Massimo Paroncini

Effect of Heat Transfer on Natural Convection in a Square Cavity With Two Source Pairs

In this paper, the influence of a small heating source, positioned in the lateral walls of a square cavity, is investigated. Numerical and experimental analyses are performed to investigate natural convection heat transfer in a square cavity heated by hot strips in the side walls. The H side square cavity is filled with air and heated by two hot strips with heights of H/4. The effect of placing the hot strips at two different positions is evaluated. The temperature distribution and the Nusselt numbers at different Rayleigh numbers are experimentally measured using both real-time and double-exposure holographic interferometry. The isothermal patterns obtained through the holographic interferometry are compared with the temperature and velocity fields from a numerical study performed using the finite-volume code Fluent.

The Natural Convective Heat Transfer in a Partially Divided Enclosure: A Study on the Influence of the Source Position

The aim of this paper is to analyse the natural convective heat transfer generated by a source with a height of 𝜁 located in two different positions inside a square enclosure of side 𝐻. In the first case, 𝛿 is 0.5 of 𝐻 while in the second case it is 0.4. The comparison is based both on the evaluation of the local and average Nusselt numbers at different Rayleigh numbers and on the study of the velocity fields at the same Rayleigh numbers in the two different configurations. The experimental analysis was carried out through a holographic interferometry, to study the heat transfer, and through a 2D-PIV system, to analyse the dynamic behaviour of the phenomenon. Finally, for 𝛿 = 0.5 we compared the experimental results with those obtained through the volume finite software Fluent 6.3.26. In the analysis, it is possible to see that the position of the source influences both the average Nusselt numbers on the hot surfaces and the development of a small bubble on the upper surface.

A 2D-PIV Study on Natural Convective Heat Transfer in a Square Enclosure With Partially Active Side Walls

The present study is an experimental and numerical analysis on the natural convection of air in square enclosures with partially active side walls. The experimental equipment is based on two different systems: an holographic interferometer and a 2D-PIV. The test cell is a square enclosure filled of air with vertical partially active side walls at different temperatures. The hot and cold regions on these sides are located in the middle of the cavity. The remaining vertical walls are made up of glass to allow an optical access to the cavity. The top and bottom surfaces of the enclosure are made up of plexiglas to reduce heat leakages. The experimental study is carried out both through the holographic interferometry, in order to obtain the average Nusselt numbers at different Rayleigh numbers, and through the 2D-PIV, in order to analyse the dynamic behaviour of the phenomenon at the same Rayleigh numbers. The average Nusselt numbers are obtained measuring the temperature distribution in the air layer trough the real-time and double-exposure holographic interferometry; the dynamic structures are the velocity vector distribution, the streamlines and the velocity maps. Finally these experimental data are compared to the results obtained through a numerical study carried out using the finite volume code, Fluent 6.2.3. The aim of this comparison is the validation of the numerical procedure. In this way it is possible to use the numerical code to enlarge the Rayleigh number range.Copyright

Free Convection in Air-Filled Cavity With a Localized Heater From Below and Cooling Lateral Walls

The paper investigates the development of natural convection in air-filled square enclosure with a heat source flush mounted on the lower horizontal surface; the cavity is symmetrically cooled from the lateral walls. The experimental analysis has been carried out with the real time holographic interferometry that makes possible the investigation of the development of the convective phenomenon, and with the double exposure technique in order to obtain the temperature distribution inside the cavity at the steady-state. The experimental analysis allows the study of a limited range of Rayleigh numbers from about 1.63·104 to 2.8·105 . On the contrary the numerical investigation makes possible to enlarge the analysis to a more wide range of Rayleigh numbers; thus the experimental analysis, has been integrated with the numerical results provided by the investigation with the commercial finite volume software Fluent 6.0. for Rayleigh number from 103 to 106 . Different convective forms have been obtained depending on Ra, on the heat source length and on its position. The Nusselt number has been evaluated on the heater; graphs with relations between average Nu, Ra, the heat source length and its position are finally presented.Copyright

Natural Convection in Square Cavities Heating From Below: Investigation of Three Different Values of the Heat Source Length

The objective of the present study is to gain some insight into fluid motion and heat transfer phenomena in the case of a square enclosure heated from below and symmetrically cooled from the sides; the effects of different values of the heat source is experimentally investigated. The localized heating is a centrally located heat source on the bottom wall; three different values of the heat source length (1/5, 2/5, 3/5 of the wall) are considered. The test cell is a square enclosure filled with air with isothermal side walls at equal temperatures Tc ; the remaining vertical walls are realized with glass to allow optical access to the cavity. The top and bottom surfaces of the enclosure are made of plexiglass and, except for the heated section, are considered to be adiabatic. The located heat source is assumed to be isothermal at a temperature Th . The temperature distribution is experimentally measured by real-time and double-exposure holographic interferometry. The real-time technique is used in order to reveal the presence of plume oscillations while the double-exposure technique is used for steady-state measurements. Holographic interferometry shows the typical advantages over the classical optical techniques, such as high precision and sensitivity, very low noise level, and the possibility of displaying the temperature distribution across the whole investigated region. The objective of the heat transfer analysis is the experimental investigation of the Nusselt number distribution around the cavity at various Rayleigh numbers and several dimensions of the heat source. Different convection forms were obtained depending on Ra and on the heat source length. The Nusselt number was evaluated on the heat source surface and it showed a symmetrical form rising near the heat source borders.Copyright

Effects of the Dimension of a Localized Heat Source on the Natural Convection in Square Enclosures: Comparison Between Numerical and Experimental Investigation

The present study investigates experimentally and numerically the natural convection of air in square enclosures with a localized heat source from below and symmetrical cooling from the sides. The heat source was centered on the bottom wall and the study analysed the effect of the variation in the heat source length on the natural convection inside the square cavity; the length of the heat source investigated are 1/5 and 2/5 of the wall The cooling was achieved by the two vertical walls and all the other zones were adiabatic; the symmetrical cooling from the sides is expected to be an efficient cooling option while the partial heating at the lower surface simulates the electronic components such as a chip. The experimental data are obtained by measuring the temperature distribution in the air layer by the real-time and double-exposure holographic interferometry and the numerical investigation was conducted using the commercial finite volumes code Fluent 6.0. Convection was studied for Rayleigh number from 103 to 106 . Different convection forms were obtained depending on Ra and on the heat source length. The Nusselt number was evaluated on the heat source surface and it showed a symmetrical form raising near the heat source borders. Graphs with relations between average Nu, Ra and the heat source length are finally presented.Copyright