Modeling study on the flow, heat transfer and energy conversion characteristics of low-power arc-heated hydrogen/nitrogen thrusters

A modeling study is conducted to investigate the effect of hydrogen content in propellants on the plasma flow, heat transfer and energy conversion characteristics of low-power (kW class) arc-heated hydrogen/nitrogen thrusters (arcjets). 1:0 (pure hydrogen), 3:1 (to simulate decomposed ammonia), 2:1 (to simulate decomposed hydrazine) and 0:1 (pure nitrogen) hydrogen/nitrogen mixtures are chosen as the propellants. Both the gas flow region inside the thruster nozzle and the anode-nozzle wall are included in the computational domain in order to better treat the conjugate heat transfer between the gas flow region and the solid wall region. The axial variations of the enthalpy flux, kinetic energy flux, directed kinetic-energy flux, and momentum flux, all normalized to the mass flow rate of the propellant, are used to investigate the energy conversion process inside the thruster nozzle. The modeling results show that the values of the arc voltage, the gas axial-velocity at the thruster exit, and the specific impulse of the arcjet thruster all increase with increasing hydrogen content in the propellant, but the gas temperature at the nitrogen thruster exit is significantly higher than that for other three propellants. The flow, heat transfer, and energy conversion processes taking place in the thruster nozzle have some common features for all the four propellants. The propellant is heated mainly in the near-cathode and constrictor region, accompanied with a rapid increase of the enthalpy flux, and after achieving its maximum value, the enthalpy flux decreases appreciably due to the conversion of gas internal energy into its kinetic energy in the divergent segment of the thruster nozzle. The kinetic energy flux, directed kinetic energy flux and momentum flux also increase at first due to the arc heating and the thermodynamic expansion, assume their maximum inside the nozzle and then decrease gradually as the propellant flows toward the thruster exit. It is found that a large energy loss (31-52%) occurs in the thruster nozzle due to the heat transfer to the nozzle wall and too long nozzle is not necessary. Modeling results for the NASA 1-kW class arcjet thruster with hydrogen or decomposed hydrazine as the propellant are found to compare favorably with available experimental data.

Determination of mercury with a flow injection quartz tube atomic absorption spectrometry

A method was developed for the determination of micro mercury in the soil, plants and the traditional Chinese medicine using flow injection quartz tube-atomic absorption spectrometry. The effect of the factors such as acidity,. the carrier solution, the flow rate of reductive solution and argon gas, etc. on the determination was studied. When vanadic oxide, nitric acid and sulfuric acid were used to decompose the sample reliable result could be obtained. The characteristic mass of the method is 59 pg, the detection limit is 0.028 mug/L, RSD is < 3.9% and the recovery is in the range of 94% &SIM; 102%.

ELECTROCATALYTIC OXIDATION AND FLOW DETECTION OF HYDRAZINE COMPOUNDS IN LIQUID-CHROMATOGRAPHY AT A VITAMIN-B-12 ADSORBED GLASSY-CARBON ELECTRODE

A vitamin B-12 chemically modified electrode (CME) was constructed by adsorption of vitamin B-12 onto a glassy carbon surface. The electrode catalyzes the electrooxidation of hydrazine compounds over a wide pH range. The electrocatalytic behavior of hydrazines is elucidated with respect to the CME preparation conditions, solution pH, operating potential, mobile phase flow rate, and other variables. When applied to liquid chromatographic detection of the analytes, the vitamin B-12 CME yielded a linear response range over 2 orders of magnitude, and detection limits at the picomole level. The vitamin B-12 CME offers acceptable catalytic stability in both batch and flow systems.

AMPEROMETRIC FLOW-INJECTION ANALYSIS OF HYDRAZINE BY ELECTROCATALYTIC OXIDATION AT COBALT TETRAPHENYLPORPHYRIN MODIFIED ELECTRODE WITH HEAT-TREATMENT

Chemically modified electrodes prepared by treating the cobalt tetraphenylporphyrin modified glassy-carbon electrode at 750-degrees (HCME) are shown to catalyze the electrooxidation of hydrazine. The oxidation occurred at +0.63 V vs. Ag/AgCl (saturated potassium chloride) in pH 2.5 media. The catalytic response is evaluated with respect to solution pH, potential scan-rate, concentration dependence and flow-rate. The catalytic stability of the HCME is compared with that of the cobalt tetraphenylporphyrin adsorbed glassy-carbon electrode. The stability of the HCME was excellent in acidic solution and even in solutions containing organic solvent (50% CH3OH). When used as the sensing electrode in amperometric detection in flow-injection analysis, the HCME permitted sensitive detection of hydrazine at 0.5 V. The limit of detection was 0.1 ng. The linear range was from 50 ng to 2.4-mu-g. The method is very sensitive and selective.

