EXPERIMENTAL VALIDATION OF PARAMETERS OF HEAVY GRAVITY PNEUMATIC HAMMERS FOR CASING PIPE RAMMING IN SOIL

Vertical penetration of steel pipes with a diameter of 530-1420 mm and to 100-150 m long in soil requires high blow energy (10-100 kJ). Design of the percussion machines using the available pneumatic hammers is constrained due to the high flow rate of an energy source required. It is of the current concern to design an air-driven percussive tool capable to ensure high blow energy at low flow rate of compressed air. This study describes the testing data of a breadboard model of a new gravity pneumatic hammer. The operating mode of the model hammer is studied, and the blow energies, blow frequencies and compressed air flow rates are evaluated as functions of air pressure in the main line. The tests proved stability of cycling operation of the model tool at the high blow energy and low flow rate of the energy source at the main line pressure of 0.36-0.77 MPa. Using the dynamic similarity criteria, the standard sizes of heavy pneumatic hammers are developed, their blow energy and air flow rate are determined, and the efficiency is evaluated.

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119 PHOTOSYNTHESIS AND RESPIRATION OF APPLE PLANTS AT DIFFERENT CARBON DIOXIDE CONCENTRATIONS

HortScience ◽

10.21273/hortsci.29.5.445d ◽

1994 ◽

Vol 29 (5) ◽

pp. 445d-445

Author(s):

Qiyuan Pan ◽

Bruno Quebedeaux

Keyword(s):

Flow Rate ◽

Dark Respiration ◽

Air Flow ◽

High Flow ◽

High Flow Rate ◽

Low Flow ◽

Crop Canopy ◽

Ambient Level ◽

Photosynthesis And Respiration ◽

Low Flow Rate

Low CO2 concentrations ([CO2]) frequently occur in dense crop canopy. To determine plant performance under sub-atmospheric [CO2], young `Gala' apple plants were phytotron-grown at 928 mmole m-2s-1 light intensity. Whole-plant photosynthesis and respiration under [CO2] between 0 and the ambient level (382 to 460 ml 1-1) were measured by monitoring [CO2] of the air entering and coming out of a 38-1 clear plexiglass gas exchange chamber at either 3.4 or 6.2 1 min-1. The chamber seals two plants of up to 77 cm height for long-term experiments. There was a linear relationship between [CO2] and net photosynthesis (Pn), with the R2 being as high as 0.99. The increase of Pn with increased [CO2] was 51% greater for the high air flow than for the low air flow. At the ambient CO2 level Pn at the high flow rate was 49% higher than that at the low flow rate. CO2 compensation points were 57.6 and 58.5 ml 1-1 at the high and low flow rates, respectively. The relationship between [CO2] and dark respiration was linear. Dark respiration decreased by 20% on average as the [CO2] increased from 0 to the ambient level, and it was 11% higher at the high flow rate than at the low flow rate. These results suggest that wind may act to reduce Pn depression in dense crop canopy by both reducing leaf resistance and atmospheric [CO2] gradient outside the boundary layer.

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Backflow effects on mass flow gain factor in a centrifugal pump

Science Progress ◽

10.1177/0036850421998865 ◽

2021 ◽

Vol 104 (2) ◽

pp. 003685042199886

Author(s):

Wenzhe Kang ◽

Lingjiu Zhou ◽

Dianhai Liu ◽

Zhengwei Wang

Keyword(s):

Centrifugal Pump ◽

Mass Flow ◽

Flow Rate ◽

Low Frequency ◽

Gain Factor ◽

Low Flow ◽

Cavity Volume ◽

Cavitating Flows ◽

Inlet Tube ◽

Low Flow Rate

Previous researches has shown that inlet backflow may occur in a centrifugal pump when running at low-flow-rate conditions and have nonnegligible effects on cavitation behaviors (e.g. mass flow gain factor) and cavitation stability (e.g. cavitation surge). To analyze the influences of backflow in impeller inlet, comparative studies of cavitating flows are carried out for two typical centrifugal pumps. A series of computational fluid dynamics (CFD) simulations were carried out for the cavitating flows in two pumps, based on the RANS (Reynolds-Averaged Naiver-Stokes) solver with the turbulence model of k- ω shear stress transport and homogeneous multiphase model. The cavity volume in Pump A (with less reversed flow in impeller inlet) decreases with the decreasing of flow rate, while the cavity volume in Pump B (with obvious inlet backflow) reach the minimum values at δ = 0.1285 and then increase as the flow rate decreases. For Pump A, the mass flow gain factors are negative and the absolute values increase with the decrease of cavitation number for all calculation conditions. For Pump B, the mass flow gain factors are negative for most conditions but positive for some conditions with low flow rate coefficients and low cavitation numbers, reaching the minimum value at condition of σ = 0.151 for most cases. The development of backflow in impeller inlet is found to be the essential reason for the great differences. For Pump B, the strong shearing between backflow and main flow lead to the cavitation in inlet tube. The cavity volume in the impeller decreases while that in the inlet tube increases with the decreasing of flow rate, which make the total cavity volume reaches the minimum value at δ = 0.1285 and then the mass flow gain factor become positive. Through the transient calculations for cavitating flows in two pumps, low-frequency fluctuations of pressure and flow rate are found in Pump B at some off-designed conditions (e.g. δ = 0.107, σ = 0.195). The relations among inlet pressure, inlet flow rate, cavity volume, and backflow are analyzed in detail to understand the periodic evolution of low-frequency fluctuations. Backflow is found to be the main reason which cause the positive value of mass flow gain factor at low-flow-rate conditions. Through the transient simulations of cavitating flow, backflow is considered as an important aspect closely related to the hydraulic stability of cavitating pumping system.

