On the longitudinal dispersion of passive contaminant in oscillatory flows in tubes

Chatwin, P. C.

doi:10.1017/s0022112075002716

Cited by 279 publications

(127 citation statements)

References 14 publications

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“…The similarity has also been suggested by Harvey et al [1996]. Shear dispersion in the main stream can be represented by a diffusive term in the longitudinal transport equation [Chatwin, 1975]. The relative effect of dispersion to advection is quantified by the Peclet number Pe --x U/D, where D is the longitudinal dispersion in the main stream, U is the mean flow velocity in the stream, and x is the longitudinal coordinate.…”

Section: Transport Modelsupporting

confidence: 57%

Temporal moment analysis of tracer discharge in streams: Combined effect of physicochemical mass transfer and morphology

Gupta¹,

Cvetković²

2000

Water Resources Research

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Abstract. In environmental applications it is often of interest to predict the rates at which contaminant mass is discharged at a given cross section of streams and rivers. We present a Lagrangian methodology for evaluating tracer discharge (mass per unit time) at specified control cross sections (CCS) of streams. The key transport processes included in the analysis are advection, degradation/decay, and kinetically controlled mass transfer in storage zones and in bed sediment. The transport in the bed sediment is described as a diffusion process, where the tracer may sorb onto the sediment. We have derived a general solution for tracer discharge in the Laplace domain wherefrom temporal moments are computed. The derived solutions may account for deterministic changes in morphological characteristics along stretches of streams. The results are illustrated for zeroth and first two moments where we show the combined effect of advection, degradation, physicochemical mass transfer, and morphology. For illustrative purposes, we assume morphology to change downstream following power laws suggested by Langbein [1947] and Leopold and Maddock [1953]. The moments depend nonlinearly on the downstream distance, following power laws that reflect the power laws for the hydraulic geometry. We define two main dimensionless parameters, namely, kinetic storage parameter a* and bed parameter M, that control the amount of tracer mass eventually discharged at any given CCS. For M •-• 0.3 the most dominant mechanism that controls the amount of ultimately discharged tracer mass is the exchange with the bed sediment. Once estimated from field data for stretches of specified streams, the dimensionless parameters can be used in the derived expressions for predictive purposes.

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Section: Transport Modelsupporting

confidence: 57%

Temporal moment analysis of tracer discharge in streams: Combined effect of physicochemical mass transfer and morphology

Gupta¹,

Cvetković²

2000

Water Resources Research

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“…Reynolds number, Re, is a dimensionless index, directly proportional to gas density, and for a specific insufflating gas, Re is also proportional to Pe. Because the data of Scherer et al and others (3,16,26) imply that the relative importance of axial dispersion increases with Re, a gas with lower density will have lower Re and will exhibit less mixing. Therefore, the impact of axial dispersion is expected to be less important for heliox than for air at large Pe.…”

Section: Impact Of Heliox As the Insufflating Gasmentioning

confidence: 94%

“…Previous work (3,16,26) demonstrates that axial dispersion is dependent on flow rate, geometry, and the fluid's physical properties, with mathematical characteristics similar to molecular diffusion. Scherer et al (16) and others (3,26) have described the combined effects of molecular diffusion and axial dispersion in terms of an effective diffusivity, D* NO,i . These experiments used nitrogen (with similar physical properties to air) as the insufflating gas.…”

Section: Impact Of Heliox As the Insufflating Gasmentioning

confidence: 99%

Probing the impact of axial diffusion on nitric oxide exchange dynamics with heliox

