Sub-atmospheric Pressure Conditions Research Articles

Thermal stratification in a scaled-down suppression pool of the Fukushima Daiichi nuclear power plants

Thermal stratification in the suppression pool of the Fukushima Daiichi nuclear power plants was experimentally investigated in sub-atmospheric pressure conditions using a 1/20 scale torus shaped setup. The thermal stratification was reproduced in the scaled-down suppression pool and the effect of the steam flow rate on different thermal stratification behaviors was examined for a wide range of steam flow rates. A sparger-type steam injection pipe that emulated Fukushima Daiichi Unit 3 (F1U3) was used. The steam was injected horizontally through 132 holes. The development (formation and disappearance) of thermal stratification was significantly affected by the steam flow rate. Interestingly, the thermal stratification in the suppression pool vanished when subcooling became lower than approximately 5°C. This occurred because steam bubbles are not well condensed at low subcooling temperatures; therefore, those bubbles generate significant upward momentum, leading to mixing of the water in the suppression pool.

Characterization of filter performance under low-pressure operation

Particulate gas filters are a critical element in the purification systems used to ensure defect-free manufacturing in semiconductor industry. In atomic layer deposition (ALD) processes, these filters are typically operated under sub-atmospheric pressure conditions, but their filtration characteristics are, often, only known at atmospheric pressure. In this study, performance of a metal filter that is typically used in low-pressure ALD precursor delivery systems is studied experimentally and theoretically down to 4.5 kPa. The experimental procedure was designed to minimize the presence of multiply charged particles in the test aerosol for different operating pressures and flowrates. The experimental results suggest that most penetrating particle size only slightly varies with pressure, but the shape of the penetration curve and the maximum value of the penetration changes significantly with pressure. The experimental data are used to test predictions of filter performance at low pressures made using classical theory. The comparison results suggest that the combination of classical theory and manufacturer-specified parameters results in large errors in calculated penetration values at low pressures. Accurate predictions are seen to be possible for particle Stokes numbers less than 0.1, when an inhomogenous filtration model is used in combination with effective filter parameters that are obtained from experimental measurements of filter efficiency and pressure drop at atmospheric pressures.Copyright © 2016 American Association for Aerosol Research

Effect of negative pressure on growth, secretion and biofilm formation of Staphylococcus aureus.

Negative pressure wound therapy (NPWT) has gained popularity in the management of contaminated wounds as an effective physical therapy, although its influence on the bacteria in the wounds remains unclear. In this study, we attempted to explore the effect of negative pressure conditions on Staphylococcus aureus, the most frequently isolated pathogen during wound infection. S. aureus was cultured in Luria-Bertani medium at subatmospheric pressure of -125 mmHg for 24 h, with the bacteria grown at ambient pressure as the control. The application of negative pressure was found to slow down the growth rate and inhibit biofilm development of S. aureus, which was confirmed by static biofilm assays. Furthermore, decreases in the total amount of virulence factors and biofilm components were observed, including α-hemolysin, extracellular adherence protein, polysaccharide intercellular adhesin and extracellular DNA. With quantitative RT-PCR analysis, we also revealed a significant inhibition in the transcription of virulence and regulatory genes related to wound infections and bacterial biofilms. Together, these findings indicated that negative pressure could inhibit the growth, virulence and biofilm formation of S. aureus. A topical subatmospheric pressure condition, such as NPWT, may be a potential antivirulence and antibiofilm strategy in the field of wound care.

Evaluation of air gap membrane distillation process running under sub-atmospheric conditions: Experimental and simulation studies

The importance of removing non-condensable gases from air gap membrane distillation (AGMD) modules in improving the water vapor flux is presented in this paper. Additionally, a previously developed AGMD mathematical model is used to predict to the degree of flux enhancement under sub-atmospheric pressure conditions. Since the mathematical model prediction is expected to be very sensitive to membrane distillation (MD) membrane resistance when the mass diffusion resistance is eliminated, the permeability of the membrane was carefully measured with two different methods (gas permeance test and vacuum MD permeability test). The mathematical model prediction was found to highly agree with the experimental data, which showed that the removal of non-condensable gases increased the flux by more than three-fold when the gap pressure was maintained at the saturation pressure of the feed temperature. The importance of staging the sub-atmospheric AGMD process and how this could give better control over the gap pressure as the feed temperature decreases are also highlighted in this paper. The effect of staging on the sub-atmospheric AGMD flux and its relation to membrane capital cost are briefly discussed.

