Analysis and Classification of Low Head Hydro Power Based on Advanced Morphological Approach

The paper discusses hydrokinetic systems low head hydro power as an element renewable resource. In the paper a review of the existing and upcoming orthogonal and axial turbines schemes is outlined. Based on a morphological approach comprehensive survey of various schemes and qualitative comparison, is presented. The proposed engineering solutions reduce the structure weight and the processability increases. These factors lead to a decrease in the cost. The engineering solutions under consideration are designed to operate in low-pressure flows, regardless of their direction. Thanks to these features, the scope of their use expands. They can be used both in high tide and in the use of the sea currents kinetic energy.

Development and Research of New Media Jet Aeration Scheme in a Loop Bioreactor Producing Microbiological Products

Jet aeration loop reactors are widely used in the chemical industry due to their high mixing intensity, possibility of significant saturation of medium with gases, and simplicity of scaling the processes when passing from laboratory equipment to industrial designs. However, to ensure the necessary amount of air in standard jet aeration schemes with ejectors, high pressure of the medium (up to 6 bars) is required in the reactor loop. This paper presents a newly developed scheme of jet aeration, based on mixing the pressure flows of medium and air supplied to the ejector by individual blowers. Experiment results of the new water aeration scheme showed that, for the formation of suspended matter in the ejector with an air content of 2–20 l per 1 l of water, a pressure of 0.3 bar in the reactor loop at an air pressure of 1 bar is sufficient. This allows usage of low-pressure pump and compressor, which form the basis for the energy consumption reduction and creates prerequisites for lowering the shear loads on a crop. The medium aeration rate during experiments was 0.220–0.266 vvm. It was found that, for each mode of joint operation of pump and compressor, it is possible to maintain a constant aeration rate, which is not significantly affected by the flowrate regulation of medium in loop.

Numerical simulation of rigid particles in Stokes flow: lubrication correction for general shape of particles

We address the problem of numerical simulation of suspensions of rigid particles in a Stokes flow. We focus on the inclusion of the singular short range interaction effects (lubrication effects) in the simulations when the particles come close one to another. As in LefebvreMerletNguyen2015, the key idea is to decompose the velocity and pressure flows in a sum of a singular and a regular part. In this article, the singular part is computed using an explicit asymptotic expansion of the solution when the distance goes to zero. This expansion is similar to the asymptotic expansion proposed in HillairetKelai2015 but is more appropriate for numerical simulations of suspensions. It can be computed for any locally convex (particles convex close to the contact point) and regular shape of particles. Using HillairetKelai2015 as an intermediate result, we prove that the remaining part is regular in the sense that it is bounded independently of the distance. As a consequence, only a small number of degrees of freedom are necessary to obtain accurate results. The method is tested in dimension 2 for clusters of two or three aligned particles with general rigid velocities. We show that, as expected, the convergence is independent of the distance.

Leakage-Flow Models for Screw Extruders

Many theoretical analyses of extrusion ignore the effect of the flight clearance when predicting the pumping capability of a screw. This might be reasonable for conventional extruder screws with “normal” clearances but leads to errors when more advanced screw designs are considered. We present new leakage-flow models that allow the effect of the flight clearance to be included in the analysis of melt-conveying zones. Rather than directly correcting the drag and pressure flows, we derived regression models to predict locally the shear-thinning flow through the flight clearance. Using a hybrid modeling approach that includes analytical, numerical, and data-based modeling techniques enabled us to construct fast and accurate regressions for calculating flow rate and dissipation rate in the leakage gap. Using the novel regression models in combination with network theory, the new approximations consider the effect of the flight clearance in the predictions of pumping capability, power consumption and temperature development without modifying the equations for the down-channel flow. Unlike other approaches, our method is not limited to any specific screw designs or processing conditions.

