Nitrogen Bubbles Research Articles

Does nitrogen gas bubbled through a low density polymer gel dosimeter solution affect the polymerization process?

Background:On account of the lower electron density in the lung tissue, the dose distribution in the lung cannot be verified with the existing polymer gel dosimeters. Thus, the aims of this study are to make a low density polymer gel dosimeter and investigate the effect of nitrogen gas bubbles on the R2 responses and its homogeneity.Materials and Methods:Two different types of low density polymer gel dosimeters were prepared according to a composition proposed by De Deene, with some modifications. In the first type, no nitrogen gas was perfused through the gel solution and water. In the second type, to expel the dissolved oxygen, nitrogen gas was perfused through the water and gel solution. The post-irradiation times in the gels were 24 and 5 hours, respectively, with and without perfusion of nitrogen gas through the water and gel solution.Results:In the first type of gel, there was a linear correlation between the doses and R2 responses from 0 to 12 Gy. The fabricated gel had a higher dynamic range than the other low density polymer gel dosimeter; but its background R2 response was higher. In the second type, no difference in R2 response was seen in the dose ranges from 0 to 18 Gy. Both gels had a mass density between 0.35 and 0.45 g.cm-3 and CT values of about -650 to -750 Hounsfield units.Conclusion:It appeared that reactions between gelatin-free radicals and monomers, due to an increase in the gel temperature during rotation in the household mixer, led to a higher R2-background response. In the second type of gel, it seemed that the collapse of the nitrogen bubbles was the main factor that affected the R2-responses.

Air-droplets as Gas Reservoir to Provide O2 to the Stored-Aqueous Droplets in Micro-channels

We present a method to supply oxygen to on-chip stored aqueous droplets surrounded by oxygen-permeable fluorinated oil in micro-channels. By generating air-droplets (air-bubbles) in between the aqueous droplets, oxygen diffuses to those aqueous droplets. This is confirmed by experiments comparing the effect of nitrogen bubbles and air-bubbles. The proposed method and device are a step towards long-term on-chip cultivation of mammalian cells and aerobic bacteria growth in droplets.

Cooling performance test of the superconducting fault current limiter

The superconducting fault current limiter (SFCL) is an electrical power system device that detects the fault current automatically and limits the magnitude of the current below a certain safety level. The SFCL module does not have any electrical resistance below the critical temperature, which facilitates lossless power transmission in the electric power system. Once given the fault current, however, the superconducting conductor exhibits extremely high electrical resistance, and the magnitude of the current is accordingly limited to a low value. Therefore, SFCL should be maintained at a temperature below the critical temperature, which justifies the cryogenic cooling system as a mandatory component. This report is a study which reported on the cooling system for the 154 kV-class hybrid SFCL owned by Korea Electric Power Corporation (KEPCO). Using the cryocooler, the temperature of liquid nitrogen (LN2) was lowered to 71 K. The cryostat was pressurized to 5 bars to improve the dielectric strength of nitrogen and suppress nitrogen bubble foaming during operation of SFCL. The SFCL module was immersed in the liquid nitrogen of the cryostat to maintain the superconducting state. The performance test results of the key components such as cryocooler, LN2 circulation pump, cold box, and pressure builder are shown in this paper.

Effect of nitric oxide on spinal evoked potentials and survival rate in rats with decompression sickness.

Nitric oxide (NO) releasing agents have, in experimental settings, been shown to decrease intravascular nitrogen bubble formation and to increase the survival rate during decompression sickness (DCS) from diving. The effect has been ascribed to a possible removal of preexisting micronuclei or an increased nitrogen washout on decompression through augmented blood flow rate. The present experiments were conducted to investigate whether a short- or long-acting NO donor [glycerol trinitrate (GTN) or isosorbide-5-mononitrate (ISMN), respectively] would offer the same protection against spinal cord DCS evaluated by means of spinal evoked potentials (SEPs). Anesthetized rats were decompressed from a 1-h hyperbaric air dive at 506.6 kPa (40 m of seawater) for 3 min and 17 s, and spinal cord conduction was studied by measurements of SEPs. Histological samples of the spinal cord were analyzed for lesions of DCS. In total, 58 rats were divided into 6 different treatment groups. The first three received either saline (group 1), 300 mg/kg iv ISMN (group 2), or 10 mg/kg ip GTN (group 3) before compression. The last three received either 300 mg/kg iv ISMN (group 4), 1 mg/kg iv GTN (group 5), or 75 μg/kg iv GTN (group 6) during the dive, before decompression. In all groups, decompression caused considerable intravascular bubble formation. The ISMN groups showed no difference compared with the control group, whereas the GTN groups showed a tendency toward faster SEP disappearance and shorter survival times. In conclusion, neither a short- nor long-acting NO donor had any protective effect against fatal DCS by intravenous bubble formation. This effect is most likely due to a fast ascent rate overriding the protective effects of NO, rather than the total inert tissue gas load.

