Experiments on parallel connected loops in single phase natural circutation: preliminary results

Natural circulation is the most important heat removal mechanism for passive protection systems in a lot of industrial applications, such as nuclear power plants, solar energy systems, reboilers and cooling of electronic systems. The aim of the present work is to investigate the flow and heat transfer characteristics of parallel loops, connected in the lower heated sections, in single-phase natural circulation. The test facility was composed by 2 vertical circuits connected in parallel; each of them was rectangular in geometry, the aspect ratio (defined as the height to width ratio) was 1.63, with circular copper tube of 4 mm (I.D.). An upper cold heat exchanger provided the heat sink, while the heat source at the bottom was a power supply system. Several calibrated thermocouples (T-type) placed in the fluid along the vertical tubes allowed the evaluation of the hot and cold legs average fluid temperature differences. Tests were carried out imposing 3 different heat sink temperatures (10, 20, 30\ub0C); for each of these temperatures the power supply at the lower heater was increased from 20 to 90 W. The fluid investigated was distillate water. The experimental results have been analysed in terms of thermal performance of the single or connected loops. Collected data have also been compared with Vijaiyan\u2019s correlation

effects of a lateral confinement on fc 72 pool boiling from a plane surface

An experimental study was carried out on pool boiling from a plane surface. The influences of two different periphery conditions (pool boiling surface confinement) were investigated. One condition involved the use of a 200 mm diameter glass cylinder (single confinement); the other condition was achieved by inserting a 70 mm diameter cylinder inside the first one (double confinement). The experiments were performed at atmospheric pressure in a saturated pool of FC-72 (dielectric fluid). The experimental data were compared with those obtained in the case of an unconfined pool boiling surface. The presence of the confinement seems to improve heat transfer performance at low and moderate heat fluxes, whereas it has no effect at the maximum heat flux. For the latter situation, the images taken during the experiments show different flow patterns on the boiling surface

Assessment of a 2D CFD model for a single phase natural circulation loop

The use of passive safety systems are more and more diffused in many technological fields. Natural circulation is probably one of the main phenomenon applied in this kind of systems: indeed, as known, by means of gravity and buoyancy forces, the fluids can circulate without any external power sources. In this paper a preliminary analysis (also by comparisons between experimental tests and numerical simulations) of a natural circulation based loop (namely a natural circulation based facility installed at University of Genova) is presented. Starting from some experimental results, the data deriving from CFD loop simulations (both in steady and in unsteady conditions) are used for a first preliminary validation, mainly in order to have a computational tool reliable and able to computationally simulate motion inversions related phenomena. The physical inversions phenomena are very well reproduced also by the a simplified numerical 2D model of the loop, and the physical considerations related to the temperature and velocity fluctuations during the transient simulations, are in agreement with the well-known observations formulated by Welander on the basis of a simple point source analysis scheme

Experimental study on the influence of power steps on the thermohydraulic behavior of a natural circulation loop

Single phase natural circulation is a heat transfer mechanism of great interest in various energy systems, including solar heaters, nuclear reactors, geothermal power production, engine and computer cooling. The present paper deals with an experimental study on the influence of power steps on the behavior of a single-phase natural circulation loop. In particular two sets of experiments were performed: constant power and variable power. Several parameters such as the amplitude of power steps as well as the period of the oscillations were experimentally investigated. The runs at constant power were carried out at different power levels from 500 W to 3000 W. The experiments at variable power were carried out for the values of 500 W, 1000 W, and 2000 W. The amplitude of steps was \ub150% or \ub120% of the input power, whereas the period of the oscillations varied between 50 s and 7200 s. All tests, both at constant power and variable power, show always an unstable behavior, i.e., temperature oscillations across the heated sections occur in the fluid. Moreover, the amplitude and the frequency of the oscillations increase as the input power increases. The thermal inertia of the loop plays a role in case of smaller time steps

Measurement of total hemispherical emittance and specific heat of aluminium and Inconel 718 by a calorimetric technique

An apparatus for the measurement of the total hemispherical emittance and specific heat of metals has been developed. The measurement principle is based on the calorimetric technique: the sample, heated by Joule effect and placed in a vacuum chamber, exchanges radiative heat transfer with the walls of the container, kept at a relatively low temperature. Emittance is deduced from the radiative heat transfer laws at the steady state. When the heating power is switched off, the specific heat of the sample can be recovered from the time history of the sample temperature during the cooling transient. Measurements have been performed on samples of aluminum Anticorodal alloy and Inconel 718 alloy under different surface conditions in the 350 \u2013630 K range