Conduit Lengths Research Articles

Study on heat transfer characteristics of pulsating heat pipe heat exchanger with asymmetric structure

The Pulsating Heat Pipe (PHP), lauded for its efficacy in heat transfer, is distinguished by its uncomplicated architecture, economical production, diminutive form, and robust adaptability to environmental conditions. This study delineates the design of an asymmetric PHP heat transfer apparatus, achieved through the alteration of select conduit lengths within the comprehensive circulation system. The thermal transfer efficacy of this apparatus was empirically scrutinized under dual dissipation modalities: natural and forced convection. It was observed that the asymmetric PHP, when devoid of oscillatory activity, maintained a heat source temperature of 25∘C, whereas the temperature escalated to 26∘C upon the initiation of pipe vibration. Under the regime of forced convection, the asymmetric PHP demonstrated expedited activation, reduced initiation temperature, and heightened oscillatory behavior compared to its natural convection counterpart, thereby facilitating the phase change condensation within the condensation segment and ensuring efficient, sustained heat dissipation. Consequently, this bolstered the PHP’s heat transfer capabilities. The thermal resistance exhibited a declining trajectory under both dissipation strategies, with forced convection consistently yielding lower thermal resistance than natural convection. Nonetheless, the decrement in thermal resistance was gradual near the critical startup juncture and throughout the initiation phase. The PHP’s equivalent thermal conductivity displayed an upward trend in tandem with the escalation of the heat source’s temperature under both dissipation methods. Despite the superior heat transfer performance at elevated heat source temperatures, the efficiency of natural convection dissipation remained suboptimal, necessitating the application of forced convection to the condensation segment to further enhance the PHP’s thermal transfer proficiency and the overall device performance.

A Time-of-Flight Estimation Method for Acoustic Ranging and Thermometry Based on Digital Lock-In Filtering.

Accurate ranging and real-time temperature monitoring are essential for metrology and safety in electrical conduit applications. This paper proposes an acoustic time-of-flight (TOF) estimation method based on the digital lock-in filtering (DLF) technique for conduit ranging and thermometry. The method establishes the relationship between the frequency and the time domain by applying a linear frequency modulated Chirp signal as the sound source and using the DLF technique to extract the first harmonic of the characteristic frequencies of the transmitted and received signals. Acoustic TOF estimation in the conduit is then achieved by calculating the mathematical expectation of the time difference between each characteristic frequency in the time-frequency relationship of the two signals. The experimental results with enhanced noise interference on different conduit lengths and various temperature conditions, proved that the proposed DLF method can establish a robust linear time-frequency relationship according to the characteristics of the Chirp signal, and the measurement accuracy of TOF has also been confirmed. Compared to the conventional method, the DLF method provides the lowest absolute error and standard deviation for both distance and temperature measurements with an enhanced robustness.

COMSOL Multiphysics\xae modelling of oxygen diffusion through a cellulose nanofibril conduit employed for peripheral nerve repair

BackgroundPeripheral nerve injury can cause significant impairment, and the current methods for facilitating repair, particularly over distances greater than approximately 1 mm, are not entirely effective. Allografts, autografts, and synthetic conduits are three of the most common surgical interventions for peripheral nerve repair; however, each has limitations including poor biocompatibility, adverse immune responses, and the need for successive surgeries. A potential new method for promoting peripheral nerve repair that addresses the shortcomings of current interventions is a biocompatible cellulose nanofibril (CNF) conduit that degrades in-vivo over time. Preliminary testing in multiple animal models has yielded positive results, but more information is needed regarding how the CNF conduit facilitates nutrient and gas flow.ResultsThe current work employs 3D modelling and analysis via COMSOL Multiphysics® to determine how the CNF conduit facilitates oxygen movement both radially through the conduit walls and axially along the length of the conduit. Various CNF wall permeabilities, conduit lengths, and nerve-to-conduit diameter ratios have been examined; all of which were shown to have an impact on the resultant oxygen profile within the conduit. When the walls of the CNF conduit were modeled to have significant oxygen permeability, oxygen diffusion across the conduit was shown to dominate relative to axial diffusion of oxygen along the length of the conduit, which was otherwise the controlling diffusion mechanism.ConclusionsThe results of this study suggest that there is a complex relationship between axial and radial diffusion as the properties of the conduit such as length, diameter, and permeability are altered and when investigating various locations within the model. At low wall permeabilities the axial diffusion is dominant for all configurations, while for higher wall permeabilities the radial diffusion became dominant for smaller diameters. The length of the conduit did not alter the mechanism of diffusion, but rather had an inverse relationship with the magnitude of the overall concentration profile. As such the modeling results may be employed to predict and control the amount and distribution of oxygenation throughout the conduit, and hence to guide experimental conduit design.

