In Next Generation Microchannel Heat Exchangers, the authors’ focus on the new generation highly efficient heat exchangers and presentation of novel data and technical expertise not available in the open literature. Next generation micro channels offer record high heat transfer coefficients with pressure drops much less than conventional micro channel heat exchangers. These inherent features promise fast penetration into many mew markets, including high heat flux cooling of electronics, waste heat recovery and energy efficiency enhancement applications, alternative energy systems, as well as applications in mass exchangers and chemical reactor systems. The combination of up to the minute research findings and technical know-how make this book very timely as the search for high performance heat and mass exchangers that can cut costs in materials consumption intensifies.
The demand for energy to satisfy the basic needs and services of the population worldwide is increasing as are the economic costs associated with energy production. As such, it is essential to emphasize energy recovery systems to improve heat transfer in thermal processes. Currently, significant research efforts are being conducted to expose criteria and analysis techniques for the design of heat exchange equipment. This book discusses optimization of heat exchangers, heat transfer in novel working fluids, and the experimental and numerical analysis of heat transfer applications.
The last few decades have seen huge developments in the use of concentrated solar power plants, communications technologies (mobile telephony and 5G networks), the nuclear sector with its small modular reactors and concentrated solar power stations. These developments have called for a new generation of heat exchangers. As well as presenting conventional heat exchangers (shell-and-tube and plate heat exchangers), their design techniques and calculation algorithms, Heat Exchangers introduces new-generation compact heat exchangers, including printed circuit heat exchangers, plate-fin heat exchangers, spiral heat exchangers, cross-flow tube-fin heat exchangers, phase-change micro-exchangers, spray coolers, heat pipe heat exchangers and evaporation chambers. This new generation of heat exchangers is currently undergoing a boom, with applications in on-board equipment in aircraft, locomotives, space shuttles and mobile phones, where the volume of the equipment is one of the most important design parameters.
Design and Operation of heat Exchangers and Their Networks presents a comprehensive and detailed analysis on the thermal design methods for the most common types of heat exchangers, with a focus on their networks, simulation procedures for their operations, and measurement of their thermal performances. The book addresses the fundamental theories and principles of heat transfer performance of heat exchangers and their applications and then applies them to the use of modern computing technology. Topics discussed include cell methods for condensers and evaporators, dispersion models for heat exchangers, experimental methods for the evaluation of heat exchanger performance, and thermal calculation algorithms for multi-stream heat exchangers and heat exchanger networks. - Includes MATLAB codes to illustrate how the technologies and methods discussed can be easily applied and developed - Analyses a range of different models, applications, and case studies in order to reveal more advanced solutions for industrial applications - Maintains a strong focus on the fundamental theories and principles of the heat transfer performance of heat exchangers and their applications for complex flow arrangement
This book focuses on the modeling and analysis of heat and fluid flow in microchannels and micro-systems, compiling a number of analytical and hybrid numerical-analytical solutions for models that account for the relevant micro-scale effects, with the corresponding experimental analysis validation when applicable. The volume stands as the only available compilation of easy to use analytically-based solutions for micro-scale heat and fluid flow problems, that systematically incorporates the most relevant micro-scale effects into the mathematical models, followed by their physical interpretation on the micro-system behavior.
This volume is greatly helpful to micro-machining and laser engineers as it offers obliging guidelines about the micro-channel fabrications through Nd:YAG laser beam micro-milling. The book also demonstrates how the laser beam micro-milling behaves when operating under wet conditions (under water), and explores what are the pros and cons of this hybrid technique. From the predictive mathematical models, the readers can easily estimate the resulting micro-channel size against the desired laser parametric combinations. The book considers micro-channels in three highly important research materials commonly used in aerospace industry: titanium alloy Ti-6Al-4V, nickel alloy Inconel 718 and aluminum alloy AA 2024. Therefore, the book is highly practicable in the fields of micro-channel heat exchangers, micro-channel aerospace turbine blades, micro-channel heat pipes, micro-coolers and micro-channel pulsating heat plates. These are frequently used in various industries such as aerospace, automotive, biomedical and micro-electronics.
This book presents the latest advances in mechanical and materials engineering applied to the machining, joining and modification of modern engineering materials. The contributions cover the classical fields of casting, forming and injection moulding as representative manufacturing methods, whereas additive manufacturing methods (rapid prototyping and laser sintering) are treated as more innovative and recent technologies that are paving the way for the manufacturing of shapes and features that traditional methods are unable to deliver. The book also explores water jet cutting as an innovative cutting technology that avoids the heat build-up typical of classical mechanical cutting. It introduces readers to laser cutting as an alternative technology for the separation of materials, and to classical bonding and friction stir welding approaches in the context of joining technologies. In many cases, forming and machining technologies require additional post-treatment to achieve the required level of surface quality or to furnish a protective layer. Accordingly, sections on laser treatment, shot peening and the production of protective layers round out the book’s coverage.
