Alina Adriana Minea

Field-Synergy and Figure-of-Merit Analysis of Two Oxide–Water-Based Nanofluids' Flow in Heated Tubes

ABSTRACT Field-synergy analysis is performed on the water–oxide nanofluid flow in circular heat sinks to examine the synergetic relation between the flow and temperature fields for heating processes. By varying the Reynolds number and the nanoparticle volume fraction, the convective heat transfer of nanofluid is investigated based on the field synergy number. For heating, the degree of synergy between the velocity and temperature fields of nanofluid flow deteriorates with the Reynolds number increase, leading to a decreased heat transfer performance of the nanofluid. By increasing the particle volume fraction, the degree of synergy between the velocity and temperature fields of the nanofluid flow can be intensified, thus going to convection heat transfer enhancement. After generating results, one can notice that the heat transfer enhancement is strongly dependent on nanoparticle type, Reynolds number, and volume fraction. The results are similar, even if the thermal conductivity of the two considered oxide nanoparticles are quite different. Additionally, a convenient figure of merit that is known as the Mouromtseff number was used as base of comparison, and the results indicated that the considered nanofluids can successfully replace water in specific applications for single-phase forced convection flow in a tube.

An Analysis of the Electricity Sector in Romania

The aim of this article is to analyze the electricity sector in Romania, considering the present situation and possible future developments. With its emerging and rapidly growing economy and with a population of 21 million people, Romania is today the worlds 49th-largest economy. The countrys electricity consumption has risen in the last years as a result of social and economic development. The electricity industry is a large and high-growth sector of the Romanian economy. In fact, the country is an electricity exporter to its neighbors. The future role of the country on the Balkan electricity market will depend on the new investments in electricity generation and transmission capacity planned for subsequent years, in order to substitute obsolete plants and to strengthen the position as an electricity producer and exporter country.

Thermal Conductivity Enhancement by Adding Nanoparticles to Ionic Liquids

Ionanofluids are a very new class of nanofluids having ionic liquids as the base fluid. Thermophysical properties of base ionic liquids (ILs) and nanoparticle enhanced ionic liquids (NEILs) are part of studying a new class of fluids for heat transfer. NEILs are formed by dispersing different volume fractions of nanoparticles in a base ionic liquid. In this article, only the thermal conductivity enhancement was considered for comparison of the different ionanofluids. NEILs show enhanced thermal conductivity compared to the base ILs. Maximum thermal conductivity enhancement was observed by adding 1 % MWCNT to [C4mim][(CF3SO2)2N] ionic liquid. However, if 0.05% MWCNT are added to [(C6)3PC14)][NTf2] no enhancement in thermal conductivity was noticed.

A Study on Uncertainties in Estimations of Thermal Conductivity of Alumina Nanofluids

An innovative way of improving the thermal conductivities of fluids is to suspend small solid particles in the fluids. Various types of powders such as metallic, non-metallic and polymeric particles can be added into fluids to form slurries. The thermal conductivities of fluids with suspended particles are expected to be higher than that of common fluids. Application of nanoparticles provides an effective way of improving heat transfer characteristics of fluids. By suspending nanophase particles in heating or cooling fluids, the heat transfer performance of the fluid can be significantly improved. Moreover, the thermal conductivity of nanofluid is strongly dependent on the nanoparticle volume fraction. So far it has been an unsolved problem to develop a sophisticated theory to predict thermal conductivity of nanofluids, although there are some semi empirical correlations to calculate the apparent conductivity of two-phase mixture. In this article few correlations were considered and differences were noted between different theories. In conclusion, a lot of uncertainties in determining thermal conductivity were noticed.

A review on analytical techniques for natural convection investigation in a heated closed enclosure: Case study

The aim of this paper is to present a theoretical analysis of a few convection problems. The investigations were started from the geometry of a classic muffle manufactured furnace. During this analytical study, different methodologies have been carefully chosen in order to compare and evaluate the effects of applying different analytical methods of the convection heat transfer processes. In conclusion, even if there are available a lot of analytical methods, natural convection in enclosed enclosures can be studied correctly only with numerical analysis. Also, in this article is presented a case study on natural convection application in a closed heated enclosure.

Influence of Microtube Heating Geometry on Behavior of an Alumina Nanofluid at Low Reynolds Numbers

A numerical program is employed to solve two-dimensional continuum-based governing differential equations for liquid flow in axisymmetric circular microchannel geometry. The effects of variable thermal properties in single-phase laminar forced convection with constant wall heat flux boundary conditions are studied. The numerical analysis of fully developed flow behavior investigates the effect of tube length on convection characteristics. The governing equations were discretized using the control volume method and solved numerically via the SIMPLE algorithm. Water - Al2O3nanofluids with different volume fractions ranged from 1% to 3% were used. This investigation covers Reynolds number in the range of 500 to 1500. The results have shown that convective heat transfer coefficient for a nanofluid is enhanced than that of the base liquid. Wall heat transfer flux is increasing with the particle volume concentration and Reynolds number. Moreover, a study on microtube length influence on heat transfer was attempted and few correlations were established. As a conclusion, a 6-11% decrease in heat transfer enhancement was noticed when the tube length is increasing in laminar flow.

A Study on Nanocomposites Behavior at Heating

Published literature is rich with investigations of mechanical properties of composites, but fewer publications are focused on thermal properties. Several publications addressing different theoretical approaches for predicting thermal conductivity of composite materials have been noted. However, one of the publications has discussed both transverse and axial thermal conductivity of a carbon fiber composite. A non-linear increase in the thermal conductivity was reported with the increase of fiber volume fraction of plain weaves and no theoretical models are able to predict this non-linearity. The result of literature search even further identified the necessity and importance of carrying out further investigations on thermal behavior of composites materials. Thermal conductivity of composites is anisotropic in nature and data about thermal conductivity of resin is known to reduce stresses related to shrinkage of composites during cure and mismatch in thermal expansion coefficients. Before conducting experiments to determine thermal conductivity of various composites, knowledge about effect of different parameters influencing thermal conductivity is essential. This paper deals with an analytical study on few nanocomposites behavior at heating.

A STUDY ON ENERGY CONSUMPTION IN ROMANIA

Romania is an upper-middle income European Union member economy of Central-Eastern Europe. It has been referred as a Tiger due to its high growth rates and rapid development. Romanian economic growth is among EU’s fastest. Romania has the 11th largest economy in the European Union by total nominal GDP and the 8th largest based on purchasing power parity and is one of the fastest growing markets in recent history with consistent annual GNP growth rates above 8%. With its emerging and rapidly growing economy and with a population of 21 million people, Romania has today become the world’s 49th largest economy. The country’s electricity consumption has risen in the last years as a result of social and economic development. The electricity industry is a large, high-growth sector in the Romanian economy. However, competition is still weak, mainly in the generation sector. There is a certain degree of competition in supply and trading of electricity, but substantial scandals have constantly accompanied the liberalization process. This article provides an overview of electricity consumption in Romania.