Pressure Drop, Air Entrainment and Moments of the Axial Velocity in the Laminar-Turbulent Transition Jet Flow in Domestic Gas Injectors

2021 ◽  
Author(s):  
William Alexander Carrillo Ibañez ◽  
Márcio Demétrio ◽  
Amir Oliveira ◽  
Fernando Pereira
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Axial Velocity ◽  
Energy Flow ◽  
Discharge Coefficient ◽  
Mixing Layer ◽  
Air Entrainment ◽  
Flow Rates ◽  
Free Jet ◽  
Internal Mixing

Abstract This works aims at characterizing the flow in the outlet of three gas injectors used in atmospheric burners and developing correlations for the discharge coefficient, air entrainment, momentum and energy flow rates. These devices have millimeter sized orifices, a cup-like region at the injector outlet and the flow occurs in the transition from the laminar to the fully turbulent regimes. The pressure drop was measured and correlated as a function of the orifice Reynolds number for the three injectors. The correlations are able to predict the discharge coefficient within ± 5% deviation from the measurements in the range 90 < Re < 4400. The axial velocity and turbulent intensity were measured at the outlet of the injectors using a hot-wire anemometer at the orifice Reynolds number of 3060, which is typical of the applications. The measurements were compared to CFD solutions using the gamma - Re-theta RANS transition model in the STAR-CCM+ commercial package. The results indicate the strong influence of the shape of the outlet cup-like region of the injectors in the development of an internal mixing layer and the external mixing layer in the free jet. The momentum and energy flow rates for the injector model with the largest cup are reduced to 50% and 21%, respectively, of the simplest gas injector. However, the gas jet in this injector carries 28% of the stoichiometric air before leaving the cup. These aspects must be taken into account in the preliminary design of atmospheric burners.

Calibration of a Small Venturimeter for Wet Steam at Low Reynolds Number

1969 ◽  
Vol 184 (3) ◽  
pp. 151-153
Author(s):  
M. D. Bennett ◽  
K. Martin
Keyword(s):  
Reynolds Number ◽  
Discharge Coefficient ◽  
Thrust Bearing ◽  
Area Ratio ◽  
Low Flow ◽  
Wet Steam ◽  
Steam Quality ◽  
Design Data ◽  
Flow Rates ◽  
Machined Parts

A device was required to measure the flow rate of steam through a small thrust bearing over the range 0–1·5 kg/h at pressures varying from 4·5 to 10 bar abs. and for steam quality varying from 0·75 dry to 100°C superheat. The ranges appeared to be outside those of existing instruments and not covered by existing design data for differential pressure devices; nor could the authors find any published work on the metering of wet steam at these low flow rates. Accordingly a 12·7-mm diameter venturimeter having an area ratio of 0·25 was made from stainless steel and has been calibrated for wet steam using a compounded differential U-tube manometer. The manometer and associated equipment is extremely simple and cheap to construct, and consists entirely of easily machined parts and standard pipe fittings. The results indicate that the discharge coefficient is very low and approximately a linear function of Reynolds number over the range tested.

Hydrodynamics behaviour of a fluid flow in micro-venturi

2012 ◽  
Vol 90 (1) ◽  
pp. 83-89 ◽  
Author(s):  
A.M. Maqableh ◽  
S.A. Ammourah ◽  
A.F. Khadrawi ◽  
M.A. Al-Nimr ◽  
A.C. Benim
Keyword(s):  
Reynolds Number ◽  
Fluid Flow ◽  
Axial Velocity ◽  
Pressure Loss ◽  
Discharge Coefficient ◽  
Diameter Ratio ◽  
The Other ◽  
Hydrodynamic Behaviour ◽  
Velocity Jump ◽  
Net Pressure

Hydrodynamic behaviour of a fluid flow in micro-venturi is investigated numerically taking into account the effect of the Knudsen number (Kn), diameter ratio (β), and Reynolds number (Re). It is found that the velocity jump in the throat of the venturi increases with increasing Re. The axial velocity takes its maximum values at the narrowest section, and these values increase with decreasing Kn. Also, it is found that the dimensionless pressure distribution and the net pressure loss increase as Kn decreases while pressure attains its maximum values at the entrance section. On the other hand, it is observed that increasing Kn and decreasing β cause the discharge coefficient to decrease.

