Effect Of Tube Length Research Articles

Effect of Tube Length on the Performance of Cooling Necklace with Vortex Tube Cold Flow Generator

The vortex tube, a compact and eco-friendly device, can generate both low-temperature cold flow and high-temperature hot flow from a room-temperature compressed gas supply. Despite its potential, there has been limited research on its application as a cooling device, particularly in the context of a cooling necklace. This study aims to fill this gap by examining the performance of the vortex tube under various conditions. The experiment was conducted indoors, with tube lengths ranging from 60 cm to 140 cm and inlet pressures from 0.2 MPa to 0.4 MPa. The results suggest that an inlet pressure of 0.4 MPa and a tube length of 60 cm are optimal for achieving the lowest temperature cold flow and minimizing heat transfer effects between the cold flow and the environment.

Effect of the leak port area and tube length on suppression of spontaneous ignition of high-pressure hydrogen

Suppression of high-pressure hydrogen spontaneous combustion is essential for the sustainable development of hydrogen energy. Previous studies have shown that suppressing hydrogen spontaneous combustion by reducing the area of the leak port is a feasible method. However, the effect of some factors, such as tube length, on this suppression method has not received attention. Therefore, the effect of leakage port areas of 10 mm, 8 mm, 6.6 mm, and 4.5 mm on the suppression of hydrogen spontaneous combustion was investigated experimentally and simulated for different pipe lengths. The results show that reducing the leak port area increases the hydrogen-air mixing path, which raises the combustible concentration. However, by reducing the leak port area, the intensity of shock waves and the maximum temperature in the tube decreased significantly, and the possibility of hydrogen spontaneous combustion decreased. This indicates that reducing the leak port area can inhibit hydrogen spontaneous combustion. In addition, within a certain leak area, increasing the tube length weakens the performance of this inhibition method. However, the effect of tube length on this method disappears as the leak area decreases. Finally, the leakage port area is reduced, changing the flow field at the nozzle, so that the spontaneous combustion flame in the near field of the nozzle undergoes extinguishment and re-ignition. The results show that reducing the area of the leakage port can effectively inhibit hydrogen self-ignition and is not affected by the length of the tube, providing a way to inhibit hydrogen self-ignition.

Flexible operations of a multi-tubular reactor for methanol synthesis from biogas exploiting green hydrogen

The present modelling work studies the steady state and transient performances of a multi–tubular fixed bed reactor for methanol production from biogas. The modelled system comprises a methanol synthesis reactor, a flash unit, and accounts for the unconverted gas recycle. The novel concept herein proposed and assessed is the possibility to run a multi–tubular methanol synthesis reactor flexibly, i.e., using the carbon dioxide present in biogas, together with renewable H2, to increase methanol productivity, only when this is economically convenient. Accordingly, the methanol synthesis multi–tubular reactor under study is run in two operating conditions: when the cost of green hydrogen is high, the excess of CO2 present in biogas is vented and the reactor is fed with CO2-lean syngas only; conversely, in the presence of affordable renewable H2, CO2 and green H2 are cofed to the reactor. This study focuses in particular on the impacts of the two working conditions on the methanol productivity, as well as on temperature profiles and transient behaviour of the reactor. The effects of tube length and number are also simulated. The study shows that the multi–tubular reactor design well manages both operating conditions and that the steady-state conditions can be reached in a few hours after the switch from one condition to the other. In view of a small scale process, simulations show that it is better to reduce the tube number rather than their length, as the latter choice would lead to unacceptable temperature hotspots, due to a worsening of convective heat transfer.

