Tilting pad thrust bearings are the key components in hydropower units. As the thrust loads increase with the unit capacities of the hydro turbines, many thrust bearings failed due to rub-impacts ...between the collar and pads. Some plants have to be shut down for up to one month to repair the damaged pads which has lead to enormous economic losses. The lubrication processes of thrust bearings are quite complex involving fluid-thermal-structural interactions between the pad, the collar, the oil film and the oil surrounding the pad. This paper reviews the bearing mechanism including the thermal-elastic deformation, the transient and dynamic characteristics, the bidirectional thrust bearing, as well as the various prediction methods on the lubrication performance. At last, an overview of some special designs including the covered materials, supporting system and hydrostatic jacking system to improve the thrust lubrication was briefly presented.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Multiple rib fractures (≥ 3 displaced rib fractures and/or flail chest) are severe chest trauma with high morbidity and mortality. Rib fixation has become the first choice for multiple rib fracture ...treatment. However, the timing of surgical rib fixation is unclear.
The present study explored whether early rib fracture fixation can improve the outcome of multiple rib fractures. The present research included patients who were hospitalized in three Jiangsu hospitals following diagnosis with multiple rib fractures. Patients received early rib fracture fixation (≤ 48 h) or delayed rib fracture fixation (> 48 h) utilizing computer-based random sequencing (in a 1:1 ratio). The primary outcome measures included hospital length of stay, intensive care unit (ICU) stay, mechanical ventilation, inflammatory cytokine levels, infection marker levels, infection, and mortality.
A total of 403 individuals were classified into two groups, namely, the early group (n = 201) and the delayed group (n = 202). Patients belonging to the two groups had similar baseline clinical data, and there were no statistically significant differences between them. Early rib fracture fixation greatly decreased the length of stay in the ICU (4.63 days vs. 6.72 days, p < 0.001), overall hospital stay (10.15 days vs. 12.43 days, p < 0.001), ventilation days (3.67 days vs. 4.55 days, p < 0.001), and hospitalization cost (6900 USD vs. 7600 USD, p = 0.008). Early rib fracture fixation can decrease inflammatory cytokine levels and infection marker levels, prevent hyperinflammation and improve infection in patients with multiple rib fractures. The timing of rib fracture fixation does not influence the surgical procedure time, operative blood loss, 30-day all-cause mortality, or surgical site infection.
The findings from the present research indicated that early rib fracture fixation (≤ 48 h) is a safe, rational, effective and economical strategy and worth clinical promotion.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Purpose: A bipolar plate with fractal-characterized microstructures can realize intelligent energy transmission and obtain a high efficiency of proton-exchange membrane fuel cells. In this paper, ...fixed abrasive lapping technology is proposed to fabricate a surface microstructure on a bipolar plate with fractal characteristics. Methodology: The kinematics of the fixed abrasive lapping process was developed and employed to numerically investigate the particle trajectories moving on the target surface by considering the different arraying forms of diamonds on the lapping plate. Findings: It was found from an analysis of both the uniformity and the fractal characteristics that the arraying form of diamonds on the lapping plate, with the distribution of latitude and longitude with an angle of 30° and a gap of concentric circles of 40 mm with a minimum radius of 70 mm and maximum radius of 190 mm, can be used to obtain the best uniformity and fractal characteristics in the fixed abrasive lapping of a bipolar plate. Conclusions: The distribution of the latitude and longitude of 40° and 30° considered in this study is expected to realize the best machining performance in the bipolar plate and present good cell performance.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Submerged systems are found in many engineering, biological, and medicinal applications. For such systems, due to the particular environmental conditions and working medium, the research on the ...mechanical and structural properties at every scale (from macroscopic to nanoscopic), and the control of the system dynamics and induced effects become very difficult tasks. For such purposes in submerged systems, piezoelectric patches (PZTp), which are light, small and economic, have been proved to be a very good solution. PZTp have been recently used as sensors/actuators for applications such as modal analysis, active sound and vibration control, energy harvesting and atomic force microscopes in submerged systems. As a consequence, in these applications, newly developed transducers based on PZTp have become the most used ones, which has improved the state of the art and methods used in these fields. This review paper carefully analyzes and summarizes these applications particularized to submerged structures and shows the most relevant results and findings, which have been obtained thanks to the use of PZTp.