K.V. Sharma

Thermal conductivity enhancement of nanoparticles in distilled water

This paper provides an overview of the important physical phenomena necessary for the determination of effective thermal conductivity of nanofluid. Increase in the specific area as well as Brownian motion are supposed to be the most significant reasons for the anomalous enhancement in thermal conductivity of nanofluid. Usual heat transfer fluids with suspended ultra fine particles of nanometre size are named as nanofluids, which have opened a new dimension in heat transfer processes. This work presents the increase of thermal conductivity with temperatures for nanofluids with water as base fluid and particles of Al2O3 or CuO as suspension material. Transient hot-wire method is used for the measurement of thermal conductivity. Heat retaining time is introduced and estimated experimentally. The heat retaining time of 0.8% volume fraction of Al22O3 nanofluid increases up to 47.05% of the base fluid and 0.8% volume fraction of CuO nanofluid increases up to 61.7% of the base fluid. The results indicate an increase of enhancement of thermal conductivity with temperature found to be agreeing excellently with a wide range of different models as well as the data published in literature.

Correlations for thermal conductivity and viscosity of water based nanofluids

The thermo-physical properties of nanofluids such as thermal conductivity, viscosity, density and specific heat of nanofluids are required for the analysis of convection heat transfer coefficients. The density and specific heat of nanofluids can be estimated with the mixture relations in literature. Information regarding the properties at different volume concentration and temperature is required for the estimation of heat transfer coefficient. The two most fundamental properties which are, experimentally, determined, are viscosity and thermal conductivity. Investigators have been determining the properties of nanofluids at different temperatures and base liquids. The present work is an attempt to analyze the available data to develop a non-linear regression equation for the estimation of thermal conductivity and viscosity of water based nanofluids. In the present study, nanofluids are considered as a homogenous medium and the parameters influencing the thermo physical properties identified. Equations are developed for the analysis of thermo-physical properties of nanofluids as a function of parameters viz., material, concentration, temperature and particle size useful for designer. The opposing nature of thermal conductivity rise and viscosity decrease with temperature; dependence of nanofluid thermal conductivity on material properties alters the range of applicability of nanofluids for heat transfer applications. The thermal conductivity and viscosity of Al2O3, ZnO and TiO2 dispersed in water are measured to validate the proposed equations. The result shows that the equations are able to predict the thermal conductivity and viscosity of different types of nanofluids of different particle diameters closely.

Heat transfer and friction factor analysis in a circular tube with Al2O3 nanofluid by using computational fluid dynamics

Turbulent fully developed flow heat transfer coefficient and friction factor of Al2O3 nanoparticles are dispersed in water and ethylene glycol in circular tube is discussed in this paper. In order to validate the heat transfer coefficient and friction factor of nanofluid in circular tube commercially available CFD software FLUENT 6.0 is used. To achieve the fully developed flow condition, the aspect ratio (L/D) of the test section is equal to 94. The thermo-physical properties of the Al2O3 nanofluid are estimated by using the equations available in literature. Thermo-physical properties of the nanofluid are considered for heat transfer coefficient and friction factor by assuming nanofluid is a single-phase fluid. Constant Wall Heat Flux (CWHF) boundary condition is incorporated for heat transfer analysis and adiabatic boundary condition is incorporated for friction factor analysis. The analysis is conducted in the volume concentration range from 0.1% to 4%. A maximum of 2.25 times heat transfer enhancement and 1.42 times of friction is obtained by using nanofluid as working medium.

The potential of wind and solar energy in Malaysia east coast: preliminary study at Universiti Malaysia Pahang (UMP)

The main objective of this article is to investigate wind and solar potential in Universiti Malaysia Pahang renewable energy resources as response to Malaysian government regarding to green technology. It is a preliminary study mainly focuses on technique of measurement and collecting potential wind and solar data. The first solar panels installation was planned to be inside Universiti Malaysia Pahang with the first wind turbine being installed at the bank of the Sungai Pahang in Pekan, Pahang. The local solar radiation regime was described with on-site measurements and calculations where the former was carried out from the beginning of 2010. The setup of the measurement device is discussed in this paper.

Turbulent forced convection of Al2O3 nanofluid in a circular tube with tape inserts at low volume concentration

Convective heat transfer coefficients with Al2O3 nanofluid under turbulent flow in a circular tube fitted with twisted tape insert is estimated. The thermo-physical properties such as thermal conductivity and viscosity are established experimentally in a wide range of volume concentration and validated with values obtained by others. The heat transfer coefficient obtained with Al2O3 nanofluid having volume concentration of 0.02% is 10% higher when compared with water flowing in the tube at Re = 22,000. Tapes of different twist ratios in the range of 5 < H/D < 15 are used as tube inserts to evaluate nanofluid heat transfer and pressure drop. Nanofluid heat transfer coefficient is enhanced by 23% and maximum pressure drop by 1.7 times with tape insert in the range of H/D tested when compared to flow in a plain tube.

Experimental investigations on thermal conductivity of water and Al2O3 nanofluids at low concentrations

Thermal conductivity properties of water-based nanofluids at low concentrations are being presented in this paper. Nanoparticles at low volume concentration in the range of 0.01 to 1% is added to water improve the properties of the base fluid. The properties are estimated at temperatures between 21°C and 45°C. The results indicate an increase of enhancement of thermal conductivity with temperature and are found to be in agreement with different models as well as the data published in the literature. Empirical equations to calculate thermal conductivity and density for varied particle concentration and temperature are established. The measured and predicted values of thermal conductivity and density have a maximum deviation of 8% and 6% in the working range, respectively.

Laminar convective heat transfer of nanofluids in a circular tube under constant heat flux

The main aim of the present investigation is to study the heat transfer behaviour of nanofluids in a circular tube under laminar flow condition by using commercially available FLUENT 6.0 software. In this analysis Al2 O2, CuO and TiO2 nanofluids are considered. Thermo-physical properties of the nanofluids (thermal conductivity, density, viscosity and specific heat) are obtained from the literature. Constant heat flux boundary condition is applied for the estimation of heat transfer coefficient of nanofluids inside a tube. All the investigations of nanofluids are carried out in the volume concentrations ranging from 0.3-2.0% and at the same Reynolds number. The values obtained from CFD analysis of nanofluids are compared with the values of water.