Flow Resistance Curves Research Articles

Effect of flow direction on circumferential velocity, radial velocity, and flow resistance characteristics of rotating gap structures

A rotating gap structure is a type of viscous flow resistance using two disks where the rotation of one disk drives the fluid within the gap, generating rotational inertia. This inertia, combined with viscous friction, determines the flow resistance characteristic curve (pressure drop vs flow rate, or Δp-Q curve). By adjusting the disk's rotational speed, the rotational inertia and the Δp-Q curve can be modified. This paper examines how the radial flow direction (positive and negative) affects the circumferential velocity, radial velocity, and the Δp-Q curve of the rotating gap structure through theoretical modeling and experiments. Results show that radial flow direction and rate influence the symmetric distribution of radial velocity and the linear distribution of circumferential velocity, altering the main components of the Δp-Q curve: the viscous flow resistance curve (Δpvis-Q) and the rotational inertia flow resistance curve (Δprot-Q). The study found that the slope of the Δpvis-Q curve is smaller for positive flow than for negative flow due to differences in radial velocity distribution. Additionally, the circumferential velocity is weakened in positive flow and enhanced in negative flow, resulting in a smaller slope of the Δprot-Q curve for positive flow. These factors cause the Δp-Q curve to deviate from linearity, with greater deviation at higher rotational speeds. Finally, experimental verification was conducted, and the measured Δp-Q curve closely matched the theoretical calculations.

Thermal and flow resistance characteristics of a parallel-pipe type natural heat transfer air-conditioning terminal device for nearly zero energy buildings

A nearly zero energy building (NZEB) can achieve significant energy saving by reducing its air-conditioning load greatly. At the same time, an NZEB should also achieve a comfortable thermal environment. In this paper, a parallel-pipe type natural heat transfer air-conditioning terminal device is proposed and studied for use in NZEB. The terminal device is able to provide both heating and cooling (including sensible and latent cooling) for a building without noise or air disturbance. The advantages of the terminal device have been demonstrated by comparing with other air-conditioning terminals. Experimental data of the heating and cooling performance of the device under different operation conditions were collected and analysed. The calculation models for the heating and cooling capacities of the device were obtained through data regression analysis, and the flow resistance curve of the device was obtained by means of experimental measurement under various flow rates. In addition, comparison was made on the heating and cooling capacities between the device and a radiant floor that also features little noise or air disturbance. Results show that the heating and cooling capacities of the device were 41.5% and 46.8% higher than the maximum capacities of the radiant floor, respectively. This research laid a foundation for the engineering application of the air-conditioning terminal device.

Possibility of the drag reduction effect application to reduce the cost of transport energy in water systems

The main aim of this paper is to present possible drag reduction effect application to reduce the energy costs in water transport systems. Results obtained in laboratory scale experiment present possibility to enhance the drag reduction effect in pipe flow by simultaneous addition to the transported water small amount of high molecular polymers and surfactants. The hypothetic mechanism of drag reduction by polymer-micellar aggregates is presented. Qualitative analysis of polymer-micellar additives influence on shape and character of flow resistance curves is performed. Complex polymer-micellar solution flow resistance curves are compared with appropriate single additive polymer or surfactant one.

Viscoelastic flow past mono- and bidisperse random arrays of cylinders: flow resistance, topology and normal stress distribution.

We investigate creeping viscoelastic fluid flow through two-dimensional porous media consisting of random arrangements of monodisperse and bidisperse cylinders, using our finite volume-immersed boundary method introduced in S. De, et al., J. Non-Newtonian Fluid Mech., 2016, 232, 67-76. The viscoelastic fluid is modeled with a FENE-P model. The simulations show an increased flow resistance with increase in flow rate, even though the bulk response of the fluid to shear flow is shear thinning. We show that if the square root of the permeability is chosen as the characteristic length scale in the determination of the dimensionless Deborah number (De), then all flow resistance curves collapse to a single master curve, irrespective of the pore geometry. Our study reveals how viscoelastic stresses and flow topologies (rotation, shear and extension) are distributed through the porous media, and how they evolve with increasing De. We correlate the local viscoelastic first normal stress differences with the local flow topology and show that the largest normal stress differences are located in shear flow dominated regions and not in extensional flow dominated regions at higher viscoelasticity. The study shows that normal stress differences in shear flow regions may play a crucial role in the increase of flow resistance for viscoelastic flow through such porous media.

THE EFFECT OF SURFACTANT AND HIGH MOLECULAR WEIGHT POLYMER ADDITION ON PRESSURE DROP REDUCTION IN PIPE FLOW

Abstract - The main aim of this paper is to present a possibility to enhance the drag reduction effect in straight pipe flow by the simultaneous addition to the transported liquid of a small amount of high molecular weight polymers and surfactants. Qualitative analysis of the polymer-micellar additive influence on the shape and character of flow resistance curves has been performed. Also multicomponent polymer-micellar solution flow resistance curves were compared with appropriate single additive polymer or surfactant solution flow resistance curves. The experimental data shows that, for polymer-micellar solutions, the stable transitional zone between the laminar and the turbulent flow regions is extended toward higher values of the critical Reynolds numbers. Occurrence of the phenomenon can be explained by the flow laminarization caused by polymer-micellar aggregates. Existence of the third extended drag reduction zone in the turbulent range of flow has also been observed for the first time.

