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Author: Jiwon Yu Publisher: ISBN: Category : Languages : en Pages :
Book Description
Experiments were performed to study forced convective heat transfer of de-ionized water (DI water) and aqueous nanofluids flowing in a microchannel. An array of temperature nanosensors, called "Thin Film Thermocouples (TFT)", was utilized for performing the experimental measurements. TFT arrays were designed (which included design of photomask layout), microfabricated, packaged and assembled for testing with the experimental apparatus. Heat removal rates from the heated surface to the different testing fluids were measured by varying the coolant flow rates, wall temperatures, nanoparticle material, nanoparticle morphology (shape and nanoparticle size) as well as mass concentrations of nanoparticles in the coolants. Anomalous thermal behavior was observed in the forced convective heat transfer experiments. Precipitation of the nanoparticles on the heat exchanging surface was monitored using Scanning Electron Microscopy (SEM) and Energy Dispersive X-Ray spectroscopy (EDX). Isolated precipitation of nanoparticles is expected to cause formation of "nanofins" leading to enhancement of surface area and thus resulting in enhanced convective heat transfer to the nanofluid coolants. However, excessive precipitation (caused due to the agglomeration of the nanoparticles in the nanofluid coolant) causes scaling (fouling) of the heat exchanging surfaces and thus results in degradation of convective heat transfer. This study shows that the surface morphology plays a crucial role in determining the efficacy of convective heat transfer involving suspensions of nanoparticles in coolants (or nanofluids). Flow visualization and quantitative estimation of near-wall temperature profiles were performed using quantum dots and fluorescent dyes. This non-contact measurement technique for temperature and flow profiles in microchannels using quantum dots is expected to make pioneering contribution to the field of experimental flow visualization and to the study of micro/nano-scale heat transfer phenomena, particularly for forced convective heat transfer of various coolants, including nanofluids. Logical extensions of this study were explored and future directions were proposed. Preliminary experiments to demonstrate feasibility showed significant enhancement in the flow boiling heat flux values for nanofluids compared to that of pure solvent (DIW). Based on the novel phenomena observed in this study several other topics for future research were suggested, such as, using Surface Plasmon Resonance (SPR) platforms to monitor precipitation of nanoparticles on microchannel surfaces in real time (e.g., for generating surface isotherms). The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/148235
Author: Jiwon Yu Publisher: ISBN: Category : Languages : en Pages :
Book Description
Experiments were performed to study forced convective heat transfer of de-ionized water (DI water) and aqueous nanofluids flowing in a microchannel. An array of temperature nanosensors, called "Thin Film Thermocouples (TFT)", was utilized for performing the experimental measurements. TFT arrays were designed (which included design of photomask layout), microfabricated, packaged and assembled for testing with the experimental apparatus. Heat removal rates from the heated surface to the different testing fluids were measured by varying the coolant flow rates, wall temperatures, nanoparticle material, nanoparticle morphology (shape and nanoparticle size) as well as mass concentrations of nanoparticles in the coolants. Anomalous thermal behavior was observed in the forced convective heat transfer experiments. Precipitation of the nanoparticles on the heat exchanging surface was monitored using Scanning Electron Microscopy (SEM) and Energy Dispersive X-Ray spectroscopy (EDX). Isolated precipitation of nanoparticles is expected to cause formation of "nanofins" leading to enhancement of surface area and thus resulting in enhanced convective heat transfer to the nanofluid coolants. However, excessive precipitation (caused due to the agglomeration of the nanoparticles in the nanofluid coolant) causes scaling (fouling) of the heat exchanging surfaces and thus results in degradation of convective heat transfer. This study shows that the surface morphology plays a crucial role in determining the efficacy of convective heat transfer involving suspensions of nanoparticles in coolants (or nanofluids). Flow visualization and quantitative estimation of near-wall temperature profiles were performed using quantum dots and fluorescent dyes. This non-contact measurement technique for temperature and flow profiles in microchannels using quantum dots is expected to make pioneering contribution to the field of experimental flow visualization and to the study of micro/nano-scale heat transfer phenomena, particularly for forced convective heat transfer of various coolants, including nanofluids. Logical extensions of this study were explored and future directions were proposed. Preliminary experiments to demonstrate feasibility showed significant enhancement in the flow boiling heat flux values for nanofluids compared to that of pure solvent (DIW). Based on the novel phenomena observed in this study several other topics for future research were suggested, such as, using Surface Plasmon Resonance (SPR) platforms to monitor precipitation of nanoparticles on microchannel surfaces in real time (e.g., for generating surface isotherms). The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/148235
Author: S. Harikrishnan Publisher: Springer Nature ISBN: 9811678456 Category : Science Languages : en Pages : 105
Book Description
This comprehensive book focuses on the basic physical features and purpose of nanofluids and miniature heat sinks. The contents demonstrate the design modification, fabrication, experimental investigation, and various applications of miniature heat sinks. The book provides context for thermal performance of miniature heat sinks as well as summaries of experimental results correlations that reflect the current technical innovations are included. This book is a useful reference for both academia and industry alike.
