Small Clearance Research Articles

Pulsed peritoneal dialysis in an experimental rat model: A first experience.

Peritoneal dialysis (PD) is commonly performed using either intermittent or tidal exchanges, whereas other exchange techniques such as continuous flow PD are little used. Previous research indicated that stirring the intra-peritoneal dialysate markedly increases small solute clearances. Here, we tested the hypothesis that stirring of the dialysate increases small solute clearances by using a novel exchange technique where the dialysate is pulsed back and forth during the treatment without addition of fresh fluid. PD was performed in anesthetized Sprague-Dawley rats with either no pulsations (20 mL fill volume), 2 mL (10%) pulses (21 mL fill volume), or 5 mL (25%) pulses (22.5 mL fill volume) utilizing a pulse flow rate of 5 mL/min. The higher fill volume for the pulsed treatments compensates for the fact that the average intra-peritoneal volume would otherwise be lower in pulsed treatments. Water and solute transport were closely monitored during the treatment. Net ultrafiltration decreased significantly during pulsed PD with the 25% pulse volume. The 60 min sodium dip was unaltered, whereas the fluid absorption rate was increased for the 25% group. Solute clearances did not significantly differ between groups, except for a slightly lower calcium clearance in the 25% group. Our data indicate that stirring the dialysate using pulsed exchanges does not provide any advantage compared to conventional exchange techniques. In contrast, pulsed treatments had slightly lower ultrafiltration and small solute transport. The present findings may have implications regarding the choice of tidal volume in automated PD, favoring smaller tidal volumes.

Research on Working Mechanism and Structural Optimization of High-Speed Bearing of Tricone Bits Based on Finite Difference Method

Abstract To analyze the working mechanism of the floating sleeve bearing of the cone bit, the life of the floating sleeve bearing was tested. The experimental results show that adhesive wear will form on the bearing surface with the increase in temperature, which is the main cause of bearing failure. This article establishes the Reynolds equation and energy equation of the oil film based on the theory of dynamic pressure lubrication of sliding bearings. The equation was numerically solved based on the finite difference method. It determines the rotational speed ratio at the equilibrium based on the trend of the frictional torque and then corrects the eccentricity in the iterative calculation process so as to analyze the tribological performance of the bearings in equilibrium under different clearance ratios. Among them, the improper configuration of the internal and external clearance ratio leads to the increase of the friction torque and the reduction of the bearing capacity. For floating sleeve bearings, the configuration with a large internal clearance and small external clearance should be adopted. Finally, the bearing structure is optimized and numerical calculations show that the tribological performance of the new type of bearings is significantly improved compared with that of ordinary cone bit bearings.

Ticagrelor modestly raises plasma riboflavin concentration in humans and inhibits riboflavin transport by BCRP and MRP4.

Riboflavin (vitamin B2) has been proposed as a biomarker for breast cancer resistance protein (BCRP) activity. In recent studies in mice, cynomolgus monkeys, and humans, BCRP-inhibiting drugs increased the plasma concentration of riboflavin. We showed recently that ticagrelor inhibits BCRP and raises the plasma concentrations of the BCRP substrate rosuvastatin in healthy volunteers. In the same drug-drug interaction study, we now investigated whether ticagrelor affects the plasma concentrations of riboflavin. Intake of 90 mg ticagrelor increased the ratio between the peak plasma riboflavin concentration and the fasting riboflavin concentration before ticagrelor administration by 1.20-fold (90% confidence interval, 1.10-1.32; P = 0.006) compared to placebo. In vitro, riboflavin was transported by BCRP and multidrug-resistance-associated protein 4 (MRP4) but no clear transport was observed by MRP2, MRP3, or the P-glycoprotein. Moreover, ticagrelor inhibited the transport of riboflavin in BCRP- and MRP4-expressing membrane vesicles with unbound 50% inhibitory concentrations of 0.020 and 1.1μM, respectively. Based on vesicle and tissue protein expression data, the small intestinal MRP4-mediated efflux clearance of riboflavin (1.2-1.4 nL/min/mg) was estimated to be similar to that mediated by BCRP (0.23-1.3 nL/min/mg). As MRP4 is expressed in the basolateral membrane of enterocytes, it may facilitate the absorption of riboflavin and impair the utility of riboflavin as a biomarker of intestinal BCRP. To conclude, ticagrelor modestly raises the plasma concentration of riboflavin probably by inhibiting intestinal BCRP. Inhibition of intestinal MRP4 may have reduced the absorption of riboflavin and limited the effect of ticagrelor on riboflavin levels.

