Vertical Tube Research Articles

Experimental study of free convection from vertical tubes with curved extended surfaces

Herein, the free convection from vertically aligned tubes with curved extended surfaces is experimentally investigated. Heat transfer rates from tubes with curved extended surfaces to the ambient air are quantified under various conditions, including under varying tube wall temperatures, numbers of extended surfaces, and heights of extended surfaces in the radial direction. A correlation for calculating the Nusselt number is suggested, drawing upon the experimental findings. The difference between the experimental outcomes and the estimates generated by this correlation falls within a 10% margin. Using the correlation, a contour diagram is generated to show the thermal resistances across different numbers and thicknesses of extended surfaces. Finally, the thermal resistance of tubes featuring curved extended surfaces is evaluated against tubes with conventional straight extended surfaces. It is found that the tube with curved extended surfaces has a thermal resistance that is 20% less than that with straight extended surfaces.

Numerical heat transfer to LBE flow in a wire-wrapped 19-rod bundle using an OpenFOAM-based solver: fourParameterFoam

The LBE-cooled fast reactor (LFR) has received significant attention due to its diverse applications. However, numerical heat transfer simulations encounter challenges with lead-bismuth eutectic (LBE) due to its low Prandtl number and high molecular thermal diffusion, often resulting in an overestimation of heat transfer using the simple gradient diffusion hypothesis (SGDH). This study aims to improve the prediction accuracy of heat transfer to LBE in numerical models by developing a solver, named fourParameterFoam, based on the turbulent model SST k-ω and algebraic heat flux model (AHFM) kθ-ɛθ within the OpenFOAM framework. The performance of SGDH models and AHFMs is compared based on heat transfer experiments in vertical tube flow with LBE. The behavior of the turbulent Prandtl number (Prt) under various flow conditions is concluded based on the SST k-ω-kθ-ɛθ model. Additionally, the applicability of the SST k-ω-kθ-ɛθ model in complex flow is validated through heat transfer experiments in a wire-wrapped 19-rod bundle with LBE flow. Local temperature variations on the heated rod surface and sub-channels are analyzed to elucidate the thermal development process in the bundle. The impact of wire spacers on flow behavior is summarized using visualization techniques, and the suitability of corresponding empirical Nusselt number correlations in LBE flow is evaluated.

Accelerated charging dynamics in shell-and-multi-tube latent heat storage systems for building applications

Thermal energy storage (TES) is an emerging technique to store the surplus energy generated during periods of excess supply and utilise it when demand arises. Phase change material (PCM) stands out as a highly efficient TES system. Enhancing heat transfer during phase change is a major challenge in creating effective PCM-based TES systems. This study focuses on enhancing the melting performance of a shell-and-tube latent heat thermal energy storage (LHTES) system. This improvement is achieved by conducting an extensive parametric study involving various geometric factors including tube position from the bottom, vertical tube spacing, tube diameter, different heat exchanger shell aspect ratios, PCM temperature, tube temperature, and PCM type. A three-dimensional model is simplified to a two-dimensional geometry for numerical simulation. The results indicate that the PCM melting time decreased by 20.6 % and 4.4 % with a 20 mm vertical tube distance compared to 15 mm and 25 mm. Among the considered scenarios, the configuration with a doubled number of tubes in width consistently exhibits a higher melt fraction throughout the entire duration. Regarding the aspect ratio, the square-shaped system demonstrates both quicker melting times and a higher energy storage rate. When comparing PCM types, it is evident that RT 35 exhibits a 3.2 % higher heat storage rate and a 44.7 % shorter melting time compared to RT 35 HC.

