydrocarbon blends. Such benchmark information on the behaviour of soot characteristics at elevated pressures would be helpful to facilitate a better interpretation of the soot emissions from engines fuelled with butanol-hydrocarbon blends as well as providing data that could be used for numerical simulation efforts. Soot volume fractions and temperature fields of laminar coflow diffusion flames of a nitrogen-diluted ethylene base fuel and of the base fuel doped with 10% n-butanol were measured at operating pressures of 3, 5, 8 and 10 bar in a high-pressure chamber with optical access. Radially resolved temperatures and soot volume fractions were inferred from spectrally resolved radiation emitted by soot from the flames, stabilized on a 3 mm diameter burner, in which carbon and nitrogen mass flow rates in the fuel stream were kept constant. Maximum soot yield decreased by about 25% to 45% when 10% of the carbon in the fuel stream is provided by n-butanol throughout the pressure range; although local enhancements in soot production were observed at 3 bar. However, increases in local soot production disappeared when the pressure is increased to 8 and 10 bar. Current results were compared to ethanol substitution in the same base fuel under identical conditions.

Experimental investigation on an R290-based organic Rankine cycle utilizing cold energy of liquid nitrogen

Organic Rankine cycle (ORC) has been widely used to utilize low-grade waste heat from low, medium, and high-temperature heat sources. Meanwhile, the research of the ORC operates in the cryogenic temperature has also attracted much attention due to the increasing requirement of liquid natural gas (LNG). However, there is still a lack of experimental research on the cryogenic ORC. In this paper, the experimental study of a cryogenic ORC using a semi-hermetic scroll expander and propane (R290) has been investigated. Liquid nitrogen is used as the cryogenic cold source in this system while the circulation water is used to simulate the low-grade waste heat. The system performance of utilizing the cold energy of the liquid nitrogen and thermal energy of the circulation water has been investigated. First, the effects of the evaporation pressure and pressure drop on system performance are examined. Moreover, the system performance between the regenerative organic Rankine cycle (RORC) and basic organic Rankine cycle (BORC) has been compared. The experimental results indicate that evaporation pressure has a significant effect on system performance, and different optimum evaporation pressure will be obtained under different liquid nitrogen mass flow rates. The maximum electrical power 673.59 W, system thermal efficiency 6.78%, and cold energy utilization efficiency 12.32% can be obtained, while the evaporation pressure and liquid nitrogen mass flow rate are 1.36 MPa and 120 kg/h, respectively. What’s more, the results also indicate that the pressure drop exhibits a high sensitivity on system performance, and there is a clear linear proportional relationship between pressure drop and electrical power. Furthermore, the comparison results show that RORC has a better system performance than BORC. The experimental results provide design and optimal operation strategy for the cryogenic organic Rankine cycle.

Experimental study on power generation plant of a 1 kW small‐scale Organic Rankine Cycle system using R290

AbstractThis work presents an experimental investigation of a small‐scale cryogenic Organic Rankine Cycle (ORC) power generation plant for cold energy utilization using scroll expander and R290. The fresh water and liquid nitrogen were used as heat source and heat sink, respectively. Furthermore, expander gross output power and isentropic efficiency, system thermal efficiency, and cold energy utilization efficiency were calculated as a principle to evaluate the overall system performance. The experimental results demonstrate that increasing pressure drop and heat source temperature will benefit the system performance in some extent, and the pressure drop exhibits a relative sensitivity to heat source temperature about the system performance. Moreover, the expander gross output power will get the peak value while the heat source and heat sink in the best matching. When the mass flow rate of liquid nitrogen at 120 kg/h, optimum pressure drop is 1.02 Mpa, and the corresponding expander gross output power, thermal efficiency, and cold energy utilization efficiency were 638.2W, 0.0586, and 0.0976, respectively. The optimum heat source temperature is 50℃ under liquid nitrogen mass flow rate of 120 kg/h, and the corresponding expander gross output power, thermal efficiency, and cold energy utilization efficiency were 674.2 W, 0.0594, and 0.099, respectively.

