Discharge Angle Research Articles

Behaviour of oblique jets released in a moving ambient

ABSTRACTAn experimental investigation is carried out to determine the trajectory, spread, dilution and cross-sectional flow structures of non-buoyant oblique jets released in a moving ambient, covering initial discharge angles from 10 to 90°. For each angle, measurements of the side view and plan view integrated concentration fields are obtained. The double-Gaussian assumption is used to characterize the cross-sectional concentration profiles, which gradually change from the axi-symmetric Gaussian of the weak-jet region to the double-vortex pair structure of the momentum puff region. In the weakly-advected region, the spread is similar to that of the jet in a stagnant ambient, while in the strongly-advected region a new spread relationship is obtained based on the double-Gaussian assumption. The spread relationships are used in an existing integral model, resulting in predictions for the trajectory and dilution that are a good match for the experimental data in the weakly- and strongly-advected regions.

A Micro Study to Determine Porosity, Hydraulic Conductivity, Permeability and the Discharge Rate of Groundwater in Ondo State Riverbeds, Southwestern Nigeria

Laboratory study of three riverbed soil samples denoted as A, B and C have been carried out by determining the soils Porosity, Hydraulic conductivity, Permeability and also investigating if there are points of convergence between the discharge rate and angle of tilt for the above mentioned samples. The experimental results for Porosity were approximately within 34% - 37%, Hydraulic conductivity was within 3.02 × 10-5 - 9.70 × 10-5 (m/s) and Permeability was within 2.74 × 10-12 - 8.80 × 10-12 (m2). Pressure generally increases as distance of flow increases for θ = 5° - 25° but there was decrease in pressure as distance of flow increases for all three samples when θ = 0°. The points of convergence for the discharge rate ranged from 0.001 × 10-10 - 4.54 × 10-10 (m3/s), while the angle of tilt convergence points ranged from 0.1° to 3.6°. There was increase in discharge rate as angle of tilt increases for all three samples.

유출각 변화에 따른 프란시스 수차 성능해석

In this study, we have numerically investigated the hydraulic efficiency with various values of discharge angle(11°, 12°, 14°, 15°, 17°, 18°, 20°) in the Francis turbine of hydropower generation under 15MW with fixed values of head range of 151m and flow rate(10.97m³/s). We also conducted the numerical analysis with constant inlet angle in the Francis turbine using the commercial code, ANSYS CFX. Hydraulic characteristics for different values of the runner blade angle are investigated. The results showed that the change of discharge angles significantly influenced on the performance of the turbine hydraulic efficiency.

Load Model of Scroll Wrap for Calculation of Bending Fatigue Strength

For calculation of bending fatigue strength of scroll wraps, the pressure loads and temperatures in compression chambers based on general profile theory are analyzed, and a load model including the pressure loads the temperatures is proposed. For the scroll wraps, their load model for bending fatigue strength includes the pressure loads and the temperatures. Their pressure loads can be simplified on the mid-areas and its temperatures are equal to the temperatures of the mid-areas. The pressure loads are of π normal angle region inner pressure load which have an interval of π normal angle, the number of regions of pressure load is equal to the number of scroll compression chamber pairs. The discharge angle has significant effect on bending fatigue strength of scroll wraps and the stability of scroll compressor.

다공튜브 오리피스 면적비 변화가 출구유동에 미치는 영향

A multi-perforated tube indicates the existence of multiple holes of various shapes on the surface of a long cylinder-type or rectangular tube, and a hole installed on the surface is called an orifice, as it is relatively small in size, compared with the surface area of the tube. In this study, the flow characteristics of a circular multi-perforated tube with many orifices on the surface were investigated experimentally and numerically. The volume flowrate issuing from each orifice, discharge angle, effective flow area ratio, and the flow fields around the orifices were measured and visualized, with the variation of the orifice area ratio, at the same blockage ratio. The volume flowrate distributions along the flow direction of the multi-perforated tube tends to be more uniform, as larger orifices were positioned at the inlet side of the multi-perforated tube, compared with no orifice area change along the flow direction.

