Molecular Flow Research Articles

Inversion in binary gas mixtures in rarefied flow conditions: Direct simulation Monte Carlo solution and comparison with the analytical solutions at free molecular regime

This paper analyzes the mixing of gases in a plane channel at rarefied conditions. The direct simulation Monte Carlo method is employed to simulate gas mixing in parallel mixers working at different Knudsen numbers and having different values of wall accommodation coefficient. Results show that the normal-to-wall component of the mole fraction gradient may have the same sign as the corresponding component of the diffusive mass flux vector near the diffuse solid walls in contrast to the predictions of Fick's law for continuum conditions. This non-continuum behavior, which is called “inversion” in the present study, will become more pronounced at higher Knudsen numbers, whereas it will become less evident for smaller wall accommodation coefficients. To confirm that the observed phenomenon is consistent with the basic physical laws governing the rarefied gas dynamics and it is not an artifact of the numerical method, a new analytical model based on the kinetic theory of gases is developed for the parallel mixers that have diffuse walls and are working in the free-molecular regime. Excellent agreement is observed between the analytical and direct simulation Monte Carlo results in the free molecular flow regime. Both methods predict the occurrence of inversion near the diffuse walls at highly rarefied flow conditions.

Comparison of different Gaussian quadrature rules for lattice Boltzmann simulations of noncontinuum Couette flows: From the slip to free molecular flow regimes

The lattice Boltzmann (LB) method can be formulated directly from the Boltzmann equation with the Bhatnagar–Gross–Krook assumption. This kinetic origin stimulates wide interest in applying it to simulate flow problems beyond the continuum limit. In this article, such a thought is examined by simulating Couette flows from the slip to free molecular flow regimes using the LB models equipped with different discrete velocity spaces, derived from the half-range Gauss Hermite (HGH), Gauss Legendre (GL), Gauss Kronrod (GK), and Gauss Chebyshev first and second quadrature rules. It is found that the conventional HGH-based LB models well describe noncontinuum Couette flows in the slip and weak transition flow regimes. Nonetheless, they suffer from significant errors with the further increasing Knudsen number, even if a large number of discrete velocities have been employed. Their results contrast with those by the LB models derived from the other Gaussian quadrature rules, which have far better accuracy at large Knudsen numbers. In particular, the GL- and GK-based LB models well capture the velocity fields of Couette flows in the strong transition and free molecular flow regimes. These numerical simulations in this article highlight the importance of velocity discretization for the LB simulations at different Knudsen numbers. They reveal that the LB models based on the Gauss Hermite (GH) quadrature rule are not always the best choice for simulating low-speed bounded flows at moderate and large Knudsen numbers; under strong noncontinuum conditions, those non-GH-based LB models proposed in this article have yielded more accurate results.

Molecular Alignment-Mediated Stick-Slip Poiseuille Flow of Oil in Graphene Nanochannels.

The flow behavior of oil in nanochannels has attracted extensive attention for oil transport applications. In most, if not all, of the prior theoretical simulations, oil molecules were observed to flow steadily in nanochannels under pressure gradients. In this study, non-equilibrium molecular dynamics simulations are conducted to simulate the Poiseuille flow of oil with three different hydrocarbon chain lengths in graphene nanochannels. Contrary to the conventional perception of steady flows of oil in nanochannels, we find that oil molecules with the longest hydrocarbon chain (i.e., n-dodecane) exhibit notable stick-slip flow behavior. An alternation between the high average velocity of n-dodecane in the slip motion and the low average velocity in the stick motion is observed, with a drastic, abrupt velocity jolt of up to 40 times occurring at the transition in a stick-slip motion. Further statistical analyses show that the stick-slip flow behavior of n-dodecane molecules originates from the molecular alignment change of oil near the graphene wall. The molecular alignment of n-dodecane shows different statistical distributions under stick and slip motion states, leading to significant changes of friction forces and thus notable velocity fluctuations. This work provides new insights into the Poiseuille flow behavior of oil in graphene nanochannels and may offer useful guidelines for other mass transport applications.