Pinning and depinning in imbibition beyond a sharp edge: A lattice Boltzmann study

The phenomenon of capillary rise or imbibition is governed by the inertia, the capillary force, the gravitational force and viscous force of fluids. Besides, the geometry also plays an important role on the imbibition dynamics since the motion of contact line could be affected by the sharp transition of geometry, and the oscillation of meniscus could be observed due to the confinement of contact line. The imbibition is a multiphase flow problem, which involves the movement of contact line and differences of fluid density and viscosity. In this paper, an axisymmetric lattice Boltzmann (LB) model based on the phase-field theory is proposed for investigating the oscillation phenomenon in the imbibition process. We also introduce a dimensionless Weber number to further analyze the pinning and depinning of contact line at the edge of capillary tube, and consider the effects of tube length and contact angle. The process of liquid spreading onto the top surface of capillary tube is presented, and several distinct phenomena are observed: depinning up and depinning down, pinning up and depinning down, pinning up and pinning down, pinning below the top edge. These transitions among different phenomena are dependent on the Weber number, which indicates the relative importance of inertial force compared to the surface tension force.

Effects of the partially open inlet on shock waves and spontaneous ignition during the leakage of hydrogen

Unexpected spontaneous combustion and shock waves can occur when high-pressure hydrogen leaks into pipelines, whilst irregular leakage ports affect their features. In this paper, shock waves and self-ignition are experimentally and numerically studied after the pressurized hydrogen is released through the partially open inlet. And the effects of tube length and release pressure are investigated. Pressure signals, light signals, and flame images are used to characterize the shockwave, self-ignition, and flame propagation. Results show that the shock-affected region can be formed near the partially open inlet. It is accompanied by complex wave structures, shock wave interactions, and shock wave focusing. The contact surface is distorted and deformed. The flow field parameters near the inlet change dramatically and are unevenly distributed, which affect the overpressure characteristics recorded by the pressure sensors. The initial intensity of the shock wave is lower than that in tubes with the fully open inlet at the early stage of the leakage. In addition, the partially open inlet influences the critical pressure at which spontaneous ignition occurs and the flame evolution inside or outside the tube. It has an inhibition effect on spontaneous ignition, but this inhibition effect weakens with increasing tube length.

Numerical investigation of flashing of propane (R-290) in a helical capillary tube

The present study addresses the expansion of pressurized liquid R-290 through a diameter capillary tube and its subsequent motion through a metastable condition entailing a change of phase through flashing phenomenon. The expansion of R-290 through a helical capillary tube is numerically simulated using a finite volume-based mixture model. For the simulation of the flashing phenomena, a homogeneous equilibrium approach is used. The Zwart–Gerber–Belamri model is deployed to represent mass transfer during flashing. ANSYS Fluent 2021 R2 software has been used for the numerical simulations. A series of UDF (user defined functions) are developed to read the recorded database of R-290 and perform the cavitation modeling. Bilinear interpolation is performed for determining the fluid properties at the corresponding pressure and temperature. The developed numerical model has been validated against the available numerical and experimental results. For the simulations, tubes with lengths of and have been considered, and the impacts of increasing length on the flow characteristics at the outlet have been determined. In this investigation, the R-290 refrigerant expands from three different condenser pressures of 16, 14, and 12 bar. Evaporator pressure is adjusted from 2 bar to 8 bar to investigate its influence on flow characteristics. The fall in evaporator pressure brings about a flow transition from subsonic to supersonic. The effects of tube length, condenser, and evaporator pressures on mass transfer rate, evaporator entry temperature, mixture quality at the evaporator entrance, and available refrigeration effects have been analyzed.

Theoretical analysis of Ledinegg instability and density wave oscillation using dimensionless numbers

