Capillary Outlet Research Articles

Molecular dynamics study of ionic liquid electrospray: Revealing the effect of types of electric fields

The microscopic behaviors and characteristics of BMIM+BF4− ionic liquid electrospray in the presence of the axial electric field and axial-radial electric field were investigated by molecular dynamics method. The formation and fragmentation of the jet, the structure characteristics of the ions, the interactions between the ions and the energy properties were analyzed. Since ionic liquid is commonly used in spacecraft thruster, their specific impulse and thrust are also evaluated. It was found that the occurrence of ionic liquid electrospray was determined by the axial voltage, not less than 0.8V/nm. The flow rate and radial voltage mainly affect the jet instability and the secondary disintegration. When the jet is broken, it is almost ejected in the form of (BMIM+BF4−)1(BMIM+) and BMIM+, but finally it presents four main clusters, including BF4−, BMIM+, (BMIM+BF4−)1 and (BMIM+BF4−)1(BMIM+). For the unbroken jet at the capillary outlet, BMIM+ is concentrated on the surface of the jet, and BF4− is concentrated inside. The number of clusters will occasionally decrease owing to coalesce. The internal bonds of BMIM+ and BF4− is likely to break, and the bond angle may also vary. In the presence of the axial-radial electric field with an axial electric field intensity of 1.2V/nm, the electrospray ionization effect is the best at the radial electric field intensity of 0.001V/nm, and the specific impulse and thrust can be obtained by adjusting the axial electric field intensity. This work provides a new insight into the microscopic mechanisms of BMIM+BF4− ionic liquid electrospray.

Microscopic mechanism of nanofluids electrospray: A molecular dynamics study

Cone-jet electrospray is widely used in various fields, such as electrospinning, nanostructured porous coating preparation, and inkjet printing, for which it can produce a large number of monodisperse and high charge-to-mass ratio droplets. A molecular dynamics method is employed to investigate the cone-jet electrospray emission behavior of nanofluids, where the microscopic mechanism of cone-jet electrospray including the formation of the cone, disintegration of the jet, stability of hydrogen bond, and interactions between molecules is revealed. In this paper, the influence of operating parameters and liquid physical properties were numerically conducted and extensively analyzed. The results show that the cone-jet electrospray only occurs in a certain range of applied voltage and flow rate, and the temperature and concentration of nanoparticles have a great effect on the jet length and the number of clusters produced by jet disintegration. When the electric field intensity increases, the length of the jet and the number of clusters increase. However, regardless of the electric field intensity, the maximum axial density is always located near the capillary outlet and the maximum radial density is located at the central axis of the capillary. As the temperature increases, the number of clusters increases significantly due to the synthetical effect of electric field-induced disintegration and evaporation, whereas the jet length is reduced. With an increase in concentration of nanoparticles at room temperature, the Taylor cone not only appears earlier but also has a larger angle. Meanwhile, the non-bonded interactions between ethanol molecules become stronger. This work provides microscopic mechanisms of nanofluids cone-jet electrospray and is potentially useful to optimize the design parameters of industrial applications.

Numerical analysis of pressure variation and gas load effects in the refrigeration system for household refrigerators

Insufficient air evacuation from a refrigeration system prior to refrigerant charging can lead to an increased non-condensable gas concentration, negatively impacting system performance. Despite its critical importance, literature on refrigeration system vacuuming procedures is notably lacking. This study developed numerical methods and constitutive models to assess gas load, validated against measured pressures using experimental setups. The model developed can be extended and applied to a wide range of vacuum systems. Examining the vacuuming process in a household refrigerator, a connected vacuum pump expedited the process, revealing higher pressures in the capillary tube and condenser outlet due to low flow conductance. The rate of pressure increase attributable to the gas load from outgassing and degassing remained below 0.6 %, deemed negligible during vacuum pump operation. A 24-hour simulation post-vacuum pump cessation showcased pressure equalization and subsequent rise due to outgassing and degassing, resulting in a 201 % increase in pressure within the compressor’s internal space connected to the process pipe. The pressure increase in the compressor attributable to outgassing amounted to 140 %, surpassing the 59 % from degassing. Notably, assuming a 3 μm crack in the process pipe led to a continuous increase in refrigerator system pressure over 24 h. Leakage significantly increases the amount of non-condensable gases inside the system, potentially leading to increased energy consumption and deterioration in system performance.

