Presence Of Volume Expansion Research Articles

Solidification of a liquid drop enclosing a bubble on an inclined surface

In the present paper, we report the numerical results of the solidification process of a liquid drop enclosing an air bubble, i.e., a hollow drop, on an inclined surface. The surface is tilted from 0° (corresponding to a horizontal surface) to 90° (corresponding to a vertical surface), and the contact angle of the drop ranges between 60° and 130°. The drop is deformed while solidification happens in the presence of volume expansion. This volume change results in the formation of a tip at the drop top. The tip becomes more asymmetric as the tilting angle, i.e., the surface angle, increases. However, the solidification time is not affected by the surface angle. During the initial stage of solidification, the drop liquid accumulates to the bottom, by gravity, and thus results in lowering the bubble position. The bubble then moves upwards due to buoyancy force. It stops moving as it is trapped by solidification. A larger bubble reduces the tip shift. We also consider the effect of the Bond number and the Stefan number on solidification.

Modeling the oxidation of a polymer-derived ceramic with chemo-mechanical coupling and large deformations

To get a better insight into the coating behavior of a polymer-derived ceramic material, we model and simulate the diffusion, oxidation and reaction-induced volume expansion of a specimen without outer mechanical loads. In this macroscale approach, we use an oxidation state variable which determines the composition of the starting material and the oxide material. The model contains a reaction rate which is based on the change of the free energy due to a change of the concentrations of the starting material, the oxide material and a diffusing gaseous material. Using this, we model a growing oxide layer in a perhydropolysilazane (PHPS)-based polymer-derived ceramic (PDC), containing silicon filler particles. Within the mechanical part of the modeling, we use the Neo-Hookean material law which allows for the consideration of volume expansion and the diffusion kinematics in terms of finite deformations. We derive this continuum formulation in 3D and reduce it later to 1D, as we show that a 1D formulation is sufficient for thin oxide layers in our consideration. In such a case, the reaction-induced volume expansion is mostly limited to strains orthogonal to the oxide layer, as the bulk material hinders transversal deformation. Both formulations, i.e., 1D and 3D, are implemented in the finite element software FEAP. We perform a parameter study and fit the results with experimental data. We investigate the diffusion kinematics in the presence of volume expansion. Additionally, we discuss the influence of the elastic energy on the reaction rate.

A numerical study of a liquid compound drop solidifying on a horizontal surface

In this study, we present the three-phase numerical simulation results of an axisymmetric compound drop solidifying on a cold plate by the front-tracking method. The compound drop initially has a hemispherical shape with a concentric inner gas core (i.e. gas bubble). The temperature of the plate is lower than the fusion temperature of the shell liquid and thus causes the shell liquid to solidify from the plate surface. It is found that the solid-liquid interface propagates parallelly to the plate during the initial stage of solidification. Then, the region near the outer interface moves faster than that near the inner gas core does. The solidification process completes around the inner core first, and the drop top is the last region to be solidified. Accordingly, a break point is available on the temporal variation of the average height of the solid-liquid interface. Besides, in the presence of volume expansion, the solidified compound drop also has an apex at the top. The numerical results show that the presence of the inner gas bubble prolongs the solidification time. We also find that varying the Stefan number St (in the range of 0.032 – 1.0) or the Bond number Bo (in the range of 0.18 – 3.2) has a minor effect on the inner gas core after complete solidification even though the solidification time decreases with an increase in St or Bo. The effects of the Prandtl number and volume change on the final product of the solidification process are also considered.

A numerical study of a liquid drop solidifying on a vertical cold wall

Solidification of a liquid drop on a vertical wall is a typical phase change heat transfer problem that exists widely in natural and engineering situations. In this study, we present the fully resolved two-dimensional simulations of such a problem by a front-tracking/finite difference method. Because of gravity, the liquid drop assumed stick to the cold wall shifts to the bottom during solidification. Numerical results show that the conical tip at the solidified drop top is still available with the presence of volume expansion, but the tip location is shifted downward, resulting in an asymmetric drop after complete solidification. The tip shift, height and shape of the solidified drop are investigated under the influences of various parameters such as the Prandtl number Pr, the Stefan number St, the Bond number, the Ohnesorge number Oh, and the density ratio of the solid to liquid phases ρsl. We also consider the effects of the growth angle ϕgr (at the triple point) and the initial drop shape (in terms of the contact angle ϕ0) on the solidification process. The most influent parameter is Bo whose increase in the range of 0.1–3.16 makes the drop more deformed with the tip shift linearly increasing with Bo. The tip shift also increases with an increase in ϕ0. However, increasing Oh (from 0.001 to 0.316), St (from 0.01 to 1.0) or ρsl (from 0.8 to 1.2) leads to a decrease in the tip shift. Concerning time for completing solidification, an increase in Bo, ϕgr or ϕ0, or a decrease in St, or ρsl results in an increase in the solidification time. The effects of these parameters on the drop height are also investigated.

