Tooth Height Research Articles

Design of Running in Control Platform for Tracking Turntable

The tracking turntable is an important device in a laser digital sight. In the normal operation of the sight, the flatness and smoothness of the turntable are the necessary conditions for the stable operation of the system. In this paper, for the problem of improving the operation accuracy of the turntable, a set of special processes and equipment is developed through the electrical and structural design. After the processing, the control box runs the turntable for a certain time, which can remove the tooth height and burr, and improve the transmission stability and transmission accuracy.

Numerical and experimental study of convergent integral embedded magnetic fluid seal

To enhance the pressure resistance of small clearance magnetic fluid seals, a new convergent integral embedded magnetic fluid seal (CIEMFS) structure was proposed. The magnetic field distributions in the radial sealing clearance and axial sealing clearance were studied, and the theoretical pressure resistance capability values were obtained. The effects of magnetic fluid injection volumes, pole tooth (PT) heights and sealing clearance on the pressure resistance capability of the CIEMFS were experimentally investigated and compared with that of the ordinary magnetic fluid seal (OMFS). The results showed that the experimental pressure resistance capability of the CIEMFS was in good agreement with the theoretical pressure resistance, and both of them were better than the OMFS. The pressure resistance capability of the CIEMFS is not only affected by the radial sealing clearance but also limited by the axial seal clearance. The height of the pole tooth and the magnetic fluid (MF) injection volume will also have an impact on the pressure resistance capability, the higher the pole tooth, the higher the pressure resistance capability of the magnetic fluid sealing (MFS) structure. As the magnetic fluid injection volume increases, the pressure resistance capability of the CIEMFS increases and then plateaus.

Macroanatomical, Histological and Microtomographic Study of the Teeth of the Komodo Dragon (Varanus komodoensis)—Adaptation to Hunting

The present study aimed to characterize the macrostructure and microstructure of the mandibular teeth of the Komodo dragon (Varanus komodoensis) and the methods it uses to obtain food. Examinations were performed using a stereoscopic microscope, autofluorescence method, histological method and computed microtomography. A detailed macro- and micro-structural description of V. komodoensis mandibular teeth were made. The mandibular teeth are laterally flattened along their entire length and the dental crown is hooked caudally. The part of the nasal margin of the tooth crown is irregular, while the caudal margin of the tooth is characteristically serrated, except for the tooth base area. There are longitudinal grooves on the lingual and vestibular surfaces up to the lower third of the tooth height. The mandibular tooth is surrounded by a cuff made of the oral mucosa, containing the opening of the venom gland. In the histological structure of the tooth, the enamel covering the tooth crown and the dentin under the enamel are distinguished. The inside of the tooth, except its basal part, is filled with the tooth chamber, while the inside of the lower part of the tooth is filled with plicidentine, which corresponds to external furrows on the enamel. The plicidentine arrangement resembles a honeycomb. A small amount of dentine folds reach up to the tooth apex. Characteristic features of the structure of the mandibular teeth in V. komodoensis may indicate their significant role, in addition to the venom glands, in obtaining food in the natural environment of this species.

Prediction of Leakage Rate and Optimization of Structural Parameter of Blade Tip Labyrinth Seal

To study the influence of the structural parameters of blade tip labyrinth seal (BTLS) on leakage flow characteristics, finite element method was used to calculate the relationship between blade tip leakage rate (BTLR) and four structural parameters such as tooth width, tooth height, tooth pitch and tooth number. With the finite element results as samples, support vector regression (SVR), back propagation (BP) neural network and extreme learning machine (ELM) were used to establish the prediction model of the relationship between BTLR and four structural parameters. The accuracy and applicability of three prediction models were compared and analyzed. The results showed that SVR algorithm has higher prediction accuracy and stability compared with other algorithms for the prediction of BTLR. The mean square error and determination coefficient of its test set are 0.00059637 and 0.99253 respectively. After that, SVR results were taken as samples of genetic algorithm to find the combination of structural parameters with the minimum BTLR. The obtained structural parameters were combined for simulation modeling calculation. Its results showed that the fluid velocity in the blade tip region is significantly reduced and the velocity transition is gentle. The difference between simulation and optimization was 0.01%. This method innovatively applies machine learning algorithm to the prediction of BTLR, and improves the problem of low speed and high cost when only using finite element method. It provides a new way to calculate BTLR. In addition, the structural parameters of BTLS are optimized to reduce BTLR. This idea expands the field of application of machine learning algorithms.