Removing the boundary influence on negatively buoyant jets

A comprehensive laboratory study of negatively buoyant discharges is presented. Unlike previous studies, here the focus is on generating data sets where influences of the bottom boundary have been eliminated. There are significant discrepancies in the published dilution data for these flows and a contributing factor is the large variation in the bottom boundary condition. A Laser-induced Fluorescence system is employed to gather flow spread, peak concentration (minimum dilution) and trajectory data for a wide range of densimetric Froude numbers and initial discharge angles. Data from these experiments are compared with previously published data, along with predictions from integral models and a revised form of the previously published semi-analytical solutions. The new data sets are not distorted by mixing processes associated with the bottom boundary and therefore provide the basis for more meaningful assessments of the predictive capabilities of existing models, given that the influences of the bottom boundary on contaminant mixing are not incorporated into these models. In general the models assessed are able to predict key geometric quantities with reasonable accuracy, but their minimum dilution predictions are conservative. Importantly dilution at the return point shows a strong dependence on the initial discharge angle and this could have important implications for the design of discharge systems.

Mixing of Newtonian and Non-Newtonian Fluids in a Cylindrical Mixer Equipped with a Side-Entry Impeller

The effects of rheological properties on the mixing flow generated in a cylindrical tank equipped with a side-entry impeller were investigated using particle image velocimetry (PIV). Velocity vector maps were obtained from the laminar and transitional flow regimes of viscous Newtonian and non-Newtonian shear-thinning fluids with yield stress. Radical changes in the discharge angle were detected under the evaluated conditions. It was observed that radial discharge and a strong tangential flow arise when the viscous forces dominate the flow. Moreover, the impeller discharge is affected when the interaction between the flow and one of the walls of the vessel is significant; thus, the flow features are defined by the Reynolds number and the restrictions imposed by the walls of the tank.

A study on the exit flow characteristics determined by the orifice configuration of multi-perforated tubes

A multi-perforated tube indicates the existence of multiple holes in various shapes on the surface of long cylinder-type or rectangular tubes, and the hole installed on the surface is called an orifice as it is relatively small in size, compared with the surface area of the tubes. In this study, flowrate distribution features and changes in discharge angle according to the blockage ratio resulting from the changes in the number of orifices and the thickness of multi-perforated tubes were investigated by means of analysis and experiment, targeting the multi-perforated tubes where rectangular orifices are installed on the both sides of square tubes. In addition, contraction coefficient and flow coefficient between orifices were analytically investigated. The more increase in blockage ratio of multi-perforated tubes, the more uniform flowrate distribution between orifices. The discharge angle becomes more and more perpendicular in the longitudinal direction of multi-perforated tubes as it gets closer to the end of orifices, exhibiting big differences at the entrance if blockage ratio is small. The more increase in the thickness of multi-perforated tubes, the more uniform flowrate distribution between orifices become as contraction coefficient increases. The flow coefficient distribution of orifices using the pressure at the entrance of the orifices of multi-perforated tubes increases in the longitudinal direction of the multi-perforated tubes, exhibiting values ranging from 0.66 to 0.68 as to BR = 0.893 ∼ 0.979.

Analysis of Loads at Crankshaft Bearing for Scroll Compressor

According to the tangential force of crank pin approximately for radial force four times, between the radial gas force Fr and tangential gas force Ft acting on the orbiting scroll, the radial force is invariableness with the spindle rotation angle, but tangential force Ft with the spindle rotation angle changes, and in the discharge angle θ* at maximum. As a result of our comprehensive analyses to loads at crankshaft bearing of the scroll compressor as well as installation angle of the counter weight and mass of the counterweight, it is concluded that the imbalance residual quantity of the crank pin tangential force effects on crankshaft bearing and radial force acting on the crank pin, which results from gas force of orbiting scroll, is balanced, and the vibration of the scroll compressor is decreased. This paper puts forward a set of formulas, which are derived based on analysis of the loads at crankshaft of scroll compressor. The formulas can be used to determine the parameters of installation angle of the counterweight and the force of loads at crankshaft for scroll compressor.

