Assessment of Different CFD Modeling and Solving Approaches for a Supersonic Steam Ejector Simulation

The effects of different modeling and solving approaches on the simulation of a steam ejector have been investigated with the computational fluid dynamics (CFD) technique. The four most frequently used and recommended turbulence models (standard k-ε, RNG k-ε, realizable k-ε and SST k-ω), two near-wall treatments (standard wall function and enhanced wall treatment), two solvers (pressure- and density-based solvers) and two spatial discretization schemes ( the second-order upwind scheme and the quadratic upstream interpolation for convective kinematics (QUICK) of the convection term have been tested and compared for a supersonic steam ejector under the same conditions as experimental data. In total, more than 185 cases of 17 different modeling and solving approaches have been carried out in this work. The simulation results from the pressure-based solver (PBS) are slightly closer to the experimental data than those from the density-based solver (DBS) and are thus utilized in the subsequent simulations. When a high-density mesh with y+ < 1 is used, the SST k-ω model can obtain the best predictions of the maximum entrainment ratio (ER) and an adequate prediction of the critical back pressure (CBP), while the realizable k-ε model with the enhanced wall treatment can obtain the best prediction of the CBP and an adequate prediction of the ER. When the standard wall function is used with the three k-ε models, the realizable k-ε model can obtain the best predictions of the maximum ER, and the three k-ε models can gain the same CBP value. For a steam ejector with recirculation inside the diffuser, the realizable k-ε model or the enhanced wall treatment is recommended for adoption in the modeling approach. When the spatial discretization scheme of the convection term changes from a second-order upwind scheme to a QUICK scheme, the effect can be ignored for the maximum ER calculation, while only the CBP value from the standard k-ε model with the standard wall function is reduced by 2.13%. The calculation deviation of the ER between the two schemes increases with the back pressure at the unchoked flow region, especially when the standard k-ε model is adopted. The realizable k-ε model with the two wall treatments and the SST k-ω model is recommended, while the standard k-ε is more sensitive to the near-wall treatment and the spatial discretization scheme and is not recommended for an ejector simulation.

Thermally controlled microfluidic back pressure regulator

By using the temperature dependence of viscosity, we introduce a novel type of microfluidic lab-on-a-chip back pressure regulator (BPR) that can be integrated into a micro-total-analysis-system. A BPR is an important component used to gain pressure control and maintain elevated pressures in e.g. chemical extractions, synthesis, and analyses. Such applications have been limited in microfluidics, since the back pressure regularly has been attained by passive restrictors or external large-scale BPRs. Herein, an active microfluidic BPR is presented, consisting of a glass chip with integrated thin-film heaters and thermal sensors. It has no moving parts but a fluid restrictor where the flow resistance is controlled by the change of viscosity with temperature. Performance was evaluated by regulating the upstream pressure of methanol or water using a PID controller. The developed BPR has the smallest reported dead volume of 3 nL and the thermal actuation has time constants of a few seconds. The pressure regulation were reproducible with a precision in the millibar range, limited by the pressure sensor. The time constant of the pressure changes was evaluated and its dependence of the total upstream volume and the compressibility of the liquids is introduced.

Comparative Analysis of Low-Grade Heat Utilization Methods for Thermal Power Plants with Back-Pressure Steam Turbines

Thermal power plants (TPPs) with back-pressure steam turbines (BPSTs) were widely used for electricity and steam production in the Union of Soviet Socialist Republics (USSR) due to their high efficiency. The collapse of the USSR in 1991 led to a decrease in industrial production, as a result of which, steam production in Russia was reduced and BPSTs were left without load. To resume the operation of TPPs with BPSTs, it is necessary to modernize the existing power units. This paper presents the results of the thermodynamic analysis of different methods of modernization of TPPs with BPSTs: the superstructure of the steam low-pressure turbine (LPT) and the superstructure of the power unit operating on low-boiling-point fluid. The influence of ambient temperature on the developed cycles’ efficiency was evaluated. It was found that the usage of low-boiling-point fluid is thermodynamically efficient for an ambient temperature lower than 7 °C. Moreover, recommendations for the choice of reconstruction method were formulated based on technical assessments.

