Thick Liner Research Articles

Magneto-Rayleigh–Taylor instability and feedthrough in a resistive liquid-metal liner of finite thickness

Magneto-Rayleigh–Taylor instability and feedthrough in a resistive liquid-metal liner of finite thickness

Selection of shaped charges parameters for producing aluminum particles with velocities in the range of 2.5–16 km/s

Testing rocket and space technology objects in ground conditions for resistance to the impact of meteoroids and fragments of space debris can be carried out using shaped charges. To substantiate the design parameters of shaped charges that ensure the formation of aluminum particles in a wide velocity range (from 2.5 to 16 km/s), numerical modeling of the formation process was carried out within the framework of a two-dimensional axisymmetric problem of continuum mechanics using three different computing codes to increase the reliability of the results. The calculations consider shaped charges with a diameter of 20–100 mm with aluminum liners of various shapes. It is shown that the formation of particles with velocities close to the lower limit of the considered range is ensured by gently sloping segmental liners of degressive thickness. To form higher-velocity particles with velocities over 5 km/s, it is proposed to use combined liners, the jet-forming part of which has the shape of a hemisphere of constant thickness or the shape of a semi-ellipsoid or semi-superellipsoid of rotation of degressive thickness.

Computational fluid dynamics and artificial neural networks for modelling lined irrigation canals with low‐density polyethylene and cement concrete liners

AbstractThis study numerically investigated the lining effect on the discharges and seepage losses of five reaches which belong to the El‐Sont Canal, Asyut, Egypt, using FLOW‐3D and Slide2 models, respectively. Two lining materials were considered, cement concrete (CC) and CC with low‐density polyethylene (LDPE) film. A cost analysis was performed to explore the feasibility of the proposed lining materials. Moreover, a parametric study was conducted by the Slide2 model to investigate the effect of canal geometry and liner properties on seepage losses. An artificial neural network (ANN) model was developed based on the Slide2 model scenarios to estimate the seepage losses from lined irrigation canals. The results showed that reach the discharge calculated from the FLOW‐3D model increased by 92%–97% and 149%–156%, while the calculated seepage losses from the Slide2 model decreased by 81%–87% and approximately 97% under CC and CC with LDPE film liners, respectively. Cost analysis revealed that the overall cost of CC with LDPE film was higher by 14% than CC. Relying on the importance of saving irrigation water and conveying water to the last reaches, CC with LDPE film is recommended for lining irrigation canals. A parametric study showed that the seepage losses were reduced by more than 96% when the ratio between liner and soil hydraulic conductivities was less than 0.01. A thick liner could maximally decrease the seepage losses by 68%, regardless of the canal geometry. As the developed ANN model showed a close agreement with the Slide2 results with coefficient of determination (R2) and mean squared error values of 0.99 and 0.05, respectively, the ANN model is recommended as a robust and rapid tool for estimating seepage losses from lined irrigation canals.

Retention Evaluation of Implant-Supported Mandibular Overdenture Using Two Different Attachment Systems: An in Vitro Study

Objective: The purpose of this in vitro study was to evaluate the retentive behavior of implant-supported overdenture using two different attachment systems (locator and milled bar-clip attachment system).
 Methods: Six edentulous mandibular models were fabricated from cold‑cure PMMA; the denture-bearing area of the acrylic resin model was covered by an approximately 1.5 mm thick silicone resilient liner to simulate mucosa. The Study models were divided into three groups: Model A (locator), Model B (milled bar-clip attachment system without extension), and Model C (milled bar-clip attachment system with 1cm extension). However, for each study model, a complete mandibular denture was constructed. Anterior, posterior, and central dislodging forces were measured by digital force gauge at the beginning of the study (Initial retention) and after 540 courses of consecutive pulling and inserting the prosthesis (final retention), which was to simulate six months of overdenture use assuming three daily removals and insertions for oral hygiene practice.
 Results: There were statistically significant differences in retention between the group models, and milled bar-clips attachment systems revealed the highest retentive capacity. However, after six months of simulated use, there was a significant retention loss; retention of Model B recorded the highest percentage loss of 55.1%, while Model A recorded the most minor retention loss of 24%. 
 Conclusions: The bar and clip attachment system offered higher retentive values than the locator attachment system. However, the retention loss was correlated to the particular attachment system, and the bar–clip attachment systems had the highest percent of retention loss. In contrast, the locator attachments were associated with acceptable retention, simplicity, and minimal retention.

