Higher Inflow Velocity Research Articles

Effects of mass and damping ratios on the flow-induced vibration of two staggered circular cylinders

The mass ratio between structure and fluid and the structural damping ratio have been shown to significantly affect the flow-induced vibration (FIV) of an isolated circular cylinder. Their influences on multiple staggered circular cylinders commonly found in offshore structures have, however, not been clearly understood. This study numerically investigates the vibration responses and flow field of two staggered circular cylinders with the shear stress transfer k–ω turbulence model and the overset mesh method. The accuracy of the numerical method adopted is validated against published experimental results, and the effects of the mass ratio and damping ratio on FIV are systematically investigated. The structural responses of the two cylinders are found more sensitive to the mass ratio than the damping ratio. The amplitude of vibration increases, in general, with a reduction in the mass ratio or damping ratio, and the vibration is much more significant when the mass ratio is less or equal to unity as compared to those from other mass ratio values. A reduction in the mass ratio is found leading to more diverse vortex shedding modes with fast transition from one into another. The self-excited dynamic forces represented by the added mass ratio ma* and added damping ratio ζa are further analyzed. It is found that the added mass ratio is positive under low inflow velocity, and it gradually becomes negative with higher inflow velocity. The added damping ratio is generally negative under low inflow velocity and it increases with the inflow velocity. Furthermore, the added damping ratio decreases with the inflow velocity only when the mass ratio is smaller than unity.

Simulation of flow and debris migration in extreme ultraviolet source vessel

Practical extreme ultraviolet (EUV) sources yield the desired 13.5 nm radiation but also generate debris, significantly limiting the lifespan of the collector mirror in lithography. In this study, we explore the role of buffer gas in transporting debris particles within an EUV source vessel using direct numerical simulations. Our study involves a 2 × 1 × 1m3 rectangular cavity with an injecting jet flow subjected to sideward outlet. Debris particles are introduced into the cavity with specified initial velocities, simulating a spherical radiating pattern with particle diameters ranging from 0.1 to 1 μm. Varying the inflow velocity (from 1 to 50 m/s) of the buffer gas reveals a morphological transition in the flow field. At low inflow velocities, the flow remains steady, whereas higher inflow velocities induce the formation of clustered corner rolls. Upon reaching sufficiently high inflow velocities, the jet flow can penetrate the entire cavity, impacting the end wall. Interestingly, the resulting recirculation flow leads to the spontaneous formation of spiraling outflow. The distinct flow structures at various inflow velocities lead to distinct patterns of particle transport. For low-speed gas, it is efficient in expelling all particles smaller than 0.4 μm, while for high-speed gas, those fine particles accumulate near the end wall and are challenging to be extracted. Our findings highlight the significance of controlling flow conditions for effective debris particle transport and clearance in diverse applications especially in EUV source vessels.

Novel optimization strategy of a flow-induced piezoelectric vibration-based energy harvesting structure

In this paper, a novel boundary layer enhancement structure as well as various bluff body arrangement strategies were proposed to optimize the voltage output performance of a piezoelectric vibration-based energy harvest equipment. A systematic investigation in both numerical and experimental approaches revealed that an inversed 6-cylinder bluff body arrangement yielded significantly better voltage output performance than the previously reported dual-cylinder arrangement. A positive correlation can be observed between both flow velocity and the voltage output, and the cantilever beam tends to oscillate at a slightly higher frequency under a higher inflow velocity. A very noticeable improvement was observed when the proposed wall structure was applied, and our numerical study revealed that the wall structure induced a relatively stable layer of fluid near the wall and led to a much more chaotic wake of the bluff bodies which may account for the performance improvement of the system.

