Under-Expanded Gas Flow at a Straight Mini-Tube Exit

2013 ◽  
Author(s):  
Takahiro Yoshimaru ◽  
Yutaka Asako ◽  
Toru Yamada
Keyword(s):  
Mass Flow ◽  
Total Pressure ◽  
Gas Flow ◽  
Pitot Tube ◽  
Outer Diameter ◽  
Flow Rates ◽  
Numerical Result ◽  
Mass Flow Rates ◽  
Tube Exit ◽  
Slight Discrepancy

This paper focuses on under-expanded gas flow at a straight mini-tube exit. Pitot total pressure of gas flow (jet) in downstream region from a straight mini-tube exit was measured to give data for validation of numerical results. A mini-tube of 495μm in diameter & 56.3 mm in length and a pitot tube of 100 μm in outer diameter were used. The pitot total pressure was measured every 0.1 mm interval in the flow and radial directions. The measurement was done for the mass flow rates of 9.71×10−5 kg/s and 1.46×10−4 kg/s. The data were accumulated for validation of the numerical result to reveal the characteristics of the under-expanded gas flow at the exit of a mini-tube. Comparisons were conducted for sample computations and a slight discrepancy can be seen between numerical and experimentally measured pitot total pressures.

Under-Expanded Gaseous Flow at a Straight Micro-Tube Exit

2014 ◽  
Vol 136 (8) ◽  
Author(s):  
Takahiro Yoshimaru ◽  
Yutaka Asako ◽  
Toru Yamada
Keyword(s):  
Total Pressure ◽  
Gas Flow ◽  
Numerical Results ◽  
Pitot Tube ◽  
Outer Diameter ◽  
Flow Rates ◽  
Gaseous Flow ◽  
Mass Flow Rates ◽  
Tube Exit ◽  
Slight Discrepancy

This paper focuses on under-expanded gaseous flow at a straight micro-tube exit. The pitot total pressure of gas flow (jet) in the downstream region from a straight micro-tube exit was measured by a total pressure pitot tube to accumulate data for validation of numerical results. A micro-tube of 495μm in diameter and 56.3 mm in length and a total pressure pitot tube of 100 μm in outer diameter were used. The pitot total pressure was measured at intervals of 0.1 mm in both the flow and radial directions. The measurement was done for the mass flow rates of 9.71 × 10−5 kg/s and 1.46 × 10−4 kg/s. The data were accumulated for validation of the numerical results to reveal the characteristics of the under-expanded gas flow at the exit of a micro-tube. Comparisons were conducted for numerical results of corresponding cases and a slight discrepancy can be seen between numerical and experimentally measured pitot total pressures.

Investigation of the Influence of Different Rim Seal Geometries in a Low-Pressure Turbine

2011 ◽  
Author(s):  
P. Schuler ◽  
K. Dullenkopf ◽  
H.-J. Bauer
Keyword(s):  
Mass Flow ◽  
Total Pressure ◽  
Gas Flow ◽  
Low Pressure ◽  
Flow Rates ◽  
Low Pressure Turbine ◽  
Hot Gas ◽  
Seal Design ◽  
Compound Design ◽  
Mass Flow Rates

The sealing of the machine’s inside against hot-gas ingestion is commonly provided by blowing relative cold compressor air radially out through the turbine wheelspace. Rim-seals located inside the wheelspace are primarily designed to keep the required amount of sealing at a minimum. A further possible function of the rim-seal follows from the desire to reduce the aerodynamic losses contributed by the interaction of the emerging sealing flow with the boundary layer of the incoming main flow. Investigations performend in the EU project MAGPI concentrate on the interaction between the sealing flow and the main gas flow and in particular on the effect of different rim seal designs regarding the loss-mechanism in a low-pressure turbine passage. Two different rim seal designs inside a linear low-pressure turbine cascade rig have been analysed in detail. Both, the simple axial gap and the more complex compound design were investigated under the influence of different sealing mass flow rates. Furthermore, a configuration without any cavity in the main gas flow served as a reference case. Extensive measurements of the total pressure loss over the turbine blade have been conducted by means of a five-hole probe. Additionally, the blade loading has been measured at several blade heights. A considerable increase of total pressure losses was observed due to the presence of a cavity with any rim seal design, even for no sealing flow. Higher sealing mass flow rates intensified this effect which becomes manifested in a strengthening of the secondary flows downstream the cascade. Experiments revealed also significant differences in loss-increment depending on the rim seal design used. Deeper insight into the interaction of the flows close to the rim seal is given by results of Laser-Doppler-Velocimetry measurements. The rounded shape of the compound design, which implies an axial overlapping, represents a promising prevention against hot-gas ingestion. While the axial gap design is characterized by higher losses, it also suffers considerable hot-gas ingestion in front of the blade leading edge. A parametric study regarding a possible optimization of the axial gap design is presented in this work.

scholarly journals Simulation and Modeling of Flow in a Gas Compressor

2015 ◽  
Vol 2015 ◽  
pp. 1-7
Author(s):  
Anna Avramenko ◽  
Alexey Frolov ◽  
Jari Hämäläinen
Keyword(s):  
Steady State ◽  
Mass Flow ◽  
Gas Flow ◽  
Simulation Method ◽  
High Mass ◽  
Ansys Fluent ◽  
Flow Rates ◽  
Mass Flow Rates ◽  
Low Mass ◽  
Flow Through

The presented research demonstrates the results of a series of numerical simulations of gas flow through a single-stage centrifugal compressor with a vaneless diffuser. Numerical results were validated with experiments consisting of eight regimes with different mass flow rates. The steady-state and unsteady simulations were done in ANSYS FLUENT 13.0 and NUMECA FINE/TURBO 8.9.1 for one-period geometry due to periodicity of the problem. First-order discretization is insufficient due to strong dissipation effects. Results obtained with second-order discretization agree with the experiments for the steady-state case in the region of high mass flow rates. In the area of low mass flow rates, nonstationary effects significantly influence the flow leading stationary model to poor prediction. Therefore, the unsteady simulations were performed in the region of low mass flow rates. Results of calculation were compared with experimental data. The numerical simulation method in this paper can be used to predict compressor performance.

