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Numerical simulation of non-Newtonian nanofluid flow in microchannel

Number of pages: 131 File Format: word File Code: 32566
Year: 2012 University Degree: Master's degree Category: Facilities - Mechanics
Tags/Keywords: heat transfer - Local network - Microchannel - Nano fluid flow - Nanofluid - Non-Newtonian nanofluid - Numerical simulation - suspension
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  • Summary of Numerical simulation of non-Newtonian nanofluid flow in microchannel

            Abstract:

    Research in the field of heat transfer of suspensions with nanometer-sized solid particles inside the base fluid has started in the last decade. Recent research in the field of nanofluids has shown that the addition of nanoparticles causes a significant increase in the heat transfer of the suspension. Another common way to improve the thermal performance of devices is to use channels with milli and micro dimensions. Considering the extent and importance of non-Newtonian fluids in various industries, the aim of this research is to numerically investigate the flow and heat transfer of non-Newtonian nanofluid in the slow flow regime inside the microchannel.

    In this thesis, the nanofluid composition of 0.5% by weight carboxymethyl cellulose-titanium oxide with nanoparticle diameter of 10 nm and different volume fractions to investigate the flow mixing in the channel and Microchannel is used. The single-phase model has been used to solve the equations. To solve the equations, a two-dimensional numerical code is written in Fortran language. For the discretization of the governing equations, the finite volume method has been used. To generate the network, the simultaneous network arrangement is used and the pressure and velocity couple equations are also solved using the modified SIMPLE algorithm. Finally, the influence of the viscous dissipation parameter, which is not very important in fluid flow in channels with normal dimensions and becomes important in microchannels, has been studied. style="direction: rtl;">Introduction

    Heating and cooling of a system by fluid is of great importance in many industries such as electronic industries, power plants, optical devices, superconducting magnets, ultra-fast computers and automobile engines. Cooling and heating systems are designed based on different methods of heat transfer. Due to this, the development of effective heat transfer techniques is very necessary due to the limitation of natural resources and the desire to reduce costs. In this chapter, the methods for improving heat transfer will be categorized first, and then the methods that will be used in this thesis will be described in more detail.

    1-1 An overview of methods for increasing heat transfer

    In the last few decades, in order to save energy and raw materials and considering economic and environmental issues, many efforts have been made to build High-efficiency heat exchanger devices have been developed, whose main purpose is to reduce the size of the thermal devices required for a given thermal load and increase the heat transfer capacity. With a general look at the work done in this field, the methods presented for this task can be divided into two general categories:

    Passive methods that do not require the application of external force.

    Active methods that require external power.

    Passive methods include the use of wide surfaces, Compact heat exchangers, ducts with non-circular sections, increased eddy heat transfer, microchannels, surface coating and polishing, surface corrugation and so on. And among the active methods, we can also mention mechanical stirring, rotating surfaces, surface oscillation, fluid oscillation, use of electric field, injection and suction, considering that in the upcoming thesis, two agents of microchannels and additives to liquids are used, these two methods will be briefly described. For more explanations, you can refer to Ramyar [7].

    1-1-6 Microchannels

    Another method of increasing heat transfer is using microchannels. The use of this method is used in different industries and devices such as cooling of electronic components, microchannel heat exchangers, cooling and lubrication of robotic systems, microelectromechanical systems and microreactors. The basis of the work of microchannels is to increase the heat transfer surface ratio.

    1-1-10 Additives to liquids

    Adding solid particles suspended in the base fluid is one of the ways to increase heat transfer.

    1-1-10 Additives to liquids

    Adding solid particles suspended in the base fluid is one of the ways to increase heat transfer. Increasing the thermal conductivity coefficient is the main idea in improving the heat transfer characteristics of fluids. Since the thermal conductivity coefficient of solid metal particles is usually greater than that of fluids, it is expected that the addition of these solid particles will increase the thermal conductivity coefficient of the base fluid. The addition of millimeter and micrometer sized particles has been known for more than 100 years [2], but the use of these particles is not possible due to practical problems such as rapid sedimentation of particles, severe wear, increased pressure drop, and the impossibility of using them in very small ducts. Another of these methods is injecting gas into liquids. By injecting air into water and ethylene glycol, an increase of up to 400% in the heat transfer coefficient has been observed [3]. 1-2 Nanofluids Recent advances in materials engineering and the development of new technologies have provided the basis for the production of nanometer-sized particles (nanomaterials). By spreading these materials in the fluid, a new type of fluid is created, which is called nanofluid. The main idea in this method is actually taken from the same method of adding solid particles to the fluid. Nanomaterials strongly affect the kinetic and thermal properties of the fluid. Compared to millimeter or micrometer sized particles, nanoparticles have more contact surface, which increases the ability to transfer energy between solid and fluid particles. Another advantage of this type of fluid is the small size of nanoparticles dispersed in it. These particles have less momentum, which prevents the corrosion of the walls of pipes and channels. The possibility of settling of these particles is less due to its light weight. In the second chapter, nanofluid, its properties and characteristics are explained in detail. Recent investigations on nanofluids, as such suspensions are often called, indicate that the suspended nanoparticles markedly change the transport properties and heat transfer characteristics of the suspension. Also, using the channels with milli and micro size can enhance the heat transfer performance of systems. Because of the importance of the non-Newtonian fluids in the process industry, the aim of this study is the investigation of the flow and heat transfer of non-Newtonian nanofluids in the microchannels.

