2011 17th International Workshop on Thermal Investigations of Ics and Systems, Sep 1, 2011
Abstract In this paper a numerical investigation is carried out on confined impinging slot-jets w... more Abstract In this paper a numerical investigation is carried out on confined impinging slot-jets with nanofluids on a horizontal heated surface at uniform temperature. The cooling fluid is a nanofluid water/Al 2 O 3 and it is assumed with constant thermo-physical proprieties. The single-phase model is employed and the flow regime is laminar. Different values of the channel height and diameter of nanoparticles are investigated. Results show the increase of Nusselt number together with pumping power.
Energy Sources Part B Economics Planning and Policy, Oct 1, 2012
Abstract The influence of economic and demographic variables on the annual electricity consumptio... more Abstract The influence of economic and demographic variables on the annual electricity consumption in Italy has been investigated in order to develop a simple and data light electricity consumption forecasting model, to be used as part of more complex planning tools. The time period considered for the historical data is from 1970–2007. Multiple and single regression models are developed using historical electricity consumption, gross domestic product (GDP), GDP per capita, and population. Annual electricity consumption ...
ABSTRACT In open cavity receivers employed in solar paraboloidal dish applications, natural conve... more ABSTRACT In open cavity receivers employed in solar paraboloidal dish applications, natural convection occurs and contributes a significant fraction of energy loss. Its characteristics hence need to be clarified so that it can be effectively minimized in order to improve the system efficiency. The investigation of natural convection loss from cavity receivers was undertaken numerically and was validated using the published experimental results for four different receiver geometries. A good agreement between experimental and numerical results was obtained. Furthermore, the numerical results of all receivers were qualitatively comparable to the predictions by other available correlations hitherto, although it was found that each correlation has a limited range of applicability arising from the particular cavity geometry and experimental conditions used to derive it. To address this shortcoming, a new correlation based on the numerical results for three of the above four receivers has been proposed. The correlation employs a new concept of an ensemble cavity length scale, to take into account the combined effects of cavity geometry and inclination. Despite a wide variety of cavity geometries and operating conditions, the proposed correlation predicts approximately 50% of the data within +/- 20% and 90% of the data within +50%. This is better than any of the other correlations published to date. The new correlation is also simpler to use than the most accurate of those previously published. [DOI: 10.1115/1.4003582]
Design and thermal control of tilted channels in air natural convection requires knowledge of rel... more Design and thermal control of tilted channels in air natural convection requires knowledge of relations between process parameters. Composite correlations of average Nusselt number in terms of channel Rayleigh number (10 Ra 9.0 104) are proposed for inclined channels with uniform symmetric or asymmetric heat flux. The thermal radiative effects are taken into account in modified Nusselt and Rayleigh numbers. The surface emissivities considered are 0.05 and 0.8. Experimental data employed to obtain the proposed correlations are in good ...
2010 14th International Heat Transfer Conference, Volume 2, 2010
Heat transfer enhancement technology has the aim to develop more efficient systems as demanded in... more Heat transfer enhancement technology has the aim to develop more efficient systems as demanded in many applications, like heat exchangers for refrigeration, automotives, process industry, solar heater etc.. Convective heat transfer may be enhanced passively by adopting different solutions. A possibility for increasing the heat transfer is to employ rough surfaces. When a fluid flows in a channel, ribs break the laminar sub-layer and create local turbulence, due to flow separation and reattachment between consecutive ribs, which ...
This paper addresses the problem of natural convection cooled channels heated with flush-mounted ... more This paper addresses the problem of natural convection cooled channels heated with flush-mounted discrete heat sources: this configuration is more realistic for the modelization of the cooling of electronic devices. The two-dimensional, laminar and steady-state problem is ...
Http Dx Doi Org 10 1080 01457630304027, Nov 30, 2010
The influence of axial fluid conduction on low Péclet number flows in the thermal entrance region... more The influence of axial fluid conduction on low Péclet number flows in the thermal entrance region of long circular tubes is investigated in this theoretical study. The convective heat transport of viscous fluids relates to a specific condition under which the first part of the tube ( x h 0) is insulated and the second part of the tube ( x > 0) receives a heat flux of uniform intensity. A conjugate one-dimensional lumped model produces a solution of compressed algebraic form that is able to deliver dependable mean bulk temperatures that are in perfect agreement with those obtained numerically by the formal conjugate two-dimensional distributed model. As a by-product of the succession of algebraic calculations within the platform of the lumped model, the critical Péclet number Pe cr has been easily quantified. This number is a figure-of-merit of remarkable importance in the modeling of forced heat convection in tubes because it establishes the threshold between two contrasting situations: one embracing axial fluid conduction (finite Pe) and the other implicating negligible axial fluid conduction (Pe M X ). In addition, the local wall temperatures were calculated with an approximate engineering procedure, showing good agreement with those determined numerically by the formal conjugate two-dimensional distributed model.