Author: Aditya Kumar Publisher: Springer Nature ISBN: 981334248X Category : Science Languages : en Pages : 230
Book Description
This book covers synthesis, characterization, stability, heat transfer and applications of nanofluids. It includes different types of nanofluids, their preparation methods as well as its effects on the stability and thermophysical properties of nanofluids. It provides a discussion on the mechanism behind the change in the thermal properties of nanofluids and heat transfer behaviour. It presents the latest information and discussion on the preparation and advanced characterization of nanofluids. It also consists of stability analysis of nanofluids and discussion on why it is essential for the industrial application. The book provides a discussion on thermal boundary layer properties in convection. Future directions for heat transfer applications to make the production and application of nanofluids at industrial level are also discussed.
Author: Vincenzo Bianco Publisher: CRC Press ISBN: 1482254026 Category : Science Languages : en Pages : 473
Book Description
Nanofluids are gaining the attention of scientists and researchers around the world. This new category of heat transfer medium improves the thermal conductivity of fluid by suspending small solid particles within it and offers the possibility of increased heat transfer in a variety of applications. Bringing together expert contributions from
Author: Sohaib Mustafa Mohammed Osman Publisher: ISBN: Category : Languages : en Pages :
Book Description
The growing demand for energy worldwide requires attention to the design and operating of heat exchangers and thermal devices to utilise and save thermal energy. There is a need to find new heat transport fluids with better heat transfer properties to increase convective heat transfer, and nanofluids are good alternatives to conventional heat transport fluids. Although extensive research has been done on the properties of nanofluids in recent decades, there is still a lack of research on convection heat transfer involving nanofluids, particularly in the transitional flow regime. This study focused on the application of nanofluids in heat exchangers as heat transport fluids by investigating forced convective heat transfer of alumina-water and titanium dioxide-water nanofluids prepared by using the one-step method. The particle size used was 46 nm and 42 nm for the aluminium oxide and the titanium dioxide respectively. Uniform heat flux boundary conditions were used by uniformly heating the rectangular channel electrically. Nanofluids with volume concentrations of 0.3, 0.5 and 1% were used for the alumina-water nanofluids, and volume concentrations of 0.3, 0.5, 0.7 and 1% were used for the titanium dioxide-water nanofluids. The viscosity of the nanofluids under investigation was determined experimentally, while the thermal conductivity and other properties were predicted by using suitable correlations from the literature. A Reynolds number range of 200 to 7 000 was covered, and the investigated flow rates included the laminar and turbulent flow regimes, as well as the transition regime from laminar to turbulent flow. Temperatures and pressure drops were measured to evaluate heat transfer coefficients, Nusselt numbers and pressure drop coefficients. Heat transfer and hydrodynamic characteristics in the transition flow regime were carefully studied and compared with those in the transition regime when flowing pure water in the same test section. The study also investigated another approach of enhancing heat transfer in heat exchangers by increasing the heat transfer area of the heat exchanger itself, and this was done by filling the rectangular test section with porous media to increase the heat transfer surface area and thus enhance heat transfer. Hence in this study, the effect of using porous media was also studied by filling the rectangular test section with high-porosity nickel foam. The permeability of the used nickel foam was determined by conducting pressure drop measurements through the nickel foam in the test section, and heat transfer and pressure drop parameters were measured and compared with those in the empty test section. The results showed that all the nanofluids used enhanced heat transfer, particularly in the transition flow regime. The 1.0% volume concentration alumina nanofluid showed maximum enhancement of the heat transfer coefficient, with values of 54% and 11% in the turbulent regime. The maximum enhancement of the heat transfer coefficient was 29.3% in the transition regime for the 1.0% volume concentration titanium dioxide-water nanofluid. The thermal performance factor in the transition flow regime was observed to be better than that in the turbulent and laminar flow regimes for all the nanofluids. The results of the nickel foam test section showed that the values of the friction coefficient were 24.5 times higher than the values of the empty test section, and the Nusselt number was observed to be three times higher when using nickel foam than without foam in the test section. No transition regime was observed for the foam-filled test section on either the heat transfer results or the pressure drop results; however, transition from laminar to turbulent was found for the test section without foam. The results of the thermal factor of the foam-filled test section showed a thermal performance factor higher than unity through the entire Reynolds number range of 2 000 to 6 500, with better thermal performance factor at lower Reynolds number.
