04-01-2013, 12:03 PM
ANALYSIS OF HEAT TRANSFER CO-EFFICIENT IN NANO FLUIDS
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ABSTRACT
Conventional fluids such as water, ethylene glycol normally used as heat transfer fluids. Various techniques are applied to enhance the heat transfer, the low heat transfer performance of these conventional fluids obstructs the performance enhancement. The use of additives is a technique applied to enhance the heat transfer performance of base fluids. Recently as an innovative material, nanometer-sized particles have been used in suspension in conventional heat transfer fluids. The fluids with these solid-particle suspended in them are called nanofluids. The suspended metallic or non metallic nanoparticles change the transport properties and heat transfer characteristics of the base fluid. In this project we have considered the problem of forced convection flow of fluid inside a uniformly heated tube that is submitted to a constant and uniform heat flux at the wall. The heat transfer coefficient was analyzed at the same Reynolds number for both base fluids and nanofluids in the CFX software. The base fluids used for this work is water and ethylene glycol. The nanoparticles to suspended in the base fluids used for this work are aluminum, aluminum oxide, copper, copper oxide and silver. And also a comparative work is done between the thermal conductivity models.
INTRODUCTION
GENERAL
Conventional fluids such as water, ethylene glycol are normally used as heat transfer fluids. They play an important role in many industry sectors including power generation, chemical production, air-conditioning transportation and microelectronics. Various techniques are applied to enhance the heat transfer; the low heat transfer performance of these conventional fluids obstructs the performance enhancement and the compactness of heat exchangers. The use of solid particles as an additive suspended into the base fluid is a technique for heat transfer enhancement. Improving of the thermal conductivity is a key idea to improve the heat transfer characteristics of conventional fluids. Since a solid metal have large thermal conductivity than a base fluid, suspending metallic solid fine particles into the base fluid is expected to improve the thermal conductivity of that fluid. The enhancement of thermal conductivity of conventional fluids by the suspension of solid particles, such a millimeter or micrometer-sized particles has been well known for more than 100 years. However they have not been of interest for practical applications due to problems such as sedimentation, erosion, and fouling and increased pressure drop of the flow channel. The recent advance in materials technology has made it possible to produce nanometer sizes particles that can overcome these problems.
NANO FLUIDS AND ITS PREPARATION
In nano technology, a particle is defined as a small object that behaves as a whole unit in terms of its transport and properties. It is further classified according to size: In terms of diameter, fine particles cover a range between 100 and 2500 nanometers, while ultra fine particles, on the other hand, are sized between 1 and 100 nanometers. Similarly to ultra fine particles, nanoparticles are sized between 1 and 100 nanometers, though the size limitation can be restricted to two dimensions. Nanoparticles may or may not exhibit size-related properties that differ significantly from those observed in fine particles or bulk materials. This suspended nano particles can change the transport and the thermal properties of the base fluid. A recent development is that nanoparticles can disperse in conventional heat transfer fluids such as water, glycol or oil to produce a new class of high efficiency heat exchange media. The superior properties of nano particle fluid mixtures relative to those of fluids without particle or with large sized particle include high thermal conductivities, stability and prevention of clogging in micro channels. A liquid suspended with particles of nanometer dimension is termed a nanofluid.
HEAT TRANSFER ENHANCEMENT
Heat transfer enhancement is an active and important field of engineering research. Based upon the research three possible mechanisms proposed for heat transfer enhancement. They are decreasing the thermal boundary layer, increasing the flow interruptions and increasing the velocity gradient near the heated surface. The addition of small particles to the fluid can some times provide heat transfer enhancement. However the works in this area provide the suspension of micro to macro size particles bear the following major disadvantages.
SCOPE OF THE PROJECT
The major improvement in heat transfer capabilities have suffered a major lacking as a result and it is important to need skills to develop new strategies in order to improve the effective heat transfer behaviors of conventional heat transfer fluids. To improve the heat transfer rate of conventional fluids the nano particles are suspended in the base fluid. In this project the two base fluids are selected namely water and ethylene glycol. To enhance the heat transfer rate of the above said base fluids the nano particles of Aluminum, Aluminum oxide, copper, copper oxide and silver were chosen. The properties of the nano fluids are calculated by formulas. The thermo physical properties of water, ethylene glycol, Aluminum, Aluminum oxide, copper, copper oxide and silver are tabulated and it is substituted in the formulas for finding the properties of nanofluids. In order to analyze the heat transfer rate of the base fluid and nanofluid CFX software is used. The nano fluids and the base fluids are analyzed under the same Reynolds number. And also a comparative work is done between the thermal conductivity models namely Maxwell, Hamilton and Crosser, Jeffrey, Davis, Bruggeman and Suresh models.