Study of pressure drop-flow rate and flow resistance characteristics of heated porous materials under local thermal non-equilibrium conditions

Porous materials are used as pneumatic components in a wide range of industrial applications. Such porous materials contain thousands of interconnected irregular micro-pores that produce a large pressure drop (ΔP) between the upstream and downstream sides of the porous material when a fluid flows through it. The relationship between the pressure drop and flow rate (i.e., the ΔP−G characteristic) and the relationship between flow resistance (γ) and flow rate (the γ-G characteristic) are two very important basic characteristics. One factor affecting them is temperature, whose variation changes the viscosity and density of the fluid. In this study, we experimentally and theoretically analyzed the effect of temperature on ΔP−G and flow resistance characteristics of porous materials by heating them under constant electric heating power. The resulting experimental ΔP−G and flow resistance curves shift upward relative to their counterparts at room temperature owing to the increase in fluid temperature, but remain within the adiabatic and room temperature curves. The temperature-effect ratio η at constant heating power increases from 1.3 to 1.7 as the flow rate decreases from 21.53×10−5kg/s to 5.80×10−5kg/s, indicating that ΔP−G and flow resistance characteristics and pumping power change significantly when a porous material is heated. Furthermore, temperature distributions were obtained numerically to gain deeper understanding of the temperature effect. The effects of heating power values, characteristic porous material coefficients, and average fluid density on ΔP−G and flow resistance characteristics were also investigated.

Effect of rolling motion on single-phase laminar flow resistance of forced circulation with different pump head

Effects of rolling motion on single-phase laminar flow resistance during forced circulation with different pump heads were investigated. Purified water was used as the working fluid and the flow rate ranged from 0.04 to 0.16m3/h. Different pump heads were obtained by a variable speed electromotor, by which the flow rate was controlled combining with a regulating valve. The experimental results indicate that the influence of rolling motion on transient flow rate and frictional resistance largely depends on the pump head. The flow rate in rolling motion oscillates periodically with its amplitude decreasing rapidly as the pump head increases, and finally, tends to be steady as the pump head further increases to a high level. The system flow resistance curve and pump performance curve are employed to analyze the characteristics of flow oscillation. When the pump supplies a low head, the frictional pressure drop fluctuates asynchronously with the flow rate and could not be predicted by conventional correlations. While the pump supplies a high head, the frictional pressure drop does not fluctuate and could be predicted by conventional correlations. Effects of rolling motion on single-phase laminar flow resistance are clarified by analyzing the velocity distribution. In spite of the above mentioned effects, rolling motion has no influence on time-averaged flow resistance regardless of the pump head.

Mechanism analysis on flow excursion of a natural circulation with low steam quality

Flow excursion was observed on the natural circulation test loop HRTL-5, which simulates the geometry and system design of the 5 MW nuclear heating reactor. By means of self-developed computational codes, a set of tools used for analyzing the flow characteristics of the natural circulation have been presented, including the characteristic curves, operational curve and the bifurcation curve. The two-dimensional disturbance analysis is adopted to explain the mechanism of the flow excursion. Analytical result shows: (1) flow excursion can occur in a natural circulation system at a suitable geometry and thermal–hydraulic conditions. (2) Characteristic curves, operational curve, bifurcation curve, and the two-dimensional disturbance analysis are the available method to analyze the flow excursion of the natural circulation. (3) The flow excursion is prior to the low steam quality density wave oscillation. (4) The onset of the flow excursion is the tangency point of the drive force curve and the flow resistance curve. (5) To operate at low heat flux to increase the inlet temperature is the effectual approach to transfer from the pressurized water state to the boiling water state, in which the flow excursion and the low steam quality density wave oscillation can be avoided.

Turbulent pipe flow of Herschel-Bulkley fluids

A modified two-equation turbulence model is used to compute the turbulent flow of Herschel-Bulkley fluids in smooth pipes. Numerical results are presented for the fully-developed friction factor, and compared with existing empirical correlations. The model is used to produce flow resistance curves over a wide range of values for the power-law index and the generalised Reynolds and Hedstrom numbers.

Laminar and turbulent flow of dilute polymer solutions in smooth and rough pipes

In this paper an empirical formula to describe the flow resistance curves λ = f( Re *) of dilute polymer solutions in smooth and rough pipes has been calculated. The experimental curves obtained by the present author and other investigators were compared with the curves derived from the formula. Experiments observing the flow of dilute aqueous solutions of polyacrylamide Rokrysol WF-2 (molecular weight, 3 × 10 6) and DP9-3981S (molecular weight, 1.5 × 10 7) through smooth and rough pipes were carried out in laminar, transitional and turbulent flow regions. The concentration of the polymer solution was varied from 0.001% to 0.05%. The pipes used had diameters of 5.8, 11.0 and 21.0 mm with roughness of between 0 and 0.5 mm.

