The use of innovative methods for the design of heating, cooling, and heat storage devices has be... more The use of innovative methods for the design of heating, cooling, and heat storage devices has been mainly oriented in the last decade toward the use of nanofluids, metal foams coupled with working fluids, or phase change materials (PCMs). A network of nine Italian universities achieved significant results and innovative ideas on these topics by developing a collaborative project in the last four years, where different approaches and investigation techniques were synergically employed. They evaluated the quantitative extent of the enhancement in the heat transfer and thermal performance of a heat exchanger or thermal energy storage system with the combined use of nanofluids, metal foams, and PCMs. The different facets of this broad research program are surveyed in this article. Special focus is given to the comparison between the mesoscopic to macroscopic modeling of heat transfer in metal foams and nanofluids, as well as to the experimental data collected and processed in the devel...
Abstract A numerical investigation on turbulent forced convection in nanofluid mixture, water–Al2... more Abstract A numerical investigation on turbulent forced convection in nanofluid mixture, water–Al2O3, in a symmetrically heated channel with ribbed upper and lower walls is carried out. Different geometric rib arrangements with triangular, rectangular and trapezoidal shapes are analyzed. The governing equations are written assuming the mixture model to describe the nanofluid behavior in a two dimensional channel heated by a constant wall heat flux. Finite volume method is used to solve the model equations. Simulations for different nanoparticle volumetric concentrations from 0%, pure water, to 4% and Reynolds numbers between 20,000 and 60,000 are accomplished. As general conclusion, it is observed that the heat transfer rate increases as nanoparticle volume fraction and Reynolds number increase but higher pumping powers are required. The comparisons allow to determine that triangular ribs present higher thermal performances than the trapezoidal ones but also higher pressure losses. Moreover, the rectangular-trapezoidal-shaped rib shows the best performance at a pitch–rib height equal to 10.
In this study, a numerical investigation of mixed convection in air in an open ended cavity, with... more In this study, a numerical investigation of mixed convection in air in an open ended cavity, with a moving plate parallel to the cavity open surface, is carried out. The moving plate has a constant velocity, whereas a vertical plate of the open cavity is heated at uniform heat flux. All the other walls are adiabatic. The numerical analysis is obtained by means of the commercial code FLUENT. Two configurations, assisting and opposing, are analyzed. In the assisting configuration, natural convection is supported by the plate motion, whereas, in the opposing configuration, natural convection and plate motion have opposing effects. The effect of different geometrical parameters, heat flux and moving plate velocity are analyzed. Results in terms of heated plate and moving plate temperature profiles are presented and simple monomial correlation equations for both the configurations are proposed between the terms Nu/Re0.6 and Ri.
This paper addresses the examination of heat transfer in parallel-plate channels using a combinat... more This paper addresses the examination of heat transfer in parallel-plate channels using a combination of two passive schemes: (1) the insertion of an auxiliary plate at the mouth and (2) the appendage of colinear insulated plates at the exit. The investigation is made by numerically solving the full elliptic Navier-Stokes and energy equation in a I-type computational domain. The channel is symmetrically heated by uniform heat flux. The working fluid is air. The results are reported in terms of induced mass flow rate and maximum wall temperatures. Further, the local Nusselt number, the mean Nusselt number and pressure profiles are presented. The analyzed Grashof numbers based on the heated plate height are 103 and 106.
ABSTRACT In this paper a high temperature thermal storage in a honeycomb solid matrix is numerica... more ABSTRACT 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 thermo physical properties are temperature independent and radiative heat transfer is taken into account whereas the effect of gravity is neglected. Air is employed as working fluid and the solid material is cordierite. The evaluation of the fluid dynamic and thermal behaviors is 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 for different mass flow rates of the working fluid and different porosity values. Results in terms of temperature profiles, temperatures fields and stored thermal energy as function of time are presented. The effects of storage medium, different porosity values and mass flow rate on stored thermal energy and storage time are shown.