    In the present work, mixing of two laminar flows of non-Newtonian nanofluids through a two dimensional microchannel is numerically investigated. The governing equations are being discretized using finite volume approach. TiO2 nanoparticles with 10nm diameter were dispersed in a 0.5 wt.% aqueous solution of carboxymethyl cellulose (CMC) to prepare non-Newtonian nanofluid. This nanofluid, as well as the base fluid, exhibits pseudoplastic behavior. The thermal and rheological properties of the base fluid and nanofluid are temperature dependent and in this paper we present a new correlation for the power law and the consistency indices with the temperature of the fluid. Also the effect of viscous dissipation term on results is taken into account.

    Keywords: non-Newtonian nanofluid, microchannel, convective heat transfer.

  • Contents & References of Numerical simulation of non-Newtonian nanofluid flow in microchannel

    List:

    Table of Contents

    Chapter One: Introduction. 1

    Introduction 2

    1-1 An overview of heat transfer enhancement methods. 2

    1-1-1 Microchannels. 2

    1-1-1 Additives to liquids. 3

    1-2 Nanofluid 3

    Chapter Two: Nanofluid and determining its properties. 4

    Introduction 5

    2-1 Nanofluid applications. 5

    2-2 parameters affecting the thermal conductivity coefficient. 6

    2-3 Determination of nanofluid properties. 6

    2-3-1 Density. 7

    2-3-2 Specific heat capacity. 7

    2-3-3 thermal conductivity coefficient. 7

    2-3-4 dynamic viscosity. 8

    The third chapter: Microchannel. 9

    Introduction 10

    3-1 Reasons for tending to micro dimensions. 10

    3-2 Classification of channels in terms of dimensions. 10

    3-3 dimensional effects in microchannel. 11

    3-3-1 Entry effect. 11

    3-3-3 Viscous loss. 13

    Chapter four: Non-Newtonian fluids. 14

    Introduction 15

    4-1 Introduction of non-Newtonian fluids. 16

    4-2 Time independent behavior of fluid. 17

    4-2-1 Thin shear behavior. 18

    4-2-1-1 Power fluid equation or Ostwald de Wael. 19

    4-2-1-1 cross viscosity equation. 21

    4-2-1-3 Ellis fluid equation. 21

    4-2-2 Visco-plastic behavior of fluid. 21

    4-2-3 Shear thickening or dilatant behavior. 24

    4-3 fluid time-dependent behavior. 26

    4-4 Viscoelastic behavior of fluid. 26

    Chapter five: review of the work done. 28

    Introduction 29

    5-1 Flow in microchannel. 29

    5-2 Nanofluids. 33

    5-3 Non-Newtonian fluid and nanofluid. 36

    4-5 Nanofluid in microchannel. 44

    5-5 Non-Newtonian fluid in microchannel. 46

    Sixth chapter: governing equations. 50

    Introduction 51

    6-1 Governing equations. 51

    6-2 Review and discretization of governing equations. 53

    6-2-1 Momentum equation in the x direction. 54

    6-2-2 Energy equation. 56

    6-2-3 Solving the pressure equation. 58

    Chapter Seven: Results. 61

    Introduction 62

    Channel 7-1. 62

    7-1-1    Rheological properties of nanofluids. 63

    7-1-1 Code verification. 64

    7-1-2 Grid independent solution. 65

    7-1-3 Results. 66

    7-2 Convergent Microchannel 76

    7-2-1 Network independent solution. 76

    7-2-2 Results. 77

    7-2 microchannels. 90

    7-2-1 Grid independent solution. 91

    7-2-2 Results. 92

    Chapter eight: Conclusion and suggestions. 109

    References 111

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    J. Koo, C. Kleinstreuer, "Viscous dissipation effects in microtubes and microchannels", International Journal of Heat and Mass Transfer, Vol. 47, pp. 3159–3169, 2004.

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    G. L. Morini and M. Spiga, "The Role of the Viscous Dissipation in Heated Microchannels", Journal of Heat Transfer, Vol. 129, pp. 308-318, 2007.

    Y. M. Hung, "Viscous Dissipation Effect on Entropy Generation for Non-Newtonian Fluids in Microchannels", International Communications in Heat and Mass Transfer, Vol. 35, pp. 1125–1129, 2008.

    Y. M. Hung, “A Comparative Study of Viscous Dissipation Effect on Entropy Generation in Single-phase Liquid Flow in Microchannels”, International Journal of Thermal Science, vol. 48, pp. 1026–1035, 2009.

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Numerical simulation of non-Newtonian nanofluid flow in microchannel
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