Volume 2: Theory and Fundamental Research; Aerospace Heat Transfer; Gas Turbine Heat Transfer; Computational Heat Transfer, 2009
Heat transfer in fluids is very important in many industrial heating and cooling equipments. Conv... more Heat transfer in fluids is very important in many industrial heating and cooling equipments. Convective heat transfer can be enhanced passively by changing flow geometry, boundary conditions or by increasing thermal conductivity of the fluid. Another possibility for increasing heat transfer with gas is to employ extended surfaces. When a fluid flows in a channel, transversal ribs can be used as fins and break the laminar sublayer creating local wall turbulence. However, as a consequence the presence of the ribs can significantly ...
Volume 4: Fatigue and Fracture, Heat Transfer, Internal Combustion Engines, Manufacturing, and Technology and Society, 2006
ABSTRACT In this paper a parametric analysis of natural convection in air in a channel-chimney sy... more ABSTRACT In this paper a parametric analysis of natural convection in air in a channel-chimney system symmetrically heated at uniform heat flux, obtained by means of a numerical simulation, is carried out. The analysed regime is two-dimensional, laminar and steady-state. The numerical procedure employs the full Navier-Stokes and energy equations in terms of the stream function-vorticity approach. Results are presented in terms of wall temperature profiles in order to show the more thermally convenient configurations which correspond to the channel-chimney system with the lowest maximum wall temperature. The analysis is obtained for a Rayleigh number in the range between 102 and 105 , for a channel aspect ratio equal to 5, 10 and 20 and the extension and expansion ratios between 1.0 and 4.0. Correlations for dimensionless mass flow rate, maximum wall temperature and average Nusselt number in terms of Rayleigh number, aspect ratio, extension and expansion ratios are presented. Geometric optimal configurations, for assigned Rayleigh number and aspect ratio, are estimated as a function of the extension ratio. For considered Rayleigh number the difference between the highest and the lowest maximum wall temperatures increases increasing the channel aspect ratio. This behaviour is as greater as the extension ratio is. These differences decrease significantly for the highest Rayleigh number value. The optimal expansion ratio values depend strongly on Rayleigh number and extension ratio values and slightly on the aspect ratio.
This paper is a report on an experimental investigation on a solar chimney that follows previous ... more This paper is a report on an experimental investigation on a solar chimney that follows previous studies of the same authors. The system herein tested is a simple natural circulation solar air loop without storage. System measured performances are shown including most significant system parameters and climatic variables. First results of a flow visualization study evidence turbulent flow characters. Empirical
2011 17th International Workshop on Thermal Investigations of Ics and Systems, Sep 1, 2011
Abstract In this paper a numerical investigation is carried out on confined impinging slot-jets w... more Abstract In this paper a numerical investigation is carried out on confined impinging slot-jets with nanofluids on a horizontal heated surface at uniform temperature. The cooling fluid is a nanofluid water/Al 2 O 3 and it is assumed with constant thermo-physical proprieties. The single-phase model is employed and the flow regime is laminar. Different values of the channel height and diameter of nanoparticles are investigated. Results show the increase of Nusselt number together with pumping power.
Energy Sources Part B Economics Planning and Policy, Oct 1, 2012
Abstract The influence of economic and demographic variables on the annual electricity consumptio... more Abstract The influence of economic and demographic variables on the annual electricity consumption in Italy has been investigated in order to develop a simple and data light electricity consumption forecasting model, to be used as part of more complex planning tools. The time period considered for the historical data is from 1970–2007. Multiple and single regression models are developed using historical electricity consumption, gross domestic product (GDP), GDP per capita, and population. Annual electricity consumption ...
ABSTRACT In open cavity receivers employed in solar paraboloidal dish applications, natural conve... more ABSTRACT In open cavity receivers employed in solar paraboloidal dish applications, natural convection occurs and contributes a significant fraction of energy loss. Its characteristics hence need to be clarified so that it can be effectively minimized in order to improve the system efficiency. The investigation of natural convection loss from cavity receivers was undertaken numerically and was validated using the published experimental results for four different receiver geometries. A good agreement between experimental and numerical results was obtained. Furthermore, the numerical results of all receivers were qualitatively comparable to the predictions by other available correlations hitherto, although it was found that each correlation has a limited range of applicability arising from the particular cavity geometry and experimental conditions used to derive it. To address this shortcoming, a new correlation based on the numerical results for three of the above four receivers has been proposed. The correlation employs a new concept of an ensemble cavity length scale, to take into account the combined effects of cavity geometry and inclination. Despite a wide variety of cavity geometries and operating conditions, the proposed correlation predicts approximately 50% of the data within +/- 20% and 90% of the data within +50%. This is better than any of the other correlations published to date. The new correlation is also simpler to use than the most accurate of those previously published. [DOI: 10.1115/1.4003582]
Design and thermal control of tilted channels in air natural convection requires knowledge of rel... more Design and thermal control of tilted channels in air natural convection requires knowledge of relations between process parameters. Composite correlations of average Nusselt number in terms of channel Rayleigh number (10 Ra 9.0 104) are proposed for inclined channels with uniform symmetric or asymmetric heat flux. The thermal radiative effects are taken into account in modified Nusselt and Rayleigh numbers. The surface emissivities considered are 0.05 and 0.8. Experimental data employed to obtain the proposed correlations are in good ...