CFD Parametric Studies for Global Performance Improvement of Open Refrigerated Display Cabinets

A detailed CFD modelling of an open refrigerated display cabinet has been formulated in a previous study. Some modifications are introduced in order to perform parametric studies dealing with low-cost geometrical and functional characteristics for improvement of the global performance and energy efficiency. The parametric studies are devoted to the analysis of the thermal response and behaviour inside the food conservation space influenced by (1) air flow rate through the evaporator heat exchanger; (2) air curtain behaviour; (3) hole dimensions and distribution of the back panel; (4) discharge and return grilles angles; and (5) flow deflectors inside the internal duct. The analysis of the numerical predictions from the parametric studies allows the development of an optimized model for the conception of an open refrigerated display cabinet with a more adequate configuration. The numerical predictions of the optimized model show lower product temperature and reduced electrical energy consumption, allowing the improvement of the food safety and the energy rationalization of the refrigeration equipment.

Mixing of inclined dense jets in stationary ambient

This paper reports results of a comprehensive experimental investigation of inclined round dense jets in an otherwise stagnant fluid. The tracer concentration field is measured for six jet discharge angles: θo = (15°, 30°, 38°, 45°, 52°, & 60°) and jet densimetric Froude number of Fr = 10–40 using the planar laser-induced fluorescence (LIF) technique; selected jet velocity measurements are made using Particle Image Velocimetry (PIV). The detailed jet mixing characteristics and turbulence properties are presented. The direct velocity measurement reveals that the mixing is jet-like until the maximum rise. Empirical correlations for the maximum jet rise height, jet dilution at maximum rise, and impact dilution are presented. Both the time-mean concentration and intermittency show that the upper jet edge spreading is similar to a positively buoyant jet; at the lower edge the buoyant instability induces significant detrainment and mass outflux for θo > 15°. The dimensionless maximum rise height Zmax/(FrD) is independent of source conditions for Fr ≥ 25, and varies from 0.44 for θo = 15° to 2.08 for θo = 60°. Dilution measurements at terminal rise show the difference in dilution is small for θo = 38°–60° and the asymptotic dilution constant is St/Fr = 0.45. The impact dilution Si is also not sensitive to jet angle for θo = 38°–60° and can be expressed as Si/Fr = 1.06 for Fr ≥ 20.The Lagrangian jet model VISJET is used to interpret the experimental results. A detailed derivation for a general formulation of the entrainment coefficient is presented. Despite the observed detrainment, the trajectory and dilution are reasonably predicted; the maximum jet rise is generally under-predicted by 10–15% and associated dilution by 30%. However, the predicted variation of jet behavior with discharge angle is in good agreement with measurements. The experimental data is also compared with predictions of alternative models that employ an ad hoc entrainment hypothesis.

Blade Exit Angle Effects on Performance of a Standard Industrial Centrifugal Oil Pump

The effects of blade discharge angle on the performance of a standard industrial centrifugal oil pump of type 65Y60 were investigated experimentally as the pump handled both water and viscous oil. A one-dimensional hydraulic loss model was established to identify such effects mathematically. The effects have been estimated analytically by using the model at various viscosities. The results showed that the blade discharge angle has significant but equal influence on the head, shaft power and efficiency of the centrifugal oil pump at various viscosity conditions. For any viscosity, the total hydraulic loss in the impeller and volute rises with increasing blade exit angle. The diffusion loss in and behind the impellers as well as the friction loss in the volute are noticed in the pump, especially for highly viscous liquids. The hydraulic loss in the impellers is about 0.8-0.6 times the loss in the volute. In order to improve the pump performance, the hydraulic loss in the volute must be kept as small as possible.

