Sub-atmospheric Conditions Research Articles

Submerged Jet Impingement Boiling of Water Under Subatmospheric Conditions

An experimental study of jet impingement boiling is presented for water under saturated and subcooled conditions. Unique to this study is the documentation of boiling curves of a submerged water jet under subatmospheric conditions. Data are reported at a fixed nondimensional nozzle-to-surface distance of H/dj = 6 and for a fixed surface-to-nozzle diameter ratio, dsurf/dj, of 23.8. Saturated jet impingement experiments are performed at three subatmospheric pool pressures of 0.176 bar, 0.276 bar, and 0.478 bar with corresponding saturation temperatures of 57.3 °C, 67.2 °C, and 80.2 °C. At each pressure, jet impingement boiling at varying Reynolds numbers are characterized and compared with pool boiling heat transfer. The effect of surface roughness and fluid subcooling is studied at the lowest pressure of 0.176 bar. Boiling curves indicate a strong dependence of heat flux on jet Reynolds number in the partially developed nucleate boiling region but only a weak dependence in the fully developed nucleate boiling region. At a fixed wall superheat, fluid subcooling is found to shift the boiling curve to the left thereby enhancing heat transfer performance. Critical heat flux is found to increase with increases in pressure, surface roughness, and Reynolds number.

On the Characteristics of a Novel Floating Sub-Atmospheric Solar Water Desalination System

This paper proposes a new floating sub-atmospheric solar water desalination system to provide the water resource for domestic to industrial usage. In addition to conventional solar stills (CSS) which only utilize incident solar radiation, the sub-atmospheric condition of this system greatly increases the productivity of the system. The mathematical model of the system is developed and the performance of the still is evaluated. The overall productivity of the still is shown to be sensitive to evaporator pressure as the most significant parameter of the system. Other parameters affecting the performance include cover transmissivity and input water temperature.

Laminar burning velocities and flame stability analysis of hydrogen/air premixed flames at low pressure

An experimental and numerical study on laminar burning velocities of hydrogen/air flames was performed at low pressure, room temperature, and different equivalence ratios. Flames were generated using a small contoured slot-type nozzle burner (5 mm × 13.8 mm). Measurements of laminar burning velocity were conducted using the angle method combined with Schlieren photography. Numerical calculations were also conducted using existing detailed reaction mechanisms and transport properties. Additionally, an analysis of the intrinsic flame instabilities of hydrogen/air flames at low pressure was performed. Results show that the behavior of the laminar burning velocity is not regular when decreasing pressure and that it depends on the equivalence ratio range. The behavior of the laminar burning velocity with decreasing pressure can be reasonably predicted using existing reaction mechanisms; however changes in the magnitude of the laminar burning velocity are underestimated. Finally, it has been found experimentally and proved analytically that the intrinsic flame instabilities are reduced when decreasing the pressure at sub-atmospheric conditions.

Laminar burning velocities and flame stability analysis of syngas mixtures at sub-atmospheric pressures

The effects of low pressure on the laminar burning velocity and flame stability of H 2/CO mixtures and equimolar H 2/CO mixtures diluted with N 2 and CO 2 were studied experimentally and theoretically. Experiments were conducted at real sub-atmospheric conditions in three places located at high altitudes 500 m.a.s.l. (0.947 atm), 1550 m.a.s.l. (0.838 atm), and 2300 m.a.s.l. (0.767 atm). Flames were generated using contoured slot-type nozzle burners and Schlieren images were used to determine the laminar burning velocity with the angle method. The behavior of the laminar burning velocity at low pressures depends on the equivalence ratio considered; it decreases at lean and very rich equivalence ratios when pressure is increased. However, a contrary behavior was obtained at equivalence ratios corresponding to the highest values of the laminar burning velocity, where it increases as pressure increases. Numerical calculations were also conducted using a detailed reaction mechanism, and these do not reproduce the behavior obtained experimentally; a sensitivity analysis was carried out to examine the differences found. At lean equivalence ratios, flame instabilities were observed for all the syngas mixtures. The range of equivalence ratios where flames are stable increases at lower pressures. This behavior is due to the increase of the flame thickness, which considerably reduces the hydrodynamic instabilities in the flame front.