Comparison of the effects of two extraction methods on the alveolar ridge preservation of Maxillary Anterior Teeth.

To compare the effects of high-speed turbodrill root extraction and piezosurgery tooth socket enlargement on the alveolar ridge preservation of maxillary anterior teeth. Thirty-six clinically eligible patients admitted to the No.2 Hospital of Baoding or the Baoding First Central Hospital from January 2018 to November 2019 were selected and randomly divided into two groups. Group-A were extracted by high-speed turbodrill root extraction, while Group-B were extracted by piezosurgery tooth socket enlargement. After extraction, GBR bone grafting and soft tissue transplantation were performed on the extraction sockets. The extraction time, integrity rate of labial bone plate of the extraction socket, pain-free rate, satisfaction rate, reduction of the height and width of the alveolar ridge, alveolar bone mineral density score, and new bone contour score of the alveolar bone of two groups were compared. Group-B was significantly superior to Group-A in terms of tooth extraction time, pain-free rate, satisfaction rate and reduction of alveolar ridge height at three sites on the palatal side, with a statistically significant difference (p<0.05). Piezosurgery tooth socket enlargement is more worthy of clinical application due to its advantages of less impact on the preservation of the palatal alveolar ridge height of the maxillary anterior teeth, shorter tooth extraction time, postoperative pain-free rate and high final satisfaction rate.

Multi-Response Optimization of Ti6Al4V Support Structures for Laser Powder Bed Fusion Systems

Laser Powder Bed Fusion (LPBF) is one of the most commonly used and rapidly developing metal Additive Manufacturing (AM) technologies for producing optimized geometries, complex features, and lightweight components, in contrast to traditional manufacturing, which limits those characteristics. However, this technology faces difficulties with regard to the construction of overhang structures and warping deformation caused by thermal stresses. Producing overhangs without support structures results in collapsed parts, while adding unnecessary supports increases the material required and post-processing. The purpose of this study was to evaluate the various support and process parameters for metal LPBF, and propose optimized support structures to minimize Support Volume, Support Removal Effort, and Warping Deformation. The optimization approach was based on the Design of Experiments (DOE) methodology and multi-response optimization, by 3D printing and studying overhang geometries from 0° to 45°. For this purpose, EOS Titanium Ti64 Grade 5 powder was used, a Ti6Al4V alloy commonly employed in LPBF. For 0° overhangs, the optimum solution was characterized by an average Tooth Height, large Tooth Top Length, low X, Y Hatching, and high Laser Speed, while for 22.5° and 45° overhangs, it was characterized by large Tooth Height, low Tooth Top Length, high X, Y Hatching, and high Laser Speed.

Comparative evaluation of variations in torque expression in maxillary incisor and canine using different bracket prescriptions placed at different crown levels by finite element (FE) method: An in-vitro analysis.

