Study of high-density hypervelocity flows and similitudes

"AEDC-TR-67-72"

A similitude for nonequilibrium phenomena in hypersonic flight,

"Part I of the present paper was supported by the Arnold Engineering Development Center under Contract no. AF-40-(601)-928. Part II is a part of project DEFENDER sponsored by the Advanced Research Projects Agency, Department of Defense, under Contract no. DA-30-069-ORD-3443."

Simulation of blunt body pressure distributions

Mode of access: Internet.

A cold model study of raceway hysteresis

The effect of a gas flow field on the size of raceway has been studied experimentally using a two-dimensional (2-D) cold model. It is observed that as the blast velocity from the tuyere increases, raceway size increases, and when the blast velocity is decreased from its highest value, raceway size does not change much until the velocity reaches a critical velocity. Below the critical velocity, raceway size decreases with decreasing velocity but is always larger than that for the same velocity when the velocity increased. This phenomenon is called raceway hysteresis. Raceway hysteresis has been studied in the presence of different gas flow rates and different particle densities. Raceway hysteresis has been observed in all the experiments. The effect of liquid flow, with various superficial velocities, on raceway hysteresis has also been studied. A study of raceway size hysteresis shows that interparticle and particle-wall friction have a very large effect on raceway size. A hypothesis has been proposed to describe the hysteresis phenomenon in the packed beds. The relevance of hysteresis to blast furnace raceways has been discussed. Existing literature correlations for raceway size ignore the frictional effects. Therefore, their applicability to the ironmaking blast furnace is questionable.

Enhancing the ratio of molecular ions to non-covalent compounds in the electrospray interface of LC-MS in quantitative analysis

A common problem encountered during the development of MS methods for the quantitation of small organic molecules by LGMS is the formation of non-covalently bound species or adducts in the electrospray interface. Often the population of the molecular ion is insignificant compared to those of all other forms of the analyte produced in the electrospray, making it difficult to obtain the sensitivity required for accurate quantitation. We have investigated the effects of the following variables: orifice potential, nebulizer gas flow, temperature, solvent composition and the sample pH on the relative distributions of ions of the types MH+, MNa+, MNH+, and 2MNa(+), where M represents a 4 small organic molecule: BAY 11-7082 ((E)-3-[4-methylphenylsulfonyl]-2-propenenitrile). Orifice potential, solvent composition and the sample pH had the greatest influence on the relative distributions of these ions, making these parameters the most useful for optimizing methods for the quantitation of small molecules.

Swash overtopping and sediment overwash on a truncated beach

New experimental laboratory data are presented on swash overtopping and sediment overwash on a truncated beach, approximating the conditions at the crest of a beach berm or inter-tidal ridge-runnel. The experiments provide a measure of the uprush sediment transport rate in the swash zone that is unaffected by the difficulties inherent in deploying instrumentation or sediment trapping techniques at laboratory scale. Overtopping flow volumes are compared with an analytical solution for swash flows as well as a simple numerical model, both of which are restricted to individual swash events. The analytical solution underestimates the overtopping volume by an order of magnitude while the model provides good overall agreement with the data and the reason for this difference is discussed. Modelled flow velocities are input to simple sediment transport formulae appropriate to the swash zone in order to predict the overwash sediment transport rates. Calculations performed with traditional expressions for the wave friction factor tend to underestimate the measured transport. Additional sediment transport calculations using standard total load equations are used to derive an optimum constant wave friction factor of f(w)=0.024. This is in good agreement with a broad range of published field and laboratory data. However, the influence of long waves and irregular wave run-up on the overtopping and overwash remains to be assessed. The good agreement between modelled and measured sediment transport rates suggests that the model provides accurate predictions of the uprush sediment transport rates in the swash zone, which has application in predicting the growth and height of beach berms. (c) 2005 Elsevier B.V. All rights reserved.

Momentum transfer effects in the transport of adsorbate at a nano-patterned surface

Adsorbate molecules scattered in the repulsive field of a surface feature in the form of a semi-cylindrical stripe may be considered as a simple model for a nano-patterned surface. The extent of scattering was conveniently expressed as the tangential momentum accommodation coefficient. An analytical result was obtained using a simple local specular reflection hypothesis in contrast to the more complicated situation of an array of atoms discussed elsewhere, in which screening and secondary reflection may occur (Nicholson and Bhatia 2005). It was also demonstrated that a simple 2D representation leads to the same result for the tangential momentum accommodation coefficient.