Volume oscillations slow down a rising Taylor bubble

A gas volume rising in a vertical tube is called a Taylor bubble when its equivalent spherical diameter is greater than the diameter of the tube. Continuity dictates that the rising velocity of such bullet-shaped bubbles must be such that the drainage flow in the liquid film separating the gas from the tube wall equals the rate at which space is vacated by the bubble tail on its rise. The numerical simulations presented here show that, if the volume of the bubble is made to execute small-amplitude oscillations, this drainage flow can be markedly decreased so that the bubble slows down so much as to very nearly stop. The mechanism is a subtle nonlinear interplay between the upward flow imposed by the bubble expansion and the inertia of the falling liquid. Two manners of excitation are considered. In the first one the liquid column above the bubble is forced to oscillate sinusoidally, e.g. by a piston. In the second one, an oscillating pressure is imposed on the top liquid surface. With the first arrangement the bubble slows down during its entire ascent by an amount depending on the oscillation frequency and amplitude. With the second one, for a given frequency, the bubble slows down only in the neighbourhood of a certain resonant depth at which the volume oscillations are maximized, but is little affected at deeper and shallower depths.

Experimental study on alkali reduction of film-coated porous ecological concrete by microbial calcium carbonate precipitation technology

Some plants do not grow due to the high pH levels of ecological concrete pore solutions. In this paper, we design and build an integrated device featuring a combined microbial film and a transverse/U-shaped grouting film. We have applied to the China Intellectual Property Office for an invention patent on this device. The device overcomes the blockage of the grouting port caused by microbial and vertical grouting. The vertical grouting tube leaves holes inside a specimen, reducing the compressive strength, while the integrated device optimizes and decreases variation in the recycling of microbial bacteria. The reduction in the pore alkalinity of porous ecological concrete resulting from the microbial grouting film of this device is larger than that resulting from a microbial sprayed film. The pH values of porous ecological concrete with microbial grouting films and microbial sprayed films are obtained by the pure slurry soaking method and solid–liquid extraction method, respectively. The pH value is lower for the film obtained by the pure slurry soaking method than for that obtained by the solid–liquid extraction method. Conversely, the pH value of porous ecological concrete with a microbial grouting film is reduced to approximately 8 at an age of 56 days. The compressive strengths of the porous ecological concrete specimens with the two films are almost the same. The results of this study provide the necessary theoretical basis for developing alkali reduction technology for porous ecological concrete with environmental and economic benefits.

CFD-DEM analysis of hydraulic conveying of non-spherical particles through a vertical-bend-horizontal pipeline

In this study, an in-depth analysis of elbow wear is performed with the assistance of a wear model by combining computational fluid dynamics with the discrete element method. After validation, a vertical–bend–horizontal pipeline is simulated with non-spherical particles: φ = 1, 0.9451, 0.8048, and 0.7433. The simulation results are used to evaluate the effects of sphericity on flows, forces, and wall erosion. The results indicate that the solid particle concentration at the center of the vertical tube increases with decreasing particle sphericity. Moreover, as particle sphericity in the pipeline decreases under the same conveying environment, the conveying velocity increases, the fluid flow rate decreases, and the kinetic energy conversion rate of the liquid and solid phases increases. Accordingly, the pressure drop of the particles in the pipe decreases with decreasing sphericity. Furthermore, the particle shape significantly affects the forces on the particles and walls as well as the wall erosion.

Effect of flow direction on heat transfer and flow characteristics of supercritical carbon dioxide