[attachment=46435]
ABSTRACT
Conventional fluids such as water, ethylene glycol normally used as heat transfer fluids. Various techniques are applied to enhance the heat transfer, the low heat transfer performance of these conventional fluids obstructs the performance enhancement. The use of additives is a technique applied to enhance the heat transfer performance of base fluids. Recently as an innovative material, nanometer-sized particles have been used in suspension in conventional heat transfer fluids. The fluids with these solid-particle suspended in them are called nanofluids. The suspended metallic or non metallic nanoparticles change the transport properties and heat transfer characteristics of the base fluid. In this project we have considered the problem of forced convection flow of fluid inside a uniformly heated tube that is submitted to a constant and uniform heat flux at the wall. The heat transfer coefficient was analyzed at the same Reynolds number for both base fluids and nanofluids in the CFX software. The base fluids used for this work is water and ethylene glycol. The nanoparticles to suspended in the base fluids used for this work are aluminum, aluminum oxide, copper, copper oxide and silver. And also a comparative work is done between the thermal conductivity models.
INTRODUCTION
GENERAL
Conventional fluids such as water, ethylene glycol are normally used as heat transfer fluids. They play an important role in many industry sectors including power generation, chemical production, air-conditioning transportation and microelectronics. Various techniques are applied to enhance the heat transfer; the low heat transfer performance of these conventional fluids obstructs the performance enhancement and the compactness of heat exchangers. The use of solid particles as an additive suspended into the base fluid is a technique for heat transfer enhancement. Improving of the thermal conductivity is a key idea to improve the heat transfer characteristics of conventional fluids. Since a solid metal have large thermal conductivity than a base fluid, suspending metallic solid fine particles into the base fluid is expected to improve the thermal conductivity of that fluid. The enhancement of thermal conductivity of conventional fluids by the suspension of solid particles, such a millimeter or micrometer-sized particles has been well known for more than 100 years. However they have not been of interest for practical applications due to problems such as sedimentation, erosion, and fouling and increased pressure drop of the flow channel. The recent advance in materials technology has made it possible to produce nanometer sizes particles that can overcome these problems.
NANO FLUIDS AND ITS PREPARATION
In nano technology, a particle is defined as a small object that behaves as a whole unit in terms of its transport and properties. It is further classified according to size: In terms of diameter, fine particles cover a range between 100 and 2500 nanometers, while ultra fine particles, on the other hand, are sized between 1 and 100 nanometers. Similarly to ultra fine particles, nanoparticles are sized between 1 and 100 nanometers, though the size limitation can be restricted to two dimensions. Nanoparticles may or may not exhibit size-related properties that differ significantly from those observed in fine particles or bulk materials. This suspended nano particles can change the transport and the thermal properties of the base fluid. A recent development is that nanoparticles can disperse in conventional heat transfer fluids such as water, glycol or oil to produce a new class of high efficiency heat exchange media. The superior properties of nano particle fluid mixtures relative to those of fluids without particle or with large sized particle include high thermal conductivities, stability and prevention of clogging in micro channels. A liquid suspended with particles of nanometer dimension is termed a nanofluid.
HEAT TRANSFER ENHANCEMENT
Heat transfer enhancement is an active and important field of engineering research. Based upon the research three possible mechanisms proposed for heat transfer enhancement. They are decreasing the thermal boundary layer, increasing the flow interruptions and increasing the velocity gradient near the heated surface. The addition of small particles to the fluid can some times provide heat transfer enhancement. However the works in this area provide the suspension of micro to macro size particles bear the following major disadvantages.
SCOPE OF THE PROJECT
The major improvement in heat transfer capabilities have suffered a major lacking as a result and it is important to need skills to develop new strategies in order to improve the effective heat transfer behaviors of conventional heat transfer fluids. To improve the heat transfer rate of conventional fluids the nano particles are suspended in the base fluid. In this project the two base fluids are selected namely water and ethylene glycol. To enhance the heat transfer rate of the above said base fluids the nano particles of Aluminum, Aluminum oxide, copper, copper oxide and silver were chosen. The properties of the nano fluids are calculated by formulas. The thermo physical properties of water, ethylene glycol, Aluminum, Aluminum oxide, copper, copper oxide and silver are tabulated and it is substituted in the formulas for finding the properties of nanofluids. In order to analyze the heat transfer rate of the base fluid and nanofluid CFX software is used. The nano fluids and the base fluids are analyzed under the same Reynolds number. And also a comparative work is done between the thermal conductivity models namely Maxwell, Hamilton and Crosser, Jeffrey, Davis, Bruggeman and Suresh models.