Polyethylene thickness does not influence aseptic revision rate with highly cross-linked liners in THA with 36-mm femoral heads.

To reduce the risk of dislocation, larger head size can be used in total hip arthroplasty (THA). However, larger head size leads to thinner acetabular liners. With conventional polyethylene, thickness of >8 mm has been advocated to reduce stress and wear rate of the polyethylene. Modern polyethylene has become more wear-resistant. In this study, we investigated if the thickness of sequentially cross-linked polyethylene (XLPE) liners is associated with failure of THA in the medium term. 3654 THAs were included (2009-2016), in which THA was performed with a XLPE liner in combination with a 36-mm femoral head. Patient and surgical characteristics were collected. We compared implant survival of THA with thin liners (<7.9 mm) and thick liners (⩾7.9 mm) with a Kaplan Meier survival analysis at 5 years, median follow-up and 10 years of follow-up with and point aseptic loosening and performed a multivariate analysis to estimate hazard ratios (HR). Median follow-up was 7.7 years (IQR 5.6-9.8). In total, 179 revision procedures were performed, where 82 revisions (46%) were performed for aseptic loosening. The survival rate at 5 years, median and 10 years of follow-up showed no statistically significant difference in implant survival. The survival rate at 10 years follow-up was for thin liners 97.1% (95% CI, 96.3-97.9) and for thick liners 98.2% (95% CI, 97.4-99.0) in the aseptic loosening group (chi-square 2.55; p = 0.11).The adjusted HR for thick liners (⩾7.9 mm) was 0.65 (95% CI, 0.38-1.08) compared with the thin liners (<7.9 mm), which was not significantly different. From this single-centre retrospective study it appears that thinner polyethylene liners are well tolerated when using second-generation highly cross-linked polyethylene. Thickness of the XLPE liners did not influence the risk of aseptic loosening of the implants in the medium term.

Modeling surface water and groundwater interactions for seepage losses estimation from unlined and lined canals

ABSTRACT This study utilized the Slide2 model to simulate surface water and groundwater interactions and estimate seepage losses from unlined and lined irrigation canals. Firstly, it was validated for an unlined canal passing through an unconfined, homogenous, and isotropic infinitely porous depth. Results revealed that the Slide2 model accurately simulated the seepage flow and estimated the seepage losses with R 2 = 0.99 and MAPE = 3.6%. Accordingly, the Slide2 model runs 54 scenarios to explore the effect of different groundwater table (GWT) locations below the canal berm, canal berm widths, and liner properties, such as liner hydraulic conductivity and thickness on the seepage losses from unlined and lined irrigation canals. The results concluded that when the GWT was above the canal surface water level (CSWL), the seepage losses tended to be lower, ensuing an inflow to the canal bed and inner side slope. Conversely, when the GWT was below the CSWL, the seepage losses tended to be higher, ensuing an outflow to the surrounding unsaturated soil. In contrast, the GWT did not affect seepage losses from lined canals. Also, a wider berm resulted in fewer seepage losses, while the canal berm was less effective for lined canals. In addition, the results proved the lining ability to reduce seepage losses. Thus, the average reduction percentage of the seepage losses for lined canal scenarios was 99.87%. Also, a thick liner could decrease the seepage losses maximally by 48.52%, regardless of the GWT location below the canal berm.