• Dimensionless number criteria determining two phase flow stability is established. • Flow direction on stability is non-monotonic, the turning point expression is given. • Increasing flow rate and power proportionally can be good or bad for stability. • Contrary conclusions of flow direction and power level on stability are clarified. • The influences of tube length and diameter on stability are discussed and presented. Two-phase flow instability is influenced by many factors. The reported parameter effects on instability boundary are incomplete and sometimes conflict. Dimensionless numbers are more effective to reveal the mechanisms and describe the instability boundary. In this paper, dimensionless numbers are used to systematically analyze various parameters’ effects. One-dimensional governing equations describing the convective boiling process in a tube are simplified to a set of linear ordinary differential equations through integration and small perturbation methods. The judging inequalities expressed by six dimensionless numbers are obtained by the Routh stability criterion. The relationship between the judging inequalities and the instability types are identified theoretically for the first time. The boundary of density wave oscillation obtained from the fourth dimensionless number inequality agrees well with experimental data. The effects of Froude number, friction number, inlet temperature, inlet and outlet flow resistances, tube length and tube diameter are discussed in detail. Some contrary conclusions presented by previous investigators are clarified. The effect of varying Froude number (or flow orientation) on system stability is non-monotonic, and the turning point expression is given. The effects of geometric parameters are complex. The effects of tube length and tube diameter on the instability boundary are discussed systematically based on Froude number and friction number when operation parameters keep unchanged. Though many of the parameters’ influences are non-monotonic, some new universal laws or findings are extracted. For example, according to the conclusions of friction number effect, increasing the steam generator working power levels (heating power and mass flow rate increase proportionally) can be good or bad for stability according to different inlet flow resistances.

Effect of tube length on the buckling pressure of collapsible tubes.

The higher incidence of obstructive sleep apnea (OSA) in men than in women has been attributed to the upper airway being longer in men. The Starling resistor is the paradigm biomechanical model of upper airway collapse in OSA where a collapsible tube (representing the pharynx) is located between two rigid tubes (representing the nasal cavity and trachea). While the Starling resistor has been extensively studied due to its relevance to many physiological phenomena, the effect of tube length on tube collapsibility has not been quantified yet. Finite element analysis of a 3-dimensional collapsible tube subjected to a transmural pressure was performed in ANSYS Workbench. The numerical methods were validated with in vitro experiments in a silicone tube whose modulus of elasticity (361±28kPa) and dimensions (length=100mm, diameter=22.2mm, and wall thickness=1.59mm) were selected so that tube compliance was similar to pharyngeal compliance in humans during sleep. The buckling pressure (transmural pressure at which the tube collapses) was quantified in tubes of three different diameters (10mm, 16mm, and 22.2mm) and ten length-to-diameter ratios (L/D=4 to 13), while keeping the wall-thickness-to-radius ratio constant at 0.143. The absolute value of the buckling pressure decreased from 4.7 to 3.3 cmH2O (461-324Pa) when L/D increased from 4 to 13. The buckling pressure was nearly independent from tube length for L/D>10. Our finding that longer tubes are more collapsible than shorter tubes is consistent with the higher incidence of obstructive sleep apnea in males than females.

Precise determination of inundation effect coefficient of film condensation on an array of horizontal new three-dimensional finned tube

To accurately evaluate the condensation heat transfer performance of new 3D finned tubes in shell-and-tube condenser, the inundation effect of the film condensation of R-134a on an array of 6 horizontal new 3D (three-dimensional) finned tubes is experimentally investigated with a new experiment method of homologous method. And the precise inundation effect coefficient of film condensation is determined. A novel test facility, whose test section contains two arrays of 8 horizontal tubes to realize the homologous method, is developed and constructed. The outer diameter of the tube and effective tube length in the test section are 19.05 and 500 mm, respectively. The condensation heat transfer coefficient of new 3D finned tube and inundation effect coefficient of new 3D finned tube bundle are determined under different conditions. The results show that the inundation effect coefficient of new 3D finned tube bundle decreases from 1.00 to 0.78 as Re increases from 75 to 1860. And the effect of heat flux on the inundation effect is more sensitive than the condensing temperature. Furthermore, for new 3D finned tube, the condensation heat transfer and inundation effect models are established, and the deviations of results between experiment and models are almost within ±6.0%. In comparison with literatures, the average inundation effect coefficient of new 3D finned tube bundle is 10.0-25.0% higher than that of 3D finned tube bundle in literatures, within 3.0% lower than that of two-dimensional finned tube bundle, and 15.2% higher than that of plain tube bundle. And the average condensation heat transfer coefficient of new 3D finned tube bundle in this article is 5.0-25.0% higher than that of 3D finned tube bundle in literatures, 10.0-30.0% higher than that of 2D finned tube bundle, and more than 10 times that of plain tube bundle. The precise inundation effect coefficients can be used as benchmark data to build precise and universal inundation effect model of 3D finned tube, and the models established in this study will help guide the thermal design of the new 3D finned tube applied in shell-and-tube condenser.