Experimental investigation of spray formation as affected by sprinkler geometry

A preliminary study at low water discharge pressures was conducted to investigate the fire sprinkler spray formation as affected by sprinkler geometry using a laser-based shadow imaging system. A sprinkler typically consists of the following components: a deflector with tines and slots, a boss above the deflector and sprinkler frame arms. Prototypes of these components were fabricated to evaluate their effects on the spray formation process. The water sheet thickness formed on non-slotted deflectors, slot spray discharge angle, sheet breakup distance from the deflector perimeter, water flux and drop size distributions were measured. It was found that deflector diameter and boss structure have little impact on drop size and sheet breakup distance. However, wider slots form larger drops. At constant operating pressure, the slot spray discharge angle is insensitive to the slot width, but sensitive to the boss that helps directing the slot spray toward the sprinkler centerline. The frame arm tends to produce a vertical spray sheet downstream of the frame arm, which increases the complexity of overall spray formation. An integral model was developed to calculate the development of water sheet thickness and speed on the deflector for different degrees of viscous effect exerted by the deflector. An empirical correlation was also established to estimate the spray flux fraction discharging from a deflector slot. The above measurements and observations are useful for the development of a spray formation model for fire sprinklers.

Inclined negatively buoyant jets 1: geometrical characteristics

Experimental results on inclined turbulent round jets with negative buoyancy discharging in a calm homogeneous fluid are presented. Six different discharge angles from 45° to 90° to the horizontal are studied, and the jet evolution is recorded by means of a video camera. Results concern the main geometrical characteristics of the jet trajectory, i.e. the initial terminal height of rise reached by the jet at flow initiation, the final terminal height of rise observed at steady state, the horizontal distance from the source at which the terminal height is observed and the horizontal distance to the point where the jet returns at the source elevation. The densimetric Froude number at the source ranges between 7 and 60, whereas the Reynolds number is generally higher than 6000. Results are given in dimensionless form and confirm theoretical considerations obtained by dimensional analysis.

Flowability of surface modified pharmaceutical granules: A comparative experimental and numerical study

Flowability – as measured by hopper discharge rate, angle of repose and Carr's index (CI) – of surface modified microcrystalline cellulose granules was investigated experimentally. Three-dimensional simulations of the granule flow were performed, using the discrete element method (DEM), including either sliding and rolling friction or sliding friction and cohesion in the model. Granule surface modification with polymer coating and lubrication was found to have a significant effect on the sliding friction coefficient. This effect was also reflected in the ensuing flow behaviour, as quantified by the experimental discharge rate and angle of repose, whereas the results for the CI were inconclusive. The numerical results demonstrated that granular flow was qualitatively different for non-cohesive and cohesive granules, occurring in the form of individual particles for the former and in larger clusters for the latter. Rolling friction and cohesion nevertheless affected the simulated discharge rate in a similar manner, producing results comparable to those observed experimentally and calculated with the Beverloo equation. The numerical results for the cohesive granules demonstrated that cohesion alone was sufficient to produce stable heaps. However, the agreement with experimental data was satisfactory only for the non-cohesive granules, demonstrating the importance of rolling friction.

Spreading of round dense jets impinging on a horizontal bottom

The radial spreading of density currents arising from the impingement of submerged round turbulent dense jets on a horizontal bottom is investigated. Experiments were conducted for spreading due to (i) the return on the bottom of negatively buoyant jets discharged upwards at four different angles, namely 45°, 60°, 75° and 85° to the horizontal and (ii) the impingement of positively buoyant jets discharged horizontally or vertically downwards to the bottom from a submerged nozzle. The jet fluid was colored saltwater solution issuing at a constant rate in a calm freshwater ambient and the spreading was recorded by means of a video camera. For the inclined negatively buoyant jets and the vertical positively buoyant ones the outer visual boundary of the density current is found to be almost circular. The radial distance from the impingement point to the outer boundary is estimated and found to correlate with time to a power of about 1/2, indicating a balance between buoyancy and drag forces. The radial distance is normalized by time and by the initial or local jet flow parameters and its variation with the discharge angle and the densimetric Froude number is presented.