Experimental and numerical investigations on flow field characteristics of pintle injector

The objective of this study is to investigate the mechanism of mixing and atomization of pintle injectors numerically and experimentally using water and nitrogen. During the experiments, three cases with identical water injection condition and different nitrogen mass flow rate were performed. The nitrogen injection velocity was adjusted by changing the cross section of the exit gap. In other words, three cases with different gas/liquid momentum ratio and Weber number were analyzed. Meanwhile, simulations consistent with test conditions were conducted to compare with the experimental data. High-speed imaging was applied to capture of the movement of the flow field. In order to obtain the atomization cone angles, a series of image processing algorithms named principal component analysis (PCA) and region growing were adopted. Conclusions can be drawn that both the experimental and numerical results show a decrease tendency of atomization cone angle with the increase of gas/liquid momentum ratio. The PCA and region growing method was verified to be feasible and accurate for calculating atomization cone angle. The distribution characteristics of Sauter mean diameter (SMD) are determined together by Weber number and gas/liquid momentum ratio. Increasing the Weber number will help to reduce SMD and make its distribution more uniform. However, the SMD near the axis line is relatively large in the case of large momentum ratio.

Effect of mass flow rate on gas propagation after vacuum break in a liquid helium cooled tube.

Vacuum break in particle accelerators is a major concern due to risks associated with personnel and extensive equipment damage. Continuing research in our lab focuses on the sudden loss of vacuum in the liquid helium cooled beam-line tubes of superconducting particle accelerators. In our previous research, we studied nitrogen gas propagation in a uniform tube system immersed in both normal helium (He I) and superfluid helium (He II). It was observed that He II has a stronger effect in slowing down the gas propagation compared to He I, but this effect was largely due to the variation of the point where condensation and deposition of the nitrogen gas on the tube inner wall. Here, we discuss our modifications to the tube system that now allow us to accurately control the starting location of gas condensation in both the He I and He II experiments. Systematic studies of gas propagation were conducted using this new tube system by varying the nitrogen mass flow rate at the tube inlet.

Experimental investigation on heat transfer characteristics of supercritical nitrogen in a heated vertical tube

The rapid variations of physical properties near the pseudocritical points and the unique heat transfer and resistance characteristics of supercritical fluids have gained a great deal of attentions in recent years. In this paper, the heat transfer characteristics of supercritical nitrogen in a heated vertical tube are investigated experimentally. The test section is an aluminum alloy tube of 6.6 m in length and 0.02 m in inner diameter with a wall thickness of 0.0085 m. The effects of different operating parameters, including pressure and mass flow rate of nitrogen, inlet temperature and mass flow rate of water, on the heat transfer characteristics are investigated. Meanwhile, the experimental data are compared with the predict values by different existing correlations, and all of them show large differences. Therefore, a new correlation has been developed to accurately predict the heat transfer coefficient based on the experimental data. The new correlation works well with 95% of the experimental data captured with a deviation of 20%. The experimental study and the new correlation may provide reference for the study of the heat transfer of supercritical fluid flow and design and operation of open rack vaporizer (ORV).

LNG boil-off gas reliquefaction by Brayton refrigeration system – Part 2: Improvements over basic configuration

Exergy analysis of reliquefaction system based on Reverse Brayton cycle (RBC), which is used to condense boil-off gas (BOG) generated in LNG carrier ships, was presented with its basic configuration in Part 1. In this paper, three modifications of the basic system are evaluated. One modification is based on intercooling and precooling of BOG before compressor suction. Others involve ambient compression of BOG. Effects of pressure ratio of RBC, mass flow rate of nitrogen, thermal sizes of heat exchangers and entry temperature of BOG to reliquefaction system on each configuration have been evaluated. Sensitivity analysis shows that 7.8% improvement of rational exergy efficiency is obtained for systems with ambient compression. When BOG enters as superheated gas, modified configurations could keep up their performance while basic system deteriorated. Higher adiabatic efficiencies of compressors and turbines improve the performance of the reliquefaction systems across the board without any additional weight or space. Design and operating parameters have been optimized with the aid of in-built optimiser tool of Aspen HYSYS® V8.6. It resulted in an improvement of rational exergy efficiency of configurations by 1%–3% and decrease of total UA by 5–7% compared to best values predicted by sensitivity analysis.

