Ideal Tube Research Articles

Computational Fluid Dynamics (CFD) in Arteriovenous (AV) Graft Implantation Through End-to-Side Anastomosis with Varying Tube Diameters Across Different Vascular Access Locations for Dialysis Treatment.

Background/Objectives: Arteriovenous (AV) graft is a procedure for hemodialysis performed in the arm. Optimizing AV graft design is vital to enhance haemodialytic efficiency in patients with kidney disease. Despite being a standard procedure, making it work optimally is still difficult due to various graft diameters and anastomosis configurations, which have limited studies. This research aims to find the ideal AV graft tube diameter on blood flow and pressure gradients and the ideal body site for AV graft implantation and to study their angles for dialysate flow. Methods: Nine models were designed in Autodesk Fusion 360 with 40°, 50°, and 60° angles each having 2 mm, 5.1 mm, and 14.5 mm diameters, all following specific equations on continuity, momentum (Navier-Stokes Equation)), and the Reynolds Stress Model (RSM). The CFD simulation of these models was performed in ANSYS Fluent with an established parameter of 0.3 m/s inlet velocity and stiff/no-slip graft and artery wall boundary condition. Results: As a result, the design with a diameter of 14.5 mm and a 40° angle was overall the most ideal in terms of minimal wall shear stress and turbulence. Conclusions: Thus the brachiocephalic area or the forearm is calculated to be the most optimal implantation site. Additionally, varying angles do affect dialysate flow, as smaller values cause less stress.

Endotracheal Cuff Pressure in Different Positions in Patients Posted for Surgery under General Anaesthesia: An Observational Study

Background: The ideal endotracheal tube cuff pressure to prevent aspiration is 20-30cmH2O. Lower pressures will result in aspiration and high pressures will lead to tracheal mucosal injuries. Change in patient position may also lead to change in cuff pressures. Our study mainly aims at measuring the cuff pressures in supine, Trendelenberg, reverse Trendelenberg, neck flexion and rotation to one side. Methods: This prospective observational study was conducted after obtaining ethical clearance and patient consent. 50 patients of ASA Classes I and II were included. All patients were intubated with Romson cuffed endotracheal tubes of size 7.5mm for females and 8.5mm for males. The cuff was inflated and cuff pressure set at 28cm H2O using CuffillsR syringe. With head in neutral position, cuff pressure was measured in 15 degree Trendelenberg and reverse Trendelenberg positions. Using angle meter app, the angles were fixed for flexion, extension, and rotation to one side at 30 degrees. The cuff pressure was recorded after 120 seconds after placing the patient in all these positions. Results: The cuff pressure increased by 12.48cm H2O flexion and the cuff pressure increased to 33.22cm H2O in extension. The cuff pressure increased to 38.10cmH2O on rotation, increased by 10.58cmH2O from neutral position in Trendelenberg position and increased by 8.74cmH2O in reverse Trendelenberg position. Conclusion: The cuff pressure changed significantly in all the positions.

Numerical investigation of the reflection of unsteady decelerating incident shock waves

The incident shock attenuation phenomenon in shock tube has received widespread interest because of its inevitable influence on experimental gas properties. However, few studies have investigated the cascading effects of the resulting nonuniformity on shock reflection in shock tunnels before the nozzle. This paper describes a numerical study on the unsteady reflection of a decelerating incident shock driven by a decelerating piston, as a simplification of the complex nonideal factors. The initial decay and uniform parameter distributions are generated based on the non-inertial frame. The results indicate that the existence of the nonuniform area forces the reflected shock wave region to undergo a transition process of attenuation and then stability. The final values of the gas parameters in zone 5 will, therefore, deviate from those given by the traditional relation for an ideal shock tube, which are only dependent on the terminal shock Mach number. This affects the determination of the total temperature T5, which is difficult to measure directly. We discuss the reconstruction of the nonuniform region with the attenuation trajectory of the incident shock wave and find that there is no one-to-one correspondence between this trajectory and the resulting nonuniformity, which introduces additional uncertainties to the predictions. Thus, an analogy method is developed through the multilevel block building algorithm, allowing the total temperature T5 to be determined using the total pressure p5 considering the effect of nonuniformity. Further assessments verify the applicability of this method in cases with multidimensional and viscous interactions.