Shape and Dimensions of Stationary Dunes in Rivers

The shape and dimensions (length, height) of sand dunes in rivers are calculated by use of the measured bed shear stress distribution downstream a rearward-facing step. The transport of sediment is split up into bed load and suspended load, which makes it possible to explain the transition to plane bed. The model can predict flow-resistance curves in alluvial streams.

Tractive Force Design of Vegetated Channels

ABSTRACT A method is presented for applying tractive force con-cepts to the design of vegetated channels. The method is developed from previously published data on flow resistance and allowable velocities in grassed water-ways. It is intended for use in its present form as a design tool, but also provides a framework in which to place refinements as the mechanics of this type of flow become more fully understood. The protective value of vegetal channel lining is con-sidered to be derived from two related, but distinct, in-teractions of the vegetation with the flow field. The first is the generation of turbulent eddies at a significant distance from the soil boundary resulting in an increase in flow resistance, and the second is a change in the structure of the turbulent eddies in immediate proximity to the boundary. The vegetation is therefore classified in terms of two indices believed to relate directly to these ac-tions. Guidelines are provided for the selection of these indices according to type and quality of cover. This approach eliminates the need for tabulating allowable velocities for each possible combination of channel slope, soil, and vegetal cover by considering the properties of the soil and those of the vegetation separately. An additional advantage is that the existing flow resistance curves are put in equational form as a single curve family.

Experimental renal hypertension in dogs. Forelimb hemodynamics.

Blood flow arid segmental intravascular pressures were measured in the pump-perfused forelimb vascular beds of 25 dogs with chronic perinephritic hypertension and 26 normotensive control dogs (either unilaterally nephrectomized or sham-operated) under pentobarbital anesthesia. Measurements were made under resting conditions (pump-perfusion pressure set equal to aortic pressure) and during response to: (1) stepwise changes in pump blood flow over the range 21-330 ml/min; (2) intrabrachial arterial injection of supramaximal doses of methacholine chloride; and (3) limb denervation. Total limb vascular resistance and segmental pressure gradients were calculated. In hypertensive dogs, as compared to normotensive dogs, resting blood flow was equal ( P >0.3) and resting limb total vascular resistance was increased ( P <0.005). Small vessel pressure gradient was increased ( P <.005) and venous pressure gradient was decreased ( P <0.005). Limb vascular resistance following methacholine injections and residual resistance following neurectomy were lower ( P <0.05) in normotensive than in hypertensive dogs. The development of hypertension was accompanied by the upward displacement of limb flow-resistance curves without discernible change in shape of the curves. These data suggest that in chronic renal hypertension in dogs: (1) the limb vascular bed participates in the increased peripheral vascular resistance; (2) the increase in limb vascular resistance is confined to the small vessel segment with no evidence found for limb venoconstriction; (3) a portion of the elevated limb vascular resistance is not attributable to neural stimuli; and (4) structural changes in vessels may account for part of the increase in limb resistance.

Physiologic and clinical estimates of the relief of nasal flow obstruction in allergic rhinitis: effects of a topical decongestant (oxymetazoline).

Precise, sensitive electronic techniques offer the prospect of quantitating nasal pressure-flow relationships in disease and the impact of medical and surgical treatment. This study considered the value of electronic posterior rhinometry, and its correlation with qualitative clinical recording of patient status, arterial blood pressure, pulse and respiration rates, in the treatment of 30 children with chronic allergic rhinitis who received oxymetazoline pediatric nasal solution three times daily for two weeks. Computer analysis plotted inspiratory, expiratory and total nasal flow resistance curves for all patients and for children above and below 6 years of age. Use of the decongestant solution was marked by a fall from the elevated control means for the resistance measurements which was significant at the 95% confidence level and persisted for 14 days after treatment had been stopped. Measurements of vital signs did not differ meaningfully from baseline determinations. The behavior of the indices for the...

Influence of state of inflation of the lung on pulmonary vascular resistance.

The relationship between the degree of pulmonary inflation and the pulmonary vascular resistance was studied in an open-chested dog preparation. It was possible to control the state of inflation and the blood flow to the lung under study. Vascular resistance could then be observed under controlled conditions. In most cases the resistance at complete collapse was very slightly higher than at moderate levels of inflation. In a few instances collapse was associated with a more marked elevation of resistance. Higher levels of inflation resulted in elevation of vascular resistance. At high levels of pulmonary blood flow and pulmonary arterial pressure, the flow resistance curve is lower than at low levels of blood flow. The resistance values obtained during deflation of the lung were consistently different at equal transpulmonary pressures from those obtained during inflation. The possible reasons for this hysteresis are discussed. Evidence is presented that the increased resistance at high levels of lung inflation is due to the effect of transpulmonary pressure on the vessels surrounding the alveoli. Submitted on January 11, 1960