Seal Concept Research Articles

Evaluating CO 2 retention risk of geological sequestration sites: physical, time-scale, and site style considerations

With some exceptions, such as fluid phase, pressure evolution, and reservoir geometry, evaluation of CO 2 retention for geological sequestration sites primarily involves well-established seal and trap concepts and methods developed by the petroleum industry. Inputs to a CO 2 retention evaluation (e.g. bed seal capacity analysis) include CO 2 phase, CO 2 and brine density, reservoir pressure and temperature, rock properties, and stress state. The inputs are used to perform capillary and mechanical seal analyses similar to the petroleum industry, but unlike hydrocarbons, CO 2 retention also occurs within the reservoir pore volume by capillary and solubility trapping, adding additional requirement for analyses using reservoir engineering concepts and methodology. Reservoir geometry types for CO 2 storage include conventional traps (depleted hydrocarbon fields, brine-filled traps) and brine-filled reservoirs that lack a conventional trap geometry (e.g. a monocline). Each geometry style and project phase (injection, near-term post-injection, long-term static) requires different retention considerations, for example the CO 2 plume extent and height. Based on a retention evaluation, retention risk and uncertainty may be articulated using a qualitative risk matrix that facilitates early screening, identification of data needs, possible mitigating strategies, and comparisons across a portfolio of potential sites. Thematic collection: This article is part of the Geoscience workflows for CO 2 storage collection available at: https://www.lyellcollection.org/topic/collections/geoscience-workflows-for-CO2-storage

A fluidic oscillator seal concept for sealing performance enhancement by controlling the kinetic energy carry-over effect

Annular gas seals are critical components in turbomachines for restricting leakage and ensuring efficiency. However, their sealing performance is significantly affected by the kinetic energy carry-over (KEC) effect. In this paper, a novel concept of the fluidic oscillator seal (FOS) is proposed. The self-oscillating flow pattern inside FOS controls the undesired KEC effect, thus enhancing the sealing performance. The effectiveness of FOS is evaluated by comparing with the cutting-edge air curtain technology (ACT). Comparison results show that FOS exhibits superior sealing performance under all the studied operation conditions. Its superiority becomes more prominent as the seal clearance and teeth number increase. The maximum discharge coefficient reduction ratio reaches up to 51.4%, over 4 times larger than ACT. Moreover, the FOS requires only about half the installation space for an equivalent leakage flow rate compared to the ACT.

Numerical analysis of a double interlocking padded finger seal performance based on thermo-fluid-structure coupling method

Non-contacting finger seals represent an advanced non-contacting and compliant seal in gas turbine sealing technology. This paper proposes a new structure of non-contacting finger seals with double interlocking pads. The numerical analysis model based on the thermo-fluid-structure coupling method for the new type finger seal was established. The influence of working conditions on leakage of the seal was studied and compared with the single padded non-contacting finger seal. The results show that the interface between the bottom of the finger pad and rotor surface is the main leakage path that forms the gas film with obvious variations of pressure and flow velocity. Under high temperature and high pressure operating conditions, the hydrodynamic effect of the gas film is enhanced, and lifting force is significantly improved. The deformation of fingers is composed of elastic deformation and thermal deformation. At room temperature, the deformation of fingers is mainly elastic deformation and points to the center of the rotor, which reduces the gas film clearance. The deformation of fingers at high temperature and high pressure creates a circumferentially convergent gap between the bottom of the pad and the rotor, which is beneficial to improve the loading capacity and to reduce leakage of the seal. Compared with the typical single padded non-contacting finger seal, the double interlocking padded finger seal proposed in this paper reduces the leakage factor by about 37%, which provides an advanced seal concept with the potential to improve sealing performance under high temperature and high pressure working conditions.

New challenges in experimental unsaturated soil mechanics. Experimental upscaling of an engineered gas-permeable seal

An example of upscaling phenomena with experimental techniques is presented and discussed within an engineered seal concept for a future deep geological repository for low and intermediate radioactive waste mainly produced by the energy/medicine/industry sectors. The seal will undergo a long-term saturation stage and subsequent gas transport through such a barrier. Consequently, gas entrapment and generation processes (dominated by the degradation of organic substances and metals) are expected to occur in the emplacement caverns along the pollutant waste storage. The case concerns a compacted 80/20 (dry mass) sand/bentonite S/B mixture with a complex microstructure that significantly evolves on hydration affecting the gas transport properties. This type of seal limits the gas pressure by increasing its gas transport capacity (gas-permeable seal). The large-scale and demonstration experiment GAST (Nagra’s GTS, Switzerland) focuses on the S/B response to saturation and the gas transport capacity in the later gas invasion phase. A series of laboratory experiments running parallel to the in situ test and bridging different scales (from bentonite inter-sand filling microstructural tests and point tests to dm-scale mock-ups) are discussed within the saturation, gas breakthrough pressure and gas dissipation process of the gas-permeable seal context.