Numerical study of the influence of amplitudes on heat transfer in a tube bundle

The objective of this study is to investigate the impact of different surface roughness levels on a staggered arrangement of tubes in a cross-flow configuration, with water as the fluid being used. The focus lies in comparing the data obtained from the rough surface configuration with that of a smooth cylinder reference point. To assist this comparison, a comprehensive two-dimensional computational fluid dynamics (CFD) model is created, which accurately represents the distinctive characteristics of each surface shape. This study also included modifying the Remax within a range of 10 000–16 000 and analyzing the outcomes of using four different tube types, each with different supernatant thicknesses labeled as [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text] accordingly. Surprisingly, the tube with a 0.4 wave surface had significantly higher average Nusselt numbers (Nu) compared to the other tubes, indicating superior performance. The ideal tube design was found based on three main metrics: The performance evaluation criterion (PEC), the global performance criterion (GPC) and the average Nu. The performance metrics encompassed the PEC, GPC and the Colburn factor [Formula: see text]. The average Nu of the wavy_0.4 tube was higher than that of the SM by 31.66–32.54%, higher than that of the wavy_0.2 tube by 19.76–20.74%, and higher than that of the wavy_0.1 tube by 9.38–16.58%. According to the statistics, a heat exchanger that cools and has a wave with an amplitude of 0 is the most efficient choice for offshore energy systems. The smooth bundle tube (SBT) demonstrated the most significant increase in GPC, with values of 9.3–12.7% and 20.3–28.3% higher than those of wavy tubes with amplitudes of 0.1 and 0.2, respectively. In addition, correlations for the Nu are given, with results verified using empirical data from Balabani et al.

Numerical modeling and optimization of tube flattening impacts on the cooling performance of the photovoltaic thermal system integrated with phase change material

In this research, a computational fluid dynamics-based numerical simulation is performed to evaluate the influence of tube flattening on the cooling performance of a photovoltaic thermal system integrated with phase change material. Such a study is executed to obtain the four evaluation parameters, including average photovoltaic panel temperature, phase change material melting percentage, tube pressure drops, and the difference between the highest and lowest temperature points on the photovoltaic panel. To obtain the optimum percentage of tube flattening to optimize the cooling performance of the systems, multi-objective optimization by utilizing response surface methodology is done by considering some design requirements, including minimizing average photovoltaic panel temperature, maximizing phase change material melting percentage, minimizing tube pressure drops, and minimizing the difference between the highest and lowest temperature points on the photovoltaic panel. Finally, a parametric analysis is done to explore how certain critical factors (solar radiation, fluid mass flow rate, phase change material thermal conductivity, phase change material enthalpy of fusion, and phase change material melting point) affect the efficiency of the systems. The findings indicate that as tube flattening rises from 0 % to 75 %, the average photovoltaic panel temperature and the difference between the highest and lowest temperature points on the photovoltaic panel decrease which is a positive effect. Conversely, increasing the tube flattening results in an increase in the tube pressure drops and a reduction in the phase change material melting percentage. These changes adversely affect the cooling performance. Considering these impacts and conducting an optimization process, the ideal tube flattening value is 54.78 %. In this optimized state, the average photovoltaic panel temperature reaches 55.21 ˚C, phase change material melting percentage comprises 42.54 %, tube pressure drops is 184.8 Pa, and the difference between the highest and lowest temperature points on the photovoltaic panel is 33.42 ˚C.

A new neurosurgical adjustable pressure suction apparatus with a mechanically controlled air inlet: the study of precise regulation and atraumatic suction.

