Effects Of Flow Parameters Research Articles

Approximate analytical solution for ionizing cylindrical shock wave in rotational axisymmetric non-ideal gas: isothermal flow

The propagation of an ionizing cylindrical shock wave in rotational axisymmetric non-ideal gas under isothermal flow condition with an azimuthal magnetic field is investigated. The electrical conductivity is assumed to be negligible in the medium ahead of the shock wave, which after the passage of the shock wave becomes infinitely large. The magnetic pressure, azimuthal fluid velocity, and axial fluid velocity are assumed to be varying according to the power law with distance from the axis of symmetry in the undisturbed medium. The zeroth and first-order approximations are discussed by the aid of the power series method. Solutions for the zeroth-order approximation are constructed in analytical form. Distributions of hydrodynamical quantities are discussed. The effect of flow parameters, namely, shock wave Cowling number c∗, adiabatic exponent γ, rotational parameter L, and gas non-idealness parameter [Formula: see text] are studied on the flow variables. Due to the consideration of a rotating medium or due to the presence of magnetic field, the total energy of the disturbance increases, while with an increase in adiabatic exponent γ the total energy of the disturbance decreases. Density and pressure vanish near the axis of symmetry, thus forming a vacuum there.

An investigation on effects of flow parameters on unsteady MHDflow in a porous medium bounded by parallel porous vertical plates

An investigation on effects of flow parameters on unsteady MHDflow in a porous medium bounded by parallel porous vertical plates

Approximate analytical solution for the propagation of shock waves in self-gravitating perfect gas via power series method: isothermal flow

For the propagation of a shock (blast) in a self-gravitating perfect gas in case of spherical and cylindrical symmetry, an approximate analytical solution is investigated. The shock wave is considered to be a strong one, with the ratio $$ \left( {\frac{C}{{V_{S} }}} \right)^{2} $$ to be a small quantity, where $$ c $$ is the sound speed in an undisturbed medium and $$ V_{S} $$ is the shock wave velocity. The initial density in the undisturbed medium is taken to be varying according to a power law. To obtain the approximate closed-form similarity solution, the flow variables are expanded in a power series of $$ \left( {\frac{C}{{V_{S} }}} \right)^{2} $$ . The first- and second-order approximations are discussed with the help of power series expansion. The analytical solutions are constructed for the first-order approximation. The distribution of the flow variables for first-order approximation in the flow field region behind the shock wave is shown in graphs for both the cylindrical and spherical geometries. The effect of flow parameters, namely, ambient density variation index $$ \alpha $$ , adiabatic exponent $$ \gamma $$ and gravitational parameter $$ G_{0} $$ , are studied on the flow variables and on the total energy of disturbance in the case of the first approximation to the solutions. It is shown that the total energy of the disturbance in the flow field region behind the shock wave decreases with an increase in initial density variation index or adiabatic exponent, i.e. shock strength increases with increase in the value of adiabatic exponent or initial density variation index. A comparison is also made between the solutions obtained for non-gravitating and self-gravitating gases.

Droplet Size Spatial Distribution Model of Liquid Jets Injected into Subsonic Crossflow

Liquid jet injected into transverse subsonic gaseous flow has been widely utilized in many industrial applications. It is useful to determine the spatial distribution of generated droplets in the near-field region for high-efficiency combustion. In this paper, we propose a simplified model to predict droplet spatial distribution in transverse subsonic gaseous flow. Linear stability analysis has been used to determine the disturbance growth rate on the surface of a liquid column. When the amplitude of disturbance is of the same order of magnitude as jet radius, the liquid jet breaks up into ligaments. We can make an assumption that the generation rate of small droplet equals to liquid breakup rates, which varies with a spatial location under this circumstance. Combining these relations with the definition of SMD (Sauter mean diameter), a semitheoretical relation to evaluate droplet spatial distribution along the liquid column can be established. The present model has been compared with empirical relation based on experiments under different conditions. Results indicate that in the surface breakup region, the current model shows great consistency with experimental observations while there exists a relatively large discrepancy between the current model and experimental observation in the column breakup region because of its strong nonlinear effect near the breakup point. In addition, the effects of flow parameters on droplet size spatial distribution have been investigated.