Axial temperature profile in buoyant plume of rectangular source fuel jet fire in normal- and a sub-atmospheric pressure

This paper investigates the axial temperature profiles in buoyant plume of rectangular source fuel jet fires. Experiments are carried out in this work by rectangular source nozzles with aspect ratio (width/length, W/L) ranged from 1:1 (axi-symmetrical) to 1:71 (linear) in Hefei city (100.8kPa) and Lhasa (64.3kPa). The axial temperature profile is theoretically deduced for different source dimensions and heat release rates, based on the conservation of Froude number (momentum/buoyancy) where its dependency on source initial momentum are then correlated from the experimental data. The previous classic correlation for plume temperature profile established by Quintiere is extended to jet fires by including the effect of source momentum as well as the dimensions of the rectangular burner. The proposed correlation is also further extended to the special sub-atmospheric pressure condition (Lhasa, 64.3kPa).

Kinetic Monte Carlo Simulation of the oscillatory catalytic CO oxidation using a modified Ziff-Gulari-Barshad model

The oxidation of CO on Pt-group metal surfaces has attracted widespread attention since a long time due to its interesting oscillatory kinetics and spatiotemporal behavior. The use of STM in conjunction with other experimental data has confirmed the validity of the surface reconstruction (SR) model under low pressure and the more recent surface oxide (SO) model which is possible under sub-atmospheric pressure conditions [1]. In the SR model the surface is periodically reconstructed below a certain low critical CO-coverage and this reconstruction is lifted above a second, higher critical CO-coverage. Alternatively the SO model proposes periodic switching between a low-reactivity metallic surface and a high-reactivity oxide surface. Here we present an overview of our recent kinetic Monte Carlo (KMC) simulation studies on the oscillatory kinetics of surface catalyzed CO oxidation. Different modifications of the lattice gas Ziff-Gulari-Barshad (ZGB) model have been utilized or proposed for this purpose. First we present the effect of desorption on the ZGB reactive to poisoned irreversible phase transition in the SR model. Next we discuss our recent research on KMC simulation of the SO model. The ZGB framework is utilized to propose a new model incorporating not only the standard Langmuir-Hinshelwood (LH) mechanism, but also introducing the Mars-van Krevelen (MvK) mechanism for the surface oxide phase [5]. Phase diagrams, which are plots between long time averages of various oscillating quantities against the normalized CO pressure, show two or three transitions depending on the CO coverage critical threshold (CT) value beyond which all adsorbed oxygen atoms are converted to surface oxide.

Lower Flammability Limits of Hydrogen and Light Hydrocarbons at Subatmospheric Pressures

The knowledge of flammability limits is essential in the prevention of fire/explosion when handling combustible gases and vapors. In this study, the lower flammability limits (LFLs) of hydrogen–air, methane–air, ethane–air, n-butane–air, and ethylene–air were measured in a closed cylindrical vessel (inner diameter 10.22 cm, length 100 cm) with upward flame propagation, at room temperature (20 °C) and initial pressure of 1.0, 0.7, 0.5, 0.3, and 0.1 atm. The LFL of hydrogen initially decreased with pressure from 1.0 to 0.3 atm, and then the LFL increased with the further decrease of pressure. In contrast, the LFLs of the hydrocarbons increased when the pressure decreased from 1.0 to 0.1 atm, except for methane for which the LFL did not change with pressure. The adiabatic flame temperatures (AFTs) at the obtained LFL concentrations of hydrogen and the hydrocarbons were also calculated at subatmospheric pressure conditions. The behaviors of the AFTs of hydrogen and the hydrocarbons were similar to those of the LFLs under the influence of low pressures. On average, at initial pressures from 1.0 to 0.1 atm and LFL concentration, the AFT of hydrogen was 730 K, of the alkanes was 1900 K, and of ethylene was 1800 K. On the basis of the LFLs and AFTs, the risk/hazard associated with fire/explosion of hydrogen and the hydrocarbons at subatmospheric pressures was also discussed.