Surge predictions in a large stormwater tunnel system using SWMM

ABSTRACT Stormwater tunnels often have massive geometries, with conduit lengths of several kilometers and a wide range of diameter sizes. Modeling rapid filling of these systems is a complex task and needs adequate methodology. One model used in hydraulic analysis of stormwater tunnels is the EPA’s Storm Water Management Model (SWMM). However, model setup conditions related to a pressurization algorithm can significantly affect SWMM’s accuracy in surge prediction. This work evaluates SWMM 5.1 accuracy in simulating rapid filling of tunnels, particularly surging conditions. This evaluation is done using a real-world tunnel geometry, the Upper Des Plaines Tunnel, which is part of Chicago’s TARP tunnel system. Variables considered in the SWMM model setup include discretization strategy and pressurization algorithm, and its results are compared with HAST predictions, a model specifically designed to represent surges in tunnels. This work shows that, with adequate setup, SWMM can represent surging in stormwater tunnels much more precisely.

Influence of dual conduit structure on solute transport in karst tracer tests: An experimental laboratory study

We conducted lab-scale experiments to investigate the mechanism of dual-peaked breakthrough curves (BTCs) in karst tracer tests. Three groups of dual conduit structures were constructed by varying: (1) the length ratio between the two conduits for a fixed length of the shorter conduit, (2) the total length of the conduits for a fixed length ratio, (3) the connection angle between the conduits. The BTCs generated by the tracing experiments were fitted by a Dual-Region Advection Dispersion (DRAD) model to derive effective transport parameters.Our results confirm that the dual conduit structure triggers the double-peaked BTCs. Increasing the conduit length for a fixed length ratio or increasing the length ratio increases peak separation. The connection angles between the two conduits θ1 and θ2 also influence the BTCs: increasing θ1 and decreasing θ2 causes the first peak to get smaller and the second peak to get larger. The DRAD model can reproduce the dual-peaked BTCs while its application to the case of single-peaked BTCs may be problematic due to strong interaction between model parameters. A method is proposed for estimating underground karstic conduit lengths from experimental dual-peaked BTCs.

Predictors of Patient-Reported Reflux After Esophagectomy

Patient-reported reflux is among the most common symptoms after esophagectomy. This study aimed to determine predictors of patient-reported reflux and to ascertain whether a preserved pylorus would protect patients from symptomatic reflux. A prospective clinical study recorded patient-reported reflux after esophagectomy from August 2015 to July 2018. Eligible patients were at least 6 months from creation of a traditional posterior mediastinal gastric conduit, had completed at least 1 reflux questionnaire, and had the pylorus treated either temporarily (≥100 IU Botox [onabotulinumtoxinA]) or permanently (pyloromyotomy or pyloroplasty). Of the 110 patients meeting inclusion criteria, the median age was 65 years, and 88 of the 110 (80%) were male. Botox was used in 15 (14%) patients, pyloromyotomy in 88 (80%), and pyloroplasty in 7 (6%). A thoracic anastomosis was performed in 78 (71%) patients, and a cervical anastomosis was performed in 32 (29%). Esophagectomy was performed for malignant disease in 105 of 110 (95%), and 78 of 110 (71%) patients were treated with perioperative chemoradiation. Multivariable linear regression analysis revealed that patient-reported reflux was significantly worse in patients with shorter gastric conduit lengths (P= .02) and in patients who did not undergo perioperative chemoradiation (P= .01). No significant difference was found between patients treated with pyloric drainage and those treated with Botox. The absence of perioperative chemoradiation therapy and a shorter gastric conduit were predictors of patient-reported reflux after esophagectomy. Although few patients had Botox, preservation of the pylorus did not appear to affect patient-reported reflux. Further objective studies are needed to confirm these findings.

Anatomic Fitting of Total Artificial Hearts for In Vivo Evaluation

Successful anatomic fitting of a total artificial heart (TAH) is vital to achieve optimal pump hemodynamics after device implantation. Although many anatomic fitting studies have been completed in humans prior to clinical trials, few reports exist that detail the experience in animals for in vivo device evaluation. Optimal hemodynamics are crucial throughout the in vivo phase to direct design iterations and ultimately validate device performance prior to pivotal human trials. In vivo evaluation in a sheep model allows a realistically sized representation of a smaller patient, for which smaller third-generation TAHs have the potential to treat. Our study aimed to assess the anatomic fit of a single device rotary TAH in sheep prior to animal trials and to use the data to develop a three-dimensional, computer-aided design (CAD)-operated anatomic fitting tool for future TAH development. Following excision of the native ventricles above the atrio-ventricular groove, a prototype TAH was inserted within the chest cavity of six sheep (28-40 kg). Adjustable rods representing inlet and outlet conduits were oriented toward the center of each atrial chamber and the great vessels, with conduit lengths and angles recorded for future analysis. A three-dimensional, CAD-operated anatomic fitting tool was then developed, based on the results of this study, and used to determine the inflow and outflow conduit orientation of the TAH. The mean diameters of the sheep left atrium, right atrium, aorta, and pulmonary artery were 39, 33, 12, and 11 mm, respectively. The center-to-center distance and outer-edge-to-outer-edge distance between the atria, found to be 39 ± 9 mm and 72 ± 17 mm in this study, were identified as the most critical geometries for successful TAH connection. This geometric constraint restricts the maximum separation allowable between left and right inlet ports of a TAH to ensure successful alignment within the available atrial circumference.

