Claudio Cianfrini

A method for predicting non-uniform steady sound fields within spaces bounded by diffusive surfaces

Abstract A method for predicting non-uniform steady sound fields within spaces bounded by diffusive surfaces is presented. The definitions of the basic physical quantities employed as well as a detailed description of the methodology application are reported. An experimental verification of the model is conducted through measurements of the sound field due to a point source within rectangular ducts of different lengths. The comparison between theoretical predictions and experimental data shows a meaningful good agreement, thus proving the reliability and effectiveness of the method developed.

Correlating equations for laminar free convection from misaligned horizontal cylinders in interacting flow fields

Steady laminar free convection in air from a pair of misaligned, parallel horizontal cylinders, i.e., a pair of parallel cylinders with their axes set in a plane inclined with respect to the gravity vector, is studied numerically. A specifically developed computer code based on the SIMPLE-C algorithm is used for the solution of the dimensionless mass, momentum, and energy transfer governing equations. Results are presented for different values of the center-to-center cylinder spacing from 1.4 up to 10 diameters, the tilting angle of the two-cylinder array from 0 deg to 90 deg, and the Rayleigh number based on the cylinder diameter in the range between 10 3 and 10 7 . It is found that the heat transfer rates at both cylinder surfaces may in principle be traced back to the combined contributions of the so-called plume effect and chimney effect, which are the mutual interactions occurring in the vertical and horizontal alignments, respectively. In addition, at any misalignment angle, an optimum spacing between the cylinders for the maximum heat transfer rate, which decreases with increasing the Rayleigh number, does exist. Heat transfer dimensionless correlating equations are proposed for any individual cylinder and for the pair of cylinders as a whole.

Laminar free convection from a vertical plate with uniform surface heat flux in chemically reacting systems

Abstract Two-dimensional steady laminar free convection from a vertical plate with uniform surface heat flux rate is studied in a gas where a reversible very fast reaction of dissociation A ↔2 B takes place at atmospheric pressure. The effective thermophysical properties of the gas in the interval of dissociation are evaluated and the governing boundary-layer equations are solved numerically by a finite-difference method with control volume formulation for a wide range of values of the independent variables which have a significant influence on the phenomenon. In the case of undisturbed fluid temperature T ∞ smaller than T 0.5 , corresponding to a rate of dissociation α =0.5, three different heat transfer regimes, marked by two critical heat fluxes, may be distinguished as the surface heat flux rate increases. The theoretical results obtained for the critical heat fluxes as well as the coefficient of convection are expressed in terms of correlations among dimensionless parameters defined through the mixture effective properties.

Free Convection Heat Transfer from a Row of Horizontal Cylinders

Steady laminar free convection in air from parallel circular cylinders set side-by-side is studied numerically. The SIMPLE-C algorithm is used for the solution of the mass, momentum, and energy transfer governing equations. Simulations are performed for tube-arrays consisting of 10 equally-spaced cylinders, for different center-to-center separation distances in the range between 1.4 and 6 cylinder-diameters, and for Rayleigh numbers spanning between 101 and 105.

Screening performance of pairs of diffusively reflecting traffic noise barriers: theory and experiments

An easy-to-apply computational procedure for the study of the acoustic performance of pairs of diffusively reflecting roadside barriers is described in detail, and an experimental verification of its predictions, carried out on a 1:10 scale model, is presented and discussed. It is shown that, in comparison with pairs of more traditional specularly reflecting noise barriers, significant attenuation benefits are obtained not only in the shadow zone behind the barriers, but also in the unprotected zone immediately above the barriers, which proves that diffusive traffic faces of the barriers may effectively help in counteracting multiple reflection effects.

A COMPARATIVE STUDY OF THE COOLING PERFORMANCE OF NEW HVAC SYSTEMS BASED ON THE REVERSED AIR CYCLE

A numerical study on the cooling performance of new air-conditioning systems based on the reversed air cycle is conducted through a specifi cally developed computer code. The main peculiarity of such HVAC systems is the combination of the roles traditionally played separately by the chiller and the air handling unit, as the expanded cool air is directly supplied to the indoor ambient for its environmental control. For any system proposed, simulations have been carried out for a wide variety of psychrometric states of both outdoor air and supply air, and for different effi ciencies of the heat exchangers and the turbomachinery. Among the main results obtained, it is found that for hot and dry climates, as well as for temperate climates, the values of the cooling performance of the most advanced confi gurations are of the same order as those typical for traditional HVAC systems served by vapour-compression refrigerating units.

Natural Convection From a Pair of Parallel Horizontal Circular Cylinders Set in Free Air With Different Alignments

Steady laminar free convection in air from a pair of parallel horizontal cylinders set in a plane inclined with respect to the gravity vector, with the horizontal and vertical positions as special cases, is studied numerically. A specifically developed computer-code based on the SIMPLE-C algorithm is used for the solution of the dimensionless mass, momentum, and energy transfer governing equations. Results are presented for different values of the center-to-center cylinder spacing from 1.4 up to 10 diameters, the tilting angle of the array from 0° to 90°, and the Rayleigh number based on the cylinder-diameter in the range between 103 and 107 .Copyright

Steady laminar-free convection on a horizontal-axis convex corner

ABSTRACT An experimental analysis of the thermofluiddynamic field and heat transfer features for steady laminar free convection in air past to a geometrical discontinuity consisting of a horizontal-axis convex corner has been conducted. In previous works the thermal field, flow and heat transfer had been studied for a horizontal-edge convex dihedron both under isothermal and given internal heat production conditions; the overall behaviour of the dihedron resulting equivalent to a totally inclined flat plate with same angle of inclination of the upper wall element and convenient length, with exception of a region immediately beyond the geometrical discontinuity where a non-negligible lower plate-induced modification of the thermofluiddynamic field occurs. In the present paper the governing equations have been solved at a large distance from the discontinuity point in order to determine the asymptotic solutions. The thermofluiddynamic field and heat transfer properties specifically pertinent to the region interested by such a phenomenon have been experimentally investigated using the Schlieren method. A modification of the temperature and its gradient profiles inside the boundary layer as well as a thermal exchange capability reduction of the field-modification region has been detected.

Analysis of natural convection on a horizontal-edge convex dihedron with on-both-sides step discontinuity in heat production

ABSTRACT A theoretical and experimental analysis of local thermal field, flow and heat transfer is conducted for steady laminar free convection in air on a horizontal-edge convex dihedron. The dihedron consisting of two superimposed flat plates characterized by the same value of internal thermal resistance and different values of internal heat production near their boundary surface. A specific thermofluiddynamic model is defined and solved by a specific numeric method, referring the dihedron behaviour to that one of an equivalent wall inclined by the same angle of the upper plate, with step discontinuity in heat production at a distance from the leading edge depending on the angle of inclination of the wall. Moreover, the local thermal fields for different values of the dihedron angle, internal heat productions ratio and distance from the discontinuity point are investigated with a Schlieren method. The local profiles of temperature and temperature gradients along the normal to the walls inside the thermal boundary layer are experimentally obtained. Calculations are made for the local convection coefficient values and the experimental correlations between dimensionless parameters are pointed out.