Innovative Heat Transfer Augmentation Techniques in Mechanical Face Seal

Excessive heat generated at the face seal contact interface has been recognized as one of main causes of failure of mechanical seals. In the past few decades various efforts have been attempted to remove heat from the contact interface uniformly in order to reduce the interfacial temperature, eliminate thermally-induced failure, and thus increase the life of a mechanical seal. Two innovative heat transfer augmentation techniques - surface texturing and built-in phase change device - have been developed in our laboratory to effectively enhance the heat transfer in mechanical face seal. Surface texturing can increase the surface area, change the near boundary flow structure and enhance the overall heat transfer rate. Experimental measurements and numerical simulations are presented that show 10% reduction of a mechanical seal contact face temperature by means of cylindrically-shaped dimples engraved circumferentially on the outside diameter of a seal ring (stationary, rotating and/or both rings). A commercially available CFD code (FLUENT) is employed to numerically confirm the experimental measurements and optimize the dimples based on their depth-to-diameter ratio, size, arrangement and shapes. Performance of a prototype mechanical face seal with built-in heat pipe is experimentally evaluated. The results demonstrate the feasibility of using phase change to remove friction heating and thus reduce interfacial temperature. In this design, the heat pipe is integrated into the seal mating ring and there is no need to modify the gland design or the flush arrangement. The results show that this design is capable of achieving significantly reduction in the seal face temperature and the friction coefficient. To gain insight into the heat transfer enhancement of the heat pipe seal ring, a one-dimensional steady state heat transfer analysis is applied to predict the ring wall temperature distribution and to estimate the saturated vapor temperature. The effective thermal conductivity of heat pipe ring is estimated. These results of prediction are in good agreement with experimental measurements

Research on the Evolution of Health Information Behavior From a Chinese Perspective

China has been undergoing a tremendous development in the reform of health system. It has great effects all the citizens and the nation as a whole. This paper aims to focus on the individuals from the aspect of information behavior. It is expected that the review on health information behavior could be conducted in a systematic way. Moreover, some statistical methods and software have been occupied in order to find out the entire progress of health information behavior. Specifically, both vertical and horizontal comparison have been conducted in this study, and a scientometric method has also be used. After a systematic and profound literature review, the whole progress has been explored and the main topics of great importance have been discovered. Moreover, highly cited papers and their relationship have also been revealed

Speaker-wire vortices in stratified anabatic Prandtl slope flows and their secondary instabilities

Stationary longitudinal vortical rolls emerge in katabatic and anabatic Prandtl slope flows due to the dominance of the normal component of the buoyancy force over flow shear. Here, we further identify self pairing of these longitudinal rolls as a unique flow structure. The topology of the counter-rotating vortex pair bears a striking resemblance to speaker-wires and their interaction with each other is a precursor to further destabilization and breakdown of the flow field into smaller structures. On its own, a speaker-wire vortex retains its unique topology without any vortex reconnection or breakup. For a fixed slope angle $\alpha=3^{\circ}$ and at a constant Prandtl number, we analyse the saturated state of speaker-wire vortices and perform a bi-global linear stability analysis based on their stationary state. We establish the existence of both fundamental and subharmonic secondary instabilities depending on the circulation and transverse wavelength of the base state of speaker-wire vortices. The dominance of subharmonic modes relative to the fundamental mode helps explain the relative stability of a single vortex pair compared to the vortex dynamics in presence of two or an even number of pairs.These instability modes are essential for the bending and merging of multiple speaker-wire vortices, which break up and lead to more dynamically unstable states, eventually paving the way for transition towards turbulence. This process is demonstrated via direct numerical simulations with which we are able to track the nonlinear temporal evolution of these instabilities

Impact of stratification mechanisms on turbulent characteristics of stable flows over flat surfaces

Flow over a surface can be stratified by imposing a fixed mean vertical temperature (density) gradient profile throughout or via cooling at the surface. These two distinct mechanisms can act simultaneously as well to establish a stable stratification in a flow. Here, we perform a series of direct numerical simulations of open channel flows to study adaptation of a neutrally stratified turbulent flow under the combined or independent action of the aforementioned stratification mechanisms. When both stratification mechanisms are active, the dimensionless stratification perturbation number enters the picture as an external flow control parameter, in addition to the Reynolds, Froude, and Prandtl numbers. Additionally, we force the fully developed flow with constant mass flow rate. This alternative way of forcing the flow enables us to keep the bulk Reynolds number constant throughout our investigation and avoid complications arising from the acceleration of the bulk flow when a constant pressure gradient approach to drive the flow were to be adopted instead. We demonstrate that significant deviations from the original Monin-Obukhov similarity formulation are possible when both stratification mechanisms are active within an otherwise weakly stable flow with contiguous turbulence, even when the flux Richardson number is well below 0.2.Independent of active stratification mechanisms, the degree of deviation from neutral dimensionless shear as a function of the vertical coordinate emerges as a good measure for the strength of stable stratification for the six different cases investigated in this study. An extended version of the Monin-Obukhov similarity also shows promise.Comment: submitted to the Journal of the Atmospheric Science

Relativistic mean-field approximation with density-dependent screening meson masses in nuclear matter

The Debye screening masses of the $\sigma$, $\omega$ and neutral $\rho$ mesons and the photon are calculated in the relativistic mean-field approximation. As the density of the nucleon increases, all the screening masses of mesons increase. It shows a different result with Brown-Rho scaling, which implies a reduction in the mass of all the mesons in the nuclear matter except the pion. Replacing the masses of the mesons with their corresponding screening masses in Walecka-1 model, five saturation properties of the nuclear matter are fixed reasonably, and then a density-dependent relativistic mean-field model is proposed without introducing the non-linear self-coupling terms of mesons.Comment: 14 pages, 3 figures, REVTEX4, Accepted for publication in Int. J. Mod. Phys.

Microbial community pattern detection in human body habitats via ensemble clustering framework

The human habitat is a host where microbial species evolve, function, and continue to evolve. Elucidating how microbial communities respond to human habitats is a fundamental and critical task, as establishing baselines of human microbiome is essential in understanding its role in human disease and health. However, current studies usually overlook a complex and interconnected landscape of human microbiome and limit the ability in particular body habitats with learning models of specific criterion. Therefore, these methods could not capture the real-world underlying microbial patterns effectively. To obtain a comprehensive view, we propose a novel ensemble clustering framework to mine the structure of microbial community pattern on large-scale metagenomic data. Particularly, we first build a microbial similarity network via integrating 1920 metagenomic samples from three body habitats of healthy adults. Then a novel symmetric Nonnegative Matrix Factorization (NMF) based ensemble model is proposed and applied onto the network to detect clustering pattern. Extensive experiments are conducted to evaluate the effectiveness of our model on deriving microbial community with respect to body habitat and host gender. From clustering results, we observed that body habitat exhibits a strong bound but non-unique microbial structural patterns. Meanwhile, human microbiome reveals different degree of structural variations over body habitat and host gender. In summary, our ensemble clustering framework could efficiently explore integrated clustering results to accurately identify microbial communities, and provide a comprehensive view for a set of microbial communities. Such trends depict an integrated biography of microbial communities, which offer a new insight towards uncovering pathogenic model of human microbiome.Comment: BMC Systems Biology 201