Computational Fluid Dynamics Study for Flow of Natural Gas through High-pressure Supersonic Nozzles: Part 2. Nozzle Geometry and Vorticity

The computational fluid dynamics technique is used to study the behavior of high-pressure natural gas when it flows through nozzles with supersonic velocities. Effect of nozzle geometry is discussed by inserting a constant area channel between the convergent and divergent parts of the system. Various conduit lengths are analyzed to show how the minimum temperature could be influenced by the geometry of the nozzle. The results also show that changing channel length can affect the position of shockwave. The results for the effect of vorticity on the performance of the nozzles show that, although losses in pressure increase due to inlet swirl flow, vorticity increases very sharply in the vicinity of the shock. It could be concluded that the region just before the shock spot is the main region where fine particles can be separated because of the large vorticity strength. Shock with reasonable strength may be favored in practical applications where fine particles separation is desired.

Seasonal changes in the ion‐mediated increase of xylem hydraulic conductivity in stems of three evergreens: any functional role?

Changes in hydraulic conductivity (Kh) were measured monthly in stems of Laurus nobilis between July 2005 and June 2006 and in March and June 2006 in stems of Prunus laurocerasus and Phillyrea latifolia. Percent enhancement of Kh (ΔKh) was recorded as KCl injected into stems compared with deionized water. Stems of L. nobilis perfused with increasing [KCl] saturated the hydraulic effect at 50 mM KCl, while P. laurocerasus and Ph. latifolia showed saturation at 17 and less than 5 mM KCl, respectively. Impressive seasonal changes in ΔKh were recorded in L. nobilis, from +120% in February to +20% during the growth period. ΔKh was negatively correlated to minimum air temperatures and was highest during winter frost. Negative correlation also existed between ΔKh and conduit lengths as detected during transition of plants from activity to winter rest and from winter to spring. In the winter, the thermal effect was prevailing. High cavitation‐induced Kh loss coincided with high ΔKh. Similar but much smaller seasonal effects on ΔKh were recorded in the other two species where, however, also smaller seasonal changes in conduit lengths were recorded. We conclude that (1) the K+‐induced effect on Kh was because of interference of the cation with pectins of intervessel pit membranes (increasingly crossed by the ionic solution in stems with shorter conduits); (2) winter frost might have an effect on ΔKh and (3) seasonal changes in ΔKh because of possible change in pectic composition may represent a mechanism to regulate water flows in planta.

Comparative analysis of end wall resistivity in xylem conduits

ABSTRACTThe hydraulic resistivity (R, pressure gradient/flow rate) through end walls of xylem conduits was estimated in seven species of diverse anatomy and affinity including a vessel‐bearing fern, a tracheid‐bearing gymnosperm, and angiosperms with versus without vessels. Conduit lengths were measured with a silicone injection method which was easier and more accurate than the usual paint injection. The R declined linearly with the removal of end walls as stems were shortened from 10 to 0.3 cm. This relationship gave the minimum R with no end walls present, or the lumen resistivity (RL). This was indistinguishable from the Hagen–Poiseuille value. The maximum R with all end walls present gave RC, the resistivity of end wall and lumen in series. Average end‐wall resistivity (RW) was the difference RC − RL and the ‘wall fraction’ was RW/RC. Wall fraction was approximately constant, averaging 0.54 ± 0.07. This suggests that end wall and lumen resistivities are nearly co‐limiting in vascular plants. Average conduit length was proportional to the diameter squared across species (r2 = 0.94). Together with a constant wall fraction, this was consistent with the end wall resistance (rw, pressure difference/flow rate) being inversely proportional to conduit length. Lower rw in longer conduits is consistent with their having more end wall pits than shorter conduits.