This work is devoted to investigating the difference in flow and heat transfer characteristics between vertical upward flow and horizontal flow of supercritical carbon dioxide (<inline-formula><tex-math id="Z-20240119215215">\begin{document}$\rm sCO_2$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="2-20231142_Z-20240119215215.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="2-20231142_Z-20240119215215.png"/></alternatives></inline-formula>) based on the pseudo-boiling theory and the experimental parameters: mass flux <i>G</i> = 496–1100 kg/m<sup>2</sup>s, heat flux <i>q</i><sub>w</sub> = 54.4–300.2 kW/m<sup>2,</sup> and pressure <i>P</i> = 7.531–20.513 MPa. The differences in flow and heat transfer characteristics between horizontal upward tube and vertical upward tube are compared at different mass fluxes, heat fluxes and pressures fully. Finally, unlike the classical treatment of flow and heat transfer for supercritical fluid, single-phase fluid assumption is abandoned, instead, the pseudo-boiling theory is introduced to deal with the flow transfer and heat transfer of <inline-formula><tex-math id="Z-20240119215113">\begin{document}$\rm sCO_2 $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="2-20231142_Z-20240119215113.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="2-20231142_Z-20240119215113.png"/></alternatives></inline-formula> in the two tubes. Supercritical fluid is regarded as a multiphase structure in this work, including a vapor-like layer near the wall and a liquid-like fluid in tube core. The results are indicated below. 1) In terms of heat transfer, the inner-wall temperature of the vertical upward tube and the bottom generatrix of horizontal tube are basically the same under normal heat transfer mode. When the heat transfer deterioration occurs in the vertical upward tube, larger supercritical boiling number (<i>SBO</i>) will cause the wall temperature peak of the vertical upward tube to be much higher than the wall temperature at top generatrix of the horizontal tube at the corresponding enthalpy. The <i>SBO</i> (<i>SBO</i> = 5.126×10<sup>–4</sup>) distinguishes between normal heat transfer deterioration and heat transfer deterioration in the vertical upward tube. In the horizontal tubes, <i>SBO</i> dominates the maximum wall temperature difference between the top generatrix and the bottom generatrix. Comparing with vertical upward tubes, higher <i>q</i><sub>w</sub>/<i>G</i> is required for the heat transfer deterioration of supercritical fluid in the horizontal tubes under the same pressure. 2) In terms of flow, the increase in slope of pressure drop in the vertical upward tube is due to the orifice contraction effect. The mechanism that dominates the variation of pressure drop in the horizontal tube is the flow stratification effect, and we show that Froude number <i>Fr</i><sub>ave</sub> can be the similarity criterion number to connect the temperature difference between the top and bottom generatrix of horizontal tube and the pressure drop. The analysis suggests that mechanisms governing horizontal flow and vertical flow of <inline-formula><tex-math id="Z-20240119215057">\begin{document}$\rm sCO_2 $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="2-20231142_Z-20240119215057.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="2-20231142_Z-20240119215057.png"/></alternatives></inline-formula> are different in heat transfer deterioration mode. For the vertical flow, the <i>SBO</i> plays a leading role, while for the horizontal flow, the <i>Fr</i> plays an indispensable role.

Numerical study on heat transfer deterioration of n-decane during pyrolysis under supercritical pressure in a vertical tube

For accelerating hypersonic vehicles, it is important to understand the effects of various factors on heat transfer deterioration. The heat transfer characteristics of supercritical n-decane with pyrolysis were numerically simulated inside a vertical tube. The effects of flow direction, mass flow rate, heat flux, inlet temperature, and flight acceleration on the heat transfer characteristics were investigated. When the inlet temperature was relatively low or the fluid was decelerated vertically upward, a typical M-shaped velocity distribution was formed, indicating the heat transfer deterioration (HTD). Furthermore, the decrease in wall heat flux, as well as the increase in mass flow rate, inlet temperature and flight acceleration in the same direction as the flow makes the HTD gradually disappear. Finally, a new relationship was established between the heat flux and the flight acceleration and inlet temperature to determine critical heat flux under which HTD developed in the upward flow.

Air Injection's Effect on a Vertical Tube with Helical Corrugation: An Empirical Investigation

Air Injection's Effect on a Vertical Tube with Helical Corrugation: An Empirical Investigation

Natural Convection Heat Transfer In Heated Vertical Tube Without Internal Rings

An experimental investigation of natural convection heat transfer in heated vertical pipes dissipating heat from the internal surface is presented. The pipes are open-ended and circular in cross section. The test section is electrically heated imposing the circumferentially and axially constant wall heat flux. The purpose of this work is to study experimentally the natural convection pipe flows at different heating levels. The test section is a vertical, open-ended cylindrical pipe dissipating heat from the internal surface. The test section is electrically heated imposing the circumferentially and axially constant wall heat flux. Heat transfer experiment is carried out for four different channels of 45mm internal diameter and 3.8mm thickness with length 450 mm. Ratios of length to diameter of the channel is taken as L/D = 10. Wall heat fluxes are maintained at q// = 250 to 3341 W/m2. A systematic experimental database for the local steady state natural convection heat transfer behaviour is obtained. A correlation is developed for average Nusselt number and modified Rayleigh number and another correlation is also developed for modified Rayleigh number and modified Reynolds number.