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Pumped-storage power stations play a regulatory role in the power grid through frequent transition processes. The pressure pulsation in the draft tube of the pump-turbine under transient processes is ...important for safe operation, which is more intense than that in the steady-state condition. However, there is no effective method to obtain the exact pressure in the draft tube in the transient flow field. In this paper, the pressure in the draft tube of a pump-turbine under steady-state and transient conditions are studied by means of CFD. The reliability of the simulation method is verified by comparing the real pressure pulsation data with the test results. Due to the distribution of the pressure pulsation in the draft tube being complex and uneven, the location of the pressure monitoring points directly affects the accurate judgement of cavitation. Eight monitoring surfaces were set in the straight cone of the draft tube and nine monitoring points were set on each monitoring surface to analyze the pressure differences on the wall and inside the center of the draft tube. The relationships between the pressure pulsation value inside the center of the draft tube and on the wall are studied. The “critical” wall pressure pulsation value when cavitation occurs is obtained. This study provides references for judging cavitation occurrences by using the wall pressure pulsation value in practical engineering.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Transient processes that occur in pumped storage power plants can cause high-pressure conditions, which in turn can result in vibrations in the pump–turbine structure and even damage to structural ...components. It is therefore crucial to research the transient process of the large pump–turbine units and the flow-induced vibrations of the structural components. The three-dimensional flow field and structural field models of a high-head prototype pump–turbine were constructed to study its flow characteristics and structural characteristics under the turbine start-up. Calculations and analyses were performed on the pressure variation and the flow-induced stress concentrations of the pump–turbine during start-up in turbine mode. The simulated pressure distributions during the turbine start-up were mapped onto the finite element calculation model of the structures of the pump–turbine to calculate the flow-induced stress concentrations. This study provides a reference to improve the design and operation of high-head prototype pump–turbines based on the findings of the flow and structural characteristics.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
The Generation IV Lead-cooled fast reactor (LFR) take the liquid lead or lead-bismuth eutectic alloy (LBE) as the coolant of the primary cooling circuit. Combined with the natural characteristics of ...lead alloy and the design features of LFR, the system is the simplest and the number of equipment is the least, which reflects the inherent safety characteristics of LFR. The nuclear main coolant pump (MCP) is the only power component and the only rotating component in the primary circuit of the reactor, so the various operating characteristics of the MCP are directly related to the safety of the nuclear reactor. In this paper, various working conditions that may occur in the normal rotation (positive rotating) of the MCP and the corresponding internal flow characteristics are analyzed and studied, including the normal pump condition, the positive-flow braking condition and the negative-flow braking condition. Since the corrosiveness of LBE is proportional to the fluid velocity, the distribution of flow velocity in the pump channel will be the focus of this study. It is found that under the normal pump condition and positive-flow braking conditions, the high velocity region of the impeller domain appears at the inlet and outlet of the blade. At the same radius, the pressure surface is lower than the back surface, and with the increase of flow rate, the flow separation phenomenon is obvious, and the turbulent kinetic energy distribution in impeller and diffuser domain shows obvious near-wall property. Under the negative-flow braking condition, there is obvious flow separation in the impeller channel.