Modeling flow in phreatic and epiphreatic Karst conduits in the Hölloch Cave (Muotatal, Switzerland)

The Hölloch cave is a site where the hydrodynamic behavior of a karst conduit network can be observed with a high degree of precision. Observed heads, discharge rates, conduit sizes, and conduit lengths have been compiled into a simple hydrodynamic model in order to check their consistency. It was possible to calibrate and satisfactorily fit the observed data. Model results show the following: (1) Flow models which are able to simulate turbulent flow in variably saturated conduit networks can adequately model conduit flow–dominated karst systems. (2) Karst systems may be strongly nonlinear, especially because of the presence of epiphreatic conduits. (3) Under certain circumstances, storage in the epiphreatic conduits and in the fissured limestone matrix can be neglected. (4) The typical effective hydraulic conductivity of karst conduits ranges between 1 and 10 m s−1, and the Louis formula is adequate to calculate head losses in those conduits. (5) Indirect measurements of flow velocity using scallop size indicate values of ∼30–40% of the maximal annual discharge, and velocity derived from pebble size indicates values of ∼150% of the maximal annual discharge.

Antenna interconnection strategies for personal communication systems

Microcellular and distributed antenna systems are two promising candidates for implementing personal communication systems. Antenna interconnection strategies for these systems are studied in order to determine cost-efficient as well as robust and flexible architectures in hexagonal layouts. To this end, some results from minimal networks theory are used, in particular, those dealing with the problem of Steiner trees. The significant reduction in conduit and cable lengths that the Steiner minimal tree (SMT) architecture provides over the star type, especially in large networks, is demonstrated. It is further shown that the SMT architecture also provides more flexibility and robustness compared to the star type. The suboptimal, but easy-to-construct, minimal spanning tree (MST) architecture is given as well, and it is compared to the SMT and star types.

A SIMPLE METHOD FOR THE DETERMINATION OF CONDUIT LENGTH AND DISTRIBUTION IN STEMS

SummaryA simple method for the determination of the lengths and distribution of conduits in plant stems and petioles is described using graphical and algebraic methods. The method proposed by Skene and Balodis (1968) is shown to give improper probability distributions. The data presented by these workers for Eucalyptus‘vessels’ is reinterpreted, giving different results, so far as the accuracy of the data will show. The need for great accuracy in determination of conduit lengths from injection profiles is emphasized.

Load ratings of cable

Operating and test data concerning the maximum safe loading of impregnated-paper-insulated lead-covered cable are presented. The results of the study may be summarized as follows: 1. The occasional operation of cable at higher temperatures than are permitted by present temperature rules effects considerable economy. 2. During emergencies, temperatures of 5 to 35 degrees centigrade (depending on kind of cable) above those permitted by the rules are safe for the insulation. 3. For extra-high-voltage solid-type cable, void formation in insulation and expansion of lead sheaths may limit allowable temperatures and temperature ranges. 4. Cracking of lead sheaths due to reciprocating cable movement into manholes may limit the temperature range for usual daily loading. Limitation is more severe for longer conduit lengths up to 500 feet, but changes little with increase from 500-to 1,000-foot lengths. 5. Cracking of sheaths in manholes due to cable movement may be reduced by improving manhole conditions. 6. For many cables a balanced design requires a lead-alloy sheath that gives increased resistance to effects of cable movement and of internal pressures. 7. Continuous field temperature surveys are essential to efficient use of large conduit and cable systems. 8. Only a small fraction of the cable ever operates at the higher temperatures. 9. Data on center empty-duct temperatures and on average heat losses over 24-hour periods give satisfactory results in heat calculations. 10. Other practices which increase load ratings are the use of different ratings for various periods of the year, the replacement of poor soil in special cases, and the use of extra-large conductors in warmer conduits.

Load Ratings of Cable

Operating and test data concerning the maximum safe loading of impregnated-paper-insulated lead-covered cable are presented. The results of the study may be summarized as follows: 1. The occasional operation of cable at higher temperatures than are permitted by present temperature rules effects considerable economy. 2. During emergencies, temperatures of 5 to 35 degrees centigrade (depending on kind of cable) above those permitted by the rules are safe for the insulation. 3. For extra-high-voltage solid-type cable, void formation in insulation and expansion of lead sheaths may limit allowable temperatures and temperature ranges. 4. Cracking of lead sheaths due to reciprocating cable movement into manholes may limit the temperature range for usual daily loading. Limitation is more severe for longer conduit lengths up to 500 feet, but changes little with increase from 500-to 1,000-foot lengths. 5. Cracking of sheaths in manholes due to cable movement may be reduced by improving manhole conditions. 6. For many cables a balanced design requires a lead-alloy sheath that gives increased resistance to effects of cable movement and of internal pressures. 7. Continuous field temperature surveys are essential to efficient use of large conduit and cable systems. 8. Only a small fraction of the cable ever operates at the higher temperatures. 9. Data on center empty-duct temperatures and on average heat losses over 24-hour periods give satisfactory results in heat calculations. 10. Other practices which increase load ratings are the use of different ratings for various periods of the year, the replacement of poor soil in special cases, and the use of extra-large conductors in warmer conduits.