Continuous-Flow Meerwein Arylation

The continuous-flow Meerwein arylation is demonstrated for a set of few aryl donors (anilines and m-aminoacetophenone) and specific radical acceptors. Homogeneous catalyst (CuBr in HBr and CuCl in HCl) was used to facilitate the reaction. The effect of parameters, viz., temperature, catalyst concentration, residence time, and concentration of the radical acceptor on the yield of the arylated product, was studied. The yield of the aryl derivative obtained by continuous-flow syntheses was always better than the respective experiments in batch mode. Flow synthesis allows easy variation in these parameters and thus allows going close to the maximum possible yields in a system where the relative rates of different reactions create a complex situation. Temperature plays a crucial role by affecting the rates as well as by governing the system homogeneity. The nitrogen bubbles generated in the reaction helped to avoid any channel blockage.

Can PFO Closure Reduce Decompression Sickness in Scuba Divers

Decompression sickness (DCS) after scuba diving is caused by nitrogen bubble formation during ascent and can cause local tissue damage, venous

Parametric analysis of the liquid hydrogen and nitrogen bubble point pressure for cryogenic liquid acquisition devices

This paper presents the parametric investigation of the factors which govern screen channel liquid acquisition device bubble point pressure in a low pressure propellant tank. The five test parameters that were varied included the screen mesh, liquid cryogen, liquid temperature and pressure, and type of pressurant gas. Bubble point data was collected using three fine mesh 304 stainless steel screens in two different liquids (hydrogen and nitrogen), over a broad range of liquid temperatures and pressures in subcooled and saturated liquid states, using both a noncondensible (helium) and autogenous (hydrogen or nitrogen) gas pressurization scheme. Bubble point pressure scales linearly with surface tension, but does not scale inversely with the fineness of the mesh. Bubble point pressure increases proportional to the degree of subcooling. Higher bubble points are obtained using noncondensible pressurant gases over the condensable vapor. The bubble point model is refined using a temperature dependent pore diameter of the screen to account for screen shrinkage at reduced liquid temperatures and to account for relative differences in performance between the two pressurization schemes. The updated bubble point model can be used to accurately predict performance of LADs operating in future cryogenic propellant engines and cryogenic fuel depots.

Ultrasonic Degassing of Aluminum Alloys

This article discusses research on using power ultrasound for degassing of molten aluminum alloys. At least three types of technique have been developed for ultrasonic degassing. The type deals with degassing using power ultrasound alone. Degassing in a small melt can be achieved within a few minutes of ultrasonic vibration. The second type is ultrasound assisted vacuum degassing. A combination of vacuum and power ultrasound makes degassing much complete and fast. The third type is ultrasound assisted lance degassing. Ultrasonic vibration is used to break up the large argon or nitrogen bubbles into much smaller ones, resulting in an increased efficiency of degassing of aluminum melt. The benefits of ultrasonic degassing include: no moving/rotation part in the degassing system; less use of argon and no use of chlorine; and less amount of dross formation during degassing. Furthermore, trace elements such as Na and Li can be removed using ultrasonic degassing. Keywords: Aluminum alloys, degassing, porosity, and power ultrasound

Effect of conservative dive profiles on the occurrence of venous and arterial bubbles in divers with a patent foramen ovale: A pilot study

Patent foramen ovale (PFO) is a risk factor for decompression sickness (DCS) in divers due to paradoxical embolization of nitrogen bubbles formed in peripheral blood during decrease of ambient pressure [1]. In our previous study we have demonstrated that catheter-based PFO closure prevented right-to-left shunting of bubbles and might prevent DCS recurrence [2]. However, the question of PFO closure is still debatable [3]. Also, randomized clinical data are lacking in this field. Therefore, the majority of divers are currently not referred for PFO closure, and various conservative dive profiles (CDP) are recommended to prevent unprovoked DCS (i.e., without violation of decompression regimen) [4].

