Post Impingement Research Articles

Experimentation and numerical modeling of SCR spray droplets pre and post impingement on a mixer plate

Selective Catalytic Reduction (SCR) systems are one of the leading techniques used in the after treatment systems of the diesel engines for the abatement of nitrogen oxides (NOx) emissions. Ammonia is used as reducing agent in the catalyst which is supplied in the mixing chamber in the form of Urea Water Solution (UWS - 32.5% urea solution) spray. After evaporation of water, urea droplets undergo a series of secondary reactions eventually leading to the formation of solid deposits on the walls of the system. This not only hinders the deNOx efficiency but also interferes with the overall after treatment system by creating back pressure. Therefore, a deep understanding of the factors and mechanisms of spray–wall interaction is a basic requirement to prevent any undesired decomposition phenomena that could lead to failure of the whole system.In the present paper, droplet diameter distributions are analyzed pre and post impingement events on a hot mixer plate surface, both experimentally and numerically. The work was performed using a commercial six-hole pressure driven injector in a test section of heated cross flow wind tunnel. Phase Doppler Anemometry (PDA) was used to measure the droplet kinetics prior and after the wall impingement on the mixer plate. Based on the data, numerical simulation was setup using a commercial CFD code, AVL FIRE and droplet characteristics as well as thermal response of the mixer plate analyzed against the experimental data.

Causes and Clinical Outcomes of Patellar Post Impingement.

BackgroundPatellar post impingement (PPI), which occurs when the post impinges on the patella, may reportedly cause poor total knee arthroplasty (TKA) outcomes. The causes of PPI and its effect on clinical outcomes and symptoms were investigated.Material and methodsThe study subjects were 100 patients who underwent TKA (65 posterior stabilized TKA, 35 bi-cruciate stabilized [BCS] TKA). Whether PPI occurred during surgery was investigated; the patients were then classified into a PPI+ group and a PPI– group, and whether the implant or patellar shape was related to the occurrence of PPI was examined. The measurement parameters included patellar shape, joint range of motion (ROM), and clinical outcome using the new Knee Society Score.ResultsThere were 38 knees in the PPI+ group and 62 knees in the PPI– group. There was no difference in patellar shape between the 2 groups, but PPI was more frequent in patients with short patellar tendon and those with low patellar height. In terms of implant type, the PPI+ group included 12 patients (18.5%) who underwent posterior stabilized TKA and 26 (74.3%) who underwent BCS TKA. There was no difference between the 2 groups in either joint ROM or new Knee Society Score. These results suggest that the position of the patella and implant shape that causes the post to be positioned anteriorly may contribute to PPI.ConclusionPPI occurred more frequently in knees with low patellar height and in patients who had undergone BCS TKA. PPI had no effect on joint ROM or clinical outcome.

증기발생기의 표준형 습분분리기 내부 유동 특성에 관한 수치해석

In the present study, a series of numerical analysis was performed to identify the flow characteristics inside the CE-type moisture separator applied to domestic steam generators. To investigate the similarity between normal operation condition of the prototype separator and experimental condition using air-water test facility with real scale and 1/2 scale test sections, single phase and two-phase calculations were carried out. The results of the single phase calculations showed that the outward flows through the flow holes on the wall turned out to be similar trend regardless of the working fluid and inlet conditions on real scale geometry. However, the pressure loss coefficient for the 1/2 scale geometry was relatively larger than that for the real scale geometry. In the two-phase calculation, Eulerian-Lagrangian method was adapted to investigate the behavior of the droplets. Two extreme conditions for the post impingement behavior of the droplet, which were escape and rebound conditions; were applied and the results between them were compared.

The role of viscous and capillary forces in the prediction of critical conditions defining super-hydrophobic and hydrophilic characteristics

The prediction of the superhydrophobic/superhydrophilic behavior from the characteristics of post impinged droplet on a surface with the alteration of physical properties of fluid or the surface properties has gained much interest for the development of anti-fogging glass, gradient surface and anti-corrosion surfaces. The abovementioned characteristics are well described by the spreading, recoiling, rolling, and bouncing behaviors of the post impinged droplet and these phenomena are controlled by viscous and capillary forces. The proper combination of the capillary and viscous forces of a fluid leads to various levels of recoiling and spreading. However, in terms of the discussed forces, the conditions to attain superhydrophobicity/superhydrophilicity are not reported. Therefore, in the current work, an attempt has been made to predict critical conditions for the attainment of both superhydrophobic and superhydrophilic characteristics in terms of fluid and surface properties defining the post impingement behavior. The analysis of droplet dynamics reveals that the ratio of viscous force to capillary force (VF/CF) is considered as the defining parameters for super-hydrophobic and hydrophilic characteristics. For the attainment of superhydrophilic characteristics, VF/CF ratio must be greater than 30 × 10−4 and value below 2.9 × 10−4 generates superhydrophobicity. Furthermore, the role of viscosity and surface tension in droplet dynamics were also investigated by using Central Composite Design (CCD) analysis methodology and it confirms the existence of strong interaction between the viscosity and surface tension.