While using preadjusted brackets, the position of the bracket on the crown is one of the deciding factors that determine the tooth's final tip, torque, height, and rotation. The final tooth position is not optimal if the bracket is placed incorrectly or if the varying crown morphology does not correspond with the bracket design. The present study was conducted to evaluate and compare the variations in torque expression in maxillary incisor and canine using different bracket prescriptions placed at different crown levels by finite element method. For the present study, three-dimensional models of maxillary right central incisor and canine were made using CREO version 4.0 software. CREO is a powerful three-dimensional (3-D) computer-based, computer-aided design (CAD) software developed by Parametric Technology Corporation (PTC) to aid in design processes. Simulation was done to replicate the clinical situation of an active palatal root torque acting on the incisor and canine. The induced palatal movement of root tips and labial movement of crowns tips, overall stress, and von Mises stress generated in the brackets and the total equivalent strains developed in the periodontal ligament (PDL) were calculated, while the values obtained were tabulated and subjected to statistical analysis. Based on the findings of the present study, the average maximum stress produced in the bracket was calculated as 265.069 Mpa in incisor and 166.742 Mpa in the canine. Likewise, the average of the maximum displacement of root apex observed in the present study was calculated as 0.01401 mm in the incisor and 0.00421 mm in the canine, while the average strain developed in the PDL was calculated as 0.0587 for incisor and 0.0498 for the canine. Furthermore, it was, also, observed that the magnitude of strain developed in the PDL increased with increase in the stress produced by the bracket prescription for both incisor and canine. Within the limitations of the present study, it was concluded that the magnitude of displacement of root apex was significantly influenced by bracket prescription and bracket position. Also, the stress developed in the bracket was influenced by bracket prescription and position, while the variation in crown morphology in the incisor and canine played a significant role in the eventual strain developed in the PDL after torque application.

О МОДЕЛИРОВАНИИ ПРОЦЕССА ТЕЧЕНИЯ РЕЗИНОВЫХ СМЕСЕЙ В КАНАЛАХ СОЭКСТРУЗИОННОЙ ГОЛОВКИ С УСИЛЕННОЙ ЗОНОЙ КОНТАКТА МАТЕРИАЛОВ

Currently, in the chemical and related industries, the process of obtaining polymeric, two-layer products with a reinforced contact zone of materials is common. These products include: caterpillar tracks, liners for tram tracks, etc. Particular attention is paid to the quality of products obtained by coextrusion. The article presents ways to solve problems of obtaining a strong connection between the layers of materials and an unstable shape of the extrudate at the outlet of the co-extrusion head. The authors propose to use a co-extrusion head with a reinforced material contact zone. In order to save time and computing resources, it is necessary to identify a rational design zone, in which sufficient calculation accuracy will be ensured. To identify the rational design zone, numerical experiments were carried out in the ANSYS software and computer system. The Maxwell model was chosen as the rheological model. Velocity and pressure distribution patterns were obtained, which can be used to solve various applied problems. It was revealed that the maximum speed is achieved in the center of the head section, while its minimum values are located along the periphery. As a result, dependences of the velocity inhomogeneity coefficient in the outlet section on the relative tooth height were drawn. The resulting regression curves are similar for the cases of the full and partial simulation zones. That is why it is sufficient to simulate the process only in the part of the extrusion head. With such a scheme, the number of finite elements will be less, which, with a given accuracy, will reduce the calculation time. The results obtained can be used in the design of co-extrusion heads for tire and rubber industries in order to replace foreign equipment with domestic developments.

ANALYSING THE MODEL-SUPPORT CONNECTION BY TORSION TEST FOR SELECTIVE LASER MELTING PROCESS

3D printing of metal parts was investigated in this research work, which connecting to the supporting of model. The connection between the support and the model is important form the viewpoint of the mechanical fixturing, the heat conduction, the removability of the support and the success of printing. In this research work, some support and tooth parameters such as the top length, the hatch distance, and base length, tooth height were investigated to create a model-support connection strength map. This knowledge makes it possible to select the most appropriate connection type between the support and the model by the requirements specified in different cases. The strength of the support-model connection was characterized by the shearing properties using the torsion test. The results are illustrated and compared by different support parameters and materials. The 316L stainless steel and Ti6Al4V alloy were investigated.

Single-lens multi-mirror laser stereo vision-based system for measuring internal thread geometrical parameters.