PREDICTION OF BINARY MIXTURE BOILING HEAT TRANSFER IN SYSTEMS WITH STRONG MARANGONI EFFECTS

This paper investigates the impact of Marangoni phenomena for low concentrations of 2-propanol/water and methanol/water mixtures. In real systems the addition of small levels of surface-active contaminants can affect the surface tension of the liquid-vapor interface and thermodynamic conditions in this region. Analysis was performed for three widely accepted binary mixture correlations to predict heat flux and superheat values for subatmospheric experimental data using bulk fluid and film thermodynamic properties. Due to the non-ideal nature of these alcohol/water mixtures, this study also employs an average pseudo single-component (PSC) coefficient in place of an ideal heat transfer coefficient (HTC) to improve the correlation predictions. This investigation evaluates the ability for these correlations to predict strong Marangoni effects of mixtures that have large surface tension variation with concentration under subatmospheric conditions. It is not always clear that evaluation of bulk fluid properties will satisfactorily account for Marangoni effects. Analysis is also performed to assess correlation predictions for interfacial film properties rather than that of the bulk fluid. The results indicate that the use of film properties along with the PSC coefficient improves heat flux model predictions of subatmospheric experimental data by as much as 59.3% for 0.015M 2-propanol and 49.1% for 0.04M methanol/water mixtures, where strong Marangoni effects are believed to be more evident.

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.

Boiling of Water at Subatmospheric Conditions With Enhanced Structures: Effect of Liquid Fill Volume

Liquid cooling with phase change has been demonstrated to be a very efficient technique for thermal management of electronics because it has the potential to achieve high heat transfer coefficients compared to single phase liquid cooling. Previous studies on liquid immersion cooling with fluorocarbons have shown the effectiveness of boiling enhancement structures in lowering boiling incipience, raising the critical heat flux, and reducing evaporator size. Two-phase thermosyphons are an alternative to liquid immersion cooling, where phase change liquid cooling can be implemented within a closed-loop device. The present study involves a two-phase thermosyphon with boiling enhancement structure in the evaporator, which is subjected to subatmospheric pressures for lowering the saturation temperature of the working fluid. The objective of the present research is to provide a detailed understanding of the effect of liquid-fill level on boiling of water with enhancement structures at subatmospheric pressures. The study will take into account the influence of system pressure and enhancement structure geometry on the boiling heat transfer. Experiments were performed at three different pressures, 9.7kPa, 15kPa, and 21kPa, using a stacked enhancement structure with three different geometries (one, four, and six layers), corresponding to three different liquid-fill levels (fill ratios of 0.5, 0.7, and 0.9). The results are compared with a base line study on subatmospheric pressure boiling from a plain surface at similar liquid-fill levels.

Kinetics and Structural Characterization of Calcium-Based Sorbents Calcined under Subatmospheric Conditions for the High-Temperature CO2Capture Process

The influence of several process parameters on the calcination of a naturally occurring limestone and a precipitated mesoporous calcium carbonate (CaCO3) sorbent structure to calcium oxide (CaO) is detailed in this study. CaCO3 calcination is an integral part of a multicyclic carbonation−calcination reaction (CCR) process that separates carbon dioxide (CO2) from high-temperature gas mixtures into a pure CO2 stream. Maintenance of high sorbent reactivity over repeated CCR cycles reduces the capital and operating cost of the CCR process. A lower calcination temperature, required to maintain high sorbent reactivity, reduces the calcination rate of CaCO3. This study investigates various process conditions such as subatmospheric calcination, sorbent dispersion in a rotary calciner, use of a high thermal conductivity sweep gas, etc. in enhancing the calcination rate at lower calcination temperatures. The high-temperature gas−solid carbonation studies of the resulting CaO sorbent prove the necessity to maintain a high porosity structure during limestone calcination.