Performance analysis of air-cooled turbine based on source terms method

Abstract Investigating turbine blade cooling and blade tip clearance leakage is crucial for reducing turbine losses and enhancing overall engine performance. Therefore, this paper uses the E3 two-stage high-pressure turbine as a case and employs the source term method to model the film cooling configuration, validating its efficacy and examining the performance parameters and flow field characteristics of air-cooled turbines under varying blade tip clearances. The outcomes demonstrate that the source term approach accurately forecasts the comprehensive performance parameters of air-cooled turbines, with blade tip clearance height predominantly impacting turbine performance in high-velocity regions. For small blade tip clearance, air-cooled turbines exhibit diminished efficiency with a decreasing expansion ratio in high-velocity regions, but they demonstrate an inverse behavior in low-velocity regions. Conversely, under conditions of larger blade tip clearances, the cooling effectiveness of air-cooled turbines is more pronounced in regions characterized by low expansion ratios and low speeds.

Thermal–Hydraulic Performance Analysis of Combined Heat Sink with Open Microchannels and Embedded Pin Fins

An open type of microchannel with diamond pin fins (OM-DPFs) is introduced for the cooling of high-performance electronic chips. For a Reynolds number (Re) of 247~1173, a three-dimensional model is established to explore the hydrothermal properties of the OM-DPF and compare it to traditional heat sinks with closed rectangular microchannels (RMs), heat sinks with open microchannels (OMs), and the results in the existing research. Firstly, the synergy between tip clearance and pin fins on the hydrothermal properties is discussed. Secondly, the entropy production principle is adopted to analyze the irreversible losses for different heat sinks. Lastly, the total efficiencies of different heat sinks are assessed. The RMs present the worst heat transfer with the lowest friction loss. For the OMs, the temperature and pressure drop are decreased slightly compared to those of the RMs, and the irreversible loss is reduced by 4% at Re = 1173 because of the small tip clearance. But the total efficiency is lower than that of the RMs because the pressure drop advantage is offset by the weak heat transfer. For the OM-DPF, the combined structure has a noticeable impact on the multiple physical fields and hydrothermal characteristics, which present the best thermal performance at the cost of the highest friction loss. The irreversible loss of heat transfer in the OM-DPF is reduced obviously, but the friction irreversible loss significantly increases at high Re values. At Re = 429, the total entropy production of the OM-DPF is reduced by 47.57% compared with the RM. Compared to the OM and the single-pin fin structure in the literature, the total efficiency of the OM-DPF is increased by 14.56% and 40.32% at Re = 614. For a pump power of 0.1 W, the total thermal resistance (Rth) of the OM-DPF is dropped by 23.77% and 21.19% compared to the RM and OM. For a similar Rth, the pump power of the combined structure is 63.64% and 42.86% lower than that of the RM and OM. Thus, the novel combined heat sink can achieve efficient heat removal while controlling the energy consumption of liquid cooling systems, which has bright application prospects.

Relationship between fill volume and transport in peritoneal dialysis-from bench to bedside.

Larger fill volumes in peritoneal dialysis (PD) typically improve small solute clearance and water removal, and vice versa-but the relationship between intraperitoneal volume and the capacities for solute and water transport in PD has been little studied. Here, it is proposed that this relative relationship is described by a simple ratio (Volumenew/Volumeold)2/3 up to a critical break-point volume, beyond which further volume increase is less beneficial in terms of solute and water removal. To scrutinize this hypothesis, experiments were conducted in a rat model of PD alongside a retrospective analysis of data from a prior clinical study. Rats underwent PD with either three consecutive fills of 8 + 8 + 8 mL (n = 10) or 12 + 12 + 12 mL (n = 10), with 45-minute dwell time intervals. This approach yielded 60 estimations of water and solute transport, characterized by osmotic conductance to glucose and solute diffusion capacities, respectively. Comparative analysis of the predictive efficacy of the two models-the simple ratio versus the break-point model-was performed using Monte Carlo cross-validation. The break-point model emerged as a superior predictor for both water and solute transfer, demonstrating its capability to characterize both experimental data from rats and clinical data from patients. The present analysis indicates that relatively simple calculations can be used to approximate clinical effects on solute and water removal when prescribing a lower or higher fill volume to patients with PD.