Experimental and analytical study of the effect of contact angle on liquid convective heat transfer in microchannels

In this paper we examine the effect of contact angle (or surface wettability) on the convective heat transfer coefficient in microchannels. Slip flow, where the fluid velocity at the wall is non-zero, is most likely to occur in microchannels due to its dependence on shear rate or wall shear stress. We show analytically that for a constant pressure drop, the presence of slip increases the Nusselt number. In a microchannel heat exchanger we modified the surface wettability from a contact angle of 20 degrees-120 degrees using thin film coating technology. Apparent slip flow is implied from pressure and flow rate measurements with a departure from classical laminar friction coefficients above a critical shear rate of approximately 10,000 s(-1). The magnitude of this departure is dependant on the contact angle with higher contact angles surfaces exhibiting larger pressure drop decreases. Similarly, the non-dimensional heat flux is found to decrease relative to laminar non-slip theory, and this decrease is also a function of the contact angle. Depending on the contact angle and the wall shear rate, variations in the heat transfer rate exceeding 10% can be expected. Thus the contact angle is an important consideration in the design of micro, and even more so, nano heat exchangers. (c) 2006 Elsevier Ltd. All rights reserved.

Scattering and tangential momentum accommodation at a 2D adsorbate-solid interface

We calculate tangential momentum coefficients for the exchange of momentum between molecules in transport and the internal surface of a membrane pore, modelled as a simple atomic structure. We introduce a local specular reflection (LSR) hypothesis, which states that impinging molecules undergo mirror-like reflection in a plane tangent to a surface atom at the point of impact. As a consequence, the components of the velocity, parallel to the direction of flow will (in general) change on impact. The overall effect is a loss of tangential momentum, since more is lost in the upstream direction than is gained in the downstream direction. The loss of tangential momentum is greater when the size ratio of fluid to solid atom is small, allowing more steeply inclined impact planes to become accessible to the fluid phase molecules. (c) 2005 Elsevier B.V. All rights reserved.

Double-heater-wire circuits and heat-and-moisture exchangers and the risk of ventilator-associated pneumonia

Objective: To compare the incidence of ventilator-associated pneumonia (VAP) in patients ventilated in intensive care by means of circuits humidified with a hygroscopic heat-and-moisture exchanger with a bacterial viral filter (HME) or hot-water humidification with a heater wire in both inspiratory and expiratory circuit limbs (DHW) or the inspiratory limb only (SHW). Design: A prospective, randomized trial. Setting: A metropolitan teaching hospital's general intensive care unit. Patients: Three hundred eighty-one patients requiring a minimum period of mechanical ventilation of 48 hrs. Interventions: Patients were randomized to humidification with use of an HME (n = 190), SHW (n = 94), or DHW (n = 97). Measurements and Main Results. Study end points were VAP diagnosed on the basis of Clinical Pulmonary Infection Score (CPIS) (1), HME resistance after 24 hrs of use, endotracheal tube resistance, and HME use per patient. VAP occurred with similar frequency in all groups (13%, HME; 14%, DHW; 10%, SHW; p = 0.61) and was predicted only by current smoking (adjusted odds ratio [AOR], 2.1; 95% confidence interval [CI], 1.1-3.9; p =.03) and ventilation days (AOR, 1.05; 95% Cl, 1.0-1.2; p =.001); VAP was less likely for patients with an admission diagnosis of pneumonia (AOR, 0.40; 95% Cl, 0.4-0.2; p =.04). HME resistance after 24 hrs of use measured at a gas flow of 50 L/min was 0.9 cm H2O (0.4-2.9). Endotracheal tube resistance was similar for all three groups (16-19 cm H2O min/L; p =.2), as were suction frequency, secretion thickness, and blood on suctioning (p =.32, p =.06, and p =.34, respectively). The HME use per patient per day was 1.13. Conclusions: Humidification technique does not influence either VAP incidence or secretion characteristics, but HMEs may have air-flow resistance higher than manufacturer specifications after 24 hrs of use.

