Influence Of Tube Diameter Research Articles

Local condensation heat transfer rates in fine passages

A novel apparatus capable of quantitative control of local heat flows to single fine passages through thermoelectric coolers has been developed. Local heat transfer coefficients for flow condensation of HCFC-123 and of R11 have been measured for a wide range of mass fluxes (70–600 kg m −2 s −1), heat fluxes (15–110 kW m −2), vapour qualities (superheated to fully condensed), and pressures (120–410 kPa) in tubes with internal diameters of 0.92 and 1.95 mm. The data show a strong influence of mass flux and local quality on the heat transfer coefficient, with a weaker influence of system pressure. The data also show a clear enhancing effect of the condensation rate (heat flux) on the heat transfer coefficient. There is very little influence of tube diameter over the range investigated. A simple model of gas–liquid shear-driven annular flows, with a turbulent liquid film and allowance for the influence of condensation rates on the gas–liquid interfacial shear force, accounts quantitatively for the major effects observed. An average overprediction of 5% is obtained for the data set of more than 2000 points, with a standard deviation of 25%. However, the model does not predict the full extent of the observed effect of condensation rate on the heat transfer coefficients and some improvement in the description of the interfacial shear force is apparently needed.

PNEUMATIC DRYING IN DILUTED PHASE: PARAMETRIC ANALYSIS OF TUBE DIAMETER AND MEAN PARTICLE DIAMETER

ABSTRACT In previous work on pneumatic drying presented by the authors, a mathematical model based on the conservation equations of momentum, mass and energy was proposed. This model was developed taking into account axial and radial profiles for gas and solids velocities, pressure and porosity in the drying tube. These dynamic profiles influenced the behavior of temperature in the gas and particulate phases, gas humidity and solids moisture content. In this work, this model has been used to perform a parametric analysis of the tube and panicle diameters in the pneumatic drying process. These variables were analyzed here for fixed conditions of gas and solids flowrates and initial values of temperatures, humidity and moisture content. Factorial planning was applied to the numerical solution of the mathematical model. Experimental data obtained in a pilot scale pneumatic dryer were used as the initial conditions in the simulation to specify the levels of the variables analyzed. Results on the influence of tube diameter and particle diameter on the drying process were obtained by statistical analysis of the responses generated by the factorial planning.

Differences in the Flow Behaviors of Polymeric and Cationic Surfactant Drag-Reducing Additives

Research on cationic surfactant drag-reducing additives has grown in recent years because of their repairability after shear degradation, making them suitable for potential applications in recirculation flows such as district heating and district cooling systems. Substantial differences between their flow behaviors and those of high-polymer, drag-reducing additives have been found. These include the influence of preshearing, the effect of mechanical shear on degradation, the influence of tube diameter, maximum drag-reduction effectiveness, and the shape of their mean velocity profiles. Examples of these different flow behaviors are described. The differences suggest that the mechanisms for causing drag reduction may be different for the two types of additives.

Gas-liquid pipe flow under microgravity conditions: influence of tube diameter on flow patterns and pressure drops

Gas-liquid pipe flow under microgravity conditions: influence of tube diameter on flow patterns and pressure drops

The Influence of Suspending Phase Viscosity on the Passage of Red Blood Cells Through Capillary-Size Micropores

Much attention has been paid to the study of blood flow in long, narrow tubes. While the influence of tube diameter and driving pressure have been examined in detail, the influence of suspending phase viscosity has generally been assumed only to affe

Numerical Study of an Unsteady Confined Jet. Application to Crossflow Filtration

This paper deals with the influence of a new flow unsteadiness on the permeate flux in crossflow filtration. A pneumatically controlled valve generates intermittent jets from the main flow, leading to the formation of large vortices moving downstream along the tubular membrane. A numerical calculation of this flow is achieved using a finite difference scheme. Influences of tube diameter and jet velocities are discussed. Application of this technique is carried out by filtering a bentonite suspension through an ultrafiltration membrane.