BackgroundAn essential surgical tool in neurosurgery is the suction tube. The skillful and accurate use of a suction tube facilitates the neurosurgical operation.ObjectiveThis study is to verify the practicality of an adjustable pressure suction tube (APS tube) and to explore the ideal APS tube diameter and tip negative pressure for different intracranial structures.MethodsAPS tubes were used to aspirate brain tissues and carotid arteries of rats. Laser speckle contrast imaging (LSCI) was used to record the blood flow velocity (BFV). We measured APS tube diameter, air inlet size, tip negative pressure and central negative pressure and calculated the correlation between them. In our department, intraoperative real-time parameters including APS tube diameter, length, air inlet size, and central negative pressure were recorded, and the tube tip negative pressure suitable for different intracranial structures and parts was calculated.ResultsAll experiments were carried out using APS tubes. Experiments on rats objectively reflected a severe structural damage to the brain and blood vessels by the suction tube, which might even result in an irreversible reduction in blood flow., Rat carotid arteries and brain tissue suffered severe damage when the tip negative pressure exceeded 33.4 ± 1.8 and 29.2 ± 2.0 kPa, respectively. BFV failed to return to the preoperative level 3 min after the operation (p < 0.05), and this decrease was more pronounced when the suction tube diameter was large (p < 0.05). The tip negative pressure was positively and negatively correlated with central negative pressure and the air inlet size, and was independent of APS tube diameter. A total of 50 operations including 39 tumor resection operations and 11 moyamoya disease bypass operations were recorded. Large-diameter APS tubes (3.5 mm) with an closed air inlet were frequently used to maintain a greater tip negative pressure before the incision of dura mater. When important structures such as motor cortex and brainstem were involved, 1.5- or 2.0-mm-diameter APS tubes were mostly used, and an air inlet was opened up to 0.7–2.1 mm to maintain a safe tip negative pressure (7.4–27.9 kPa).ConclusionAPS tubes with a mechanical knob provide stable and precise adjustment of the tip negative pressure, avoiding excessive negative pressure that causes serious damage to the intracranial structure. And, this allows the surgeon to hold the suction tube more freely and operate at any angle with an appropriate fulcrum near the incision to achieve efficient atraumatic suction and enhance surgical safety.

A novel angiographic method to estimate arterial blood flow rates using contrast reflux: Effect of injection parameters.

Contrast reflux, which is the retrograde movement of contrast against flow direction, is commonly observed during angiography. Despite a vast body of literature on angiography, the hemodynamic factors affecting contrast reflux have not been studied. Numerous methods have been developed to extract flow from angiography, but the reliability of these methods is not yet sufficient to be of routine clinical use. To evaluate the effect of baseline blood flow rates and injection conditions on the extent of contrast reflux. To estimate arterial flow rates based on measurement of contrast reflux length. Iodinated contrast was injected into an idealized tube as well as a physiologically accurate model of the cervico-cerebral vasculature. A total of 194 high-speed angiograms were acquired under varying "blood" flow rates and injection conditions (catheter size, injection rate, and injection time). The length of contrast reflux was compared to the input variables and to dimensionless fluid dynamics parameters at the catheter-tip. Arterial blood flow rates were estimated using contrast reflux length as well as a traditional transit-time method and compared to measured flow rates. Contrast reflux lengths were significantly affected by contrast injection rate (p < 0.0001), baseline blood flow rate (p= 0.0004), and catheter size (p= 0.04), but not by contrast injection time (p= 0.4). Reflux lengths were found to be correlated to dimensionless fluid dynamics parameters by an exponential function (R2 = 0.6-0.99). When considering the entire dataset in unison, flow estimation errors with the reflux-length method (39% ± 33%) were significantly higher (p= 0.003) than the transit-time method (33% ± 36%). However, when subgrouped by catheter, the error with the reflux-length method was substantially reduced and was significantly lower (14% ± 14%, p < 0.0001) than the transit-time method. Results show correlations between contrast reflux length and baseline hemodynamic parameters that have not been reported previously. Clinically relevant blood flow rate estimation is feasible by simple measurement of reflux length. In vivo and clinical studies are required to confirm these correlations and to refine the methodology of estimating blood flow by reflux.