An investigation into the sensory application of DBD plasma actuators for pressure measurement

This paper investigates the effect of air pressure on the current used by dielectric barrier discharge (DBD) plasma actuators and the voltage limits for plasma production in these actuators. The purpose of this research was to determine whether DBD plasma actuators have potential for application as a pressure sensor at sub-atmospheric pressure conditions. It was found that these actuators were sensitive to air pressure and possessed a distinct, non-linear relationship between the electrical current consumed by them and ambient pressure. It was also found that lower and upper voltage limits for plasma production increased approximately linearly with pressure.

A Comprehensive Insight in the MOCVD of Aluminum through Interaction between Reactive Transport Modeling and Targeted Growth Experiments

Growth experiments and reactive transport modeling were combined to formulate a comprehensive predictive model for aluminum growth from dimethylethylamine alane. The growth-rate profile was experimentally investigated as a function of substrate temperature. The reactive transport model, built under the computational fluid dynamics software PHOENICS, was used to reproduce the experimental measurements and to contribute to the understanding of the aluminum growth process, under sub-atmospheric pressure conditions. The growth mechanism of aluminum films was based on well established in literature reaction order and activation energy of homogeneous and heterogeneous chemical reactions. The reactive transport model was used further to investigate the effect of some key operating parameters on the process output. Simulation results are suggestive of modifications in the operating parameters that could enhance the growth rate and the spatial uniformity of the film thickness.

Double-Evaporator Thermosiphon for Cooling 100 kWh Class Superconductor Flywheel Energy Storage System Bearings

This paper presents an idea for a thermosiphon that uniquely implements two integrated evaporators to cool two HTS (High Temperature Superconductor) bulk sets in different locations, simultaneously. A so-called double-evaporator thermosiphon was designed, fabricated and tested using nitrogen as the working fluid under sub-atmospheric pressure conditions. The operating target temperature was approximately 65 K. To confirm the feasibility of the double-evaporator thermosiphon, experiments during the cool down process and steady state operation were extensively conducted on the double-evaporator thermosiphon (Ltot = 1075 mm, do = 160 mm). The double-evaporator thermosiphon worked successfully at steady state operation. The results showed that it had a maximum total temperature difference between the condenser and the evaporator of 1.3 K and a temperature difference between the two evaporators of 0.6 K at a heat flow of 87 W. This thermosiphon was designed for actual application to a 100 kWh SFES (Superconducting Flywheel Energy Storage) system. The potential impact of superior heat transfer characteristics of the double-evaporator thermosiphon is discussed in the paper.

Experimental study on the double-evaporator thermosiphon for cooling HTS (high temperature superconductor) system

A cryogenic thermosiphons is an efficient heat transfer device between a cryocooler and a thermal load that is to be cooled. This paper presents an idea of thermosiphon which contains two vertically-separated evaporators. This unique configuration of the thermosiphon is suitable for the purpose of cooling simultaneously two superconducting bearings of the HTS (high temperature superconducting) flywheel system at the same temperature. A so-called double-evaporator thermosiphon was designed, fabricated and tested using nitrogen as the working fluid under sub-atmospheric pressure condition. The interior thermal condition of the double-evaporator thermosiphon was examined in detail during its cool-down process according to the internal thermal states. The double-evaporator thermosiphon has operated successfully at steady-state operation under sub-atmospheric pressure. At the heat flow of 10.6 W, the total temperature difference of the thermosiphon was only 1.59 K and the temperature difference between the evaporators was 0.64 K. The temperature difference of two evaporators is attributed to the conductive thermal resistance of the adiabatic section between the evaporators. The method to reduce this temperature difference has been investigated and presented in this paper. The proper area selection of condenser, evaporator 1, and evaporator 2 was studied by using thermal resistance model to optimize the performance of a thermosiphon. The superior heat transfer characteristic of the double-evaporator thermosiphon without involving any cryogenic pump can be a great potential advantage for cooling HTS bulk modules that are separated vertically.