English

English

Three-Dimensional Thermo-Hydraulic Analysis of Solar Air Heater With Equilateral Prism-Shaped Rib Roughness

Abstract Thermal transport and flow friction characteristics due to roughness on the absorber plate of solar air heater are evaluated by applying three-dimensional finite volume based code. Renormalization group (RNG) k–ɛ model is employed to capture the turbulent nature of the flow. The effect of equilateral prism-shaped rib roughness geometrical parameters in terms of relative roughness height (e/D) and relative roughness pitch (p/e) on heat transfer and flow friction is analyzed. Further, the effect of flow parameter, Re in the range of 4000–18,000 is also explored. Results are elucidated in terms of average Nusselt number, friction factor, turbulent kinetic energy, and eddy dissipation. Results are compared with a smooth absorber plate solar air heater. Thermo-hydraulic performance of the roughened solar air heater is analyzed. Noteworthy augmentation in heat transport is obtained. The thermal enhancement factor is calculated for optimal performance and found to vary from 1.7 to 3.5. However, friction factor and pressure loss for roughened plate is significantly higher than its smooth counterpart. The pressure drop across the test section increases with the rise in roughness height due to flow obstruction. A minimum value of the friction factor enhancement ratio worth 2.13 is obtained. Enhancement in thermal transport and pressure losses are combined by introducing a thermo-hydraulic performance factor (THHP). For the range of parameters investigated, the optimum value of the thermo-hydraulic performance factor is found to be 3.41. Correlations for average Nusselt number and friction factor are offered at the end.

Approximate analytical solution for shock wave in rotational axisymmetric perfect gas with azimuthal magnetic field: Isothermal flow

The propagation of cylindrical shock wave in rotational axisymmetric perfect gas under isothermal flow condition with azimuthal magnetic field is investigated. Distributions of gas dynamical quantities are discussed. The density, magnetic pressure, azimuthal fluid velocity and axial fluid velocity are assumed to be varying according to power law with distance from the axis of symmetry in the undisturbed medium. Approximate analytical solutions are obtained by expanding flow variables in power series. Zeroth-order and first-order approximations are discussed with the aid of power series method. Solutions for zeroth-order approximation are constructed in approximate analytical form. The effect of flow parameters namely: shock Cowling number $$C_{0}$$, ambient density variation index q and adiabatic exponent $$\gamma $$ are studied on the flow variables. Consideration of magnetic pressure increases the total energy of disturbance of zeroth order while with increase in ambient density variation index or adiabatic exponent, the total energy of disturbance decreases.

CFD Analysis of Shrouded Diffuser Wind Turbine

The power in the wind is well known to be proportional to the cubic power of the wind velocity approaching a wind turbine. This means that even small amount of its acceleration gives large increase in the power output. Brimmed diffuser shrouds for small wind turbines are being used to accelerate the wind velocity in small wind regimes. The objective of the Paper is to analyze the flow characteristics of brimmed diffuser shroud and to optimize the physical dimensions. CFD analyses are carried out by varying its physical dimensions with the aim of achieving augmented velocity. The effect of flow parameters with the presence of diffuser is analyzed by comparing it with bare wind turbine. The physical dimensions of brimmed diffusers are the parameters considered in this study. The study has been carried with proposed splitted diffuser design. The power yield of the turbine for shifting speeds is gotten and analyzed.The CFD tool CFX would be used to anlayse the flow field around the diffuser. Performance of wind turbine under various operating conditions is generally obtained through an experimental testing and could be cost prohibitive. In this case the computational fluid dynamics analysis provides better results. The capability of using computational fluid dynamics is a test to determine its viability for determining its performance parameters.

Experimental investigation on non-boiling heat transfer of two-component air-oil and air-water slug flow in horizontal pipes