Effect of Catheter-Based Patent Foramen Ovale Closure on the Occurrence of Arterial Bubbles in Scuba Divers

This study sought to evaluate the effect of catheter-based patent foramen ovale (PFO) closure on the occurrence of arterial bubbles after simulated dives. PFO is a risk factor of decompression sickness in divers due to paradoxical embolization of bubbles. To date, the effectiveness of catheter-based PFO closure in the reduction of arterial bubbles has not been demonstrated. A total of 47 divers (age 35.4 ± 8.6 years, 81% men) with a PFO (PFO group) or treated with a catheter-based PFO closure (closure group) were enrolled in this case-controlled observational trial. All divers were examined after a simulated dive in a hyperbaric chamber: 34 divers (19 in the PFO group, 15 in the closure group) performed a dive to 18 m for 80 min, and 13 divers (8 in the PFO group, 5 in the closure group) performed a dive to 50 m for 20 min. Within 60 min after surfacing, the presence of venous and arterial bubbles was assessed by transthoracic echocardiography and transcranial color-coded sonography, respectively. After the 18-m dive, venous bubbles were detected in 74% of divers in the PFO group versus 80% in the closure group (p = 1.0), and arterial bubbles were detected in 32% versus 0%, respectively (p = 0.02). After the 50-m dive, venous bubbles were detected in 88% versus 100%, respectively (p = 1.0), and arterial bubbles were detected in 88% versus 0%, respectively (p < 0.01). No difference was observed in the occurrence of venous bubbles between the PFO and closure groups, but the catheter-based PFO closure led to complete elimination of arterial bubbles after simulated dives. (Nitrogen Bubble Detection After Simulated Dives in Divers With PFO and After PFO Closure; NCT01854281).

Gas–liquid–liquid three-phase flow pattern and pressure drop in a microfluidic chip: similarities with gas–liquid/liquid–liquid flows

We report a three-phase slug flow and a parallel-slug flow as two major flow patterns found under the nitrogen-decane-water flow through a glass microfluidic chip which features a long microchannel with a hydraulic diameter of 98 μm connected to a cross-flow mixer. The three-phase slug flow pattern is characterized by a flow of decane droplets containing single elongated nitrogen bubbles, which are separated by water slugs. This flow pattern was observed at a superficial velocity of decane (in the range of about 0.6 to 10 mm s(-1)) typically lower than that of water for a given superficial gas velocity in the range of 30 to 91 mm s(-1). The parallel-slug flow pattern is characterized by a continuous water flow in one part of the channel cross section and a parallel flow of decane with dispersed nitrogen bubbles in the adjacent part of the channel cross section, which was observed at a superficial velocity of decane (in the range of about 2.5 to 40 mm s(-1)) typically higher than that of water for each given superficial gas velocity. The three-phase slug flow can be seen as a superimposition of both decane-water and nitrogen-decane slug flows observed in the chip when the flow of the third phase (viz. nitrogen or water, respectively) was set at zero. The parallel-slug flow can be seen as a superimposition of the decane-water parallel flow and the nitrogen-decane slug flow observed in the chip under the corresponding two-phase flow conditions. In case of small capillary numbers (Ca ≪ 0.1) and Weber numbers (We ≪ 1), the developed two-phase pressure drop model under a slug flow has been extended to obtain a three-phase slug flow model in which the 'nitrogen-in-decane' droplet is assumed as a pseudo-homogeneous droplet with an effective viscosity. The parallel flow and slug flow pressure drop models have been combined to obtain a parallel-slug flow model. The obtained models describe the experimental pressure drop with standard deviations of 8% and 12% for the three-phase slug flow and parallel-slug flow, respectively. An example is given to illustrate the model uses in designing bifurcated microchannels that split the three-phase slug flow for high-throughput processing.

The Continuum of Metabolic Stress According to the Gas Model of Alzheimer’s Disease

