This paper presents experimental studies on the optimization of two-phase fluid flow in an airlift pump. Airlift pumps, also known as mammoth pumps, are devices applied for vertical transport of liquids with the use of gas. Their operating principle involves the existence of a density gradient. This paper reports the results of experimental studies into the hydrodynamic effects of the airlift pump. The studies involved optical imaging of two-phase gas-liquid flow in a riser pipe. The visualization was performed with high-speed visualization techniques. The studies used a transparent model of airlift pump with a rectangular cross-section of the riser. The assessment of the airlift pump operation is based on the image grey-level analysis to provide the identification of two-phase flow regimes. The scope of the study also involved the determination of void fraction and pressure drops. The tests were carried out in a channel with dimensions 35 × 20 × 2045 mm with the gas flux range 0.2–15.0 m³/h. For the assessment of the two-phase flow pattern Probability Density Function (PDF) was applied. On the basis of the obtained results, a new method for selecting the optimum operating regime of airlift pump was derived. This method provides the finding of stability and efficiency of liquid transport. It can also be applied to determine the correlation between the total lifting efficiency and the required gas flux for proper operation of the airlift pump.

The paper presents the results of research on liquid flow maldistribution in the shell side of a shell-and-tube heat exchanger (STHE). This phenomenon constitutes the reason for the formation of the velocity reduction area and adversely affects heat transfer and pressure drop. In order to provide details of the liquid distribution in STHE, two visualization methods were utilized. First, computational fluid dynamics (CFD) code coupled with the k-ε model and the laser-based particle image velocimetry (PIV) technique was applied. The tests were carried out for a bundle comprising 37 tubes in an in-line layout with a pitch d_z/t = 1.5, placed in a shell with D_in = 0.1 m. The STHE liquid feed rates corresponded to Reynolds numbers Re_in equal to 16,662, 24,993, and 33,324. The analysis demonstrated that the flow maldistribution in the investigated geometry originates the result of three main streams in the cross-section of the shell side: central stream, oblique stream, and bypass stream. For central and oblique streams, the largest velocity reduction areas were formed in the wake of the tubes. On the basis of the flow visualization, it was also shown that the in-line layout of the tube bundle helps to boost the wake region between successive tubes in a row. Additionally, unfavorable vortex phenomena between the last row of tubes and the lower part of the exchanger shell were identified in the investigations. The conducted studies confirmed the feasibility of both methods in the identification and assessment of fluid flow irregularities in STHE. The maximum error of the CFD method in comparison to the experimental methods did not exceed 7% in terms of the pressure drops and 11% in the range of the maximum velocities.

The article presents the results of flow investigations downstream of a standard and slotted orifice plate, obtained using both experimental measurements with the Particle Image Velocimetry (PIV) method and numerical calculations performed in a CFD environment. The aim of the study was a detailed analysis of the velocity field structure and an evaluation of the prediction accuracy of different turbulence models in relation to experimental data. The study employed models from the k-ε and k-ω groups, which were compared in terms of their agreement with measurement results in various flow regions. The study demonstrated that no single turbulence model guarantees optimal results across the entire investigated domain. Model selection should therefore be adapted to the analyzed flow region k-ω models in the vicinity of the orifice and k-ε models in the developed flow region. The findings have significant practical implications for the engineering of orifice flow meters, enabling a more informed use of CFD methods in the design and validation of industrial measurement systems.

This article reports the results of a study into the effect of operating parameters on the occurrence and course of gas–liquid two-phase phenomena during the fogging process carried out with the use of a conical pressure-swirl nozzle. Four alternatives of the stub regulation angles and four values of pressure of air supply to the nozzle were tested as part of the current research. The range of the investigated variables was common for the operation of fumigators used to prevent the spread of SARS-CoV-2 virus. The liquid flow rate (weighting method), the field of velocity, and turbulent flow intensity factor, as well as velocity profiles over the section of 1 m from the nozzle were determined using the particle image velocimetry (PIV) technique. The obtained results were correlated with the measurements of the diameters of spray droplets using the laser light scattering (LLS) technique. On the basis of this research, a dependence between the nozzle parameters and the spray cone pattern was identified in terms of dynamics and droplet diameter distribution. As a result of the research, a wide range of parameters were identified in which the fogging process was carried out in a stable and repeatable manner. There were exceptions to this rule only in the cases when there was a deficiency of the liquid necessary to generate a two-phase mixture.

This paper contains the results of experimental study concerned with liquid mixing process using a stirrer located in a rectangular vessel. The current study applied Digital Particle Image Velocimetry technique (DPIV). On the basis of non-invasive measurements, velocity vector profiles were determined with regard to the velocity of the mixing process, and they were subsequently applied for identification and assessment of liquid circulation in a vessel. The correlation between the rotational speed of the stirrer and fluctuations and directions of the liquid flow velocity were determined. This paper focuses on the assessment of the mixing intensity resulting from the rectangular geometry of the vessel. The study proposes and develops a dependence between the shape of the velocity profile of the circulating liquid and the intensity of the mixing process. The study demonstrates the existence of suitable conditions for performing mixing processes in rectangular vessels.