The use of innovative methods for the design of heating, cooling, and heat storage devices has be... more The use of innovative methods for the design of heating, cooling, and heat storage devices has been mainly oriented in the last decade toward the use of nanofluids, metal foams coupled with working fluids, or phase change materials (PCMs). A network of nine Italian universities achieved significant results and innovative ideas on these topics by developing a collaborative project in the last four years, where different approaches and investigation techniques were synergically employed. They evaluated the quantitative extent of the enhancement in the heat transfer and thermal performance of a heat exchanger or thermal energy storage system with the combined use of nanofluids, metal foams, and PCMs. The different facets of this broad research program are surveyed in this article. Special focus is given to the comparison between the mesoscopic to macroscopic modeling of heat transfer in metal foams and nanofluids, as well as to the experimental data collected and processed in the devel...
Abstract A numerical investigation on turbulent forced convection in nanofluid mixture, water–Al2... more Abstract A numerical investigation on turbulent forced convection in nanofluid mixture, water–Al2O3, in a symmetrically heated channel with ribbed upper and lower walls is carried out. Different geometric rib arrangements with triangular, rectangular and trapezoidal shapes are analyzed. The governing equations are written assuming the mixture model to describe the nanofluid behavior in a two dimensional channel heated by a constant wall heat flux. Finite volume method is used to solve the model equations. Simulations for different nanoparticle volumetric concentrations from 0%, pure water, to 4% and Reynolds numbers between 20,000 and 60,000 are accomplished. As general conclusion, it is observed that the heat transfer rate increases as nanoparticle volume fraction and Reynolds number increase but higher pumping powers are required. The comparisons allow to determine that triangular ribs present higher thermal performances than the trapezoidal ones but also higher pressure losses. Moreover, the rectangular-trapezoidal-shaped rib shows the best performance at a pitch–rib height equal to 10.
In this study, a numerical investigation of mixed convection in air in an open ended cavity, with... more In this study, a numerical investigation of mixed convection in air in an open ended cavity, with a moving plate parallel to the cavity open surface, is carried out. The moving plate has a constant velocity, whereas a vertical plate of the open cavity is heated at uniform heat flux. All the other walls are adiabatic. The numerical analysis is obtained by means of the commercial code FLUENT. Two configurations, assisting and opposing, are analyzed. In the assisting configuration, natural convection is supported by the plate motion, whereas, in the opposing configuration, natural convection and plate motion have opposing effects. The effect of different geometrical parameters, heat flux and moving plate velocity are analyzed. Results in terms of heated plate and moving plate temperature profiles are presented and simple monomial correlation equations for both the configurations are proposed between the terms Nu/Re0.6 and Ri.
This paper addresses the examination of heat transfer in parallel-plate channels using a combinat... more This paper addresses the examination of heat transfer in parallel-plate channels using a combination of two passive schemes: (1) the insertion of an auxiliary plate at the mouth and (2) the appendage of colinear insulated plates at the exit. The investigation is made by numerically solving the full elliptic Navier-Stokes and energy equation in a I-type computational domain. The channel is symmetrically heated by uniform heat flux. The working fluid is air. The results are reported in terms of induced mass flow rate and maximum wall temperatures. Further, the local Nusselt number, the mean Nusselt number and pressure profiles are presented. The analyzed Grashof numbers based on the heated plate height are 103 and 106.
ABSTRACT In this paper a high temperature thermal storage in a honeycomb solid matrix is numerica... more ABSTRACT 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 thermo physical properties are temperature independent and radiative heat transfer is taken into account whereas the effect of gravity is neglected. Air is employed as working fluid and the solid material is cordierite. The evaluation of the fluid dynamic and thermal behaviors is 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 for different mass flow rates of the working fluid and different porosity values. Results in terms of temperature profiles, temperatures fields and stored thermal energy as function of time are presented. The effects of storage medium, different porosity values and mass flow rate on stored thermal energy and storage time are shown.
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Papers by Assunta Andreozzi