Increase In Pressure Loss Research Articles

Scramjet combustion with bumpy struts

In this study, the following strut configurations were proposed to improve the combustion performance of a scramjet combustor with a strut: (1) BS-1: strut with periodic rectangular bumps and (2) BS-2: strut with periodic trapezoidal and triangular bumps. These bumps were arranged on both sides of the rear part of the struts. By using a validated numerical simulation method, the performance and combustion flow fields of scramjet combustors with a normal strut (NS) and two BSs were compared and analyzed under an inlet Mach number of 2.0 and hydrogen jet at sonic speeds. The effects of the two BSs on the performance of the scramjet combustor and their mechanisms were investigated. The results demonstrated that in the two BS combustors, the flow disturbance and streamwise vortices induced by the bumps, additional oblique shock waves at the leading edge of the rear straight section, and upstream shift in the interaction position between the reflected oblique shock wave and shear layer resulted in a significant increase in total pressure loss. However, the flow disturbance and streamwise vortices not only significantly increased the shear layer thicknesses and interfacial area between the fuel and air, which contributed to a more stable and efficient combustion by increasing the size of the near-field high-turbulent-kinetic-energy region and expanding the combustion region, but also enhanced heat and mass convection between the core region and main stream on both sides, yielding a higher flame propagation speed. Therefore, the combustion was significantly promoted in the two BS combustors. BS-2 had a stronger disturbance effect on the flow and induced stronger streamwise vortices, resulting in a greater total pressure loss compared with that observed in BS-1. However, the triangular bumps of BS-2 increased the width of the narrow part of the recirculation zone, which made the fuel distribution downstream of BS-2 combustor more conducive to maintaining a larger combustion region, thus achieving more efficient combustion. Compared with the NS combustor, BS-1 and BS-2 combustors reduced the distances by 49.4% and 54.1%, respectively, when the combustion efficiency reached 95%, and by 47.9% and 53.1%, respectively, when the combustion efficiency reached 100%, with the total pressure loss at the outlet increasing by 2.16% and 3%, respectively. Therefore, the results suggest that the two BSs have the potential to significantly enhance the combustion of scramjet combustors, making them a promising avenue for further research and optimization.

Effect of different strut design on the mixing performance of H2 fueled two-strut based scramjet combustor

Strut fuel injection approach significantly influences the combustion mechanism inside the scramjet engines. To address this issue, researchers are nowadays mainly focused on a scramjet model with two struts. As the performance of the two-strut model is improved as compared to the original single-strut model as per the latest research findings, therefore the current research is focused on the impact of the different shapes of the two-strut on the combustion flow-field study of scramjet engines. Initially, experimental data from the already-published literature for a single strut is used to validate the implemented simulation techniques. Then, to investigate the combustion performance, different shapes of the two-strut are included in the already-existing DLR scramjet combustor. The SST k-ω turbulence model and steady RANS equations are used to carry out the numerical simulation. The semi-circular trailing edge half-wedge strut, with a combustion efficiency of roughly 92%, is the most effective strut configuration obtained in the current study. The findings also revealed that the semi-circular trailing edge half-wedge strut profile attains a stronger as well as a wider wake region, ensuring better combustion performance, and indicating that the two-strut model can be used as an efficient flame holder in subsequent works. Next, an analysis of how various inward fuel injection angles affect the performance of the optimum strut shape in terms of mixing efficiency and total pressure loss is provided. According to the study, an increase in the inward fuel injection angle significantly improves the mixing performance of the two-strut scramjet combustor. Additionally, the mixing and total pressure loss profiles reveal that the geometry with a 60° strut injection angle achieves early complete mixing within 0.145 m at the cost of only a slight increase in total pressure loss, and this outcome may lead to the development of a short-length supersonic combustor to minimize the drag forces and heat generation. Last but not the least, the optimal inward fuel injection angle (60°) of the two-strut and its effects on mixing performance under different freestream conditions are investigated, illustrating that mixing efficiency decreases with increasing Mach number in the same manner as single strut geometry.

