François Rémi Carrié

Thermal and ventilation modelling of large highly-glazed spaces

Abstract Highly-glazed spaces are attractive in many ways (solar heating, aesthetics, etc.), however, their thermal behaviour remains difficult to predict. In such spaces, the assumptions or methods generally used in building thermal simulation tools — e.g. homogeneous air temperature in the room, simplified calculations of radiative heat transfer between walls, absence of airflow modelling within the room — do not seem appropriate. We have developed a new model (AIRGLAZE) to improve the prediction of the thermal behaviour of large highly-glazed spaces. It consists of an envelope module to calculate conductive and radiative heat transfer in the building envelope. It is coupled with a zonal airflow model to predict air motion within the room. Particular attention is paid to sun patch modelling and the internal distribution of shortwave and longwave radiation within the building; direct retransmission, reflection to the outside, and transmission to other zones of the building are taken into account. The results of AIRGLAZE are compared with measurement data from two experimental test cells: the IEA Annex 26 experimental atrium, and a test cell at ENTPE. Compared to the one-air-node approach, the zonal method significantly reduces the mean discrepancy with measurement data during stratified conditions (from 3.9°C down to 0.4°C for the Annex 26 atrium). In general, experimental and numerical results tally well in both cases.

Particle Deposition in a Two-Dimensional Slot from a Transverse Stream

ABSTRACT This paper addresses the problem of coarse mode particle deposition in a two-dimensional slot from a transverse flow. A dimensional analysis enables us to identify five independent dimensionless groups: the leak Reynolds number, Re, the dimensionless velocity gradient of the approaching flow, α, the Stokes number, Stk, the slot aspect-ratio, e/h, and the interception parameter, dp/h.. A sticky aerosol (MMD ≊3–7 μm; GSD ≊ 2–3) was injected into a 15 cm diameter duct and blown out through a rectangular opening (3 × 40 mm; e = 0.6 mm) drilled in a direction perpendicular to the flow. A video camera was set up to continuously monitor the leak behavior in time. The image then was digitized, enabling us to assess the slot-width as a function of time. It appeared that the slot could be sealed in less than 20 minutes. These results were compared with a simplified model based on a scale analysis of the deposition velocity on the slot thickness. Agreement between predicted and measured leak-widths is very ...

Duct leakage in European buildings : status and perspectives

A large number of modern European buildings are equipped with ducted air distribution systems. To investigate the implications of duct leakage, a field study was performed on 42 duct systems in Belgium and France. The measurement data confirm the findings of the few earlier experimental investigations on these matters in Europe. In our sample, the leakage rate appears to be typically three times greater than the maximum permitted leakage adopted in EUROVENT 2/2 (Class A). The advantages of tight ducts are illustrated with a theoretical case study on a balanced ventilation system with heat recovery. It indicates that the overall effectiveness of the system reduces drastically if the ducts are leaky. The savings potential of an airtight duct policy at the European level is calculated (a) based on estimates of the number of buildings equipped with mechanical ventilation systems, and (b) assuming market penetration scenarios of rehabilitation techniques. At the European level, the cumulative savings potential over a period of 10 years appears to be in the region of 10 TW h (36 pJ).

INFLUENCE OF RAPID THERMAL ANNEALING PARAMETERS ON PROPERTIES OF YBaCuO THIN FILMS SPUTTERED ON POLYCRYSTALLINE ZIRCONIA

Abstract High-Tc YBaCuO thin films have been prepared on polycrystalline ZrO 2 substrates by low temperature r.f. diode sputtering, followed by rapid thermal annealing (RTA). The gas atmosphere during RTA influences the roughness of the films and time/temperature parameters are critical. A Tc ( R = 0) of 85 K has been obtained with c-axis oriented films, but these have low Jc (1500 A.cm −2 at 77 K). Besides, repeated RTA processes are a suitable way to increase the grain size and improve the orientation of the films.

Experimental investigation of aerosol deposition on slot- and joint-type leaks

Abstract This paper deals with the quantification of the sealing effectiveness of slot- and joint-type leaks by aerosol deposits. A sticky aerosol (MMAD ≈4.9 μm ; GSD ≈2.7) was injected into a duct and blown out through machined slot- and joint-type leaks located on the duct wall. For both leak-types, the crack exit was a rectangular opening of 1.7×50 mm . The pressure difference across the leaks was kept constant during the plugging process, while the airflow rate through the openings was continuously monitored. The deposition patterns were recorded and the average deposition efficiencies were obtained through the measurement of the particle mass collected in the crack. Instantaneous sealing rates were obtained from the leakage airflow time series. The normalized sealing rate (NSR) introduced in this paper allows one to compare the instantaneous sealing efficiencies as the leaks are subjected to various boundary conditions. For our specific leak geometries and boundary conditions, the three key results of these experiments are: (a) inertial impaction near the entry point is the major cause of the decline of the leakage flow rate for either type of leak; (b) the pressure variations in the 100– 400 Pa range do not have a significant effect on the average deposition efficiency; (c) the average deposition efficiency of the slot- and joint-type leaks used are in the range of 25% and 85%, respectively. We also observed that there exists a critical joint-leak size below which the NSR decreases significantly.

Rapid thermal annealing of YBaCuO thin films sputtered on substrates

Abstract We have determined the rapid thermal annealing (RTA) conditions that optimize both the surface quality and the superconducting properties of YBaCuO films deposited on silicon-based substrates. This process has allowed a very thin nitride layer (45A) to be a good diffusion barrier; silica acting as a sticking layer. A T(onset) in the 87–91 K range has been obtained, with T(R = 0) ∼- 60 K and Jc ∼- 500 A.cm−2 at T(R = 0) 2 . Repeated RTA cycles might by a way to improve these figures.

YBaCuO thin films used as electrical switch or current limiter

We have sthdied the ability of high Te supereonduotors to operate as electrical switches or current limiters . For this purpose, we have usi YBaCuO films, deposit&I on polycrystalline zirconia slabs by various techniques: conventional two-step processes as well as rapid thermal annealing have been consider&1 . The main results are that with a Tc(onset) of 91 K, the variation of the critical current density versus fruency shows that it will be possible to use the films at 50-60 Hz, although we ne&i to improve our low current density films to demonstrate this.

In situ characterization of YBaCuO thin films during rapid thermal annealing

Rapid Thermal Annealing (RTA) is rather unusual in the field of high Tc superconductor processing, in spite of beeing a classical procedure for semiconductor technologies. Nevertheless, when looking at the few results reported on YBaCuO thin films annealed by RTA, this thermal treatment appears as an attractive way, either to increase the efficiency of a diffusion barrier, when substrates such as silicon are used, or as a rapid step to improve YBaCuO grain growth after deposition. The first characterization of YBaCuO thin films during RTA is reported here, based on four probe resistivity measurements. The influence of two parameters are studied: i) the dwell temperature of the RTA cycle, ii) the gas nature during the process.