Ba0.5Sr0.5Co0.8Fe0.2O3-delta ceramic hollow-fiber membranes for oxygen permeation

Setf-supported asymmetric hollow-fiber membranes of mixed oxygen-ionic and electronic conducting perovskite Ba0.5Sr0.5Co0.8Fe0.2O3-delta (BSCF) were prepared by a combined phase-inversion and sintering technique. The starting inorganic powder was synthesized by combined EDTA-citrate complexing process followed by thermal treatment at 600 degrees C. The powder was dispersed in a polymer solution and then extruded into hollow-fiber precursors through a spinneret. ne fiber precursors were sintered at elevated temperatures to form gastight membranes, which were characterized by SEM and gas permeation tests. Performance of the hollow fibers in air separation was both experimentally and theoretically studied at various conditions. The results reveal that the oxygen permeation process was controlled by the slow oxygen surface exchange kinetics under the investigated conditions. The porous inner surface of the prepared perovskite hollow-fiber membranes considerably favored the oxygen permeation. The maximum oxygen flux measured was 0.031 mol-m(-2).s(-1) at 950 degrees C with the sweep gas flow rate of 0.522 mol(.)m(-2).s(-1). To improve the oxygen flux of BSCF perovskite membranes, future work should be focused on surface modification rather than reduction of the membrane thickness. (c) 2006 American Institute of Chemical Engineers.

Modelling of transient heat transfer in annealing furnaces

This is a study of heat transfer in a lift-off furnace which is employed in the batch annealing of a stack of coils of steel strip. The objective of the project is to investigate the various factors which govern the furnace design and the heat transfer resistances, so as to reduce the time of the annealing cycle, and hence minimize the operating costs. The work involved mathematical modelling of patterns of gas flow and modes of heat transfer. These models are: Heat conduction and its conjectures in the steel coils;Convective heat transfer in the plates separating the coils in the stack and in other parts of the furnace; and Radiative and convective heat transfer in the furnace by using the long furnace model. An important part of the project is the development of numerical methods and computations to solve the transient models. A limited number of temperature measurements was available from experiments on a test coil in an industrial furnace. The mathematical model agreed well with these data. The model has been used to show the following characteristics of annealing furnaces, and to suggest further developments which would lead to significant savings: - The location of the limiting temperature in a coil is nearer to the hollow core than to the outer periphery. - Thermal expansion of the steel tends to open the coils, reduces their thermal conductivity in the radial direction, and hence prolongs the annealing cycle. Increasing the tension in the coils and/or heating from the core would overcome this heat transfer resistance. - The shape and dimensions of the convective channels in the plates have significant effect on heat convection in the stack. An optimal design of a channel is shown to be of a width-to-height ratio equal to 9. - Increasing the cooling rate, by using a fluidized bed instead of the normal shell and tube exchanger, would shorten the cooling time by about 15%, but increase the temperature differential in the stack. - For a specific charge weight, a stack of different-sized coils will have a shorter annealing cycle than one of equally-sized coils, provided that production constraints allow the stacking order to be optimal. - Recycle of hot flue gases to the firing zone of the furnace would produce a. decrease in the thermal efficiency up to 30% but decreases the heating time by about 26%.

Catalytic pyrolysis of agricultural residues for bio-oil production

Agricultural residues from Thailand, namely stalk and rhizome of cassava plants, were employed as raw materials for bio-oil production via fast pyrolysis technology. There were two main objectives of this project. The first one was to determine the optimum pyrolysis temperature for maximising the organics yield and to investigate the properties of the bio-oils produced. To achieve this objective, pyrolysis experiments were conducted using a bench-scale (150 g/h) reactor system, followed by bio-oil analysis. It was found that the reactor bed temperature that could give the highest organics yield for both materials was 490±15ºC. At all temperatures studied, the rhizome gave about 2-4% higher organics yields than the stalk. The bio-oil derived from the rhizome had lower oxygen content, higher calorific value and better stability, thus indicating better quality than that produced from the stalk. The second objective was to improve the bio-oil properties in terms of heating value, viscosity and storage stability by the incorporation of catalyst into the pyrolysis process. Catalytic pyrolysis was initially performed in a micro-scale reactor to screen a large number of catalysts. Subsequently, seven catalysts were selected for experiments with larger-scale (150 g/h) pyrolysis unit. The catalysts were zeolite and related materials (ZSM-5, Al-MCM-41 and Al-MSU-F), commercial catalysts (Criterion-534 and MI-575), copper chromite and ash. Additionally, the combination of two catalysts in series was investigated. These were Criterion-534/ZSM-5 and Al-MSU-F/ZSM-5. The results showed that all catalysts could improve the bio-oils properties as they enhanced cracking and deoxygenation reactions and in some cases such as ZSM-5, Criterion-534 and Criterion-534/ZSM-5, valuable chemicals like hydrocarbons and light phenols were produced. The highest concentration of these compounds was obtained with Criterion-534/ZSM-5.