Dynamic analysis of whipping behavior induced by the circumferential fracture of high energy pipes considering fluid-structure interaction effect

To analyze the dynamic characteristics of whipping behavior induced by the circumferential fracture of high energy pipes, a numerical model of the piping system was presented based on the bidirectional fluid-structure interaction method. The reliability of this model was validated against experimental results. Furthermore, the dynamic characteristics of whipping behavior were studied, as well as the effects of some main parameters. The numerical results suggest that the entire whipping behavior can be divided into four stages: free-whipping stage Ⅰ, free-whipping stage Ⅱ, collision stage and periodic stage. The dynamic response of whipping behavior is different in the four stages and is dominated by a single mode with a frequency of 29.35 Hz under the combined action of the thrust force and U-bolt restraints. The increase of inlet flow rate causes the enhancement of thrust force and thus makes its dynamic response more complicated. The parameter analysis shows that the whipping behavior can be suppressed by choosing the small initial clearance, setting the suitable gap and increasing the straight segment length of U-bolt restraints. The above results are helpful to understand the dynamic characteristics of whipping behavior and provide valuable suggestions for the optimization of the protection measures.

Heat-Dissipating Mobile Antenna: A Novel Mobile Antenna Concept with Extremely Small Clearance and Integrated Heat-Dissipating Function

Heat-Dissipating Mobile Antenna: A Novel Mobile Antenna Concept with Extremely Small Clearance and Integrated Heat-Dissipating Function

Turbulent flow field in maglev centrifugal blood pumps of CH-VAD and HeartMate III: secondary flow and its effects on pump performance.

Secondary flow path is one of the crucial aspects during the design of centrifugal blood pumps. Small clearance size increases stress level and blood damage, while large clearance size can improve blood washout and reduce stress level. Nonetheless, large clearance also leads to strong secondary flows, causing further blood damage. Maglev blood pumps rely on magnetic force to achieve rotor suspension and allow more design freedom of clearance size. This study aims to characterize turbulent flow field and secondary flow as well as its effects on the primary flow and pump performance, in two representative commercial maglev blood pumps of CH-VAD and HeartMate III, which feature distinct designs of secondary flow path. The narrow and long secondary flow path of CH-VAD resulted in low secondary flow rates and low disturbance to the primary flow. The flow loss and blood damage potential of the CH-VAD mainly occurred at the secondary flow path, as well as the blade clearances. By contrast, the wide clearances in HeartMate III induced significant disturbance to the primary flow, resulting in large incidence angle, strong secondary flows and high flow loss. At higher flow rates, the incidence angle was even larger, causing larger separation, leading to a significant decrease of efficiency and steeper performance curve compared with CH-VAD. This study shows that maglev bearings do not guarantee good blood compatibility, and more attention should be paid to the influence of secondary flows on pump performance when designing centrifugal blood pumps.

Shared-Aperture Three-Antenna Module Using a Single Floating Metal With Small Clearance for 5G Mobile Terminals

Shared-Aperture Three-Antenna Module Using a Single Floating Metal With Small Clearance for 5G Mobile Terminals

A new contact force model for revolute joints considering elastic layer characteristics effects

The contact forces generated during the motion of revolute joints with clearances significantly impact the dynamic performance of mechanisms, making it essential to develop an accurate contact force model. Traditional contact models often neglect the influence of elastic layers or assume that the bushing thickness is equal to its radius, which limits their applicability. To address the dynamic contact problem in revolute joints with small clearances, this study employs an improved Winkler elastic foundation model and introduces an elastic layer correction coefficient to refine the static contact model. The model's validity is verified using the finite element method. Building on this, a new contact force model is proposed, incorporating the optimal damping term from multiple continuous contact models. Finally, experimental validation is conducted using the crank-slider mechanism and typical applications in the Variable Stator Vane (VSV) mechanism. The results demonstrate that the proposed contact force model effectively predicts the dynamic characteristics of mechanisms with clearances.