Pressure Exchanger for Energy Recovery in a Trans-Critical CO2 Refrigeration System

Trans-critical CO2 vapor compression (VC) refrigeration cycles require a high compression ratio, which is associated with high expansion losses. To recover these expansion losses, a pressure exchange process between the low- and high-pressure sides of the VC cycle is proposed and examined in this study. The proposed pressure exchange system is an open type constant volume process where the high- and low-pressure flows mix inside the system. This prototype is inspired by the pressure exchangers used in reverse-osmosis (RO) desalination systems. In this system, a 2D model was generated and modeled using the computational fluid dynamics (CFD) technique. The numerical model ignored any losses due to leakage or hydraulic friction and the process is considered adiabatic. For the modeling, it was assumed that the inlet conditions for the two pressure exchanger flows are similar to the flow conditions at the evaporator and gas cooler outlets in a VC cycle. Two parameters are examined to test the validity of the system and understand their effect on the performance, including the inlet flow rate represented by the inlet velocity and the process time represented by the speed of rotation. A total of nine cases were simulated and analyzed in this study.

Optimization of megakaryocyte trapping for platelet formation in microchannels

Platelets (PLTs) are responsible for stopping the bleeding. They are small cell fragments produced from megakaryocytes (MKs) in the bone marrow. Low platelet count is a significant health problem for a patient. PLTs can usually be stored for up to 5 days prior to transfusion. Instantaneous production of PLTs from isolated and stored MKs is crucial for the patient?s health. Thanks to microfluidic platforms, PLTs can be produced instantaneously from MKs. Herein, we have computationally studied fluid dynamics in the microchannels with slit structures and different inlet geometries. Analysis of the flow dynamics was performed by the commercial analysis software. The effects of flow rates and the angle between the inlet channels on the MKs trapping were investigated. The optimization of the angle between inlet channels and flow rates of main and pressure flows was done with Response Surface Methodology (RSM) by counting the trapped MKs. The optimum conditions lead to the percentage of trapped MKs were 100 with a relative deviation of <1%. We also concluded that flow rates to trapping a higher amount of MKs are as important as the angle between the inlet channels.

Application of Network Analysis to Flow Systems with Alternating Wave Channels: Part B. (Superimposed Drag-Pressure Flows in Extrusion)

Due to progress in the development of screw designs over recent decades, numerous high-performance screws have become commercially available in single-screw extrusion. While some of these advanced designs have been studied intensively, others have received comparatively less attention. We developed and validated a semi-numerical network-theory-based modeling approach to predicting flows of shear-thinning polymer melts in wave-dispersion screws. In the first part (Part A), we systematically reduced the complexity of the flow analysis by omitting the influence of the screw rotation on the conveying behavior of the wave zone. In this part (Part B), we extended the original theory by considering the drag flow imposed by the screw. Two- and three-dimensional melt-conveying models were combined to predict locally the conveying characteristics of the wave channels in a discretized flow network. Extensive experiments were performed on a laboratory single-screw extruder, using various barrel designs and wave-dispersion screws. The predictions of our semi-numerical modeling approach for the axial pressure profile along the wave-dispersion zone accurately reproduce the experimental data. Removing the need for time-consuming numerical simulations, this modeling approach enables fast analyses of the conveying behavior of wave-dispersion zones, thereby offering a useful tool for design and optimization studies and process troubleshooting.

Study of radial burning of holes in titanium shells of high-pressure tanks with oxygen containing gas

The paper presents the results of the experimental study of radial burning of holes in titanium samples simulating a fragment of the shell of a high-pressure tank filled with gaseous oxygen or oxygen-containing gas. The tests revealed the possibility of a large increase in the orifice area (140–2 250 times compared with the initial value) as a result of the burning of small through-holes when oxygen-containing gas of the increased pressure flows through them and allowed us to determine the apparent radial burning rate at various oxygen concentrations. The proposed mathematical dependence of the hole size in the titanium shell after their radial burning on the process parameters may be of interest for the analysis of processes occurring in engineering systems in case of some off-nominal and emergency situations. Key words: radial burning of holes, titanium tank, oxygen-containing gas, off-nominal and emergency situations.