Three-phase computation of solidification in an open horizontal circular cylinder

We present numerical simulations of solidification in an open vertical circular cylinder with the presence of a gas phase and natural convection. The numerical technique used is a two-dimensional front-tracking method combined with an interpolation method. A simple tri-junction condition, in terms of the growth angle ϕgr, is included due to the presence of three phases. Effects of various dimensionless parameters such as the Prandtl number Pr, the Stefan number St, the Rayleigh number Ra, the Weber number We, the dimensionless initial temperature θ0, the density ratio of the solid to liquid phases ρsl and the thermal expansion coefficient ratio of the gas to liquid phases βgl are investigated. Numerical results show that, the shape of the solidified phase is strongly affected by ρsl and ϕgr. Volume expansion (ρsl<1.0) produces a “cone-like” top surface while shrinkage (ρsl>1.0) forms a cavity at the center of the cylinder. An increase in ϕgr in the range of 0–15° results in an increase in the slope of the top solid interface near the center. Decreasing St in the range of 1.0–0.01, with the presence of volume expansion, results in a steeper solid interface near the center. Without volume change (ρsl=1.0), the top surface of the solidified phase becomes more curved with an increase in Pr in the range of 0.01–10, Ra in the range of 103–5×105, or We in the range of 10−5–4×10−3. In contrast, varying θ0 (in the range of 1.0–2.5) or βgl (in the range of 5×10−4–5×10−1) has a very minor effect on the top surface. In addition, the effects of these parameters on the evolution of the solidification front are also investigated.

The spot sign predicts hematoma expansion, outcome, and mortality in patients with primary intracerebral hemorrhage.

ObjectiveThe purpose of this study was to retrospectively review cases of intracerebral hemorrhage (ICH) medically treated at our institution to determine if the CT angiography (CTA) 'spot sign' predicts in-hospital mortality and clinical outcome at 3 months in patients with spontaneous ICH.MethodsWe conducted a retrospective review of all consecutive patients who were admitted to the department of neurosurgery. Clinical data of patients with ICH were collected by 2 neurosurgeons blinded to the radiological data and at the 90-day follow-up.ResultsMultivariate logistic regression analysis identified predictors of poor outcome; we found that hematoma location, spot sign, and intraventricular hemorrhage were independent predictors of poor outcome. In-hospital mortality was 57.4% (35 of 61) in the CTA spot-sign positive group versus 7.9% (10 of 126) in the CTA spot-sign negative group. In multivariate logistic analysis, we found that presence of spot sign and presence of volume expansion were independent predictors for the in-hospital mortality of ICH.ConclusionThe spot sign is a strong independent predictor of hematoma expansion, mortality, and poor clinical outcome in primary ICH. In this study, we emphasized the importance of hematoma expansion as a therapeutic target in both clinical practice and research.

Diagnostic, Prognostic, and Therapeutic Implications of Brain Natriuretic Peptide in Dialysis and Nondialysis‐Dependent Chronic Renal Failure

Premature cardiovascular disease is the leading cause of morbidity and mortality in patients with end-stage renal failure. Natriuretic peptides, specifically brain natriuretic peptide, are released from the heart in response to chamber distension and thus increased in the presence of volume expansion and cardiac overload. Their physiological role is to cause vasodilatation and promote natriuresis to maintain volume homeostasis. Increasingly serum levels of brain natriuretic peptide are used to both diagnose and manage cardiovascular disorders. Furthermore, augmenting the beneficial hemodynamic actions of brain natriuretic peptide may have a therapeutic role in decompensated heart failure. However, the diagnostic role of serum brain natriuretic peptide levels in patients with advanced renal dysfunction remains to be defined. These patients have a high prevalence of left ventricular disorders, specifically left ventricular hypertrophy, which may reduce the diagnostic utility of brain natriuretic peptide. In addition, ventricular stretch may be determined by intravascular volume status rather than by cardiac dysfunction. Nonetheless, as the prognosis of patients with end-stage renal failure and co-existing heart failure is so poor, the availability of a further marker of cardiac ''distress'' may in the future become a useful diagnostic tool and in due course may become a primary goal for titration and tailoring of therapy.

