B. Bon

Bio: B. Bon is an academic researcher from University of Miami. The author has contributed to research in topics: Inverse problem & Optimization problem. The author has an hindex of 1, co-authored 1 publications receiving 333 citations.

A Review of two-phase flow dynamic instabilities in tube boiling systems

Abstract: The earliest research in the field of two-phase flow was conducted by Lorentz (1909) The studies on the analysis of two-phase flow instabilities by Ledinegg (1938) created considerable interest concerning the phenomenon of thermally induced flow instability in two-phase flow systems The objective of this review is to sum up the experimental and theoretical work carried out by various investigators over a period of several years, demonstrating and explaining three main instability modes of two-phase flow dynamic instabilities, namely, density-wave type, pressure-drop type and thermal oscillations, encountered in various boiling flow channel systems The typical experimental investigations of these instabilities in tube boiling systems are indicated and the most popular models to predict the two-phase flow dynamic instabilities, namely the homogenous flow model and the drift-flux models are clarified with the solution examples and the validation of the model results with experimental findings are also provided

Alpert multi-wavelets for functional inverse problems: direct optimization and deep learning

Abstract: Abstract Computational engineering models often contain unknown entities (e.g. parameters, initial and boundary conditions) that require estimation from other measured observable data. Estimating such unknown entities is challenging when they involve spatio-temporal fields because such functional variables often require an infinite-dimensional representation. We address this problem by transforming an unknown functional field using Alpert wavelet bases and truncating the resulting spectrum. Hence the problem reduces to the estimation of few coefficients that can be performed using common optimization methods. We apply this method on a one-dimensional heat transfer problem where we estimate the heat source field varying in both time and space. The observable data is comprised of temperature measured at several thermocouples in the domain. This latter is composed of either copper or stainless steel. The optimization using our method based on wavelets is able to estimate the heat source with an error between 5% and 7%. We analyze the effect of the domain material and number of thermocouples as well as the sensitivity to the initial guess of the heat source. Finally, we estimate the unknown heat source using a different approach based on deep learning techniques where we consider the input and output of a multi-layer perceptron in wavelet form. We find that this deep learning approach is more accurate than the optimization approach with errors below 4%.

Two-phase flow instabilities: A review

Abstract: An updated review of two-phase flow instabilities including experimental and analytical results regarding density-wave and pressure-drop oscillations, as well as Ledinegg excursions, is presented. The latest findings about the main mechanisms involved in the occurrence of these phenomena are introduced. This work complements previous reviews, putting all two-phase flow instabilities in the same context and updating the information including coherently the data accumulated in recent years. The review is concluded with a discussion of the current research state and recommendations for future works.

Pool boiling and flow boiling on micro- and nanostructured surfaces

Abstract: This study reviews recent experimental investigations performed on pool and flow boiling over nano- and micro engineered structures for enhancements in boiling heat transfer, namely heat transfer coefficient (HTC) and critical heat flux (CHF). Modified surfaces having nano/micro porous features of mainly irregular shapes through anodic oxidation processes, coating of metallic and non-metallic layers, deposition of powder materials, and roughening for improving boiling heat transfer have been of research interests of many researchers. In addition, pool boiling and flow boiling studies on artificial structures, mainly fabricated on a plain surface, such as pins, pillar fins, grooves (in different shapes, i.e. rectangular, square, cylinder, etc.) for increasing the heated surface area, or cavities created on substrates for increasing bubble nucleation sites were also considered for both micro and nano scale. The results reported in recent investigations on pool boiling and flow boiling from micro/nanostructured surfaces were included, and a comprehensive overview was provided.

Ledinegg instability in microchannels

Abstract: The static Ledinegg instability in horizontal microchannels under different flow conditions and fluids pertinent to electronics cooling was studied experimentally and numerically. Two fluids, water at sub-atmospheric pressures and refrigerant HFE-7100, were examined for a range of heat fluxes, mass fluxes, and channel hydraulic diameters. Numerical predictions from the developed pressure gradient model agree well with results from the flow boiling experiments. The model was used to quantify the susceptibility of the system to the Ledinegg instability. A parametric instability study was systematically conducted with varying system pressure, heat flux, inlet subcooling, and channel size with and without inlet restrictor. Increasing system pressure and channel diameter, reducing parallel channel number and channel length, and including an inlet restrictor can enhance the flow stability in microchannels.

Flow boiling instabilities in microchannels and their promising solutions – A review

Abstract: The present work has been undertaken with an aim to address major challenges during two-phase flow boiling in microchannels. A comprehensive review of literatures has been presented that highlights the problems of two-phase flow boiling and its suppression techniques. Emphasis has been given to the recent literatures addressing the issues of flow boiling instabilities in microchannels. The broad aspects that have been covered are overview of instabilities, their causes, consequences and suppression techniques. Major attention has been paid to highlight the promising solutions that have been investigated to mitigate the instabilities. Study revealed that inception of instabilities is inherent during flow boiling. Nevertheless, it is more sensitive to trigger-out in microchannels compare to macro or conventional channels. Researchers have common agreement over the causes of instabilities and their consequences such as pressure and temperature fluctuations, severe unstable flow boiling, flow reversal, early CHF (critical heat flux) and dry out. It has been identified that instabilities during flow boiling depends on mass flow rate, flow regimes, bubble dynamics, inlet subcooling, inlet compressibility and coolant properties. Study also revealed that in the recent year’s more attention has been paid to overcome the instability and issue has been addressed simultaneously with heat transfer enhancement studies. In order to suppress the instability various techniques have been investigated however, geometrical modification has been prominently considered to overcome the instability phenomenon.

Twenty first century cooling solution: Microchannel heat sinks.

Abstract: Due to rapid evolution in a wide range of technologies in twentieth century, heat dissipation requirement has increased very rapidly especially from compact systems. There is an urgent need for high-performance heat sinks to ensure the integrity and long life of these petite systems. Use of forced convection cooling has been limited by the requirement of the excessively high flow velocity and associated noise and vibration problems. Microchannel heat sink seems to be most reliable cooling technology due to its superior command over heat carrying capability. Understanding the flow boiling phenomena in microchannel heat sink experimentally and analytically has been topic of intense research in twenty first century. In this review paper, the experimental studies on flow visualization, pressure drop and heat transfer characteristics of microchannels presented by different researchers are summarized. Some different flow patterns observed in microchannel geometry such as bubble nucleation in thin film, periodic variation of flow pattern, flow circulation, bubble suppression and cross-channel flow are explained briefly. The influence of vapour quality, heat flux, mass flux and channel geometry on pressure drop and heat transfer characteristics of microchannel are reported. Different correlations reported for single and two phase heat transfer characteristics are compared. The comparative analysis showed that available single phase and two phase correlations are inconsistence and large variation is observed among these correlations for same channel geometry, fluid and operating condition. Different instabilities associated with microchannels are also briefly presented.