Liquid Seals Research Articles

CFD Simulation of an Intermediate Temperature, Two-phase Loop Thermosiphon for Use as a Linear Focus Solar Receiver

Abstract A horizontal two-phase loop thermosiphon (HLTS) has been developed as a potential receiver for commercial line focusing collectors. The design consists of a horizontal evaporator, an ascending tube (riser), a condenserand a descending tube (downcomer) with U-turn. Dowtherm A, which is suitable for the temperature range of 200∼400 o C was adopted as the working fluid in the HLTS. The heat and mass transfer regimes of the HLTS at different condenser inclination anglesin the heat flux input of 8.5 kW/m 2 were simulated using the VOF model. Theresults show thata liquid seal was formed in the U-turn section which effectively prevents the bidirectional flow in the loop. Nucleate boiling and drop-wise condensation regimes were observed. Different flow phenomena, i.e.stratified fluid flow and drop-wise flow, were found in the horizontal and the inclined condensers, respectively. An inclined angle of 5° was found to effectively improve the heat transfer performance compared with the horizontal model in this study although higher performance could be achieved in higher inclinational angles. Overall, by incorporating all of the salient two-phase mechanisms, this approach enables researchers to optimize the geometric design of a HLTS.

Numerical Analysis on Static and Dynamic Characteristics of Liquid Annular Seals With Partial Helical Grooves in Axial Direction

Numerical Analysis on Static and Dynamic Characteristics of Liquid Annular Seals With Partial Helical Grooves in Axial Direction

四角穴付シールの静および動特性に関する実験的解析

四角穴付シールの静および動特性に関する実験的解析

Study of liquid sealed no-core fiber interferometer for sensing applications

We report an experimental investigation on liquid sealed no-core (NCF) fiber based on modal interferometer and applied for temperature sensing applications. The sensor fabrication was very simple and inexpensive because that requires only a splice section of NCF in the middle of single mode fiber (SMF). After fabrication, the interferometer was packed into a liquid-sealed capillary tube and then the sensing measurements were carried out by detecting wavelength sweeping. An experimental demonstration shows that the fabricated interferometer exhibits a high linear response with sensing range and can be easily controlled by tuning the refractive index of the sealed liquid. The highest temperature sensitivity is found to be 201.17pm/°C.

Numerical study on rotordynamic coefficients of the seal of molten salt pump

Molten salt pump is applied to pump high-temperature molten salt as the primary coolant of a molten salt reactor. The pump, generally a vertical rotor system, suffers from radial force generated by the liquid seal component, and the rotordynamic characteristics of the pump are affected considerably. In this paper, the rotordynamic coefficients of the tooth-on-stator liquid seal in molten salt pump are studied. The flow in the seal region is simulated using computational fluid dynamics technique. Parameters of the inlet loss and the pre-swirl at the inlet region of the seal are calculated. The coefficients of resistance and the wall parameters are obtained from the simulation results by data fitting method. The rotordynamic coefficients are analyzed based on the bulk-flow model of liquid seal. The rotordynamic characteristics, with and without the liquid seal, of the objective molten salt pump are inspected. The first critical speed of the rotor is found to increase. Harmonic analysis shows that the pump, being sensitive to unbalance force though, can operate safely under its design specifications.

A new transient CFD method for determining the dynamic coefficients of liquid annular seals

Currently, the dynamic characteristics of annular seals are numerically investigated mainly by solving the bulk flow equations using perturbation method, or by simulating the perturbed flow field of annular seal using CFD method. The adopted disturbance way is generally the circular whirling motion of rotor around seal centre with constant speed. Relative to the transient CFD simulation, the quasisteady CFD simulation introducing Moving reference frame (MRF) has been widely used by researchers. Both the dynamic mesh problem and the time-consuming problem suppress the use of transient CFD simulation in annular seal research. In the paper, a new transient CFD method based on rotor’s variable-speed whirl is presented to improve the time-consuming problem and all the (total 20) dynamic coefficients of concentric liquid seal can be obtained by only two transient CFD simulations, one for the variable-speed cylindrical whirl and the other for the variable-speed conical whirl. The results are compared with those from the experiment, the quasi-steady CFD method and the traditional transient CFD method based on constant-speed whirl. The comparisons show that the new transient method can keep the good accuracy of traditional transient method and meantime largely save the computational time.