A New Elastic Non Contacting Sealing Concept for Valves

The hydraulic binary counter concept was proposed as a means to realize compact and lightweight digital hydraulic cylinder drives for exoskeleton actuation. This counter principle is based on hydraulically actuated switching valves which have a hysteretic response with respect to the pilot pressure. Manufacturing tolerances of the tiny components caused unexpected high leakage which, in turn, led to a malfunction of the system.
 In this paper a new sealing concept, is introduced to solve this problem. It is based on a non-contact seal (sealing gap), which exploits a self-regulating, elasto-hydrodynamic effect to reduce a rather large initial gap h0 – to allow a rough tolerance – into a very small sealing gap h(x) to avoid dry friction of valve spool movement on the one hand but have very small leakage on the other hand.
 As sealing, an annular flexible ring made, e.g. of PTFE, is used which combines sufficient flexibility to allow this self adapting mechanism to a sufficient extent and to stay the high pressure loads.
 For the mathematical analysis of the concept, an approximate elasto-hydrodynamic analytical model is used. It sets the gap pressure, obtained from the Reynold’s equation for the sealing gap, the elastic restoring forces of the sealing ring, and the imparting pressure in equilibrium.
 The sealing concept is then simulated with a numerical model built with the finite element code ABAQUS, this results are compared with the one of the analytical model.
 It solves the Reynolds equation by a user defined subroutine. The simulation results indicate that this sealing principle delivers way better results than standard gap seals despite its rough manufacturing tolerances with one order of magnitude higher tolerance ranges. The application of this concept is not limited to small valves as needed for exoskeleton hydraulics but can be transferred to conventional type of hydraulics as well.

Development of a test-rig for advanced rotor–stator seals used in jet engines: Part II

Advanced rotor–stator seals are becoming more and more common in the latest generation of jet engines. In order to develop new radial seals and fully understand existing ones, testing needs to be done under full-scale conditions. It is necessary to be able to evaluate a new seal concept at “scale one”, under representative operating temperatures, pressure and rotational speed. This article – published in two instalments – presents details of an advanced new test-rig that is able to achieve this goal. It describes many facets of its design, construction, commissioning and use, and the challenges associated with its development.

Development of a test-rig for advanced rotor–stator seals used in jet engines: Part I

Advanced rotor–stator seals are becoming more and more common in the latest generation of jet engines. In order to develop new radial seals and fully understand existing ones, testing needs to be done under full-scale conditions. It is necessary to be able to evaluate a new seal concept at “scale one”, under representative operating temperatures, pressure and rotational speed. This article – published in two instalments – presents details of an advanced new test-rig that is able to achieve this goal. It describes many facets of its design, construction, commissioning and use, and the challenges associated with its development. The first instalment, which appears here, looks at key characteristics of the test-rig, provides an overview of its mechanical design and airflow loop, and lists associated references. The second instalment will be published in the January 2022 issue of Sealing Technology.

Leakage and Rotordynamic Characteristics for Three Types of Annular Gas Seals Operating in Supercritical CO2 Turbomachinery