Effect of Trailing Edge and Span Morphing on the Performance of an Optimised NACA6409 Wing in Ground Effect

Abstract A CFD investigation was carried out on a three-dimensional NACA6409 wing in ground effect at a Reynolds number of 320,000. Using a Multi-Objective-SHERPA algorithm, a root angle of 4 degrees angle of attack, a tip angle of 6 degrees, a forward sweep and a tip chord of 20% of the root chord produced an optimum aerodynamic efficiency across all ground clearances. Optimisation showed a gain in aerodynamic efficiency of 41% at h/c = 0.05 ground clearance and a 31% gain at h/c = 0.2 compared to a rectangular planform wing. Next FishBAC camber morphing was applied to the optimised wing varying the morphing start locations along the chord at both the tip and root. A later start location produced the highest aerodynamic efficiency but increased manufacturing complexity. Extendable span morphing was also tested and was found increasing the span from 1c to 1.5c increased the aerodynamic efficiency of the optimised wing by 27.4% at h/c = 0.1. Varying the span from 0.8c to 1.2c in ground effect had a small effect on the drag for small ground clearances, for large ground clearances the total drag decreased as the span increased. Smaller gains were seen when the span morphing was applied to the rectangular wing. The FishBAC morphing was applied in the spanwise direction to morph the wing tip, sealing the flow beneath the wing. Also, the proportion of the morphing wing tip caused the trailing edge to be closer to the ground further enhancing ground effect.

Development of a wafer cooling system using ionic liquid under high vacuum condition for semiconductor fabrication device

Herein, vacuum-compatible semiconductor-wafer-immersion-cooling method is proposed as an alternative to helium gas cooling, which becomes challenging to maintain in high-vacuum conditions during semiconductor manufacturing. This method aims to simultaneously maintain a high vacuum and achieve high cooling performance. It involves supplying a low-vapor-pressure ionic liquid (IL), a type of room-temperature molten salt, into the gap between the wafer and the wafer stage, using liquid pressure to float and cool the wafer. The proposed cooling device was prototyped, and experimentally investigated the IL cooling performance. The results showed that, even under high vacuum with order of 10−4 Pa, IL can fully immerse the 80 μm-scale small clearance between wafer and wafer stage and demonstrate high cooling performance for heated wafers. The proposed method has been proven to achieve both high vacuum and high cooling performance. It is expected as an alternative to helium gas cooling in semiconductor manufacturing.

Online Hemodiafiltration: A New Perspective for Patients With End-Stage Renal Disease.

Introduction Online hemodiafiltration (OL-HDF) is the most effective renal replacement therapy (RRT), which allows the enhanced removal of small and large uremic toxins by combining diffusion and convective transport of solutes. Although the goal of OL-HDF is to provide greater clearance of solutes with a preference for intermediate molecules responsible for many of the complications of chronic kidney disease (CKD), the studies reported to date and their meta-analyses are conflicting in nature and do not show a significant advantage of convective therapies on patient prognosis. Materials and methods At the Clinic of Nephrology and Dialysis, University Hospital "St. Marina", Varna, Bulgaria, 41 patients were monitored in a retrospective study for a two-year period, randomized into two groups, conducting OL-HDF after dilution and hemodialysis (HD) with the aim of studying the effect of convective therapies on the clinical outcome, the achieved quality of life, and the prognosis of the patient. Results The study found a significantly higher quality of life in patients undergoing OL-HDF with significantly higher values ​​of indicators of dialysis adequacy and nutritional status, better control of the anemic syndrome with the reduction of erythropoietin doses, significantly lower frequency of episodes of intradialytic hypotension with improved recovery, and 3.6-fold lower risk of death compared with conventional dialysis. Discussion Three major randomized controlled trials have compared survival outcomes in patients receiving HD or post-dilution OL-HDF, reporting conflicting results. Meta-analyses of the published studies have also been unable to provide a clear and definitive answer regarding the potential benefits of choosing one treatment over the other. Overall mortality, anemia, phosphate control, and small molecule clearance appear to be insufficiently influenced by the treatment method. On the other hand, cardiovascular mortality, hemodynamic stability, and clearance of middle and protein-bound molecules seem to be better in patients treated with OL-HDF. Conclusions Despite the conflicting data reported so far, OL-HDF is associated with better clinical outcome and prognosis for end-stage renal disease (ESRD) patient and undoubtedly warrants extensive future study with a view to improved quality of life in the growing dialysis population.

