Steady Flow System Research Articles

Shear-DSC study on the crystal-isotropic phase transition of semidilute aqueous cetyltrimethylammonium bromide (CTAB) solutions

A differential scanning calorimeter equipped with a steady shear flow system (Shear-DSC) was developed, and the effects of shearing on the crystal-isotropic phase transition were investigated for aqueous cetyltrimethylammonium bromide (CTAB) solutions at 4, 18, and 26 wt%. At 18 wt%, where rod-like micelles are formed in the isotropic phase, the transition temperature Ttrs changes with the shear rate γ˙. At low shear rate (γ˙<1s−1), Ttrs decreases as γ˙ increases due to an increase in the surface energy of the crystal grains. At high shear rate (γ˙>30s−1), Ttrs increases as γ˙ increases because of the orientational ordering of rod-like micelles induced by shearing in the isotropic phase, leading to the formation of a nematic structure. The latter change is suppressed for the solution at 26 wt% because the nematic phase is formed without shearing, whereas it disappears at 4 wt% indicating that the spherical micelles are not deformed by shearing.

Application of Qual2e Model for River Water Quality Modelling

QUAL2E is modeling software which simulates up to 15 water quality parameters in branching stream system. The model uses mathematical equations like finite-difference solution of the adjective- dispersive mass transport and reaction equations. The program computes a series of steady- state water surface profiles and simulates changes in flow conditions along the stream. The model is applicable only to dendritic streams that are well mixed and it assumes that the major transport mechanism, advection and dispersion are significant only along the main direction of flow of the stream. QUAL2E can operate as either a steady state or a dynamic model and it simulates dynamic dial heat budget and water quality kinetics for a one dimensional and steady flow system. QUAL2E program performs dissolved oxygen balance by including source and sink terms in mass balance equation and is used to quantify the non point sources loading rate, determine the pollutants, calculate the phosphorus and estimate the natural conditions. It accommodates four types of hydraulic and mass load functions in addition to local climate factors: headwater-inputs, point sources, inflow/outflow and downstream boundary conditions.

Entransy definition and its balance equation for heat transfer with vaporization processes

Entransy balance equations and the corresponding optimization principles for heat conduction, heat convection and thermal radiation have been established. This paper develops the entransy balance equation for a low speed steady flow system with vaporization processes. The definition of enthalpy entransy for a substance from solid state to vapor state is proposed. The expressions of entransy and entransy dissipation are derived with differential volume element integration and the concept of enthalpy entransy. The heat transfer between a vaporization stream and a hot stream in a heat exchanger is also analyzed with the entransy approach. The theoretical results show that the minimum entransy-dissipation-based thermal resistance always leads to the maximum heat exchanger effectiveness. A numerical example compared with the entropy generation approach verifies the theoretical analyses. For a heat exchanger network undergoing vaporization processes, the minimum entransy-dissipation-based thermal resistance is proved to be applicable as the optimization criteria for the maximum heat exchange rate. The minimum entransy-dissipation-based thermal resistance principle is applied to two numerical cases for the thermal conductance distribution optimization to obtain the maximum heat exchange rate.

Influence of Unsteadiness on the Analysis of Pressure Gain Combustion Devices

Pressure gain combustion has been the subject of scientific study for over a century due to its promise of improved thermodynamic efficiency. In many recent application concepts, pressure gain combustion is used as a component in an otherwise continuous, normally steady flow system, such as a gas turbine or ramjet engine. However, pressure gain combustion is inherently unsteady. Failure to account for the effects of this periodic unsteadiness can lead to misunderstanding and errors in some performance calculations. This paper clarifies the accounting by presenting a consistent method of thermodynamic cycle analysis for a device using pressure gain combustion technology. The incorporation of the unsteady pressure gain combustion process into the conservation equations for a continuous flow device is presented. Most important, the appropriate method for computing the conservation of momentum is presented. It will be shown that proper, consistent analysis of cyclic conservation principles produces more realistic performance predictions. Specifically, for the ramjet example used, appropriate predictions of both the thermal efficiency (from energy conservation) and specific thrust (from momentum conservation) are developed.

