RICERCA ITALIANA     

Research program

Study and Optimization of Buoyancy-controlled Thermal Systems

University Co-ordinator

Università degli Studi de L'AQUILA - INGEGNERIA MECCANICA, ENERGETICA E GESTIONALE - L'AQUILA(AQ)

Research Unit Leader

Dario AMBROSINI

Description

Research activity of this Unit will involve experimental investigation of natural convection. In recent years this Unit developped and tested different non-intrusive diagnostic tools, such as holographic interferometry (see Scientific Background) and its digital version, called electro-optic holography or TV-holography.
The research program will involve investigation of natural convection in open channels and from circular cylinders in closed cavities. Research will be performed in collaboration with the Research Units of Genova, Modena-Reggio Emilia and Trieste, so as to investigate the case studies both numerically and experimentally, as described below.

Step 1)

Research program has two main topics:

a) natural convection in open channels with conductive ribs;

b) transient and stationary natural convection from circular cylinders at low Rayleigh numbers in closed cavities.

The activity a) will be performed in collaboration with the Research Unit of Genova. The test section consists of a vertical channel formed by a flat wall, heated at constant temperature faced to a flat adiabatic wall. The heated wall is made of aluminium and connected to a plane heater to provide the desired surface temperature conditions. The surface exposed to the convective air flow is roughened by transverse, square and/or rectangular ribs, placed at regular intervals. In this step ribs are conductive.
This Unit hosts a holographic interferometer (see Scientific Background) while Genova Research Unit hosts a Schlieren apparatus (see Genova Scientific Background). As described earlier, these techniques are based on different optical measurements and can be regarded as complementary.
The combination of the two techniques (schlieren and interferometry) applied to the same test section provides additional information to be used in code validation and direct comparison of experimental results. The Research Units of Genova and L'Aquila have a good experience of joint work on this subject as witnessed by reference A-D, where schlieren and interferometry results were found in excellent agreement in the case of natural convection inside vertical flat channels.
As described earlier (see Genova Scientific Background), Schlieren technique gives directly the convective coefficient h.
This Unit will repeat Genova's experiment in vertical channels with conductive ribs. Holographic interferometry maps the thermal field in terms of isothermal lines. These maps can then be processed to obtain the heat transfer coefficient.
Experimental results obtained by the Research Units of Genova and L'Aquila will be given to the Research Units of Trieste and Modena -Reggio Emilia, which will perform, with different algorithms, numerical simulations of the experiments.

The activity b) will be performed in collaboration with the Research Unit of Modena - Reggio Emilia.
As described earlier, literature about natural convection from circular cylinders at low Rayleigh numbers, is scarce: there is a certain lack of experimental data about stationary behavior and about the effect of thermal capacity, which practically acts as a thermal inertia, during transient heat transfer.
Experimental investigations will use interferometric techniques to map the thermal fields and digital recording to follow the time evolution of phenomena. The effect of cylinders diameter and of the heating rate will be evaluated, with the aim of developing a more complete phenomenological theory and obtaining experimental data to compare with numerical investigation. This will be a joint activity with the Research Unit of Modena-Reggio Emilia, which will simulate the experiments using different algorithms.

Step 2)

The second step will involve the data reduction of the results obtained in Step 1) to develop semi-empirical correlations.
Furthermore, experimental investigation of free convection in vertical channel will be repeated considering non-conductive ribs.
This will be a joint activity with Genova Research Unit. The experimental results will be given to the Research Units of Trieste and Modena -Reggio Emilia for numerical simulations and for developing optimisation procedure for the identification of best corrugation geometries from the thermal point of view.
Finally, as a natural completion of the activities in Step 1) and Step 2), this Unit will also consider new and/or optimized optical techniques to obtain the thermal field and the convective heat transfer coefficient.