A numerical study on premixed hydrogen/air flames in a narrow channel with thermally orthotropic walls

Premixed hydrogen/air micro-flame stabilizations in a narrow channel confined by two parallel plates with thermally isotropic and orthotropic wall materials are numerically studied using a OpenFOAM-based, reacting flow code. For a range of simulated equivalence ratios and inflow velocities, two modes of flame shapes (convex-shaped and concave-shaped) are observed, accompanying with variations of the number of heat release rate peaks in flame structures, which can be attributed to the appearance of some critical O-participating and H-participating elementary reactions. Flame stability limits are studied for three sets of wall thermal conductivities of k = 16 W/m K, k = 128 W/m K (isotropic) and kxx = 128 W/m K &kyy = 16 W/m K (orthotropic). The low velocity limits show invariant with wall thermal conductivities, while the high velocity limits in descending order are found to be: “k = 128 W/m K” > “kxx = 128 W/m K &kyy = 16 W/m K” > “k = 16 W/m K”. The logic behind is the competition between two mechanisms: the wall pre-heating effects and the transverse heat losses to the ambient. The critical convective heat transfer coefficients that reflect the combustor's ability to resist heat losses are also investigated among the three cases. The reduction of the transverse thermal conductivity can have a high critical coefficient value in the low-inflow velocity regime while makes negligible impacts on extending the critical coefficient in the high-inflow velocity regime. In summary, the use of thermally orthotropic wall materials leads to a slightly decreased high velocity limit (~3% lower) but a considerably increased critical convective heat transfer coefficient in the high-inflow velocity-regime (~25% higher), as compared to the thermally isotropic combustor of k = 128 W/m K.

Wall-impinging laminar premixed n-dodecane flames under autoignitive conditions

Laminar one-dimensional (1D) flames in a stagnation flow stabilised at a wall are used to study flame–wall interaction under diesel engine conditions. The thermochemical conditions correspond to that of the Engine Combustion Network (ECN) Spray A reference case. A range of inflow velocities is considered, where the lowest inflow velocity is chosen such that the flame is detached from the inlet. The presence of a wall is shown to have a significant impact on the flame structure and emission formation. The 1D flame and homogeneous reactor results exhibit two distinct reaction zones due to low- and high-temperature chemistry (LTC and HTC, respectively). The burner-stabilised flames are overall dominated by autoignition for all inflow velocities. For the impinging jet flames, the response of the LTC reaction zone follows closely that of the burner-stabilised flames up to relatively high inflow velocities. The HTC reaction zone, however, deviates strongly from the burner-stabilised flames, already at low inflow velocities and quenches at high inflow velocities. A budget analysis revealed a strong contribution from diffusion in the HTC reaction zone, resulting in an increasing importance of deflagrative combustion as opposed to autoignition. This trend was attributed to enhanced strain rates at higher inlet velocity leading to higher gradients. Wall heat transfer was also investigated. The highest wall heat transfer rates were observed for mixtures between Φ=1.0 and Φ=1.5 and for inlet velocities just below the quenching limit. This was attributed jointly to the higher peak product temperatures for these mixtures and to their enhanced resilience to quenching under strain which leads to higher temperature gradients at the wall just before quenching. NO formation was studied. The highest NO formation was observed near Φ=1.0, though the response to strain rate was different for stoichiometric and rich mixtures, which was attributed to differing NO formation pathways.

Ultra-lean hydrogen-enriched oscillating flames behind a heat conducting bluff-body: Anomalous and normal blow–off

This paper presents a numerical study of ultra-lean hydrogen-methane flames stabilized behind a rectangular, highly conducting metallic bluff body acting as a flame holder. Using high fidelity numerical simulations, we show that lean inverted steady flames exist below normal flammability limits. They have distinct stabilization mechanism from pure methane flames. These flames are blown-off for sufficiently small velocities, a phenomenon called anomalous blow-off. At even leaner conditions oscillating ultra–lean hydrogen-methane flames can be established. These oscillating flames exist within a rather small range of equivalence ratios and inflow velocities, and move to mean locations closer to the flame holder as the reactant flow is increased. We show that the oscillations are associated with the shedding of flame balls from the downstream end of a “residual flame” that remains attached. Unlike their steady counterparts, the oscillating flames exhibit blow-off at both low velocities (anomalous blow-off) and at sufficiently high inflow velocities (normal blow-off). We show that normal blow-off is linked to heat losses to the flame holder.

