Mahesh V. Panchagnula

Three-dimensional equilibrium shapes of drops on hysteretic surfaces

In this paper, we study equilibrium three-dimensional shapes of drops on hysteretic surfaces. We develop a function coupled with the publicly available surface energy minimization code Surface Evolver to handle contact angle hysteresis. The function incorporates a model for the mobility of the triple line into Surface Evolver. The only inputs to the model are the advancing and receding contact angles of the surface. We demonstrate this model’s versatility by studying three problems in which parts of the triple line advance while other parts either recede or remain stationary. The first problem focuses on the three-dimensional shape of a static pendant drop on a vertical surface. We predict the finite drop volume when impending sliding motion is observed. In the second problem, we examine the equilibrium shapes of coalescing sessile drops on hysteretic surfaces. Finally, we study coalescing puddles in which gravity plays a leading role in determining the equilibrium puddle shape along with hysteresis.

Trends in Multiphase Modeling and Simulation of Sprays

The characteristic features of sprays pose unique challenges to multiphase flow methods that are used to model and simulate their behavior. This article reviews the principal modeling challenges posed by sprays, and discusses the capabilities of different modeling approaches by classifying them according to the basis for their statistical representation and the level of closure. The article goes on to provide guidelines for their comparative assessment and also a perspective on the outlook for spray modeling. Multiphase flow simulation approaches that are used for spray computations are classified according to scale, accuracy, computational cost and problem complexity. The requirements of a simulation method to be successfully used for spray computation are then discussed. The review concludes with a perspective on the outlook for spray simulation methods.

Rayleigh-Taylor Instability Induced Liquid Atomization

The destabilization of a two-fluid interface is of interest in various applications ranging from spray formation to ocean-wave currents. In most practical spray systems, instabilities that occur on the interface lead to form fragments. Among such instabilities, those caused due to the radial motion of the interface in a cylindrical configuration (Rayleigh-Taylor) are of current interest. We study the instability characteristics of a cylindrical bubble surrounded by an infinite medium of liquid. Linear stability analysis is used as a tool to understand the mechanics. A general dispersion relation has been derived for an inviscid, immiscible and incompressible pair of fluids. This dispersion relation is used to predict the most unstable wavenumber as well as the dominant instability growth rate. It was found that the Bond number is a primary determinant of the most unstable wavenumbers, dominant instability growth rate as well as the neutral stability points. Surprisingly, it was also found out that radial velocity alone (in the absence of radial acceleration) is sufficient to destabilize a cylindrical interface, unlike in the case of either planar or spherical polar configurations.

Derivation & validation of glycosylated haemoglobin (HbA 1c ) cut-off value as a diagnostic test for type 2 diabetes in south Indian population

Background & Objectives: Glycosylated haemoglobin (HbA1c) has been in use for more than a decade, as a diagnostic test for type 2 diabetes. Validity of HbA1c needs to be established in the ethnic population in which it is intended to be used. The objective of this study was to derive and validate a HbA1c cut-off value for the diagnosis of type 2 diabetes in the ethnic population of Rayalaseema area of south India. Methods: In this cross-sectional study, consecutive patients suspected to have type 2 diabetes underwent fasting plasma glucose (FPG) and 2 h post-load plasma glucose (2 h-PG) measurements after a 75 g glucose load and HbA1c estimation. They were classified as having diabetes as per the American Diabetes Association criteria [(FPG ≥7 mmol/l (≥126 mg/dl) and/or 2 h-PG ≥11.1 mmol/l (≥200 mg/dl)]. In the training data set (n = 342), optimum cut-off value of HbA1c for defining type 2 diabetes was derived by receiver-operator characteristic (ROC) curve method using oral glucose tolerance test results as gold standard. This cut-off was validated in a validation data set (n = 341). Results: On applying HbA1c cut-off value of >6.3 per cent (45 mmol/mol) to the training data set, sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) for diagnosing type 2 diabetes were calculated to be 90.6, 85.2, 80.8 and 93.0 per cent, respectively. When the same cut-off value was applied to the validation data set, sensitivity, specificity, PPV and NPV were 88.8, 81.9, 74.0 and 92.7 per cent, respectively, although the latter were consistently smaller than the proportions for the training data set, the differences being not significant. Interpretation & conclusions: HbA1c >6.3 per cent (45 mmol/mol) appears to be the optimal cut-off value for the diagnosis of type 2 diabetes applicable to the ethnic population of Rayalaseema area of Andhra Pradesh state in south India.

Effect of Flow Pulsation on Transport and Secondary Atomization of a Polydisperse Evaporating Spray

In the present work a 1D plug flow evaporator has been considered to study the evaporation, atomization and transport of polydisperse droplets in a pulsating air stream. The pulsation in the air flow is very common in the real combustor due to the thermo acoustic instabilities. Population balance modeling approach is used to study the continuous evaporation and atomization process. An Eulerian-Eulerian multiphase framework is used to capture the polydispersity of the system. For the evaporation the fixed drop size methodology of the D2 law has been used whereas, for the atomization the conservation of mass has been considered during the breakage. The objective of this work is to study the pulsation frequency on the dispersion of droplets without and with presence of the evaporation and atomization rate. From the results, clustering of particles in different locations has been identified. The variation of Sauter Mean Diameter (SMD) is presented and the non-linear behaviour has been identified in the process.Copyright