Tube Diameter Research Articles

Electrical and thermal performance analysis of hybrid photovoltaic/thermal water collector using meta-heuristic optimization

The photovoltaic/thermal (PV/T) flat-panel technology has numerous advantages over PV modules and separately mounted solar thermal collectors regarding overall effectiveness and space-saving. Hybrid PV/T solar collectors’ thermal and electrical performance is influenced by design parameters like mass flow rate, tube diameter, tube spacing, packing factor, and absorber conductivity. This paper focused on using several meta-heuristic optimization techniques, incorporating the following: multiverse algorithm, dragonfly algorithm, sine–cosine algorithm, moth-flame algorithm, whale algorithm, particle swarm algorithm, ant-lion algorithm, grey wolf algorithm, and particle swarm optimization algorithm in PV/T collector optimal design according to maximum total efficiency obtained. The outcomes of the various algorithms revealed that the maximum electrical efficiency of the PV/T collector ranged from 13.85 to 14.28%, while the maximum thermal efficiencies ranged from 41.41 to 52.08% under standard test conditions (1000 W/m2 and 25 °C). The optimized values for the design parameters of the PV/T collector were as follows: the absorber conductivity was determined to be 356.6 W/m K, the packing factor was optimized to 0.7, the mass flow rate was set at 0.019 kg/s, the tube width was determined to be 0.035 m, and the tube spacing was optimized to 0.0524 m. The results indicated that the grey wolf optimizer (GWO) algorithm proved to be highly effective in optimizing the design parameters of PV/T collectors. Furthermore, the study examined the relationship between the temperature of PV modules and PV/T collectors by considering variations in mass flow rate, packing factor, and tube width at different solar radiation levels. The results confirmed that the PV/T collector temperature exhibited improvements compared to the PV module temperature. As a result, this led to higher electrical efficiency and an overall increase in the total efficiency of the PV/T collector.

Waste heat recovery from exhaust gases using porous metal fins: a three-dimensional numerical study

Abstract The objective of this study is to investigate the impact of different porous metal samples on the hydro-thermal characteristics of a single cylinder with porous fins using computational fluid dynamics. Commercially used porous samples with pore densities of 10, 20, and 40 PPI were used in this study for heat recovery from exhaust flue gas. The three-dimensional computational domain with porous aluminium fins attached to a tube over which high-temperature exhaust gas flows in a crossflow arrangement mimics a waste heat recovery system. Computations were performed at Reynolds number of 6000-9000, using the realisable κ-ϵ turbulence model. Three fin diameter to tube diameter ratios (Df/D = 2, 2.5, and 3) were considered. The local thermal non-equilibrium model is implemented for energy transfer, as it is more accurate for a high-temperature gradient scenario in a waste heat recovery system. The foam sample with the highest pore density was observed to have the highest pressure drop due to low permeability. A maximum heat transfer and Nusselt number were achieved for a 40 PPI foam sample due to a reduced flow rate inside the porous zone. The overall performance of metal foam samples at varying fin diameters was evaluated based on the area goodness factor (j/f) and a heat transfer coefficient ratio to pumping power per unit heat transfer surface (Z/E). Analysis of these two parameters suggests using 20 PPI foam at Df/D = 2.

Energy optimization of parabolic dish solar concentrator coupled to organic Rankine cycle: Experimental and analytical investigation of cavity receiver design and covering effects

Concentrated solar power (CSP) systems offer a promising solution for sustainable energy, but achieving high and stable efficiency requires careful design optimization. This study evaluated the overall performance of a parabolic dish solar concentrator coupled to an Organic Rankine Cycle (ORC) system through experimental and analytical assessments. The research examined the impact of cavity receiver shape (cylindrical vs. spherical) and the use of a glass cover on thermal efficiency. Additionally, the effectiveness of a cone structure to reduce spillage losses and improve optical efficiency was explored. Testing showed a significant improvement in system performance, with an increase from 75 % for the open cavity to 90 % for the sealed cavity equipped with the cone structure (15 % increase). This highlights the importance of receiver design in reducing heat loss. To further optimize the system, a numerical model was developed and validated against experimental measurements. The simulation demonstrated that the overall system performance is significantly influenced by the water outlet temperature from the cavity receiver and the pressure drop within it. The model suggests that overall performance could be enhanced from 4.6 % to higher than 6 % by optimizing factors like water mass flow rate, cavity tube diameter, and the selection of a more suitable ORC working fluid (e.g., R245fa instead of R134a).