Programming protein phase-separation employing a modular library of intrinsically disordered precision block copolymer-like proteins creating dynamic cytoplasmatic compartmentalization

The control of supramolecular complexes in living systems at the molecular level is an important goal in life-sciences. Spatiotemporal organization of molecular distribution & flow of such complexes are essential physicochemical processes in living cells and important for pharmaceutical processes. Membraneless organelles (MO) found in eukaryotic cells, formed by liquid-liquid phase-separation (LLPS) of intrinsically disordered proteins (IDPs) control and adjust intracellular organization. Artificially designed compartments based on LLPS open up a novel pathway to control chemical flux and partition in vitro and in vivo. We designed a library of chemically precisely defined block copolymer-like proteins based on elastin-like proteins (ELPs) with defined charge distribution and type, as well as polar and hydrophobic block domains. This enables the programmability of physicochemical properties and to control adjustable LLPS in vivo attaining control over intracellular partitioning and flux as role model for in vitro and in vivo applications. Tailor-made ELP-like block copolymer proteins exhibiting IDP-behavior enable LLPS formation in vitro and in vivo allowing the assembly of membrane-based and membraneless superstructures via protein phase-separation in E. coli. Subsequently, we demonstrate the responsiveness of protein phase-separated spaces (PPSSs) to environmental physicochemical triggers and their selective, charge-dependent and switchable interaction with DNA or extrinsic and intrinsic molecules enabling their selective shuttling across semipermeable phase boundaries including (cell)membranes. This paves the road for adjustable artificial PPSS-based storage and reaction spaces and the specific transport across phase boundaries for applications in pharmacy and synthetic biology.

ACTIVE TECHNOLOGICAL CONTROL OF THE THICKNESS AND UNIFORMITY OF SPRAYING OF THIN FILMS

A method is proposed for active technological control and management of the deposition of thin conductive films, which makes it possible to obtain films of a given and uniform thickness over its entire surface. In the control method, wire resistive witnesses are used as primary measuring transducers, which are installed in specified areas of the molecular flow of the sprayed substance. Wire resistive witnesses change resistance depending on the thickness of the film deposited on them. In the process of deposition, according to information from wire witnesses, the molecular flow from the evaporator in certain areas is blocked by electromechanical shutters, which ensures uniform thickness of the deposited film. Experimental verification of the developed method and the system implementing it showed a decrease in the spread of film thickness over the entire surface of the substrate from 7 to 2 % on average.

Yi-Qi-Jian-Pi formula ameliorates immune function in acute-on-chronic liver failure by upregulating autophagy and mitochondrial biogenesis in CD8+ T lymphocytes.

A key event in the pathogenesis of acute-on-chronic liver failure (ACLF) is the imbalance in the systemic immune response; immunosuppression in patients with ACLF contributes to poor prognosis. The Yi-Qi-Jian-Pi formula (YQJPF) may improve T lymphocyte immune function in patients with ACLF. To investigate the immune mechanism of YQJPF in vivo and in vitro. An ACLF rat model was established by injection of CCl4, lipopolysaccharide, and D-galactosamine. We examined the effect of different doses of YQJPF (6.43, 12.87, 25.74g/kg) on liver injury and immune function in the ACLF rat model. Magnetic-activated cell sorting was used to sort the CD8+ T lymphocytes in the spleen for lymphocyte function detection. In primary CD8+ T lymphocytes and Jurkat cell lines, the expression of mitochondrial function and biogenesis and autophagy related markers were detected using molecular biological methods and flow cytometry analysis. YQJPF improved the peripheral blood lymphocyte count and proportion of CD8+ T lymphocytes in ACLF rats, increased pro-inflammatory factors (IL-2, IFN-λ, and TNF-α), and reduced anti-inflammatory factors (IL-10 and TGF β1). YQJPF also improved metabolism and mitochondrial homeostasis in CD8+ T lymphocytes, alleviated lymphocyte immune dysfunction by promoting autophagy, upregulated mitochondrial biogenesis by promoting PGC-1α, NRF-1, and TFAM expression, and regulated the relationship between autophagy and mitochondrial biogenesis via PGC-1α. Our results suggest that YQJPF could improve immune function in a rat model of ACLF, possibly via affecting the homeostasis of lymphatic mitochondria in CD8+ T lymphocytes. YQJPF may enhance lymphocyte mitochondrial biosynthesis and promote lymphocyte autophagy. PGC-1α is a possible upstream regulatory target of YQJPF.

Gas flow measurement of evaporated liquid nanoflows

Following the miniaturisation of fluidic components, the demand for traceable measurements of micro and nanoflows is increasing in various technological fields such as pharmaceuticals, biotechnology and automotive industry. Gravimetric flow measurement methods are accurate at microflows and above, but have a lower limit of about 5nLmin−1. Several alternative approaches have been developed to circumvent this limit. Here a measurement setup and proof of principle is presented for a method measuring the gas flows generated by complete evaporation of liquid ethanol nanoflows. The gas flow measurement is based on the well-established method of determining the pressure drop across a geometrically precisely defined circular opening in the molecular flow regime. Liquid flow rates from a syringe pump in the range of 5nLmin−1 to 200nLmin−1 are measured with an expanded uncertainty as low as 340pLmin−1 at instantaneous flow rates. Strategies to further improve accuracy are discussed.