509 四角穴付きシールの静および動特性に関する数値解析 : 穴の配列が特性に及ぼす影響(OS5-2 機械力学(1)機械の動的解析と設計問題)

509 四角穴付きシールの静および動特性に関する数値解析 : 穴の配列が特性に及ぼす影響(OS5-2 機械力学(1)機械の動的解析と設計問題)

Stability and bifurcation behaviour of a Laval‐Rotor considering fluid forces in compliant liquid seals

AbstractThis contribution discusses the influence of fluid forces, stemming from compliant, contact‐free annular rotor seals, on the steady state stability and bifurcation behaviour of a rotor. The model used in this work consists of a Laval‐Rotor where the disc runs in a turbulently streamed seal. The compliance of the seal is reduced to a visco‐elastically supported outer seal ring. In order to account for the fluid seal forces the Childs‐Hirs‐model is used. An investigation of the eigenvalues shows that the compliance of the seal support may lead to a significant increase in the stable operating range. A stability‐loss via Hopf‐, Hopf‐Hopf or secondary Hopf‐Bifurcations can occur depending on the system parameters. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Experimental and numerical study of the lubrication regimes of a liquid mechanical seal

The paper presents an experimental and numerical study of the different lubrication regimes occurring in the sealing gap of a mechanical seal with water as sealed fluid. For this purpose, an industrial seal has been tested in a wide range of rotation speeds and fluid pressure values. Friction torque, temperature and leakage were measured and compared to numerical results. These results were obtained on a multi-scale mixed lubrication model considering heat transfer in the solids and seal rings deflections. A satisfactory correlation was obtained demonstrating the relevance of the model. The model is then used to analyze the lubrication regimes.

Theoretical and experimental analysis for leakage rate and dynamic characteristics of herringbone-grooved liquid seals

In this paper, a theoretical analysis method for leakage rate and dynamic characteristics of herringbone-grooved liquid seals is proposed. Steady-state velocities and leakage rate are figured out first with the inertia term of the fluid combined with mass conservation within the seals. Subsequently, the rotordynamic coefficients are solved based on the investigation of Iwatsubo and Childs. Laboratory tests were performed on a specially designed test rig. Detailed comparisons between the experimental results and theoretical predictions show a good agreement on the leakage rate and hydraulic forces for five model seals, which provide an evidence of validation of the analysis method developed in this paper. Moreover, the influence of rotational speed and pressure difference on the leakage rate and rotordynamic coefficients of herringbone-grooved seals is discussed. The results show that the operating conditions and seal structures greatly influence the sealing and rotordynamic performances, which is helpful for designing herringbone-grooved seals.

Highly sensitive liquid-sealed multimode fiber interferometric temperature sensor

A highly sensitive optical fiber temperature sensor based on liquid-sealed coreless multimode fiber (also called no core fiber, NCF) interferometer is proposed and experimentally demonstrated. By inserting the interferometer into a liquid-sealed capillary, a simple and highly sensitive fiber temperature sensor can be implemented. Owing to the high thermo-optic coefficient of the liquid and thermal expansion of the sealant, the interferometric spectra of the proposed sensor are shifting obviously with the variation of temperature; temperature response of the sensor can be effectively modulated through this way. Experimental results show that the sensitivity of the temperature sensor can be improved by tuning the refractive index (RI) value of the sealed liquid; a maximum value of 5.15nm/°C has been obtained when the RI value of the sealed liquid is 1.450, it is close to the RI of the NCF.

Effect of pre-oxidation on the ablation resistance of ZrB2–SiC coating for SiC-coated carbon/carbon composites

To improve ablation resistance of carbon/carbon (C/C) composites at high temperature, ZrB2–SiC coating was prepared on surface of SiC-coated C/C composites by supersonic atmosphere plasma spray. The coated C/C composites were pre-oxidized in air at 1373K. In the present work, the influence of pre-oxidation treatment on the microstructure and ablation resistance of ZrB2–SiC coating was investigated. Ablation resistance of coated C/C composites was tested in oxyacetylene torch environment with the heat flux of 2400kW/m2. Results show that the liquid glass phase seals defects in the as-sprayed coating after pre-oxidation for 15min and a dense coating is obtained. The pre-oxidation coating can protect C/C composites for 90s, which is due to the formation of a dense oxides layer and the molten ZrO2 layer.