Oversized diameter helium pulsating heat pipe

A cryogenic pulsating heat pipe (PHP) whose capillary tube diameter does not satisfy the classical Bond number (Bo) criterion has been experimentally tested and showcased in this work. Helium is the working fluid employed and the PHP diameter is ∼ 1.75 times its recommended critical diameter of 0.57mm. All the investigations reported till date on helium PHP have adhered to tube diameter of 0.5mm evidently meeting the Bo < 4 criterion. However, this helium PHP corresponds to Bo = 12 at 4.2K and, in fact, is the first cryogenic PHP demonstrating its functionality at such a high Bond number for helium. The motivation for such an investigation is initially presented with a deliberation on different PHP critical diameter criteria. A hypothesis emphasizing on the need to re-evaluate the upper limit of tube diameter for cryogenic PHPs is proposed. In support of this, a closed-loop PHP constructed from a 1mm inner diameter stainless steel tube is utilized. It is composed of 20 parallel channels and has a projected length of 0.4m. The functionality of this large diameter helium PHP is validated by experimentally characterizing its thermal performance and pressure as a function of heat load up to 1.5 W within an exhaustive range of filling ratios (10 to 90 %). This is conducted both in vertical and horizontal orientation. Zones where the PHP quickly surpasses the helium critical temperature and pressure values and still functioning are identified. Finally, its reliability is exhibited by 65 h stability test conducted at constant operational conditions.

Effect of tube bend angle on liquid propulsion system priming event pressures

Experimental work was performed to measure the priming event pressure transient levels in unrestricted liquid propulsion system tubing. An existing water hammer experimental setup was utilized, where system tubing diameter, length, and bend angle were examined. Experiments were performed under both atmospheric and low-pressure pre-test element conditions to understand any impact of tube bend angle on the mitigation of priming event pressure transients inside the liquid system. Experimental results showed pressure levels were influenced by a combination of tube diameter, length, and pre-test pressures; however, tube bend angle had minimal to no discernible change on the average peak pressure levels or rise times to peak pressure for all conditions examined.

Study on the electrostatic shedding and crushing characteristics of ethanol and diesel droplets

The study of electrostatic shedding and crushing characteristics of droplets is the basis of understanding electrostatic atomization, and the study of its shedding and crushing behavior in electrostatic field is conducted. Micropump drive is used to control the flow rate, electrostatic generation device to form a stable electric field, light lighting and high-speed camera to obtain the dynamic behavior of shedding and crushing process, and use digital image processing technology to extract the process parameters. The results show that: when the capillary tube diameter and flow are unchanged, when the electric field voltage is low, the droplet deviates and falls off, the diesel droplet is smaller than the ethanol; when the electric field voltage is moderate, the droplet is closed or deformed into wave strip; only when the flow rate increases and the electric field voltage is large, the average particle size of ethanol is smaller than diesel, indicating that the electrostatic atomization effect of ethanol with small surface tension is significantly better than that of diesel oil.

Behavior of Circular Hollow Steel-Reinforced Concrete Columns under Axial Compression

The circular hollow steel-reinforced concrete (HSRC) column consists of an inner circular hollow steel tube and outer circular hollow reinforced concrete (RC). This design provides several advantages, including being lightweight, having a wide sectional profile, and having a high flexural stiffness. This paper aims to investigate the behavior of the circular HSRC columns under axial compression through testing and finite element (FE) modeling. An FE model was established to simulate the circular HSRC columns under axial compression, which was validated against the test data. Additionally, the load distribution and the interface stress between the outer hollow RC and inner steel tube were analyzed. Subsequently, a systematic parametric analysis was conducted on the diameter (d) and thickness (t) of the steel tube; slenderness ratio (λ); strength of concrete (fcu); yield strength of steel tube (fsy), longitudinal rebar (fly), and stirrup (fgy); as well as the stirrup spacing (s). The critical influencing factors of the circular HSRC columns under axial compression were identified. fcu, λ, d, fly, and fsy dramatically influence the bearing capacity, and the stiffness is notably affected by λ and fcu. Finally, three simplified design methods were summarized and evaluated for calculating the bearing capacity of the circular HSRC columns under axial compression.

