Flow Visualization of Unsteady and Transient Phenomena in a Mixed-Flow Multiphase Pump

2016 ◽  
Author(s):  
Alberto Serena ◽  
Lars E. Bakken
Keyword(s):  
Two Phase Flow ◽  
Flow Patterns ◽  
Operating Conditions ◽  
Tip Clearance ◽  
Homogeneous Distribution ◽  
Phase Flow ◽  
Two Phase ◽  
Inlet Flow ◽  
Transient Phenomena ◽  
Multiphase Pump

The flow inside of turbomachines rotating channels, when operating away from the design point, is intrinsically unsteady; two-phase flow and part-load operation further complicate the analysis, introducing additional challenges. Transient phenomena, linked to the typical unsteadiness of multiphase flows (bubble formation, coalescence or breakdown, segregation and gas locking) and to variable inlet flow compositions, as in case of slug flow, require advanced analysis tools which can reveal the local flow mechanisms responsible for performance degradation and instabilities. General trends can be outlined, but the air accumulation zones and two-phase flow patterns are highly dependent on the machine design. The flow regimes vary from a homogeneous distribution of fine bubbles, evenly dispersed and carried away by the main flow, to more complex flow patterns, especially when the phases separate or the bubbles coalesce forming a gas pocket which adheres to a wide portion of the channel wall. Tests are performed on a multiphase pump laboratory, recently installed at the Norwegian University of Science and Technology, which allows a complete optical access to the pump channels and fine adjustments in the inlet configuration and the tip clearance gap; the air can be injected from different locations producing transient regimes too. A high speed camera provides an interesting insight into the transient flow phenomena. This paper focuses on these specific ones: - Irregular backflow and swirl at the inlet section - Gas accumulation zones and contribution of the tip leakage to mixing - Flow pattern shift to phase segregation, as the relative flow is reduced - Origin of pump blockage, when increasing gas contents cannot be carried away by the water phase - Flow and machine parameters response to a variation in the inlet flow Tests are performed at various operating conditions — rotational speed, mixture composition and impeller tip clearance. The study is completed with the time and frequency domain analysis of the pressure pulsations at surging and during specific transient events.

The Effects of Inlet Flow Conditions on Gas-Liquid Two-Phase Flow in a Micro Tube

2007 ◽  
Author(s):  
Shota Hayashi ◽  
Nobuhide Kasagi ◽  
Yuji Suzuki
Keyword(s):  
Heat Transfer ◽  
Pressure Loss ◽  
Two Phase Flow ◽  
Flow Patterns ◽  
Phase Flow ◽  
Flow Conditions ◽  
Two Phase ◽  
Inlet Flow ◽  
Annular Flows ◽  
Inlet Conditions

In the present study, the effects of inlet geometry on the microscale two-phase flow patterns have been examined. The relationships among the flow pattern, the void fraction, the pressure loss and the heat transfer coefficient have been also investigated under different inlet flow conditions. At the inlet, a stainless steel tube is inserted into the micro glass tube, of which inner diameter is 300 and 600 μm. The gas and liquid paths and the diameter of the inner tube are interchangeable. The flow patterns are recorded at the inlet and also in the developed region in the micro tubes. The flow patterns observed in the 600 μm tube are bubbly, slug, churn and annular flows, while bubbly and churn flows are not present in the 300 μm tube. For bubbly and slug flows, bubble formation process is found to be strongly affected by the inlet conditions. Accordingly, the pressure loss as well as the heat transfer rate are changed. In addition, the bubble size is not uniquely determined; bubbles of different sizes are observed in repeated experiments under the same inlet flow conditions. On the other hand, for churn and annular flows, the flow patterns are not affected by the inlet conditions.

Visualization study of gas–liquid two-phase flow patterns inside a three-stage rotodynamic multiphase pump

2016 ◽  
Vol 70 ◽  
pp. 125-138 ◽  
Author(s):  
Jinya Zhang ◽  
Shujie Cai ◽  
Yongjiang Li ◽  
Hongwu Zhu ◽  
Yongxue Zhang
Keyword(s):  
Two Phase Flow ◽  
Flow Patterns ◽  
Phase Flow ◽  
Two Phase ◽  
Multiphase Pump

scholarly journals Two-Phase Flow Mass Transfer Analysis of Airlift Pump for Aquaculture Applications

Fluids ◽  
2021 ◽  
Vol 6 (6) ◽  
pp. 226
Author(s):  
Rashal Abed ◽  
Mohamed M. Hussein ◽  
Wael H. Ahmed ◽  
Sherif Abdou
Keyword(s):  
Mass Transfer ◽  
Oxygen Transfer ◽  
Transfer Rate ◽  
Two Phase Flow ◽  
Oxygen Transfer Rate ◽  
Flow Patterns ◽  
Oxygen Mass Transfer ◽  
Phase Flow ◽  
Two Phase ◽  
Airlift Pump