Abstract The balance piston seal in multiple-stage centrifugal compressors and axial turbines sustains the largest pressure drop through the machines and therefore plays an important role in successful full load operation at high rotational speed. This is especially true for power dense turbomachines in supercritical CO2 power cycles that generate or expend higher fluid pressures (above the critical value 7.3 MPa) and density (close to water 1000 kg/m3), because the fluid forces generated by the balance piston seals are directly proportional to the fluid density and the pressure drop across the seal. This paper presents a comprehensive assessment and comparison on the leakage and rotordynamic performance of three types of annular gas seals for application in a 14 MW supercritical CO2 turbine. These three seals represent the main seal types used in high-speed rotating machines at the balance piston location in efforts to limit internal leakage flow and achieve rotordynamic stability, including a labyrinth seal (LABY), a fully partitioned pocket damper seal (FPDS), and a hole-pattern damper seal (HPS). These three seals were designed to have the same sealing clearance and similar axial lengths. To enhance the seal net damping capability at high inlet preswirl condition, a straight swirl brake was also designed and employed at seal entrance for each type seal to reduce the seal inlet preswirl velocity. Numerical results of leakage flow rates, rotordynamic force coefficients, cavity dynamic pressure, and swirl velocity developments were analyzed and compared for three seal designs at high positive inlet preswirl (in the direction of shaft rotation), using a proposed transient computational fluid dynamic (CFD)-based perturbation method based on the multiple-frequency elliptical-orbit rotor whirling model and the mesh deformation technique. To take into account of real gas effect with high accuracy, a table look-up procedure based on the National Institute of Standards and Technology reference fluid properties database was implemented, using an in-house code, for the fluid properties of CO2 in both supercritical and subcritical conditions. Results show that the inlet swirl brake can significantly reduce the preswirl velocity at seal entrance, lowering the effective damping crossover frequency fco (or even fco = 0) to maximize the full operational frequency range of the machines. In stability analysis phase of a MW-scale supercritical CO2 turbine/compressor, the seal stiffness effects on the rotor mode shape must be evaluated carefully, where the seal stiffness is sufficiently large (comparable to the bearing stiffness). From a rotordynamic viewpoint, the HPS seal with entrance swirl brake is a better seal concept for the balance piston seal in supercritical CO2 turbomachinery, which possesses the largest positive effective damping throughout the entire subsynchronous frequency range.

Simple Solution for Single Final Vial Filling of Ga-68 Radiopharmaceuticals in One Hot Cell Isolator at Small-Scale Radiopharmacy Laboratories under Aseptic Conditions

A simple solution for fulfilling biosafety and national drug agency demands of radiation and biosafety during Ga-68 radionuclide containing radiopharmaceutical production (RP) by small scale laboratories has been demonstrated based on a novel sterile seal concept of multi-layer bag system prototype. These mid-and inner enclosures of the prototype with vial inside were sterilized by 50 kGy of gamma radiation. The microbial safety validation based on two-week testing confirmed successful sterilization of the sealing bags with vails. The analysis of physicochemical properties, namely mechanical properties, gel fraction studies revealed that sterilization did not cause any undesired changes in developed materials, compared to non-irradiated control samples.

Aerodynamic performance of augmented supersonic nozzles

The objective of this study is to understand how internal engine corrugated seals affect the aerodynamic performance of a convergent/divergent supersonic nozzle all the while promoting mixing. These corrugated seals are designed to protrude into the flow to alter the design pressure ratio of the nozzle through changes in area ratio. Measurements comprise axial thrust for nozzle pressure ratios ranging continuously from overexpanded to underexpanded nozzle flow states. Optical flow measurements using a z-type schlieren system are also used to qualitatively visualize the affect of protrusion depth on shock strength and boundary layer thickness at the nozzle exit. Findings reveal the effect of the corrugated seals on the double-shock pattern that forms from the imperfect expansion of the gas through this sharp throat nozzle. As much as a 2% increase in thrust coefficient is observed with one of the corrugated seal concepts and over a broad operating envelop corresponding to both overexpanded and underexpanded nozzle states.

Hermetically Sealed Squeeze Film Damper for Operation in Oil-Free Environments

The following work advances a new concept for a hermetically sealed squeeze film damper (HSFD), which does not require an open-flow lubrication system. The hermetically sealed concept utilizes a submersed plunger within a contained fluidic cavity filled with incompressible fluid and carefully controlled end plate clearances to generate high levels of viscous damping. Although the application space for a hermetic damper can be envisioned to be quite broad, the context here will target the use of this device as a rotordynamic bearing support damper in flexibly mounted gas bearing systems. The effort focused on identifying the stiffness and damping behavior of the damper while varying test parameters such as excitation frequency, vibration amplitude, and end plate clearance. To gain further insight to the damper behavior, key dynamic pressure measurements in the damper land were used for identifying the onset conditions for squeeze film cavitation. The HSFD performance is compared to existing gas bearing support dampers and a conventional open-flow squeeze film dampers (SFD) used in turbomachinery. The damper concept yields high viscous damping coefficients an order of magnitude larger than existing oil-free gas bearing supports dampers and shows comparable damping levels to current state of the art open-flow SFD. The force coefficients were shown to contribute frequency-dependent stiffness and damping coefficients while exhibiting amplitude independent behavior within operating regimes without cavitation. Finally, using experimentally based force density calculations, the data revealed threshold cavitation velocities, approximated for the three end seal clearance cases. To complement the experimental work, a Reynolds-based fluid flow model was developed and is compared to the HSFD damping and stiffness results.