Heat Curing of Soy Protein Films at Atmospheric and Sub‐atmospheric Conditions

ABSTRACT: The effect of heat curing at atmospheric or subatmospheric conditions on selected properties (moisture content, water vapor permeability (WVP), color, tensile strength (TS), elongation (E), and total soluble matter (TSM) content) of cast soy protein isolate films was investigated. Films were heat cured at 85 °C for 6, 12, 18, or 24 h at absolute pressures of 101.3, 81.32, or 61.32 kPa. Heat‐cured films had increased (P < 0.05) TS and decreased (P < 0.05) WVP and E compared to control, unheated films. Heat treatment under vacuum reduced the WVP of films faster than heat curing at atmospheric pressure. High TS values, low E values, and low TSM values were also reached within short heating time under vacuum. However, vacuum treatment increased the size and number of cavities in cured films as evidenced by scanning electron micrographs.

Development of high-resolution N_2 coherent anti-Stokes Raman scattering for measuring pressure, temperature, and density in high-speed gas flows

Mean and instantaneous measurements of pressure, temperature, and density have been acquired in an optically accessible gas cell and in the flow field of an underexpanded sonic jet by use of the high-resolution N(2) coherent anti-Stokes Raman scattering (CARS) technique. This nonintrusive method resolves the pressure- and temperature-sensitive rotational transitions of the nu = 0 ? 1 N(2) Q-branch to within Domega = 0.10 cm(-1). To extract thermodynamic information from the experimental spectra, theoretical spectra, generated by a N(2) spectral modeling program, are fit to the experimental spectra in a least-squares manner. In the gas cell, the CARS-measured pressures compare favorably with transducer-measured pressures. The precision and accuracy of the single-shot CARS pressure measurements increase at subatmospheric conditions. Along the centerline of the underexpanded jet, the agreement between the mean CARS P/T/rho measurements and similar quantities extracted from a Reynolds-averaged Navier-Stokes computational fluid dynamic simulation is generally excellent. This CARS technique is able to capture the low-pressure and low-temperature conditions of the M = 3.4 flow entering the Mach disk, as well as the subsonic conditions immediately downstream of this normal shock.

Detailed chemical kinetic mechanisms for combustion of oxygenated fuels

Thermodynamic properties and detailed chemical kinetic models have been developed for the combustion of two oxygenates: methyl butanoate, a model compound for biodiesel fuels, and methyl formate, a related simpler molecule. Bond additivity methods and rules for estimating kinetic parameters were adopted from hydrocarbon combustion and extended. The resulting mechanisms have been tested against the limited combustion data available in the literature, which was obtained at low temperature, subatmospheric conditions in closed vessels, using pressure measurements as the main diagnostic. Some qualitative agreement was obtained, but the experimental data consistently indicated lower overall reactivities than the model, differing by factors of 10 to 50. This discrepancy, which occurs for species with wellestablished kinetic mechanisms as well as for methyl esters, is tentatively ascribed to the presence of wall reactions in the experiments. The model predicts a region of weak or negative dependence of overall reaction rate on temperature for each methyl ester. Examination of the reaction fluxes provides an explanation of this behavior, involving a temperature-dependent competition between chain-propagating unimolecular decomposition processes and chain-branching processes, similar to that accepted for hydrocarbons. There is an urgent need to obtain more complete experimental data under well-characterized conditions for thorough testing of the model.

Measurement of Thermal Comfort and Indoor Air Quality Aboard 43 Flights on Commercial Airlines

This paper reports the results of thermal comfort and indoor air quality measurements aboard aircraft from 43 flights on commercial airlines with a duration of more than 1 h. The measurements were performed continuously during the whole flight (from the departure gate to the arrival gate), and the parameters monitored were temperature, relative humidity and carbon dioxide concentration. The results were then compared with the ASHRAE Standards for the thermal comfort (ASHRAE Standard 55-92) and indoor air quality (ASHRAE Standard 62-89). The evaluation of the indoor air quality was based mainly upon comparison of the carbon dioxide concentrations measured with standards and recommendations for the indoor environment. Overall, the levels of relative humidity were far lower than the limit set by the ASHRAE Standard 55-92. The levels of carbon dioxide on most flights were higher than that recommended by the ASHRAE Standard 62-89. The results of this study, mainly the low level of humidity and high concentrations of carbon dioxide, led us to expect that the crew and the passengers would have been dissatisfied with their degree of thermal comfort and the quality of the air in the cabin. This conclusion is based simply on a comparison of our measurements with the values stated in the ASHRAE Standards. However, we must bear in mind that these were developed for an indoor environment at atmospheric pressure. More research is needed to study the validity of these standards for sub-atmospheric conditions.