Airlift pumps can be used in the aquaculture industry to provide aeration while concurrently moving water utilizing the dynamics of two-phase flow in the pump riser. The oxygen mass transfer that occurs from the injected compressed air to the water in the aquaculture systems can be experimentally investigated to determine the pump aeration capabilities. The objective of this study is to evaluate the effects of various airflow rates as well as the injection methods on the oxygen transfer rate within a dual injector airlift pump system. Experiments were conducted using an airlift pump connected to a vertical pump riser within a recirculating system. Both two-phase flow patterns and the void fraction measurements were used to evaluate the dissolved oxygen mass transfer mechanism through the airlift pump. A dissolved oxygen (DO) sensor was used to determine the DO levels within the airlift pumping system at different operating conditions required by the pump. Flow visualization imaging and particle image velocimetry (PIV) measurements were performed in order to better understand the effects of the two-phase flow patterns on the aeration performance. It was found that the radial injection method reached the saturation point faster at lower airflow rates, whereas the axial method performed better as the airflow rates were increased. The standard oxygen transfer rate (SOTR) and standard aeration efficiency (SAE) were calculated and were found to strongly depend on the injection method as well as the two-phase flow patterns in the pump riser.

Two-Phase Flow and Heat Transfer in Rectangular Micro-Channels

2003 ◽  
Author(s):  
Weilin Qu ◽  
Seok-Mann Yoon ◽  
Issam Mudawar
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Flow Pattern ◽  
Two Phase Flow ◽  
Flow Patterns ◽  
Heat Sinks ◽  
Phase Flow ◽  
Micro Channel ◽  
Two Phase ◽  
Micro Channels

Knowledge of flow pattern and flow pattern transitions is essential to the development of reliable predictive tools for pressure drop and heat transfer in two-phase micro-channel heat sinks. In the present study, experiments were conducted with adiabatic nitrogen-water two-phase flow in a rectangular micro-channel having a 0.406 × 2.032 mm cross-section. Superficial velocities of nitrogen and water ranged from 0.08 to 81.92 m/s and 0.04 to 10.24 m/s, respectively. Flow patterns were first identified using high-speed video imaging, and still photos were then taken for representative patterns. Results reveal that the dominant flow patterns are slug and annular, with bubbly flow occurring only occasionally; stratified and churn flow were never observed. A flow pattern map was constructed and compared with previous maps and predictions of flow pattern transition models. Annual flow is identified as the dominant flow pattern for conditions relevant to two-phase micro-channel heat sinks, and forms the basis for development of a theoretical model for both pressure drop and heat transfer in micro-channels. Features unique to two-phase micro-channel flow, such as laminar liquid and gas flows, smooth liquid-gas interface, and strong entrainment and deposition effects are incorporated into the model. The model shows good agreement with experimental data for water-cooled heat sinks.

Liquid–Liquid Two-Phase Flow Patterns in a Serpentine Microchannel

2012 ◽  
Vol 51 (13) ◽  
pp. 5056-5066 ◽  
Author(s):  
P. S. Sarkar ◽  
K. K. Singh ◽  
K. T. Shenoy ◽  
A. Sinha ◽  
H. Rao ◽  
...  
Keyword(s):  
Two Phase Flow ◽  
Flow Patterns ◽  
Phase Flow ◽  
Two Phase

High Speed Imaging and Two-Phase Flow Patterns During Flow Boiling in a Single Microchannel

2008 ◽  
Author(s):  
Jacqueline Barber ◽  
Khellil Sefiane ◽  
David Brutin ◽  
Lounes Tadrist
Keyword(s):  
High Speed ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Pressure Sensors ◽  
Flow Patterns ◽  
Bubble Nucleation ◽  
Phase Flow ◽  
Vapour Bubble ◽  
Two Phase ◽  
Over Time

Boiling in microchannels remains elusive due to the lack of full understanding of the mechanisms involved. A powerful tool in achieving better comprehension of the mechanisms is detailed imaging and analysis of the two phase flow at a fundamental level. We induced boiling in a single microchannel geometry (hydraulic diameter 727 μm), using a refrigerant FC-72, to investigate several flow patterns. A transparent, metallic, conductive deposit has been developed on the exterior of rectangular microchannels, allowing simultaneous uniform heating and visualisation to be conducted. The data presented in this paper is for a particular case with a uniform heat flux of 4.26 kW/m2 applied to the microchannel and inlet liquid mass flowrate, held constant at 1.33×10−5 kg/s. In conjunction with obtaining high-speed images and videos, sensitive pressure sensors are used to record the pressure drop profiles across the microchannel over time. Bubble nucleation, growth and coalescence, as well as periodic slug flow, are observed in the test section. Phenomena are noted, such as the aspect ratio and Reynolds number of a vapour bubble, which are in turn correlated to the associated pressure drops over time. From analysis of our results, images and video sequences with the corresponding physical data obtained, it is possible to follow visually the nucleation and subsequent both ‘free’ and ‘confined’ growth of a vapour bubble over time.

A model for predicting two-phase flow patterns transitions in an annulus: inclinations from horizontal to near-vertical

2021 ◽  
pp. 117379
Author(s):  
Marciellyo Ribeiro de Oliveira ◽  
Marcio Ferreira Martins ◽  
Humberto Belich ◽  
Leandro Amorim
Keyword(s):  
Two Phase Flow ◽  
Flow Patterns ◽  
Phase Flow ◽  
Two Phase
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