Flow Visualization and Heat Transfer Characteristics of Oscillating Fluid through Pin-Fin Array in a Rectangular Channel

This work experimentally investigated the fluid flow and heat transfer characteristics of the pin-fin heat sink with the oscillating air flow. The oscillating air flow would be unstable in the passages among the fins due to the periodical change of flow rate. It might enhance the overall heat-transfer performance. At the present study, the pin-fin heat sinks with various fin heights were installed in the rectangular channel, resulting in different bypass clearances between the pin fins and the shroud of the test channel. The smoke flow visualizations for the oscillating-flow system were completed. The heat-transfer tests under the asymmetrically heated condition were performed to obtain the average Nusselt numbers. The smoke lines with obvious waves in the transverse direction were found in the results of the flow visualizations. By comparing to the steady flow system, there was about 20∼34% increment in the overall heat-transfer performance at the operating state without bypass clearance. However, if the bypass clearance was too big, the heat-exchange capacity of the oscillating flow was less than that of the steady flow. It demonstrates that the oscillating flow promotes the cooling performance of pin-fin heat sink at the non-bypass and specified bypass conditions.

Hydrodynamic Performance of a Prototype Bioprosthetic Valve Derived from the Pulmonary Valve of Phoca groenlandica

Biological valves offer significant advantages over mechanical valves, and for this reason, we studied the possibility of using a new animal source such as that of Phoca groenlandica. Four aortic and four pulmonary leaflets were cut radially and their uniaxial tensile testing was evaluated. Three prototype pulmonary valves of Phoca groenlandica preserved in buffered glutaraldehyde solution 0.625% at pH 7.4 were mounted on a 19, 21, and 27 mm novel support system (stent) with heart shape commissural posts covered with polytetrafluoroethylene. The valves were tested in a steady flow system, the peak pressure gradients (PPGs) were measured, and the effective orifice areas (EOAs) were calculated for the flows of 3, 4, 5, 6, and 8 L/min. There were five different measurements for each flow variant. Aortic and pulmonary leaflets present no statistically significant difference in failure strength (p = 0.93). The PPGs across the valves for the flow of 3, 4, 5, 6, and 8 L/min for all three tested valves were low and the corresponding calculated EOAs were large. The new bioprosthetic valve derived from the pulmonary valve of Phoca groenlandica mounted on this novel support system presented a satisfactory hydrodynamic performance in a steady flow system. More research is needed before it can be considered suitable for human cardiac valve replacement.

Transonic Shocks in Multidimensional Divergent Nozzles

We establish existence, uniqueness and stability of transonic shocks for steady compressible non-isentropic potential flow system in a multidimensional divergent nozzle with an arbitrary smooth cross-section, for a prescribed exit pressure. The proof is based on solving a free boundary problem for a system of partial differential equations consisting of an elliptic equation and a transport equation. In the process, we obtain unique solvability for a class of transport equations with velocity fields of weak regularity(non-Lipschitz), an infinite dimensional weak implicit mapping theorem which does not require continuous Frechet differentiability, and regularity theory for a class of elliptic partial differential equations with discontinuous oblique boundary conditions.

A method for computing the degree of mixing in steady continuous flow systems

The degree of mixing was first proposed by Danckwerts and further discussed by Zwietering more than 50 years ago to measure mixing performance of a continuous flow system. Although the measure has been widely discussed in mixing literature, there has never been a method to compute its value for a general continuous flow. In this paper, a method is developed to compute this measure for a general steady continuous flow system for the first time. The method is based on the recently developed mean age theory. The governing equations for the mean age and higher moments of age are also derived for different types of tracer introduction other than pulse input in the current mean age theory.

Exergetic performance analysis of a recirculating aquaculture system

This paper examines exergetic aspects of a Recirculation Aquaculture System (RAS) for Black Sea trout (Salmo trutta labrax) fingerling rearing at the Trabzon Central Fisheries Research Institute, Turkey. In its thermodynamic analysis, each component of the RAS is treated as a steady-state steady flow system and its exergetic efficiencies are studied. In addition, the following parameters are measured and recorded in experiments: the mass flow rates, inlet and outlet temperatures and of the system components, surrounding temperatures, and electrical work utilized by the components in the RAS. Based on these experimental data, inlet and outlet exergy values, exergy losses, and exergetic efficiencies of each component in the system are determined to assess their performance. Moreover, the overall system exergy efficiency is determined. The results show that exergy efficiencies of the system components are highly affected by varying input exergy flows as a function of the surrounding temperature and chiller’s operating period.