PULM4: Silicone-Based Hollow Fiber Membrane Lungs For Long-Term Extracorporeal Respiratory Supports: Initial Results From A Pilot Study Using A Goat Model

Background: There has been an increasing demand of organs for lung transplant to save those who suffer from end-stage lung disease. However, the number of organ donations have never matched that of candidate recipients, leading to a high mortality rate on the waiting period for transplant. One potential approach to decrease the wait-list mortality is to develop an artificial gas-exchange device that can support lung function until the time of transplantation. We’ve started to develop a gas-exchange system that consists of silicone-based membrane lungs with methacryloyloxyethyl phosphorylcholine (MPC) polymer coating and tubing system for a longer-term use. Objective: The purpose of this study was to evaluate the long-term durability, oxygenation, and pressure loss of newly developed artificial lungs using a large animal model. Materials and methods: The surface area of the membrane lung is approximately 2 m2. Central ECMO from the pulmonary artery to the left atrium was introduced to a healthy female goat via left thoracotomy under general anesthesia (N=3). Unfractionated heparin infusion was utilized for anticoagulation (target activating clotting time: 150-200 sec). After recovery from the surgery, blood gas and flow pressure before and after the artificial lung with flow rates of 1, 2, and 3 L/min were tested weekly. Daily physiological data, regular blood biochemistry and coagulation tests, and histopathological findings after autopsy were also evaluated. Thrombus adhesion to the silicone membrane was evaluated using an electron microscopy after the experiments. Results: Durations for testing the artificial lungs were 53, 58, and 100 days. The experiments were terminated due to an accidental tubing event, a sudden cardiac complication, and massive renal hemorrhage. Averages of oxygen transfer rates (ml/min) and oxygen pressure gradients (mmHg) at each flow rate were 63.3 and 466.5 at 1 L/min, 118.3 and 291.3 at 2 L/min, and 152.7 and 138.2 at 3 L/min. Averages of flow pressures through the artificial lungs at each flow rate were 21.7 mmHg at 1 L/min, 44.7 at 2 L/min, and 66.9 at 3 L/min. No significant increase of pressure loss or decrease of oxygenation was observed throughout the experimental periods. Thrombus at the inlet of the membrane was mainly observed, but those inside and near the outlet were minor, indicating the long-term antithrombotic property of the polymer coating. Electron microscopical examinations revealed minimal thrombus formation on the hollow fiber membrane inside the lung. At autopsy, although micro-infarction and thrombus were observed in the heart and kidney, native lungs were well maintained without appreciable congestion. Conclusion: The newly developed MPC polymer-coated silicone-based lungs could be used stably for more than 50 days. Improving the oxygenation in higher blood flow rates with reduced pressure loss is our ongoing subject to work on.

Enhanced performance of a microchannel with rectangular vortex generators

Microchannel heat sinks and heat exchangers are widely used in the cooling of electronic systems. However, it is still important to enhance the heat transfer in the microchannel so that the intense heat generated can be removed. Vortex generators (VGs) create secondary flow structures in the flow, increasing the fluid mixing, thinning the thermal boundary layer, and ultimately boosting heat transfer. Here, we have controlled the flow structure and improved the heat transfer with the lowest possible pressure loss by placing VGs of different sizes, numbers, and angles of attack in a microchannel. The improvement in heat transfer is accelerated as vortex intensity increases. The angle of attack has a significant impact on vortex formation lengths, which reach high dimensions around 90°. Furthermore, increasing the VG length significantly increases the vortex formation lengths. The number of VG pairs has a significant impact on heat transfer and pressure losses. As the number of VG pairs increases, so does the area occupied by the secondary flow regions in the microchannel, increasing the fluid mixture and boosting heat transfer. The highest enhancement in heat transfer using VGs is obtained at around 230%, while the corresponding increase in pressure loss is 950%. According to the JF factor which we consider a performance evaluation criteria, the best result is around 1.38. The Genetic Aggregation Response Surface Methodology has been applied to numerical results. The related method is realized to produce results that are consistent with the numerical results within a ±5% error interval. All the input parameters considered in the sensitivity analysis have an impact of at least 10% on the output parameters.