Transient analysis of a noise suppression method with aerating techniques in capillary tubes

Flow-induced noise is closely related to the flow characteristics through an adiabatic capillary tube and a transition pipe, most existing methods for suppressing flow-induced noise are passive. An aerating technique is proposed based on the pressure feedback in the transition pipe to actively suppress flowinduced noise. The 3-D simulations of flashing are presented by performing the Schnerr-Sauer cavitation model coupling with the mixture model. For the turbulence model, the large eddy simulation approach is used. With the installation of aerating module, the pressure fluctuation in the transition pipe is weakened significantly, and the phenomenon of bubble collapse is suppressed. Numerical results illustrate that the transient pressure of the monitoring points downstream of the capillary outlet oscillates seriously due to the bubble bursting. The shedding process of the bubble group is observed according to the vaporliquid interface in the transition pipe. In addition, the oscillations of monitored transient pressure are suppressed with the application of aerating module. Then the noise source can be partially reduced actively in essence. This paper is devoted to understanding the two-phase flow characteristics of refrigerants in a transition pipe and presents a practical method to suppress noise near the capillary outlet.

Capillary electrophoresis Western blot using inkjet transfer to membrane

Traditional Western blots are commonly used to separate and assay proteins; however, they have limitations including a long, cumbersome process and large sample requirements. Here, we describe a system for Western blotting where capillary gel electrophoresis is used to separate sodium dodecyl sulfate-protein complexes. The capillary outlet is threaded into a piezoelectric inkjetting head that deposits the separated proteins in a quasi-continuous stream of <100 pL droplets onto a moving membrane. Through separations at 400 V/cm and protein capture on a membrane moving at 2 mm/min, we are able to detect actin with a limit of detection at 8 pM, or an estimated 5 fg injected. Separation and membrane capture of sample containing 10 proteins ranging in molecular weights from 11 – 250 kDa was achieved in 15 min. The system was demonstrated with Western blots for actin, β-tubulin, ERK1/2, and STAT3 in human A431 epidermoid carcinoma cell lysate.

Effects of Heat Reflux on Two-Phase Flow Characteristics in a Capillary of the ADN-Based Thruster.

During the working process of the ADN-based thruster, continuously, heat generated by the chemical reaction in the combustion chamber will transfer along the upstream capillary, the propellant in the capillary continuously absorbs heat under the effect of heat transfer from the wall and undergoes a phase change when the saturation temperature is reached. In this study, effects of the downstream heating temperature (623 K to 923 K) on mass flow rate and pressure change in the capillary were investigated based on the established test platform. Simultaneously, the VOF (volume of fraction) model, and the Lee phase transition model coupled with the Navier–Stokes method was utilized to simulate the spatial distribution of the gas-liquid propellant in the capillary. The results show that the ADN-based propellant firstly formed bubbles on the inner wall surface near the exit of the capillary, and these vapor bubbles moved and grew upstream along the capillary. Due to the cooling effect of the ADN-based propellant inflow, the temperature distribution of the front chamber and capillary gradually reached equilibrium. Bubbles were constantly generated in the capillary, and as the heat reflux intensified, the total volume of bubbles in the capillary continued increasing. Single-phase flow, annular flow, wave flow, and segment plug flow appeared sequentially along the axial direction of the capillary, and the proportion of gas phase volume fraction at the capillary outlet section gradually increased.

Application of aerating techniques for noise suppression in capillary tubes

A method for suppressing noise in capillary tubes was developed with aerating techniques. The refrigerant R600a was added to the outlet of a throttling capillary from the end of a transition tube between the capillary and evaporator. To investigate the flow characteristic of R600a in the transition tube, a two-phase flow quasi-steady simulation was performed using the mixture model. The Schnerr–Sauer cavitation model was used, and the turbulence model was realizable k − ɛ. Numerical results show that the local pressure and negative mass transfer rate can both be reduced at the downstream of the capillary where bubbles collapse, when bypass capillaries are used in the aerating model. An experimental system was built to measure the noise in a transition tube with/without a bypass capillary. Results show that the noise sound pressure level decreased by 2 dB on average when aerating techniques were used. This research describes the complex mechanism of the throttling flashing process and provides an effective method to suppress the noise in capillary tubes, which will be beneficial to improve occasional sharp noise in a household refrigerator.