Chemical synthesis of isotopically labelled (M+4) purine nucleosides and their incorporation into DNA oligomers

Development of accurate and sensitive analytical methods to measure the level of biomarkers, such as 8-oxo-guanine or its corresponding nucleoside, 8-oxo-2’-deoxyguanosine, has become imperative in the study of DNA oxidative damage in vivo. Of the most promising techniques, HPLC-MS/MS, has many attractive advantages. Like any method that employs the MS technique, its accuracy depends on the use of multiply, isotopically-labelled internal standards. This project is aimed at making available such internal standards. The first task was to synthesise the multiply, isotopically-labelled bases (M+4) guanine and (M+4) 8-oxo-guanine. Synthetic routes for both (M+4) guanine and (M+4) 8-oxo-guanine were designed and validated using the unlabelled compounds. The reaction conditions were also optimized during the “dry runs”. The amination of the 4-hydroxy-2,6-dichloropyrimidine, appeared to be very sensitive to the purity of the commercial [15]N benzylamine reagent. Having failed, after several attempts, to obtain the pure reagent from commercial suppliers, [15]N benzylamine was successfully synthesised in our laboratory and used in the first synthesis of (M+4) guanine. Although (M+4) bases can be, and indeed have been used as internal standards in the quantitative analysis of oxidative damage, they can not account for the errors that may occur during the early sample preparation stages. Therefore, internal standards in the form of nucleosides and DNA oligomers are more desirable. After evaluating a number of methods, an enzymatic transglycolization technique was adopted for the transfer of the labelled bases to give their corresponding nucleosides. Both (M+4) 2-deoxyguanosine and (M+4) 8-oxo-2’-deoxyguanosine can be purified on micro scale by HPLC. The challenge came from the purification of larger scale (>50 mg) synthesis of nucleosides. A gel filtration method was successfully developed, which resulted in excellent separation of (M+4) 2’-deoxyguanosine from the incubation mixture. The (M+4) 2’-deoxyguanosine was then fully protected in three steps and successfully incorporated, by solid supported synthesis, into a DNA oligomer containing 18 residues. Thus, synthesis of 8-oxo-deoxyguanosine on a bigger scale for its future incorporation into DNA oligomers is now a possibility resulting from this thesis work. We believe that these internal standards can be used to develop procedures that can make the measurement of oxidative DNA damage more accurate and sensitive.

Development of multiphase and multiscale mathematical models for thermal spray process

High velocity oxyfuel (HVOF) thermal spraying is one of the most significant developments in the thermal spray industry since the development of the original plasma spray technique. The first investigation deals with the combustion and discrete particle models within the general purpose commercial CFD code FLUENT to solve the combustion of kerosene and couple the motion of fuel droplets with the gas flow dynamics in a Lagrangian fashion. The effects of liquid fuel droplets on the thermodynamics of the combusting gas flow are examined thoroughly showing that combustion process of kerosene is independent on the initial fuel droplet sizes. The second analysis copes with the full water cooling numerical model, which can assist on thermal performance optimisation or to determine the best method for heat removal without the cost of building physical prototypes. The numerical results indicate that the water flow rate and direction has noticeable influence on the cooling efficiency but no noticeable effect on the gas flow dynamics within the thermal spraying gun. The third investigation deals with the development and implementation of discrete phase particle models. The results indicate that most powder particles are not melted upon hitting the substrate to be coated. The oxidation model confirms that HVOF guns can produce metallic coating with low oxidation within the typical standing-off distance about 30cm. Physical properties such as porosity, microstructure, surface roughness and adhesion strength of coatings produced by droplet deposition in a thermal spray process are determined to a large extent by the dynamics of deformation and solidification of the particles impinging on the substrate. Therefore, is one of the objectives of this study to present a complete numerical model of droplet impact and solidification. The modelling results show that solidification of droplets is significantly affected by the thermal contact resistance/substrate surface roughness.