Invited commentary

The current manuscript addresses the concept of “adequate” seal zones to treat blunt thoracic aortic injury (BTAI). All thoracic endograft devices currently available in the United States recommend a proximal seal zone of 20 mm as well as distal seal zones of 20 mm. It is well known that these devices were designed, tested, and validated for the treatment of thoracic aorta aneurysms. Conceptually, the boundary conditions to achieve endograft seal are different for aortic dissection, penetrating ulcers, saccular aneurysms, and BTAI. However, we know very little about those boundary conditions other than our collective clinical experience in treating these conditions with thoracic endovascular aortic repair. In the case of BTAI, it is foreseeable that simply covering the acute tear with 5 mm of seal may be enough to protect the patient from aortic rupture and death. The difference in 5 mm and 20 mm of seal zone may require coverage of the left subclavian artery and may advance the endograft into a landing zone with more angulation. In the current series, none of the cases that required coverage of the left subclavian artery required revascularization, although it is possible that arm malperfusion may occur later in life. Two of the seven patients with left subclavian coverage required additional endografts to treat malpositioning of the proximal stent on the lesser curvature. The authors report a 100% technical success rate for patients treated with 20 mm of proximal seal and 93% for patients with <20 mm of seal. The authors believed the reduced technical success rate was due to inadequate sizing of devices and not related to the shorter seal zone. The authors' experience adds to our knowledge of treating BTAI and demonstrated good clinical outcomes with both strategies of treatment. The decision to select a shorter seal zone for BTAI will be dictated by the surgeon's ability to adequately identify the location of the aortic tear and effectively to achieve seal in an emergent setting. For these concerns, the TRANSFIX study investigators and the Gore C-Tag trial chose a 20-mm proximal seal zone for inclusion criteria in treating BTAI.1Starnes B.W. Dwivedi A.J. Giglia J.S. Woo K. TRANSFIX Study InvestigatorsEndovascular repair for blunt thoracic aortic injury using the Zenith Alpha low-profile device.J Vasc Surg. 2015; 62: 1495-1503Abstract Full Text Full Text PDF PubMed Scopus (12) Google Scholar, 2Farber M.A. Giglia J.S. Starnes W.B. Stevens S.L. Holleman J. Chaer R. et al.TAG 08-02 clinical trial investigatorsEvaluation of the redesigned conformable GORE TAG thoracic endoprosthesis for traumatic aortic transection.J Vasc Surg. 2013; 58: 651-658Abstract Full Text Full Text PDF PubMed Scopus (34) Google Scholar Both trials yielded a 100% technical success rate, which parallels the experience in the current manuscript. Short-term results of left subclavian artery salvage in blunt thoracic aortic injury with short proximal landing zonesJournal of Vascular SurgeryVol. 68Issue 4PreviewThoracic endovascular aortic repair (TEVAR) is the standard treatment of blunt thoracic aortic injury (BTAI). The concept of seal was derived from the treatment of aneurysms and has been adopted for BTAI. Given the location of injury in BTAI, left subclavian artery (LSA) coverage is sometimes necessary. In these often healthier aortas, a shorter proximal landing zone may be acceptable and beneficial in avoiding some complications. Current practice patterns vary, and long-term effects of LSA coverage remain unknown. Full-Text PDF Open Archive