Design aspects of forced circulation evaporators of high salty water from the view point of scale formation

In this paper, dryout phenomenon was studied for vertical tubes working at the operating condition of forced circulation evaporator in zero liquid discharge systems to find the maximum allowable value of temperature difference between evaporator effects in which scale formation and fouling do not occur. Eulerian two-fluid approach coupled with Rensselaer Polytechnic Institute wall boiling model was used to simulate upward flow subcooled boiling. Critical near-wall void fraction was used as the criterion of dryout. The value of the critical temperature difference was investigated for 36 cases. Values varied from 4.8 to 10.7 °C for different amounts of tube length, tube diameter and mass flux. In addition, the effect of tube length, tube diameter and mass flux on critical temperature difference was analyzed. The results showed that critical temperature difference decreased approximately linearly with an increase in tube length. Furthermore, the value of critical temperature difference decreased with the increase in tube diameter and decrease in mass flux and the effect of tube diameter is more significant at higher mass fluxes.

Numerical investigation of nucleate pool boiling outside a vertical tube under sub-atmospheric pressures

In this paper, nucleate pool boiling outside a vertical tube under sub-atmospheric pressure conditions has been numerically studied. The volume-of-fluid interface tracking technique is implemented on the basis of a two dimensional axis-symmetric Eulerian-Eulerian multiphase framework. The phase change model is applied into a computational fluid dynamics platform by user-defined functions. The numerical model results are compared with experimental data at both atmospheric and sub-atmospheric pressures, and good agreement is obtained. From the validation results, the logarithm of the mass transfer coefficient is linear to saturation temperature and wall heat flux, respectively. The simulations are performed under operating pressure of 1–10 kPa, heat flux from 22.4 to 77.7 kW/m2, and liquid subcooling of 0–20 K. The effects of tube length and liquid height on the boiling heat transfer have been studied. The two-phase flow patterns and bubble behaviors under different pressure conditions were analyzed and compared. Under lower pressures, because of the increase of liquid subcooling with the liquid height, boiling occurs at the top of the tube wall firstly, and then gradually develops downwards. The bubbles keep growing while they slide upwards along the wall and coalesce with the adjacent bubbles but the bubbles will not detach from the wall until leaving the top part of the tube. The bubble sliding velocity increases with the bubble size and tube height. From the computational results, the wall superheat increases with the decreasing operating pressure and the liquid subcooling under the same heat fluxes. The required heat flux for the onset of nucleate boiling is higher for the boiling outside a vertical tube than that for the boiling on a horizontal plate. Different from the sub-atmospheric pool boiling on a horizontal surface, the heat transfer over a vertical tube is not sensitive to the change of the liquid height. Furthermore, the averaged wall temperature is higher on the longer tubes due to the severe bubble coalescence.

Heat transfer characteristics of in-tube steam condensation process under stratified flow

For stratified flow condensation process, the heat transfer mechanisms in the film condensation zone above the vapour-liquid interface and the condensate zone below the interface shows significant differences. In the multi-effect evaporation device, due to the high sensitivity of the thermal performance to the variation of the heat transfer parameters, the heat transfer parameters distributions in the film condensation zone and in the condensate zone are worth exploring. In this paper, a validated distributed parameter model was established to simulate the heat transfer and flow process in a single tube of the falling film evaporator. The variation of the heat flux in the condensate zone was presented under various operating conditions. The concept of the effective tube length and the partition map of the in-tube condensation heat transfer process were proposed for the better understanding of the flow and heat transfer process. Results show that the heat transfer in the condensate zone to the total heat transfer can accounts for more than 10% of the total heat transfer, thus cannot be neglected. For the design of falling film evaporator, the condensation heat transfer process in the tube should be located in the high-efficiency heat transfer section. The steam mass flow rate, heat transfer temperature difference and the length of the heat transfer tube should matched to each other to guarantee the condensation heat transfer process be located in the high-efficiency heat transfer zone.