Stress Survival of a Genetically Engineered Pseudomonas in Soil Slurries: Cytochrome P-450cam-Catalyzed Dehalogenation of Chlorinated Hydrocarbons.

Biological treatment of hazardous chemical wastes has potential as an effective, practical, and economically viable process in above the ground treatment systems that consist of both genetically engineered microorganisms (GEMs) and bioreactors with process control instruments to create ideal conditions for biodegradation. A strain of Pseudomonas putida coexpressing cytochrome P-450cam and luciferase (lux) that provides both the reductive detoxification potential of the hemoprotein and a mechanism for its reduction in the absence of "normal" P-450 redox partners was evaluated for its ability to survive and remain metabolically competent under nutrient stress in soil slurry microcosms. More than 74% of the cells of engineered Pseudomonas were culturable after 7 days of multiple nutrient (C,N,P) starvation. The diagnostic luminescence and carbon monoxide-difference spectra for the two engineered traits could be detected in a significant fraction of the surviving population. The GEM could be revived after repeated desiccation and starvation using Luria broth, benzoate, or citrate as nutrients. Soil slurries inoculated with the GEM transformed hexachloroethane (HCE) to tetrachloroethylene (tetraCE) 8-10-fold faster than uninoculated slurries. The GEM also transformed the insecticide, gamma-HCH (gamma-3,4,5,6-hexachlorocyclhexene), to gamma-3,4,5,6-tetrachlorocyclohexene (gammatetraCH) in soil slurries under subatmospheric conditions. These results indicate that GEMs can be constructed with broad substrate range detoxification catalysts such as cytochrome P-450 for remediation.

Effect of Burning Rate Modifiers on Subatmospheric Flame Temperatures of AP/HTPB Composite Solid Propellants

Using 30 um. pt and Pt 13 percent Rh thermocouples, flame temperatures of uncatalysed andcatalysed ammonium perchlorate/hydroxyl-terminated polybutadiene (AP/lffPB) composite solidpropellants were measured under subatmospheric conditions. Ferric oxide F e 2 and copper chromite(CC) were the catalysts used. The study demonstrates that Fe2O3 catalysed propellant, notwithstandingits least combustion efficiency undt;r subatmospheric conditions and weak gas-phase flame, has themaximum burning rate enhancement. This is argued to be due to the increased surface and subsurfacereactions caused by Fe2O3. CC-catalysed propellant burns to the least subatmospheric pressure withminimum loss in combustion efficiency indicating that this class of propellant may be more suitablefor base-bleed applications.

Loudspeaker utilizing magnetic liquid suspension of the voice coil

A loudspeaker is provided with a viscous magnetic fluid suspension for the voice coil, rather than the corrugated disk suspension that is conventionally used. Specially designed vent passages are formed in the magnet assembly, in order to prevent internal pressure build-ups, or subatmospheric conditions, that could cause the magnetic fluid to be blown out of the magnetic gap, in which the voice coil is located. The vent passages permit use of a relatively low viscosity fluid to be used for the fluid suspension. A fluid viscosity of about fifty (50) centipoise is contemplated.

Numerical modeling of buoyant ethanol-air wick diffusion flames

A numerical model based on a conserved-scalar approach is presented for buoyant ethanol-air wick diffusion flames at atmospheric and subatmospheric conditions. The model incorporates an equation that describes the interface condition of wick combustion. The prediction yields similarity solutions for flat-plate ethanol-air wick diffusion flames, but not for cylindrical wick diffusion flames. The flat-plate solution yields a mass burning rate per unit surface area following the x −1 4 dependence of the classical similarity solution, where x is the streamwise distance. A pressure dependence of P 0.644 is predicted for the flat-plate overall mass burning rate, in agreement with the P 2 3 dependence reported in the literature. The cylindrical wicks have a mass burning rate per unit surface area that deviates from the x −1 4 dependence. The predicted mass burning rate, however, does not substantially deviate from the flat-plate solution for cylinders with a moderate aspect ratio (of the order one). The deviation in mass burning rate is most pronounced when needle-like cylinders are considered. The variable-property effects are also examined. The results show that the Chapman gas and constant-Prandtl-number assumptions are not adequate for wick diffusion flames, even at the subatmospheric-pressure condition studied.