The Change of Flow Pattern from Stratified to Stratified-Wavy for Condensation in Wire on Tube Heat Exchangers

Flow patterns inside wire-on-tube condensers with different refrigerant mass flow rates were studied in a theoretical study. In this study, tubes with diameters of 3.25 mm (3/16"), 4.83 mm (1/4") and 6.29 mm (5/16") were used. R-134a and R-600a cooling fluids were used at condensing temperatures of 54.4°C, 45°C, and 35°C. The results of this study were obtained using Equal Equation Solver (EES) software. The proposed model was able to predict the type of refrigerant flow pattern based on the limitations reported in previous studies. It was possible to distinguish four kinds of flow patterns: laminar, wavy laminar, plugged, and spiral. The first variation in flow pattern from laminar to wavy laminar flow found between 0.8 and 0.39, and a second variation in flow pattern found from wavy laminar flow to plug or slug flow between 0.15 and 0.05. For the refrigerant conditions, the condensation temperature did not affect the flow pattern. When using R-134a, the inner tube diameter had no effect on the flow pattern. Change occurs with R-600a as inner diameter was increased.

Comparison of heat transfer characteristics of a heat exchanger with straight helical tube and a heat exchanger with coiled flow reverser

Vertical shell and coiled tube heat exchangers are an important aspect of numerous industrial processes and are renowned for their high heat transfer efficiency, versatility, compact design, easy manufacturability and maintenance. As a novel technique, a coiled flow reverser was used to enhance the thermal performance of shell and coiled tube heat exchangers. Therefore, the impact of employing a coiled flow reverser on the heat transfer characteristics and pressure drop in a counter-current shell and tube heat exchanger is investigated using both numerical and experimental approaches. The results are compared to a straight helical coiled tube heat exchanger. The numerical simulations were carried out by employing computational fluid dynamics (CFD) techniques, and the SIMPLE scheme was implemented through the second-order upwind discretization method. The laboratory device used for experimentation features a shell with an inner diameter of 15 cm, and the coil pitch and coil diameter of both coiled tubes are set at 3 cm and 12.1 cm, respectively. Results reveal that the overall heat transfer coefficient of the heat exchanger with a coiled flow reverser is 39.5 % to 49.9 % higher than that of the heat exchanger with a straight helical tube. The effectiveness ratio of the heat exchanger with coiled flow reverser to the straight helical tube heat exchanger ranges from 1.254 to 1.379. Optimal results are observed at a cold flow rate of 6 LPM and a hot flow rate of 1 LPM for both heat exchangers. Additionally, the coiled flow reverser enhances heat transfer performance at the cost of increased pressure drop. Numerical results are in good agreement with experimental findings, establishing the reliability of the study.

Axial compressive behavior of bamboo sheet twining tube-confined concrete columns with an inner original bamboo tube

The bamboo is widely distributed around the world and the product process is developed well, the biomass bamboo fiber composite is potential to providing strong confinement for concrete, therefore in this paper, bamboo sheet twining tube-confined concrete columns with an inner original bamboo tube (BSTCB) is proposed. This column is a new structure that consists of an external bamboo fiber composite tube and an internal original bamboo tube filled with concrete between the outer and inner tubes. A total of 18 specimens were tested in axial compression. The effects of BCT thickness and original bamboo tube diameter on the mechanical properties of the specimens were analyzed. The experimental results suggested that BCT has a strong lateral confinement ability. The strength and deformability of concrete increased significantly when BCT thickness increased. When the number of BCT layers was in the range of 6–18 layers, the increase in peak stress ranged from 7.7 % to 12.8 % and the increase in ultimate strain ranged from 6.4 % to 24.0 %. The increase in the diameter of the original bamboo tubes had a positive effect to the deformation capacity, while limited effect on the concrete compressive strength. Within the change in diameter from 90 mm to 110 mm, the reduction in concrete strength is within 6.0 %, and the change in ultimate strain ranges from 8.5 % to 14.1 %. Finally, the peak stress and strain of the concrete were evaluated using the existing FRP-confined concrete model, and the full stress-strain curve of the concrete was obtained.