The Properties of Different Starches under the Influence of Glucono-Delta-Lactone at Different Concentrations.

In this study, glucono-delta-lactone (GDL), which is Generally Recognized as Safe (GRAS), was added to native starches to modify their physicochemical properties. The effects of GDL on the molecular weight, pasting properties, flow behavior, gel syneresis, and crystallization properties of potato, tapioca, and corn starches were investigated. GPC results showed that as the GDL concentration increased, the molecular weight of amylose increased, whereas that of amylopectin decreased. An analysis using the Rapid Visco Analyzer revealed that the addition of GDL improved the pasting properties of potato starch, with reduced peak viscosity and breakdown viscosity, and it also improved setback viscosity. On the other hand, tapioca starch degraded substantially after GDL addition, indicating a lower tendency for short-term retrogradation, as reflected in the lower setback viscosity. The effects of GDL on corn starch pasting properties were very similar to those observed for tapioca starch, but the changes were relatively subtle. In terms of flow behavior, GDL addition decreased and increased the flow index values of the potato and tapioca starch pastes, respectively. However, the effect of GDL addition on the flow index value of the corn starch paste was found to be insignificant. The results also showed that the percentage of syneresis under the influence of GDL depended on the starch botanical origin-that is, potato starch, 14-18%, tapioca starch, 10-13%, and corn starch, 17-20%-which was substantiated by crystallinity analysis. It was observed that GDL has the potential to be used for starch modification because it creates desirable functionalities with the advantage of being a green-labelled ingredient.

Argon Gas Flow Through Micro- and Nano-pipettes

Glass micropipettes and nanopipettes are widely used for injection to or aspiration from living cells, and nanopipettes can be also used for nano-fabrication by deposition. Here, we show a non-destructive and contamination-free method of examining the inside of glass micropipettes and nanopipettes by argon gas flow through the pipettes from the tip-top to the tube-end. The exit pressure for each pipette was measured at the entrance pressure of 50 kPa, and the semi-log plot of the vacuum conductance versus pipette inner diameter is compared with the calculation using tapered tube approximation assuming molecular flow. The experimental results were consistent in trend with the calculation, and the difference between the experimental results and the calculation was due to the intermediate gas flow as the pipette inner diameter increases. Therefore, the formula of the calculation was transformed using the Gompertz function to fit the experimental results well. By utilizing the plot of the inner diameter dependence of the exit pressure, the inner diameter of glass pipettes can be estimated from our developed gas flow method.

Identification of starvation-mimetic bioactive phytocomponent from Withania somnifera using in-silico molecular modelling and flow cytometry-based analysis for the management of malaria

Multidrug resistance episodes in malaria increased from 3.9% to 20% from 2015 to 2019. Synchronizing the clinical manifestation in chronological sequence led to a unique impression on glucose demand (increased up to 100-fold) by the parasite-infected RBCs. Hence, restriction in the glucose uptake to parasite-infected RBCs could be an alternative approach to conquer the global burden of malaria to a greater extent. A C28 steroidal lactone Withaferin A (WS-3) isolated from Withania somnifera leave extract shows better thermodynamically stable interactions with the glucose transporters (GLUT-1 and PfHT) to standard drugs metformin and lopinavir. MD simulations for a trajectory period of 100 ns reflect stable interactions with the interactive amino acid residues such as Pro141, Gln161, Gln282, Gln283, Trp388, Phe389, and Phe40, Asn48, Phe85, His168, Gln169, Asn311 which potentiating inhibitory activity of WS-3 against GLUT-1 and PfHT respectively. WS-3 was non-hemotoxic (%hemolysis <5%) for a high concentration of up to 1 mg/ml in the physiological milieu. However, the %hemolysis significantly increased up to 30.55 ± 0.929% in a parasitophorous simulated environment (pH 5.0). Increased hemolysis of WS-3 could be due to the production of ROS in an acidic environment. Further, the inhibitory activity of WS-3 against both glucose transporters was supported with flow cytometry-based analysis of parasite-infected RBCs. Results show that WS-3 has low mean fluorescence intensities for both target proteins compared to conventional drugs, suggesting a potential sugar transporter inhibitor against GLUT-1 and PfHT for managing malaria. Communicated by Ramaswamy H. Sarma