Modeling of sand transport and elbow erosion in horizontal two-phase slug flow

Horizontal wells play an important role in maximizing the recovery of hydrocarbons from oil and gas reservoirs. During production, if the rate of production of produced fluids with sand particles is low, the deposition of sand particles in horizontal flow lines can wreak havoc on production systems in such a way as to cause increased pressure loss and reduction or loss of production when the pipe is partially or completely blocked. On the other hand, if the production rate of fluids is high, the impact of sand particles on the wall of the pipe will erode the inner surface of the pipe fittings. In this case, erosion can be severe enough to cause a hazardous spill and complete shutdown of systems. Therefore, it is important to quantify the sand transport and erosivity of different flow regimes. Under moderate velocities, there exists a flow regime which is called slug flow which is characterized by the intermittent appearance of liquid slugs propagating through the pipe. Studying the sand deposition and erosion due to sand particles entrained in intermittent flows is extremely difficult since the solid particle velocity magnitudes are coupled with several multiphase flow parameters such as phase distribution and slippage between the phases. This work focuses on the improvement of mechanistic models for predicting critical deposition of sand particles in horizontal pipes and erosion in horizontal-horizontal elbows. In this investigation, a modified model is proposed to better predict the critical deposition velocity and the characteristic particle velocity as a function of the slug flow characteristics. The model predictions are compared with the sand transport and erosion data collected at the University of Tulsa and other research institutions. The results show that the new approach provides improved predictions for sand transport and maximum erosion in standard elbows when compared with existing models.

Stop-flow discharge operation aggravates spacer scaling in CDI treating brackish hard water

Brackish water desalination has become a major opportunity to fulfill the rising clean water needs globally. Capacitive deionization (CDI) is an attractive electrochemical separation technology to treat water salinity, and the innovative discharge operation, termed stop-flow (SF) discharge, has demonstrated high efficiency to minimize the brine volume. This work systematically compared the desalination performance of CDI when single-pass and SF discharge operation modes were respectively used. Results showed that while the SF discharge operation could achieve remarkably higher water recovery (>80 %), this inevitably resulted in the deterioration of CDI performance when the feed contained higher concentrations (5 mM) of Ca2+ and SO42−. Compared to the electrodes, the spacer and the desalination chamber could be more vulnerable to scaling in brackish water desalination. With the formation of glauberite and gypsum in SF discharge operation, the carbon materials from the electrodes constantly existed on the scaled spacer, which contributed to the blocking of the flow path and a significant increase in pressure loss. This study provides insight into the scaling mechanism for SF discharge in multi-cycle operation, which is crucial for the design of CDI materials and optimization of operating protocols for brackish water desalination.

Numerical Study of Film-Cooling and Aerodynamic Performance of Contoured Cratered Holes

Film cooling with discrete cratered holes has been proven to be one of the effective ways to increase the cooling effectiveness for flat-plate conditions. Up to now, there has been a lack of relevant research on various discrete cratered holes under cascade conditions. In this paper, the cooling and aerodynamic performances of a reference contoured cratered hole and two optimized contoured cratered holes are studied employing the numerical analysis method. The velocity and temperature fields for the film cooling are obtained by solving the steady-state Reynolds-averaged Navier-Stokes equations with the Shear Stress Transport turbulence closure. The numerical results show that these two optimized holes significantly enhance the cooling performance with an ignorable increment of pressure loss compared to the reference hole. When the cooling hole is placed at the pressure or suction side, the local pressure gradient plays a key role in developing the downstream flow field for either cooling hole. Furthermore, the pressure loss is mainly affected by the blowing ratio and the film cooling hole location. The pressure loss in the hole and its contribution to the total pressure loss increase with the increase of the blowing ratio.

Numerical study of perforated obstacles effects on the performance of solar parabolic trough collector.

The current work presents and discusses a numerical analysis of improving heat transmission in the receiver of a parabolic trough solar collector by introducing perforated barriers. While the proposed approach to enhance the collector's performance is promising, the use of obstacles results in increased pressure loss. The Computational Fluid Dynamics (CFD) model analysis is conducted based on the renormalization-group (RNG) k-ɛ turbulent model associated with standard wall function using thermal oil D12 as working fluid The thermo-hydraulic analysis of the receiver tube with perforated obstacles is taken for various configurations and Reynolds number ranging from 18,860 to 81,728. The results are compared with that of the receiver without perforated obstacles. The receiver tube with three holes (PO3) showed better heat transfer characteristics. In addition, the Nusselt number (Nu) increases about 115% with the increase of friction factor 5-6.5 times and the performance evaluation criteria (PEC) changes from 1.22 to 1.24. The temperature of thermal oil fluid attains its maximum value at the exit, and higher temperatures (462.1K) are found in the absorber tube with perforated obstacles with three holes (PO3). Accordingly, using perforated obstacles receiver for parabolic trough concentrator is highly recommended where significant enhancement of system's performance is achieved.