MATERNAL AND PATERNAL EFFECTS ON OFFSPRING INTERNALISING PROBLEMS: FINDINGS FROM FAMILY DATA AND EXTENDED GCTA ANALYSES

Barium sulfate deposition on the inner surface of a tube is one of the most serious oil field problems affecting oil field water injection systems. The effects of tube length, liquid volume, deposition time, the profile of the Ba2+ concentration in the outlet and the pressure drop in the tubing were evaluated using a graphite furnace atomic absorption spectrometer (GFAAS) and pressure transducer methods. The deposition model of BaSO4 in the tube is presented using coupled mass balance and fluid flow equations. The deposition model contains two governing parameters, the kinetic coefficient and the deposition coefficient, which can be estimated from experimental data. The predictions from the simplified model for barium sulfate scale were in good agreement with experimental data and laboratory observations. In addition, it was proved that many factors are important for deposition kinetics, including the accumulated barium ion amount, the initial flow rate, the initial barium concentration and the deposition time. Scanning electron microscopy (SEM) images of the inlet and outlet of the tube reveal the deposition thickness and morphology.

Study on the mechanical properties and microstructure of Zr-2.5wt%Nb pressure tube material

In order to study the mechanical properties and the anisotropy of a Zr-2.5 wt%Nb pressure tube material, tensile tests along the principal tube directions, which are axial, transverse and radial, were performed at room temperature using a pressure tube. The effect of tube length was evaluated, by using samples from the tube's back-end, middle, and front-end. Strong anisotropy among the principal directions was found, and increased strengths were obtained with increased distance from the front-end location. Microstructure analysis by X-ray diffraction, electron backscatter diffraction, and scanning electron microscopy indicated that increasing defect density along the tube was the main reason for the increasing strength. Although texture mainly determined the anisotropy of the tensile strengths, the ratio between the axial and radial strengths could be considerably altered by hydride plates. Depending on how the hydride plate was placed with regard to the deformation direction, the yield strength and strain hardening ability were reduced differently by the hydride. The deterioration effect of the hydrides did not show linear dependency on the hydrogen contents due to other microstructure variations. We had a brief discussion about which parameters might result in the non-linear change found in the deterioration along the tube.

The Effect of Tube Length and Cold Exit Diameter on The Cold Flow Temperature of Vortex Tube Using High Temperature Working Gas

Vortex tube has been using widely in industry for the cooling process. It is working as a refrigerator which split compressed gas into the hot and cold stream without using any electrical or chemical process. In term of application, the effect of geometrical parameters on the cold flow temperature of vortex tube by using high temperature compressed gas is obscure, and effect of certain working gas has yet to be vigorously researched. Thus, the objective of this analysis is to determine the effect of length of the vortex tube, cold exit diameter and different high temperature working gas. There are 3 different tube length, 3 different cold diameter, and 7 different types of gas are used. The models are designed from SolidWork with several parameters. Simflow, which is free software, is selected to analyse the effect on model numerically. From the results, it is clear that the optimum tube length, cold exit diameter, and working gas are L = 175 mm, d = 4 mm and helium, respectively.

Numerical Estimation of Heat Recovery within a Distributed Incinerator Using Water and Hydrocarbons as Working Fluids

The potential of a cogeneration system combined with a small combustion furnace was investigated in this study. The heat transfer between the exhaust gas and working fluid flowing in a spiral tube heat exchanger was estimated numerically and the amount of vapor generated was predicted. The combustion chamber had a 0.49 m3 inside volume with a chimney height of 2.5 m and an inner diameter of 0.28 m. A uniform gas side temperature condition that was referenced from the results of a preliminary experiment and a computational fluid dynamics simulation were adopted to simplify calculations and clarify the effects of working fluids. The amounts of heat recovery when utilizing water and other types of working fluids (Pentane, Butane) were compared. The most effective tube length considering pressure drop and phase change was also predicted. Isentropic theoretical thermal efficiency and T-s diagrams are analyzed to evaluate the vapor-power conversion rate using waste heat. As a result, a potential the heat recovery rate of approximately 100 kW at a 150 kg/h mass flow rate is expected.