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A Meanline Model for Impeller Flow Recirculation

Volume 6: Turbomachinery, Parts A, B, and C ◽

10.1115/gt2008-51349 ◽

2008 ◽

Cited By ~ 10

Author(s):

Xuwen Qiu ◽

David Japikse ◽

Mark Anderson

Keyword(s):

Flow Rate ◽

Recirculation Zone ◽

Reverse Flow ◽

Low Flow ◽

Suction Surface ◽

Blade Loading ◽

Flow Recirculation ◽

Impeller Outlet ◽

Active Flow ◽

Low Flow Rate

Flow recirculation at the impeller inlet and outlet is an important feature that affects impeller performance, especially the power consumption at a very low flow rate. Although the mechanisms for this flow phenomenon have been studied, a practical model is needed for meanline modeling of impeller off-design performance. In this paper, a meanline recirculation model is proposed. At the inlet, the recirculation zone acts as area blockage to relieve the large incidence of the active flow at a low flow rate. The size of the blockage is estimated through a critical area ratio of an artificial “inlet diffuser” from the inlet to throat. The intensity of the reverse flow can then be calculated by assuming a linear velocity profile of meridional velocity in the recirculation zone. At the impeller outlet, a recirculation zone near the suction surface is established to balance the velocity difference on the pressure and suction sides of the blade. The size and the intensity of the outlet recirculation zone is assumed related to blade loading, which can be evaluated based on flow turning and Coriolis force. A few validation cases are presented showing a good comparison between test data and prediction by the model.

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Experimental Investigation of Surge Phenomena in a Transonic Centrifugal Compressor With Inlet Distortion

Volume 2E: Turbomachinery ◽

10.1115/gt2020-15426 ◽

2020 ◽

Author(s):

Sasuga Ito ◽

Masato Furukawa ◽

Satoshi Gunjishima ◽

Takafumi Ota ◽

Kazuhito Konishi ◽

...

Keyword(s):

Flow Rate ◽

Centrifugal Compressor ◽

Flow Instability ◽

Pressure Sensors ◽

Low Flow ◽

Inlet Distortion ◽

Transonic Centrifugal Compressor ◽

Response Pressure ◽

Surge Phenomena ◽

Low Flow Rate

Abstract Inlet distortion has influence on the aerodynamic performance of turbomachinery such as compressors, turbines and fans. On turbochargers, bent pipes are installed around the compressor due to the spatial limitations in the engine room of the vehicle. As the result, the compressor is operated with the distorted inflow. In the low flow rate operation, the distorted inflow also affects the flow instability like stall and surge. Especially, the operation range on the low flow rate side is defined based on the flow rate where surge occurs, so it is important to investigate the effect of the distorted inflow on surge. In this study, the effect of the inlet distortion to surge phenomena has been investigated by the experiments with a transonic centrifugal compressor. A bent pipe has been installed at the upstream of the compressor to generate a distorted flow. Experiments have been also conducted under the condition that a straight pipe was installed upstream of the compressor, and unsteady measurements with high response pressure sensors and an I-type hot wire probe have been carried out to each experiments. In addition, Fast Fourier transform (FFT) and Wavelet transform have been applied to the unsteady measurement results obtained from each experiment.

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A Comparative Assessment of Spalart-Shur Rotation/Curvature Correction in RANS Simulations in a Centrifugal Pump Impeller

Mathematical Problems in Engineering ◽

10.1155/2014/342905 ◽

2014 ◽

Vol 2014 ◽

pp. 1-9 ◽

Cited By ~ 5

Author(s):

Ran Tao ◽

Ruofu Xiao ◽

Wei Yang ◽

Fujun Wang

Keyword(s):

Kinetic Energy ◽

Centrifugal Pump ◽

Flow Rate ◽

Comparative Assessment ◽

Turbulence Kinetic Energy ◽

Low Flow ◽

Pump Impeller ◽

Curvature Correction ◽

Centrifugal Pump Impeller ◽

Low Flow Rate

RANS simulation is widely used in the flow prediction of centrifugal pumps. Influenced by impeller rotation and streamline curvature, the eddy viscosity models with turbulence isotropy assumption are not accurate enough. In this study, Spalart-Shur rotation/curvature correction was applied on the SSTk-ωturbulence model. The comparative assessment of the correction was proceeded in the simulations of a centrifugal pump impeller. CFD results were compared with existing PIV and LDV data under the design and low flow rate off-design conditions. Results show the improvements of the simulation especially in the situation that turbulence strongly produced due to undesirable flow structures. Under the design condition, more reasonable turbulence kinetic energy contour was captured after correction. Under the low flow rate off-design condition, the prediction of turbulence kinetic energy and velocity distributions became much more accurate when using the corrected model. So, the rotation/curvature correction was proved effective in this study. And, it is also proved acceptable and recommended to use in the engineering simulations of centrifugal pump impellers.

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