Oilfield pipes with out-of-tolerance internal thread can lead to failures, so the internal thread geometric parameters need to be measured. To tackle the problem of the low efficiency, poor accuracy, easy wear, and poor accessibility of existing methods, a single-lens multi-mirror laser stereo vision-based system for measuring geometric parameters of the internal thread is proposed, which allows the measurement of three parameters in one setup by completely reproducing the three-dimensional (3D) tooth profiles of the internal thread. In the system design, to overcome the incomplete representation of imaging parameters caused by insufficient consideration of dimensions and structural parameters of the existing models, an explicit 3D optical path model without a reflecting prism is first proposed. Then, considering the intervention of the reflecting prism, a calculation model for the suitable prism size and the final imaging parameters of the vision system is proposed, which ensures the measurement accessibility and accuracy by solving the problem that the existing system design only depends on experience without theoretical basis. Finally, based on the American Petroleum Institute standard, internal thread geometric parameters are obtained from the vision-reconstructed 3D tooth profiles. According to the optimized structural parameters, a vision system is built for measuring the internal thread geometric parameters of two types of oilfield pipes. Accuracy verification and typical internal thread measurement results show that the average measurement errors of the vision system proposed for the pitch, taper, and tooth height are 0.0051 mm, 0.6055 mm/m, and 0.0071 mm, respectively. Combined with the vision measurement time of 0.5 s for the three parameters, the above results comprehensively verify the high accuracy and high efficiency of the vision-based system.

Vision measurement system for geometric parameters of tubing internal thread based on double-mirrored structured light.

Geometric parameter measurement of tubing internal thread is critical for oil pipeline safety. In response to the shortcomings of existing methods for measuring internal thread geometric parameters, such as low efficiency, poor accuracy, and poor accessibility, this paper proposes a vision system for measuring internal thread geometric parameters based on double-mirrored structured light. Compared to previous methods, our system can completely reproduce the internal thread tooth profiles and allows multi-parameter measurement in one setup. To establish the correlation between the structural and imaging parameters of the vision system, three-dimensional (3D) optical path models (OPMs) for the vision system considering the mirror effect of the prism is proposed, which extends the scope of the optical path analysis and provides a theoretical foundation for designing the structural parameters of the vision system. Moreover, modeling and three-step calibration methods for the vision system are proposed to realize high-accuracy restoration from the two-dimensional (2D) virtual image to the actual 3D tooth profiles. Finally, a vision measurement system is developed, and experiments are carried out to verify the accuracy and measure the three geometric parameters (i.e., taper, pitch, and tooth height) of typical internal threads. Based on the validation results using the reference system, the vision measurement accuracy and efficiency are 6.7 and 120 times that of the traditional system, which verifies the measurement effectiveness and accuracy of the vision system proposed in this paper.

Numerical study of a novel SMA-based self-centering beam-to-column connection

As an alternative option for conventional rigid beam-to-column welded connections, self-centering steel beam-to-column connections were developed to reduce or eliminate the residual deformation of the structure and mitigate or avoid structural damages. This paper presents a finite element analysis of a novel self-centering beam-to-column connection with shape memory alloy (SMA) tendons as recentering and energy dissipation elements and comb-teeth dampers (CTDs) as supplementary energy dissipation devices. Firstly, the configuration and structural behavior of the proposed connection is depicted and explained; then, with the aid of previous experimental models, the validation of finite element modeling methods is examined. In the following, detailed numerical models are established and analyzed to assess the effects of key design parameters on the cyclic behavior of the proposed connection. Finally, an analytical model is formulated to predict the whole cyclic behavior of the proposed system. The results indicate a great recentering and energy dissipation capacity for the proposed connection. It is shown that incorporating CTDs in the proposed connection can significantly enhance the cyclic response of the connection with roughly no adverse impact on self-centering ability. It is also concluded that there must be an adequate initial prestress in SMA tendons to exploit the maximum recentering ability of the proposed connection. Furthermore, comparing the structural performance metrics of the proposed connection reveals that the connections with higher damper geometric shape coefficients own higher ultimate strength and better energy dissipation capacity with almost unchanged recentering capability. Conversely, the longer the damper teeth height is, the lower performance parameters in the connections could be observed. Results also show reasonable concordances between the analytical model predictions and finite element analysis results. The results of this study can serve as tools to facilitate the practical design of SMA-based self-centering connections.