Author: Hafiz Muhammad Ali Publisher: Academic Press ISBN: 012819281X Category : Technology & Engineering Languages : en Pages : 304
Book Description
Hybrid Nanofluids for Convection Heat Transfer discusses how to maximize heat transfer rates with the addition of nanoparticles into conventional heat transfer fluids. The book addresses definitions, preparation techniques, thermophysical properties and heat transfer characteristics with mathematical models, performance-affecting factors, and core applications with implementation challenges of hybrid nanofluids. The work adopts mathematical models and schematic diagrams in review of available experimental methods. It enables readers to create new techniques, resolve existing research problems, and ultimately to implement hybrid nanofluids in convection heat transfer applications. Provides key heat transfer performance and thermophysical characteristics of hybrid nanofluids Reviews parameter selection and property measurement techniques for thermal performance calibration Explores the use of predictive mathematical techniques for experimental properties
Author: Roy T. Strandberg Publisher: ISBN: Category : Aluminum oxide Languages : en Pages : 324
Book Description
The purpose of the research was to examine the heat transfer and fluid dynamic performance of various nanofluids in heating and cooling applications using empirical and computational methods. Two experiments were performed to characterize and compare the performance of a Al2O3/60% ethylene glycol (60% EG) nanofluid to that of its base fluid. In the first experiment, the nanofluid was comprised of Al2O3 nanoparticles with 1% volumetric concentration in a 60% ethylene glycol/40% water (60% EG by mass) solution to that of 60%EG in a liquid to air heat exchanger. The test bed used in the experiment was built to simulate a small air handling system typical of that used in heating, ventilating and air conditioning (HVAC) applications. Previously established empirical correlations for thermophysical properties of fluids were used to determine the values of various parameters (e.g. Nusselt number, Reynolds number, and Prandtl number). The testing shows that the 1% Al2O3 nanofluid generates a marginally higher heat rate than the 60% EG under certain conditions. At Re=3,000, the nanofluid produced a heat rate that was 2% higher than that of the 60% EG. The empirically determined Nusselt number associated with the convection inside the coil tubing follows the behavior predicted by the Dittus-Boelter correlation quite well (R2=0.97), while the empirically determined Nusselt number for the 60% EG follows the Petukhov correlation similarly well (R2=0.97). Pressure loss and hydraulic power for the nanofluid were higher than for the base fluid over the range of conditions tested. The exergy destroyed in the heat exchange and fluid flow processes were between 8 and 13% higher for the nanofluid over the tested range of Reynolds numbers. The objective of the second study was to experimentally characterize and compare the performance of a nanofluid comprised of Al2O3 nanoparticles with 1, 2 and 3% volumetric concentrations in a 60% EG solution to that of 60% EG in a liquid to air heat exchanger. In this experiment, the heating system was operated in a higher temperature regime than in the first experiment. As in the first experiment, the test bed used in the experiment simulated a small air handling system typical of that used in HVAC applications. Entering conditions for the air and liquid were selected to emulate typical operating conditions of commercial air handling systems in sub arctic regions (such as Alaska). In the experiment the nanofluids generally did not perform as well as expected based on previous analytical work. The performance of the 1% nanofluid was generally equal to that of the base fluid considering identical entering conditions. However, the 2% and 3% nanofluids performance was considerably worse than that of the base fluid. The higher concentration nanofluids exhibited heat rates up to 14.6% lower than that of the 60%EG, and up to 44.3% lower heat transfer coefficient. The 1% Al2O3/60% EG exhibited 100% higher pressure drop across the coil than the base fluid considering equal heat output. In the computational portion of the research, the performance of a microchannel heat sink (MCHS), similar to those used to cool microprocessors filled with various nanofluids and the corresponding base fluid without nanoparticles are examined. The MCHS is modeled using a three- dimensional