The effect of two-phase flow regime on hydrodynamics and mass transfer in a horizontal-tube gas-liquid reactor

1985 ◽  
Vol 50 (3) ◽  
pp. 745-757 ◽  
Author(s):  
Andreas Zahn ◽  
Lothar Ebner ◽  
Kurt Winkler ◽  
Jan Kratochvíl ◽  
Jindřich Zahradník
Keyword(s):  
Mass Transfer ◽  
Pressure Drop ◽  
Flow Regime ◽  
Liquid Flow ◽  
Horizontal Tube ◽  
Liquid Holdup ◽  
Two Phase ◽  
Flow Rates ◽  
Type Relation ◽  
Good Agreement

The effect of two-phase flow regime on decisive hydrodynamic and mass transfer characteristics of horizontal-tube gas-liquid reactors (pressure drop, liquid holdup, kLaL) was determined in a cocurrent-flow experimental unit of the length 4.15 m and diameter 0.05 m with air-water system. An adjustable-height weir was installed in the separation chamber at the reactor outlet to simulate the effect of internal baffles on reactor hydrodynamics. Flow regime maps were developed in the whole range of experimental gas and liquid flow rates both for the weirless arrangement and for the weir height 0.05 m, the former being in good agreement with flow-pattern boundaries presented by Mandhane. In the whole range of experi-mental conditions pressure drop data could be well correlated as a function of gas and liquid flow rates by an empirical exponential-type relation with specific sets of coefficients obtained for individual flow regimes from experimental data. Good agreement was observed between values of pressure drop obtained for weirless arrangement and data calculated from the Lockhart-Martinelli correlation while the contribution of weir to the overall pressure drop was well described by a relation proposed for the pressure loss in closed-end tubes. In the region of negligible weir influence values of liquid holdup were again succesfully correlated by the Lockhart-Martinelli relation while the dependence of liquid holdup data on gas and liquid flow rates obtained under conditions of significant weir effect (i.e. at low flow rates of both phases) could be well described by an empirical exponential-type relation. Results of preliminary kLaL measurements confirmed the decisive effect of the rate of energy dissipation on the intensity of interfacial mass transfer in gas-liquid dispersions.

scholarly journals Parametric optimization of a stamped longitudinal vortex generator inside a circular tube of a solar water heater at low Reynolds numbers

2021 ◽  
Vol 3 (8) ◽  
Author(s):  
Felipe A. S. Silva ◽  
Luis Júnior ◽  
José Silva ◽  
Sandilya Kambampati ◽  
Leandro Salviano
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Drop ◽  
Reynolds Numbers ◽  
Geometric Parameters ◽  
Vortex Generators ◽  
Longitudinal Vortex ◽  
Solar Water Heater ◽  
Water Heater ◽  
Solar Water

AbstractSolar Water Heater (SWH) has low efficiency and the performance of this type of device needs to be improved to provide useful and ecological sources of energy. The passive techniques of augmentation heat transfer are an effective strategy to increase the convective heat transfer coefficient without external equipment. In this way, recent investigations have been done to study the potential applications of different inserts including wire coils, vortex generators, and twisted tapes for several solar thermal applications. However, few researchers have investigated inserts in SWH which is useful in many sectors where the working fluid operates at moderate temperatures. The longitudinal vortex generators (LVG) have been applied to promote heat transfer enhancement with a low/moderate pressure drop penalty. Therefore, the present work investigated optimal geometric parameters of LVG to enhance the heat transfer for a SWH at low Reynolds number and laminar flow, using a 3D periodical numerical simulation based on the Finite Volume Method coupled to the Genetic Algorithm optimization method (NSGA-II). The LVG was stamped over a flat plate inserted inside a smooth tube operating under a typical residential application corresponding to Reynolds numbers of 300, 600, and 900. The geometric parameters of LGV were submitted to the optimization procedure which can find traditional LVG such as rectangular-winglet and delta-winglet or a mix of them. The results showed that the application of LGVs to enhance heat transfer is an effective passive technique. The different optimal shapes of the LVG for all Reynolds numbers evaluated improved more than 50% of heat transfer. The highest augmentation heat transfer of 62% is found for the Reynolds number 900. However, the best thermo-hydraulic efficiency value is found for the Reynolds number of 600 in which the heat transfer intensification represents 55% of the pressure drop penalty.

Pressure Drop Measurements for Air Flow Through Open-Cell Aluminum Foam

2004 ◽  
Author(s):  
Nihad Dukhan ◽  
Angel Alvarez
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Flow Rate ◽  
Aluminum Foam ◽  
Flow Direction ◽  
The Other ◽  
Turbulent Regime ◽  
Thick Sample ◽  
Open Cell ◽  
Two Samples

Wind-tunnel pressure drop measurements for airflow through two samples of forty-pore-per-inch commercially available open-cell aluminum foam were undertaken. Each sample’s cross-sectional area perpendicular to the flow direction measured 10.16 cm by 24.13 cm. The thickness in the flow direction was 10.16 cm for one sample and 5.08 cm for the other. The flow rate ranged from 0.016 to 0.101 m3/s for the thick sample and from 0.025 to 0.134 m3/s for the other. The data were all in the fully turbulent regime. The pressure drop for both samples increased with increasing flow rate and followed a quadratic behavior. The permeability and the inertia coefficient showed some scatter with average values of 4.6 × 10−8 m2 and 2.9 × 10−8 m2, and 0.086 and 0.066 for the thick and the thin samples, respectively. The friction factor decayed with the Reynolds number and was weakly dependent on the Reynolds number for Reynolds number greater than 35.

