Temperature moderation in a structure by solidification of a phase-change material

Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.The current numerical study focuses on the feasibility of temperature moderation in a structure located at mid-storey in a multi-storey building, by using a phase-changing paraffin wax stored on an aluminum tray under the floor tile. Inside the building, at each level, walls are exposed to the ambient. In winter the walls are cooled, and the paraffin wax serves as the heat source, by solidifying in day-time, and melting at night. The numerical model relates to day-time temperature variations, outside and inside the structure. The heat conduction from the paraffin wax is coupled with the free convection of air in the space, radiation between the inside surfaces, heat conduction across the walls and accumulation in the walls. The dimensions of the analyzed structure are: 8m long, 8m wide and 2.5m high. Effects of wax layer thickness and of fins along the tray, on the rate of solidification are parametrically investigated. The simulations are performed for the structure using Fluent 6.3 software.dc201

A Hybrid Global Minimization Scheme for Accurate Source Localization in Sensor Networks

We consider the localization problem of multiple wideband sources in a multi-path environment by coherently taking into account the attenuation characteristics and the time delays in the reception of the signal. Our proposed method leaves the space for unavailability of an accurate signal attenuation model in the environment by considering the model as an unknown function with reasonable prior assumptions about its functional space. Such approach is capable of enhancing the localization performance compared to only utilizing the signal attenuation information or the time delays. In this paper, the localization problem is modeled as a cost function in terms of the source locations, attenuation model parameters and the multi-path parameters. To globally perform the minimization, we propose a hybrid algorithm combining the differential evolution algorithm with the Levenberg-Marquardt algorithm. Besides the proposed combination of optimization schemes, supporting the technical details such as closed forms of cost function sensitivity matrices are provided. Finally, the validity of the proposed method is examined in several localization scenarios, taking into account the noise in the environment, the multi-path phenomenon and considering the sensors not being synchronized

Atomic Parity Violation : Principles, Recent Results, Present Motivations

We review the progress made in the determination of the weak charge, Q\_w, of the cesium nucleus which raises the status of Atomic Parity Violation measurements to that of a precision electroweak test. Not only is it necessary to have a precision measurement of the electroweak asymmetry in the highly forbidden 6S-7S transition, but one also needs a precise calibration procedure. The 1999 precision measurement by the Boulder group implied a 2.5 sigma deviation of Q\_w from the theoretical prediction. This triggered many particle physicist suggestions as well as examination by atomic theoretical physicists of several sources of corrections. After about three years the disagreement was removed without appealing to "New Physics". Concurrently, an original experimental approach was developed in our group for more than a decade. It is based on detection by stimulated emission with amplification of the left- right asymmetry. We present our decisive, recent progress together with our latest results. We emphasize the important impact for electroweak theory, of future measurements in cesium possibly pushed to the 0.1% level. Other possible approaches are currently explored in several atoms

A randomised trial of intrapericardial bleomycin for malignant pericardial effusion with lung cancer (JCOG9811)

Safety and efficacy of intrapericardial (ipc) instillation of bleomycin (BLM) following pericardial drainage in patients with malignant pericardial effusion (MPE) remain unclear. Patients with pathologically documented lung cancer, who had undergone pericardial drainage for MPE within 72 h of enrolment, were randomised to either arm A (observation alone after drainage) or arm B (ipc BLM at 15 mg, followed by additional ipc BLM 10 mg every 48 h). The drainage tube was removed when daily drainage was 20 ml or less. The primary end point was survival with MPE control (effusion failure-free survival, EFFS) at 2 months. Eighty patients were enrolled, and 79 were eligible. Effusion failure-free survival at 2 months was 29% in arm A and 46% in arm B (one-sided P=0.086 by Fisher's exact test). Arm B tended to favour EFFS, with a hazard ratio of 0.64 (95% confidence interval: 0.40–1.03, one-sided P=0.030 by log-rank test). No significant differences in the acute toxicities or complications were observed. The median survival was 79 days and 119 days in arm A and arm B, respectively. This medium-sized trial failed to show statistical significance in the primary end point. Although ipc BLM appeared safe and effective in the management of MPE, the therapeutic advantage seems modest

IPACK2005-73113 TRANSIENT PERFORMANCE OF A FINNED PCM HEAT SINK

ABSTRACT The present study explores numerically the transient performance of a heat sink based on a phase change material (PCM), during the process of melting. Heat is transferred to the sink through its horizontal base, to which vertical fins made of aluminum are attached. The phase change material is stored between the fins. Its properties, including the melting temperature, latent and sensible specific heat, thermal conductivity and density in solid and liquid states, are based on a commercially available paraffin wax. A parametric investigation is performed for melting in a relatively small system, 10mm high, where the fin thickness is 1.2mm, and the distance between the fins varies from 2mm to 8mm. The temperature of the base varies from 12°C to 24°C above the mean melting temperature of the PCM. Transient numerical simulations are performed, yielding temperature evolution in the fins and the PCM. The computational results show how the transient phase-change process, expressed in terms of the volume melt fraction of the PCM, depends on the thermal and geometrical parameters of the system, which relate to the temperature difference between the base and the mean melting temperature, and to the thickness of the PCM laye

Baffle jetting modelling

International audienceHorizontal flow in the lower part of the reactor pressure vessel was found responsible for the so-called baffle jets impinging in the direction almost perpendicular to the nuclear fuel rods axes. This flow may generate flow-induced vibrations of the fuel rods that can damage the rods.As opposed to the flow-induced vibrations in a purely cross-flow situation, as in the case of e.g. heat exchanger tubes, the flow direction in the bottom part of the core barrel is of a combined axial and cross flow nature. One of peculiarities of the baffle jet and fuel rods interaction is the vicinity of the solid walls of the core barrel; also, the velocity profile impacting onto the fuel rods is non-uniform.The present study aims to further investigate the nature of flow field in the geometry relevant to the baffle jetting in the pressurized water reactors (PWRs). A separate effect study is conducted in order to assess the ability of a number of turbulent models to predict the complicated flow field in the case of baffle jets. Conclusions were drawn for the models’ ability to predict both the time-average and the transient, spectral, characteristics of the flow.An experimental program PANACHET was employed in CEA, France, for the study of baffle jetting. Flow velocity was measured for the conditions mimicking the flow field in the bottom periphery part of the core barrel. The PANACHET experiments were simulated using the models validated in the separate effects study