The chimney tube in musical acoustics: A textbook-level formulation for students and musicians.

The chimney tube, comprising connected body and chimney segments with respective diameters d1 and d2, is ubiquitous in musical acoustics and can be a useful analog for flute embouchure holes, woodwind toneholes, and organ pipes. Most treatments are complex and not readily accessible to lay audiences. Simple expressions for the input impedance of ideal chimney tubes are derived by two methods. Chimneys short compared to the overall length of the resonator are shown to have effective lengths larger than their physical length by the factor (d1/d2)2 when the chimney is open and smaller by the same factor when closed. Examples presented range from a simple cylindrical tube open at both ends to the classic Helmholtz resonator. Insights are provided about tonehole placement and the tradeoffs between a tonehole's position and diameter; how the resonance frequencies of an open-open chimney tube with a short chimney do not depend on which end is used as the input; and the interesting way in which a long chimney can change the spacing of the resonances from the 1:2:3 pattern of a cylinder open at both ends to the characteristic 1:3:5 pattern of a cylinder open at one end and closed at the other.

Ideal Depth of Endotracheal Intubation at the Vocal Cord Level in Pediatric Patients Considering Racial Differences in Tracheal Length.

Numerous formulas that can predict endotracheal intubation depth at the corner of the mouth or the nasal wing of patients have been reported, even though the oral and nasal cavity anatomies differ among patients. Therefore, the purpose of this study was to derive a simple and reliable formula to predict the ideal endotracheal tube insertion depth at the vocal cord level in pediatric patients. The current study was conducted as a retrospective observational study, involving 425 and 335 cardiac pediatric patients in Germany and Japan, respectively, and aimed to determine a formula for predicting tracheal length and ideal depth of endotracheal intubation at the vocal cord level in pediatric patients. The distance between the vocal cords and the carina tracheae was defined as the tracheal length, and was measured on preoperative chest radiographs obtained in the supine position. The tracheal length in cardiac pediatric patients ranged from 6 to 10% of the body height in Germany and from 7 to 11% in Japan. This study revealed racial differences in the tracheal length, that is, in the ideal depth of endotracheal intubation at the vocal cord level. This study suggests that an adequate endotracheal intubation depth can be achieved by inserting endotracheal tubes at the vocal cord level with the minimum tracheal length of each racial group in pediatric patients, for example, 6% and 7% of the body height in Europeans and Asians, respectively. If the endotracheal tube inserted with this method appears to be shallow on chest radiographs, this does not represent an increased risk of accidental extubation, due to an excessively short intubation depth, because the minimum tracheal length for each racial group is considered. That is, it is not due to the endotracheal tube insertion length, but is likely due to the tracheal length of the patient, who has a relatively long tracheal length in the racial group.

Ideal endotracheal tube insertion depth in neonates with a birthweight less than 750g.

Appropriate management of the endotracheal tube (ETT) insertion depth is important. The depth calculated using Tochen's formula is overestimated in extremely-low- birthweight infants, particularly those with a birthweight <750g. Gestational age has been shown to be particularly useful in the Neonatal Resuscitation Program, 7th edition.5 However, a randomized trial for estimating the ETT insertion depth failed to show the advantage of using gestational age over birthweight.6 Therefore, we aimed to estimate the appropriate ETT insertion depth in neonates weighing <750g. This was a single-center, retrospective observational study including neonates weighing <750g who required intubation. The appropriate depth was determined by adjusting the distance between the actual ETT position and the area from the first to the second thoracic vertebra on the radiograph. Correlations between gestational age and physique were investigated using Pearson's correlation coefficient. We examined small-for- gestational-age (SGA) infants and non-SGA infants separately. Forty neonates were enrolled in this study. The mean gestational age and birthweight were 26.3weeks and 620g respectively. Twenty infants were SGA. The ETT position was deep in 35 of 40 cases, with the strongest correlation between weight and ETT insertion depth. The correlation with gestational age was not observed in this study. Our study showed that the ideal ETT insertion depth at birth correlates with birthweight in neonates weighing <750g. Therefore, determination by gestational age may not be feasible in populations with a high proportion of SGA infants.