The effects of unburned-gas temperature and pressure on the unstable behavior of cellular-flame fronts generated by intrinsic instability in hydrogen-air lean premixed flames under adiabatic and non-adiabatic conditions: numerical simulation based on the detailed chemical reaction model

ABSTRACT The effects of unburned-gas temperature and pressure on the unstable behavior of cellular-flame fronts in hydrogen-air lean premixed flames are elucidated by numerical simulations. The detailed chemical reaction mechanism with seventeen reversible reactions of eight reactive species and a diluent is adopted for hydrogen-air combustion and heat loss is taken into account. The burning velocity of a planar flame increases as the unburned-gas temperature increases, and it decreases as the unburned-gas pressure and heat loss increase. In the dispersion relation, the growth rate increases and the unstable range widens when the unburned-gas temperature increases. The former decreases and the later narrows when the heat loss becomes larger. The normalized growth rates become large under the non-adiabatic conditions. The normalized burning velocity of a cellular flame is large when the pressure is high and heat loss is large, and it decreases as the temperature increases at high pressure. This shows that the high unburned-gas temperature at high pressure weakens the instability in hydrogen-air lean premixed flames. With increasing the domain size, the burning velocity of a cellular flame increases, and the cellular-flame front becomes more unbalance. This is an aspect of the long-wavelength disturbance to the unstable behavior of cellular-flame front.

Surrogate modeling of pressure loss & mass transfer in membrane channels via coupling of computational fluid dynamics and machine learning

Spacers are integral to the operation of membrane systems for both structural purposes and improving mass transfer dynamics that drive water permeation at the cost of increased pressure losses. 321 computational fluid dynamics (CFD) simulations were performed to provide high-fidelity data on hydrodynamic and mass transport behavior of spacer-filled membrane channels. CFD simulations were used to investigate the impact of the geometric parameters of spacers on pressure loss and concentration polarization in membrane channels. Spacer designs were characterized using six parameters that were varied in simulations to sample the domain of commercially available designs. Machine learning models were trained on CFD data to produce surrogate models for predicting pressure loss and mass transfer coefficients. These surrogate models consider more geometric parameters than existing empirical equations resulting in more representative and flexible models that can be integrated into existing module-scale or system-scale modeling software. Surrogate models were coupled with a particle swarm optimization algorithm and found that spacer designs with a diameter of 0.3 mm, length of 3.6 mm, angle between 42 and 46°, and moderate diameter necking (~60 %) best balances the trade-off between reduced concentration polarization and increased pressure losses in membrane channels with channel velocities between 0.05 and 0.35 m/s.

Fluid flow and heat transfer in a rectangular ribbed channel with a hierarchical design for turbine blade internal cooling

• New design concept to develop high-performance internal cooling of turbine blades. • Greatly reduced pressure loss is achieved with negligible heat transfer reduction. • The underlying physics of pressure drop and heat transfer performance is clarified. • Various designs are examined to verify the feasibility of the new design concept. For internal cooling of a turbine blade, various advanced rib turbulators can markedly contribute to the heat transfer enhancement while suffering a great increase in pressure loss. In those designs, ribs with the same configuration are periodically and evenly mounted on the channel wall. In this context, this work proposes a hierarchical design concept to optimize the rib arrangement with the desired reduction in pressure loss. In terms of the rib height, this new design concept is implemented to construct three new rib configurations. Based on an established turbulence model, three-dimensional (3D) numerical simulations are entirely adopted to verify the feasibility of the new configuration in a wide Reynolds number range. The numerical results demonstrate that the optimal configuration with a linearly decreasing rib height can greatly reduce the pressure loss with a slight heat transfer deterioration. The negligible reduction in the heat transfer performance results from the enhanced fluid impingement on the reattachment region because of the lowering effect of the mainstream, although small ribs weaken the fluid impingement. The marked pressure drop reduction comes from the combination of the lowering effect and small ribs which constrains the separation vortex behind ribs. Furthermore, the comparison of the overall thermal performance is carried out considering a wide range of the Reynolds number, pitch ratios, and aspect ratios. The optimal configuration can greatly enhance the overall thermal performance up to 138.3% for the factor ( Nu / Nu 0 )/( f / f 0 ) and up to 32.5% for the factor ( Nu / Nu 0 )/( f / f 0 ) 1/3 . Eliminating the entrance effect of developing flow, the increment in the overall thermal performance is considerably reduced but still keeps at a high level. Finally, it is significantly highlighted that as a simple but effective improvement, the hierarchical design concept presents great potential in developing high-performance internal cooling of turbine blades.