Air Injection Impact on Thermal Performance of Vertical Tube with Helical Corrugations: Upward Flow

Air Injection Impact on Thermal Performance of Vertical Tube with Helical Corrugations: Upward Flow

CFD modelling of the air preheater fired with gas mixture to find the cause of the preheater damage

Since various fuels, such as natural gas, blast furnace gas, coke oven gas, and a mixture of the three, are burned in the boiler, there is a danger of corrosion caused by sulphuric acid. Sulphur dioxide produced after combustion and condensed water vapour from flue gases on cold tube surfaces form sulphuric acid. Sulphuric acid solution flowing down the vertical tubes of the air heater causes corrosion not only of the air heater tubes but also of the horizontal water heater tubes located below. A simulation of the flow and heat exchange on the flue gas and air sides was performed to determine the areas of the air heater where the temperature of the air heater tubes is low and condensation may occur. Based on the measured air and flue gas mass flows, the measured flue gas temperatures behind the heater, and the air temperature at its inlet, the flue gas temperature before the air heater was determined using the ε-NTU (Effectiveness-Number of Transfer Units) method. Based on CFD modelling and experimental research, the areas in the heater where sulphuric acid can form at given outside air temperatures were determined.

Air separation and N2 purification with Ba0.15Sr0.85FeO3-δ via a two-step thermochemical process

Thermochemical air separation to produce high-purity N2 was demonstrated in a vertical tube reactor via a two-step reduction–oxidation cycle with an A-site substituted perovskite Ba0.15Sr0.85FeO3–δ (BSF1585). BSF1585 particles were synthesized and characterized in terms of their chemical, morphological, and thermophysical properties. A thermodynamic cycle model and sensitivity analysis using computational heat and mass transfer models of the reactor were used to select the system operating parameters for a concentrating solar thermal-driven process. Thermal reduction up to 800 °C in air and temperature-swing air separation from 800 °C to minimum temperatures between 400 and 600 °C were performed in the reactor containing a 35 g packed bed of BSF1585. The reactor was characterized for dispersion, and air separation was characterized via mass spectrometry. Gas measurements indicated that the reactor produced N2 with O2 impurity concentrations as low as 0.02 % for > 30 min of operation. A parametric study of air flow rates suggested that differences in observed and thermodynamically predicted O2 impurities were due to imperfect gas transport in the bed. Temperature swing reduction/oxidation cycling experiments between 800 and 400 °C in air were conducted with no statistically significant degradation in N2 purity over 50 cycles.

Experimental study of the natural deposition of submicron aerosols on the surface of a vertical circular tube with non-condensable gases

This paper constructed an experimental platform containing a space heat exchanger tube, and performed aerosol deposition experiments under different deposition mechanisms. The objective was to study the effect of the passive containment heat removal system on the natural deposition of submicron aerosols during post-accident operation of severe accidents. By controlling the variables, we obtain the impact of gravity deposition, thermophoretic, and diffusiophoresis deposition mechanisms on submicron aerosols in the presence of a space heat exchanger tube using the experimental data stripping method. The study found that the gravitational settling rate of aerosols in two-phase mixtures at the same temperature and pressure is about 1.5 times higher than in dry air. Although submicron aerosols are subject to thermophoretic settling in the presence of temperature differences, due to the small surface area of the heat exchanger tube, the potential thermophoretic sedimentation accelerating effect on the particles can be ignored if the mixed gas temperature difference is within 2000 K/m. Unlike the steam condensation on the flat plate surface, when vapor condenses on the heat exchanger tube surface, as the steam proportion and condensation rate increase, it is easy to cause the accumulation of non-condensable gas. This phenomenon can reduce the reverse diffusion slip of the particles and enhance the influence of Stefan flow in the diffusionphoresis deposition process. The above effects make the experimental results of aerosol diffusiophoresis deposition closer to the SF model when the vapor fraction is 70 %. When the vapor fraction is 50 %, the predictions of the WM model, which considers the average mass flow of the gas mixture, are more applicable. When the condensation rate continuously increases, the convective mass transfer of vapor condensation will be enhanced, and the deposition rate of particles will be further enhanced.