Experimental Investigation of two-phase nitrogen Cryo transfer line

A 6-m long liquid nitrogen based cryo transfer line has been designed, developed and tested at IPR. The test objectives include the thermo-hydraulic characteristics of Cryo transfer line under single phase as well as two phase flow conditions. It is always easy in experimentation to investigate the thermo-hydraulic parameters in case of single phase flow of cryogen but it is real challenge when one deals with the two phase flow of cryogen due to availibity of mass flow measurements (direct) under two phase flow conditions. Established models have been reported in the literature where one of the well-known model of Lockhart-Martenelli relationship has been used to determine the value of quality at the outlet of Cryo transfer line. Under homogenous flow conditions, by taking the ratio of the single-phase pressure drop and the two-phase pressure drop, we estimated the quality at the outlet. Based on these equations, vapor quality at the outlet of the transfer line was predicted at different heat loads. Experimental rresults shown that from inlet to outlet, there is a considerable increment in the pressure drop and vapour quality of the outlet depending upon heat load and mass flow rate of nitrogen flowing through the line.

Experimental analysis of velocity slip at the wall for gas flows of nitrogen, R134a, and R600a through a metallic microtube

This paper reports measurements of mass flow rate of nitrogen, R134a, and R600a through a commercially available stainless steel microtube, which closely reproduces the case of gas leakage through micrometric clearances found in compressor valves. The accuracy of the measurements in the whole rarefaction range considered was verified through comparisons with predictions from the BGK kinetic model and results from the Navier–Stokes equations with modified boundary conditions. Furthermore, values of the tangential momentum accommodation coefficient (TMAC) were obtained by using an analytical approach derived from the solution of the Navier–Stokes equations with modified second-order boundary conditions. An incomplete accommodation is observed for all gases, with α = 0.933 ± 0.004 for nitrogen, 0.956 ± 0.004 for R134a, and 0.974 ± 0.008 for R600a. The results for all gases were very similar, indicating that the gas chemical composition does not significantly affect the flow through microtubes with rough internal surfaces, even when heavy polyatomic molecules are considered.

Correlation between film structures and potential limits for hydrogen and oxygen evolutions at a-C:N film electrochemical electrodes

A correlation between film structures and the width of the potential windows defined by the dihydrogen and dioxygen evolutions in aqueous media at nitrogen-doped amorphous carbon thin film electrodes prepared using a filtered cathodic vacuum arc system is reported. A range of film structures were obtained by changing the nitrogen mass flow rate during deposition, and the film structures were determined using electron energy-loss spectroscopy. For the film electrodes, the width of the potential windows in 0.1 M NaOH and in 0.1 M H 2SO 4 at a current density of 100 μA/cm 2 exceed those for glassy carbon electrodes, and increase with an increase in the sp 3 C fraction in the a-C:N materials. A film electrode with a rich sp 2 C content, has a lower electrical resistance, but still possesses a relatively large potential window. These features combined allow the materials to be tailored for particular electroanalysis.

Deacidification and recovery of distillates in the physical refining of edible oils

AbstractA pilot plant‐scale continuous deodorization installation was developed to simultaneously test several technological changes in the classical deodorization process: use of nitrogen as stripping gas, heating of the gas above the liquid oil, and use of shell‐and‐tube condensers for the recovery of distillates. Deacidification trials were first carried out on mixtures of commercial refined sunflower oil and high‐oleic distillates, and subsequently on bleached olive and sunflower oils. The performance of usual working conditions was analyzed: nitrogen mass flow rate, oil temperature and oil mass flow rate. Marked differences were not observed in the results of the final acidity, compositions of free fatty acids and sterols in the deacidified oil. However, the use of shell‐and‐tube condensers makes it possible to recover liquid distillates in better conditions than in the classical process for their further concentration, while at the same time reducing process pollution.

2408 ガスバリア膜の被覆によるステンレス鋼の高温酸化特性の改善(S09-2 新表面改質技術と界面,環境,S09 表面改質)

Stainless steel is widely used as a corrosion-resistant material. However, stainless steel corrodes at high temperature (573K〜) due to the oxidization and grain boundary corrosion. To delay the oxidation at high temperature, coating of gas barrier film will be useful method. The purpose of this study is to improve the corrosion-resistant of SUS304 at high temperature by coating transparent SiO_xN_y film which has gas barrier properties. In addition, the influence of inlet nitrogen mass flow rate ratio (N_2/Ar+N_2) on the oxidation properties at 773K and on the state of a chemical bond were examined. The SiO_xN_y films were deposited onto polished SUS304 by unbalanced dc magnetron sputtering apparatus. To examine the oxygen transmission rate (OTR) of SiO_xN_y films, PET was also used as substrate. The results showed that good OTR was obtained for N_2/Ar+N_2<0.10 on PET substrate. The similar tendency was obtained for SUS304 deposited film heated up to 773K.