Stability Analysis of the Secondary Motion of a Textured Piston

Piston–cylinder pairs are very common in industrial mechanisms. While a piston is primarily designed for axial reciprocating motion, the occurrence of secondary motions—lateral and rotational—due to the small clearance between the piston and the cylinder may lead to frictional contact, energy loss, wear and an increase in unwanted leakage. This study focuses on mitigating the secondary motion of a ringless piston. The influence of a Rayleigh step bearing and partial surface texturing with numerous micro-dimples on the dynamic stability of the secondary motion is studied. A linear model was used to obtain the trajectory of the secondary motion and Floquet theory was applied to analyze the stability and draw stability maps. The influence of various texturing and step parameters, including the dimple area density and aspect ratio for partial texturing, as well as the length and depth of treatment for both partial texturing and step profiles, on the stability of the secondary motion was examined. The normalization method is presented, enabling the expansion of the results for various operating conditions and geometries. Conclusions and guidelines regarding the optimal parameters, in terms of a wider stability range and higher decay rate, are formulated.

THE INFLUENCE OF SMALL CLEARANCES IN THE SPHERICAL JOINTS OF THE SYSTEMS ON THEIR DYNAMIC RESPONSE

The paper highlights the influence of small clearances in the spherical joints on their natural frequencies and modes of vibration. Joints with bearings made of materials that involve low friction in the coupling (Teflon and HDPE polyethylene) were considered.Two cases of coupling by means of the spherical joints were considered, namely: the coupling angle of the bars in the spherical joint being of 00 and of 900, respectively.The size of the clearance influences the first natural frequency of the system in the sense of decreasing it, but also in the modification of the vibration modes of the system when even a small clearance appears in the joint.

Structure optimization design approach of friction pairs for low-temperature rise wet brake in hydraulic motor

Cam-lobe radial-piston hydraulic motors are widely used in large heavy-duty machinery as direct-drive components of hydraulic systems. Due to their extremely high output torque and power density, the wet brake equipped with the hydraulic motors are necessary to achieve ultra-high braking torque in a compact space. However, due to a large number of internal friction pairs and small fit clearance between multiple friction pairs in wet brake, the rotation of the friction pairs in non-braking state will cause large friction torque loss and obvious temperature rise, thereby leading to the thermal failure of wet brake. How to optimize the structure of friction pairs to reduce the temperature rise of wet brake in non-braking state is a persistent challenge. Existing structure optimization design approaches of friction pairs in brakes mainly focus on the structure of each friction pair, which ignore the effect of fit clearance between the friction pairs on the temperature rise of brakes. Nevertheless, the fit clearance between friction pairs is an important factor that affect the temperature rise. For that, this study proposes a two-step structure optimization design approach of friction pairs for low-temperature rise wet brake in hydraculic motor, which simultaneously considers the fit clearance between the friction pairs and the structure of each friction pair. In this approach, the design process could be divided into two steps: firstly, the influence of fit clearance between multiple friction pairs on the temperature rise of wet brake in non-braking state is analyzed and optimized by the temperature rise theoretical model; secondly, in order to further reduce the temperature rise of wet brake, the oil groove structure of each friction plate are introduced and optimized by fluid-solid-thermal coupling simulation method. By this approach, the low-temperature rise structure of friction pairs with the optimized fit clearance between multiple friction pairs and oil grooves of each friction plate. Finally, a series of experiments are conducted to verify the effectiveness of the design approach. The result show that the temperature rise of wet brake could be effectively reduced 12 % by optimizing the structure of wet brake, demonstrating that the structure optimization design approach could provide a theoretical guidance to design low-temperature rise wet brake for large torque hydraulic motors.