The present article focuses on the model metabolic stress in AD. This novel model proposes that nitrogen nanobubbles, having invaded the brain interstitial fluid from the blood through glucose transporter-1 (GLUT-1), cause the pressure to increase in the close surroundings, before being embedded in amyloid-β fibrils in the form of cerebral amyloid angiopathy that fixes the pollutant. Following the huge increase in the surrounding pressure, molecular oxygen, the regular form of oxygen in a low PO2 solute, gather into oxygen nanobubbles, leading to various normal responses, albeit damaging. Therefore, nanobubbles trigger the NADPH oxidase-NO antibubble biomachinery that produces superoxide and peroxynitrite. The high NADPH/NADP+ turnover is supported by the pentose phosphate pathway. Oxygen nanobubbles in mitochondria could explain the impairment of complexes I and IV. The amyloid percolation well model might resolve the issue of the coimmunoprecipitation of Aβ with the latter complexes, Aβ stabilizing oxygen bubbles, as it might stabilize nitrogen bubbles in the ISF. The permeabilization of the mitochondrial membrane by unspecific pores fixes the overpressure on the mitochondria. The bubble-induced crowding of the respiratory chains causes energy depletion due to the disruption of oxidative phosphorylation, leading to the irreversible injury of respiration, also known as Warburg effect. The main consequence is a deficit in the cholinergic system. Last, the peroxynitrite/CO2 system is deciphered as a CO2 antibubble buffer, rescuing the impaired carbonic anhydrase in AD. Sometimes, CO2 is not released from peroxynitrite, and then produces nitrite anions and carbonyl radicals after intermediate reactions. These respectively lead to the nitrotyrosination and carbonylation of numerous proteins but hold the cells free from a CO2 bubble-induced disruption of the cytoplasmic and the mitochondrial membranes. The AD Gas Model paves the way to new approaches to address the pathophysiology of the most devastating brain disease in human beings.

Pressure Difference for Moving Nitrogen Bubbles in a Waving Duct

A duct with varying cross-sections can show some essential features of the motion of foam in porous media. In this paper, the effective viscosity of the bubbles train moving through cylindrical ducts with sinusoidal cross-section was experimentally measured. The test tube has total length of 1.14 m and has constrictions at interval of 0.0095 m. It is found that the foam effective viscosity is much higher than water viscosity and it is possible to extend the foam rheology correlations in constant cross section ducts to predict the flow differences in waving ducts.

A study of gas bubbles in liquid mercury in a vertical Hele-Shaw cell

High-quality observations of mesoscopic gas bubbles in liquid metal are vital for a further development of pyrometallurgical gas injection reactors. However, the opacity of metals enforces the use of indirect imaging techniques with limited temporal or spatial resolution. In addition, accurate interface tracking requires tomography which further complicates the design of a high-temperature experimental setup. In this paper, an alternative approach is suggested that circumvents these two main restrictions. By injecting gas in a thin layer of liquid metal entrapped between two flat and closely spaced plates, bubbles in a Hele-Shaw flow regime are generated. The resulting quasi-2D multiphase flow phenomena can be fully captured from a single point of view and, when using a non-wetted transparent plate material, the bubbles can be observed directly. The feasibility of this approach is demonstrated by observations on buoyancy-driven nitrogen bubbles in liquid mercury in a vertical Hele-Shaw cell. By using a moving high-speed camera to make continuous close up recordings of individual bubbles, the position and geometry of these bubbles are quantified with a high resolution along their entire path. After a thorough evaluation of the experimental accuracy, this information is used for a detailed analysis of the bubble expansion along the path. While the observed bubble growth is mainly caused by the hydrostatic pressure gradient, a careful assessment of the volume variations for smaller bubbles shows that an accurate bubble description should account for significant dynamic pressure variations that seem to be largely regime dependent.

Assessment of Mass-Transfer Effects during Polyether Production from 1,3-Propanediol

A mathematical model is developed to simulate condensation polymerization of 1,3-propanediol to produce polytrimethylene glycol (PO3G) polyether. The model includes improved mass-transfer expressions that account for nonzero concentrations of water and monomer inside nitrogen bubbles and for increasing overall bubble surface area due to increases in bubble residence time. An objective function that accounts for the mole fractions of evaporated monomer, water and propanal is considered for parameter estimation. Improvements in the predicted monomer and water concentrations in the polymer and evaporation rates of monomer and water can be observed compared to a previous model.[5, 6] However, predictions of degree of polymerization do not improve noticeably. Recommendations including revisions of the chemical mechanism to include additional reactions and accounting for evaporation of linear and cyclic oligomers in future models are suggested.

Biologically enhanced degassing and precipitation of magnesium carbonates derived from bicarbonate solutions