Shin

Condorelli

Rose-Gottron

et al. 2004

Journal of Applied Physiology

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Shin, Hye-Won, Peter Condorelli, Christine M. Rose-Gottron, Dan M. Cooper, and Steven C. George. Probing the impact of axial diffusion on nitric oxide exchange dynamics with heliox. J Appl Physiol 97: 874 -882, 2004. First published April 30, 2004 10.1152/ japplphysiol.01297.2003.-Exhaled nitric oxide (NO) is a potential noninvasive index of lung inflammation and is thought to arise from the alveolar and airway regions of the lungs. A two-compartment model has been used to describe NO exchange; however, the model neglects axial diffusion of NO in the gas phase, and recent theoretical studies suggest that this may introduce significant error. We used heliox (80% helium, 20% oxygen) as the insufflating gas to probe the impact of axial diffusion (molecular diffusivity of NO is increased 2.3-fold relative to air) in healthy adults (21-38 yr old, n ϭ 9). Heliox decreased the plateau concentration of exhaled NO by 45% (exhalation flow rate of 50 ml/s). In addition, the total mass of NO exhaled in phase I and II after a 20-s breath hold was reduced by 36%. A single-path trumpet model that considers axial diffusion predicts a 50% increase in the maximum airway flux of NO and a near-zero alveolar concentration (CA NO) and source. Furthermore, when NO elimination is plotted vs. constant exhalation flow rate (range 50 -500 ml/s), the slope has been previously interpreted as a nonzero CANO (range 1-5 ppb); however, the trumpet model predicts a positive slope of 0.4 -2.1 ppb despite a zero CANO because of a diminishing impact of axial diffusion as flow rate increases. We conclude that axial diffusion leads to a significant backdiffusion of NO from the airways to the alveolar region that significantly impacts the partitioning of airway and alveolar contributions to exhaled NO. gas exchange; model; exhaled breath NITRIC OXIDE (NO) performs many important functions in the lungs and has been regarded as a potential noninvasive marker of lung inflammation (2). The characteristics of NO gas exchange are unique compared with other endogenous gases because exhaled NO is thought to have a significant alveolar and airway source (6,8,15,22). A two-compartment model is commonly used to characterize NO exchange dynamics for healthy and diseased lungs (9,11,13,20,21,23,24,27,29), by partitioning exhaled NO into airway and alveolar contributions using three flow-independent NO exchange parameters: maximum flux of NO from the airways (JЈaw NO ), the diffusing capacity of NO in the airways (Daw NO ), and the steady-state alveolar concentration (CA NO ). However, the two-compartment model considers only convection of NO in the airways as a transport mechanism and has neglected axial diffusion of NO in the gas phase to preserve mathematical simplicity.Recently, our laboratory (17) and others (31) separately demonstrated theoretically that axial diffusion may play an important role in NO transport. During exhalation, the concentration of NO is higher in the airways compared with the alveoli, creating a gradient for diffusion of NO from the air...

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“…To solve (6) and (7) for T, a temperature distribution of the following form [34] is assumed for both the fluid and the solid:…”

Section: And Hencementioning

confidence: 99%

Study of Conjugate Heat Transfer in Electromagnetic Liquid Metal Dream Pipe

Puvaneswari

Karthikeyan

2017

Archive of Mechanical Engineering

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The combined effect of conjugation, external magnetic field and oscillation on the enhancement of heat transfer in the laminar flow of liquid metals between parallel plate channels is analyzed. In order to make our results useful to the design engineers, we have considered here only the wall materials that are widely employed in liquid metal heat exchangers. Indeed, all the results obtained through this mathematical investigation are in excellent agreement with the available experimental results. The effective thermal diffusivity κ e is increased by 3 · 10 6 times due to oscillation and that the heat flux as high as 1.5 · 10 10 (W/m 2 ) can be achieved. Based on our investigation, we have recommended the best choice of liquid metal heat carrier, wall material and its optimum thickness along with the optimum value of the frequency to maximize the heat transfer rate. At the optimum frequency, by choosing a wall of high thermal conductivity and optimum thickness, an increase of 19.98% in κ e can be achieved. Our results are directly relevant to the design of a heat transfer device known as electromagnetic dream pipe which is a very recent development.

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On the longitudinal dispersion of passive contaminant in oscillatory flows in tubes

Cited by 279 publications

References 14 publications

Temporal moment analysis of tracer discharge in streams: Combined effect of physicochemical mass transfer and morphology

Temporal moment analysis of tracer discharge in streams: Combined effect of physicochemical mass transfer and morphology

Probing the impact of axial diffusion on nitric oxide exchange dynamics with heliox

Study of Conjugate Heat Transfer in Electromagnetic Liquid Metal Dream Pipe

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