O pacto federativo e a democracia nas constituições estaduais

A democracia não é conceito fechado ou estanque, e sua fonte normativa não advém apenas da Constituição da República. Embora, no Brasil, o pacto federativo, nos moldes em que se encontra, imponha limites aos Estados-membros, é possível que, em suas respectivas Constituições, ressaltando a máxima de sua autonomia, sejam instituídos instrumentos que permitam uma maior participação popular e direitos e garantias fundamentais ao exercício da cidadania, ainda que não previstos na Carta Republicana. Democracia, assim, não é só o que está na Constituição da República, mas também nas Constituições estaduais, em especial, nos pontos em que privilegiam uma maior participação popular, seja na iniciativa legislativa, seja na tomada de decisões. Para tanto, a discussão proposta no presente artigo é analisar o pacto federativo, a repartição de competências aos Estados-membros, e a possibilidade de ampliação da democracia por meio das Constituições estaduais. Seu objetivo geral é analisar não apenas o alcance do pacto federativo na Constituição da República e na repartição de competências entre os entes federados, mas também a (im)possibilidade de os Estados-membros inovarem em suas Constituições estaduais e obterem a ampliação da democracia por meio de instrumentos jurídico-políticos, direitos e garantias fundamentais. Para elaboração do estudo, foi utilizado o método indutivo, com as técnicas doreferente, das categorias operacionais, da pesquisa bibliográfca e do fichamento.

Short-term results of left subclavian artery salvage in blunt thoracic aortic injury with short proximal landing zones

ObjectiveThoracic endovascular aortic repair (TEVAR) is the standard treatment of blunt thoracic aortic injury (BTAI). The concept of seal was derived from the treatment of aneurysms and has been adopted for BTAI. Given the location of injury in BTAI, left subclavian artery (LSA) coverage is sometimes necessary. In these often healthier aortas, a shorter proximal landing zone may be acceptable and beneficial in avoiding some complications. Current practice patterns vary, and long-term effects of LSA coverage remain unknown. MethodsA single-institution experience with BTAI for TEVAR was examined from 2006 to 2017. The primary outcome was failure of sealing, endoleak, or persistent aortic injury on follow-up imaging. A centerline was used to measure the length of the landing zone, aortic diameter, and other parameters. Post-TEVAR computed tomography scans were examined for evidence of residual aortic injury. ResultsA total of 30 TEVARs were performed for BTAI. The mean age of the patients was 38.7 years (standard deviation [SD], 19.8 years), and 70% were male. The mean injury severity score was 36.75 (SD, 13.1). Treated patients had grade 2 (36.7%) or grade 3 (63.3%) BTAI. The LSA was salvaged in 23 cases and covered in seven cases. The mean landing zone in LSA uncovered cases was 16 mm (SD, 10.4 mm). There were 15 patients (65%) who had a landing zone <20 mm, and eight (35%) patients had a landing zone >20 mm. The mean landing zone in the seven covered cases was 1.8 mm (SD, 2.4 mm). Procedural success was 96% for the uncovered group and 100% for the covered group. On follow-up imaging, there was only one residual endoleak in all surviving patients (n = 25). Five patients did not have postoperative imaging, two (7%) of whom died of nonaorta-related issues. ConclusionsTEVAR for BTAI in patients with short proximal landing zones of 10 to 20 mm as well as in select patients with landing zones of 5 to 10 mm appears to be safe and efficacious. The aorta demonstrates no residual injury after TEVAR, with the graft acting potentially more as a bridge to allow healing. Long-term issues regarding LSA coverage have been difficult to ascertain and to evaluate because of historically poor follow-up in this population of patients. However, potential issues with LSA coverage and revascularization may be avoided by preserving the subclavian artery even with shorter proximal landing zones.

Strengthening standards, transparency, and collaboration to support medicine evaluation: Ten years of the European Network of Centres for Pharmacoepidemiology and Pharmacovigilance (ENCePP).

Strengthening standards, transparency, and collaboration to support medicine evaluation: Ten years of the European Network of Centres for Pharmacoepidemiology and Pharmacovigilance (ENCePP).

Experimental trials of a sealed ocean kinetic energy harvester for underwater mooring platforms

A full-scale prototype of sealed ocean kinetic energy harvester for underwater mooring platforms was tested on a Stewart platform, a 6-degree-of-freedom ocean motion simulation device, and the overall sealed ocean kinetic energy harvester concept was confirmed. Initial results were collected and significant insights discovered. Experimental results show that the optimal resonant frequency for maximum power output is 1 Hz at high load resistances (large amplitude), or is 1.1 Hz at low load resistances (small amplitude), due to the nonlinear effect. It also demonstrates that the optimal output power takeoff damping is 300 Ω at 1.1 Hz resonant frequency or is 600 Ω at 1.0 Hz resonant frequency or is 100 Ω at nonresonant frequencies. Moreover, the fluctuation impulses in output power curve indicate that the sealed ocean kinetic energy harvester needs great overload capability, and the energy storage system is essential to even out power fluctuations.