Experimental Research on Aerated Supercavitation Suppression of Capillary Outlet Throttling Noise

The aim of this work is the reduction of the throttling noise when the capillary is used as a throttling device. Based on the theory of bubble dynamics, two-phase flow, and aerated supercavitation, four different sizes of aerated devices used in refrigerator refrigeration systems are designed. Throttling noise and the temperature and pressure of inlet and outlet of the capillary are measured under stable operation. To compare the noise suppression effects in different groups of experiments, we introduced the cavitation number to analyze, revealed the principle of aerated supercavitation to suppress noise, and combined the results of Fluent simulations to get the relationship between the noise suppression effect and the aerated quality. The experimental results showed that the aerated device can obviously suppress the throttling noise of the capillary outlet, up to 2.63 dB(A), which provides a new way for reducing the capillary throttling noise.

Cavitation characteristics and suppression research of refrigerant in capillary tube

Cavitation is easy to form and develop due to the large pressure drop during throttling in the refrigeration system. To effectively suppress the throttling cavitation phenomenon, an aerating method through bypass capillary is proposed. Based on the Homogeneous Equilibrium Mixture (HEM) model, the Schnerr-Sauer cavitation model and the Realizable k-ε turbulence model were adopted, and the throttling process in the capillary tube and transition tube was simulated by Fluent, and the pressure distribution and vapor volume fraction distribution in the capillary tube and transition tube were obtained for both original model and aerating model. Results show that after adopting the aerating technology, the vapor volume fraction at the capillary outlet is almost unchanged, while the vapor volume fraction in the transition tube is obviously increased, which indicates that the bubble collapsing phenomenon in the transition tube is weakened, and then realized the purpose of suppressing the cavitation effect.

ФАКТОРЫ, ВЛИЯЮЩИЕ НА ЭЛЕКТРОМИГРАЦИЮ ПРОКАИНА ГИДРОХЛОРИДА В УСЛОВИЯХ КАПИЛЛЯРНОГО ЭЛЕКТРОФОРЕЗА

The article discusses the influence of various factors on procaine hydrochloride electromigration under conditions of electrophoretic separation by capillary electrophoresis. The rate of voltage rise in the capillary electrophoresis system has been studied and a device making it possible to measure the potential in the system independent of the program software has been developed. The influence of the difference in hydrostatic pressure at the inlet and outlet of the quartz capillary and the difference in the approach to the analysis when changing the base electrolyte are investigated. The influence of the sample injected zone length on reproducibility of assay results of procaine hydrochloride has been studied. In order to improve separation efficiency and reproducibility of quantitative analysis results it is recommended to replace the base electrolyte after each analysis, as well as to inject the sample avoiding short injection values and high pressure. The values of apparent mobility of the test substance which can be used in the development of methods for procaine hydrochloride assay by capillary electrophoresis are calculated. The research results obtained can be applied in chemical and pharmaceutical laboratories as well as in scientific research.

Perturbations of the Depth of Liquid Penetration Into the Capillary During Bubble Departures

Abstract In the present paper, the influence of bubble size on liquid penetration into the capillary was experimentally and numerically studied. In the experiment, bubbles were generated from a glass capillary (with an inner diameter equal to 1 mm) in a glass tank containing distilled water, tap water or an aqueous solution of calcium carbonate. These liquids differ in the value of their surface tension, which influences the bubble size. During experimental investigations, air pressure fluctuations in the gas supply system were measured. Simultaneously, the videos showing the liquids’ penetration into the capillary were recorded. Based on the videos, the time series of liquid movements inside the capillary were recovered. The numerical models were used to study the influence of bubble size on the velocity of liquid flow above the capillary and the depth of liquid penetration into the capillary. It was shown that the air volume flow rate and the surface tension have the greatest impact on the changes of pressure during a single cycle of bubble departure (Δp). The changes in pressure during a single cycle of bubble departure determine the depth of liquid penetration into the capillary. Moreover, the values of Δp and, consequently, the depth of liquid penetration can be modified by perturbations in the liquid velocity above the capillary outlet.

Characteristics of Air Resistance in Aerostatic Bearings

The definition of air resistance is nonuniform when analyzing the bearing capacity, stiffness, and stability of an orifice throttling aerostatic restrictor. In this study, a capillary tube similar to the inlet section of an aerostatic restrictor is used as the research object, and the Bernoulli equation under adiabatic conditions is established. Through an experiment, the pressure and temperature of the capillary tube inlet and outlet and the flow through the capillary tube are measured. Based on the air resistance definition, the empirical formula of the coefficient k is obtained, and the theoretical air resistance of the capillary path is calculated. The relative error between the theoretical air resistance and experimental air resistance is kept within 10%. The comparison results verify the accuracy of the air resistance theory and provide a basis for the subsequent establishment of a universal definition of air resistance. Subsequently, air resistance can be used to design aerostatic bearings and help improve their characteristics.