Set III of this encyclopedia is a new addition to the previous Sets I and II. It contains 26 invited chapters from international specialists on the topics of numerical modeling of two-phase flows and evaporation, fundamentals of evaporation and condensation in microchannels and macrochannels, development and testing of micro two-phase cooling systems for electronics, and various special topics (surface wetting effects, microfin tubes, two-phase flow vibration across tube bundles). The chapters are written both by renowned university researchers and by well-known engineers from leading corporate research laboratories. Numerous 'must read' chapters cover the fundamentals of research and engineering practice on boiling, condensation and two-phase flows, two-phase heat transfer equipment, electronics cooling systems, case studies and so forth. Set III constitutes a 'must have' reference together with Sets I and II for thermal engineering researchers and practitioners.
Hybrid Nanofluids: Preparation, Characterization and Applications presents the history of hybrid nanofluids, preparation techniques, thermoelectrical properties, rheological behaviors, optical properties, theoretical modeling and correlations, and the effect of all these factors on potential applications, such as solar energy, electronics cooling, heat exchangers, machining, and refrigeration. Future challenges and future work scope have also been included. The information from this book enables readers to discover novel techniques, resolve existing research limitations, and create novel hybrid nanofluids which can be implemented for heat transfer applications. - Describes the characterization, thermophysical and electrical properties of nanofluids - Assesses parameter selection and property measurement techniques for the calibration of thermal performance - Provides information on theoretical models and correlations for predicting hybrid nanofluids properties from experimental properties
Two-phase microfluidic heat exchangers have the potential to meet the large heat dissipation demands of high power electronics and computing systems. Two-phase cooling systems face practical challenges brought on by the growth and advection of the vapor phase in the confined geometries, which lead to large pressure drops, increased thermal resistance and the formation of detrimental flow instabilities. One proposed solution to these issues is phase separation, whereby the vapor is locally separated from the two-phase flow through a porous hydrophobic membrane. This dissertation describes a series of studies conducted to develop an understanding of the factors that influence vapor separation and its impact on the hydraulic and thermal characteristics of two-phase heat exchangers. Flow phenomena are a critical component in developing this understanding of phase separation. High speed visualization of adiabatic and diabatic vaporizing flows was carried out in a single 124[Mu]m by 98[Mu]m copper microchannel with a 65[Mu]m thick, 220nm pore diameter hydrophobic PTFE membrane wall. During adiabatic air-water flow, wavy-stratified and stratified flow dominated lower liquid velocities, while plug and annular type flows dominated at the higher velocities. Analysis found that air removal could be improved by increasing the venting area, increasing the trans-membrane pressure or using thinner, high permeability membranes. Diabatic water-vapor experiments with mass flux velocities of 140 and 340 kg/s-m2 and exit qualities up to 20% found that stratified type flows dominate at lower mass fluxes while cyclical churn-annular flow became more prevalent at the higher mass-flux and quality. The observed flow regimes are hypothesized to play a significant role in determining the pressure drop and heat transfer coefficient during flow boiling. To study the impact of various geometric and membrane factors on the performance of a phase separating microchannel heat exchanger dissipating 100W of heat, a numerical model incorporating vapor separation and transport during two-phase flow boiling in a microchannel was developed. The impact of substrate thermal conductivity and thickness, membrane permeability and thickness, liquid channel density, liquid and vent channel diameter and vent-to-liquid channel diameter ratio was studied and compared for a standard non-venting heat exchanger, a vapor venting heat exchanger and a non-venting heat exchanger occupying the same increased volume as the venting heat exchanger. The numerical study found that the venting heat exchanger had improved pressure drop and device temperatures for all tested conditions when compared against a standard heat exchanger but only under very limited conditions when compared against the volumetrically equivalent non-venting heat exchanger. The study indicates that the best venting heat exchanger performance is achieved when the membrane conductance is of the same order or higher than that of the microchannel; this can be achieved through the use of thin high permeability membranes coupled with small hydraulic diameter microchannels. Finally, a study was conducted to explore the fabrication methods to build a vapor separating heat exchanger and to quantify the operating performance of multichannel silicon and copper phase separating devices. A copper parallel microchannel heat exchanger with nineteen 130[Mu]m square microchannels was built and tested at heat fluxes of up to 820 kW/m2 and water mass fluxes of between 102 and 420 kg/s-m2. Normalized pressure drop was improved by as much as 60% and average substrate temperature by a maximum of 4.4°C between the non-venting control and vapor venting device under similar operating conditions. Comparison between the experimental results and simulation predictions found higher than expected pressure drop improvements at higher mass fluxes and poorer heat transfer coefficients at the lowest mass flux. Based on the flow phenomena study these discrepancies are believed to be due to the mass flux and vapor quality dependent two-phase flow structures. The encouraging experimental and numerical results motivate further study into phase separation methods, materials and flow physics. The development of a high performance phase separating heat exchanger, with the thermal benefits of two-phase boiling flow and the hydraulic benefits of single-phase liquid flow, would strongly enable the adoption and application of two-phase heat exchangers to provide effective and efficient cooling for next generation high power computing systems.