Scattering of plane compressional waves by a variable thickness circular lined tunnel

The determination of the dynamic stress concentration factor (DSCF) associated to a circular lined tunnel with variable thickness liner incident upon by compressional P-waves is of particular interest. Due to the lack of symmetry, the treatment of such a problem via the traditional wave-function expansion method is not possible. To circumvent this dilemma it is proposed to employ the dynamic equivalent inclusion method (DEIM). As it will be shown, this method which is based on the notions of the eigenstress and eigenbody-force fields provides an accurate solution for the problem under consideration. In the simple special case where a tunnel with a concentric liner is subjected to plane compressional P-waves the exact wave-function expansion solution given in the literature is recovered. The effect of liner thickness variability on the static and dynamic stress concentration along the interior surface of the liner and along the liner-matrix interface is studied in detail through numerical examples. The maximum value of the DSCF for the concrete and steel liners with positive and negative values of eccentricity is obtained and compared with those of the corresponding concentric cases. It is observed that the eccentricity of the liner results in different behaviors of the stress concentration for the hard (steel) and soft (concrete) liners.

In vivo creep and wear performance of vitamin-E-diffused highly crosslinked polyethylene in total hip arthroplasty.

An acetabular liner thickness of around 6mm remains the "gold standard" in total hip arthroplasty. Some surgeons have been recommending the use of the thickest possible liner because contact stress and strain in articulating surfaces decrease with increasing the wall thickness. The purpose of this study was to determine whether in vivo creep and wear performance could be enhanced using a thicker liner over the standard thickness in vitamin-E-diffused highly crosslinked polyethylene (HXLPE). One hundred and twenty-two hips were allocated to age-matched, sex-matched, and body mass index-matched two subgroups implanted either with a 6.8- or 8.9-mm-thick vitamin-E-diffused HXLPE liner against 28-mm cobalt-chrome femoral head, and followed-up for 7years. Linear and volumetric penetration of femoral head into the liners attributed to creep and wear were analyzed for each group. Compressive creep strain generated at the initial 6months was significantly larger in the 6.8-mm group (2.6%) than in the 8.9-mm group (2.2%). The linear steady-state wear observed after 2years was 0.0019 and 0.0015mm/year, whereas the volumetric steady-state wear was 0.54 and 0.45 mm3/years in the 6.8- and 8.9-mm-thick groups, respectively. Although less strain in the thicker group resulted in a slightly less wear, it did not reach significant differences in the steady-state wear rates between the groups. No clinical significance for using a thicker liner over the standard thickness (6.8mm → 8.9mm) was confirmed in the vitamin-E-diffused HXLPE according to the 7-year follow-up. The wear rates for both thicknesses were very low enough to prevent osteolysis, and no mechanical failure was observed at any follow-up interval. Nevertheless, since the significantly higher strain was seen in the thinner liner, further follow-up is needed to compare the longer term wear and the incidence of osteolysis and component fracture.

Study on Optimization Design of Electromagnetic Loading liner

Electromagnetic loading liner is a new way to obtain a jet, which utilizes the Lorentz force to collapse the liner. To form effective jet, the jet critical forming model of electromagnetic loading is established based on the traditional jet critical forming conditions and electromagnetic loading characteristics. Through dimensional analysis, control variable method and theoretical calculation, the upper and lower critical peak current distributions are obtained. Finally, the loading current of 1mm thick liner structure is optimized by the critical peak current distribution diagram. The jet forming of the liner under the optimized current loading is calculated through theoretical simulation. The whole liner forms a jet, and the jet velocity, kinetic energy and liner utilization are much improved, which verifies the reliability of the critical current distribution diagram.

Metal-on-crosslinked polyethylene in total hip arthroplasty - an excellent combination at fifteen to twentyyears of follow-up.