Measurements of electron number density and temperature in a supersonic plasma jet by optical emission spectroscopy

The results of experimental studies of the shock-wave region of the supersonic plasma jet flow formed by a pulsed capillary discharge with a polymeric wall are presented. Using optical emission spectroscopy of high spatial resolution, a detailed picture of the evolution of the radial profiles of the electron number density and temperature along the initial section of an underexpanded plasma jet, starting from the capillary outlet and ending with the flow stagnation zone, has been obtained. It was found that the profiles of the electron number density and temperature reflect all the features of the shock-wave flow region, tracing the influence of intercepting, central and reflected shock waves.

Steady-state performance of capillary tubes for small-scale vapour compression systems using different refrigerants

• Fixed capillary tube geometry with straight, helical and SLHX sections. • A model was proposed to determine the steady-state operation of the capillary tubes. • Refrigerant velocity was shown to increase with the capillary tubes elongation. • Refrigerant outlet state of the capillary tube is determined. • Refrigerants R134a, R1234yf, R1234ze (E), R513A, R600, R600a are investigated. The operational performance of small-scale refrigeration systems is mainly decided by their capillary tubes outlet parameters, wherein an accurate determination of the pressure and vapour quality is a prerequisite. Experiments have been performed for a capillary tube (CT) with specified geometry consisting of a straight, a helical and a suction line heat exchanger (SLHX) section. The capillary tube is incorporated in a small refrigeration system operated with R600a. In addition, a model was developed to determine the steady-state operation of the capillary tubes (activated with R134a, R1234yf, R1234ze(E), R600, R600a, R152a and R513A refrigerants) and validated. The highest and lowest value of the vapour quality was discerned to be 0.3132 (for R1234yf) and 0.2124 (for R600), respectively. The relative errors between the experimental and model results for the CT outlet pressure and temperature were ranged from 1.16 to 5.35% and 0.12–0.81%, respectively. It is asserted that the present strategy may contribute towards the precise estimation of the pressure and vapour quality to customize the working performance of small scale refrigeration systems.

Experimental Study of Vapor Supercavitation Suppression of Capillary Outlet Jet Noise

The degree of bubble bursting at the inlet of an evaporator is the key factor to determine the size of the injection noise at the capillary outlet. In this study, by using the theory of cavitation dynamics, the transition tube between the capillary and evaporator is improved to suppress the bubble bursting at the entrance of the evaporator, so as to reduce the jet noise at the outlet of the capillary. The influence of aeration structure on noise reduction of a refrigerator (Haier BCD-520) was studied by numerical simulation, and experiments were carried out. The results show that the admixture structure significantly inhibits the bubble bursting and reduces the injection noise by 1.5 dB(A).

Induced Self-aspiration Electrospray Ionization Mass Spectrometry for Flexible Sampling and Analysis.

Electrospray ionization (ESI) operating in pulse mode can enhance the utilization efficiency of the electrospray ions by a mass spectrometer. Herein, a novel ionization technique called induced self-aspiration-electrospray ionization (ISA-ESI) was developed based on self-aspiration sampling and capacitive induction. The sample solution polarized in a strong electric field was pulsed drawn into a capillary that was connected to a subambient chamber. The sample solution with polarized ions forms a charged liquid column, which can initiate an electrospray when reaching the capillary outlet. In addition to the self-aspiration ability, the use of a constant high voltage supply and no electrical contact with the solution can also simplify the sampling and ionization operation, enabling a convenient ESI mass spectrometry analysis. The developed ISA-ESI source has been used for multidimensional monitoring of chemical reactions as well as liquid extraction surface analysis of plant tissues. It was expected that this special ionization method could be extended to automated high-throughput ESI-MS analysis.

Numercial analysis on the thermal performance of capillary heat exchange system in metro running tunnel

Abstract During the operation of the capillary heat exchange system in the metro tunnel, the pipe length, pipe spacing and air velocity have different effects on the heat transfer effect and show certain rules. Taking Kunming as an example, a single-factor analysis method was used to establish multiple-capillary model, and the variation of different influencing factors in the heat transfer process was obtained. On this basis, a single-capillary model was established to analyze the thermal interference variation of the pipe spacing between the two models. Under the condition of ensuring the capillary outlet water temperature and heat flux, the relevant parameters of the capillary heat exchanger were optimized. The results show that the pipe length of the capillary heat exchanger should be kept within 3–5 m, the pipe spacing is maintained at 20–30 mm, and the capillary heat exchanger of each set can be operated in parallel to ensure that heat exchanger have better heat transfer performance. During the system stop running, the air velocity in winter and summer has different effects on the recovery of surrounding rock.