Dissolved Oxygen and pH Modeling of a Periphyton Dominated, Nutrient Enriched River

Nutrient enrichment of the South Umpqua River, Oregon was linked to periphyton growth and large diel fluctuations in dissolved oxygen and hydrogen ion (pH) concentrations using the water quality model QUAL2Kw. The available data provide a good case study for the relatively new water quality model. QUAL2Kw simulates a dynamic diel heat budget and water quality kinetics for a one-dimensional, steady-flow system and is part of a family of models meant to serve as an update to the widely used QUAL2E. The model was used to quantify nonpoint source loading, determine the pollutant of concern, estimate natural conditions, and calculate a phosphorus total maximum daily load during summer, low-flow conditions. Control of both nonpoint and point sources is required to achieve the low instream phosphorus concentrations necessary to meet water quality criteria. To our knowledge, this is the first paper that reports on the application of a model for computing the maximum allowable load necessary to manage the diel variation in pH.

Entropy generation during microcombustion

We use an entropy balance to formulate the entropy generation equation in a flame zone of a cylindrical microcombustor tube. In deriving this equation, we define a nondimensional radius as the ratio of the tube radius to the flame thickness, and we set up a thermal model of the flame zone by applying an energy balance for a steady flow system to the flame zone. Based on this model, we obtain a relationship between the flame temperature and the nondimensional radius. Given this relationship, the effects of the fuel, fuel-air ratio, unburned gas temperature, and tube radius on entropy generation are analyzed. The occurrence of minimum entropy generation is predicted. The efficient operating conditions of the microcombustor are suggested.

Exergy analysis of a vapour-compression refrigeration/heat pump cycle with chimney

The greatest speciality of this work is using chimneys with different heights above the condenser instead of a condenser's fan on the vapour-compression refrigeration/heat pump system chosen as an experimental set. Exergy analyses of natural convection with and without chimneys and forced convection on the same experimental set have been made with acceptances of steady state-steady flow system on each part of the set. Temperatures and pressures on each point of the system are measured and then specific enthalpies and entropies of them are determined. The coefficients of performance in refrigeration and heat pump modes and the exergies of each point, irreversibilities and second law efficiencies for each part of the system are calculated and given in tables comparatively. In this study, it is seen that the values for natural convection with chimney are between the forced convections and natural convections.

A physical basis for calculating instrument spatial weighting functions in homogeneous systems

Starting with a streamline‐based argument, the theoretical basis for a spatial weighting function in a steady, homogenous, and isotropic flow system is developed for both compressible and incompressible flow. A physical interpretation of spatial weighting functions in terms of the ratio of steady state energy dissipation rate per unit volume of porous medium to total energy dissipation rate over the entire flow domain is formulated. Finally, applications of the spatial weighting functions are presented based on calculated gas minipermeameter mass flux fields for the conventional surface probe and a new small drill hole probe configuration. Spatial weighting function distributions indicate that with diverging flow field instruments, such as the gas minipermeameter, porous medium volumes in the inlet vicinity are heavily weighted, with volumes near the seal boundaries shown to be extremely important. The technique described allows one to quantify the size and shape of the subvolume of a domain contributing to a hydraulic conductivity or intrinsic permeability measurement. For heterogeneous systems it is suggested that the spatial weighting function for a given instrument will be heterogeneity dependent and therefore nonunique. However, extending the weighting function concept to heterogeneous and/or transient systems is an important research priority.

Optically programming DNA computing in microflow reactors

The programmability and the integration of biochemical processing protocols are addressed for DNA computing using photochemical and microsystem techniques. A magnetically switchable selective transfer module (STM) is presented which implements the basic sequence-specific DNA filtering operation under constant flow. Secondly, a single steady flow system of STMs is presented which solves an arbitrary instance of the maximal clique problem of given maximum size N. Values of N up to about 100 should be achievable with current lithographic techniques. The specific problem is encoded in an initial labeling pattern of each module with one of 2N DNA oligonucleotides, identical for all instances of maximal clique. Thirdly, a method for optically programming the DNA labeling process via photochemical lithography is proposed, allowing different problem instances to be specified. No hydrodynamic switching of flows is required during operation — the STMs are synchronously clocked by an external magnet. An experimental implementation of this architecture is under construction and will be reported elsewhere.