Experimental and simulation analysis of the performance of premixed vertical ejectors

Infrared gas stoves have advantages such as rapid combustion speed and high thermal efficiency. The ejector, a pivotal component of the infrared gas stove, plays a crucial role in influencing the mixing ratio of gas and air. The vertical ejector is modeled and the simulation method is validated through experiments. The impact of structural parameters on the vertical ejector performance is investigated in this paper, like the contraction tube length, inlet diameter, and mixing tube length. The simulation results indicate that with the change in the contraction tube length, the excess air coefficient peaks at approximately 1.16. An increase in mixing tube length leads to a decreasing trend in the excess air coefficient. For ejectors with throat diameters of 9.8 mm, 11.2 mm, and 12.6 mm, their excess air coefficient reaches peak values at diffusion angles of 3.5°, 4.7°, and 5.0°, respectively. Furthermore, Response Surface Methodology is utilized to study the comprehensive influence of structural parameters on ejector performance and obtain the optimal structure. The excess air coefficient is 1.13 with the optimal geometric structure.

Prediction of the sulfur driven autotrophic denitrification process via CFD-DEM approach

Sulfur driven autotrophic denitrification is an economic and efficient means to purify the nitrogenous wastewater. The long-term experimental study is quite time-consuming and expensive. In this work, a coupled computational fluid dynamics-discrete element method (CFD-DEM) is implemented to investigate the performance of long-term operating sulfur autotrophic denitrification process. The evolution of particle accumulation and nitrate removal efficiency in the packed bed reactors with different tube diameters and sulfur particle sizes are simulated. It is found that the NO-3-N removal rates for different tube diameters are close and a wider particle size distribution is shown in the slender reactor. The small particle bed shows a better NO-3-N removal efficiency.

Comparative analysis of heat transfer prediction for falling film evaporation on the horizontal tube based on machine learning methods

Precise prediction of heat transfer for falling film evaporation is necessary for the horizontal tube falling film evaporator design. In this study, models to predict the heat transfer are compared, which are developed by traditional Least Square method (LSM) and Machine Learning (ML) methods, including Support Vector Regression (SVR), Artificial Neural Network (ANN) and Random Forest Regression (RFR). The training data is obtained by a series of experiments, containing 510 experimental data of fresh water and seawater of salinities from 30 to 60 g/kg. The experiments were conducted with the test tube diameter of 19, 25.4 and 38 mm and with the heat flux of 7.7–12 kW/m2. All ML models behave better performances than the LSM model and the SVR model is suggested as the best model to predict the heat transfer, considering the prediction accuracy and generalization ability comprehensively. SHapley Additive exPlanations (SHAP) is used to explain the relationships between Nusselt number and input variables, which also helps to resolve controversial issues about the effects of spray density and tube diameter on the heat transfer. The importance of variables is ranked, in which the tube pitch and seawater salinity are regarded as the most influential variables. Besides, the limitations and performance of models are analyzed in terms of both dataset and algorithms.

Theoretical prediction model for the compressive behavior of the hybrid tube considering compression angle

