Lower Diameter Ratios Research Articles

Heat recovery from hot water drainage: CFD simulation, energy efficiency and exergoeconomic analysis of concentric tube heat exchangers

This study investigates the performance and economic viability of a heat recovery concentric tube heat exchanger (HR-CTHE) integrated with water heating systems using either electricity or natural gas. The system recovers heat from hot water drainage to preheat cold water, thereby enhancing energy efficiency. Computational Fluid Dynamics (CFD) simulations are conducted, examining cold and hot water drain Reynolds numbers ranging from 1,000 to 20,000, hot water drain inlet temperatures from 303 K to 333 K, diameter ratios from 1.25 to 3, and inner diameters from 0.01 m to 0.05 m. Results indicate that at an inlet temperature of 333 K and a hot water Reynolds number of 20,000, the heat recovery rate reaches approximately 20,000 W, and the preheated cold water temperature can achieve 316 K. Exergetic efficiency is highest at 0.4392 for a diameter ratio of 1.25 and an inner diameter of 0.01 m. Economic evaluations using Net Present Value (NPV) and discounted payback period indicate that coupling HR-CTHE with electric heaters is more attractive, providing higher savings and quicker returns on investment compared to natural gas heaters. For instance, integrating HR-CTHE with electric water heaters yields a discounted payback period as short as 0.2 years. In contrast, for natural gas heaters, the payback period is around 2.2 years under similar conditions. The exergoeconomic analysis further demonstrates that natural gas heaters achieve cost-effectiveness only under high hot water Reynolds numbers and inlet temperatures, while electric heaters show significant benefits at moderate to high Reh. The study concludes with recommendations for optimizing HR-CTHE performance and cost-effectiveness, emphasizing higher hot water inlet temperatures, lower diameter ratios, and appropriate Reynolds numbers for both fluids.

Impact of nanodroplets on solid spheres

Rising nanoscale technologies arouse interest in investigating the impact dynamics of nanodroplets. In this work, the impact of nanodroplets on solid spheres is investigated by the molecular dynamics simulation method, to comprehensively report outcome regimes and reveal the curvature effect, in wide ranges of Weber numbers (We) from 1.5 to 235.8, diameter ratios (λ) of nanodroplets to solid spheres from 0.3 to 5, and contact angles (θ) from 105° to 135°. Five outcomes are identified, including deposition, bouncing, splash, covering, and dripping. The former three outcomes are found in the high diameter ratio range (λ > 1), showing similar dynamic behaviors with impacts on flat surfaces, whereas in the low diameter ratio range (λ ≤)1, splash disappears, and covering and dripping take place additionally. At each contact angle, the outcomes are recorded in λ-We phase diagrams. It is found that the bouncing, splash, covering, and dripping are all promoted by decreasing diameter ratios; in addition, the critical Weber numbers for trigging bouncing and splash increase with decreasing θ. However, the critical We of the boundary between the bouncing to other regimes in the low diameter ratio range is not sensitive to wettability owing to the relatively small diameter of solid spheres. For quantitatively describing the curvature effect, the boundaries between the deposition and bouncing regimes in the high diameter ratio range and between the bouncing and other regimes in the low diameter ratio range are established. Both the established models show satisfactory agreement with the boundaries in the phase diagrams.

Influence of Flash Graphene on the acoustic, thermal, and mechanical performance of flexible polyurethane foam

In this study, flexible polyurethane foam (PUF) composites were prepared using three types of Flash Graphene (FG) produced from different feedstock material. The acoustic, thermal, and mechanical properties of foam composites containing 0.025 wt% FG were characterized. It was shown that PUF-1 and PUF-3 had higher sound absorption in the frequency range of 500–2000 Hz compared to neat PUF (baseline). PUF-3 experienced a 47% reduction in thermal expansion coefficient relative to the baseline. The tensile strength and compressive modulus of all composites increased by 16–26% and 33–37% respectively. Compression force deflection and tear strength did not change relative to the baseline. This may be explained by the relatively low flake diameter and aspect ratio of each FG which led to agglomeration and impacted load transfer between the filler and matrix. Overall, the addition of 0.025 wt% FG1 and FG3 improved acoustic, thermal, and tensile properties of PUF without diminishing compression force deflection and tear resistance. PUF reinforced with FG had similar or enhanced properties compared to PUF containing commercially available, exfoliated graphene nanoplatelets (GNP). This supports the use of FG as a relatively sustainable, low-cost alternative to exfoliated GNP or chemical vapor deposition (CVD)-grown graphene in porous polymer composites.