Will Bioceramics be the Future Root Canal Filling Materials?

Filling the root canal is necessary when the dental pulp is lost as the dead space will be colonised by bacteria, leading to reinfection of the root canal and treatment failure. Treatment methodology depends on the extent of root formation and the choice of materials available. This review looks at the classical clinical methods and also queries if the newer materials change the treatment rationale. There is considerable confusion with nomenclature for some classes of dental materials. The newer materials have specific features that may not address the treatment needs. Nonetheless, the use of bioceramics and related materials definitely modifies and improves treatment outcome. The classical treatment methods for filling the root canals of both immature and mature teeth are quite well-established in clinical practice. Open apices are treated with calcium hydroxide paste for an extended period of time to stimulate barrier formation at the apex, and the roots are then obturated in a similar way to adult teeth using a solid cone and root canal sealer. With the introduction of bioceramics and related materials, treatment of the immature apex has been shortened to one to two visits. Bioceramic root canal sealers have changed the concept of root canal obturation from the concept of hermetic seal and inert materials to biological bonding and activity. The introduction of these materials has certainly changed the clinical outcomes of filling the root canals. Treatment time has been reduced, which is beneficial for the treatment of paediatric patients. The chemical bond and antimicrobial properties of the sealers in conjunction with hydraulic properties are promising and can potentially improve the clinical success of treatment. Further research is necessary to be able to define clinical protocols for the use of these materials in order to optimise their properties.

Low-Leakage Shaft-End Seals for Utility-Scale Supercritical CO2 Turboexpanders

Supercritical carbon dioxide (sCO2) power cycles could be a more efficient alternative to steam Rankine cycles for power generation from coal. Using existing labyrinth seal technology, shaft-end-seal leakage can result in a 0.55–0.65% points efficiency loss for a nominally 500 MWe sCO2 power cycle plant. Low-leakage hydrodynamic face seals are capable of reducing this leakage loss and are considered a key enabling component technology for achieving 50–52% thermodynamic cycle efficiencies with indirect coal-fired sCO2 power cycles. In this paper, a hydrodynamic face seal concept is presented for utility-scale sCO2 turbines. A 3D computational fluid dynamics (CFD) model with real gas CO2 properties is developed for studying the thin-film physics. These CFD results are also compared with the predictions of a Reynolds-equation-based solver. The 3D CFD model results show large viscous shear and the associated windage heating challenge in sCO2 face seals. Following the CFD model, an axisymmetric finite-element analysis (FEA) model is developed for parametric optimization of the face seal cross section with the goal of minimizing the coning of the stationary ring. A preliminary thermal analysis of the seal is also presented. The fluid, structural, and thermal results show that large-diameter (about 24 in.) face seals with small coning (of the order of 0.0005 in.) are possible. The fluid, structural, and thermal results are used to highlight the design challenges in developing face seals for utility-scale sCO2 turbines.

ChemInform Abstract: Development of Bilayer Glass‐Ceramic SOFC Sealants via Optimizing the Chemical Composition of Glasses — A Review

AbstractReview: 112 refs.

A Review of Similarities between Hakim Tirmizi and Ibn Arabi, with Regard to the Issue of wilayat (authority)

Wilayat (authority) is one of the most important issues in theoretical Sufism. The main reason for dealing with this epistemic issue in Islamic mysticism is perhaps rooted in Islamic texts, especially the Quran, which has led to numerous interpretations and views provided by commentators. In the meantime, the mystical interpretations have had a significant role in changing the meaning and concept of the term and in proposing various discussions in this regard. Among these views, it can be referred to the view of Hakim Tirmizi, Iranian Sufi in the fifth century and that of Ibn Arabi, the founder of theoretical Sufism in the seventh century. The importance of the discussion lies in the fact that there are significant doctrinal and rhetorical similarities between these two famous Sufis, such that the influence of Tirmizi's view on Ibn Arabi cannot be ignored or denied. Proposing the theory of the need for wilayat (authority) and wali (religious authority), the concept of preference of wilayat over prophecy, the characteristics of true wali of the Most High God, and finally the concept and instance of seal of wilayat and seal of prophecy are among the key issues related to wilayat. The present paper seeks to study these issues from the view of Tirmizi and Ibn Arabi's views due to their particular importance in order to find their views and refer to their doctrinal similarities.