Compression Test and Finite Element Analysis for Failure Criterion of the Tibial Post of a Posterior-Stabilized Knee Prosthesis

Post cam mechanism of Posterior Stabilized (PS) knee prostheses is useful to realize intrinsic stability for cases with severe degeneration. However, some retrieval studies report severe failure of the polyethylene tibial post. We thought that severe failures were caused by high loads during daily activities. In the current study, we performed a compression test and a finite element analysis of the mechanical forces produced in the tibial post in posterior-stabilized knee prostheses in order to develop a specification for the tibial posts found in the polyethylene inserts of PS knee prostheses. Anterior tibial post impingement and posterior tibial post impingement were simulated. The surface pressure values detected in the compression test were consistent with those obtained in the FE analysis. Of the three designs, the lowest von Mises stress values were generated inside the round tibial post; therefore, tibial posts should be round. The risk of tibial post failure was low when 500 or 1000 N was loaded onto the knee joint. It was suggested that tibial post failure occurs when the shear strain at the base of the tibial post exceeds 0.1.

Anterior Tibial Post Impingement During Stair Climbing: A Kinematic Analysis and Clinical Outcomes

BackgroundAnterior tibial post impingement during gait and stair ambulation was reported in knees with posterior-stabilized prostheses. However, the link between anterior post impingement and knee kinematics and between anterior post impingement and the clinical outcome has not been well investigated. Therefore, the purpose of this study was to assess the anterior impingement to clarify the relevant kinematics and clinical results including patient-reported outcomes. MethodsWe analyzed 40 well-functioning knees in 20 patients with a posterior-stabilized prosthesis due to osteoarthritis and who were followed up for 2 years or more. Dynamic lateral radiographs during stair-climbing activity were analyzed using a shape-matching technique, and anterior post impingement and the clinical outcome were assessed. ResultsAnterior impingement of the tibial post was observed in 13 knees (33%) during the latter half of the stance phase and at the beginning of the swing phase with the average implant flexion angle of −2.4°. Implant flexion was significantly smaller, while the femoral component was located more posterior in the impingement knees. The posterior tibial slope was significantly greater in the impingement group (6.7° ± 2.0°, 5.3° ± 1.9°, respectively; P = .041); however, no significant differences were demonstrated in anteroposterior laxity and patient-derived assessments. ConclusionTo avoid anterior post impingement, the posterior tibial slope should be made at 5° or less. Femoral notch-anterior post articulation should be designed to have good congruency in order to act as an anterior stabilizer in the case of impingement at knee extension.

Impingement of the patellar component against the tibial post depends on the design of the post-cam mechanism: Comparison between 12 posterior stabilized total knee prostheses

BackgroundPatella–post impingement (PPI), contact of the patellar component with the tibial post, occurs during deep knee flexion after posterior stabilized total knee arthroplasty (TKA). In a previous pilot study, only two product lines were investigated. The aim of this study was to compare PPI between 12 contemporary posterior stabilized knee prostheses. MethodsTwelve posterior stabilized knee prostheses were implanted in full-length sawbone models of the femur and tibia using a navigation system. The distance between the lower edge of the patellar component and the cut surface of the tibia was defined as the tibial–patellar clearance (TPC), which represents the length of the patellar tendon. The TPC was set from 20 to 40 mm and the knee was moved from full extension to deep flexion while the knee angle at which PPI occurred (PPI angle) was recorded. ResultsThe PPI angle differed between prostheses (P < 0.05). Shorter TPCs resulted in smaller PPI angles and longer TPCs resulted in larger PPI angles (P < 0.05). To achieve more than 130° of flexion without PPI, the TPC should be prepared at a minimum of 20 mm for the NexGen LPS-Flex, Persona PS, Legion PS, and Evolution PS, 22 mm for the Attune RP and Journey II, 24 mm for the Triathlon PS, PFC Sigma PS, and Attune PS, and 26 mm for the NRG PS, Vanguard PS, and Vanguard RP. ConclusionsThe design of the tibial post significantly affects the PPI angle. To avoid PPI during deep flexion, appropriate TPC should be prepared during surgery.

