Aerothermal modeling program, phase 2

The main objectives of the Aerothermal Modeling Program, Phase 2 are: to develop an improved numerical scheme for incorporation in a 3-D combustor flow model; to conduct a benchmark quality experiment to study the interaction of a primary jet with a confined swirling crossflow and to assess current and advanced turbulence and scalar transport models; and to conduct experimental evaluation of the air swirler interaction with fuel injectors, assessments of current two-phase models, and verification the improved spray evaporation/dispersion models

Partnership of obstetrician and neonatologist to improve neonatal outcome in peri-viable and premature babies: a cross sectional survey

Background: Collaboration between obstetricians and paediatricians/Neonatologists provides the best quality care to infants and their mothers. Present study was conducted to evaluate the practices of obstetricians and neonatologists’ partnership to improve neonatal outcome.Methods: Present cross-sectional, observational study was conducted on 50 Obstetricians and 50 paediatricians/ neonatologists during October 2021 to evaluate the practices of obstetricians and neonatologists’ partnership to improve neonatal outcome.Results: In present study, among 50 obstetricians and 50 pediatricians/ neonatologists, all i.e., 100 (100%) feel that partnership of obstetrician and neonatologist in managing pre-viable pregnancy improves neonatal outcome. Among 50 obstetricians, all i.e., 50 (100%) said that they will explain the need for caesarean section and if necessary classical caesarean section. All said they will explain the need and advantages of steroids. Among 50 pediatricians/ neonatologists, majority i.e., 44 (88%) said that they will explain the need for caesarean section and if necessary classical caesarean section. All said they will explain the need and advantages of steroids. Among 50 obstetricians, majority i.e., 45 (90%) said that they will explain thoroughly the risk to the baby, survival, short term complications and disability, 30 (60%) each said that they will explain thoroughly the risk of RDS, need of resuscitation, need of NICU for baby, uncertainty of hospital stay and outcome. Among 50 pediatricians/ neonatologists, all i.e., 50 (100%) each said that they will explain thoroughly the risk to the baby, survival, short term complications and disability, the risk of RDS, need of resuscitation, need of NICU for baby, uncertainty of hospital stay and outcome. Expressions of pediatricians/ neonatologists were significantly different on counselling aspects of mother and baby.Conclusions: In present study, majority of obstetricians and pediatricians/ neonatologists were of opinion that partnership between them surely improves neonatal outcome in peri viable and preterm babies. 

Autocatalytic plume pinch-off

A localized source of buoyancy flux in a non-reactive fluid medium creates a plume. The flux can be provided by either heat, a compositional difference between the fluid comprising the plume and its surroundings, or a combination of both. For autocatalytic plumes produced by the iodate-arsenous acid reaction, however, buoyancy is produced along the entire reacting interface between the plume and its surroundings. Buoyancy production at the moving interface drives fluid motion, which in turn generates flow that advects the reaction front. As a consequence of this interplay between fluid flow and chemical reaction, autocatalytic plumes exhibit a rich dynamics during their ascent through the reactant medium. One of the more interesting dynamical features is the production of an accelerating vortical plume head that in certain cases pinches-off and detaches from the upwelling conduit. After pinch-off, a new plume head forms in the conduit below, and this can lead to multiple generations of plume heads for a single plume initiation. We investigated the pinch-off process using both experimentation and simulation. Experiments were performed using various concentrations of glycerol, in which it was found that repeated pinch-off occurs exclusively in a specific concentration range. Autocatalytic plume simulations revealed that pinch-off is triggered by the appearance of accelerating flow in the plume conduit.Comment: 10 figures. Accepted for publication in Phys Rev E. See also http://www.physics.utoronto.ca/nonlinear/papers_chemwave.htm

On the transient thermal response of thin vapor chamber heat spreaders: governing mechanisms and performance relative to metal spreaders

Vapor chambers can offer a passive heat spreading solution for thermal management in electronics applications ranging from mobile devices to high-power servers. The steady-state operation and performance of vapor chambers has been extensively explored. However, most electronic devices have inherently transient operational modes. For such applications, it is critical to understand the transient thermal response of vapor chamber heat spreaders and to benchmark their transient performance relative to the known behavior of metal heat spreaders. This study uses a low-cost, 3D, transient semi-analytical transport model to explore the transient thermal behavior of thin vapor chambers. We identify the three key mechanisms that govern the transient thermal response: (1) the total thermal capacity of the vapor chamber governs the rate of increase of the volume-averaged mean temperature; (2) the effective inplane diffusivity governs the time required for the spatial temperature profile to initially develop; and (3) the effective in-plane conductance of the vapor core governs the range of the spatial temperature variation, and by extension, the steady-state performance. An experiment is conducted using a commercial vapor chamber sample to confirm the governing mechanisms revealed by the transport model; the model accurately predicts the experimental measurements. Lastly, the transient performance of a vapor chamber relative to a copper heat spreader of the same external dimensions is explored as a function of the heat spreader thickness and input power. The mechanisms governing the transient behavior of vapor chambers are used to explain the appearance of key performance thresholds beyond which performance is superior to the copper heat spreader. This work provides a foundation for understanding the benefits and limitations of vapor chambers relative to metal heat spreaders in transient operation and may inform the design of vapor chambers for improved transient performance

On the Transient Thermal Response of Thin Vapor Chamber Heat Spreaders: Optimized Design and Fluid Selection

