Value Of Pressure Loss Coefficient Research Articles

CFD study of pressure loss characteristics of multi-holed orifice plates using central composite design

The study on the use of multi-holed orifice plate for measuring flow rate is a growing area of research. As compared to standard orifice plate, multi-holed orifice plates (MO) have number of advantages, such as, these plates require minimum straight piping at the upstream without compromising the pressure losses and provide better accuracy in the measurement of flow rates. In this study, a systematic methodology is adopted for investigating the effect of different geometrical parameters on pressure loss coefficient and values of parameters under investigation varied using central composite design. The geometrical parameters chosen for the study are: (a) Number of holes; (b) Multi-hole Diameter ratio and (c) Compactness of holes. Commercial computational fluid dynamics code (ANSYS Fluent) is employed to perform simulations for 15 different settings of these parameters to analyze their effect on pressure loss coefficient and flow development length at downstream of multi-holed orifice plates. It is found that values of pressure loss coefficient is a strong function of multi-hole diameter ratio, whereas, the flow conditioning properties are strongly affected by the number of holes.

Experimental study of effect of stenosis geometry on flow parameters

A stenosis is a narrowing in a tubular organ or structure. In medicine, vessel stenosis poses health risks for people. In this work, experimental investigations of pressure loss coefficient for varying stenosis eccentricity and shape were performed. Five models of different geometry were studied; all models were stenosis of 75 % area reduction. The flow conditions approximate physiological flow. The measuring range of Reynolds number was from 130 to 2730, measured values of pressure loss coefficient were from 12 to 20. The steady experimental results indicated that static pressure loss coefficient is affected by the shape of stenosis, but it was affected more significantly by the eccentricity. Visualization experiments have been performed in Polycarbonate models.

New Method of Hydraulic Performance Evaluation on Emitters with Labyrinth Channels

Hydraulic performance of the emitter is crucial in drip-irrigation systems. Considering the limitations of evaluating an emitter’s hydraulic performance, a new method was proposed by using a pressure loss coefficient (PLC) as the evaluation index, which was derived from frictional and local losses of the fluid in labyrinth channels. The value of PLC can be obtained through numerical calculations of flow rates and pressure heads of the emitter by a Reynolds stress model (RSM). In addition, experiments were also carried out to measure the emitter’s PLC, and the results are found to be consistent with those obtained through numerical analysis. The new evaluation method can be used to predict and compare the hydraulic performance of this specific type of labyrinth channel with a range of dimensions.

The prediction of airflow generated noise in ventilation system bends.

This paper describes recent work on the prediction of airflow generated noise in ducts based upon pressure loss characteristics. Strategies employed to reduce turbulence by smoothing the flow around a bend include the use of turning vanes, and a large radius of curvature with the associated use of splitters. The effect of these strategies on the regenerated noise is examined for a range of common bends including mitred bends, with and without turning vanes, and radiussed bends, with and without splitters. The effect of bends with different aspect ratios is also examined. An excellent collapse of measured data onto a single characteristic curve is reported for each configuration based upon standard values of pressure loss coefficients. It is suggested that that these characteristic curves might form the basis for a practical prediction method.

Noise Generation in Ventilation Systems by the Interaction of Airflow with Duct Discontinuities: Part 1 Bends

Discontinuities in air duct systems give rise to turbulence and some of this turbulence results in airflow generated noise. One potential source of flow generated noise in ducts is the presence of a bend. Various strategies are employed to reduce turbulence by smoothing the flow around a bend, such as the use of turning vanes, large radius of curvature and the associated use of splitters, and these will also affect the noise generated. Recent work on the prediction of airflow generated noise in ducts based upon pressure loss characteristics is applied to a range of bends including mitred bends, with and without turning vanes, and radiussed bends, with and without splitters. The effect of bends with different aspect ratios is also examined. An excellent collapse of measured data onto a single characteristic curve is reported for each configuration based upon standard values of pressure loss coefficients. It is suggested that these characteristic curves might form the basis for a practical prediction method.

雪氷粒子の水力輸送に関する基礎的研究 氷粒子の抗力係数

In this paper, drag coefficients of sphere and non-sphere ice particles and its effects on pressure loss in icewater two-phase flow were described. Drag coefficients of sphere ice particles fell close to the previous CD-Res curve (drag coefficient-particle Reynolds number), while those of non-sphere ice particles were in the range of 1-6 in this experiment.Particle motion in water was analyzed by the equation of motion taking into account Basset term. By comparing the experimented particle trajectories with calculated ones, it was confirmed that the Basset term played an important role in motion of particles with densities near that of water such as snow, ice and polystyrene.Pressure loss for ice-water two-phase flow was measured and compared with the results calculated by Durand'sand Newitt's equation. The use of adequate drag coefficient in Durand's equation gave a good agreement between the experimental results and calculated ones at low velocities. At high velocities, a discrepancy was observed because Durand's equation always gave positive values, but negative values of pressure loss coefficients were obtained in this experiment. Newitt's equation showed larger values than the experiments because this equation was applicable to the flow with a moving bed.

Laminar free convection flow rate in a vertical tube

This paper considers the flow rate of a laminar free convection inside a fully heated or a partly heated and partly cooled vertical tube placed in a large space. A theory based on a one-dimensional model which uses the Graetz solution for forced convection in a tube and which considers the pressure losses at the tube inlet and exit and in the hydrodynamic developing region is proposed for the range Gr Pr < 100. For the fully heated tube, the theory is compared with a two-dimensional numerical analysis and actual measurements using a quartz fiber anemometer. Their agreement is good when proper values of pressure loss coefficients are used in the theory. For the partly heated and partly cooled or partly adiabatic tube in thermally stratified and non-stratified ambients, the agreement between the theory and the experiment is also good. The effects of the tube-to-ambient temperature difference, the representative temperature of the stratified ambient, the tube length-to-diameter ratio and the temperature dependence of fluid properties upon the average mass velocity inside the tube are also clarified.