A study on post impingement effects of urea-water solution spray on the heated wall of automotive SCR systems

The post impingement effects of urea-water solution spray on the heated wall of automotive SCR systems was numerically investigated in a constant volume chamber using STAR CCM+ CFD code. The turbulence flow was modelled by realizable k-ε two-layer model together with standard wall function and all y+ treatment was applied along with two-layer approach. The Eulerian-Lagrangian approach was used for the modelling of multi phase flow. Urea water solution (UWS) was injected onto the heated wall for the wall temperature of 338, 413, 473, 503 & 573 K. Spray development after impinging on the heated wall was visualized and measured. Droplet size distribution and droplet evaporation rates were also measured, which are vital parameters for the system performance but still not well researched. Specially developed user defined functions (UDF) are implemented to simulate the desired conditions and parameters. The investigation reveals that wall temperature has a great impact on spray development after impingement, droplet size distribution and evaporation. Increasing the wall temperature leads to longer spray front projection length, smaller droplet size and faster droplet evaporation which are preconditions for urea crystallization reduction. The numerical model and parameters are validated comparing with experimental data.

Nonuniform Jet Array Impingement on a Curved Surface

Experiments to investigate the effect of varying jet hole diameter and jet spacing on heat transfer and pressure loss from jet array impingement on a curved target surface are reported. The jet plate configurations studied have varying hole diameters and geometric spacing for spatial tuning of the heat transfer behavior. The configuration also includes a straight section downstream of the curved section, where the effect on heat transfer and pressure loss is also investigated. The jet plate holes are sharp-edged. A steady-state measurement technique utilizing temperature-sensitive paint (TSP) was used on the target surface to obtain local heat transfer coefficients. Pressure taps placed on the sidewall and jet plate of the channel were used to evaluate the flow distribution in the impingement channel. For all configurations, spent air is drawn out in a single direction which is tangential to the target plate curvature. First row jet Reynolds numbers ranging from 50,000 to 160,000 are reported. Further tests were performed to evaluate several modifications to the impingement array. These involve blocking several downstream rows of jets, measuring the subsequent shifts in the pressure and heat transfer data, and then applying different turbulator designs in an attempt to recover the loss in the heat transfer while retaining favorable pressure loss. It was found that by using W-shaped turbulators, the downstream surface average Nusselt number increases up to ∼13% as compared with a smooth case using the same amount of coolant. The results suggest that by properly combining impingement and turbulators (in the post impingement section), higher heat transfer, lower flow rate, and lower pressure drop are simultaneously obtained, thus providing an optimal scenario.

Impingement of the patellar component against the tibial post after posterior stabilized and constrained TKA: a pilot study.

Patella-post impingement (PPI), contact of the patellar component with the tibial post, occurs during deep knee flexion after posterior stabilized total knee arthroplasty (TKA). PPI can cause anterior knee pain, increased patellar pressure, wear of the polyethylene patellar component and tibial post, and poor range of motion. There have been no reports on the relationship between PPI and tibial post design. The aim of this study was to compare different tibial post designs with regard to PPI incidence. Five posterior stabilized total knee prostheses were implanted in full-length models of the femur and tibia (Sawbones) using a navigation system. The thickness of the tibial component was 10mm in all prostheses. The patella was set on a transparent polypropylene sheet, which was fixed to the tibial tubercle. The distance between the lower edge of the patellar component and the cut surface of the tibia was defined as the tibial-patellar clearance (TPC), which represents the length of the patellar tendon. The TPC was varied from 18 to 40mm and the knee was moved from full extension to deep flexion while the knee angle at which PPI occurred (PPI angle) was recorded. The PPI angle differed between tibial post designs (p < 0.05). Shorter TPCs resulted in smaller PPI angles and longer TPCs resulted in larger PPI angles (p < 0.05). This is the first study to analyze the relationship between PPI and the design of tibial post. Our results clearly show that tibial post design and TPC affect PPI. To avoid patellar component and tibial post impingement in deep flexion, appropriate TPC must be achieved during surgery. Improvements in tibial post design, especially in constrained prostheses, are also desirable. This study highlights the potential risk of PPI during deep flexion after TKA.