conjugate heat transfer and fluid dynamic finite-volume model over a range of conditions. The model incorporates a fixed heat flux of 1,000,000 W/m2 at the base of the solid domain. The thermophysical properties of the fluids are based on empirically obtained correlations, and vary with temperature. Nanofluids considered include 60% Ethylene Glycol/40% Water solutions with CuO, SiO2, and Al2O3 nanoparticles dispersed in volumetric concentrations ranging from 1 to 3%. The flow conditions analyzed are in the laminar range (50£Re£300), and consider multiple inlet temperatures. The analyses predict that when compared on an equal Reynolds number basis, the 60%EG/3% CuO nanofluid exhibits the highest heat transfer coefficient, and the largest reduction in average base temperature. At an inlet Reynolds number of 300, and an inlet temperature of 308K the nanofluid is predicted to have an average heat transfer coefficient that is 30% higher than that of the base fluid, while the average temperature on the base of the heat exchanger is 1K lower than that of the base fluid. In contrast, the inlet pressure required for these entering conditions is 192% higher than that for the base fluid, while the required hydraulic power to drive the flow is 366% higher than that of the base fluid. The enhanced heat transfer performance potential of nanofluids comes at the expense of generally higher pumping power consumption.
Author: W. J. Minkowycz Publisher: CRC Press ISBN: 1439861951 Category : Science Languages : en Pages : 335
Book Description
Featuring contributions by leading researchers in the field, Nanoparticle Heat Transfer and Fluid Flow explores heat transfer and fluid flow processes in nanomaterials and nanofluids, which are becoming increasingly important across the engineering disciplines. The book covers a wide range, from biomedical and energy conversion applications to mate
Author: Zhixiong Li Publisher: Elsevier ISBN: 0128219246 Category : Technology & Engineering Languages : en Pages : 368
Book Description
Nanofluid in Heat Exchanges for Mechanical Systems: Numerical Simulation shows how the finite volume method is used to simulate various applications of heat exchanges. Heat transfer enhancement methods are introduced in detail, along with a hydrothermal analysis and second law approaches for heat exchanges. The melting process in heat exchanges is also covered, as is the influence of variable magnetic fields on the performance of heat exchange. This is an important reference source for materials scientists and mechanical engineers who are looking to understand the main ways that nanofluid flow is simulated and applied in industry. Provides detailed coverage of major models used in nanofluid analysis, including the finite volume method, governing equations for turbulent flow, and equations of nanofluid in presence of variable magnetic field Offers detailed coverage of swirling flow devices and melting processes Assesses which models should be applied in which situations
Author: K.R.V. Subramanian Publisher: CRC Press ISBN: 0429886985 Category : Science Languages : en Pages : 532
Book Description
Nanofluids are solid-liquid composite material consisting of solid nanoparticles suspended in liquid with enhanced thermal properties. This book introduces basic fluid mechanics, conduction and convection in fluids, along with nanomaterials for nanofluids, property characterization, and outline applications of nanofluids in solar technology, machining and other special applications. Recent experiments on nanofluids have indicated significant increase in thermal conductivity compared with liquids without nanoparticles or larger particles, strong temperature dependence of thermal conductivity, and significant increase in critical heat flux in boiling heat transfer, all of which are covered in the book. Key Features Exclusive title focusing on niche engineering applications of nanofluids Contains high technical content especially in the areas of magnetic nanofluids and dilute oxide based nanofluids Feature examples from research applications such as solar technology and heat pipes Addresses heat transfer and thermodynamic features such as efficiency and work with mathematical rigor Focused in content with precise technical definitions and treatment
Author: Jiwon Yu
Author: Jiwon Yu
Author: S. Harikrishnan
Author: Aditya Kumar
Author: Vincenzo Bianco
Author: Sohaib Mustafa Mohammed Osman
Author: Hafiz Muhammad Ali
Author: Roy T. Strandberg
Author: W. J. Minkowycz
Author: Zhixiong Li
Author: K.R.V. Subramanian