Hybrid Seal Research Articles

Leakage performance of hybrid brush seals under high differential pressure conditions

A three-dimensional axial fluid-porous medium-flow field model was designed for the sealing properties of the hybrid brush seal (HBS) seal structure under complex operating conditions. Using a computational fluid dynamics model in view of non-Darcy porous media, the pressure and velocity distributions of the sealing medium in the flow path were simulated, and the flow characteristics of the hybrid brush seal were analysed to obtain the leakage of the hybrid seal structure. The results show the implication of pressure ratio (Rp) on the labyrinth brush seal leakage rate and pressure distribution. Compared with typical brush seal test results, as the inlet and outlet pressure ratio (Rp) increases, the more obvious the hybrid brush seal sealing effect is, when the pressure ratio is 3 bar, the spillage of the hybrid brush seal is reduced by about 39%.

Research into the lubrication of a rotary lip seal using ferrofluid

The paper presents the results of research into a hybrid seal which is a combination of standard rotary lip seals and a magnetic fluid seal. To maintain the magnetic fluid in the friction zone region, either a specially shaped pole piece was used or the shaft was modified accordingly. The research study concerns the allowable operating pressure and lubrication conditions in short-term and durability tests after which shaft wear was also assessed. Magnetic fluids with different rheological and magnetic properties were considered. The test results showed that the long-term operation of a hybrid seal is possible. The requirements, however, are the appropriate value of the magnetic field and dynamic viscosity of the magnetic fluid.

CFD를 활용한 브러쉬 실의 회전체동특성 해석

To improve the efficiency of steam turbines, this study examines the application of a brush seal with bristles having a minimum clearance in the rotor. To maximize the reduction of leakage, a hybrid seal was employed to replace one or two of the labyrinth teeth with bristles. In the design of the brush or hybrid seal, a dynamic coefficient prediction method was developed to evaluate vibration characteristics, in addition to the use of a leakage prediction method. In this paper, we propose a 3D computational fluid dynamics (CFD) analytical method based on dynamics analysis using the relative coordinate system, assuming that the bristle element is a porous medium and comparing the results with published experimental results. With the exception of K (direct stiffness), the dynamic characteristics of the brush seal with the bristles contacted with the rotor, k (cross coupled stiffness), C (damping), and c (cross coupled damping), were quite small and the vibration characteristics of the brush seal were relatively unaffected. Compared to the experimental results, 3D CFD analytical results of the hybrid seal revealed that K was 17.5% smaller, k was 3% larger, and C was 10% larger.

CFD를 활용한 스팀터빈 하이브리드(브러쉬+래버린스) 실의 누설특성 해석

A steam turbine has to have a gap between rotating part and a non-rotating part. Leakage occurs from the gap, which causes a reduction in the efficiency of the rotating machine and efforts have been made to reduce the leakage flow rate through the seal. It has been reported that hybrid seals with brush elements have better leakage reduction performance than labyrinth seals. This study is to present the CFD analysis method for predicting the leakage characteristic of the hybrid seal. The CFD analysis of labyrinth seal and hybrid seal was conducted and the analytical results were compared with the experimental results to verify the validity of the analysis. Based on the above results of the analysis of the leakage characteristic, the design direction of the brush seal was presented through the leakage characteristic according to the parameters of the brush seal.

Durability Testing of Idlers for Belt Conveyors

Abstract The main purpose of idlers is to provide the correct shaping, support and protection of a belt conveyor, reduce motion resistance as well as support for transported materials. The durability of idlers depends on numerous construction, engineering and operational factors. In practice, the idler bearings are often damaged due to wear and tear, jamming or seizure and the calculated durability does not comply with the actual lifetime of a bearing (Antoniak 2007). According to laboratory and operational practices, the quality of currently manufactured standard idlers is low and their average durability is approximately one year (Gladysiewicz, Orzel, Noga 2012). Idlers do not meet the requirements specified in the PN-M-46606:2010 standard, even at the stage of their production, which is confirmed by tests carried out in the Department of Mechanical Devices Testing – the Central Mining Institute (GIG). Taking the above into consideration, testing stands which allow the testing of static and dynamic resistance of idlers' movements as well as stands for examing the idlers' water-tightness and dust-tightness in accordance with the PN-M-46606:2010 standard have been designed and constructed in the Department of Mechanical Devices Testing – the Central Mining Institute. The abovementioned testing stands were extended with additional functions, with regard to the above specified standard, facilitating the measurement of the temperature of bearing assemblies and to test the influence of rotational speed and idler loading in regards to durability. The tests were carried out on idlers with diameters of ϕ133 and ϕ 159 mm, with a bearing assembly equipped with a single-raw ballbearing. A newly developed type of hybrid seal (labyrinth-lip), registered in the Patent Office of the Republic of Poland under the number W.121582 on 17 December 2012 (Pytlik, Rabsztyn 2012), was used in the idler with the diameter of ϕ133. A typical labyrinth seal was used in the idler with the diameter of ϕ159. On the basis of the durability tests carried out on both of these idlers it can be concluded that the applied research methodology describes the test conditions of idlers, in a manner as close as possible to their actual operational conditions, which were subject to a variety of factors for a total time of 116 hours, they included: dust, water, loads and variable rotational speed. This methodology allowed us to determine, even at the stage of laboratory tests, the suitability of a particular idler to certain operational conditions.

