Assessment of heating and evaporation modelling based on single suspended water droplet experiments

The work described in this paper is undertaken with the purpose of providing a detailed assessment of the current modelling capabilities of the effects of fire suppression systems (e.g., sprinklers) in fire-driven flows. Such assessment will allow identifying key modelling issues and, ultimately, improving the reliability of the numerical tools in fire safety design studies. More specifically, we studied herein the heating and evaporation of a single water droplet. This rather 'simple' configuration represents the first step in a tedious and rigorous verification and validation process, as advocated in the MaCFP (Measurement and Computation of Fire Phenomena) working group (see https://iafss.org/macfp/). Such a process starts ideally with single-physics 'unit tests' and then more elaborate benchmark cases and sub-systems, before addressing 'real-life' application tests. In this paper, we are considering the recently published comprehensive and well-documented experimental data of Volkov and Strizhak (Applied Thermal Engineering, 2017) where a single suspended water droplet of initial diameter between 2.6 and 3.4 mm is heated up by a convective hot air flow with a velocity between 3 and 4.5 m/s and a temperature between 100 and 800 degrees C. In the present numerical study, 36 experimental tests have been simulated with the Fire Dynamics Simulator (FDS 6.7.0) as well as with an in-house code. The results show that the droplet lifetime is overpredicted with an overall deviation between 26 and 31%. The deviation in the range 300-800 degrees C is even better, i.e., 5-8%, whilst the cases of 200 and, more so 100 degrees C, showed much stronger deviations. The measured droplet saturation temperatures did not exceed 70 degrees C, even for high air temperatures of around 800 degrees C, whereas the predicted values approached 100 degrees C. A detailed analysis shows that the standard Ranz & Marshall modelling of the non-dimensional Nusselt and Sherwood numbers may not be appropriate in order to obtain a simultaneous good agreement for both the droplet lifetime and temperature. More specifically, the heat-mass transfer analogy (i.e., Nu = Sh) appears to be not always valid

Parametric numerical analysis of fire-induced pressure variations in a well-confined and mechanically ventilated compartment

The investigation of a fire in a well-confined and mechanically ventilated compartment is of primary importance for the nuclear industry. In normal operating conditions, a ventilation network system is set-up to ensure confinement via an appropriate pressure cascade. In the event of a fire, the subsequent pressure build-up alters the confinement level significantly and therefore changes the level of safety of the installation. The fire-induced pressure variations depend mainly on the: (1) HRR (Heat Release Rate) history of the fire, (2) heat losses to the walls, (3) leakage area, and (4) operating conditions of the fans. A numerical parametric analysis on the latter three parameters, using the Fire Dynamics Simulator (FDS 5.5.3), have shown that a change in the initial ventilation parameters (i.e. operating conditions of the fans and/or leaks), which can be sometimes difficult to determine, may lead to substantial changes in the pressure profiles. However, only a change in the thermal boundary conditions (i.e. presence or no of insulation) produces significant changes in the gas temperature

A Time-Triggered Constraint-Based Calculus for Avionic Systems

The Integrated Modular Avionics (IMA) architec- ture and the Time-Triggered Ethernet (TTEthernet) network have emerged as the key components of a typical architecture model for recent civil aircrafts. We propose a real-time constraint-based calculus targeted at the analysis of such concepts of avionic embedded systems. We show our framework at work on the modelisation of both the (IMA) architecture and the TTEthernet network, illustrating their behavior by the well-known Flight Management System (FMS)

Large Eddy simulations of the ceiling jet induced by the impingement of a turbulent air plume

In this paper, a sensitivity study is performed with FireFOAM 2.2.x for a hot air jet plume impinging onto a flat horizontal ceiling. The plume evolution and the induced ceiling flow are considered. The influence of the level of turbulence imposed at the inlet, in terms of intensity and eddy length scale, is discussed. Also, the effect of the turbulence model constant is examined. For the case considered, the best results are obtained when no sub-grid scale (SGS) model is used. If a SGS model is used, the level of turbulence at the inlet and the choice of the turbulence model constant are shown to have a significant effect on the prediction of plume's spreading and the ceiling flow velocity. The eddy length scale at the inflow does not have significant impact on the results. Comparisons with the available experimental data indicate that FireFOAM is capable of predicting the mean velocity-field well. In the near field region, an under-estimation of the turbulent velocity fluctuations is observed, whereas reasonably good agreement is obtained in the far field

Financial openness and financial development in the South Mediterranean Sea countries : institutional approach and calculation of development thresholds

The central theme of the paper is the financial development issue in a context of financial globalization for the south Mediterranean sea (SMS) countries. The choice of this theme is motivated by the importance of the economic development and the growth in these countries, who are usually the subject of political instabilities, and are distinguished by weak political institutions. Our aim in this paper is to point out that the financial openness in the conditions of the SMS countries would be prejudicial for its financial development. In contrast, the financial openness would be beneficial for the financial development in the presence of the adequate legal and institutional development. This is our main hypothesis. To do so, we used an econometric panel error-correction model with nonoverlapping data for the period 1980-2005. The model links financial development indicators to institutional and legal indicators, in order to calculate institutional thresholds. The actual state of the institutional and legal environment in the region would not allow them to ameliorate the efficiency of their financial systems. Then, it's not recommended, if we trust on the results founded, to operate a financial openness. Instead of opening the "financial frontiers", it's better to prepare this transition by an improvement of the institutional and the legal environment.peer-reviewe

Theoretical analysis of the liquid thermal structure in a pool fire

The paper presents a theoretical work on liquid heat-up in the case of a pool fire. It is assumed that the convective currents occurring within the upper layer of the liquid are induced by Rayleigh-Bénard instabilities that are caused by in-depth radiation. The upper layer depth has been estimated based on the analytical solution of a 1-D Fourier’s equation for the temperature with a source term for in-depth radiation. The model has been assessed against experimental data for a 9 cm – diameter methanol steady-state pool fire and three different liquid depths (18, 12 and 6 mm). The general trend, i.e., increase in the upper layer depth as the bottom boundary temperature increases, is well captured. In order to ensure that the well-mixed upper layer is at a temperature near the boiling point (as suggested by the experimental data), an improvement is proposed based on a radiative heat balance integral method. In addition to the above, a novel methodology is developed for the calculation of the ‘effective’ thermal conductivity as a means to circumvent detailed calculations of heat transfer within the liquid