Improved design of available atmospheric corrosion monitoring sensor with a higher sensitivity to low NaCl deposition

• A novel sensor that monitors the corrosion behavior of material was designed. • The sensor shows good responses to surface wetting and electrolyte development. • The sensor shows high resolutions in corrosion detection under low NaCl conditions. • The sensor provides perspectives on current atmospheric corrosion sensor design. The development of electrochemistry-based sensors is central to in-situ atmospheric corrosion monitoring of materials under conditions of both outdoor and indoor exposures. In this work, an improved design with an exposed Cu teeth height in the two member electrodes of the traditional EIS-based atmospheric corrosion sensor makes the sensor more sensitive under the thin electrolyte layer. With the noble design, the improved sensor exhibits a high sensitivity in surface electrolyte generation when the NaCl deposition is higher than 20 mg/m 2 , and a good corrosion rate response to NaCl deposition as low as 2 mg/m 2 . The grooves between adjacent exposed Cu teeth facilitate the formation of electrolyte layer under the hygroscopic effect of NaCl deposition, and thus improve sensitivity of the sensor to low NaCl deposition. Therefore, the improved sensor has broad potential applications in field conditions to monitor low NaCl deposition induced thin electrolyte layer evolution and corrosivity assessment of the atmosphere.

Numerical simulation and flat tensile strength optimization of metal zipper

Metal zippers are widely used in various engineering fields because of their compact structure, simple principle, and convenience. The flat pull strength is one of the most important indexes to judge the performance of a zipper. The methods used to optimize and improve the flat pull strength of a zipper are important for obtaining higher reliability. In this paper, the method of finite element analysis is used to establish the numerical model of the flat tensile strength for a 5# metal zipper. Relevant numerical results were comparatively discussed with experimental results. Based on the constructed finite element model, the design of the zipper pull strength was optimized. The influences of the chain tooth characteristic parameters such as the thickness of the chain tooth, the height of the chain tooth, the width of the chain tooth, and the spacing between the chain teeth on the pull strength were analyzed. The results show a good agreement between numerical simulation results and testing results. The optimization of characteristic parameters for the 5# metal zipper teeth was subsequently performed. The optimized structure indeed increases the frictional contact force between the teeth and enables the meshing between the teeth more consistent which eventually improves the flat pull strength.