Design considerations towards the construction of hybrid floating brush seal (HFBS)

The hybrid floating brush seal (HFBS) represents an advance in brush seal technology by combining brush seal and film riding face seal technologies to create a hybrid seal that allows both axial and radial excursions of the sealed shaft without damage to seal integrity. At the same time, it eliminates interface surface speeds between the rotor and the brush bristles. This accomplishment is possible because the brush seal, which forms the primary seal, rotates with the shaft, while floating against a hydrodynamic face seal surface, which makes up the secondary seal. The present paper presents continuation work (Int J of Rotating Machinery, 7, 2002) and will concentrate on the methodology of (i) designing and choosing brush characteristics, and (ii) the design of the face seal that allows the floating of the brush plates against it. The brush simplified analytical model predicts the effects of centrifugal force on the bristles and allows implementation of a methodology for choosing and optimizing bristle geometry. The face seal design concentrates on ensuring seal integrity and dynamic stability of the entire assembly.

Compressor Discharge Brush Seal for Gas Turbine Model 7EA

AbstractSingle-shaft, heavy-duty industrial gas turbines are extremely sensitive to compressed air bypassing at compressor discharge plane. This plane represents the highest pressure location in entire gas turbine unit (GTU). Standard method to minimize compressed air leakage is labyrinth seal that is integral part of the cylindrical element here called "inner barrel." The inner barrel is also the part of compressor discharge diffuser. This paper describes the efforts related to conversion of standard labyrinth seal into the hybrid seal that is combination of labyrinth and brush seals.

Hybrid Brush Pocket Damper Seals for Turbomachinery

Pocket damper seals perform a dual function: both sealing the pressurized gas around a rotating shaft and providing large amounts of vibration damping. The annular cavity between the labyrinth seal teeth is subdivided into separate annular cavities around the circumference of the rotor by partitioning walls. Also, the upstream and downstream teeth have different radial clearances to the rotor. These seals have been shown to provide a remarkable amount of direct damping to attenuate vibration in turbomachinery, but they generally leak more than conventional labyrinth seals if both seals have the same minimum clearance. Conversely, brush seals allow less than half the leakage of labyrinth seals, but published test results show no significant amount of damping. They are considered to be a primary choice for the seals in new aircraft engine designs because of their low leakage. This paper will describe a recently invented hybrid brush/pocket damper seal that combines high damping with low leakage. Previous brush seal results were studied and calculations were made to select a brush seal to combine with the pocket damper design. The result is a hybrid seal with high damping and low leakage. A special design feature can also allow active vibration control as a bonus benefit. A computer code written for the original pocket damper seal was modified to include the brush element at the exit blade. Results from the computer code indicate that the hybrid seal can have less leakage than a six bladed (or 6 knives) labyrinth seal along with orders of magnitude more damping. Experimental evaluations of the damping and leakage performance of the hybrid seal are being conducted by the authors. The experimental work reported here tested the damping capability of the new hybrid brush seal by exciting the seal journal through an impedance head. A conventional six-bladed labyrinth seal of the same working dimensions was also tested. The brush hybrid pocket damper seal is found to leak less than the labyrinth seal while producing two to three times more damping than the original pocket damper seal (orders of magnitude more than the conventional labyrinth). [S0742-4795(00)01102-9]

Effects of Compression, Staging, and Braid Angle on Braided Rope Seal Performance

Future turbine engines and industrial systems will be operating at increased temperatures to achieve more demanding efficiency and performance goals. In the highest temperature sections of the engine new material systems such as ceramics and intermetallics are being considered to withstand the harsh thermal environment. Components constructed of these low expansion-rate materials experience thermal strains and a resulting reduction of life when rigidly attached to high expansion-rate, superalloy support structures. Seals are being designed to both seal and to serve as compliant mounts allowing for relative thermal growths between high temperature but brittle primary structures and the surrounding support structures. Previous seal research yielded several braided rope seal designs which demonstrated the ability to both seal and serve as a compliant mount. The hybrid seal was constructed of an all-ceramic (alumina-silica) core overbraided with a superalloy wire sheath (cobalt based superalloy). The all ceramic seal was constructed of an all-ceramic (alumina-silica) core overbraided with multiple ceramic (alumina-silica) sheath layers. Program goals for braided rope seals are to improve flow resistance and/or seal resilience. To that end, the current report studies the test results of: baseline and modified hybrid seals; two stage hybrid and two stage all-ceramic seal configurations; and single stage hybrid and single stage all-ceramic seal configurations for a range of seal crush conditions. Hybrid seal modifications include increasing the sheath braid angle and core coverage. For the same percent seal cross-sectional crush, results show that increasing the hybrid seal braid angle increased seal stiffness and seal unit load, resulting in flows approximately one third of the baseline hybrid seal flows. For both hybrid and all-ceramic seals, two stage seal configurations significantly outperformed single stage configurations. Two stage seal flows were at least 30% less than the single stage seal flows for the same seal crush. Furthermore, test results of single stage seals indicate that for both all-ceramic and hybrid seals, a specific seal crush condition exists at which minimum flows are achieved (i.e. increasing seal crush beyond a certain point does not result in better flow performance). Flow results are presented for a range of pressures and temperatures from ambient to 1300 F, before and after scrubbing. Compression tests results show that for both all-ceramic and hybrid seals, seal preload and stiffness increase with seal crush, but residual seal interference remains constant.

High temperature bellows hybrid seal

High temperature bellows hybrid seal