Gas-liquid slug flow in horizontal pipes occurs frequently in industrial applications and its heat transfer characteristics are very important but complicated due to the intermittent flow structures. This paper aims at investigating the heat transfer mechanism of both air-oil and air-water slug flow in horizontal pipes. An experimental setup was fabricated to investigate the flow and heat transfer characteristics of air-oil and air-water slug flow under cooling conditions in horizontal pipes. The test section was made of a copper pipe with I.D. of 26 mm and a polyvinyl chloride pipe with I.D. of 63 mm using concentric geometry. The effect of flow parameters, such as liquid flow rate, gas flow rate, two-phase pressure drop multiplier, void fraction and slug frequency on heat transfer of gas-liquid slug flow was comprehensively investigated. The heat transfer coefficient of two-phase flow was significantly improved by the introduction of air and the maximum two-phase heat transfer enhancement ratio for air-water and air-oil flow were 150% and 300%, respectively. The circumferential temperature distribution and local heat transfer coefficient were also investigated. The local heat transfer coefficient at the bottom was around 25% higher than that at the top due to the uneven distribution of liquid and gas inside the pipe. Finally, a semi-empirical heat transfer correlation for gas-liquid slug flow was developed based on Reynolds and Chilton–Colburn analogies. The newly developed correlation predicts 96% of the present experimental two-phase heat transfer data within ±20% error and the mean relative deviations of the correlations are estimated to be -2.02% and +2.85% for Ref ≤ 2300 and Ref > 2300, respectively. This research helps researchers and engineers to better understand the heat transfer mechanism of gas-liquid slug flow.

Decomposition characteristics of natural gas hydrates in hydraulic lifting pipelines

For the sake of guiding parameter setting of the hydraulic lifting pipeline system for cutter-suction mining of natural gas hydrates (“hydrates” for short) on the seabed, the decomposition characteristics of hydrates in hydraulic lifting pipelines and the effects of flow parameters on decomposition characteristics were studied in this paper. A temperature–pressure model for the hydrate hydraulic lifting pipeline, a hydrate decomposition mass transfer model and a pipeline multiphase flow model were established using mathematical modeling method according to thermodynamics and fluid mechanics. Then, the relationships of the temperature and pressure of pipeline fluid, the amount of hydrate particulate matter and the decomposition surface vs. the underwater depth under the effect of different influencing factors during the transformation from solid–liquid two-phase flow to solid–liquid–gas three-phase flow were analyzed. And the following research results were obtained. First, the decomposition of hydrate slows down and the decomposition surface moves upward slightly with the increase of flow rate in the pipeline. Second, particle size basically has no effects on the temperature and pressure of pipeline fluid, the hydrate phase equilibrium pressure and hydrate decomposition surface. However, only the hydrate particles whose diameter is smaller than 0.2 mm can be completely decomposed in the pipeline while the decomposition of those whose particles size is greater than 2.0 mm is negligible. Third, if the back pressure at the outlet is positive, the decomposition surface moves upward and the decomposition of hydrate slows down with the increase of the back pressure. And if the back pressure at the outlet is negative, the decomposition surface moves downward and the decomposition of hydrate speeds up with the increase of the back pressure. Fourth, the decomposition of hydrate slows down and the decomposition surface moves upward with the increase of mineral depth. However, the decomposition rate and decomposition surface are basically unchanged when the mineral depth is below 1500 m under water. Fifth, the experimental results are basically consistent with the numerical simulation results, and it is indicated that the newly established models are of high reliability. In conclusion, decomposition surface height and decomposition rate can be adjusted by controlling flow rate and outlet back pressure rationally during the cutter-suction mining of hydrates while the influences of particle diameter and mining depth on gas production need not be taken into consideration.

Effect of pipe inclination on flow behaviour of fine-grained settling slurry

The effect of flow parameters of fine-grained settling slurry on the pressure drop-velocity relationship, deposition limit velocity and local concentration distribution was studied in an experimental pipe loop of inner diameter D = 100 mm with inclinable pipe sections for pipe inclination ranging from – 45° to +45°. The slurry consisted from water and narrow particle size distribution glass beads of mean diameter d50 = 0.18 mm. The concentration distribution was studied with application of a gamma-ray densitometry. The deposition velocity was defined as the flow velocity at which stationary deposit started to be formed at the pipe invert. The study revealed the stratified flow pattern of the studied slurry in inclined pipe sections, for slurry velocities below to the deposition limit sliding or stationary bed were created in ascending pipe sections. For low pipe inclination (α < ± 25°) the effect of inclination on local concentration distribution was not significant. Mean transport concentration for descending flow was lower than that for the ascending flow Deposition limit in inclined pipe was slightly lower than that in horizontal pipe. Frictional pressure drops in ascending pipe were higher than that in descending pipe, the difference decreased with increasing velocity and inclination.