Failure Inducement Factor Analysis and Optimal Design Method of Ball Bearing Cage for Aviation Motor

In experiments of aviation motor bearings, when the deep-groove ball bearings are subjected to an overturning moment at high speed, it often happens that the rivet on the cage breaks and the debris invades the raceway, resulting in bearing failure. To address the problem of early failure of deep-groove ball bearing cages and rivets in aviation motors, the causes of early failure were analyzed from the aspect of cage design in this study. The influence of the raceway and cage structure parameters on the dynamic contact characteristics of the rolling element and cage under the action of overturning torque were analyzed, the weak link of the cage was determined, and the cage design parameters were optimized. The results show that with an increase in the cage width and pocket radius, the impact force between the ball and cage first decreases and then increases, and the tilt angle of the cage gradually decreases. A larger channel radius and smaller clearance can slow down the interaction between the cage and the rolling element and make the cage run more smoothly. Increasing the thickness of the cage can ensure that the rivet part of the cage is at a low stress level, and the risk of premature fatigue failure at the rivet part can be reduced by maintaining a small gap–fit relationship between the rivet and rivet holes. The research results indicate that the working condition adaptability of the bearing cage for aviation motors can be improved, and the design method for this type of bearing can be enhanced.

Thermo-Fluid–Structural Coupled Analysis of a Mechanical Seal in Extended Loss of AC Power of a Reactor Coolant Pump

We proposed a numerical method to investigate the thermo-fluid–structural coupled characteristics of a mechanical seal of a reactor coolant pump (RCP), especially during extended loss of AC power (ELAP) operation. We developed a finite element program for the general Reynolds equation, including the turbulence effect to calculate the pressure, opening force, and leakage rate of fluid lubricant and the two-dimensional energy equation to calculate the temperature distribution of the fluid lubricant. We verified the accuracy of the developed program by comparing the simulated temperature distribution and leakage rate of this study with those of previous research. Heat conduction and elastic deformation due to pressure and temperature changes at the seal structure were analyzed using an ANSYS program. The results showed that temperature more significantly affected the elastic deformation of the seal structure near clearance than pressure both under normal and ELAP operating conditions. High temperature and pressure of the coolant under ELAP operating conditions deform the seal structure, resulting in a much smaller clearance of the fluid film than normal operating condition. However, even with a small clearance under ELAP operation, the leakage rate slightly increases due to the high internal pressure of the coolant. This research will contribute to the development of robust mechanical seals for RCPs by accurately predicting the characteristics of mechanical seals, especially when the RCP is operating under ELAP.

The impact of dialysate flow rate on haemodialysis adequacy: a systematic review and meta-analysis.

Patients with kidney failure treated with maintenance haemodialysis (HD) require appropriate small molecule clearance. Historically, a component of measuring 'dialysis adequacy' has been quantified using urea kinetic modelling that is dependent on the HD prescription. However, the impact of dialysate flow rate on urea clearance remains poorly described in vivo and its influence on other patient-important outcomes of adequacy is uncertain. We searched Embase, MEDLINE and the Cochrane Library from inception until April 2022 for randomized controlled trials and observational trials comparing a higher dialysate flow rate (800ml/min) and lower dialysate flow rate (300ml/min) with a standard dialysis flow rate (500ml/min) in adults (age ≥18years) treated with maintenance HD (>90 consecutive days). We conducted a random effects meta-analysis to estimate the pooled mean difference in dialysis adequacy as measured by Kt/V or urea reduction ratio (URR). A total of 3118 studies were identified. Of those, nine met eligibility criteria and four were included in the meta-analysis. A higher dialysate flow rate (800ml/min) increased single-pool Kt/V by 0.08 [95% confidence interval (CI) 0.05-0.10, P<.00001] and URR by 3.38 (95% CI 1.97-4.78, P<.00001) compared with a dialysate flow rate of 500ml/min. Clinically relevant outcomes including symptoms, cognition, physical function and mortality were lacking and studies were generally at a moderate risk of bias due to issues with randomization sequence generation, allocation concealment and blinding. A higher dialysate flow increased urea-based markers of dialysis adequacy. Additional high-quality research is needed to determine the clinical, economic and environmental impacts of higher dialysate flow rates.