2010 14th International Heat Transfer Conference, Volume 2, 2010
Heat transfer enhancement technology has the aim to develop more efficient systems as demanded in... more Heat transfer enhancement technology has the aim to develop more efficient systems as demanded in many applications, like heat exchangers for refrigeration, automotives, process industry, solar heater etc.. Convective heat transfer may be enhanced passively by adopting different solutions. A possibility for increasing the heat transfer is to employ rough surfaces. When a fluid flows in a channel, ribs break the laminar sub-layer and create local turbulence, due to flow separation and reattachment between consecutive ribs, which ...
This paper addresses the problem of natural convection cooled channels heated with flush-mounted ... more This paper addresses the problem of natural convection cooled channels heated with flush-mounted discrete heat sources: this configuration is more realistic for the modelization of the cooling of electronic devices. The two-dimensional, laminar and steady-state problem is ...
Http Dx Doi Org 10 1080 01457630304027, Nov 30, 2010
The influence of axial fluid conduction on low Péclet number flows in the thermal entrance region... more The influence of axial fluid conduction on low Péclet number flows in the thermal entrance region of long circular tubes is investigated in this theoretical study. The convective heat transport of viscous fluids relates to a specific condition under which the first part of the tube ( x h 0) is insulated and the second part of the tube ( x > 0) receives a heat flux of uniform intensity. A conjugate one-dimensional lumped model produces a solution of compressed algebraic form that is able to deliver dependable mean bulk temperatures that are in perfect agreement with those obtained numerically by the formal conjugate two-dimensional distributed model. As a by-product of the succession of algebraic calculations within the platform of the lumped model, the critical Péclet number Pe cr has been easily quantified. This number is a figure-of-merit of remarkable importance in the modeling of forced heat convection in tubes because it establishes the threshold between two contrasting situations: one embracing axial fluid conduction (finite Pe) and the other implicating negligible axial fluid conduction (Pe M X ). In addition, the local wall temperatures were calculated with an approximate engineering procedure, showing good agreement with those determined numerically by the formal conjugate two-dimensional distributed model.
Volume 2: Theory and Fundamental Research; Aerospace Heat Transfer; Gas Turbine Heat Transfer; Computational Heat Transfer, 2009
Heat transfer in fluids is very important in many industrial heating and cooling equipments. Conv... more Heat transfer in fluids is very important in many industrial heating and cooling equipments. Convective heat transfer can be enhanced passively by changing flow geometry, boundary conditions or by increasing thermal conductivity of the fluid. Another possibility for increasing heat transfer with gas is to employ extended surfaces. When a fluid flows in a channel, transversal ribs can be used as fins and break the laminar sublayer creating local wall turbulence. However, as a consequence the presence of the ribs can significantly ...
Volume 4: Fatigue and Fracture, Heat Transfer, Internal Combustion Engines, Manufacturing, and Technology and Society, 2006
ABSTRACT In this paper a parametric analysis of natural convection in air in a channel-chimney sy... more ABSTRACT In this paper a parametric analysis of natural convection in air in a channel-chimney system symmetrically heated at uniform heat flux, obtained by means of a numerical simulation, is carried out. The analysed regime is two-dimensional, laminar and steady-state. The numerical procedure employs the full Navier-Stokes and energy equations in terms of the stream function-vorticity approach. Results are presented in terms of wall temperature profiles in order to show the more thermally convenient configurations which correspond to the channel-chimney system with the lowest maximum wall temperature. The analysis is obtained for a Rayleigh number in the range between 102 and 105 , for a channel aspect ratio equal to 5, 10 and 20 and the extension and expansion ratios between 1.0 and 4.0. Correlations for dimensionless mass flow rate, maximum wall temperature and average Nusselt number in terms of Rayleigh number, aspect ratio, extension and expansion ratios are presented. Geometric optimal configurations, for assigned Rayleigh number and aspect ratio, are estimated as a function of the extension ratio. For considered Rayleigh number the difference between the highest and the lowest maximum wall temperatures increases increasing the channel aspect ratio. This behaviour is as greater as the extension ratio is. These differences decrease significantly for the highest Rayleigh number value. The optimal expansion ratio values depend strongly on Rayleigh number and extension ratio values and slightly on the aspect ratio.
This paper is a report on an experimental investigation on a solar chimney that follows previous ... more This paper is a report on an experimental investigation on a solar chimney that follows previous studies of the same authors. The system herein tested is a simple natural circulation solar air loop without storage. System measured performances are shown including most significant system parameters and climatic variables. First results of a flow visualization study evidence turbulent flow characters. Empirical
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