Dynamic responses of anchored ducted flames to harmonic velocity forcing

This paper aims at developing a computationally inexpensive method to investigate the premixed flame instabilities. The kinematic G-equation is combined with a two-dimensional discrete vortex method, and the conformal mapping is applied to make calculations for complicated geometries more efficiently. The vortex dynamics and flame response to harmonic velocity forcing of an anchored ducted V-flame are investigated, and the effects of harmonic forcing, Reynolds number, and bluff body geometry are examined. Results show that the vortex structures, flow instability, and flame response are closely coupled with each other. The unsteady vortex structures generate instabilities at the flame base, and the convection of the flame wrinkles then influences the flame dynamics downstream. The flame heat release fluctuates with larger amplitude under low-frequency forcings, while the phase of the flame transfer function is quasi-linear with increasing forcing frequency. Both higher inflow velocity and sharper bluff body corners can result in more unsteady large-scale vortex structures and hence influence the flame responses.

Multi-Objective Design Optimization of Precoolers for Hypersonic Airbreathing Propulsion

A precooling heat exchanger has been the key mechanism for realizing turbine-based combined-cycle engines at high flight Mach numbers. A multi-objective design optimization coupling surrogate-assisted evolutionary algorithms with numerical simulation has been carried out with respect to three design objectives, that is, maximization of heat transfer effectiveness, total pressure recovery, and compactness. Physical insights into the underlying compressible aerodynamic and aerothermal phenomena in the bare tube bank geometry have been gained through scrutinizing the flowfields for the representative cases. With the nature of operating conditions having relatively high inflow velocity, tube bank configurations that are potentially prone to have flow choking are removed in the optimization process. The results from the optimization have been investigated by analyzing the selected individuals on the Pareto-optimal front and performing sensitivity analysis with the aid of surrogate models. The effects of uncertainties in the design parameters on the precooler performance have been examined. The unconventional tube profiles comprising elliptic and obround sections are found to effectively reduce unfavorable flow separation and permit smaller tube spacing ratios, yielding higher heat transfer rate per unit volume than the conventional circular tube bank.

Modeling the effect of fiber orientation on local yield stress in flow of pulp suspensions

A model that takes into account the local yield stress in pulp suspensions (2-3%) was derived. In this model the yield stress was assumed to decrease due to a reduction in the number of contact points between fibers in a network when the fibers are oriented in the shear field. The local yield stress described by the number of contact points multiplied by the friction force in the fiber connections was implemented in a CFD solver to describe the yield stress in the non-Newtonian single-phase Bingham model. Model results were compared with experimental UVP data from a study performed earlier on the flow of pulp suspensions at two concentrations after a sudden expansion. First model parameters were estimated with experimental data from a case with a concentration of 1.8% and an inflow velocity of 1.2 m/s. Then the model was used to predict five other cases. The proposed model was able to capture both the decrease in centerline velocity and the increase in the width of the jets at higher inflow velocities. At low inflow velocities the predicted jet lengths were too short compared to the experimental measured jet length due to under prediction of fiber alignment.

Aerodynamic performance of an over-the-wing propeller configuration at increasing Mach number

Over-the-wing propeller configurations and particularly channel wing concepts show increased climb performance, and through effective acoustic shielding, reduced noise emissions when compared to a conventional tractor configuration. The main aerodynamic mechanisms could be identified by steady flow simulations of a simplified wing geometry and actuator disk. At take-off, where the thrust coefficient is very high, the drag of the wing decreases much stronger than the thrust of the propeller. This paper investigates the cruise conditions where the thrust coefficient is by one order of magnitude lower. The numerical results give evidence that, even at a moderate flight Mach number of 0.6, the beneficial influence of the over-the-wing propeller on the drag coefficient of the wing is negligibly small. On the other hand, the amount of propeller efficiency that is lost through high inflow velocity above the wing increases with Ma due to compressibility effects. As a result, the propulsive efficiency of an over-the-wing configuration is 16 % smaller than the reference (tractor). Semi-empirical correlations show that even at very low Mach numbers a drawback of at least 5 % remains. Although repositioning the propeller at the wing trailing edge may recover 4 % of the propulsive efficiency at Ma = 0.6, it is not advisable to give up most of the noise-shielding effect at take-off which is an important advantage of the channel wing.