Vapor chambers provide highly effective heat spreading to assist in the thermal management of elec- tronic devices. Although there is a significant body of literature on vapor chambers, most prior research has focused on their steady-state response. In many applications, electronic devices generate inherently transient heat loads and, hence, it is critical to understand the transient thermal response of vapor cham- bers. We recently developed a semi-analytical transport model that was used to identify the key mech- anisms that govern the thermal response of vapor chambers to transient heat inputs (Int. J. Heat Mass Trans. 136 (2019) 995–1005). The current study utilizes this understanding of the governing mechanisms to develop design guidelines for improving the performance of vapor chambers under transient operating conditions. Two key aspects of vapor chamber design are addressed in this study: first, a parametric op- timization of the wall, wick, and vapor-core thicknesses; and second, the selection of the working fluid. A protocol is demonstrated for selecting these parameters given the external vapor chamber envelope di- mensions and boundary conditions. The study helps provide a framework for designing vapor chambers subject to transient heat loads, and to differentiate such design from the practices followed traditionally for steady-state operation

A Validated Time-Stepping Analytical Model for 3D Transient Vapor Chamber Transport

Advances in the computational performance of electronic devices have created a clear need for improved methods of passive thermal management. This has led to renewed interest in the use of vapor chambers as heat spreaders in applications ranging from mobile devices to high-performance-computing and power electronics systems. While there has been significant effort to develop vapor chambers for these applications, their designs have largely relied on steady-state analyses and performance prediction. In many applications, however, the heat load is inherently transient in nature. Heat spreader design must consider transient performance in response to these use-case scenarios. While detailed numerical models of transient vapor chamber operation have been developed, a transient modeling approach with low computational cost is needed for parametric study and quick assessment of vapor chamber performance in system-level models. In the current work, a low-cost, transient vapor chamber model is developed targeting the geometries and operating conditions typical of thermal management applications. The model considers mass, momentum, and energy transport in the vapor chamber wall, wick, and vapor core as well as phase change at the wick-vapor interface. The governing equations are simplified to a system of first-order differential equations based on a scaling analysis and assuming a functional form for the temperature profile along the thickness dimension. The errors in the temperature and pressure fields due to these simplifying assumptions are estimated for a wide range of operating conditions. These estimates indicate low errors in the model predictions over the range considered. For two example cases, the model predictions are compared to a finite-volume-based numerical model. Any deviation from the numerical model prediction is on the same order as the errors estimated based on the simplifying assumptions. The time-stepping analytical model is demonstrated to have a computational cost reduction of three to four orders of magnitude compared to the finite-volume based model

Working-Fluid Selection for Minimized Thermal Resistance in Ultra-Thin Vapor Chambers

The behavior of a vapor chamber is strongly coupled to the thermophysical properties of the working fluid within. It is well known that these properties limit the maximum power (heat load) at which a vapor chamber can operate, due to incidence of the capillary limit. At this limit, the available capillary pressure generated within the wick structure balances the total pressure drop incurred along the path of fluid flow within the wick. A common figure of merit prioritizes working fluids that maximize this capillary-limited operating power. The current work explores working fluid selection for ultra-thin vapor chambers based on a thermal performance objective, rather than for maximized power dissipation capability. A working fluid is sought in this case that provides the minimal thermal resistance while ensuring a capillary limit is not reached at the target operating power. A resistance-network-based model is used to develop a simple analytical relationship for the vapor chamber thermal resistance as a function of the working fluid properties, operating power, and geometry. At small thicknesses, the thermal resistance of vapor chambers becomes governed by the saturation temperature gradient in the vapor core, which is dependent on the thermophysical properties of the working fluid. To satisfy the performance objective, it is shown that the choice of working fluid cannot be based on a single figure of merit containing only fluid properties. Instead, the functional relationship for thermal resistance must be analyzed taking into account all operating and geometric parameters, in addition to the thermophysical fluid properties. Such an approach for choosing the working fluid is developed and demonstrated

Screening effects in flow through rough channels

A surprising similarity is found between the distribution of hydrodynamic stress on the wall of an irregular channel and the distribution of flux from a purely Laplacian field on the same geometry. This finding is a direct outcome from numerical simulations of the Navier-Stokes equations for flow at low Reynolds numbers in two-dimensional channels with rough walls presenting either deterministic or random self-similar geometries. For high Reynolds numbers, when inertial effects become relevant, the distribution of wall stresses on deterministic and random fractal rough channels becomes substantially dependent on the microscopic details of the walls geometry. In addition, we find that, while the permeability of the random channel follows the usual decrease with Reynolds, our results indicate an unexpected permeability increase for the deterministic case, i.e., ``the rougher the better''. We show that this complex behavior is closely related with the presence and relative intensity of recirculation zones in the reentrant regions of the rough channel.Comment: 4 pages, 5 figure

Assessment of menopausal symptoms using modified menopause rating scale among urban women doctors of India

Background: The study was conducted to assess the commonly reported menopausal symptoms among urban women doctors using modified menopause rating scale (MRS).Methods: The study was carried out in the society by google link. Convenient sample of 100 women doctors were included in the study. Menopausal symptoms were assessed using modified MRS.Results: In present study, 3 (3%) female doctors had premature menopause, 5 had menopause at 40-44 years, 15 (15%) had menopause at 45-49 years, 77 (77%) had menopause while no patient had menopause after 55 years. Hot flushes were seen in 70 (79%) women, heart discomfort/ palpitation was seen in 2 (2%) women, muscle and joint problems were seen in 30 (30%) women, sleeping problems were seen in 20 (20%) women. Depressive mood was seen in 2 (2%) women, irritability was seen in 12 (12%) women, an anxiety was seen in 22 (22%) women while physical and mental exhaustion was seen in 34 (34%%) women. Sexual problems were seen in 32 (32%) women, bladder problems were seen in 8 (8%) women dryness of the vagina was seen in 35 (35%) women (Table 6).Conclusions: Hot flushes and joint problems were the most common followed by urogenital symptom, sleep disturbance, and anxiety in the study. Menopausal symptoms were less prevalent. Busy schedule, self-confidence due to independent nature and constructive work might be the reason