The influence of suspending phase viscosity on the passage of red blood cells through capillary-size micropores

Much attention has been paid to the study of blood flow in long, narrow tubes. While the influence of tube diameter and driving pressure have been examined in detail, the influence of suspending phase viscosity has generally been assumed only to affect the blood viscosity in a linearly proportional manner, hence the practice of normalizing apparent blood viscosity values by the suspending phase viscosity to give a relative viscosity ( e.g., Pries et al., 1992). While this assumption is probably valid for long tubes, it apparently does not hold for blood flow in short tubes (and by extension also for flow in short or branching capillary segments in vivo) in which RBC deformation plays a more significant role. In this paper we present a series of experiments using the Cell Transit Analyzer (CTA) in which the influence of driving pressure and suspending phase viscosity on RBC passage through short, narrow tubes has been systematically evaluated. Over the range studied (1 to 10 cm water), the influence of driving pressure was found to be unremarkable, in that RBC velocity scaled directly and linearly with pressure. This finding is consistent with previous studies. However, a distinct intercept was observed in the linear relationship between RBC pore transit time and suspending phase viscosity, which presumably arises as a consequence of RBC deformation either at the pore entrance or within the pore. Two simple mathematical models for the suspending phase-viscosity/transit-time relationship were considered. The results show that making CTA measurements over a range of suspending medium viscosities is a simple and practical way to obtain additional information about RBC mechanical properties.

Gas-liquid pipe flow under microgravity conditions: Influence of tube diameter on flow patterns and pressure drops

Gas-liquid flow experiments have been performed in small tubes of 19 mm, 10 mm and 6 mm diameter, during parabolic flights, for a range of superficial liquid velocities from 0.1 to 2 m/s and superficial gas velocities from 0.05 m/s to 10 m/s. Results are compared to those previously obtained by Colin et al., /1/, in a 40 mm i.d. tube. The flow patterns identified are: bubbly flow, slug flow and a pattern halfway between slug and annular flows. The main difference between the experiments in small tubes and the previous ones, concerns the transition between bubbly flow and slug flow, the role of coalescence and the wall friction factor. Coalescence is shown to play a major role in the transition from bubbly to slug flow. In particular at small Reynolds number coalescence seems to be partly inhibited. Single-phase flow correlations for wall shear stress underestimate the wall friction factor in the intermediate range of Reynolds number between laminar and turbulent flow.

The theory and practice of retrograde infusion: influence of tube diameter on drug delivery.

This work identifies a model for the flow dynamics of retrograde drug infusion, thereby helping to clarify the influence of variables on drug dilution in the apparatus and hence drug infusion rate. The study is a 2(3) factorial design that focuses on the influence of tube diameter (0.065 vs. 0.120 inches) in conjunction with changes in injected drug volume (2.0 vs. 5.0 ml) and iv flow rate (2.0 vs. 10.0 ml h-1). Each of the three variables was shown to exert a statistically significant (p = 0.01) effect on the total volume of fluid necessary to clear a dose from the retrograde apparatus. In all cases studied, smaller diameter tubes, larger injected drug volumes, and slower iv flow rates decreased the total volume fraction (F0.95). Within the confines of the study, practitioners may use an F0.95 value of 1.5 to predict the time at which a patient's retrograde drug infusion is likely to be complete. This, in turn, may be used to facilitate proper timing of blood sampling for therapeutic drug monitoring as well as other pharmacokinetic manipulations.

In vitro blood flows through small tubes.

This text recalls the main sequences of a videofilm in which we have looked at the blood flow through small diameter tubes, varying from 200 to 500 micron diameter, using a video equipment where the camera is fixed to a phase contrast microscope. Flows of two fluid model through converging-diverging small tubes have been studied both theoretically and experimentally, where we have considered the influence of tube diameter, stenosis, flow rate, haematocrit upon the red blood cells repartitions and the thickness of peripheral plasma layer.

On the Influence of Tube Diameter on the Development of Gaseous Detonation

AbstractStreak photographs of the transition from slow‐burning to detonation have been obtained by self‐light photography of the flame using a rotating drum camera. Experiments were performed with stoichiometric hydrogen‐oxygen mixtures contained in plastic tubes closed at one end and ignited by pilot flames. The investigation included the effect of tube diameter and distance of ignitor from closed end on the development of detonation.The plots of detonation induction distances and times as a function of tube diameter indicate the existence of asymptotes. Above a certain value of tube diameter there should be no further increase of induction distance and time with increasing tube diameter. A graph of average detonation induction velocity, that is, the ratio of average induction distance to time, shows that wall effects are noticeable only for tubes with a diameter smaller than about 1 cm. Maximum observed flame velocities, attaining the value of 3.1 km/sec, have been observed immediately following the onset of retonation before the combustion front settles down to the Chapman‐Jouguet detonation with a velocity of 2.8 km/sec. The plot of world lines on the log‐log scale revealed that the development process can be bracketed between two asymptotes, one corresponding to an acceleration which decreases, or is sometimes even negative, and the other with acceleration that increases with time. The average value of observed accelerations was of an order of 106 m/sec2.