Flame dynamics in lean premixed [formula omitted]/air combustion in a mesoscale channel

The dynamics and stabilization of fuel lean premixed CO/H2/air atmospheric pressure flames in meso-scale channels were investigated numerically, using detailed gas phase chemistry and transport. Experiments in a channel flow reactor by means of chemiluminescence detection of the excited OH radical allowed for model validation at steady conditions and identification of the conditions at which unsteady flame dynamics were present. A detailed parametric study of the influence of wall temperature and CO:H2 ratio on the ensuing flame dynamics was performed. The numerical results revealed different flame modes which included oscillatory ignition, random ignition spots, as well as steady weak and V-shaped flames. The wall temperature stability intervals of these modes changed with the CO:H2 ratio. The richest variety was found for molar CO:H2 ratios between 4 and 10, while at lower ratios the random and the weak modes were absent. At higher ratios all the dynamic modes were suppressed. The Computational Singular Perturbation (CSP) method was used to obtain insights into the physicochemical processes responsible for the weak flames, which were found at relatively high inflow velocities compared to previous studies, and V-shaped flames. A kinetic explanation of the phenomena was supported by the CSP analysis.

Prognostic predictors in pericardiectomy for chronic constrictive pericarditis

Prognosis after pericardiectomy remains to be clearly elucidated, especially in Asian countries, where the causes of constrictive pericarditis differ from those in Western countries. We aimed to investigate the preoperative prognostic factors and clinical outcomes after pericardiectomy in patients with chronic constrictive pericarditis. Preoperative clinical and imaging characteristics were evaluated in 85 consecutive patients with chronic constrictive pericarditis without other valvular or ischemic heart diseases who underwent pericardiectomy. Causes were idiopathic in 49 patients (57.6%) and tuberculous in 36 patients (42.4%). All-cause death was observed for a median of 38.5 months. Of 85 patients, 15 (17.6%) died during follow-up. These 15 patients who died during follow-up had higher aspartate aminotransferase, smaller left ventricular end-systolic dimension index, and higher early diastolic mitral inflow velocity before pericardiectomy than the 70 patients who survived. Multivariate Cox proportional analysis showed that diabetes mellitus (hazard ratio, 4.610; P = .024) and high early diastolic mitral inflow velocity (hazard ratio, 1.050/cm/s; P = .002) before pericardiectomy were independent predictors of mortality after pericardiectomy. The preoperative cutoff value for early diastolic mitral inflow velocity in predicting mortality after pericardiectomy was 71 cm/s (sensitivity of 84.6% and specificity of 52.2%), and there was a significant difference in survival between groups divided by this cutoff value of early diastolic mitral inflow velocity (P = .029). Preoperative high early diastolic mitral inflow velocity and diabetes mellitus were predictors of poor prognosis after pericardiectomy in patients with chronic constrictive pericarditis. These results suggest that preoperative Doppler echocardiographic evaluation may be valuable not only for diagnosing constrictive pericarditis but also for predicting prognosis after pericardiectomy.

Distributed lock-in drives broadband vortex-induced vibrations of a long flexible cylinder in shear flow

AbstractA slender flexible body immersed in sheared cross-flow may exhibit vortex-induced vibrations (VIVs) involving a wide range of excited frequencies and structural wavenumbers. The mechanisms of broadband VIVs of a cylindrical tensioned beam of length-to-diameter aspect ratio 200 placed in shear flow, with an exponentially varying profile along the span, are investigated by means of direct numerical simulation. The Reynolds number is equal to 330 based on the maximum velocity, for comparison with previous work on narrowband vibrations in linear shear flow. The flow is found to excite the structure at a number of different locations under a condition of wake–body synchronization, or lock-in. Broadband responses are associated with a distributed occurrence of the lock-in condition along the span, as opposed to the localized lock-in regions limited to the high inflow velocity zone, reported for narrowband vibrations in sheared current. Despite the instantaneously multi-frequency nature of broadband responses, the lock-in phenomenon remains a locally mono-frequency event, since the vortex formation is generally synchronized with a single vibration frequency at a given location. The spanwise distribution of the excitation zones induces travelling structural waves moving in both directions; this contrasts with the narrowband case where the direction of propagation toward decreasing inflow velocity is preferred. A generalization of the mechanism of phase-locking between the in-line and cross-flow responses is proposed for broadband VIVs under the lock-in condition. A spanwise drift of the in-line/cross-flow phase difference is identified for the high-wavenumber vibration components; this drift is related to the strong travelling wave character of the corresponding structural waves.