Cross-linked polyethylene (PE) has been used with great clinical success in total hip arthroplasty (THA) since its debut in the late 1990's. However, reports regarding this bearing couple near the end of its second decade of service are still scant. The aim of this study was to first determine the long term clinical and radiological results and second Investigate what factors affect wear rates using a metal-on-crosslinked PE bearing articulation. 55 THAs using a single brand of cross-linked liner, cementless cup and 28mm hip ball were performed in 44 patients. Age, sex, Charlson Comorbidity Index (CCI) and need for revision surgery were recorded. Linear and volumetric wear was determined using the Martell method. Mean age at operation was 51.2 (29-73 ± 12.1) years. Mean duration of follow-up was 16.9years (range 15.0-20.1 ± 1.1years). Osteolysis was not present in the latest follow-up radiographs. Median linear and volumetric wear rate was 0.038mm/year (95% CI 0.032-0.047) and 7.115mm3/year (95% CI 6.92-17.25) respectively. Acetabular component position was not found to be related to both linear and volumetric wear. No significant difference was found in the linear and volumetric wear rates of thinner and thicker liners (8mm or below and > 8mm) (p = 0.849 and p = 0.64 respectively). Metal-on-crosslinked PE is associated with low linear and volumetric wear rates which has virtually obviated osteolysis and has translated to excellent survivorship even at long term follow up. In-vivo oxidation does not appear to be of clinical concern at this point.

Difference Between Screw Cement Filling and Adequate Osteotomy With Thick Liner for Primary Total Knee Arthroplasty in Patients With Rand IIb Tibial Defects

BackgroundThe effectiveness of 2 treatment options, screw-cement fill, and adequate osteotomy with a thick liner, in treating patients with Rand IIb tibial defects (tibial plateau defects to a depth of 5 to 10 millimeters) in primary total knee arthroplasty (TKA) has not yet been demonstrated. Therefore, we performed a retrospective study to evaluate the differences between these 2 treatments. MethodsWe retrospectively analyzed patients who underwent primary TKA for Rand IIb tibial plateau defects from 2015 to 2020 from a department database. Patients were categorized into the screw-cement and thick liner groups based on the different options used to repair tibial defects. We evaluated Knee Society Score, range of motion (ROM), Insall-Salvati index (ISI), and Forgotten Joint Score (FJS) in both groups. We also compared differences in prosthesis survival, stiffness, myasthenia, and joint clicking between the 2 groups at mean 2 years postoperatively (range, 2 to 2.3). A power analysis was performed on the number of cases in the cohort. ResultsPostoperative femur-tibia mechanical axis (FTMA) correction was significantly higher in the screw-cement group than in the thick-liner group: 18.8 (±5.6°) versus 15.4 (±5.9°) (P < .01); At mean 2 years after surgery, the American Knee Society Functional Score improvement values were higher in the thick-liner group than in the screw-cement group: 36.3 (±12.4) versus 42.4 (±16.4) (P = .05). Postoperative ISI scores were 0.95 (±0.12) points in the screw-cement group and 0.89 (±0.13) points in the-thick liner group (P = .03). There were no statistically significant differences in the Knee Society Clinical Score, ROM, FJS, stiffness, myasthenia, joint clicking, and revision rate. ConclusionThe results of this study showed no significant difference in clinical outcomes between the 2 reconstruction strategies of the screw cement fill technique and the adequate osteotomy and thick liner technique for Rand IIb tibial plateau defects. However, in patients who have FTMA deformities greater than 20° or in younger patients who need to preserve bone volume, we recommend the screw cement filling technique to ensure stable postoperative results and to prepare these patients for possible later surgery.

Validation and modification of a semi-empirical model for sound absorption by perforated liners in the absence of flow based on comparisons with data from full scale measurements

There is much current interest in improving the efficiency gas turbines used in aircraft engines and thereby reducing their carbon emissions. The perforated combustor liners in gas turbine silencers absorb the sound associated with thermo-acoustic instabilities and thereby reduce them. A semi-empirical model has been developed to predict the absorption of perforated liners in the absence of bias flow as a function of frequency in terms of liner characteristic such as orifice diameter, thickness, spacing, orientation and perforation ratio and liner configuration which requires an additional model for the impedance of the cavity behind the liner. The expression used for impedance includes a cavity factor which corrects for the change in combustor liner diameter. Predictions of energy absorption coefficient spectrum are compared with data from measurements on several configurations of full-scale liners. It is found that predictions using the standard tangent term in the cavity impedance do not agree with data at frequencies below 500 Hz as well as predictions that use a cosine term instead. The resulting model, which is validated by the data comparisons, should be useful in optimising liner characteristics for manufacture.