Liquid seal for temperature sensing with fiber-optic refractometers.

Liquid sealing is an effective method to convert a fiber-optic refractometer into a simple and highly sensitive temperature sensor. A refractometer based on the thin-core fiber modal interferometer is sealed in a capillary tube filled with Cargille oil. Due to the thermo-optic effect of the sealing liquid, the high refractive-index sensitivity refractometer is subsequently sensitive to the ambient temperature. It is found that the liquid-sealed sensor produces a highest sensitivity of −2.30 nm/°C, which is over 250 times higher than its intrinsic sensitivity before sealing and significantly higher than that of a grating-based fiber sensors. The sensing mechanisms, including the incidental temperature-induced strain effect, are analyzed in detail both theoretically and experimentally. The liquid sealing technique is easy and low cost, and makes the sensor robust and insensitive to the surrounding refractive index. It can be applied to other fiber-optic refractometers for temperature sensing.

Lubrication film flow control by oriented dimples for liquid lubricated mechanical seals

Apart from the function such as micro-hydrodynamic bearings, lubrication reservoir and debris traps, surface textures can be used to control the lubricant׳s flow. In this paper, the leak control feasibility is numerically validated by processing some different oriented dimples on the mechanical seals, including the elliptical, diamond, triangular and rectangular shapes. The streamline-Upwind/Petrov–Galerkin (SUPG) finite element method is used to solve the Reynolds equation by considering mass conservation. Parametric study is performed to analyze the effect of the geometric parameter on the sealing performance such as the flow rate and the load-carrying capability. The reverse pumping capability is compared among these oriented dimples.

An efficient adaptive finite element method algorithm with mass conservation for analysis of liquid face seals

To improve lubrication effect and seal performance, complicated geometrical hydrodynamic grooves or patterns are often processed on end faces of liquid lubricated mechanical seals. These structures can lead to difficulties in precisely estimating the seal performance. In this study, an efficient adaptive finite element method (FEM) algorithm with mass conservation was presented, in which a streamline upwind/Petrov-Galerkin (SUPG) weighted residual FEM and a fast iteration algorithm were applied to solve the lubrication equations (Reynolds equation). A mesh adaptation technique was utilized to refine the computation domain based on a residual posterior error estimator. Validation, applicability, and efficiency were verified by comparison among different algorithms and by case studies on seals’ faces with different groove structures. The study investigated the influence of the order of shape function and the mesh number on the leakage balance. Mesh refinement occurred mainly in cavitation zones when cavitation happened, otherwise it occurred in regions with a high pressure gradient. Numerical experiments verified that the proposed algorithm is a fast, effective, and accurate method to simulate lubrication problems in the engineering field apart from end face seals.

The effect of mechanical and chemical polishing techniques on the surface roughness of heat-polymerized and visible light-polymerized acrylic denture base resins.

The purpose of this study was to compare the effects of mechanical polishing (MP) and chemical polishing (CP) on the average surface roughness (Ra) of heat-cured (HC) and light-cured (LC) denture base acrylic resins. A total of 120 specimens (30×15×3mm) were prepared from one HC and one LC acrylic resin. To remove nodules and gross surface irregularities, all specimens were finished with a lathe-mounted small acrylic bur and 360-grit sandpaper. Ten finished specimens of each acrylic resin were randomly assigned to each of six polishing techniques: Resilit High-luster Polishing Liquid (RHPL), Universal Polishing Paste, Abraso-star K50, pumice, Jet Seal Liquid, or Acrypoint. MP was performed with an automatic polishing machine for 2min, under 50rpm and 500g of load. CP was performed by immersing the HC and LC specimens in preheated methyl methacrylate at 75±1°C for 10s. The surface roughness of the acrylic resin specimens was measured with a contact profilometer. The Ra values were analyzed by two-way analysis of variance, post hoc Scheffe's test, and paired t-test (p⩽0.05). Polished and tested acrylic resin surfaces were evaluated by scanning electron microscopy. MP was more effective than CP. The smoothest surface was obtained with the use of the RHPL on the LC (0.05±0.01μm) or HC (0.07±0.01μm) acrylic resin. Two-way ANOVA showed a statistically significant difference between MP and CP. MP produced the smoothest surface of denture base acrylic resin. The mean surface roughness values after MP and CP were not influenced by the type of acrylic resin.