PAPER PHYSICS: An experimental study of the turbulent mixing layer in concentrated fiber suspensions

Turbulence structures in a free mixing layer after a backward-facing step were studied in concentrated pulp suspensions (0.5-3% by weight) using Laser Doppler Anemometry (LDA) at two predetermined average inflow velocities (0.9 and 1.8 m/s). Both average and fluctuating velocities were investigated and the findings were compared with measurements in water. The experimental findings show that both the average velocities and the RMS velocities in the mixing layer decreased with an increase in concentration. Furthermore, by analyzing the energy spectra at the center of the mixing layer, it was possible to extract the inertial sub-range of pulp suspensions with a concentration of 0.5% at the lower inflow velocity and in suspensions up to a concentration of 1% at the higher inflow velocity. At higher concentrations the turbulence was damped by the fiber network and no turbulence structures could be extracted. The energy content at lower frequencies was higher in the pulp suspensions than in the experiments in pure water.

Aneurysm Inflow-Angle as a Discriminant for Rupture in Sidewall Cerebral Aneurysms

The ability to discriminate between ruptured and unruptured cerebral aneurysms on a morphological basis may be useful in clinical risk stratification. The objective was to evaluate the importance of inflow-angle (IA), the angle separating parent vessel and aneurysm dome main axes. IA, maximal dimension, height-width ratio, and dome-neck aspect ratio were evaluated in sidewall-type aneurysms with respect to rupture status in a cohort of 116 aneurysms in 102 patients. Computational fluid dynamic analysis was performed in an idealized model with variational analysis of the effect of IA on intra-aneurysmal hemodynamics. Univariate analysis identified IA as significantly more obtuse in the ruptured subset (124.9 degrees+/-26.5 degrees versus 105.8 degrees+/-18.5 degrees, P=0.0001); similarly, maximal dimension, height-width ratio, and dome-neck aspect ratio were significantly greater in the ruptured subset; multivariate logistic regression identified only IA (P=0.0158) and height-width ratio (P=0.0017), but not maximal dimension or dome-neck aspect ratio, as independent discriminants of rupture status. Computational fluid dynamic analysis showed increasing IA leading to deeper migration of the flow recirculation zone into the aneurysm with higher peak flow velocities and a greater transmission of kinetic energy into the distal portion of the dome. Increasing IA resulted in higher inflow velocity and greater wall shear stress magnitude and spatial gradients in both the inflow zone and dome. Inflow-angle is a significant discriminant of rupture status in sidewall-type aneurysms and is associated with higher energy transmission to the dome. These results support inclusion of IA in future prospective aneurysm rupture risk assessment trials.

Reply to “Letter to the editor: ‘Postulated functional advantages of a looped as opposed to a linearly arranged heart’”