Contact stress analysis of the anterior tibial post in bi-cruciate stabilized and mobile-bearing posterior stabilized total knee arthroplasty designs

In posterior-stabilized (PS) total knee arthroplasty (TKA), unexpected wear and fracture of the tibial post due to anterior post impingement have been reported. The purpose of this study was to determine the contact stress on the anterior aspect of the tibial post in four contemporary TKA designs. We evaluated one bi-cruciate stabilized design (Journey II) and three mobile-bearing PS designs (Vanguard RP, PFC Sigma RP, and NexGen LPS Mobile). The contact conditions at the anterior aspect of the tibial post were determined upon application of a posterior force of 100N to individual implants. Each measurement was sequentially performed five times, and the data were compared within and across designs using analysis of variance and a post-hoc test. The contact stress of the Journey II and Vanguard RP was less than the compressive yield stress for polyethylene (10MPa) at all tested flexion angles and degrees of rotation. The PFC Sigma RP did not show anterior tibial post impingement under any experimental conditions. The NexGen LPS Mobile demonstrated bilateral edge loading at the anterior tibial post and exceeded 10MPa of contact stress in some test conditions. Thus, the differences among implants in terms of the dimensions of the femoral anterior cam or intercondylar notch and the anterior aspect of the tibial post in the axial and sagittal planes led to significant differences in contact conditions. The present study helps the surgeon to be more aware that various contact conditions of the anterior aspect of the tibial post can occur in individual TKA designs.

Continuous Sagittal Radiological Evaluation of Stair-Climbing in Cruciate-Retaining and Posterior-Stabilized Total Knee Arthroplasties Using Image-Matching Techniques

In this study, we evaluated the in vivo kinematics of stair-climbing after posterior stabilized (PS) and cruciate retaining (CR) total knee arthroplasty (TKA) using radiographic-based image-matching techniques. Mid-flexion anteroposterior stability was demonstrated in all knees after CR TKA. However, paradoxical femoral translation at low flexion angles was seen in both designs. The post-cam mechanism did not function after PS TKA. Larger posterior tibial slope in PS TKA was linked to forward sliding of the femur at mid-flexion and unintended anterior tibial post impingement at knee extension. CR TKA is more sagittally stable in mid-flexion during stair climbing and attention must be given to minimize posterior tibial slope when using late cam-post engaging PS TKA designs.

Posterior Sliding of the Femur During Stair Ascending and Descending in a High-Flex Posterior Stabilized Total Knee Arthroplasty

This study investigated the anteroposterior stability of the femur during stair motions. We examined 18 knees with a clinically successful high-flexion posterior stabilized total knee arthroplasty to evaluate the in vivo kinematics of stair ascending and descending using two- to three-dimensional registration. Posterior sliding of the femur was observed while shifting weight to the leg during stair ascending and descending in almost all knees. Anterior tibial post impingement was observed in 10 knees when the knee was extended in stair ascending, whereas in stair descending, the impingement was observed in 14 knees when posterior sliding of the femur occurred. The impingement contributed to the stabilization of the knee during stair motion; however, impingement may result in additional polyethylene wear and tibial post failure.

Factors in High-Flex Posterior Stabilized Fixed-Bearing Total Knee Arthroplasty Affecting In Vivo Kinematics and Anterior Tibial Post Impingement During Gait

One of the most important issues in high-flex posterior stabilized total knee arthroplasty (TKA) is anterior tibial post impingement. We examined 20 knees and 2 TKA designs to evaluate the in vivo kinematics during gait using fluoroscopic image analysis. The AP positions in both stance and swing phases were significantly larger and more anterior in J-curved design TKA compared with Single radius design TKA. Anterior tibial post impingement was observed in five knees implanted with Legacy-flex, and in four of the five knees they were not hyperextended. No impingement was observed with NRG. Less constraint and tibial posterior slope might lead to large AP translations and anterior tibial post impingement. Implant design and operative procedures for high-flexion TKAs affect the in vivo kinematics and the occurrence of anterior tibial post impingement.

Mobile-bearing Total Knee Arthroplasty

Premature polyethylene wear is a major cause of total knee arthroplasty (TKA) failure. It has been attributed to numerous factors including poor surgical technique, reduced polyethylene thickness, poor locking mechanisms of modular fixed bearing tibial components, gamma irradiation sterilization techniques in the presence of oxygen, and low conformity implant designs. The incidence of implantation of TKA into younger patients who have increased activity requirements and longevity expectations is increasing. This requires continued analysis of design features lessening polyethylene wear. The purpose of this manuscript is to review clinical and basic scientific studies of factors influencing polyethylene wear, focusing on the potential benefits of mobile bearing TKA which potentially reduce long-term polyethylene wear by providing increased implant conformity and reduced polyethylene contact stresses. In vivo kinematic studies have shown self-alignment of the polyethylene bearing with the femoral component typically occurs in rotating platform TKA designs which should hypothetically lessen polyethylene surface stresses, minimize stabilizing post impingement, and increase the potential for enhanced polyethylene longevity.