Effect of strut profile, angled injection, and blunting of leading edge on mixing of supersonic hydrogen-air streams

Mixing fuel and air in a scramjet combustor is one of the key challenges in its development due to the short residence time available. Strut based injection is considered a viable alternative and is widely investigated. In the present work, the effect of the strut profile, angled injection of fuel, and the blunting of the leading edge of the strut on the mixing of fuel and air is studied using the Finite Volume Method (FVM). The base case chosen is an experiment with Hydrogen fuel injection from a strut at Mach 2.3 in a supersonic air stream of Mach 2. The popular strut profiles of diamond and wedge shapes are considered. The mixing due to wedge strut with dual injection from the trailing face and the effect of the inclination angle of the two fuels is studied. It is observed that the wedge strut with single fuel injection results in the highest mixing efficiency. Compared to the diamond strut, the distance to reach the complete mixing of fuel and air is reduced by 100 mm for the wedge strut with single injection. The high thermal load on the leading edge of the strut requires blunting (and rounding) for heat removal, and its effect is also investigated. The blunting of the leading edge of the strut leads to a decrease in mixing efficiency and an increase in total pressure loss as well as rise in entropy compared to a strut with pointed leading edge. Blunted wedge strut with single injection requires 40 mm more length for complete mixing than wedge strut with pointed leading edge. Also, after blunting, its rounding increases the mixing efficiency slightly but reduces the total pressure loss and entropy rise noticeably.

The Influence of Combustor Hot Streaks on the Aerodynamic Performance of a Turbine Center Frame

Abstract This paper investigates the influence of combustor temperature non-uniformities on modern engine turbine center frames (TCFs). Due to their position in an engine, coupled with the trends of more aggressive designs, increased turbine inlet temperatures (TIT), and utilization of lean-burn combustors, turbine center frames are exposed to even higher temperatures and non-uniform temperature flow fields. These temperature non-uniformities, or hot streaks (HS), were previously studied at the combustor—high-pressure turbine (HPT) interface, but there is no available research in the open literature that clarifies their influence on the TCF performance. A new test bench, designed specifically for fundamental research on hot streaks, was set up at the Institute for Thermal Turbomachinery and Machine Dynamics at the Graz University of Technology, Austria. The test bench features a 90 deg sector cascade of an engine representative TCF geometry, equipped with a hot streak generator and a flow conditioning grid. Experimental data were gathered by means of five-hole probe area traverses at the TCF inlet and outlet planes. Two individual clocking positions of hot streaks were investigated, as well as three different radial positions for each of the clocking scenarios. Hot streaks were injected upstream of the flow conditioning grid, generating a representative temperature ratio at the TCF inlet plane. Results show that the hot streaks have migrated radially outwards and are characterized by different temperature distributions, depending on the injection position. An increase in pressure loss and thermal loading of the strut and the shroud are observed.

Numerical investigation of heat transfer performance of an air heater with delta flow obstruction

Air heaters are a vital component in many engineering systems, including room heating and agricultural dryers. The use of flow obstacles improves the convective heat transfer coefficient by interrupting the formation of a laminar sub-layer. In the previous studies reported, the thermal and frictional effects of various flow obstacle geometries were studied, but they are limited to non-inclined obstacles. The current research examines the thermal and hydraulic characteristics of air heaters with inclined and non-inclined delta shape obstacles using numerical techniques and compares the results with empirical predictions and literature data. The influence of flow rate and angle of attack (α) on Nusselt number (Nu) and friction factor (f) were evaluated using CFD for Reynolds numbers (Re) ranging from 5000 to 20,000 and for α ranging from 300 to 900. A rectangular duct (300 mm × 50 mm) with a constant heat flux of 800 W/m2 at the bottom surface of the air heater with delta obstructions of relative obstacle height (e/H) of 0.5 with a constant transverse (Pt/b) of 1.5 and longitudinal pitch (Pl/e) of 3 was considered. The Nu, f and Thermal Enhancement Factor (TEF) were calculated and investigated for various flow rates and attack angles. The predicted Nu and f values demonstrated a good agreement with empirical correlations, with an average variation of 5.68 percent and 7.2 percent, respectively. The CFD results were also consistent with earlier published experimental findings. The results indicate that using a delta obstruction enhances heat transfer rate considerably at the cost of increased pressure loss. The use of delta-shaped flow obstruction increases Nusselt number in the range of 71–162, with a 6–9.6 times increase in friction factor. A maximum TEF of 1.69 was obtained for the air heater with delta obstruction with α = 300 at Re = 5000.