Slip flow in fixed and fluidized bed plasma reactors

The characteristics of low-pressure gas low through fixed and fluidized bed plasma reactors for the study of plasma-solid reactions are presented. In the plasma fluidized bed reactor (PFBR), solid particles are fuidized at subatmospheric conditions in a resonantly sustained high frequency 2.45 GHz) plasma. The reactor operates in a previously uninvestigated regime of fuidization and microwave breakdown. A modified version of Darey's law is developed to describe and compare fixed and fluidized bed behavior, as well as to rationalize experimental measurements of pressure drop and gas flow in the absence of information about the bed temperature profile. The study has shown for a bed operating in or near the slip flow region that minimum fluidization can be predicted for slip flow fluidization in the absence of a plasma. However, the results of this work indicate that the mass fluxes and pressure drops at minimum fluidization in the presence of a plasma are significantly different from nonplasma fuidized bed. The pressure drop at minimum fluidization, in the presence of a high-frequency electrical discharge, is as much as 25% above that required to levitate the bed contents, and appears to corroborate otherfndings that link increased stability of the bed with the presence of electromagnetic fields.

Small-Scale Experiments Conducted to Support Investigation of HypotheticalDesign-Basis LOCA Phenomena in the Advanced Test Reactor

This paper reports on an unheated, integral thermal-hydraulic facility scaled to the Advanced Test Reactor (ATR) designed, constructed, and operated to gather simulated large-break loss-of-coolant accident (LOCA) data for use in assessing codes used in ATR analysis. Eighteen experiments were performed in the facility to establish a data base consisting of qualitative and quantitative information for assessment purposes. The effects of initial liquid temperature, break location, and use of safety injection are examined. The results obtained offer significant insights about thermal-hydraulic processes in a complex loop during subatmospheric pressure operating conditions similar to those expected during a hypothetical LOCA in the ATR.

RELAP5 Simulation of Advanced Test Reactor Scaled LOCA Experiments 7, 8, 12, and 14

AbstractThe RELAP5 computer code is used to simulate four small-scale loss-of-coolant accident (LOCA) experiments conducted at Idaho National Engineering Laboratory (INEL). The purpose of the study is to help assess RELAP5 under conditions similar to those expected during a large-break LOCA at INEL’s Advanced Test Reactor (ATR). During an ATR large-break LOCA, it is expected that the primary system pressure will rapidly decrease from the initial operating pressure (∼2.55 MPa) to subatmospheric conditions governed by the primary coolant temperature. Flashing will occur in the high points of the system and air ingress from the break is possible. The RELAP5 code had not previously been assessed under these conditions. The results show that RELAP5 accurately predicted pressures, water levels, and air ingress behavior, thus providing confidence in the ability of the code to simulate an ATR large-break LOCA.

Ignition of composite propellant at subatmospheric pressures by means of carbon dioxide laser

AbstractIgnition behavior of solid propellant composed of 25 wt% polybutadiene and 75% ammonium perchlorate under subatmospheric conditions has been studied using a carbon dioxide laser whose radiant flux is uniformalized. Data of ignition time in Ar, N2 and He atmospheres, and critical radiant flux and pressures over which ignition might be achieved, were obtained. Moreover, the data were compared with theoretical values, taking account of variable heat conductivity for the ambient gases with a surface ignition hypothesis.It is concluded that these ambient gases participate in the pre‐ and post‐ignition reactions and the ignition preventive behavior of He atmosphere is not predictable merely based on its high transport properties. The detailed observation of the ignition transient near the critical pressure revealed that the ignition in Ar atmosphere occurs in gas phase under less than 100 torr whereas in He atmosphere it occurs always at the condensed phase surface.