Dissociation of Plasma Atrial Natriuretic Peptide Responses to Upright Posture and Furosemide Administration in Patients with Normal-, Low Renin Essential Hypertension and Primary Aldosteronism

Plasma levels of atrial natriuretic peptide (ANP) were measured in patients with normal renin essential hypertension (n = 12), low renin essential hypertension (n = 11) and primary aldosteronism due to aldosterone producing adenoma (APA, n = 8) and idiopathic hyperaldosteronism (IHA, n = 3) after overnight rest in the supine position and after 4 h upright posture and furosemide administration. Plasma renin activity (PRA) and aldosterone (Aldo) levels were also determined. Compared to normal renin essential hypertension (33.6 +/- 2.2 pg/ml), basal plasma ANP was significantly higher in low renin essential hypertension (66.8 +/- 6 pg/ml), IHA (54.1 +/- 6.3 pg/ml) and APA before (62.4 +/- 4.9 pg/ml) but not after adrenal surgery (22 +/- 3 pg/ml). After upright posture and furosemide administration plasma ANP was decreased (p less than 0.01) in patients with low renin and, less markedly, with normal renin essential hypertension, however not in IHA and APA. In about half of the patients with low renin essential hypertension, unchanged PRA after upright posture and furosemide administration was associated with increased plasma Aldo and decreased ANP levels. We conclude that (i) the relatively high basal plasma ANP levels in low renin essential hypertension, IHA and APA may reflect the presence of volume expansion in these patients; (ii) the hormonal responses to upright posture and furosemide administration in patients with normal and low renin essential hypertension may indicate a counterregulatory role of ANP during activation of the renin-angiotensin-aldosterone system; (iii) the high plasma ANP, which is unresponsive to upright posture and furosemide administration, in patients with APA and IHA may be a potentially interesting new finding whose pathophysiological significance remains to be established.

Segmental analysis of sodium reabsorption during renal vein constriction.

Clearance and micropuncture studies were performed in rats to identify the nephron site(s) of altered sodium reabsorption during partial renal vein constriction in the presence and absence of volume expansion. Renal vein constriction increased fractional deliver of sodium to the late proximal tubule from 52 +/- 3 to 61 +/- 4% in euvolemia and from 59 +/- 3 to 65 +/- 3% in volume expansion. In euvolemia, fractional delivery of sodium to the early distal tubule was 13 +/- 3% before and 24 +/- 6% after renal vein constriction. In volume expansion, fractional delivery of sodium to the early distal tubule decreased from 15 +/- 3 to 9 +/- 2% in response to renal vein constriction. We conclude that renal vein constriction decreases sodium reabsorption by the proximal tubule both in euvolemia and in volume expansion but that it increases sodium reabsorption by the superficial loop of Henle only in the presence of volume expansion.

Regulation of glomerular filtration and proximal tubule reabsorption.

In this review current hypotheses for the regulation of filtration rate and the subsequent reabsorption of that filtrate by the proximal tubule are discussed. In the rat the filtration rate is highly plasma flow dependent because of the phenomenon of filtration equilibrium. On the other hand, in man and dog filtration rate is much less dependent on renal plasma flow. In these species glomerular capillary pressure rather than glomerular plasma flow may be the primary determinant of filtration. Three hypotheses for the autoregulation of glomerular filtration are discussed. Of these the myogenic theory, which holds that increases in perfusion pressure result in an intrinsic contraction of the smooth muscle in the walls of the afferent arterioles, remains the best, if not completely adequate, explanation for the phenomenon. The role of a macula densa feedback mechanism is controversial, although data are presented which strongly militate against this hypothesis. Similarly, the prostaglandins, although important in determining vascular resistance, probably do not mediate autoregulation. Two prevalent hypotheses for the regulation of fluid reabsorption by the proximal tubule, the physical factor hypothesis and the humoral hypothesis, are discussed. Data presented indicate that peritubule Starling forces have a marked effect on isotonic reabsorption by the proximal tubule in the presence of volume expansion and enhanced backleak into the proximal tubule lumen. However, in hydropenia and diminished backleak, changes in peritubule capillary Starling forces have little effect on proximal sodium reabsorption. Thus, the physical factor mechanism is a rather insensitive regulator of proximal reabsorption in the absence of volume expansion. Hormones known to regulate sodium transport per se, such as aldosterone, have no effect on sodium reabsorption by the proximal tubule. In contrast, those hormones primarily regulating anion reabsorption in the proximal tubule, such as parathyroid hormone, have significant effects on fluid reabsorption. Thus, the humoral regulation of anion reabsorption has secondary effects on proximal sodium reabsorption.