Gaseous slip flow analysis of a micromachined flow sensor for ultra small flow applications

The velocity slip of a fluid at a wall is one of the most typical phenomena in microscale gas flows. This paper presents a flow analysis considering the velocity slip in a capacitive micro gas flow sensor based on pressure difference measurements along a microchannel. The tangential momentum accommodation coefficient (TMAC) measurements of a particular channel wall in planar microchannels will be presented while the previous micro gas flow studies have been based on the same TMACs on both walls. The sensors consist of a pair of capacitive pressure sensors, inlet/outlet and a microchannel. The main microchannel is 128.0 µm wide, 4.64 µm deep and 5680 µm long, and operated under nearly atmospheric conditions where the outlet Knudsen number is 0.0137. The sensor was fabricated using silicon wet etching, ultrasonic drilling, deep reactive ion etching (DRIE) and anodic bonding. The capacitance change of the sensor and the mass flow rate of nitrogen were measured as the inlet-to-outlet pressure ratio was varied from 1.00 to 1.24. The measured maximum mass flow rate was 3.86 × 10−10 kg s−1 (0.019 sccm) at the highest pressure ratio tested. As the pressure difference increased, both the capacitance of the differential pressure sensor and the flow rate through the main microchannel increased. The laminar friction constant f ⋅ Re, an important consideration in sensor design, varied from the incompressible no-slip case and the mass sensitivity and resolution of this sensor were discussed. Using the current slip flow formulae, a microchannel with much smaller mass flow rates can be designed at the same pressure ratios.

Optimal design of an auto-thermal ammonia synthesis reactor

This paper presents the simulation and optimal design of an auto-thermal ammonia synthesis reactor. The main objective in the optimal design of an auto-thermal ammonia synthesis reactor is the estimation of optimal length of reactor for different top temperatures with the constraints of energy and mass balance of reaction and feed gas temperature and mass flow rate of nitrogen for ammonia production. Thousands of combinations of feed gas temperature, nitrogen mass flow rate, reacting gas temperature and reactor length are possible. In the present study, NAG subroutine (D02EJF) in MATLAB (with analytical Jacobian) for simulation in combination with Quasi-Newton (QN) method for optimization is used to verify the contradictory results reported using gear package of old NAG subroutine (D02EBF), which is now replaced with D02EJF, in combination with simple GA in earlier literature. And the new NAG subroutine shows a unimodal characteristic of the objective function, compared to a multimodal one found in the past study. It is found that new routine (D02EJF) neither showed any spikes, reverse reaction effect nor the equation became unstable even at a high top temperature of 800 K. New results are obtained for reactor length and optimal cost of reactor.

Correlation between processing and properties of TiO xN y thin films sputter deposited by the reactive gas pulsing technique

Titanium oxynitride thin films were deposited by d.c. reactive magnetron sputtering from titanium metallic target and from oxygen and nitrogen as reactive gases. The nitrogen mass flow rate was maintained constant whereas that of the oxygen was pulsed during the deposition. A constant pulsing period was used and the introduction time of the oxygen was systematically changed from 0 to 100% of the period time. The reactive gas pulsing technique allowed to prepare TiO x N y films with various metalloid concentrations (0≤ x≤2.0 and 0≤ y≤1.0) and led to changes of the crystallographic structure from f.c.c. TiN to tetragonal TiO 2. The variations of the metalloid content in the films result in changes in the electrical and optical properties and the reverse evolution of the oxygen and nitrogen content correlates with the transition from metallic to semiconducting behavior. The sputtering conditions were investigated taking into account the poisoning phenomena of the surface of the target from real time measurements of the target potential and from the reactive atmosphere, followed by mass spectrometry. Such diagnostics allowed to understand and to control better the advantageous role of the reactive gas pulsing technique and conducted to close relationships between the process parameters and the film properties.