Review of Critical Flowmeters for Gas Flow Measurements

1962 ◽  
Vol 84 (4) ◽  
pp. 447-457 ◽  
Author(s):  
B. T. Arnberg
Keyword(s):  
Mass Flow ◽  
Flow Measurement ◽  
Gas Flow ◽  
Flow Measurements ◽  
Flow Rates ◽  
Real Gas ◽  
Discharge Coefficients ◽  
Critical Nozzles ◽  
Mass Flow Rates ◽  
Flow Functions

Critical flowmeters for accurately measuring the mass flow rates of nonreacting real gases were reviewed. Discussions were presented on theoretical flow functions, on parameters for correlating discharge coefficients, and on the importance of real gas properties. The performance characteristics of critical nozzles and orifices of several designs were reviewed. Approaches were discussed to problems which must be researched before the fullest potential of this type of flow measurement can be realized.

scholarly journals Inert Gas and Refrigerating Vapor Mass Flow Rates Ratio: A Much Promising Parameter for Diffusion-Absorption-Refrigeration Systems Performances Evaluation

2021 ◽  
Vol 8 (2) ◽  
pp. 253-258
Author(s):  
Djallel Zebbar ◽  
Souhila Zebbar ◽  
Sahraoui Kherris ◽  
Kouider Mostefa
Keyword(s):  
Mass Flow ◽  
Gas Flow ◽  
Inert Gas ◽  
Coefficient Of Performance ◽  
Working Fluid ◽  
Absorption Refrigeration ◽  
Flow Rates ◽  
Mass Flow Rates ◽  
Diffusion Absorption ◽  
Vapor Mass

This paper is consecrated to the thermodynamic study and analysis of diffusion-absorption-refrigeration (DAR) plants. The mass and energy balances analysis at the evaporator has allowed to highlight a new and original parameter, which can be used to analyze DAR system performances. It is the ratio of inert gas to refrigerant vapor mass flow rates at the evaporator inlets. This coefficient, which expression has been for the first time deduced mathematically, informs about the quality of the cycle and its performance, which are deeply affected by the growth of the inert gas flow energy expended to drive the refrigerant through the evaporator. The study shows that the coefficient of performance is decreasing with the increase of the mass flow rates ratio. The latter can be also used to find the optimal operating mode for the DAR machine with a specified working fluid.

Investigation of Effects of Radial Distortion on Transonic Fan Behavior

2010 ◽  
Author(s):  
Dmytro M. Voytovych ◽  
Guoping Xia ◽  
Chenzhou Lian ◽  
Charles L. Merkle
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Total Pressure ◽  
Pressure Ratio ◽  
Tip Vortex ◽  
Flow Rates ◽  
Mass Flow Rates ◽  
Transonic Fan ◽  
Total Pressure Ratio

The flow analysis around blades of a transonic fan is presented for both clean and radially distorted inlets. Computations are shown for four-blade passages that are accomplished with a second order accurate code using a k-ω turbulence model. The mass flow rate along a speed line is controlled by varying a choked nozzle downstream of the fan. The results show good agreement with data for three speed lines. In the near-stall region, the flow first becomes unsteady and then unstable with the unsteadiness increasing at lower speeds. The four-blade simulations remained stable to lower mass flow rates than the single-blade simulations. In the near-stall vicinity, tip vortex breakdown occurred creating a low momentum zone near the blade tip on the pressure side that grew as the mass flow was decreased until it eventually blocked the passage. The presence of distortion reduced the operational range and moved the stall line to higher mass flow rates. At high speeds distortion reduced both the mass flow rate and total pressure ratio while at lower speeds, the choking mass flow rate was reduced, but the total pressure ratio was slightly improved. The flow separation near the hub on the suction side was caused by the distortion. Its size was decreasing with rotational speed.

Sheath Flow Focusing in Supersonic Jet Spectroscopy

1987 ◽  
Vol 41 (8) ◽  
pp. 1351-1357 ◽  
Author(s):  
Steven W. Stiller ◽  
Murray V. Johnston
Keyword(s):  
Mass Flow ◽  
Gas Flow ◽  
Supersonic Jet ◽  
Nozzle Geometry ◽  
Spectral Broadening ◽  
Flow Rates ◽  
Sheath Flow ◽  
Focusing Effect ◽  
Sample Stream ◽  
Mass Flow Rates

The mechanism of cooling in sheath-flow-focused supersonic jet expansions is examined. Cooling is found to be strongly influenced by the sheath gas flow properties but independent of the carrier gas in the sample stream. These results indicate that considerable turbulence and mixing between the sheath and sample gases occur downstream from the orifice. However, mixing cannot be complete, since, relative to results with a conventional jet expansion, a substantial enhancement of analyte is obtained along the centerline of a sheath-flow-focused jet expansion. Spectral broadening at “high” analyte mass flow rates within the sample stream is found to arise from inefficient cooling. There are limits to both how large and how small the nozzle orifice can be. Small orifices result in spectral broadening, even at very low analyte mass flow rates. Large orifices may have Reynolds numbers sufficient to cause turbulent flow, which degrades the focusing effect. The optimum nozzle geometry and gas flow conditions for sheath-flow-focused jet expansions are discussed.

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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