Experimental investigation of water vapor condensation from flue gas in different rows of a heat exchanger model

Condensing heat exchangers (HE) are used in many applications because of their usability with different fluids and a wide operating range in terms of pressure, temperature and power. Despite that, the thermal design of condensing heat exchangers is still not optimized, due to the complexity of the condensation process and lack of related research.This paper presents results of experimental investigations of biofuel flue gas water vapor condensation on vertical tubes in different rows of a tube bundle in a crossflow. The effects of water vapor mass fraction, inlet flue gas temperature and the Reynolds number on heat transfer when the inlet cooling water temperature and flow rate are constant were analyzed. The results obtained showed that the main parameters which had the most influence on the condensation process were the water vapor mass fraction in the flue gas and its temperature at the inlet to the test section. In the range of inlet flue gas Reynolds numbers investigated, the Re effect on heat transfer was not as significant as the effect of the parameters indicated above. However, the Re number had some influence on the heat transfer variation along the inline tube bundle. A comparison of the average Nu number in the case of dry air with the experimentally determined average Nu number, even with low condensable gas mass fraction (6 %), showed that it increased considerably. A correlation was proposed, which helps to determine the average Nu number for the heat exchanger in the range of experiments performed.

Investigation on Phase Evaluation of Ilmenite Ore by Carbothermal Reduction and Carboiodination Reaction

This article presented the thermochemical calculation and experimental investigation on the phase evaluation of ilmenite ore (FeTiO3) via carbothermal reduction and carboiodination reaction for titanium production using graphite as a reducing agent. The carbothermal reduction and carboiodination reactions were performed in two different furnaces. The carbothermal reduction was evaluated at a temperature of 1550°C with inert argon gas utilizing a horizontal tube furnace. The carboiodination reactions were evaluated in temperatures ranging from 900°C, 950°C, and 1000°C using a vertical tube furnace with mixed iodine gas with argon gas. XRF and XRD were used for analyzing the chemical compositions and the phase evolutions of raw ilmenite ore and the reduced samples, respectively. The findings showed that the Perak ilmenite ore predominantly has a greater concentration of TiO2 (71.27wt%), Fe2O3 (18.85wt%), and some other oxides like aluminum oxide and quartz. In addition, XRD revealed that the ilmenite phase was converted into rutile (TiO2) titanium oxide (Ti3O5, Ti2O3), titanium carbide (TiC), and iron (Fe) phases, after the carbothermal reduction process. However, after the carboiodination reaction, the ilmenite and rutile phases remained at temperatures 900°C, 950°C, and 1000°C. The HSC Chemistry software was used in the determination of the thermochemical calculation and the possible reactions during the reaction which play an important role in shortening the reduction process. The results revealed the carboiodination process is a promising process that can reduce energy consumption and shorten the titanium production processes, and it needs more studies.