Letters to the EditorReply to “Letter to the editor: ‘Postulated functional advantages of a looped as opposed to a linearly arranged heart’”Hiroshi Watanabe, Seiryo Sugiura, and Toshiaki HisadaHiroshi WatanabeDepartment of Human and Engineered Environmental Studies, Graduate School of Frontier Sciences, The University of Tokyo, Chiba, Japan, Seiryo SugiuraDepartment of Human and Engineered Environmental Studies, Graduate School of Frontier Sciences, The University of Tokyo, Chiba, Japan, and Toshiaki HisadaDepartment of Human and Engineered Environmental Studies, Graduate School of Frontier Sciences, The University of Tokyo, Chiba, JapanPublished Online:01 Feb 2010https://doi.org/10.1152/ajpheart.01103.2009MoreSectionsPDF (29 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInEmailWeChat reply: We appreciate Kilner's (1) interest in our simulation study evaluating the significance of cardiac looping on pumping function of the heart using the finite element model (4). Although he agreed with us that the conservation of momentum of blood flowing into chamber contributes only modestly to the ejection, he pointed out another aspect of cardiac looping as a potentially potent modulator of cardiac function.According to Kilner et al. (3), the salient feature of the looping is the redirection of flow in the ventricular chamber that facilitates the atrioventricular coupling through the momentum of the blood flow. Especially, vigorous inflow during exercise pushes the ventricular wall while being decelerated and stores elastic energy in the wall. Recoil of the stretched ventricular wall not only boosts the ejection flow but pulls the atrium to enhance its filling. However, we again question such a hypothesis because of the following reasons.First, even with the high-inflow velocity, for example 1.3 m/s as reported by Kilner et al. (2), the roughly estimated kinematic energy of inflow [1/2 × 90 ml × 1.06 g/cm3 × (1.3 m/s)2 ≈ 0.081 J] is much smaller than the external work done by the myocardium with high contractility (e.g., 90 ml × 180 mmHg ≈ 2.1 J).Second, although under relatively low heart rate (100 beats/min), we have confirmed that the end-diastolic ventricular shape does not differ appreciably even if the fluid is not included for simulation.The concept of atrioventricular coupling is very attractive, but the quantitative analysis may not support it. Similar simulations are needed to evaluate such an effect using the whole heart model with both ventricles and atria to accurately answer this question.DISCLOSURESNo conflicts of interest are declared by the author(s).REFERENCES1. Kilner PJ, Henein MY, Gibson DG. Letter to the editor: “Postulated functional advantages of a looped as opposed to a linearly arranged heart”. Am J Physiol Heart Circ Physiol. doi: 10.1152/ajpheart.00842.2009.Google Scholar2. Kilner PJ. Our tortuous heart in dynamic mode—an echocardiographic study of mitral flow and movement in exercising subjects. Heart Vessels 12: 103–110, 1997.Crossref | PubMed | ISI | Google Scholar3. Kilner PJ, Yang GZ, Wilkes AJ, Mohiaddin RH, Firmin DN, Yacoub MH. Asymmetric redirection of flow through the heart. Nature 404: 759–761, 2000.Crossref | PubMed | ISI | Google Scholar4. Watanabe H, Sugiura S, Hisada T. The looped heart does not save energy by maintaining the momentum of blood flowing in the ventricle. Am J Physiol Heart Circ Physiol 294: H2191–H2196, 2008.Link | ISI | Google ScholarAUTHOR NOTESAddress for reprint requests and other correspondence: H. Watanabe, Dept. of Human and Engineered Environmental Studies, Graduate School of Frontier Sciences, Univ. of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba, Japan (e-mail: [email protected]). Download PDF Previous Back to Top Next FiguresReferencesRelatedInformationCited ByThe role of flow rotation in the adult right atrium: a 4D flow cardiovascular magnetic resonance study16 April 2020 | Physiological Measurement, Vol. 41, No. 3Kinking and Torsion Can Significantly Improve the Efficiency of Valveless Pumping in Periodically Compressed Tubular Conduits. Implications for Understanding of the Form-Function Relationship of Embryonic Heart Tubes19 November 2017 | Journal of Cardiovascular Development and Disease, Vol. 4, No. 4Left Ventricular Fluid Mechanics: The Long Way from Theoretical Models to Clinical Applications4 September 2014 | Annals of Biomedical Engineering, Vol. 43, No. 1Quantification of left and right atrial kinetic energy using four-dimensional intracardiac magnetic resonance imaging flow measurementsPer M. Arvidsson, Johannes Töger, Einar Heiberg, Marcus Carlsson, and Håkan Arheden15 May 2013 | Journal of Applied Physiology, Vol. 114, No. 10Quantification of left and right ventricular kinetic energy using four-dimensional intracardiac magnetic resonance imaging flow measurementsM. Carlsson, E. Heiberg, J. Toger, and H. Arheden15 February 2012 | American Journal of Physiology-Heart and Circulatory Physiology, Vol. 302, No. 44-D blood flow in the human right ventricleAlexandru G. Fredriksson*, Jakub Zajac*, Jonatan Eriksson, Petter Dyverfeldt, Ann F. Bolger, Tino Ebbers, and Carl-Johan Carlhäll1 December 2011 | American Journal of Physiology-Heart and Circulatory Physiology, Vol. 301, No. 6 More from this issue > Volume 298Issue 2February 2010Pages H727-H727 Copyright & PermissionsCopyright © 2010 the American Physiological Societyhttps://doi.org/10.1152/ajpheart.01103.2009History Published online 1 February 2010 Published in print 1 February 2010 Metrics