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Cavitation is an important issue in pumps and usually starts on the blade leading-edge. For fixed blades with constant rotational speeds and specific flow rates, the incident angle, which is between ...the flow direction and the blade installing direction, on the blade leading-edge plays the key role in the cavitation process. The leading-edge shape is crucial on the local flow separation, pressure distribution, and cavitation. Hence, the influence of the leading-edge shape on cavitation has been studied in the current work in a centrifugal pump impeller. The blunt, sharp, ellipse and round leading-edge cases were compared using numerical simulation and verified by experimental data. Results show different features of cavitation. The round and ellipse leading-edge impellers have higher inception cavitation coefficient. It was caused by the sudden pressure drop on leading-edge arc or elliptical arc. The sharp and blunt leading-edge impellers have a wide flow-separation region on leading-edge with a wide low-pressure region. This is because of the sudden turn in geometry on the leading-edge corner. Cavitation grew quickly after inception and caused rapid head-drop in the sharp and blunt leading-edge impellers. Results suggest the critical cavitation performance is dominated by the leading-edge low-pressure area while the inception cavitation is mostly affected by the minimum pressure value on the leading-edge. The critical cavitation performance can be evaluated by checking the leading-edge low-pressure area. The inception cavitation can be evaluated by checking the minimum pressure value on the leading-edge. These strategies can be used in the further leading-edge designs.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Pump–turbine units with high heads are subjected to strong pressure pulsations from the unsteady transient flow in fluid channels, which can produce severe vibrations and high stresses on the ...pump–turbine structural components. Therefore, reducing transient flow-induced stresses on prototype reversible pump–turbine units is an important measure for ensuring their safe and efficient operation. A high-head prototype reversible pump–turbine with a rated head of 440 m was used to investigate the transient flow characteristics and the flow-induced-stresses in this study. First, the flow passages of the pump–turbine unit and the structure of the reversible pump–turbine runner were constructed with CAD tools. Next, CFD simulations at the full load were performed to investigate the pressure pulsation characteristics of the pump turbine in both the time domain and the frequency domain. After this, the pressure files calculated by the CFD were exported and applied to a finite element model of the pump–turbine runner to calculate the transient flow-induced dynamic stresses. The results show that the pressure pulsations in the flow passage are closely related to the rotational speed, the guide vane number, and the runner blade number of the pump–turbine unit. The maximum flow-induced stresses on the pump–turbine runner at the full load were below 2 MPa and lower than the allowable value, which reveals that the designs of the pump–turbine runner and the flow passage are acceptable. The conclusions can be used as a reference to evaluate the design of high-head pump–turbines units. The approaches used to carry out the transient flow-induced stress calculations can be applied not only to pump–turbines units but also to other types of fluid turbomachinery such as pumps, turbines, fans, compressors, turbochargers, etc.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
The ventilation rate of cigarettes is an important indicator that affects the internal quality of cigarettes. When producing cigarettes, the unit may experience unstable ventilation rates, which can ...lead to a decrease in cigarette quality and pose certain risks to smokers. By establishing the ventilation rate prediction model, guide the design of unit parameters in advance, to achieve the goal of stabilizing unit ventilation rate, improve the stability of cigarette ventilation rate, and enhance the quality of cigarettes. This paper used multiple linear regression networks (MLR), backpropagation neural networks (BPNN), and genetic algorithm-optimized backpropagation (GABP) to construct a model for the prediction of cigarette ventilation rate. The model results indicated that the total ventilation rate was significantly positively correlated with weight (
P
< 0.01), circumference, hardness, filter air permeability, and open resistance. The results showed that the MLR models' (RMSE = 0.652,
R
2
= 0.841) and the BPNN models’ (RMSE = 0.640,
R
2
= 0.847) prediction ability were limited. Optimization by genetic algorithm, GABP models were generated and exhibited a little better prediction performance (RMSE = 0.606,
R
2
= 0.873). The results indicated that the GABP model has the highest accuracy in the prediction of predicting ventilation rate and can accurately predict cigarette ventilation rate. This method can provide theoretical guidance and technical support for the stability study of the ventilation rate of the unit, improve the design and manufacturing capabilities and product quality of short cigarette products, and help to improve the quality of cigarettes.
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