Phase Reduction and Thermodynamic Analysis of Ilmenite Ore by Carbothermal-Iodination using Different Carbon Reductants

The present study is on the combination of carbothermal reduction and iodination reaction (carboiodination) process for the phase reduction of ilmenite ore (FeTiO3). The aim is to understand the phase reduction and thermodynamic reaction analysis of ilmenite ore by a combined method of carbothermal-iodination using different carbon reductants (graphite and palm char). Graphite was used as a standard carbon reductant while palm char as a renewable carbon reductant was prepared via the pyrolysis technique. Ilmenite was mixed with carbon reductants and then first reduced by using a carbothermal reduction process at 1550℃. Then, the reduced samples were further investigated with iodination reaction in different temperature ranges of 900-1000 °C using a vertical tube furnace with mixed argon and iodine gas (0.2 L/min). The proximate and ultimate analyses of carbon reductants were analysed by CHON analyser and their microstructure by using SEM, while XRF and XRD were used for analyzing the chemical compositions and the phase reductions of raw ilmenite ore and reduced samples, respectively. The thermodynamics of possible reactions during carbothermal-iodination reactions were calculated by HSC Chemistry 6.0 software. By comparing graphite and palm char, palm char had an amorphous structure, with porous and high carbon content showing high potential for usage as a reductant in titanium extraction from ilmenite ore. The phases of ilmenite ore were ilmenite, rutile, and anatase transformed into rutile, pseudobrookite, and titanium oxide detected by XRD. Further reduction was performed by palm char where more rutile (TiO2) and titanium oxide (Ti3O5) developed from the iodination reaction at the highest temperature compared to graphite due to better properties and amorphous structure. The rutile and titanium oxide were found as stable phases from the thermodynamic analysis and confirmed with XRD. From the findings, the combination of carbothermal-iodination of ilmenite ore was possible and promising for rutile (TiO2) production in mineral extractions.

Peristaltic flow of incompressible nano fluid Al2O3/water under the effect of heat addition/absorption inside a vertical cylindrical tube

Peristaltic flow of incompressible nano fluid Al2O3/water under the effect of heat addition/absorption inside a vertical cylindrical tube

Investigation of effect of cooling water characteristics on flue gas condensation along vertical tube heat exchanger

Flue gas condensing heat exchangers obtain the highest thermal efficiency of power boilers through the recovery of sensible and latent heat of condensation from flue gases containing certain amount of water vapor. Many parameters influence the operation of economizers, among them the amount of water vapor in the flue gas and cooling water parameters. This paper presents experimental results obtained for various local parameters of vertical tube bundle economizer when the flue gas water vapor mass fraction is 6 % and 14 % and when different cooling water inlet flow rates and temperatures are applied. The results showed that the change in the water flow rate had negligible effect on variation of the local flue gas and cooling water temperature along heat exchanger. However, its effect on the condensate flux and the local Nusselt number was significant. The cooling water temperature and, especially, water vapor mass fraction had a great impact on the average Nu number, but the effect of the flue gas Re number was less evident. It was determined that there exists a ratio of cooling water to flue gas mass flow rate, where the operation of the economizer is optimal in terms heat transfer and condensation efficiency.

Blast wave induced strain measurements in polymers using FBG sensor inside shock tube

Polypropylene and polytetrafluoroethylene (Teflon) have several applications in the aerospace industry and the study of their behaviour in high speed impact events is of great significance. This paper demonstrates the use of FBG sensors for measuring blast wave induced strain in aerospace grade polymer samples inside a Vertical Shock Tube (VST). FBG strain measurement assembly incorporating the polymer test sample and embedded FBG sensor has been designed and developed for suitably mounting it in the driven section of the VST. Experiments are carried out by impacting the polymer samples with blast waves of different peak pressures generated inside VST. PCB pressure transducer is used to record the blast pressure profile in the VST. A systematic study of strain profiles developed in the polymer test samples and their dependence on incident blast wave parameters has been carried out. The strain profiles measured by FBG in both the polymer samples are analysed using FFT and continuous wavelet transform analyses. FEM analysis is carried out using ABAQUS dynamic explicit to simulate the blast wave induced compression in polymers for different blast wave peak pressures and compared with experimental results. The application of FBG sensors to measure blast wave induced dynamic strain inside polymer materials and their capability to withstand the harsh environment of impulse test facilities like shock tubes has been demonstrated.