AbstractThe oblique collision happening in vehicle accidents poses a huge threat to passive safety, which causes great difficulties in the design of energy absorption (EA) structures and the prediction of EA capacity due to its highly nonlinear deformation characteristics. This study aims to establish a theoretical prediction model for the compression performance of Carbon Fiber Reinforced Polymer (CFRP)/Al hybrid tube considering the loading angle. First, a high‐precision FE model was established to obtain the influence laws of tube diameter, Al thickness, and CFRP thickness on the crashworthiness of CFRP/Al hybrid tubes, laying the foundation for subsequent theoretical model validation. Second, by summarizing the deformation modes of hybrid tubes generated by various parameter combinations, a modified global origami deformation assumption was proposed under multi‐angle compression conditions, and the key terms in energy composition are extracted based on the initial and final states of folding elements. Third, a theoretical model for predicting the mean crushing forces (MCFs) of hybrid tubes was established by revealing the correlation mechanism between energy composition terms and loading angle. Finally, the theoretical prediction model was validated by experiment and simulation results and the application premise was given. Results showed that the theoretical prediction model was proved to be of high accuracy, as the average absolute prediction errors of MCF under axial, 10°, 20°, and 30° compression conditions were 6.54%, 4.63%, 3.72%, and 3.93%, respectively. This study provides valuable guidance for the forward design and development of multi‐material hybrid structures facing complex crushing conditions.Highlights An analytical model of the hybrid circular tubes considering compression angle is newly proposed. Deformation mode and axial crushing response are analyzed by experiments. The major energy dissipation mechanism for hybrid circular tubes is explicitly derived. The Al thickness has the most significant impact on energy absorption. The recommendations for the design and development of hybrid tube are provided.

Flame propagation characteristics and gas-phase oxidation of nitrous oxide and propane

Nitrous oxide and fuel blends propellant as one of the substitutes for highly toxic hydrazine are under investigation. This study investigated the flame structure and dynamics of stoichiometric nitrous oxide and propane mixture (N2O/C3H8) by using polymethyl methacrylate (PMMA) tubes of varying inner diameters (5, 10, 15, and 50 mm) and a consistent length (1400 mm). The influence of tube diameter on flame acceleration was analyzed. The results reveal that within the 50-mm diameter tube, the flame propagation speed increased as the flame front moved forward in the tube, achieving a maximum speed of 532 m/s. In the tubes with 5-, 10-, and 15-mm diameters, all three stages—deflagration, transition to detonation, and detonation attenuation—were observed. Notably, the flame acceleration rate and maximum propagation velocity increased with the tube diameter, with the maximum velocities in the 5-, 10-, and 15-mm tubes being 1900, 2060, and 2140 m/s, respectively. The oxidation pathways of C3H8 reacting with N2O were studied using the B3LYP/6–31++G** method based on density functional theory. Thus, the study could determine changes in the configurations of reactants, intermediates, transition states, and products; the characteristics of the potential energy associated with the reaction pathways; and the reaction laws and thermodynamic parameters.

Field-driven polyelectrolyte-polymer collisions in nanochannels.

Even though dilute (unentangled) polymer solutions cannot act as gel-like sieving media, it has been shown that they can be used to separate DNA molecules in capillary electrophoresis. The separation then comes from sporadic, independent DNA-polymer collisions. We study polymer-polymer collisions in nanochannels (i.e., channels that are smaller than the normal size of the polymers), a situation where a polyelectrolyte is forced to migrate "through" isolated uncharged molecules during electrophoresis. We use Langevin dynamics simulations to explore the nature of these collisions and their effect on the net motion of the two polymer chains. We identify several types of collisions, including some that are unique to nanochannels. When the uncharged polymer is much larger than the polyelectrolyte, the system is reminiscent of gel electrophoresis, and we propose a modified empirical reptation model to explain the data, with an orientation factor that depends on the tube diameter. We also observe that the duration of a collision is a non-monotonic function of the polymer size ratio when the two chains are of comparable size, a surprising resonance-like phenomenon, which, combined with the asymmetric nature of molecular conformations during collision, suggests possible ratchet-like mechanisms that could be used to sort polyelectrolytes in nanodevices.

Assessing the impact of sample size and geology on earthen embankment design and construction

This technical paper investigates the influence of sample size and geologic characteristics on the geotechnical design of levee embankments. Sample quality plays a vital role in quantifying engineering properties for levee embankment projects, and numerous studies have highlighted the impact of sample disturbance on such engineering properties. Despite this evidence, conventional tube and piston samplers of different diameters continue to be widely used, potentially leading to underestimation of shear strength. The paper focuses on comparing 7.6 cm and 12.7 cm diameter undisturbed Shelby tube samples and CPT data collected from three levee sites in the Greater New Orleans Area, Louisiana, USA, which encompass diverse geologic histories. The study aims to assess the effect of industry used samples size and geology on levee construction costs. The findings provide valuable insights into optimizing sample collection methods and improving geotechnical design for earthen embankments.