Численный анализ взрывного формирования алюминиевых частиц в диапазоне скоростей 2…16 км/c

Explosive gun launchers are used to test rocket and space systems for their resistance to the impact of meteoroids and fragments of space debris. This work applies numerical simulation within the framework of the two-dimensional axisymmetric problem of continuum mechanics and substantiates design parameters of the shaped charges that form compact aluminum particles weighing up to 1 g and more in a wide range of speeds (from 2 km/s to 16 km/s). Simulation was carried out in relation to the shaped charges of different diameters (from 20 mm to 100 mm) using the ANSYS/AUTODYN, ERUDIT and KOLDUN computer systems. It is shown that charges of larger diameter are required to form faster particles identical in mass. Besides, it is necessary to use segmental cumulative liners of digressive thickness to form particles approaching the lower boundary of the indicated speed range. Wherein, to form faster particles moving at the speeds from 10 km/s to 16 km/s, it is necessary to implement the combined shaped charge liners, where the jet-forming part is shaped as a semi-ellipsoid or a semi-superellipsoid of rotation of the digressive thickness.

Contact stress and sliding wear damage tolerance of hydroxyapatite and carbon nanotube reinforced polyethylene cup liner against zirconia femoral head

A finite element modeling (FEM) approach is carried out to estimate the contact stresses such as von-Mises and shear stress on the acetabular cup liner, made up of ultra-high molecular weight polyethylene (UHMWPE)-hydroxyapatite (HAp)-carbon nanotubes (CNT) based composites. The highlights of this work include the effects of liners' material (UHMWPE-HAp-CNT composites), radial clearance (0.05 to 1 mm), and liners' wall thickness (3 to 8 mm) on contact stresses. The thick liner (thickness: 8 mm) with conformal geometry (radial clearance 0.05 mm) produced the lowest contact stresses (von-Mises: 13.8–17.5 MPa and shear stress: 2.3–3.3 MPa). In contrast, the thin liner (thickness: 3 mm) with higher radial clearance (1 mm) showed the highest von-Mises stress (78.6–131.0 MPa) and shear stress (17.0–23.3 MPa). According to ISO 7206–1, nearly 6–7 times reduced contact stresses were observed because of the wider articulating contact area provided by thick cup liner and its conformity with respect to the femoral head. The UHMWPE-2 wt % CNT composite (UC) showed low von-Mises stress (16.1 MPa) and lowest shear stress (2.3 MPa); thus, it is the most damage tolerant material (wear rate: 2.6 × 10-7 mm3/Nm). The excellent mechanical properties such as hardness (165 MPa), elastic modulus (2.28 GPa), and tensile strength (36.7 MPa) are reasoned to elicit an increased sliding-wear resistance of UC. Thus, CNT-based UHMWPE composite can be the potential acetabular cup liner with a thickness of 8 mm and clearance of 0.05 mm without plastic deformation.

Comparison of Tensile Bond Strength of Permasoft® and GC Reline Soft® Resilient Liners after Denture Base Surface Pretreatment