Thermal stress development of liquid silicone rubber seal under temperature cycling

Liquid Silicone Rubber (LSR) is commonly used as gasket or seal material in many industrial applications. The temperature dependent material property of polymeric rubbers will result in stress relaxation/creep. The development of compressive stress in LSR between two clamping metal plates under temperature cycling is discussed in this paper. It is found that (a) in addition to stress relaxation, thermal expansion or contraction of the material contributes the most in the observed stress variation during temperature change, and (b) the stiffness of LSR appears to change according to temperature history.

Theoretical analysis and experimental study on breakaway torque of large-diameter magnetic liquid seal at low temperature

The existing researches of the magnetic liquid rotation seal have been mainly oriented to the seal at normal temperature and the seal with the smaller shaft diameter less than 100 mm. However, the large-diameter magnetic liquid rotation seal at low temperature has not been reported both in theory and in application up to now. A key factor restricting the application of the large-diameter magnetic liquid rotation seal at low temperature is the high breakaway torque. In this paper, the factors that influence the breakaway torque including the number of seal stages, the injected quantity of magnetic liquid and the standing time at normal temperature are studied. Two kinds of magnetic liquid with variable content of large particles are prepared first, and a seal feedthrough with 140 mm shaft diameter is used in the experiments. All experiments are carried out in a low temperature chamber with a temperature range from 200°C to −100°C. Different numbers of seal stages are tested under the same condition to study the relation between the breakaway torque and the number of seal stages. Variable quantity of magnetic liquid is injected in the seal gap to get the relation curve of the breakaway torque and the injecting quantity of magnetic liquid. In the experiment for studying the relation between the breakaway torque and the standing time at the normal temperature, the seal feedtrough is laid at normal temperature for different period of time before it is put in the low temperature chamber. The experimental results show that the breakaway torque is proportional to the number of seal stages, the injected quantity of magnetic liquid and the standing time at the normal temperature. Meanwhile, the experimental results are analyzed and the torque formula of magnetic liquid rotation seal at low temperature is deduced from the Navier-Stokes equation on the base of the model of magnetic liquid rotation seal. The presented research can make wider application of the magnetic liquid seal in general. And the large-diameter magnetic liquid rotation seal at low temperature designed by using present research results are to be used in some special fields, such as the military field, etc.

The Application of Bridgman’s Seal and B-Ring Seal in the Process of Pump Head Auto-Frettage

In this paper,it is described that the seal selected and structure design of plunger hole and liquid export seal in the pump head’s experiment of extra-high pressure and auto-frettage. Then,Bridgman’s seal and design account for gasket is chose. And liquid export seal used B-ring is chose and analyzed by FEM. The results provide a basis for the experiment about pump head’s extra-high pressure and auto-frettage.

On the Dynamic Properties of Pump Liquid Seals

Rotordynamic instability due to fluid flow in seals is a well known phenomenon that can occur in pumps as well as in steam turbines and air compressors. While analysis methods using bulk-flow equations are computationally efficient and can predict dynamic properties fairly well for short seals, they often lack accuracy in cases of seals with complex geometry or with large aspect ratios (L/D above 1.0). This paper presents the linearized rotordynamic coefficients for a liquid seal with large aspect ratio subjected to incompressible turbulent flow. The fluid-induced forces acting on the rotor are calculated by means of a three-dimensional computational fluid dynamics (3D-CFD) analysis, and are then expressed in terms of equivalent linearized stiffness, damping, and fluid inertia coefficients. For comparison, the seal dynamic coefficients were calculated using two other codes: one developed with the bulk flow method and one based on the finite difference method. The three sets of dynamic coefficients calculated in this study were used then to predict the rotor dynamic behavior of an industrial pump. These estimations were then compared to the vibration characteristic measured during the pump shop test, results indicating that the closest agreement was achieved utilizing the CFD generated coefficients. The results of rotor dynamic analysis using the coefficients derived from CFD approach, improved the prediction of both damped natural frequency and damping factor for the first mode, showing substantially smaller damping factor which is consistent with the experimentally observed instability of the rotor-bearing system. As result of continuously increasing computational power, it is believed that the CFD approach for calculating fluid excitation forces will become the standard in industry.