Genetic variability in growth, volume and stem stability traits for Eucalyptus clones in North-western India

Ten clones of Eucalyptus camaldulensis planted at central plains of north-western India were evaluated for growth traits, stem stability and wood volume at different age rotations. A significant amount of genetic variations were found for all traits assessed i.e. height, diameter at breast height (DBH), form quotient, volume and stem stability. Clones P-23 was observed best for DBH, volume and stem stability against the winds (wind firmness) and tree architecture because of low height diameter ratio (more stem stability), whereas P-46 was found best for height with less taper stem. High heritability was observed for height and volume clearly suggested the potentiality of the clonal material for the improvement through selection and evaluation. Genetic advance for height and DBH is increased substantially par se with the increase in the age of tree. The high correlation between the volume and dbh in eucalypt clones means that the selection based on dbh represents the volume with adequate accuracy. Volume equations were developed for height, dbh and form quotient functions. Volume is increased by 14.07% at compound rate of DBH as explained by bivariate fit of volume by DBH and model is highly fit (r 2 =0.8389). Negative effect has been observed by form quotient for volume estimation in clonal plantations of Eucalyptus .

The expression and role of tenascin C in abdominal aortic aneurysm formation and progression.

OBJECTIVESUp-regulation of tenascin C (TNC), a matricellular protein, produced mainly by vascular smooth muscle cells (VSMC), is associated with the progression and dilation of abdominal aortic aneurysms (AAA). The aims of this study were (i) to evaluate whether serum levels of TNC in patients with AAA patients correlate with aortic diameter and (ii) to clarify the role of TNC in formation and progression of AAA in a murine model.METHODSIn 15 patients with AAA serum levels of TNC were measured and correlated with aortic diameters. Moreover, in a murine calcium chloride AAA model, the impact of TNC deficiency on AAA diameter was evaluated. Finally, human VSMC were incubated with TNC to clarify its regulating potential.RESULTSIn the clinical cohort, there was a trend of correlation between serum TNC levels and AAA diameter (P = 0.055). TNC knock out mice with AAA showed significantly lower diameter ratios compared to the wild-type group (WT) 3 weeks (P < 0.05) and 10 weeks (P < 0.05) after AAA induction. Immunohistochemistry revealed increased TNC expression in aortic tissue from WT with AAA as compared sham-operated mice. Furthermore, WT with AAA showed a more disrupted Elastin structure than TNC knock out mice 10 weeks after AAA induction. In human aortic VSMC, TNC incubation induced expression of remodelling associated proteins.CONCLUSIONSTNC might play a causative role in the formation, dilation and progression of AAA. Our results indicate that TNC might be a biomarker as well as a potential therapeutic target in the treatment of AAA.

低直径比圆柱随机填充床化学链燃烧数值模拟

低直径比圆柱随机填充床化学链燃烧数值模拟

Hydrodynamic performance of multiple co-axial heave plates with different diameters

ABSTRACTHeave plates are structural components of a floating structure whose primary purpose is to increase damping and added mass in heave or pitch direction. If multiple plates are stacked along a common axis, then the relative diameters and spacing in between are important factors affecting the performance. In the present study, hydrodynamic coefficients of single, double and triple disks are experimentally investigated in different arrangements as Uniform, Concave and Convex edge shapes. It is observed that each disk in a multiple arrangement with lower diameter ratio have better hydrodynamic performance compared to the cases with higher diameter ratio when the spacing is small compared to the mean diameter. Some hydrodynamic aspects affecting floating structure design are also discussed in this paper.

Transient numerical simulation of the coaxial borehole heat exchanger with the different diameters ratio

In this paper, the thermal and hydrodynamic performance of the coaxial borehole heat exchanger (CBHE) with different diameters ratio, during heat injection into the ground are investigated. For this purpose, the energy and Reynolds Averaged Navier-Stokes (RANS) equations with SST k-ω turbulence model are numerically solved to simulate transient fluid flow and heat transfer. Numerical simulation results are validated with results of available experimental data. The reduction of heat transfer between the annular and central region and the increase of heat transfer between the annular region and ground is the main objective of this study to improve the thermal performance of the CBHE. The results show that the temperature difference between the inlet and outlet of the CBHE rises with the decrease of diameter ratio. In order to reduce costs, instead of using a CBHE with a high diameter ratio and more borehole depth, it is better to use a CBHE with a low diameter ratio and borehole depth. Also, the optimal diameter ratio is calculated for the lowest pumping power. Of course, due to the insignificance of the pumping power against the heat transfer at the different diameters ratio, the CBHE with a lower diameter ratio is recommended because it has better thermal performance and cooling.