Fuel-Spray Characteristics of High Pressure Gasoline Injection in Flowing Fields.

The direct infection into the cylinders has been regarded as a way of the reduction in fuel consumption and pollutant emissions. The spray produced from the direct injector is of paramount importance in GDI (Gasoline Direct Injection) engines in that the primary atomization process must meet the requirement of quick and complete evaporation and combustion especially to prohibit the excessive HC emissions. The interaction between air flow and fuel spray was investigated in a steady flow system embodied in a wind tunnel to simulate the variety of flow inside the cylinder of the GDI engine. The direct Mie scattered and Shadowgraph images presented the macroscopic view of the liquid sprays and vapor fields. The velocity and particle size of fuel droplets were investigated by Phase Doppler Anemometer (PDA) system. The processes of atomization and evaporation with a GDI injector were observed and consequently utilized to construct the data-base for the spray and fuel-air mixing mechanism as a function of the flow characteristics.

Respirator Filter Reuse Test Using the Laboratory Simulant Mycobacterium Tuberculosis (H37RA Strain)

All respirators certified under Title 42, Code of Federal Regulations, Part 84, can be used by healthcare workers for protection against Mycobacterium tuberculosis (Mtb). Questions have been raised regarding the possibility of the respirator becoming contaminated with Mtb or other organisms due to reuse, handling, and storage in plastic bags. This study was conducted to: (1) determine whether, and for how long, avirulent Mtb (strain H37Ra) survives on respirator material, and (2) measure levels of contamination (assess contamination by environmental bacteria and fungi due to storage in airtight bags) potentially spread to the respirator's interior surface due to normal mechanical handling (removal and re-insertion of the respirator into airtight bag). Six models of filtering facepiece respirators were challenged with a concentration of 105 to 106 colony forming units (CFUs) H37Ra per liter of air in a steady flow system. Respirator interior and exterior surfaces were swab sampled on days -1 (prior to exposure), 0 (day of exposure), 1, 3, 7, 10, 14, 21, and 28. Between samplings, each respirator was stored at room temperature in a Zip-lock™ bag. Seven days after exposure the number of viable organisms decreased from a mean range of 27 to 131 colony forming units per square centimeter (CFU/cm2) to zero CFU/cm2 on the exterior of the different respirator models. While several respirators had interior contamination immediately following challenge, no transfer of exterior H37Ra was observed. Some colony growth was recoverable from day 14 to 28 indicating there was some incidental contamination with environmental bacteria to the interior of the respirator after repeated handling and storage.

A novel method for efficient drug delivery.

Local delivery of anti-thrombotic and anti-restenotic drugs is desired to achieve high concentrations of agents which may be rapidly degraded systemically or which exhibit very short half-lives in vivo. In this article, the operating characteristics of a novel local drug delivery method are described and its effectiveness demonstrated computationally and experimentally. Computational models used a finite volume method to determine the concentration field. Optical dye density measurements of Evans blue in saline were performed in an in vitro steady flow system. Modeling parameters were kept in the physiologic range. Experimental flow visualization studies demonstrated high concentrations of infusate near the vessel wall. Computational studies predicted high, clinically significant drug concentrations along the wall downstream of the infusion device. When the radial infusion velocity is large (infusion flow rate, Qinf>0.5% of the main flow rate, Q), the wall concentration of the infused drug remains high, e.g., levels are greater than 80% of the infusate concentration 5 cm downstream of the infusion device. At lower infusion rates (Qinf<0.001Q), the drug concentration at the wall decreases exponentially with axial distance to less than 25% of the infusate concentration 5 cm downstream of the infusion device, although therapeutic drug levels are still readily maintained. The near wall drug concentration is a function of flow conditions, infusion rate, and the drug diffusivity. Good agreement was obtained between computational and experimental concentration measurements. Flow simulation and experimental results indicate that the technique can effectively sustain high local drug concentrations for inhibition of thrombosis and vascular lesion formation.