Protein A tangential flow affinity membrane cartridge for extracorporeal immunoadsorption therapy

Tangential flow affinity membrane cartridge (TFAMC) fs a new model of immunoadsorption therapy for hemoperfusion. Recombinant Protein A was immobilized on the membrane cartridge through Schiff base formation for extracorporeal IgG and immune complex removal from blood. Flow characteristics, immunoadsorption capacity and biocompatibility of protein A TFAMC were studied. The results showed that the pressure drop increased with the increasing flow rate of water, plasma and blood, demonstrating reliable strength of membrane at high now rare. The adsorption capacities of protein A TFAMC for IgG from human plasma and blood were measured. The cartridge with 139 mg protein A immobilized on the matrix (6 mg protein A/g dry matrix) adsorbed 553 mg IgG (23.8 mg IgG/g dry matrix) from human plasma and 499.4 mg IgG (21.5 mg IgG/g dry matrix) from human blood, respectively. The circulation time had a major influence on IgG adsorption capacity, but the flow rate had little influence. Experiments in vitro and in vivo confirmed that protein A TFAMC mainly adsorbed Ige and Little of other plasma proteins, and that blood cell damage was negligible. The extracorporeal circulation system is safe and reliable. Copyright (C) 1999 John Wiley & Sons, Ltd.

Characteristics of elution profile in radial chromatography under linear conditions

Based on the mass balance equations of solute transfer in the radial chromatographic column, the theoretical expression to describe the column efficiency and shape of elution profile is obtained under linear isotherm case. Moreover, the tendency for the variation of column efficiency and symmetry of peak profile is systematically discussed. The results showed that in radial chromatography the relationship between the column efficiency and volumetric flow rate is similar with that relationship in axial chromatography; relatively high column efficiency still can be obtained under high flow rate in radial chromatography. Accompanying the increase of retention factor of solutes and injection time, the column efficiency decreases monotonously. The effect of column diameter and column length on the column efficiency interfere with each other. It is more advantageous to increase the column efficiency by applying columns with larger column diameter and shorter column length. According to the discussion of the effect of diffusion on the column efficiency, radial chromatography is proved to be suitable for the separation of samples with relatively high diffusion coefficient, which predicts its obvious advantage in the preparative separation of samples such as proteins and DNA.

HEATING IN VASCULAR TISSUE AND FLOW-THROUGH TISSUE PHANTOMS INDUCED BY FOCUSED ULTRASOUND

High intensity focused ultrasound (HIFU) can be used to control bleeding, both from individual blood vessels as well as from gross damage to the capillary bed. This process, called acoustic hemostasis, is being studied in the hope that such a method would ultimately provide a lifesaving treatment during the so-called "golden hour", a brief grace period after a severe trauma in which prompt therapy can save the life of an injured person. Thermal effects play a major role in occlusion of small vessels and also appear to contribute to the sealing of punctures in major blood vessels. However, aggressive ultrasound-induced tissue heating can also impact healthy tissue and can lead to deleterious mechanical bioeffects. Moreover, the presence of vascularity can limit one’s ability to elevate the temperature of blood vessel walls owing to convective heat transport. In an effort to better understand the heating process in tissues with vascular structure we have developed a numerical simulation that couples models for ultrasound propagation, acoustic streaming, ultrasound heating and blood cooling in Newtonian viscous media. The 3-D simulation allows for the study of complicated biological structures and insonation geometries. We have also undertaken a series of in vitro experiments, in non-uniform flow-through tissue phantoms, designed to provide a ground truth verification of the model predictions. The calculated and measured results were compared over a range of values for insonation pressure, insonation time, and flow rate; we show good agreement between predictions and measurements. We then conducted a series of simulations that address two limiting problems of interest: hemostasis in small and large vessels. We employed realistic human tissue properties and considered more complex geometries. Results show that the heating pattern in and around a blood vessel is different for different vessel sizes, flow rates and for varying beam orientations relative to the flow axis. Complete occlusion and wall- puncture sealing are both possible depending on the exposure conditions. These results concur with prior clinical observations and may prove useful for planning of a more effective procedure in HIFU treatments.

Low demographic variability in wild primate populations: fitness impacts of variation, covariation, and serial correlation in vital rates.

In a stochastic environment, long-term fitness can be influenced by variation, covariation, and serial correlation in vital rates (survival and fertility). Yet no study of an animal population has parsed the contributions of these three aspects of variability to long-term fitness. We do so using a unique database that includes complete life-history information for wild-living individuals of seven primate species that have been the subjects of long-term (22-45 years) behavioral studies. Overall, the estimated levels of vital rate variation had only minor effects on long-term fitness, and the effects of vital rate covariation and serial correlation were even weaker. To explore why, we compared estimated variances of adult survival in primates with values for other vertebrates in the literature and found that adult survival is significantly less variable in primates than it is in the other vertebrates. Finally, we tested the prediction that adult survival, because it more strongly influences fitness in a constant environment, will be less variable than newborn survival, and we found only mixed support for the prediction. Our results suggest that wild primates may be buffered against detrimental fitness effects of environmental stochasticity by their highly developed cognitive abilities, social networks, and broad, flexible diets.