Numerical Study for the Thermal Energy Storage Using PCM in Concentric Cylinders

A new simulation is proposed for storage thermal energy using concentric cylinders filled with a phase change material PCM. The concentric cylinders are arranged where each two concentric cylinders are considered as insulated unit from the outer surface and exposed to internal flow. The numerical method is applied to solve the energy conservation equation of concentric cylinders of PCM using finite volume method with heat capacity method for latent heat of PCM. The fourth order Runge–Kutta method is used to solve the energy balance equation of heat transfer fluid. The effect of diameter ratio of concentric cylinders, initial temperature of PCM, inlet temperature of working fluid and Reynolds number are studied. The results are presented as the temperature distribution of PCM and melt fraction. The results illustrated that at take a constant volume of PCM (constant volume of the space between concentric cylinders) the low diameter ratio gives faster melting also, the inlet temperature of working fluid gives big effect on the melting process. The present results are validated with other work and give a good agreement.

Study on the mechanics of a coiled tubing within a marine ‘pipe-in-pipe’ system with a low diameter ratio

ABSTRACTTo better understand the mechanics of coiled tubing working within the risers connected to Floating liquefied natural gas (FLNG), this paper studied a specific marine ‘pipe-in-pipe’ system with a low diameter ratio. The experimental results showed that the axial load on the inner pipe of an unfixed system increased with the increase in injected length. In this case, the ‘force-in’ was always larger than the ‘force-out’. The changing trend of force-in and force-out within the unfixed system was essentially found to be stable after a sinusoidal buckling of the inner pipe. Even though the magnitudes of force-in and force-out did not increase a lot, the injected length increased significantly. Relationship of force-in, as well as force-out, between fixed and unfixed system when the pipe was buckled sinusoidally and helically was found. The results help in working of a coiled tubing within small diameter marine risers.

Efficacy of feedback respiratory training on respiratory muscle strength and quality of life in children with spastic cerebral palsy: Randomized controlled trial

Background/aim Respiratory muscle weakness and a low upper to lower chest diameter ratio are common respiratory dysfunction manifestations in children with cerebral palsy (CP), which negatively affect their quality of life. This study was conducted to investigate the effect of incentive spirometry (IS) training on these manifestations in those children. Materials and methods Totally, 30 children with spastic diplegic CP, aged between 6 and 12 years, were randomly assigned into two groups: the study group and the control group. Both groups received a traditional physical therapy program for 60 min. The study group received also IS training twice per session (15 min each). Children in both groups received 20 training sessions (five times/week for 4 weeks). Outcomes Respiratory muscle strength, ratio of upper to lower chest wall, gross motor function, and health-related quality of life were assessed before and after training. Results After training, significant improvements of maximal inspiratory pressure, maximal expiratory pressure, and ratio of upper to lower chest wall were obtained in the study group (P=0.002, 0.002, 0.005, respectively), whereas nonsignificant changes were obtained in the control group (P=0.719, 1, 0.284, respectively). In addition, a significant difference was observed between both groups in maximal inspiratory pressure, maximal expiratory pressure, but in favor of study group (P=0.001, 0.001, respectively), whereas there was a nonsignificant difference in the ratio of upper to lower chest wall, gross motor function, and health-related quality of life (P=0.279, 0.527, 0.876, respectively). Conclusion Feedback respiratory training improves respiratory muscle strength in spastic CP children.

The effect of nanoparticle packing on capacitive electrode performance.