Fractionation and Mold Filling of Semisolid Slurries I: Isothermal Condition

The fractionation and mold filling of semisolid slurries were numerically investigated for a range of mold geometry, inflow velocity, nozzle diameter, and fraction solid. The slurry was assumed to be a shear-thinning, non-Newtonian fluid. Fractionation was determined from the trajectories of isothermal particles injected into the slurry. The results in dicate fractionation is reduced with a tapered mold, high-inflow velocity, large nozzle diameter relative to mold, and low fraction solid.

Prevalence and predictors of audible physiological third heart sound in a population sample aged 36 to 37 years.

A physiological third heart sound (S3) is common in youth but allegedly very rare after the age of 40 years. The mechanism of its disappearance is not known. The aim of this work was to study the prevalence and predictors of physiological S3 in a population-based sample of persons approaching 40 years of age. A random sample of 120 persons born in 1954 was invited; 93 (42 men) entered the study. Their physical activity, alcohol and tobacco consumption, and salt intake were quantified by diary follow-up. The presence of an S3 was determined by auscultation and confirmed by phonocardiography. Left ventricular (LV) size, mass, and systolic function were assessed by M-mode echocardiography and LV filling by Doppler velocimetry of transmitral flow. An audible S3 was detected in 22 subjects, 1 of whom had heart disease. The prevalence of physiological S3 was 23.1%. Subjects with physiological S3 had a lower body mass index (22.3 +/- 2.8 versus 24.6 +/- 4.1 kg/m2 [mean +/- SD], P = .005), lower heart rate (63 +/- 7 versus 68 +/- 10 beats per minute, P = .015), higher peak early diastolic transmitral velocity (67 +/- 10 versus 58 +/- 8 cm/s, P = .002), and higher acceleration of early diastolic velocity (717 +/- 148 versus 622 +/- 122 cm/s2, P = .012) than those without S3. No differences were noted in the lifestyle characteristics, blood pressure, or LV mass and systolic function. Body mass index and peak early diastolic transmitral velocity were independent predictors of physiological S3 in logistic regression analysis. Nearly one fourth of persons approaching their forties still have an audible physiological S3. The presence of S3 is predicted by leanness and a high early diastolic LV inflow velocity; the disappearance of S3 is unlikely to be secondary to increasing blood pressure and relative LV hypertrophy, as is widely presented, but reflects a more primary age-related alteration of LV early diastolic function.

AN INVESTIGATION INTO TEMPERATURE VARIATION INSIDE THE HOT-WATER STORAGE TANK OF A SOLAR COLLECTOR HEATER

A theoretical model for unsteady one-dimensional temperature field inside the hot-water storage tank of a thermosyphonic solar system is carried out. Hot water flows into a vertical storage tank via its top central line at low constant rates. The measured temperature profiles along the central axis inside the storage tank of a V-trough thermosyphonic solar heater are observed to be in line with the analytical predictions. The linearity of the temperature profiles as checked experimentally is distinctly observed for high inflow velocities of the hot water into the storage tank.

Temperature Distribution Inside Hot Water Storage Tanks of Solar Collectors

An analytical experimental investigation into the temperature field inside the hot water storage tank of a solar collector was carried out. A transient two-dimensional semi-infinite cylindrical length model with time-and-space boundary-conditions dependency was selected. Conduction and convection heat-transfer modes in the axial direction together with conduction in the radial direction were neglected, since these were considered to be small in comparison with the axial conduction and convection diffusion terms, which in turn were considered small relative to the energy stored. Good agreement between theoretical and experimental prediction was verified. The radial direction temperature dependency disappeared for axial lengths greater than one quarter of the tank depth for most practical operating conditions especially for low inflow velocities and low inlet to outlet temperature ratios. The axial conduction term in the governing equation can be dropped out for inflow velocities greater than a certain critical value without distorting the theoretical consequences. Temperature profiles in the axial direction of a cylindrical storage tank can be assumed to be linear especially for high inflow velocities as well as low temperature differences at inlet and outlet of the storage tank.