Objectives: The surface treatment of intaglio denture base surface by sandblasting followed by Methyl Methacrylate (MMA) monomer might enhance the bond strength of resilient liners. The purpose of this study was to evaluate and compare Tensile Bond Strength (TBS) of two resilient liners after surface treatment of Polymethyl Methacrylate (PMMA) resins by sandblasting and MMA monomer. Materials and Methods: One hundred and sixty PMMA resin blocks were randomly divided into eight groups of 20 blocks each based on type of resilient long term liner used (P=PermaSoft and G=GC Reline Soft) and the surface treatment performed (C=untreated Controls, S=Sandblasted, M=MMA monomer treated and SM=Sandblasted and MMA monomer treated: Group PC (PermaSoft untreated Controls), PS (PermaSoft Sandblasted), PM (PermaSoft MMA monomer treated) and PSM (PermaSoft Sandblasted and MMA monomer treated, GC (GC Reline Soft untreated Controls), GS (GC Reline Soft Sandblasted), GM (GC Reline Soft MMA monomer treated) and GSM (GC Reline Soft Sandblasted and MMA monomer treated). Each specimen was prepared by joining two PMMA resin blocks having standard dimensions of 10 × 10 × 40mm with either of the resilient liner of thickness of 10 × 10 × 3mm. The prepared 80 specimens were subjected to testing of TBS by universal testing machine. Also, the types of failure, whether adhesive, cohesive or mixed, were determined by stereomicroscope. One-way ANOVA followed by Tukey post hoc test was used to compare TBS of different surface treatment group with similar resilient liner. Student T-test was used to compare TBS of different resilient liner with similar surface treatment. The level of significance was set at 0.05. Results: There was highly significant difference in mean TBS of four surface treatment subgroups within both the groups (P&lt;0.001). The Tukey post hoc test showed significant difference (P&lt;0.05) between group PC=0.837 ± 0.120MPa and PSM=1.104 ± 0.234MPa; and GS=1.304 ± 0.261MPa and GM=2.053 ± 0.784MPa and highly significant difference (P&lt;0.001) between group PS=0.741 ± 0.103 MPa) and PSM=1.104 ± 0.234MPa); and GS=1.304 ± 0.261MPa) and GSM=2.176 ± 0.262MPa. The mean TBS of GC Reline Soft was significantly higher (&lt;0.001) than PermaSoft in various surface treatment groups. The overall modes of failures were predominantly cohesive type (63.75%) followed by mixed type (18.75%) and adhesive type (17.50%). Conclusions: All groups tested had mean bond strength values greater than the minimum acceptable standard (0.44MPa) for clinical application. MMA monomer treatment alone or in combination with sandblasting resulted in increase of the mean TBS whereas sandblasting resulted in decrease of the mean TBS of both PermaSoft and GC Reline Soft specimens.

Centrifuge Modeling of Chloride Ions Completely Breakthrough Kaolin Clay Liner

The 2 m thick compacted clay liner with a permeability coefficient of 1 × 10−7 cm/s is required in the Chinese technical specifications about landfills. The processes of chloride ion completely breakthrough low permeability barriers (k ≤ 1 × 10−7 cm/s) were modeled at 50 g in a geo-centrifuge. A measuring system was used to monitor solute velocity and conductivity. The entire process of chloride ion completely breaking through 2 m Kaolin clay liner was modeled successfully, which provided a valuable testing technology for centrifuge modeling of contaminant transport through low-permeable clay. The analyses results indicated the breakthrough time of conservative pollutant for the 2 m clay liner with a hydraulic conductivity of 1.0 × 10−9 m/s under Δhw of 40 m was 1.6 years. As for strongly adsorptive pollutants, the breakthrough time t0.1 increased by 9 times when Rd increased from 1 to 10, which indicates that the effect of Rd on the performance of the liner was significant.

Dry and Wet Lubrication Analysis for Multi-Material Hip Assembly

Hip joint repair/replacement is one of the most thriving orthopedic surgical procedures in the human body. The group of patients undergoing hip replacement considerably includes young and physically active persons with varying movements thus requiring longer product life and ease of maintenance. Perfect lubrication in hip assembly ensures a low wear rate and better product life. The present work focuses on dry and wet lubrication analysis of complete implant assembly instead of an individual part. The assembly consists of a stem, head, liner and cup, each made of different materials like a ceramic femoral head mounted over a metallic femoral stem with a polyethylene liner and a metallic acetabular cup. In this work, eight metal-materials are considered for stem/cup, three ceramic materials for the head and two polyethylene materials for the liner. The combinations of these materials are evaluated for various mechanical parameters. Dry (µ = 0.13) and wet (µ = 0.05) lubricating conditions between the liner and femoral head have been considered and their effects on the head, liner and cup have been evaluated for the optimization of Hip joint design. Fifty percent of re-surgery cases arise because of excessive wear out resulting in aseptic loosening of the femoral head and liner interface. Femoral head of size 28 mm diameter with 2 mm thick liner and 3 mm thick acetabular cup are modeled and are analyzed for axial pay load of 2.3 kN. The maximum von mises stress and total deformation for various material combinations of implant assembly have been compared to select the most suitable one for the arthroplasty implantation. The combination of CoCrMo – Ceramics – HXLPE – CoCrMo demonstrates minimum stress and deformation for all three parts i.e. femoral head, liner and acetabular cup under present loading and boundary conditions. ZTA is emerged as the preferred ceramic material for femoral head having a higher compressive strength.