Anterior tibial post impingement in a posterior stabilized total knee arthroplasty

Despite the numerous long-term success reports of posterior stabilized (PS) total knee arthroplasty (TKA), recent retrieval studies of various PS TKA designs revealed wear and deformation on the anterior side of the tibial post. This study investigated the mechanisms of anterior impingement of the post with the femoral component. Seven cadaveric knees were tested to study kinematics and tibial post biomechanics during simulated heel strike using an in vitro robotic testing system. Intact knee kinematics and in situ anterior cruciate ligament (ACL) forces were determined at hyperextension (0° to −9°) and low flexion angles (0° to 30°) under the applied loads. The same knee was reconstructed using a PS TKA. The kinematics and the tibial post contact forces of the TKA were measured under the same loading condition. The ACL in the intact knee carried load and contributed to knee stability at low flexion angles and hyperextension. After TKA, substantial in situ contact forces (252.4 ± 173 N at 9° of hyperextension) occurred in the tibial post, indicating anterior impingement with the femoral component. Consequently, the TKA showed less posterior femoral translation compared to the intact knee after the impingement. At 9° of hyperextension, the medial condyle of the intact knee translated 0.1 ± 1.1 mm whereas the medial condyle of the TKA knee translated 5.6 ± 6.9 mm anteriorly. The lateral condyle of the intact knee translated 1.5 ± 1.0 mm anteriorly whereas the lateral condyle of the TKA knee translated 2.1 ± 5.8 mm anteriorly. The data demonstrated that anterior tibial post impingement functions as a substitute for the ACL during hyperextension, contributing to anterior stability. However, anterior post impingement may result in additional polyethylene wear and tibial post failure. Transmitted impingement forces might cause backside wear and component loosening. Understanding the advantages and disadvantages of the tibial post function at low flexion angles may help to further improve component design and surgical techniques and thus enhance knee stability and component longevity after TKA.

Modeling on Spray-Wall Interaction for Direct Gasoline Injection Engines

This study is focused to propose the new spray-wall interaction model for application of direct injection engine systems. In this paper, the experimental approaches are discussed for two kinds of droplet-spray regime. As the 1st step, small non-dispersed droplets or droplet array impinge on the heated flat wall with the variation of droplet Weber number, impingement angle and wall temperature. In the 2nd step, actual spray through the gasoline injector for D.I.S.I. Is impinged on the flat wall. Here, droplet behavior on the wall and post impingement properties are measured by high-speed photographic systems. Then, the new submodel is constructed based on droplets experimental results. This new model is incrporated into KIVA-3 code. And the results calculated by this model are compared with experimental results. It was found that the results by this model for the spray dispersion near the wall were consistent well with the actual process over all boiling state conditions.

Tibial post impingement in posterior-stabilized total knee arthroplasty.

Reports of posterior-stabilized total knee replacements have shown excellent clinical success. However, tibial post-femoral cam impingement has been seen in modular component retrievals. This finding has been associated with transmission of rotational forces to the modular tray-polyethylene interface with subsequent backside polyethylene wear and the development of osteolysis. Femoral cam-tibial post designs that allow hyperextension and limit rotational constraint may minimize this impingement. Technical considerations including the avoidance of femoral component flexion and posterior tibial slope will minimize anterior tibial post impingement.

Study of Lubricant Jet Flow Phenomena in Spur Gears

Lubricant jet flow impingement and penetration depth into a gear tooth space were measured at 4920 and 2560 using a 8.89-cm- (3.5-in.) pitch dia 8 pitch spur gear at oil pressures from 7 × 104 to 41 × 104 N/m2 (10 psi to 60 psi). A high speed motion picture camera was used with xenon and high speed stroboscopic lights to slow down and stop the motion of the oil jet so that the impingement depth could be determined. An analytical model was developed for the vectorial impingement depth and for the impingement depth with tooth space windage effects included. The windage effects on the oil jet were small for oil drop size greater than 0.0076 cm (0.003 in.). The analytical impingement depth compared favorably with experimental results above an oil jet pressure of 7 × 104 N/m2 (10 psi). Some of this oil jet penetrates further into the tooth space after impingement. Much of this post impingement oil is thrown out of the tooth space without further contacting the gear teeth.