This contribution reports the results of batch and semibatch experiments involving bubbling of nitrogen in aqueous solutions of magnesium bicarbonate, with and without the addition of either carbonic anhydrase (CA) or Scenedesmus alga to the solution. Precipitation of nesquehonite occurred during both an accelerated degassing of CO2 induced by sparging small nitrogen bubbles (representative diameter of 20μm), and during slow degassing engendered by introducing large nitrogen bubbles (representative diameter of 5mm). The response of the system during low rates of degassing closely approached quasi-thermodynamic predictions, which permitted an estimation of the level of supersaturation of nesquehonite, prior to the onset of precipitation. Small bubbles and CA significantly increased rates of degassing and indirectly the production of nesquehonite, as the rate of degassing can limit the precipitation process. The response of the system during rapid rates of degassing, prior to precipitation, was not entirely consistent with quasi-thermodynamic predictions. During precipitation, higher rates of degassing produced similar alkalisation and precipitation trends to that observed for lower rates of degassing. Our results agree with the formation of travertine deposits in nature, where the degassing of solutions enriched with inorganic carbon, and enhanced alkalisation by microorganisms, have been shown to influence carbonate formation. The results demonstrate a catalytic effect of CA on the rate limiting carbonate reactions, increasing CO2 exchange between nitrogen and water, and indirectly accelerating the precipitation of carbonates for a system controlled by rate of degassing. The results of this study have applications to large-scale storage of CO2 by mineralisation.

Two-dimensional numerical simulation of single bubble rising behavior in liquid metal using moving particle semi-implicit method

Gas-lift pump in liquid metal cooling fast reactor (LMFR) is an innovative conceptual design to enhance the natural circulation ability of reactor core. The two phase flow characteristics of gas–liquid metal make significant improvement of the natural circulation capacity and reactor safety. It is important to study bubble flow in liquid metal. In present study, the rising behaviors of a single nitrogen bubble in 5 kinds of common stagnant liquid metals (lead bismuth alloy (LBE), liquid kalium (K), sodium (Na), potassium sodium alloy (Na–K) and lithium lead alloy (Li–Pb)) and in flowing lead bismuth alloy have been numerically simulated using two-dimensional moving particle semi-implicit (MPS) method. The whole bubble rising process in liquid was captured. The bubble shape, rising velocity and aspect ratio during rising process of single nitrogen bubble were studied. The computational results show that, in the stagnant liquid metals, the bubble rising shape can be described by the Grace's diagram, the terminal velocity is not beyond 0.3 m/s, the terminal aspect ratio is between 0.5 and 0.6. In the flowing lead bismuth alloy, as the liquid velocity increases, both the bubble aspect ratio and terminal velocity increase as well. This work is the fundamental research of two phase flow and will be important to the study of the natural circulation capability of Accelerator Driven System (ADS) by using gas-lift pump.

Mathematical Model of Polyether Production From 1,3‐Propanediol

AbstractA mathematical model is developed for condensation polymerization of 1,3‐propanediol to produce Cerenol polyether. The effect of the super‐acid catalyst is considered explicitly in the proposed reaction mechanism. The main reactions include protonation/deprotonation equilibrium, polycondensation, carbocation formation, end degradation, and transetherification. Formation of propanal and secondary hydroxyl ends is also considered. Mass transfer of water, propanal, and monomer from the liquid phase into nitrogen bubbles is included in the model. The proposed model predicts the time evolution of number average molecular weight and concentrations of water, propanal, monomer, and unsaturated end groups, along with evaporation rates of small molecules. Data from isothermal batch experiments are used to estimate model parameters. Steep upward trends in degree of polymerization and in concentration of unsaturated ends are not predicted well at long reaction times based on the current model. magnified image

Effect of carrier gas composition on transferred arc metal nanoparticle synthesis

Metal nanoparticles are used in a great number of applications; an effective and economical production scaling-up is hence desirable. A simple and cost-effective transferred arc process is developed, which produces pure metal (Zn, Cu, and Ag) nanoparticles with high production rates, while allowing fast optimization based on energy efficiency. Different carrier gas compositions, as well as the electrode arrangements and the power input are investigated to improve the production and its efficiency and to understand the arc production behavior. The production rates are determined by a novel process monitoring method, which combines an online microbalance method with a scanning mobility particle sizer for fast production rate and size distribution measurement. Particle characterization is performed via scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction measurements. It is found that the carrier gas composition has the largest impact on the particle production rate and can increase it with orders of magnitude. This appears to be not only a result of the increased heat flux and melt temperature but also of the formation of tiny nitrogen (hydrogen) bubbles in the molten feedstock, which impacts feedstock evaporation significantly in bi-atomic gases. A production rate of sub 200 nm particles from 20 up to 2,500 mg/h has been realized for the different metals. In this production range, specific power consumptions as low as 0.08 kWh/g have been reached.

Regularity of Nitrogen Macrosegregation in High Nitrogen Steel

We studied the nitrogen macrosegregation of the HNS, and found that there were severe vertical segregation and horizontal segregation. Both of them are normal segregation. The study shown that the overflow area of nitrogen bubbles in the process of solidification is due to the nitrogen macrosegregation.