Mass Transfer Coefficient behind an Orifice in Two-phase Flow

Gas–liquid two-phase flow directly determines the efficiency and stability of the aeration tank. In this paper, a gas–liquid two-phase testbed is built to explore the aeration performance and internal flow in an aeration tank, including an inverted-umbrella impeller (immersion depth of 0 mm, rotational speed of 250 r/min). Also, the running process is simulated by computational fluid dynamics (CFD) with a population balance model (PBM), and mass transfer coefficient is compared to the experiment. The experimental results show that there is a big difference in bubble diameter, ranging from 0.4 to 1.6 mm. The simulation shows that the impeller intensely draws air above the free surface into the shallow liquid, and the circulation vortex entrains it to the bottom areas faster. Compared with the experiment, the simulated interfacial area and standard oxygen mass transfer coefficient is 12% more and 3% less, respectively. The results reveal that CFD-PBM coupled model can improve the accuracy of calculation, resulting in the simulation of gas–liquid two-phase flow.

Download Full-text

Experimental investigation of heat transfer performance coefficient in tube bundle of shell and tube heat exchanger in two-phase flow

Archives of Thermodynamics ◽

10.2478/aoter-2014-0006 ◽

2014 ◽

Vol 35 (1) ◽

pp. 87-98 ◽

Cited By ~ 2

Author(s):

Marcin Karaś ◽

Daniel Zając ◽

Roman Ulbrich

Keyword(s):

Heat Transfer ◽

Mass Transfer ◽

Heat Transfer Coefficient ◽

Transfer Coefficient ◽

Mass Transfer Coefficient ◽

Tube Bundle ◽

Limiting Current ◽

Phase Flow ◽

Two Phase ◽

Tube Heat Exchanger

Abstract This paper presents the results of studies in two phase gasliquid flow around tube bundle in the model of shell tube heat exchanger. Experimental investigations of heat transfer coefficient on the tubes surface were performed with the aid of electrochemical technique. Chilton-Colburn analogy between heat and mass transfer was used. Twelve nickel cathodes were mounted on the outside surface of one of the tubes. Measurement of limiting currents in the cathodic reduction of ferricyanide ions on nickel electrodes in aqueous solution of equimolar quantities of K3Fe(CN)6 and K4Fe(CN)6 in the presence of NaOH basic solution were applied to determine the mass transfer coefficient. Controlled diffusion from ions at the electrode was observed and limiting current plateau was measured. Measurements were performed with data acquisition equipment controlled by software created for this experiment. Mass transfer coefficient was calculated on the basis of the limiting current measurements. Results of mass transfer experiments (mass transfer coefficient) were recalculated to heat transfer coefficient. During the experiments, simultaneously conducted was the the investigation of two-phase flow structures around tubes with the use of digital particle image velocimetry. Average velocity fields around tubes were created with the use of a number of flow images and compared with the results of heat transfer coefficient calculations.

Download Full-text

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

Fluids ◽

10.3390/fluids6060226 ◽

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.

Download Full-text