STUDYING THE MOTIVATION OF PATIENTS WHO APPLY WITH ORTHODONTIC ASSISTANCE

Introduction. Preserving and strengthening the health of the population has always been one of the key issues in society. Dental care is one of the most demanded types of medical care, improving the quality of its provision is an important task of health care. Given the importance of paying attention to the patient's opinion in different treatment methods for a successful outcome and the influence of different factors on the success of the treatment from the patient's and the clinician's point of view, it seems necessary to conduct a study to assess the patient's expectation before and after orthodontic treatment in order to evaluate the possible variables.&#x0D; The purpose of the study is to evaluate data on the motivation of patients seeking orthodontic care that can help orthodontists meet the patients’ expectations and needs and achieve a successful treatment outcome.&#x0D; Materials and methods. We surveyed 300 patients aged 15 to 58 years (37.3% men, 62.7% women, average age is 25.4 years) who went fro dental care to the "University Clinical Dental Polyclinic" of the Uzhhorod National University. We applied the anonymous questionnaire method. A wide range of questions included in the questionnaire enabled us to analyze the motives for seeking orthodontic care in relation to demographic variables: age, gender, level of education and profession of parents.&#x0D; Results. The results of the study have shown that the majority of patients (89.3%) are motivated to align their front teeth, both on the upper and lower jaw (highest frequency), and 17.3% of them want to align their back teeth (lowest frequency). There are correlations between the gender of patients and the motivation to straighten the front teeth (p&lt;0.009), and women demonstrate a higher motivation for this type of correction. As the mother's level of education increases, the motivation to change the height of the front teeth grows as well (p&lt;0.03) in order to improve the condition of the teeth and gums when smiling (p&lt;0.001). The assessment of the relationship between the presence and absence of motivation to change the state of the teeth according to the mother's education level reveals a statistically significant negative relationship between the motivation to change the height of the front teeth (p&lt;0.03), improving the appearance of the teeth and gums when smiling (p&lt;0.001) and the level of education of the mother. The assessment of the relationship between the presence and absence of motivation to improve the teeth positioning by the father's education level reveals only a statistically significant negative relationship between the motivation to move the teeth of the lower jaw back or forward and the father's education level (p&lt;0.02). Conclusion. Alignment of anterior teeth (89.3%) and improvement of the appearance of teeth or gums when smiling has been found as the main reasons for patients to seek orthodontic care. The study has also shown that the patient's gender and the mother's education level have the most significant relationship with his/her motivation to change the position of the teeth, while the father's education and age have the least significant relationship with their motivation. Assessing the views of patients who seek orthodontic treatment and their expectations from the treatment is one of the main factors to consider when providing orthodontic treatment.

Structural Optimization, Fabrication, and Corrosion Behaviors of Biodegradable Mg-Nd-Zn-Zr Alloy Hemostatic Clip

In this study, the process of ligating blood vessels via biodegradable Mg alloy hemostatic clips with toothless, transverse teeth, and embedded teeth was simulated through finite element analysis (FEA). The results showed that the transverse tooth clip caused the minimum stress (0.81489 MPa) to blood vessels. Furthermore, the effects of clips with transverse teeth of different parameters, including lower tooth length, tooth height, and tooth pitch, on clamped blood vessels were studied. The numerical simulation results showed that the three optimal parameters for clips with transverse teeth were 0.2, 0.1, and 0.1 mm, respectively. Then, the optimally designed clip based on the Mg–Nd–Zn–Zr alloy was manufactured and evaluated using immersion tests. Results from the corrosion behavior study showed that closed clips (0.118 ± 0.041 mg·cm−2·day−1) corroded slightly faster than open clips (0.094 ± 0.041 mg·cm−2·day−1). Moreover, micromorphological observations showed that no cracks appeared on the closed clips, indicating that the Mg alloy had excellent performance and avoided stress corrosion cracking (SCC). Thus, the new type of Mg alloy clip kept good blood vessel closure during FEA and exhibited no corrosion cracking during the degradation process, making it a promising candidate for applications with biodegradable hemostatic clips.

Pipe Thread Parameter Detection System Based on Machine Vision

In order to achieve non-contact pipe thread detection with high-precision, high-efficiency and make the use of pipe threads safer, using machine vision and image processing technology to measure and analyze the geometric parameters of pipe threads. The projection matrix and distortion coefficient of the camera are obtained by Zhang Zhengyou’s calibration method, and the distortion coefficient is used to correct the distortion of the collected image. After that, grayscale processing is performed on the RGB (Red, Green, Blue) image obtained by the collection and correction, fusion filtering and denoising, threshold segmentation to obtain the binary image, and then the Canny operator is used to detect the thread edge information on the binary image. Then the pipe thread parameter measurement algorithm is proposed based on the extracted pipe thread image characteristics. Finally, the feasibility of the measurement algorithm is verified by using the measured data of 60 sets of pipe threads. The test results show that the measured values of tooth height and crest height obtained by this algorithm are concentrated near the standard value, with high accuracy and precision, and the overall data fluctuation is small.