Analysis of the Steady Flow Characteristics Through a Poppet Valve

This paper describes the flow characteristics in the near throat region of a poppet valve under steady flow conditions. An experimental and theoretical procedure was undertaken to determine the total pressure at the assumed throat region of the valve, and also at a downstream location. Experiments of this type can be used to accurately determine the flow performance of a particular induction system. The static pressure recovery was calculated from the near throat region of the valve to the downstream location and was shown to be dependant on valve lift. Total pressure profiles suggest that for this particular induction system, the majority of pressure loss occurs downstream of the valve for lift/diameter ratios up to 0.1, and upstream of the valve for lift/diameter ratios greater than 0.1. Negligible pressure recovery was shown to exist from the cylindrical periphery of the valve head to the downstream location for all valve lifts, indicating that the flow had probably separated completely from the trailing edge of the valve seating face. The calculated discharge coefficients, based on the geometric throat static pressure measurements on the seating face, were in general less than those determined using the downstream static pressure, by as much as 12% in some instances towards the valves lower mass flow rate range.

Liquid-Liquid Flow in a Capillary Microreactor: Hydrodynamic Flow Patterns and Extraction Performance

The capillary micro reactor, with four stable operating flow patterns and a throughput range from grams per hour to kilograms per hour, presents an attractive alternative to chip-based and microstructured reactors for laboratory- and pilot-scale applications. In this article, results for the extraction of 2-butanol from toluene under different flow patterns in a water/toluene flow in long capillary microreactors are presented. The effects of the capillary length (0.4-2.2 m), flow rate (0.1-12 mL/min), and aqueous-to-organic volumetric flow ratio (0.25-9) on the slug, bubbly, parallel, and annular flow hydrodynamics were investigated. Weber-number-dependent flow maps were composed for capillary lengths of 0.4 and 2 m that were used to interpret the flow pattern formation in terms of surface tension and inertia forces. When the capillary length was decreased from 2 to 0.4 m, a transition from annular to parallel flow was observed. The capillary length had little influence on slug and bubbly flows. The flow patterns were evaluated in terms of stability, surface-to-volume ratio, throughput, and extraction efficiency. Slug and bubbly flow operations yielded 100% thermodynamic extraction efficiency, and increasing the aqueous-to-organic volumetric ratio to 9 allowed for 99% 2-butanol extraction. The parallel and annular flow operating windows were limited by the capillary length, thus yielding maximum 2-butanol extractions of 30% and 47% for parallel and annular flows, respectively.

Numbered-up gas-liquid micro/milli channels reactor with modular flow distributor

Gas-liquid processing in microreactors remains mostly restricted to the laboratory scale due to the complexity and expenditure needed for an adequate numbering-up with a uniform flow distribution. Here, the numbering-up is presented for multi-phase (gas-liquid) flow in microreactor suitable for a production capacity of kg/h. Based on the barrier channels concept, the barrier-based micro/milli reactor (BMMR) is designed and fabricated to deliver flow non-uniformity of less than 10%. The BMMR consists of eight parallel channels all operated in the Taylor flow regime and with a liquid flow rate up to 150. mL/min. The quality of the flow distribution is reported by studying two aspects. The first aspect is the influence of different viscosities, surface tensions and flow rates. The second aspect is the influence of modularity by testing three different reaction channels type: (1) square channels fabricated in a stainless steel plate, (2) square channels fabricated in a glass plate, and (3) circular channels (capillaries) made of stainless steel. Additionally, the BMMR is compared to that of a single channel regard the slug and bubble lengths and bubble generation frequency. The results pave the ground for bringing multi-phase flow in microreactor one step closer for large scale production via numbering-up. © 2012 Elsevier B.V.

Flow patterns and pressure drop of ionic liquid-water two-phase flows in microchannels