Flow-induced noise generation at the outlet of a capillary tube

The aim of this work is the identification of noise generation mechanisms at the outlet of an adiabatic capillary tube used as throttling device in a cooling cycle. For this purpose, experiments are carried out on a R-600a test bench designed for systematic investigations on flow-induced capillary noise. The experiments are performed using a copper capillary tube with an inner diameter of 0.6 mm. The test bench enables process control with a continuous change of the capillary outlet pressure, while the inlet pressure and temperature remain constant. A similar process takes place in a refrigerator at the beginning of the on-cycle, when the compressor starts to pull down the evaporation pressure. Correlations between various operating conditions and the emitted airborne noise can thus be established. The evaluation of the sound pressure level profiles provides a method to indicate the change of flow regimes at the capillary tube outlet, using flow pattern maps from literature. We identify two different noise generation mechanisms: In case of intermittent flow regimes, pressure pulses evoked by the fluid lead to fluctuating unsteady noise excitations. During non-intermittent flow regimes, on the other hand, uniform noise excitations strongly correlate with the vapor velocity of the two-phase flow.

High Throughput Screening of Serum γ-Glutamyl Dipeptides for Risk Assessment of Nonalcoholic Steatohepatitis with Impaired Glutathione Salvage Pathway.

Nonalcoholic fatty liver disease (NAFLD) is the most common preventable chronic liver disorder in developed countries, the prevalence of which is increasing worldwide due to its association with obesity and type 2 diabetes. However, the exact mechanisms of NAFLD pathophysiology remain poorly understood including its progression to the more severe nonalcoholic steatohepatitis (NASH). New advances for early detection and monitoring of NASH progression are limited due to the lack of specific blood biomarkers, thus requiring invasive liver biopsies for histopathology. Herein, multisegment injection-capillary electrophoresis-tandem mass spectrometry (MSI-CE-MS/MS) is validated as a high throughput, robust, and quantitative platform for targeted analysis of a panel of 16 serum γ-glutamyl dipeptides from a cohort of NASH adult patients from Japan (median age = 53 years, median BMI = 27 kg/m2, n = 116). Multiplexed separations based on MSI-CE-MS/MS enable the design of unique data workflows that rely on customizable serial sample injection formats for accurate determination of γ-glutamyl dipeptides with quality control. Also, the introduction of a liquid coolant device to the capillary outlet improves long-term migration time stability in CE. Unsupervised pattern recognition methods revealed two distinctive NASH subgroups based on their contrasting γ-glutamyl dipeptide status despite patients having similar clinical phenotypes and NASH activity scores (median NAS ≈ 6.0). There was an inverse correlation between serum γ-glutamyl dipeptide concentrations and γ-glutamyltransferease (GGT) enzyme activity (r = -0.46; p = 2.5 × 10-7), which was indicative of a low-risk (n = 64) as compared to a high-risk (n = 52) patient subgroup with impaired glutathione salvage pathway and likely poor clinical prognosis. Our findings highlight the key role of defects in the γ-glutamyl cycle for differentiation of NASH patients, which may enable better risk assessment of long-term survivorship as a complement to standard liver enzyme screens and histopathology.

Nanolitre-scale cell based on L-shaped silica capillary and optical fibre for absorption photometric detection in capillary liquid chromatography

Miniaturised photometric detection cell based on the 150 μm I. D. L-shaped fused silica capillary (L-cell) and silica optical fibre is discussed in this paper. Light enters the cell via right angle bend and transmitted light is collected by silica optical fibre inserted into the capillary outlet. Ray trace analysis reveals that L-cell geometry works as a waveguide and effectively eliminates parasitic light, which is guided by the wall of any fused silica capillary cell. Low total level of stray light is further documented by measurement of absorbance of acetone-water mixture at 266 nm with the observed upper limit of dynamic range 2.2 AU. 3-mm L-cell has a volume of 53 nL and exhibits effective optical path 2.7 mm. Cell variance determined in the flow rate range 1–10 μL min−1 indicates, that 3-mm L-cell is optimal for use with 200–300 μm I. D. capillary columns. Furthermore, isocratic separation of alkylbenzenes mixture at 0.5 μL min−1 demonstrates effective use of 0.5-mm L-cell (8.8 nL) and possible performance of longer L-cells with high efficiency 100 μm I. D. capillary column.