Effects of channel sizes on traffic of solid in water in oil compound droplets through a vertical channel

The purpose of this article is to investigate the effects of channel sizes on the traffic of S/W compound droplets through a vertical channel. Compared with the horizontal channel, a vertical channel can effectively inhabit the contact of compound droplets with the channel wall, thus improving the survival rate. It is also found that the effects of tube length on droplet traffic are always dependent on the oil phase flow rate. In a short tube (L = 2.0 cm), the survival rate increases as the oil phase flow rate increases. This may be due to significant prevention of coalescence among S/W compound droplets under a high oil phase flow rate. However, in a long tube (L = 7.5 cm), the survival rate decreases with increasing oil phase flow rate, because disturbance of a water droplet can peel off the water phase coated on the surface of the solid particles. During the traffic process, the distance between water droplets and S/W compound droplets decreases linearly with time because of the larger diameter of the compound droplets. These study results can provide a useful guide for the preparation of high-throughput S/W compound droplets in a controllable and reproducible manner.

Heat transfer analysis of multi-row helically coiled tube heat exchangers for surface water-source heat pump

An experiment system simulating the uniform flow of surface water with low velocities was established to investigate the heat transfer performance of multi-row helically coiled tube (MHCT) heat exchangers for surface water-source heat pump. Four experimental modes of variable temperatures and velocities of surface water and medium were performed on eight MHCT configurations with different geometric parameters including horizontal spacing, vertical spacing and tube length. The results demonstrate that when the surface water velocity changes and the other parameters are constant, the outside Nusselt number depends on the Reynolds number. Conversely, it depends on the Rayleigh number. Both the inside and outside Nusselt numbers increase with vertical spacing and horizontal spacing. The effect of vertical spacing is more obvious on the outside Nusselt number, but can be neglected on the inside Nusselt number. By comparison, the correlations of single-row helically coiled tubes cannot accurately calculate the inside Nusselt number of the MHCT, and the influence of surface-water velocity on the outside Nusselt number is not negligible. The correlations for the prediction of the inside and outside Nusselt numbers are developed. Additionally, the effect of tube length on the Nusselt number is small, and can be ignored for engineering applications.

The Effect of Tube Length, Cold Exit Diameter and Working Gas on The Cold Flow Temperature of Vortex Tube

A vortex tube is a simple device which works as a refrigerator, also known as Ranque Vortex Tube, Hilsch Vortex Tube, and Ranque–Hilsch vortex tube. It is used to obtain desired hot and cold gas and is widely used for spot cooling in industry. In vortex tube, the effect of geometrical parameters on the cold flow temperature of vortex tube is still unclear, and effect of certain working gas is unidentified. Hence, the objective of this analysis is to determine the effect of length of the vortex tube, cold exit diameter and different working gas. 3 different tube lengths, 3 different cold exit diameters, and 8 different types of gas are used. Simflow, which is free software, is selected to analyse the effect numerically. From the results, it is clear that the optimum tube length, cold exit diameter, and working gas are L = 175 mm, d = 4 mm and helium, respectively.

Effect of surfactants and dispersion methods on properties of single-walled carbon nanotube fibers formed by wet-spinning

Single-walled carbon nanotube (SWCNT) fibers are promising lightweight materials with high mechanical strength and high electrical conductivity. In a previous report, we showed a clear correlation between the fiber properties and the effective tube length of the constituent SWCNTs. According to the results, the dispersion conditions of SWCNTs in aqueous solutions were improved by changing the surfactants and dispersion methods used to prevent the reduction of their length during fiber processing. Systematic studies revealed that the mechanical properties and electrical conductivity of the SWCNT fibers were improved by decreasing their cross-sectional area and increasing the effective length of the SWCNTs.