Abstract 3321: Development of a CTC-based novel diagnostic technology for unresectable non-small cell lung cancer

Abstract BACKGROUND: PD-L1 in pathological tissue samples is known as a biomarker for immune checkpoint inhibitors (ICI) to unresectable non-small cell lung cancer (NSCLC) patients. However, collecting pathological tissue is highly invasive, and lower invasive test is needed. As an alternative diagnostic target, circulating cancer cells (CTCs) that are known to exist in the peripheral blood of cancer patients are garnering attention. PURPOSE: The goal of this study is to verify the utility of CTC analysis isolated by a novel system (Sysmex, Hyogo) against pathological testing of tumor samples. The primary objective is to determine whether CTCs can be detected in unresectable NSCLC patients, and the secondary objective is to evaluate the relationship between CTCs and clinicopathological features or clinical outcome. METHODS: Blood samples were collected from 45 patients with unresectable NSCLC and 17 healthy controls. CTCs were size-dependently enriched from whole blood, immunofluorescent stained with pan-CK (AE1/AE3), PD-L1, CD45/34/16, and Hoechst, and analyzed by Molecular Imaging Flow Cytometry (MI-1000). Fluorescence intensity and cell images of each marker were obtained by MI-1000. RESULTS: Cells positive for Hoechst but negative for blood cell markers were defined as non-blood cells (NBCs). Pan-CK positive NBCs were defined as CTCs. A similar number of NBCs were detected in both patients and healthy controls. When using a threshold set at two standard deviations above the mean fluorescence intensity of pan-CK and PD-LI of NBCs in healthy controls, 28.9% of patients had two or more CTCs. On the other hands, PD-L1 positive NBCs were only detected in patients, and the sensitivity of detecting CTCs or PD-L1 positive NBCs was 86.7%. Concordance with PD-L1 expression of tumor tissue was evaluated for three parameters: the number of PD-L1 positive NBCs, the median and the mean fluorescence intensities. The AUC in each case was low, indicating no concordance between PD-L1 expression of tumor tissue and CTCs. Additionally, no relation was found with the overall survivals and progression-free survival when comparing patients divided into two groups: those with two or more PD-L1 positive cells and those with less than two. CONCLUSION: The detected rate of pan-CK positive cells was low (&amp;lt;30%), but increased to 86.7% when pan-CK negative and PD-L1 positive NBCs, which are not found in healthy controls, were included. However, further studies are needed to evaluate whether these NBCs are CTCs. In addition, there was no association between PD-L1 positive NBCs and PD-L1 expression of tumor tissue or clinical outcome in this study. Recently, we have verified that the detected ratio of CTCs could be improved by adding a CK8/18 marker and hence, plan to verify the clinical usefulness of detecting CTCs using CK8/18. Citation Format: Mami Onishi, Eri Morita, Tetsuya Sakai, Yoshitaka Zenke, Masatoshi Yanagida, Koichi Goto. Development of a CTC-based novel diagnostic technology for unresectable non-small cell lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3321.

Abstract 1026: A novel detection system of circulating tumor cells based on size-dependent enrichment with immunofluorescent staining of CK8/18 in advanced non-small cell lung cancer