Coronary artery plaque growth: A two-way coupled shear stress-driven model.

Atherosclerosis in coronary arteries can lead to plaque growth, stenosis formation, and blockage of the blood flow supplying the heart tissue. Several studies have shown that hemodynamics play an important role in the growth of coronary artery plaques. Specifically, low wall shear stress (WSS) appears to be the leading hemodynamic parameter promoting atherosclerotic plaque growth, which in turn influences the blood flow and WSS distribution. Therefore, a two-way coupled interaction exists between WSS and atherosclerosis growth. In this work, a computational framework was developed to study the coupling between WSS and plaque growth in coronary arteries. Computational fluid dynamics (CFD) was used to quantify WSS distribution. Surface mesh nodes were moved in the inward normal direction according to a growth model based on WSS. After each growth stage, the geometry was updated and the CFD simulation repeated to find updated WSS values for the next growth stage. One hundred twenty growth stages were simulated in an idealized tube and an image-based left anterior descending artery. An automated framework was developed using open-source software to couple CFD simulations with growth. Changes in plaque morphology and hemodynamic patterns during different growth stages are presented. The results show larger plaque growth towards the downstream segment of the plaque, agreeing with the reported clinical observations. The developed framework could be used to establish hemodynamic-driven growth models and study the interaction between these processes.

Effects of tracheal intubation and tracheal tube position on regional lung ventilation: an observational study.

Anaesthesia and positive pressure ventilation cause ventral redistribution of regional ventilation, potentially caused by the tracheal tube. We used electrical impedance tomography to map regional ventilation during anaesthesia in 10 patients with and without a tracheal tube. We recorded impedance data in subjects who were awake, during bag-mask ventilation, with the tracheal tube positioned normally, rotated 90° to each side and advanced until in an endobronchial position. We recorded the following measurements: ventilation of the right lung (proportion, %); centre of ventilation (100%=entirely ventral); global inhomogeneity (0%=homogenous); and regional ventilation delay, an index of temporal heterogeneity. We compared the results using Student's t-tests. Relative to subjects who were awake, anaesthesia with bag-mask ventilation reduced right-sided ventilation by 5.6% (p=0.002), reduced regional ventilation delay by 1.6% (p=0.025), and moved the centre of ventilation ventrally from 51.4% to 58.2% (p=0.0001). Tracheal tube ventilation caused a further centre of ventilation increase of 1.3% (p=0.009). With the tube near the carina, right-sided ventilation increased by 3.2% (p=0.031) and regional ventilation delay by 2.8% (p=0.049). Tube rotation caused a 1.6% increase in right-sided ventilation compared with normal position (p=0.043 left and p=0.031 right). Global inhomogeneity remained mostly unchanged. Ventral ventilation with positive pressure ventilation occurred with bag-mask ventilation, but was exacerbated by a tracheal tube. Tube position influenced ventilation of the right and left lungs, while ventilation overall remained homogenous. Tube rotation in either direction resulted in ventilation patterns being closer to when awake than either bag-mask ventilation or a normally positioned tube. These results suggest that even ideal tube positioning cannot avoid the ventral shift in ventilation.

Hőátadási tényező meghatározása köpenytéri hőátadás esetén

Ezen cikk témája az iparban használatos csőköteges hőcserélők köpenytéri hőátadási tényezőjének meghatározási módszereinek áttekintése. Bár néhány irodalom megtalálható a témával kapcsolatban, viszont magyar fordításban meglehetősen kisszámú forrás érhető el. A köpenytéri hőátadási tényezőt számos, a hőcserélő geometriájától függő módosító tényező befolyásolja. Ezen tényezők: a terelőlemez vágási korrekciós tényező, a terelőlemez hézag korrekciós tényező, a csőköteg bypass korrekciós tényező, az egyenlőtlen áramlási zóna korrekciós tényező, a falviszkozitási korrekciós tényező valamint az ideális csőköteg hőátadási tényező. Jelen publikációban ezen módosító tényezők számítási módszerei és jellemző értékei kerülnek bemutatásra.