Metaheuristics applied to the optimization of a compact heat exchanger with enhanced heat transfer surface

• A combined geometry of louvered fins and vortex generators is numerically simulated. • Parametric study on the influence of 8 independent variables on j and f. • Independent optimization of all the variables involved in the VG geometry. The heat exchanger compactness is a key factor in several engineering applications, such as, in automotive applications that use enhanced heat transfer surfaces on the air side to improve the convective heat transfer coefficient. In this study, a combined geometry of louvered fins and vortex generators is numerically simulated to optimize the thermohydraulic behavior of a compact heat exchanger. The influence of eight parameters of the enhanced surface on its thermohydraulic performance is analyzed. The thermohydraulic performance is evaluated through the Performance Evaluation Criterion, which relates the Colburn factor and the friction factor, i.e., the heat transfer enhancement and the increment of the pressure losses of the actual model with respect to a reference one. A metaheuristic tool, based on the NSGA-II genetic algorithms, combined with multi-objective optimization technique, is applied. The objective functions used in the optimization are obtained with numerical methods and computational fluid dynamics techniques. As a novelty, the optimization was carried out individually and under non-stationary flow conditions, for a total of eight magnitudes associated with the vortex generators. The optimized geometry is able to enhance the convective heat transfer between 6.55% and 19.63%, with an increase in pressure losses varying from 10.95% to 20.67% depending on the Reynolds number.

Whey Protein Hydrolysates Improved the Oxidative Stability and Water-Holding Capacity of Pork Patties by Reducing Protein Aggregation during Repeated Freeze-Thaw Cycles.

The effects of whey protein hydrolysates (WPH) on myofibrillar protein (MP) oxidative stability and the aggregation behavior and the water-holding capacity of pork patties during freeze–thaw (F–T) cycles were investigated. During F–T cycles, the total sulfhydryl content and zeta potential of MP decreased, while peroxide value, surface hydrophobicity, particle size, pressure loss and transverse relaxation times increase. The oxidative stability and the water-holding capacity of pork patties were enhanced by the addition of WPH in a dose-dependent manner, whereas the MP aggregation decreased. The addition of 15% WPH had the most obvious effects on the pork patties, which was similar to that of the 0.02% BHA. After nine F–T cycles, the POV, surface hydrophobicity, particle size and pressure loss of the pork patties with 15% WPH were reduced by 17.20%, 30.56%, 34.67% and 13.96%, respectively, while total sulfhydryl content and absolute value of zeta potential increased by 69.62% and 146.14%, respectively. The results showed that adding 15% WPH to pork patties can be an effective method to inhibit lipid and protein oxidation, reducing protein aggregation and improving the water-holding capacity of pork patties during F–T cycles.

Specific pressure loss calculations for tailings hydrotransport at the Kachkanar GOK

Mining transportation systems are evolving through the introduction of continuous transportation solutions, hydraulic pipeline transport being the most common of them. Considering the high labor and energy intensity of equipment operation, accelerated hydroabrasive wear of pipelines, and elevated metal consumption, respective mining hydrotransport efficiency assessments indicate a significant streamlining potential. Energy intensity of any transportation process depends on the specific head loss Icm and the concentration of the solid phase. Lower pressure losses and higher concentrations reduce the energy requirements for pumping a given volume of solid materials (tailings) and, consequently, improve the resulting hydraulic transport efficiency. The purpose of this work was to establish the change patterns for specific head losses at varying solid phase concentrations in the flow during hydraulic transportation of overflow hydrocycloning products via 800–1000 mm metal pipes with a mass fraction of the solid phase of 17 % (±5 %), as well as to develop recommendations for the design of tailing facilities of the Kachkanar GOK. The experiments conducted have established that specific head losses are directly proportional to concentrations of the solid phase in the tailings slurry. Higher solid phase concentrations and hydrotransport system throughput lead to increased pressure losses. This happens because elevated solid phase concentrations trigger the manifestation of rheological properties of the slurry in the liquid flow, affecting the specific head loss. The research results obtained are reflected in the reconstruction and development design for the plant.