Abstract Background: Detection of circulating tumor cells (CTCs) in the blood is a potentially noninvasive tool for cancer diagnosis, monitoring and prognosis evaluation. However, the CTC detection is difficult because of the rarity of CTCs, especially in non-small cell lung cancer (NSCLC), and the detection sensitivity of CTCs was reported to be less than 50% in NSCLC patients. Herein, we developed a novel CTC detection system and evaluated its performance in advanced NSCLC patients. Methods: Whole blood samples were collected from stage IV or recurrence NSCLC patients. CTC detection was performed with a novel system (Sysmex Corporation, Hyogo, Japan) by using size-dependent enrichment for capturing CTCs and immunofluorescent staining reagents including anti-cytokeratin (CK, AE1/AE3 or CK8/18) (specific for epithelial cells), anti-CD45 (specific for leukocyte) and Hoechst (for nucleus). Fluorescence intensity and cell images of each marker were obtained by Molecular Imaging Flow Cytometry (MI-FCM). Circulating cells that were positive for Hoechst and anti-CK but negative for anti-CD45 were defined as CTCs. To confirm whether CTCs detected were derived from lung cancer origin, CTCs obtained from patients with EGFR mutations were subjected to single cell sorting, whole genome amplification and PCR analysis for the mutation detection. Results: A total of 20 NSCLC patients (10 EGFR mutant, 10 EGFR wild-type) were enrolled in this study. Of these, CTCs were detected in 16 (80%) patients (number of CTCs, 1 to 66 in 4.5ml whole blood) when CK8/18 was used as epithelial cell staining, but in only 11 (55%) patients (1 to 6 CTCs) when using AE1/AE3. The detection sensitivity of CTCs based on CK8/18 was significantly higher compared to that based on AE1/AE3 in our novel system (80% vs. 50%, p = 0.03). The number of CTCs was significantly lower in EGFR mutation-positive patients than in EGFR wild-type patients (median number of CTCs, 3 vs. 22, p = 0.01). Furthermore, among 10 EGFR mutation-positive patients, EGFR mutations were detected in CTCs derived from 6 (60%) patients. All the mutation types detected in CTCs were matched with those identified in the corresponding primary tumors. Conclusion: Our novel CTC detection system demonstrated that the detection rate of CTCs (80%) was higher than those in previous studies. Further studies are needed for the clinical application of this system. Citation Format: Tetsuya Sakai, Yoshitaka Zenke, Mami Onishi, Eri Morita, Masatoshi Yanagida, Yuji Shibata, Hiroki Izumi, Kaname Nosaki, Hibiki Udagawa, Shingo Matsumoto, Kiyotaka Yoh, Koichi Goto. A novel detection system of circulating tumor cells based on size-dependent enrichment with immunofluorescent staining of CK8/18 in advanced non-small cell lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1026.

OPTIMIZATION OF THE GEOMETRIC PARAMETERS OF THE MOLECULAR STAGE OF A VACUUM PUMP WITH SCREW CHANNELS ON THE ROTOR

A technique for optimizing the geometric parameters of the molecular stage of a turbo molecular vacuum pump with helical channels made on the rotor is considered. In the axial section of the rotor, the channels have a rectangular shape. As a result of numerical experiments by the Monte Carlo method in the molecular gas flow regime, the influence of each geometrical parameter of the rotor on the main pumping characteristics of the molecular stage was established. The developed program makes it possible to optimize the geometric parameters of the helical channels of the molecular stage for given overall dimensions of the rotor in order to obtain the maximum speed of action and pressure ratio.

Suivi de la maladie résiduelle dans les leucémies aiguës myéloïdes

AbstractMeasurable residual disease (MRD) status of acute myeloid leukemia (AML) patients is an independent prognostic factor for risk stratification and treatment decisions, combined with other well-established AML features such as cytogenetics analysis and mutation profiling at diagnosis. The MRD can be evaluated by molecular assays and/or flow cytometry. To date, MRD evaluation by molecular technics is highly dependent on the biomarker analyzed and the assay. qPCR is highly sensitive but is only suitable for mutational hotspots. High-throughput sequencing (NGS) allows comprehensive mutational profiling in many genes but requires molecular barcodes and complex bioinformatics analysis to achieve sufficient sensitivity. This method still needs to be standardized and has yet to be further validated in clinical trials. Finally, two cytometric approaches are used to evaluate MRD: the detection of blasts expressing an aberrant immunological phenotype associated with leukemia (LAIP) and the identification of CD34+CD38- leukemic stem cells (LSC) expressing at least one aberrant marker absent on hematopoietic stem cells.

A compact and highly collimated atomic/molecular beam source

We describe the design, characterization, and application of a simple, highly collimated, and compact atomic/molecular beam source. This source is based on a segmented capillary design, constructed using a syringe needle. Angular width measurements and free molecular flow simulations show that the segmented structure effectively suppresses atoms traveling in off-axis directions, resulting in a narrow beam of Helium atoms having a width of 7 mrad (full width half maximum). We demonstrate an application of this source by using it for monitoring real-time changes in surface coverage on a clean Cu(110) surface exposed to oxygen by measuring the specular reflectivity of the Helium beam generated using this source.

Vacuum chamber conditioning and saturation simulation tool (VacuumCOST): Enabling time-dependent simulations of pressure and NEG sticking in UHV chambers

Modern particle accelerators, synchrotrons, and other machines requiring UHV frequently make use of NEG coatings to achieve low pressures and resulting high beam stability and lifetime. It is the nature of NEG pumps and coatings, that a limited amount of gas can be pumped before saturation is reached, at which point the NEG must be re-activated to pump efficiently again. While the pumping mechanism and absorption limits are well understood and software packages exist for simulating the steady-state vacuum systems, there is a need for simulating the temporal evolution of the pumping capability of NEG coatings in regions of high outgassing rates such as near crotch absorbers. This paper presents a simple framework, written in Python, for running time-dependent simulations of NEG-coated vacuum systems in molecular flow, by making use of the command-line interface of the already widely used MolFlow simulation software. It also compares simulation results with accelerator pressure measurements.

