Salvatore Tamburrino

Numerical Investigation on Mixed Convection in Triangular Cross-Section Ducts with Nanofluids

Convective heat transfer can be enhanced passively by changing flow geometry and boundary conditions or by improving the thermal conductivity of the working fluid, for example, introducing suspended small solid nanoparticles. In this paper, a numerical investigation on laminar mixed convection in a water-Al2O3-based nanofluid, flowing in a triangular cross-sectioned duct, is presented. The duct walls are assumed at uniform temperature, and the single-phase model has been employed in order to analyze the nanofluid behaviour. The hydraulic diameter is equal to 0.01 m. A fluid flow with different values of Richardson number and nanoparticle volume fractions has been considered. Results show the increase of average convective heat transfer coefficient and Nusselt number for increasing values of Richardson number and particle concentration. However, also wall shear stress and required pumping power profiles grow significantly.

Numerical investigation on sensible thermal energy storage with porous media for high temperature solar systems

In this paper different high temperature TES components are numerically analyzed. The difference is defined by the different type of porous medium employed in the storage. Two different porous media are considered: spheres or foams. In all cases a ceramic material is considered. In the formulation of the model it is assumed that the system geometry is cylindrical, the fluid and the solid thermophysical properties are temperature independents, the radiation heat transfer mechanism is taken into account. The commercial CFD Fluent code is used to solve the governing equations in transient regime and in local thermal non-equilibrium (LTNE). Numerical simulations are carried out at different mass flow rates of the heat-carrying fluid. The results show the effects of the porosity and of the working fluid mass flow rate on the stored thermal energy and on the storage time.

Numerical Study of Transient Natural Convection in Air in Vertical Divergent Channels

This article carries out a numerical, transient, two-dimensional analysis of natural convection in air in a divergent channel, characterized by two inclined flat plates heated at a uniform heat flux. The flow is assumed to be laminar and incompressible. Simulations allow to detect the complex structures of the flow inside and outside the channel. Results, in terms of temperature distributions, average Nusselt and Reynolds profiles, depending on time as a function of the divergence angle and channel spacing, are presented. Flow visualizations and stream function contours confirmed the disturbances inside the channel for the highest divergence angles (>5°). Correlations in terms of Nusselt numbers as a function of Rayleigh and Rayleigh modified numbers, ranging from 7.6 × 102 to 1.3 × 109 and from 30 to 8.2 × 108, respectively, were proposed. They were in very good agreement with the experimental relations.

Effect of Solid Thickness on Transient Heat Conduction in Workpieces Irradiated by a Moving Heat Source

In this paper a three dimensional conductive field is analyzed and solved by means of the COMSOL Multiphysics code. The investigated work-pieces are made up of a simple brick-type solid. A laser source with combined donut-Gaussian distributions is considered moving with a constant velocity along motion direction. The solid dimension along the motion direction is assumed to be infinite or semi-infinite, while finite width (2ly) and thickness (s) are considered. Thermal properties are considered temperature dependent and the materials are considered isotropic. Surface heat losses toward the ambient are taken into account. Results are presented in terms of profile temperature to evaluate the effect of solid thickness.

Heat Transfer Behaviors of Thermal Energy Storages for High Temperature Solar Systems

Solar energy is an important alternative energy source that will likely be utilized in the future. One main limiting factor in the application of solar energy is its cyclic time dependence. Therefore, solar systems require energy storage to provide energy during the night and overcast periods. Although the need of thermal energy storage also exists for many other thermal applications, it is particularly notable for solar applications. It can improve the efficient use and provision of thermal energy whenever there is a mismatch between energy generation and use. In sensible thermal storage, energy is stored by changing the temperature of a storage medium. The amount of energy input to thermal energy storage by a sensible heat device is proportional to the difference between the storage final and initial temperatures, the mass of storage medium and its heat capacity. Each medium and porous matrix has its own advantages and disadvantages.