Application of H2 and CO2 addition in driver section on shock tube ignition delay measurement

AbstractShock tube is an effective tool to study the reaction dynamic. As a key parameter, the accuracy measurement of ignition delay time depends on the pressure plateau sustained time. Helium is the most frequently used as driver gas in the shock tube related study. To seek a wider scope of driver gas, H2 was attempted in this paper. The driver capability of H2 and He was compared by theory analysis and experiment, respectively. In addition, to acquire a longer test time, H2/CO2 as driver gas was adopted to test the tailoring condition. Using a 1‐D ideal shock tube assumption, the driver gas tailoring curve is calculated. Results show that the driver capability of H2 is obviously stronger than that of He gas and H2/CO2 group driver gas performs as well as He/N2 group driver gas. The pressure plateau sustained time can extend to 11 ms under tailoring condition by H2/CO2 mixture driving. Furthermore, the comparison of H2‐based and He‐based driver gas models shows no obvious impact on ignition delay measurement. Hence, using H2 as driver gas is more economic because of its cheaper price than He, and it can reduce the experiment risk because of the relative lower diaphragm burst pressure. However, the adverse result is that the vacuum time turns more than one third longer compared with non‐H2 driving mode.

Filling accuracy and imprecision of commercial evacuated sodium citrate coagulation tubes

Current recommendations advocate that blood tubes for coagulation testing should be filled not less than 90% of their nominal filling volume, since under- or over-filling >10% may generate unreliable results of some hemostasis assays. This study was hence aimed to explore filling accuracy and precision of commercial blood tubes. Between-lot variations of 3 different lots (20 tubes per lot) of 3.2% citrate blood tubes manufactured by Becton Dickinson, Greiner and Kima were studied. One additional lot from each manufacturer was assessed in triplicate (three series of 20 tubes), to assess within-lot variation. All tubes were first weighed empty and then filled with distilled water by a syringe, under ideal filling conditions. Filled tubes were weighed again, in duplicate. For each 20 tubes series, mean bias (deviation from the ideal tube filling volume) and imprecision (coefficient of variation; CV%) were calculated. All biases were within ±10%. Within-lot and between-lot variation in filling volume was acceptable, and comprised between 0.4 and 2.4%. Greiner tubes were the most accurate (bias, −1.0 to 2.4%), followed by Kima (bias, −7.8 to −5.9%) and Becton Dickinson (bias, −9.6 to 3.3%) tubes. The highest between-lot difference was noted for Becton Dickinson tubes (up to 12.9%), followed by Greiner and Kima tubes (up to 3.4 and 1.8%, respectively). Although coagulation tubes filling accuracy was within ±10% for all three tested manufacturers, the overall bias was found to be variable among manufacturers and lots. Major effort shall be made by blood tube manufacturers for improving standardization of their products.

Evolution of a new geometric profile for an ideal tube inversion for crash energy absorption

Circular tubes under axial load undergoing deformation through inversion phenamena are referred to as invertubes. Inversion phenomena controls high initial peak crush force which is a fundamental requirement of an energy absorbing structure in road vehicles and helps in achieving nearly 100% stroke and crush force efficiencies. This rare combination of these three features offers a good potential for invertubes to be an ideal choice for impact crash energy absorption. Researchers have always attempted to predict inversion forces in invertubes in terms of geometrical and material parameters through empirical relations; and often ignored the geometric imperfections on plastic deformation and their influence on the inversion process. Limited knowledge exist on inversion using stainless steel SS304 material. In this paper, series of attempts are made to evolve a new invertube profile with SS304 material to achieve desirable inversion charecterisitics for an ideal energy absorption. In this process, the effect of geometric parameters and their imperfections that contribute to effective inversion of invertubes have been studied in detail through FEA and experiments. A new invertube profile has been proposed that addresses anamolies in existing literature and inversion characteristics of this profile have been validated experimentally in a quasi-static environment.