Nanoparticles pack together to form macro-scale electrodes in various types of devices, and thus, optimization of the nanoparticle packing is a prerequisite for the realization of a desirable device performance. In this work, we provide in-depth insight into the effect of nanoparticle packing on the performance of nanoparticle-based electrodes by combining experimental and computational findings. As a model system, polypyrrole nanospheres of three different diameters were used to construct pseudocapacitive electrodes, and the performance of the electrodes was examined at various nanosphere diameter ratios and mixed weight fractions. Two numerical algorithms are proposed to simulate the random packing of the nanospheres on the electrode. The binary nanospheres exhibited diverse, complicated packing behaviors compared with the monophasic packing of each nanosphere species. The packing of the two nanosphere species with lower diameter ratios at an optimized composition could lead to more dense packing of the nanospheres, which in turn could contribute to better device performance. The dense packing of the nanospheres would provide more efficient transport pathways for ions because of the reduced inter-nanosphere pore size and enlarged surface area for charge storage. Ultimately, it is anticipated that our approach can be widely used to define the concept of "the best nanoparticle packing" for desirable device performance.

Plasmon-Enhanced Light Absorption in GaAs Nanowire Array Solar Cells.

In this paper, we propose a plasmon-enhanced solar cell structure based on a GaAs nanowire array decorated with metal nanoparticles. The results show that by engineering the metallic nanoparticles, localized surface plasmon could be excited, which can concentrate the incident light and propagate the energy to nanowires. The surface plasmon can dramatically enhance the absorbance of near-bandgap light, and the enhancement is influenced by the size and material of nanoparticles. By optimizing the particle parameters, a large absorbance enhancement of 50 % at 760 nm and a high conversion efficiency of 14.5 % can be obtained at a low diameter and period ratio (D/P ratio) of 0.3. The structure is promising for low-cost high-performance nanoscale solar cells.

Numerical investigation on the head-on collision between unequal-sized droplets with multiple-relaxation-time lattice Boltzmann model

Droplet collision is a fundamental and important phenomenon in multiphase flow. Compared with equal-sized droplet collision, unequal-sized cases have been much less examined and understood. In the present study, the high density ratio lattice Boltzmann multiphase model proposed by Lee et al. (2010) and Lee (2009) is realized into the multiple-relaxation-time formulation in the axisymmetric cylindrical coordinate, which succeeds in achieving both high density ratio and low viscosity. Using this model, the head-on droplet collision between unequal-sized droplets is investigated from the aspects of the diameter ratio, Ohnesorge number (Oh), and the Weber number (We) by discussing their effects on the time-resolved evolutions of droplet shape, flow field, and the mixing process. It is found that the diameter ratio is crucial in determining the droplet dynamics and outcome, since at low diameter ratio the droplet deforms slightly and exhibits the characteristics of surface wave propagation. Whereas, as the diameter ratio increases the droplet deforms more largely and symmetrically, which is easier to result in reflexive separation, and gas bubble is likely to be entrapped in the droplet at medium diameter ratio. Besides, it is found that the initial smaller droplet tends to spread or penetrate more into the larger one with increasing diameter ratio, while the “mixing pattern” (whether axially nailed into, or penetrate/spread from the side) is not obviously affected by the diameter ratio. The Oh number is found to affect the mixing process more than the droplet dynamics and the outcome, since at low Oh number the smaller droplet penetrates axially into the larger one, at medium Oh number it tends to spread on the larger one’s surface, while at high Oh number it accumulates at its initial side. The effect of We number on mixing is found to be relevant with the Oh number and diameter ratio. As We number increases, at high Oh number the initial smaller droplet spreads more widely on the larger one’s surface; at low Oh number, the initial smaller droplet penetrates axially deeper into the larger one at low diameter ratio, while tends to spread on the larger one’s side surface at large diameter ratio.

Gas–solid flow simulation of fines clogging a packed bed using DEM–CFD

In ironmaking blast furnace processes, the gas and fines pass a solid particle packed bed during the course of a reduction reaction. It is reported that unreacted fines deposit in the packed bed, causing a local ventilation resistance, which in turn decreases the process efficiency. A three-dimensional simulation combining the discrete element method and computational fluid dynamics (DEM–CFD) was performed to understand the individual behavior of fines in this process. State of the art DEM–CFD simulations were carried out and more than 1.4 million fines were tracked in this study. The searching cells were optimized to increase the calculation speed. A deposition simulation of the gas and fines was performed using this method in a cylindrical packed bed. The fines configuration and the packed bed structure were evaluated for studying the clogging phenomenon. The packed particle to fines diameter ration is given by 7.38≤Dp/dp≤11.34. At sufficient low diameter ratio (such as Dp/dp=7.38), stagnant fines cause cluster formation, and they concentrate at the bottom of the packed bed. Our results show that clogging by the fines depends on the packed bed structure. Stress distribution in the cluster is not constant, and bottleneck particles support the entire cluster. The pressure drop has also been calculated, and the calculation results agree with previous experimental results.