Effect of nanoparticles in nanofluid on thermal performance in a miniature thermosyphon

An experiment was performed to investigate the effect of nanoparticles in the nanofluid on the thermal performance in a miniature thermosyphon. The nanofluids consisted of de-ionized water and CuO nanoparticles having an average size of 30nm. The experimental results show that the water-CuO nanofluids can greatly enhance the boiling heat transfer performance of the evaporator in thermosyphon compared with that using water at subatmospheric pressure conditions. A much lower and more uniform wall temperature of the thermosyphon can be obtained by substituting the nanofluids for water. Boiling heat transfer coefficients and the critical heat flux (CHF) of the nanofluids in the evaporator of the thermosyphon have significant increase compared with those of de-ionized water. There was an optimal mass concentration which was estimated to be 1.0wt% to achieve the maximum heat transfer performance. Operating pressure has very remarkable influences on both the heat transfer coefficients and the CHF of nanofluids, which greatly increase with the decrease of the test pressure. The heat transfer coefficient and the CHF can increase, respectively, about 160% and 120% at the pressure of 7.45kPa compared with those of water. The experimental study confirmed that the heat transfer performance of the miniature thermosyphon can evidently be strengthened by using water-CuO nanofluids.

Optimization and evaluation of low-pressure gas chromatography–mass spectrometry for the fast analysis of multiple pesticide residues in a food commodity

A fast method of analysis for 20 representative pesticides was developed using low-pressure gas chromatography–mass spectrometry (LP-GC–MS). No special techniques for injection or detection with a common quadrupole GC–MS instrument were required to use this approach. The LP-GC–MS approach used an analytical column of 10 m×0.53 mm I.D., 1 μm film thickness coupled with a 3 m×0.15 mm I.D. restriction capillary at the inlet end. Thus, the conditions at the injector were similar to conventional GC methods, but sub-atmospheric pressure conditions occurred throughout the analytical column (MS provided the vacuum source). Optimal LP-GC–MS conditions were determined which achieved the fastest separation with the highest signal/noise ratio in MS detection (selected ion monitoring mode). Due to faster flow-rate, thicker film, and low pressure in the analytical column, this distinctive approach provided several benefits in the analysis of the representative pesticides versus a conventional GC–MS method, which included: (i) threefold gain in the speed of chromatographic analysis; (ii) substantially increased injection volume capacity in toluene; (iii) heightened peaks with 2 s peak widths for normal MS operation; (iv) reduced thermal degradation of thermally labile analytes, such as carbamates; and (v) due to larger sample loadability lower detection limits for compounds not limited by matrix interferences. The optimized LP-GC–MS conditions were evaluated in ruggedness testing experiments involving repetitive analyses of the 20 diverse pesticides fortified in a representative food extract (carrot), and the results were compared with the conventional GC–MS approach. The matrix interferences for the quantitation ions were worse for a few pesticides (acephate, methiocarb, dimethoate, and thiabendazole) in LP-GC–MS, but similar or better results were achieved for the 16 other analytes, and sample throughput was more than doubled with the approach.

Fungitoxic Activity of 12 Essential Oils against Four Postharvest Citrus Pathogens: Chemical Analysis of Thymus capitatus Oil and its Effect in Subatmospheric Pressure Conditions

The fungitoxic activity against Penicillium digitatum, Penicillium italicum, Botrytis cinerea, and Alternaria citri of 12 essential oils (EOs) distilled from medicinal plants is reported. The results of the in vitro trials show strong fungitoxic activity of Thymus capitatus (L.) Hofmgg EOs, which inhibited the growth of the four fungi at a concentration of 250 ppm (vol/vol). The other 11 essences reduced the development of the fungi from 95 to 9% at 250 ppm (vol/vol). The fungitoxic activity of T. capitatus EOs (75, 150, and 250 ppm) on healthy orange fruits, inoculated with P. digitatum (108 conidia ml−1) by spraying and placed in 10-liter desiccators, was weak at atmospheric pressure (3 to 10% inhibition at all three concentrations), while in vacuum conditions (0.5 bar), conidial mortality on the exocarp was high (90 to 97% at all three concentrations).These data proved not to be statistically different from treatments with thiabendazole-TBZ (2,000 ppm). Scanning electron microscope observations showed that T. capitatus EO vapors altered the morphology of P. digitatum hyphae and conidia. The gas-chromatographic analyses of thyme EO indicated that carvacrol was present at 81 to 83%, p-cymene at 4.5 to 5%, γ-terpinene at 2.6 to 3.3%, caryophyllene at 1.5 to 1.6%, β-myrcene at 1.6%, and linalool at 1.1 to 1.2%. Carvacrol proved to be the most important fungitoxic compound among the thyme EO constituents, but, unlike thyme EO, it caused alterations to the fruit at the concentration of 75 ppm.