Boundary layer drug delivery using a helical catheter

Background: A catheter-based approach for local endovascular drug delivery has been developed. The catheter is deployed percutaneously, while the end of the catheter is in the form of a helix that is placed just proximal to the vascular site to be treated. The helices are in contact with the vessel wall. A number of small holes is drilled in the coils of the catheter through which drug is infused, so that the infused drug remains within the blood fluid `boundary layer' adjacent to the vessel wall. This approach is expected to be highly efficient for administration of antithrombotic and antiproliferative agents that target processes leading to vascular occlusion, heart attacks, and strokes. Methods: The helical catheter was qualitatively evaluated using optical dye density measurements of Evans blue dye infused using an in vitro steady flow system under a physiologic range of conditions. To further demonstrate the efficiency of the technique, its capacity to inhibit thrombosis was evaluated in a baboon thrombosis model. The catheter was inserted into a femoral arteriovenous shunt (blood flow rate=100 ml/min) and placed proximal to a segment of highly thrombogenic Dacron vascular graft (4.0 mm i.d.). Integrelin (an inhibitor of platelet glycoprotein IIb/IIIa; doses: 0.25–1.0 μg/min) and hirudin (an antithrombin; doses: 10–100 μg/min) were used to inhibit thrombus formation. Results: Experimental flow visualization studies demonstrated that high concentrations of the infused Evans blue dye were retained near the vessel wall. In the animal experiments, platelet deposition on the Dacron graft surface was reduced by 82–97% (Integrelin) and 68–92% (hirudin) over 1–2 h of blood exposure. The local antithrombotic effects produced were found to be 200-fold and 30-fold more efficient than systemic administration of the same agents. Conclusions: Local drug infusion using the helical catheter approach can achieve high drug concentration levels at target sites, may avoid systemic effects, and can reduce cost of therapy by reducing total drug requirements.

F平面上での2次元定常な流れに於ける保存量と山を越える流れへの応用

A steady-flow system on an f-plane whose velocity is uniform in one horizontal direction, say y direction, is considered. The velocity far upstream in the other horizontal direction, say minus x direction, is assumed to be horizontal and dependent only on the vertical coordinate, say z. The potential temperature, Bernoulli function or potential vorticity is not necessarily conserved along the stream lines projected onto the 2-dimensional (z, x) vertical plane, although they are conserved along the true stream lines in the 3-dimensional (z, x, y) space. In this note, a temperature-like quantity Θ, an energy-like quantity B and a vorticity-like quantity Q, which are conserved along the projected stream lines on the (z, x) vertical plane, are constructed. They become functions of the 2-dimensional stream function ψ=ψ(z, x). As in the case of the true Bernoulli function and potential vorticity, Q=Q[ψ] is the derivative of B=B[ψ], i. e., Q[ψ]=dB[ψ]/dψ.As an application of the conservation laws, a problem of hydrostatic neutral flow with a horizontal rigid lid over a mountain is exactly solved. In particular, both the z and x components of velocity are shown not to be affected by the rotation.

Experimental evaluation of velocity and power estimation for ultrasound blood flow imaging, by means of a two-dimensional autocorrelation approach

This paper evaluates experimentally the performance of a novel axial velocity estimator, the 2D autocorrelator, and its Doppler power estimation counterpart, the 2D zero-lag autocorrelator, in the context of ultrasound color flow mapping. The evaluation also encompasses the well-established 1D autocorrelation technique for velocity estimation and its corresponding power estimator (1D zero-lag autocorrelator), to allow performance comparisons under identical conditions. Clutter-suppressed in vitro data sets from a steady-flow system are used to document the effect of the range gate and ensemble length, noise level and angle of insonation on the precision of the velocity estimates. The same data sets are used to examine issues related to the estimation of the Doppler signal's power. The first-order statistics of power estimates from regions corresponding to flow and noise are determined experimentally and the ability of power-based thresholding to separate flow signals from noise is characterized by means of ROC analysis. In summary, the results of the in vitro evaluation show that the proposed 2D-autocorrelation form of processing is consistently better than the corresponding 1D-autocorrelation techniques, in terms of both velocity and power estimation. Therefore, given their relatively modest implementation requirements, the 2D-autocorrelation algorithms for velocity and power estimation appear to represent a superior, yet realistic, alternative to conventional Doppler processing for color flow mapping.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>