Numerical Analysis on Nanofluid Mixed Convection in Triangular Ducts Heated by a Constant Heat Flux

The enhancement of heat transfer represents a very important issue regarding several industrial heating or cooling equipments. This goal can be achieved by means of different techniques; for example, by adopting passive methods like changing flow geometries or by enhancing the thermal conductivity of the working fluids. Thus, an innovative way of improving the thermal conductivity of base fluids consists into introduce suspended small solid nanoparticles.In this paper a numerical investigation on laminar mixed convection with Al2O3/water based nanofluids in a triangular channel is presented. Duct surfaces were heated by means of a constant and uniform heat flux. The analysis was performed in laminar steady state regime for particle size in nanofluids equal to 38 nm, by adopting a single-phase model approach. The base fluid was water and alumina (Al2O3) nanoparticles were dispersed at different concentrations. Different Richardson number values were considered in order to solve a 3-D model of triangular duct. Results are presented for the fully developed regime flow in terms of surface shear stress and heat transfer convective coefficient, Nusselt number and required pumping power profiles. Comparisons with results related to the fluid dynamic and thermal behaviors are carried out in order to evaluate the enhancement due to the presence of nanoparticles in terms of volumetric concentration. The increase of average convective heat transfer coefficients and Nusselt number values for increasing values of Richardson number and particle concentration is observed by analyzing the obtained results. However, also wall shear stress and required pumping power profiles increase as expected.Copyright

Numerical Investigation on Nanofluid Mixed Convection in Triangular Ducts Heated by a Uniform Heat Flux

Heat transfer enhancement technology covers a very important role in designing efficient heating and cooling equipments. This goal can be achieved by means of different techniques. Convective heat transfer can be improved actively or passively, for example, by adopting special surfaces or by increasing the thermal conductivity of the working fluids. Thus, the use of suspended solid nanoparticles in the working fluids can be taken into account. In this paper a numerical investigation on laminar mixed convection with Al2O3/water based nanofluids in a triangular channel is presented. A uniform and constant heat flux on the channel surfaces is assumed and the single-phase model approach has been employed in order to describe the nanofluid behaviour. The analysis has been performed in the steady state regime for particle size in nanofluids equal to 30 nm. The CFD code Fluent has been employed in order to solve the three-dimensional numerical model and different Richardson number values and nanoparticle volume fractions have been considered. Results are presented for the fully developed regime flow. The increase of average convective heat transfer coefficients and Nusselt number values for increasing values of Richardson number and particle concentration is observed by analyzing the obtained results. However, also wall shear stress and required pumping power profiles increase as expected.Copyright

Thermal Energy Storages Analysis for High Temperature in Air Solar Systems

In this paper a high temperature thermal storage in a honeycomb solid matrix is numerically investigated and a parametric analysis is accomplished. In the formulation of the model it is assumed that the system geometry is cylindrical, the fluid and the solid thermophysical properties are temperature independent and radiative heat transfer is take into account whereas the effect of gravity are neglected. Air is employed as the working fluid and the solid material is cordierite. The evaluation of the fluid and thermal behaviors are accomplished assuming the honeycomb as a porous medium. The Brinkman-Forchheimer-extended Darcy model is used in the governing equations and the local thermal non equilibrium is assumed. The commercial CFD Fluent code is used to solve the governing equations in transient regime. Numerical simulations are carried out with storage medium at different mass flow rates of the working fluid and different porosity values. Results show the effects of storage medium, different porosity values, porosity effect and mass flow rate on stored thermal energy and storage time. Results in terms of temperature profiles and stored thermal energy as function of time are presented.Copyright

Numerical Simulation of Transient Temperature Fields in Solids Irradiated by Moving Gaussian and Donut Sources

This work presents a three-dimensional heat transfer model developed for laser material processing with a moving Gaussian and donut heat sources, using Comsol Multhiphysics 3.5 code. The laser beam, having a defined power distribution, strikes the surface of an opaque substrate of semi infinite length but finite width and depth moving with a uniform velocity in the positive axial direction. The solid dimension along the motion direction is assumed to be infinite or semi-infinite, while a finite width and thickness are considered. Thermal properties are considered temperature dependent. Surface heat losses toward the ambient are taken into account. The results are presented in terms of temperature profiles and thermal fields are given for some Biot and material thicknesses at a constant Peclet number.

Effect of Impinging Jet on Heat Conduction in Workpieces Irradiated by a Moving Heat Source

A three dimensional conductive field is analyzed and solved by means of the COMSOL Multiphysics code. The investigated work-pieces are made up of a simple brick-type solid. A laser source with combined donut-Gaussian distributions is considered moving with a constant velocity along motion direction. The solid dimension along the motion direction is assumed to be infinite or semi-infinite, while finite width (2ly) and thickness (s) are considered. Thermal properties are considered temperature dependent and the materials are considered isotropic. Surface heat losses toward the ambient are taken into account. Several convective heat flux values on the upper surface, with corresponding Biot numbers, and Peclet numbers are considered with negligible radiative heat losses.Results are presented in terms of profile temperatures to evaluate the effect of impinging jet.