Variability analysis of droplet distribution of oil-in-water emulsions with a multi-scale first-order difference conductance series

In attempt to depict the variability of oil droplet distribution in oil-in-water emulsions, we propose an algorithm of “area discrepancy” from multi-scale first-order difference scatter plot. With the intention to assess the applicability of this algorithm, we investigate typical nonlinear systems by extracting an “inhomogeneous distribution index” (IHs), and conclude that IHs can satisfactorily discriminate the differences in signals as well as presents a superior anti-noise ability. In this regard, we conduct an experiment of vertical upward oil-in-water emulsions in a 20 mm inner diameter (ID) testing pipe and collect fluctuating signals of a high resolution arc type conductivity probe (ATCP), through which the effects of flow parameters on IHs in oil-in-water emulsions are elucidated from the perspective of statistical analysis. The results indicate that the variation in IHs with changing mixture velocity and water-cut is beneficial for understanding dynamic evolution of oil droplets in oil-in-water emulsions.

Flow of viscoplastic suspensions in a hydraulic fracture: implications to overflush

The study is devoted to modeling of multiphase flows of immiscible viscoplastic fluids in a hydraulic fracture. In the framework of the lubrication approximation, three-dimensional Navier-Stokes equations are reduced to hyperbolic transport equations for the fluid tracers and a quasi-linear elliptic equation in terms of the fluid pressure. The governing equations are solved numerically using the finite-difference approach. A parametric study of the displacement of Bingham fluids in a Hele-Shaw cell is carried out. It is found that fingers developed through the pillar of a yield-stress suspension trigger the development of unyielded zones. An increase in the Bingham number leads to an increase in the so-called finger shielding effect, which manifests itself via an increase in the overall finger penetration zone and a decrease in the total number of fingers. The effect of flow parameters on the displacement of hydraulic fracturing proppant-laden suspension by a clean fluid in the vicinity of the perforation zone is carried out. This particular case is considered in application to overflush at the end of a stimulation treatment, when a small portion of a thin clean fluid is injected to wash out the particles from the wellbore into the fracture. It is found that an increase in the yield stress and the viscosity contrast between the fracturing and the overflush fluids typically reduces the area of the cavity thus mitigating the risk of loosing the conductive path between the wellbore and the fracture after the fracture closure.

Effect of Flow Parameters on Pelton Turbine Performance by Using Different Nozzles

Effect of Flow Parameters on Pelton Turbine Performance by Using Different Nozzles

Numerical investigation on ash fouling characteristics of flue gas heat exchanger

The particulate deposits on flue gas heat exchanger surfaces can increase thermal resistance, reduce heat transfer efficiency and increase the instability of equipment operation. Reasonable designing of heat exchanger is of vital importance to efficiently avoiding ash fouling. This paper adopted a numerical model to predict the collision, adhesion and rebound of fly ash particles on the surface of flue gas heat exchanger. The effects of flow parameters and geometry parameters on fouling rate were examined for six row tube heat exchangers, and the feasibility of using oval tube was explored for the purpose of fouling reduction. It was confirmed that particle deposits accumulate primarily in the flow stagnation region, recirculation region, the vortex separation and the reattachment regions. Increasing the velocity can lead to a lower deposit rate. The big particles tend to deposit on the front of tubes, and the small particles are easy to follow the fluid and deposit on both the front and the back of tubes. The elliptical tube is recommended for the fouling reduction of heat exchangers, while the arrangement of tube bundles depend on the typical diameter of fly ash to soothe ash fouling.

Forming of film surface of very viscous liquid flowing with gas in pipes

The study presents the possible use of optoelectronic system for the measurement of the values, which are specific for hydrodynamics of two-phase gas liquid flow in vertical pipes, where a very-high-viscosity liquid forms a falling film in a pipe. The experimental method was provided, and the findings were presented and analysed for selected values, which characterize the two-phase flow. Attempt was also made to evaluate the effects of flow parameters and properties of the liquid on the gas-liquid interface value, which is decisive for the conditions of heat exchange and mass transfer in falling film equipment. The nature and form of created waves at various velocities were also described.