Application of the ideal soil model and tube hydraulics to study filtration processes

Some regularities of filtration processes are considered in the article. On the basis of experimental studies of fluid motion in capillary tubes of various types, tortuosity is modelled. These experiments demonstrate that the model of ideal soil in the form of cylindrical tubes should take into account the rheological dependence of the Newtonian fluid on the pressure gradient, that is, deviation from linearity. Determination of the permeability of a porous medium is ambiguous and depends on the conditions, scales, and methods of investigation. The Darcy’s law requires refinement because of the nonlinearity of viscosity at different filtration velocities. Based on the analysis of modelling results, a non-linear dependence is suggested that resembles the Leverett function suitable for both linear filtration and beyond linearity and has concave and convex parts.

Surveying the Literature

Surveying the Literature

Dynamic pressure sensitivity determination with Mach number method

Measurements of pressure in fast transient conditions are often performed even if the dynamic characteristic of the transducer are not traceable to international standards. Moreover, the question of a primary standard in dynamic pressure is still open, especially for gaseous applications.The question is to improve dynamic standards in order to respond to expressed industrial needs. In this paper, the method proposed in the EMRP IND09 ‘Dynamic’ project, which can be called the ‘ideal shock tube method’, is compared with the ‘collective standard method’ currently used in the Laboratoire de Métrologie Dynamique (LNE/ENSAM).The input is a step of pressure generated by a shock tube. The transducer is a piezoelectric pressure sensor.With the ‘ideal shock tube method’ the sensitivity of a pressure sensor is first determined dynamically. This method requires a shock tube implemented with piezoelectric shock wave detectors. The measurement of the Mach number in the tube allows an evaluation of the incident pressure amplitude of a step using a theoretical 1D model of the shock tube. Heat transfer, other actual effects and effects of the shock tube imperfections are not taken into account. The amplitude of the pressure step is then used to determine the sensitivity in dynamic conditions.The second method uses a frequency bandwidth comparison to determine pressure at frequencies from quasi-static conditions, traceable to static pressure standards, to higher frequencies (up to 10 kHz).The measurand is also a step of pressure generated by a supposed ideal shock tube or a fast-opening device. The results are provided as a transfer function with an uncertainty budget assigned to a frequency range, also deliverable frequency by frequency. The largest uncertainty in the bandwidth of comparison is used to trace the final pressure step level measured in dynamic conditions, owing that this pressure is not measurable in a steady state on a shock tube. A reference sensor thereby calibrated can be used in a comparison measurement process.At high frequencies the most important component of the uncertainty in this method is due to actual shock tube complex effects not already functionalized nowadays or thought not to be functionalized in this kind of direct method.After a brief review of both methods and a brief review of the determination of the transfer function of pressure transducers, and the budget of associated uncertainty for the dynamic calibration of a pressure transducer in gas, this paper presents a comparison of the results obtained with the ‘ideal shock tube’ and the ‘collective standard’ methods.

Thermoelastic stress in concentrating solar receiver tubes: A retrospect on stress analysis methodology, and comparison of salt and sodium

Temperature distribution in nonaxisymmetrically concentrating solar thermal receivers tubes is calculated for the steady-state solution with a Gauss-Seidel iteration in cylindrical coordinates. The classical plane-biharmonic thermoelastic approach to nonaxisymmetrically heated tube stress is applied. Calculation of the dominant axial thermal stress component is included. Validation is obtained with the linear-elastic thermal stress OpenFOAM® solver. Thermoelastic stress in stainless steel 316 Schedule 5S DN25 (1″) tubes containing liquid sodium is found to be 35% lower than in tubes containing molten salt. The difference is due to the higher conductivity of liquid sodium which maintains a smaller temperature difference between the front and back tube sides. A simplified thermal stress formula is shown to be erroneous if not implemented as originally documented. The sensitivity of tube thermoelastic stress to tube material and flow properties is illustrated with parameter variation, and the impact of solar concentrated heat flux is explored with some typical and ideal tube circumference flux profiles.