Biomechanical Analysis of Multi-Material Hip Implant Assembly

In present work, a 3D multi-material Charnley’s femoral stem with standard geometry model, i.e., 28mm diameter femoral head and 2mm thick liner, has been developed and analyzed for mechanical behavior like stress, strain, and deformation. An axial load of 2.3kN has been used to analyze for twelve multi-material combinations of CoCr and Ti materials for stem, with three femoral head ceramics materials (alumina, zirconia, and ZTA) and UHMWPE for liner. These mechanical parameters are also well validated with published literature and have been evaluated for investigating the functionality and suitability of biomaterials. Changing the femoral head does not make any significant impact on the mechanical parameters. The preliminary simulation result demonstrates that CoCrMo with Zirconia and UHMWPE demonstrates the most minimum deformation and maximum stress generation. However, CoCrMo leads to modulus mismatch due to its very high modulus. So, implant with less deformation and moderate stress, i.e. Ti-6Al-7Nb is preferred over CoCrMo.

Application of PET as a non-metallic liner for the 6.8 L type-4 cylinder based on the hydrogen cycling test

This study aims to find the evidence that polyethylene terephthalate (PET) is pertinent, with respect to the risk of thermal degradation during fueling, as a liner material of a type-4 composite cylinder for storing 6.8 L of compressed hydrogen. In particular, one type-4 cylinder with the PET liner of thickness 0.6 mm and one type-3 cylinder for comparison have simultaneously undergone 6 cycles of fast fueling (0.15 MPa/s) and fast defueling (0.55 MPa/s) with hydrogen gas in the range of 2 to 45 MPa. The hydrogen temperatures in cylinders, which were measured by a specially-devised thermocouple inserted in each cylinder, change within the range of −30.0 to 70.0 °C. Although the temperature in the type-4 cylinder rises higher than that in the type-3 cylinder due to the lower heat conductivity of PET, it does not exceed 85 °C, which is the limit set by the international standards, EC No. 79. Furthermore, from the measurements of the deformation by the laser displacement sensors, the type-4 cylinder swells less than the type-3 cylinder. The pressure-displacement analysis shows that the deformation of type-4 cylinders occurs reversibly, i.e., defueling makes the cylinder regain its previous shape. In essence, PET is safe against thermal degradation when applied as a liner of a 6.8 L type-4 cylinder for hydrogen storage.

Analysis of Factors for Compacted Clay Liner Performance Considering Isothermal Adsorption

The concentration profiles and breakthrough curves of the 2 m thick compacted clay liner (CCL) given in the specification were compared, considering three different adsorption isotherms (upper convex, linear, and lower concave). In addition, the effects of transport parameters, sorption isotherms, and source concentrations on pollutant migration were analyzed. The results showed that the dimensionless breakthrough curves of different source concentrations considering the linear adsorption isotherm coincided with each other, as the partition coefficient of the linear adsorption isotherm was constant. For the lower concave isotherm, the migration of a large source concentration was slowest, because the partition coefficient of the lower concave isotherm increased with an increase in concentration. For the upper convex isotherm, the migration of a large source concentration was fastest, because the partition coefficient decreased with an increase in concentration. The effects of the nonlinear isotherms on the shape of the outflow curve were similar to the effects of a change in the hydrodynamic dispersion (Dh): the concentration front of the upper convex isotherm was narrower, which was similar to the effect of a reduction in Dh (i.e., PL), and the concentration front of the lower concave isotherm was wider and similar to the effect of an increase Dh (i.e., PL). Therefore, the diffusion and adsorption parameters were fitted separately in the study, in case the nonlinear adsorption behavior was mistakenly defined as linear adsorption.