Single- and multi-objective optimization of internal gear flowforming process based on increasing tooth height and reducing force and built-up edge

Flowforming is an incremental metal forming process in which deformation occurs gradually between the roller and mandrel. This process has been widely used for manufacturing of high-precision tubular parts and seamless tubes. Internal gear flowforming process is a new method for manufacturing an internal gear that requires no additional machining process. In this study, the design of experiment method and regression analysis were used to obtain tooth height, force, and built-up edge as functions of the effective parameters, including feed rate, roller diameter, attack angle, and thickness reduction percentage. Next, the simulated annealing and genetic algorithm were used for, respectively, single- and multi-objective optimization of the obtained functions. The goal of optimization was to reduce the force and built-up edge and increase the tooth height. In single-objective optimization, the maximum tooth height was 0.576 mm, the minimum force was 1606.63 N, and the minimum built-up edge was 0.448 mm. In multi-objective optimization, an optimal set of tooth height, force, and built-up edge (Pareto front) is obtained.

High shear mixer works as a heat exchanger enhancing the liquid–liquid direct contact heat transfer

As an indispensable unit equipment in industrial production, the design of efficient heat exchangers is of great significance to improve energy utilization rate. In this paper, the in-line high shear mixer (HSM) was investigated as a heat exchanger for the first time by experiments and assisted with CFD simulations, and the heat transfer performance was measured using kerosene and thermal water as the heat transfer fluids. Effects of operational parameters, including rotor speed, fluids temperature and flow rate, as well as the structural parameters, involving the rotor teeth number, teeth height, and the shear gap, were studied on the volume heat transfer coefficient and the heat transfer efficiency of such inline HSM. The results indicated that the volume heat transfer coefficient can be significantly improved by increasing the rotor speed and the flow rate of the heat transfer fluids, but reducing the heat transfer temperature difference, whereas increasing the thermal fluid flow rate deteriorates heat transfer efficiency. Furthermore, the structural parameters including rotor teeth number and teeth height, the shear gap within the stator and rotor were optimized to enhance the heat transfer of HSM. The optimal HSM possesses a shear gap of 0.5 mm, a teeth height of 10 mm and a teeth number of 6, which can generate larger turbulent energy dissipation rate and higher shear rate, meanwhile make more fluids jet out of the shear gap and stator hole. The maximum volume heat transfer coefficient and heat transfer efficiency can be up to 2522.8 kW·m−3·°C−1 and 92.4% with the optimal structure. Finally, the dimensionless correlations of heat transfer performance were established to guide the operating mode and structural design of high-efficiency high shear mixer.

Influence of tooth geometrical shape on the leakage and rotordynamic characteristics of labyrinth seals in a cryogenic liquid turbine expander

Cryogenic liquid turbine expanders have been used in many refrigeration systems to save energy, and rotor stability is a top concern in their development. The present study focuses on the influence of tooth geometrical shape on the leakage and rotordynamic characteristics of labyrinth seals in a cryogenic liquid expander, whose rotordynamic characteristics are typically special because of the thermodynamic effect of cryogenic liquid and a large pressure drop. Computational fluid dynamics (CFD) simulations are conducted in thirteen-teeth labyrinth seals with isosceles trapezoid shaped teeth and two types of right-angle trapezoid shaped teeth for a given geometric parameter through the whirling rotor method and total energy model. The flow behavior in the three labyrinth seals with different tooth geometrical shapes is explored, and their influence on the leakage and rotordynamic characteristics of the labyrinth seal is obtained. The results show that the leakage flow rate of the labyrinth seal with front right angle trapezoid shaped teeth is 1.1% and 0.6% less than that with rear right angle trapezoid shaped teeth and isosceles trapezoid shaped teeth, respectively, because of a larger divergence angle and more leakage flow involved in dissipation, while the labyrinth seal with isosceles trapezoid shaped teeth produces a larger fluid-induced tangential force opposite to the direction of whirling velocity and is more favorable for rotor stability. In addition, a parametric study is conducted to analyze the influence of clearance, tooth height, tooth thickness and inclination angle on the leakage and rotordynamic characteristics of the three labyrinth seals.