The Influence of Air Circulation, Jet Discharge Momentum Flux and Nozzle Design Parameters on the Tightness of an Upwards Blowing Air Curtain

Air curtains are used to eliminate airflows through doorways (doorway tightness). In this paper the impacts of air circulation, jet discharge momentum flux and nozzle design parameters on the tightness of an upwards blowing air curtain are presented. The tightness values were measured using a tracer gas decay method in the laboratory hall. Measurements were undertaken for two nozzle widths, 30 mm and 120 mm, and for two different discharge angles, 10° and 30°. According to the study, the upper limit for the tightness of the upwards blowing air curtain is 80%. The difference in tightness between a recirculated and non-circulated air curtain is significant, being 20%. The selection of the jet design parameters can be undertaken fairly freely as long as the force balance at the doorway is valid. When the jet discharge momentum is optimal, the effect of the nozzle width, discharge angle and discharge velocity on the tightness of the air curtain is small. To keep the tightness level of the air curtain high enough, regardless of outdoor temperature fluctuation, a jet velocity controlling system is recommended. In the typical outdoor temperature range for Finland (-30°C to +10°C), the lack of a jet velocity controlling system reduces the tightness of the air curtain by 20 to 60% depending on the nozzle width and discharge angle. When selecting the jet design parameters by the moment of momentum principle in a relatively tight building (n50-value < 4.2 1/h), it is recommended to use a value of 0.6 - 0.7 times the doorway height for the stack neutral pressure height in order to achieve an airtight air curtain and to avoid the breakthrough phenomenon.

A jet at an oblique angle to a cross-flow

We present the results of a preliminary experimental investigation into the behaviour of non-buoyant oblique discharges in a moving ambient fluid. Light Attenuation techniques are employed to measure trajectory, spread and integrated dilution data. A series of experiments have been conducted where the angle between the discharge direction and that of the ambient motion varied from 0 to 90 degrees. The experiments confirm that the nature of the discharge in the strongly advected region is only a function of this discharge angle. For angles less than or equal to 20 ° trends in the data obtained in the strongly advected region resemble that of a Gaussian weak-jet. For discharge angles of 40 ° and above the variation in strongly advected data was consistent with that of an advected line momentum puff, where the local tracer and velocity fields resemble those of a vortex pair. However, for flows released at discharge angles between 20 ° and 40 °, the formation of a Gaussian weak-jet or an advected line momentum puff could not be clearly identified in the strongly advected region. A conceptual model based on a set of analytical solutions is outlined and this provides the basis for interpreting the experimental data. Lagrangian integral numerical models are also developed to aid in the interpretation of the data.

The effect of blade angle on the flow and pressure distributions in the vicinity of the diffuser blades of a room air conditioner

Many studies on air-conditioning systems are more focused on the individual thermal comfort rather than the thermal efficiency, due to an increase in health concerns. There are several factors influencing the thermal comfort, such as temperature, humidity, convection and air movement, etc. Numerical analyses were performed to investigate the effect of blade angle on the flow characteristics in the vicinity of diffuser blades of a room air conditioner (RAC), with three different blade discharge angles of 45.1°, 58.6° and 116°. We used the commercial code FLUENT to calculate the two-dimensional steady thermal flow fields with different impeller rotational velocities. The angular velocities were located within the range from 900 rpm to 1200 rpm. Turbulence closure was achieved using a standard k-ɛ model. A moving reference frame (MRF) approach was adopted to simulate the flow field generated by the impeller in an RAC. The results were graphically depicted with various geometrical configurations and operating conditions.

Parametric evaluation of refrigerated air curtains for thermal insulation

The refrigerated air curtain used for cavity insulation in the present study is an idealization of the refrigerated air curtain used in supermarket food display cabinets. The thermal insulation performance of refrigerated air curtains is very important for perishable food storage and energy saving for refrigerated display cabinets. Thermal insulation ability of recirculated refrigerated air curtains was numerically studied in the present work. The results show that the refrigerated air curtains are negatively buoyant jets and tend to flow toward the inside cabinet due to stack pressure, so the initial momentum must be sufficiently large to sustain the pressure difference across the air curtain and assure the thermal insulation. The length–width ratio and the discharge angle of the air curtains, the height–depth ratio of the cavity and the dimension and position of the inside shelves would greatly influence the thermal insulation performance of air curtains, therefore were extensively discussed. The maximum Richardson numbers or the optimum parameter selections in each situation were presented for practical design of refrigerated air curtains used in multi-deck display cabinets.