Spontaneous condensation of carbon dioxide in flue gas at supersonic state

A cleaning method of removing CO2 from flue gas by supersonic flow is investigated. A condensation flow model is developed based on the classical droplet nucleation and growth theory. The non-equilibrium phase transition in supersonic flow is predicted by adding transport equations. The effects of converging-diverging nozzle, inlet subcooling and gas composition on CO2 spontaneous condensation in flue gas are studied. The results show that the nozzle with Witoszynski curve is the first to nucleate, at x = 0.121 m. Without considering the backpressure, the shrinkage ratio and diverging angle only affect the flow behavior behind the throat. With the increase of shrinkage ratio or diverging angle, the liquid mass fraction increases from 0.062 to 0.085 and 0.056 to 0.089 respectively, but there are hazards such as increased pressure loss and reduced nozzle flow rate. The diverging length has no significant effect on the flow behavior but the increase of length can prolong the droplet growth time. The higher inlet subcooling not only makes the supersonic flow reach the critical state in advance, from x = 0.121 m to x = 0.111 m, but also significantly improves the droplet growth rate, from 0.649 m/s to 0.854 m/s. The increase of CO2 concentration greatly enhances the mass and heat transfer process.

Turbulent convective heat transfer behavior of supercritical water flowing upward in 2 × 2 rod bundle channels with various spacers

The turbulent flow and heat transfer characteristics of supercritical water, flowing in vertical 2 × 2 rod bundle channel, are numerically investigated to find useful methods to improve the cooling performance in the core of a supercritical water-cooled reactor. The heat transfer behavior as a function of mass flux and inlet temperature is analyzed and discussed. Standard grid and helical wire spacers are added to the channel, and overall heat transfer performance is evaluated and compared. The results indicate that the fuel rods can be cooled more effectively when the fluid temperature is near the pseudocritical point due to the high specific heat capacity at this temperature and pressure, and the local heat transfer coefficient can be improved greatly from the application of grid spacers; however, heat transfer enhancement only happens in limited regions downstream of the grid spacers. By contrast, strong swirl flow can be induced by a helical wire, thus the mixing of coolant is strengthened, and the convective heat transfer is enhanced. However, local hot spots also occur in the region near the wires. Both grid and helical wire spacers will lead to an increase in pressure loss, but the additional pressure drop induced by the helical wire is smaller, hence better comprehensive heat transfer performance is achieved for a wire-wrapped channel. Moreover, heat transfer performance can also be enhanced by reducing the pitch of the spacers. This suggests that applying spacers and optimizing their configurations and structures is helpful to achieving better cooling performance in rod bundle channels.

Modified Stirling cycle thermodynamic model IPD-MSM and its application

A Stirling cycle is a thermoelectric conversion method with high efficiency and reliability. The Stirling cycle applies to small- and medium-sized power space nuclear reactors or radioisotope heat sources. A high-precision and well-predicted Stirling cycle thermodynamic model is the key to optimizing and improving the Stirling engine for space. The present study modified the classical Simple model by incorporating the local pressure loss into the pressure loss. An improved second-order adiabatic model based on the Simple model, namely the Incorporated Pressure Drop-modified Simple Model (IPD-MSM), was proposed. The prediction of the IPD-MSM shows well with the changing tendency of the GPU-3 Stirling engine experimental data. Moreover, this model has better prediction accuracy at high-pressure and high-frequency conditions than other adiabatic models, such as CAFS and ISAM. The thermodynamic properties of He, H2, and Helium-Xenon mixtures in the Stirling cycle were also analyzed. Results show that the He-Xe mixture reaches the highest output power and thermal efficiency when the mole percentage of Xe is approximately 2%. The mechanism is as follows: the addition of Xe leading to the reduction in non-ideal heat transfer loss exceeds the increase in pressure loss. The addition of Xe leads the pressure loss to increase abruptly as the mole percentage of Xe exceeds 2%. The characteristics and application analysis of H2, He, and He-Xe mixture were discussed. The present study provided theoretical support for the Stirling cycle analysis for space missions and the selection of working fluids.