Smoke Control in High-Rise Residential Buildings with Stair Pressurization Systems

Stair pressurization systems are designed to create a smoke-proof barrier, preventing the ingress of smoke into staircases within buildings. In tall buildings over 25 m, evacuation strategies can utilize phased or simultaneous evaluation of multiple storeys. This paper examines the performance of a stair pressurization with a differing number of doors open starting from two doors, with an incremental step of two up to a total of 10 doors into the shaft. Simulations using Fire Dynamics Simulation (FDS) have shown that a system that would pass commissioning requirements allows smoke in the shaft if there are more than four doors open simultaneously. The required airflow to prevent smoke ingress was found to be above an average flow speed of 0.7 m/s. Past this limit, the amount of smoke that leaks into the staircases continues to increase as more doors open. The study suggests that standards regarding stair pressurization systems should be updated to account for realistic evacuation scenarios, including the system’s cascade settings, number of storeys, and expected evacuation time, as evidenced by the smoke leakage once four doors were open and the drop-in flow rate between two-door and four-door open cases

Natural convection in building-integrated photovoltaic systems: a computational study

One of the very significant challenges in building-integrated photovoltaic (BIPV) systems is the overheating of the PV cells. The double-skin configuration, which allows natural ventilation to provide passive cooling of the PV cells, has been used as a cost-effective means of solving the difficulty. This research has been undertaken to improve the understanding of the flow and heat transfer phenomena in the channel formed by the double-skin thereby enhancing the cooling of PV cells by natural convection.A novel in-house LES computer code has been proposed to model the buoyancy-driven flow. Based on comparison with experimental data, it is shown that LES with the subgrid-scale Vreman model (VM) is able to capture the large-scale turbulent structures, whereas the Smagorinsky model (SM) yields unphysical results due to its more dissipative formulation. Several dynamic variants of SM have also been found to give results that do not agree with experimental data because of the ad hoc clipping procedure. A comprehensive parametric study has been performed using VM with varying channel widths, convective heat fluxes, inclination angles, and external disturbances. It is demonstrated that the average heat transfer is enhanced as (i) the convective heat flux or channel width increases, (ii) the inclination angle from the horizontal plane increases, and (iii) substantial amount of disturbances are present in the ambient. In each case, the augmentation of heat transfer is consistently due to turbulence production, thereby suggesting a promising outcome to adopt the findings listed above for the passive cooling of PV systems. The effect of including radiation in the numerical model has also been found to yield better prediction of wall temperature, thereby improving the comparison between numerical results and experimental data. Dynamic variants of VM have also been proposed and validated by conducting LES of natural convection in a rectangular cavity. It is found that disturbances resembling Tollmien-Schlichting waves occur in the transition zone to trigger the breakdown of the laminar flow. The comparison of the LES results with experimental data from the literature shows that VM with global equilibrium can capture the coherent structures correctly, whereas the standard VM and VM with Germano yield postponed transition. This suggests that much finer grid is desired when using the latter models to better capture the weak transitional boundary layer

Thermal Performance of Nanofluids in Microchannel Equipped with a Synthetic Jet Actuator

Numerical investigations of heat transfer enhancement in three-dimensional micro-channels with singlesynthetic jet using Al2O3-water, CuO-water and TiO2-water combinations were conducted. The effects of different types of nanoparticles at particle volume concentrations of 1%, 2% and 5% on the thermal erformance in the micro-channel were examined. The numerical tool was validated against existing xperimental data on the heat transfer characteristic of nanofluids in micro-channel. Heat transfer enhancement using nanofluids based on the eulerian model was assessed for the cases without synthetic jet operator and with synthetic jet operator. In general, the thermal performance was greatly influenced by the thermal conductivity and dynamic viscosity of the type of nanofluids used. As the particle volume concentration increased, the heat transfer performance also improved. The result showed that the heat transfer performance of nanofluids with Al2O3 and CuO used in this study was better than that of pure water with the operation of th e synthetic jet actuator. Overall, nanofluids with Al2O3-water at 5% particle volume concentration showed the best cooling performance whereas nanofluids with TiO2 fails to improve the thermal performance.15 page(s

Natural convection in an asymmetrically-heated open-ended channel: A three-dimensional computational study

Buoyancy-driven flows in an asymmetrically heated open-ended channel which occur in fa\ue7ade and roof building-integrated photovoltaic systems were investigated using large-eddy simulation. The channel inclination angle was varied from 30o to 90o to the horizontal, whereas the channel height-towidth aspect ratio remained at 20. In each case, a uniform heat flux was applied along the top wall whereas the bottom wall was assumed to be adiabatic. It is shown that typical dynamics of largescale structures in the flow and thermal fields of natural convection in the channels are successfully modeled numerically by the use of LES. The effects of varying the inclination angle on the heat transfer in the channel are explored by examining the mean flow fields and in addition, the effects of radiation have been considered. Both experimental and numerical results show that open-ended channels with low inclination angles are characterized by a low chimney effect which leads to a decreased flow rate and a delay in transition to turbulence, thereby decreasing the heat transfer coefficient and leading to higher temperatures on the heated wall. A correlation describing the local Nusselt number in the channel is also developed in order to characterize the global heat transfer behavior

Modelling of natural convection in vertical and tilted photovoltaic applications

none7This investigation aims to examine and infer useful engineering information of the physical mechanisms which are found in applications of building-integrated photovoltaic (BIPV) systems for façades and roofs. Buoyancy-driven flow in heated open-ended channels was modelled with the channel inclination angle ranging from 15° to 90° and the channel height-to-width ratio being 20. In each case, a uniform heat flux was applied along the top wall and the bottom wall was assumed to be adiabatic. Effect of varying inclination angle on the velocity and temperature fields is explored through the mean and turbulence quantities. A comparison between experimental and modelling results shows that open-ended channels with low inclination angles are characterised by low chimney effect and induced flow rate, thereby decreasing the heat transfer along the photovoltaic panels. In addition, propagation of disturbances and vortical structures in the channel which are necessary to enhance heat transfer are less eminent in these cases. Furthermore, heat transfer characteristics of turbulent natural convection in tilted channels are recast in terms of relevant dimensionless parameters so that they may be readily applied in cases with the aspect ratio and heat fluxes which are considered in this study.Affiliazioni: UNSW Sydney INSA LyonG.E. Lau;E. Sanvicente;G.H. Yeoh;V. Timchenko;M. Fossa;C. Ménézo;S. Giroux-JulienG. E., Lau; E., Sanvicente; G. H., Yeoh; V., Timchenko; Fossa, Marco; C., Ménézo; S., Giroux Julie