Eco-Friendly Separation of Antihyperlipidemic Combination Using UHPLC Particle-Packed and Monolithic Columns by Applying Green Analytical Chemistry Principles

Efficient separation of pharmaceuticals and metabolites with the adequate resolution is a key factor in choosing the most suitable chromatographic method. For quality control, the analysis time is a key factor, especially in pharmacokinetic studies. High back pressure is considered as one of the most important factors in chromatography’s flow control, especially in UHPLC. The separation of the anti-hyperlipidemic mixtures was carried out using two columns: a column silica-based particle packed UHPLC and a monolithic column. The systematic suitability of the two columns was compared for the separation of Fenofibrate, its active metabolite, Fenofibric acid and Pravastatin using Atorvastatin as an internal standard. Separation on both columns was obtained using ethanol: buffer potassium dihydrogen orthophosphate pH = 3 (adjusted with orthophosphoric acid) (75:25 v/v) as mobile phase and flow rate 0.8 mL/min. The analytes’ peak detection was achieved by using a PDA detector at 287 nm, 214 nm, 236 nm, and 250 nm for Fenofibrate, Fenofibric acid, Pravastatin, and Atorvastatin, respectively. Reduction of back-pressure was achieved with the monolithic column, where the analytes could be completely separated in less than 1.5 min at a flow rate of 5 mL/min. The principles of Green Analytical Chemistry (GAC) were followed throughout the developed method using environmentally safe solvents.

Production Enhancement in Intermittent Gas Lift Wells Using Sweeping Pipe Bend - Successful Case Histories from Various Onshore Fields in India

Objectives In wells which are producing on intermittent gas lift (IGL), the injected gas cannot sweep the entire liquid volume to the surface from the bottom of the tubing as there is continuously some fluid falling back in the tubing. The fallback can be described as the difference between the volume of the slug at the start of the gas injection and the volume of the actual produced slug at the surface. This fallback of liquid happens due to the fact that the gas has a tendency to flow through the liquid slug and letting the liquid to fall. The intensity of the liquid fallback increases more when there is increase in back pressure at wellhead. In order to minimize this liquid falling back in wells on intermittent gas lift, the sweeping pipe bend technology has been used in the various onshore fields operated by ONGC which has resulted in substantial gains and has been brought out in the paper. Process Gas break through and fallback are affected by three factors including the development of the gas bubble, the velocity of the slug flowing upward in the tubing, and wellhead restrictions caused due to presence of many 90-degree bends. To prevent gas breakthrough and to optimize the liquid fallback to minimum 5-7 % per 1000 feet of lift, it is recommended to maintain 1000 feet/min of minimum velocity of slug. Slower is the velocity of the slug which is moving up in the tubing, the longer time it takes for the gas to break through the liquid. At 1000 feet/min velocity, the wellhead restrictions can result in fallback losses due to breakthrough of gas in the well. In general, the flow path through the Christmas tree into the flowline is rather tortuous, moving first through a tee to the wing valve, then through other 90-degree ells before finally reaching the flowline. These restrictions further result in slowdown of the velocity of the slug thus resulting in more liquid to fallback and subsequently in significant production losses. Results In order to overcome the aforementioned problem and to reduce fallback in an intermittent gas lift well, sweeping pipe bend technology was considered and in the first phase implemented in 5 identified wells of different fields of ONGC Assets. With the help of sweeping pipe bend, the flow pattern becomes streamlined and number of 90-degree bends reduces or eliminates resulting in substantial reduction in the back pressure thus reducing the fall back. The implementation of the technology has resulted in an average liquid gain of 20.3% per well. Various guidelines for successful application of sweeping pipe bend have also been brought out in the paper. Additive Information 650 candidate wells operating on intermittent gas lift have been identified for the implementation of Sweeping Pipe Bends. As per the analysis, the implementation of Sweeping Pipe Bend is likely to result in a liquid gain of about 1000 m3/day from these wells.