Sustainable dye extraction: Annatto powder production in a fountain confined spouted bed

AbstractThis study proposes an efficient and sustainable process for annatto powder production using a fountain confined spouted bed. With widespread applications in industries such as food, pharmaceuticals, and cosmetics, conventional extraction methods face environmental and economic challenges. Our study explores a solvent‐free and eco‐friendly approach using mechanical attrition within a fountain confined spouted bed, offering a cost‐effective solution for annatto cultivation. We systematically investigated the impact of four parameters—fountain confiner position and length, draft tube diameter, and airflow velocity—employing experimental design, multiple regression analysis, particle swarm optimization, and computational fluid dynamics–discrete element method (CFD‐DEM) simulations. The proposed optimization condition shows significantly higher collision intensity, improving annatto powder production compared to other central composite design tests. This study contributes to developing of a sustainable and economically viable method for dye production, with potential implications for annatto‐producing regions globally.

A Cold Flow Model of Interconnected Slurry Bubble Columns for Sorption-Enhanced Fischer–Tropsch Synthesis

For technical application with continuous operation of sorption-enhanced (SE) reactions, e.g., Fischer–Tropsch, a special reactor concept is required. SE processes are promising due to the negative effects of water on conversion and catalyst. The reactor concept of two interconnected slurry bubble columns combines the reaction with in situ water removal in the first, and sorbent regeneration in the second column with continuous exchange of slurry between the two. The liquid circulation rate (LCR) between the columns is studied in a cold flow model, measured by an ultrasonic sensor. The effects of different operating and geometric parameters, e.g., superficial gas velocity, liquid level and tube diameter on gas holdup and LCR are discussed and modelled via artificial intelligence methods, i.e., extremely randomized trees and neural networks. It was found that the LCR strongly depends on the gas holdup. The maximum of 4.28 L min−1 was reached with the highest exit, widest tube and highest superficial gas velocity of 0.15 m s−1. The influence of liquid level above the exit was marginal but water quality has to be considered. Both models offer predictions of the LCR with errors &lt; 6%. With an extension of the models, particle circulation can be studied in the future.

Photocatalytic removal of VOCs on TiO2 nanotube layers. Effect of layer thickness and humidity

The current work is focused on the influence of TiO2 nanotube (TNT) layer thickness, texture properties and chemical nature of volatile organic compounds (VOCs) on the efficiency of their photocatalytic oxidative removal. Attention was also given to the evaluation of the degree of mineralisation and the influence of air humidity. The fabricated TNT layers have a thickness from 2to13 μm, TiO2 mass from 0.27 to 1.15 mg cm−2, tube diameter of 108 ± 17 nm and porosity of 74 ± 5 %. Values of areal SBET determined from Kr adsorption are higher than the inner surface area of the TNT layer calculated from morphology parameters, this suggests the rough nature of the inner surface of nanotubes. Acetaldehyde was more easily degraded in comparison to hexane which was explained by a simpler chemical structure. The degree of acetaldehyde mineralisation was almost 100 %, suggesting the formation of no intermediates, analysis confirmed negligible formation of formaldehyde. In contrast, degree of hexane mineralisation was lower, 80 %. An increase in humidity has a negative effect on the photocatalytic performance; this effect is more significant for non-polar hexane compared to water-miscible acetaldehyde. The conversion of hexane and absorptance of the TNT layer at 365 nm increase similarly with increasing thickness. Hexane conversion increases significantly up to a layer thickness of about 4 μm where more than 80 % of incident light is absorbed. The simultaneous degradation of four pollutants (acetaldehyde, acetone, heptane and toluene) results in the highest degradation rate of acetaldehyde and the lowest for heptane, this was attributed to their different solubility in water as well as to their different adsorption.