The two-phase flow of a hydrophobic ionic liquid and water was studied in capillaries made of three different materials (two types of Teflon, FEP and Tefzel, and glass) with sizes between 200µm and 270µm. The ionic liquid was 1-butyl-3-methylimidazolium bis{(trifluoromethyl)sulfonyl}amide, with density and viscosity of 1420kgm and 0.041kgms, respectively. Flow patterns and pressure drop were measured for two inlet configurations (T- and Y-junction), for total flow rates of 0.065-214.9cmh and ionic liquid volume fractions from 0.05 to 0.8. The continuous phase in the glass capillary depended on the fluid that initially filled the channel. When water was introduced first, it became the continuous phase with the ionic liquid forming plugs or a mixture of plugs and drops within it. In the Teflon microchannels, the order that fluids were introduced did not affect the results and the ionic liquid was always the continuous phase. The main patterns observed were annular, plug, and drop flow. Pressure drop in the Teflon microchannels at a constant ionic liquid flow rate, was found to increase as the ionic liquid volume fraction decreased, and was always higher than the single phase ionic liquid value at the same flow rate as in the two-phase mixture. However, in the glass microchannel during plug flow with water as the continuous phase, pressure drop for a constant ionic liquid flow rate was always lower than the single phase ionic liquid value. A modified plug flow pressure drop model using a correlation for film thickness derived for the current fluids pair showed very good agreement with the experimental data. © 2013 Elsevier Ltd.

Advanced Ceramic Substrate with Ordered and Designed Micro-Structure for Applications in Automotive Catalysts

This study describes an innovative monolith structure designed for applications in automotive catalysis using an advanced manufacturing approach developed at Imperial College London. The production process combines extrusion with phase inversion of a ceramic-polymer-solvent mixture in order to design highly ordered substrate micro-structures that offer improvements in performance, including reduced PGM loading, reduced catalyst ageing and reduced backpressure.

This study compares the performance of the novel substrate for CO oxidation against commercially available 400 cpsi and 900 cpsi catalysts using gas concentrations and a flow rate equivalent to those experienced by a full catalyst brick when attached to a vehicle. Due to the novel micro-structure, no washcoat was required for the initial testing and 13 g/ft3 of Pd was deposited directly throughout the substrate structure in the absence of a washcoat.

Initial results for CO oxidation indicate that the advanced micro-structure leads to enhanced conversion efficiency. Despite an 79% reduction in metal loading and the absence of a washcoat, the novel substrate sample performs well, with a light-off temperature (LOT) only 15 °C higher than the commercial 400 cpsi sample.

To test the effects of catalyst ageing on light-off temperature, each sample was aged statically at a temperature of 1000 °C, based on the Bench Ageing Time (BAT) equation. The novel substrate performed impressively when compared to the commercial samples, with a variation in light-off temperature of only 3% after 80 equivalent hours of ageing, compared to 12% and 25% for the 400 cpsi and 900 cpsi monoliths, respectively.

An analysis of stage performance in automotive turbocharger centrifugal compressors

As the concept of engine downsizing becomes ever more integrated into automotive powertrain development strategies, so too does the pressure on turbocharger manufacturers to deliver improvements in map width and a reduction in the mass flow rate at which compressor surge occurs. A consequence of this development is the increasing importance of recirculating flows, both in the impeller inlet and outlet domains, on stage performance.
The current study seeks to evaluate the impact of the inclusion of impeller inlet recirculation on a meanline centrifugal compressor design tool. Using a combination of extensive test data, single passage CFD predictions, and 1-D analysis it is demonstrated how the addition of inlet recirculation modelling impacts upon stage performance close to the surge line. It is also demonstrated that, in its current configuration, the accuracy of the 1-D model prediction diminishes significantly with increasing blade tip speed.
Having ascertained that the existing model requires further work, an evaluation of the vaneless diffuser modelling method currently employed within the existing 1-D model is undertaken. The comparison of the predicted static pressure recovery coefficient with test data demonstrated the inherent inadequacies in the resulting prediction, in terms of both magnitude and variation with flow rate. A simplified alternative method based on an equivalent friction coefficient is also presented that, with further development, could provide a significantly improved stage performance prediction.

A Numerical Study of the Flow Fields in a Highly Off-Design Variable Geometry Turbine

Conventionally, radial turbines have almost exclusively used radially fibred blades. While issues of mechanical integrity are paramount, there may be opportunities for improving turbine efficiency through a 3D blade design without exceeding mechanical limits. Off-design performance and understanding of the secondary flow structures now plays a vital role in the design decisions made for automotive turbocharger turbines. Of particular interest is extracting more energy at high pressure ratios and lower rotational speeds. Operating in this region means the rotor will experience high values of positive incidence at the inlet. A CFD analysis has been carried out on a scaled automotive turbine utilizing a swing vane stator system. To date no open literature exists on the flow structures present in a standard VGT system. Investigations were carried out on a 90 mm diameter rotor with the stator vane at the maximum, minimum and 25% mass flow rate positions. In addition stator vane endwall clearance existed at the hub side. From investigation of the internal flow fields of the baseline rotor, a number of areas that could be optimized in the future with three dimensional blading were identified. The blade loading and tip leakage flow near inlet play a significant role in the flow development further downstream at all stator vane positions. It was found that tip leakage flow and flow separation at off-design conditions could be reduced by employing back swept blading and redistributing the blade loading. This could potentially reduce the extent of the secondary flow structures found in the present study.