Monte Carlo study of four dimensional binary hard hypersphere mixtures

A multithreaded Monte Carlo code was used to study the properties of binary mixtures of hard hyperspheres in four dimensions. The ratios of the diameters of the hyperspheres examined were 0.4, 0.5, 0.6, and 0.8. Many total densities of the binary mixtures were investigated. The pair correlation functions and the equations of state were determined and compared with other simulation results and theoretical predictions. At lower diameter ratios the pair correlation functions of the mixture agree with the pair correlation function of a one component fluid at an appropriately scaled density. The theoretical results for the equation of state compare well to the Monte Carlo calculations for all but the highest densities studied.

Fetal Diagnosis of Interrupted Aortic Arch

To determine the frequency of prenatal detection among liveborn patients with an interrupted aortic arch (IAA), the accuracy of prenatal diagnosis, and the anatomic features associated with IAA in the fetus. The prenatal diagnosis of an IAA is challenging. The data on the features and outcomes of fetal IAA are limited. This was a retrospective review of the fetuses and neonates diagnosed with IAA at the Children's Hospital Boston. From 1988 to 2009, 26 fetuses were diagnosed with an IAA. Of these, 21 were live born, and 5 pregnancies were terminated. Of these 21 patients, 18 were confirmed to have an IAA after birth and 3 had severe aortic coarctation. Of the 56 patients diagnosed with an IAA as neonates, 3 had a prenatal echocardiogram that did not include the correct diagnosis. Among the liveborn patients with a postnatally confirmed IAA, 24% were diagnosed prenatally, which increased from 11% during the first 7-year period to 43% more recently. Also, 15% of the prenatally diagnosed patients with IAA had a family history of structural or genetic anomalies. In fetuses with an IAA, echocardiographic Z-scores for the aortic valve and ascending aorta were significantly lower than in normal fetuses, but the left ventricular dimensions were normal. Aortopulmonary diameter ratios were abnormally low. In conclusion, although the identification of IAA on a prenatal echocardiogram can be challenging, a number of anatomic features can facilitate the diagnosis. In particular, a low aortopulmonary diameter ratio in the absence of a ventricular size discrepancy should prompt consideration of this diagnosis. Despite the diagnostic challenges, the frequency of prenatal diagnosis of the IAA is increasing.

Compensation for Joule–Thomson effect in flowrate measurements by GMDH polynomial

The international standard for flowrate measurements ISO-5167 recommends the temperature sensor to be located downstream of the differential device what may cause a significant error in the measurement of the flowrate of natural gas, especially at high differential pressure, low temperature and low diameter ratio. The flowrate generally needs to be compensated for the temperature change due to the Joule–Thomson effect caused by the constriction of the metering device. The accurate compensation involves double calculation of both the natural gas properties and the flowrate. To decrease the computational load, an automatic correction of the flowrate by the GMDH polynomial surrogate is proposed. By using the compound measure of the approximation error and the execution time for model selection, the modified GMDH algorithm searches for the satisfactory model fulfilling the constraints of real-time application. The automatic correction of the flowrate measurements of a natural gas is simulated and the corresponding results are discussed. The derived model can be equally used for a natural gas specified by composition or by physical properties.

Split Ends and Cracking Problem During Hot Rolling of Continuously Cast Steel Billets

The paper presents a detailed analysis of split end and cracking problems that occurred during hot rolling of thermomechanically treated (TMT) grade steel bars. The major analytical tool was a multiscan computer-controlled ultrasonic image analysis system for analysis of the defects observed on transverse cut slices of the billets under investigation. The possible reasons for billet cracking during hot rolling such as a low Mn/S ratio, high casting speed, high degree of superheat, and high inclusion content in steel were analyzed. Additionally in the process parameters such as low roll diameter, high friction, and low reduction ratio were also analyzed. The cracking appeared to be associated with large surface/internal defects, axial porosity, off-centered cavities/porosities, off-centered cracks, and inclusion bands. The analysis results suggested methods to prevent such defects in continuously cast steel billets and to reduce/eliminate split end problems. The casting parameters should include: (a) Mn/S ratio >35, (b) degree of superheat <60 °C, and (c) casting speed: <3.0 m/min, where roll radius and initial thickness of the workpiece should be optimized.