scholarly journals Evaluation of a Humidified Nasal High-Flow Oxygen System, Using Oxygraphy, Capnography and Measurement of Upper Airway Pressures

2011 ◽  
Vol 39 (6) ◽  
pp. 1103-1110 ◽  
Author(s):  
J. E. Ritchie ◽  
A. B. Williams ◽  
C. Gerard ◽  
H. Hockey
Keyword(s):  
Healthy Volunteers ◽  
Airway Pressure ◽  
Gas Flow ◽  
Air Entrainment ◽  
High Flow ◽  
Positive Pressure ◽  
Mean Airway Pressure ◽  
Flow Rates ◽  
Oxygen Fraction ◽  
Airway Pressures

In this study, we evaluated the performance of a humidified nasal high-flow system (Optiflow™, Fisher and Paykel Healthcare) by measuring delivered FiO2 and airway pressures. Oxygraphy, capnography and measurement of airway pressures were performed through a hypopharyngeal catheter in healthy volunteers receiving Optiflow™ humidified nasal high flow therapy at rest and with exercise. The study was conducted in a non-clinical experimental setting. Ten healthy volunteers completed the study after giving informed written consent. Participants received a delivered oxygen fraction of 0.60 with gas flow rates of 10, 20, 30, 40 and 50 l/minute in random order. FiO2, FEO2, FECO2 and airway pressures were measured. Calculation of FiO2 from FEO2 and FECO2 was later performed. Calculated FiO2 approached 0.60 as gas flow rates increased above 30 l/minute during nose breathing at rest. High peak inspiratory flow rates with exercise were associated with increased air entrainment. Hypopharyngeal pressure increased with increasing delivered gas flow rate. At 50 l/minute the system delivered a mean airway pressure of up to 7.1 cmH2O. We believe that the high gas flow rates delivered by this system enable an accurate inspired oxygen fraction to be delivered. The positive mean airway pressure created by the high flow increases the efficacy of this system and may serve as a bridge to formal positive pressure systems.

scholarly journals Net-exergetic, hydraulic and thermal optimization of coaxial heat exchangers using fixed flow conditions instead of fixed flow rates

2021 ◽  
Vol 9 (1) ◽  
Author(s):  
Tobias Blanke ◽  
Markus Hagenkamp ◽  
Bernd Döring ◽  
Joachim Göttsche ◽  
Vitali Reger ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Laminar Flow ◽  
Mass Flow ◽  
Flow Rate ◽  
Heat Exchangers ◽  
Circular Ring ◽  
Flow Conditions ◽  
Flow Rates ◽  
Mass Flow Rates ◽  
Pipe Radius

AbstractPrevious studies optimized the dimensions of coaxial heat exchangers using constant mass flow rates as a boundary condition. They show a thermal optimal circular ring width of nearly zero. Hydraulically optimal is an inner to outer pipe radius ratio of 0.65 for turbulent and 0.68 for laminar flow types. In contrast, in this study, flow conditions in the circular ring are kept constant (a set of fixed Reynolds numbers) during optimization. This approach ensures fixed flow conditions and prevents inappropriately high or low mass flow rates. The optimization is carried out for three objectives: Maximum energy gain, minimum hydraulic effort and eventually optimum net-exergy balance. The optimization changes the inner pipe radius and mass flow rate but not the Reynolds number of the circular ring. The thermal calculations base on Hellström’s borehole resistance and the hydraulic optimization on individually calculated linear loss of head coefficients. Increasing the inner pipe radius results in decreased hydraulic losses in the inner pipe but increased losses in the circular ring. The net-exergy difference is a key performance indicator and combines thermal and hydraulic calculations. It is the difference between thermal exergy flux and hydraulic effort. The Reynolds number in the circular ring is instead of the mass flow rate constant during all optimizations. The result from a thermal perspective is an optimal width of the circular ring of nearly zero. The hydraulically optimal inner pipe radius is 54% of the outer pipe radius for laminar flow and 60% for turbulent flow scenarios. Net-exergetic optimization shows a predominant influence of hydraulic losses, especially for small temperature gains. The exact result depends on the earth’s thermal properties and the flow type. Conclusively, coaxial geothermal probes’ design should focus on the hydraulic optimum and take the thermal optimum as a secondary criterion due to the dominating hydraulics.

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