Heat transfer characteristics of nanofluid under the action of magnetic field based on molecular dynamics and flow states

Theoretical analysis, numerical simulations, and experimental studies are used to comprehensively investigate the changes in the heat transfer characteristics of Fe3O4–water magnetic nanofluid under different types of magnetic fields and the heat transfer mechanism, providing new ideas for its practical application. By combining the fundamental conservation theorem and the Boussinesq approximation, dimensionless control equations have been established. The analysis of the variation pattern of the calculated values of the source terms under different boundary conditions, as well as the order of magnitude analysis, concludes that: the enhanced trend of Brownian motion and thermophoretic motion is the main reason for the enhanced heat transfer capability of the magnetic nanofluid; where the thermophoretic motion contributes slightly more to the heat transfer; the increase in Joule heat is the reason for the further enhancement of the heat transfer capability by the magnetic field. Volume fraction, temperature, and magnetic field strength are positively correlated with the average convective heat transfer coefficient. The reason for magnetic fields to enhance heat transfer is revealed by the deflection of the magnetic nanofluid by the magnetic body flow under local magnetic fields to form localized reflux. The alternating magnetic field further enhances the ability of magnetic fields to enhance heat transfer in magnetic nanofluids. Overall, the effect of the applied magnetic field on the motion of the magnetic nanoparticles causes the disruption of the thermal boundary layer, which is responsible for the enhanced heat transfer capacity of magnetic nanofluids.

Numerical simulation optimization of neutral flow dynamics in low-power Hall thruster

This paper utilizes a low-power Hall thruster to investigate its flow field’s neutral flow dynamics. Specifically, under a free molecular flow with a high Knudsen number (Kn>10), we employ the flow conductance theory to investigate the interplay between the internal structural parameters of the thruster flow field and its conductance, which is directly reflected in the neutral gas distribution.Hence, first, we increase the number and diameter of the orifices in the buffer chamber so that the baffle effectively increases the flow field conductance, and thus the number density (nn) of the neutral gas in the discharge channel increases. This phenomenon reduces the ionization mean free path (λi) and thus increases the utilization rate (ηi) of the neutral gas. Then, we alter the baffle orifices distribution to an unequally spaced distribution and stagger the outlet orifices, resulting in a highly homogeneity neutral gas distribution in the circumferential direction, ultimately increasing the effective outlet area and reducing the backflow probability of the neutral gas molecules. This operation reduces the low-frequency oscillation amplitude and thus enhances the thruster’s operation stability. Finally, we explore the influence of the entire operating conditions, especially temperature and mass flow rate variations, on the universality of the simulation results. Overall, this work provides a new concept for optimizing the neutral flow field dynamics of a Hall thruster.

OPTIMIZATION OF GEOMETRIC PARAMETERS OF HELICAL CHANNELS IN A MOLECULAR VACUUM PUMP

A method of optimization of geometrical parameters of a molecular stage of a turbomolecular vacuum pump with helical channels made on the stator under the molecular gas flow regime is considered. In axial section of stator the channels have rectangular shape. As a result of numerical experiments, the influence of each geometrical parameter on the main pumping characteristics of the molecular stage has been determined by the Monte-Carlo method.

Reynolds Analogy Coefficient in the Longitudinal Cylindrical Couette Problem: from the Continuous Medium to Free Molecular Flow

The gas Couette flow for a cylindrical geometry of bounding surfaces that move in the longitudinal direction relative to their symmetry axis is considered. For a monoatomic gas, the relation between the shear stress and the energy flux transferred to the longitudinal-flow surface (Reynolds analogy) is studied. In the case of continuous medium and free molecular flow regimes, simple explicit analytical expressions for the Reynolds analogy coefficient are obtained, which depend only on the Eckert number and are independent of the ratio of the cylinder radii. The transitional regime for various values of the Knudsen number is studied using the direct simulation Monte Carlo (DSMC) method. It is shown that, in this case, the Reynolds analogy coefficient at a fixed ratio of the radii and the Knudsen number depends on the relative velocity and temperatures of the surfaces mainly through the Eckert number. A relationship between the linear energy fluxes transferred to the cylindrical surfaces is found.