Convective heat transfer in supercritical flows of CO2 in tubes with and without flow obstacles

Heat transfer measurements to CO2-cooled tubes with and without flow obstacles at supercritical pressures were obtained at the University of Ottawa’s supercritical pressure test facility. The effects of obstacle geometry (obstacle pitch, obstacle shape, flow blockage) on the wall temperature and heat transfer coefficient were investigated. Tests were performed for vertical upward flow in a directly heated 8mm ID tube for a pressure range from 7.69 to 8.36MPa, a mass flux range from 200 to 1184kg/m2s, and a heat flux range from 1 to 175kW/m2. The results are presented graphically in plots of wall temperature and heat transfer coefficient vs. bulk specific enthalpy of the fluid. The effects of flow parameters and flow obstacle geometry on supercritical heat transfer for both normal and deteriorated heat transfer are discussed. A comparison of the measurements with leading prediction methods for supercritical heat transfer in bare tubes and for spacer effects is also presented. The optimum increase in heat transfer coefficient was found to be for blunt obstacles, having a large flow blockage, and a short obstacle pitch.

Diffusion-thermo effect with hall current on unsteady hydromagnetic flow past an infinite vertical porous plate

An unsteady hydromagnetic flow past an infinite vertical porous plate has been analyzed to show the effect of an additional cross transport phenomenon, i.e. heat flux caused by concentration gradient in addition to the heat flux caused by temperature gradient. The effect of magnetic field on the fluid temperature and the heat transfer between fluid and wall is of considerable importance affecting the flow. Further, Hall current, an additional electric current density so generated perpendicular to both applied electric field and magnetic field has been taken into consideration in the present study. Moreover, the Dufour effect has been considered in energy equation leaving the equations of thermal diffusion and mass diffusion coupled. The coupled non-linear equations are solved by applying a special function Hhn(x). The effects of flow parameters are shown with the help of graphs and tables. A phenomenal observation, i.e. a radical change is marked near the plate in respect of Dufour number in the presence of suction. Further, it is to note that suction induces backflow in conjunction with opposing buoyancy forces. Hall current contributes to greater skin friction at the bounding surface.

A CFD study of the parameters influencing heat transfer in microchannel slug flow boiling

Boiling heat transfer in microchannels has been investigated extensively in the last two decades. However, most results from independent experimental studies display a substantial disagreement on the influence of the flow conditions and mechanisms on the heat transfer performance. The objective of the present paper is to clarify by means of CFD simulations the effect of the primary flow parameters on the saturated flow boiling heat transfer performance of a slug flow within a horizontal, circular microchannel. The vapor quality, heat flux, mass flux, channel diameter, bubble frequency, and saturation temperature are the parameters under analysis. The numerical model is based on the volume of fluid method included within ANSYS Fluent v. 14.5, which is here augmented by implementing ad-hoc models to calculate the surface tension force, the mass and energy transfer at the interface due to phase change, and to generate a continuous stream of bubbles with an arbitrary frequency. The high fidelity of the numerical framework provides unprecedented insight on the effect of these flow parameters on the bubble dynamics and heat transfer performance, which are tightly interrelated in microchannel slug flow boiling. In principle, the heat transfer performance is enhanced by flow conditions promoting a thin liquid film surrounding the elongated vapor bubbles and by the flow within short liquid slugs between the bubbles. Furthermore, numerous interesting secondary effects driven by the different flow conditions are observed and described according to the underlying flow dynamics: time-dependent interfacial waves on the bubble surface which significantly reduce the local film thickness; the response time of the channel wall temperature to changes of the flow boundary conditions at different channel sizes; the liquid film thickness dependence on the bubble length and on the liquid slug length; the heat transfer dependence on heat flux via the bubble generation frequency. A dimensional analysis is finally conducted in order to identify the nondimensional groups relevant to the microchannel bubble dynamics and heat transfer in the slug flow regime.

Mass transfer effects on an unsteady MHD free convective flow of an incompressible viscous dissipative fluid past an infinite vertical porous plate

In this paper, a numerical solution of mass transfer effects on an unsteady free convection flow of an incompressible electrically conducting viscous dissipative fluid past an infinite vertical porous plate under the influence of a uniform magnetic field considered normal to the plate has been obtained. The non-dimensional governing equations for this investigation are solved numerically by using the Ritz finite element method. The effects of flow parameters on the velocity, temperature and concentration fields are presented through the graphs and numerical data for the skin-friction, Nusselt and Sherwood numbers are presented in tables and then discussed.