Growth Kinetics and Deposition‐Related Properties of Subatmospheric Pressure Chemical Vapor Deposited Borophosphosilicate Glass Film

Growth kinetics of borophosphosilicate glass (BPSG) films prepared by the chemical reaction of tetraethylorthosilicate (TEOS), triethylborate, and triethylphosphate, with ozone‐oxygen mixture has been studied using a single‐wafer deposition chamber at 373–458°C under reduced pressure or subatmospheric pressure condition (SABPSG). Based on the comparison of the effective reaction rate constants and other kinetic features, the similarity of BPSG deposition kinetic for different types of precursors and deposition conditions are shown. Fourier transform infrared spectroscopy, X‐ray fluorescence analysis, secondary ion mass spectrometry, stress measurement, optical microscopy, scanning electron microscopy, atomic force microscopy, surface laser scanning, capacitance‐voltage, current voltage, and surface charge analysis techniques have been used for the characterization of SABPSG film properties. Moisture absorption and surface defect formation phenomena have been studied for both as‐deposited and furnace annealed films with boron and phosphorus ranging from 3 to 6 wt %. The liquid state, solid state, and crystalline BPSG surface defects have been characterized and their relationships have been shown. A multipath and multistep reaction mechanism scheme of TEOS‐ozone BPSG deposition process with the formation of active intermediate products, a scheme of porous TEOS‐ozone BPSG film with embedded dopant‐rich clusters, and a scheme of defect formation and growth on BPSG films are discussed. Empirical equations of quantitatively optimized BPSG dopant concentration range are presented by taking into account flow properties, defect formation, and moisture absorption processes in the film. © 1999 The Electrochemical Society. All rights reserved.

Hood Characteristics for Siphon‐Shaft Spillways

A shaft spillway is equipped with a hood in order to operate as a siphon. Appropriate hood dimensions and shape are searched by using cylindrical hoods of different dimensions for a standard bellmouthed shaft. The hood, sized and streamlined according to experimental results, showed a good performance concerning the discharge and subatmospheric pressure conditions. Design charts for discharge coefficient as well as critical hood and shaft‐crest pressures are presented for such a siphon‐shaft spillway, and a design example is given.

Pressure dependence of the particle bed dryout heat flux

As a basic study for the post-accident heat removal, the dryout heat flux was measured by simulating decay heat of debris by induction-heating of a steel ball bed. The experimental ranges were the steel ball diameter: 1 mm, 1.5 mm, 2 mm and 3 mm and the system pressure: 0.02–0.5 MPa. As a whole trend, the experimental result agreed fairly well with the prediction based on Lipinski's 0-D model. In detail, however, the dryout heat flux deviated toward a lower value at a high pressure, but toward a higher value at a low pressure. This upward deviation was especially pronounced for a small particle below 1.5 mm diameter at a subatmospheric pressure condition. Comparing the results between free and fixed beds of 1 mm diameter particles, we decided this phenomena resulted from the local formation of a vapor channel due to the movement or levitation of the particle bed.

Scalding Poultry by Steam at Subatmospheric Pressures

The poultry industry needs to replace the long existing, almost universally used immersion scalding method by methods that would be more sanitary and esthetically acceptable, provide a safer, more stable product, and minimize pollution and water requirements. There have been several efforts to develop scalding by mixtures of air and steam maintained at proper temperatures; commercial models have been built and tested but so far no substantial commercial use developed.This report describes preliminary tests that establish the possibility of scalding birds for feather removal by exposing them to an atmosphere of steam under controlled subatmospheric pressure and temperature conditions. Scalding was carried out in a cylindrical metal vacuum chamber, connected to a mechanical vacuum pump and condenser and a manually controlled inflow of steam. The system permitted establishment of uniform steam atmospheres of desired temperatures (± 1°F.) within 15 seconds, in the range from 52°C. (125°F.) to 60°C. (140°F.),…