Data-based mechanistic modelling approach to determine the age of air in a ventilated space

In literature, local mean age of air is used as an important index to evaluate indoor air quality in ventilated rooms. In this research, a data-based mechanistic approach is used to model the spatial–temporal mass distribution in an imperfectly mixed forced ventilated installation. A first-order transfer function model has proved to be sufficiently good in describing the mass transfer dynamics $(R_t^2=0.987)$ of the system. Furthermore, it was possible to fully understand the physical meaning of the model parameter. The parameter is found to be an inverse of the age of air. This Data-Based Modelling approach proved to be more robust when dealing with measurement noise. Finally, the modelled age of air was validated with a classical step up determination of the age of air for experimental data. Good correlation $(R_t^2=0.77)$ was found between both results, which proved the physical background of the model parameter.     

Heat flux profile upon building facade with side walls due to window ejected fire plume: An experimental investigation and global correlation

This paper investigates the heat flux profile upon building facade with side wall constraints due to ejected fire plumes from a window of an under-ventilated compartment fire. A reduced-scale model (1:8), consisting of a cubic fire compartment with a facade wall attached and two side walls located symmetrically at both sides of the window is developed. The window dimensions and the side wall distances are changed in experiments, representing different ventilations and constraints on fire plume entrainment. Five heat flux gauges are employed in measurement of vertical heat flux profile upon the facade wall. Results show that with the decrease in separation distance of side walls, the heat flux increases for small windows where dimensionless excess heat release rate ${\dot{Q}}_{ex}^{⁎}\ge 1.3$ (“(half) axisymmetric fire” regime), meanwhile shows weak dependency on side wall separation distance for large windows where ${\dot{Q}}_{ex}^{⁎}<1.3$ (“wall fire” regime). A new global formula is proposed to characterize the vertical profile of heat flux based on Lee’s model without side walls as further modified by a parameter K in relation to the separation distance of side walls and characteristic length scales of the window. Experimental data for different windows and side wall separation distances are well collapsed by the proposed formula.     

Window ejected flame width and depth evolution along facade from under-ventilated enclosure fires

This paper investigates window ejected flame width and depth evolutions along facade from under-ventilated enclosure fires. Experiments are carried out by 1:4 scale model. Two CCD cameras are employed to record the evolutions of flame depth and width. The flame base position (vertical height above the bottom of the opening), flame depth (width) along with their maximum values and corresponding positions (vertical height above the flame base position) are measured and analyzed by non-dimensional scaling. It is found that the flame base position is independent of fire heat release rate and its ratio to opening height is nearly the same. The flame depth for all heat release rates and the flame width for openings with aspect ratio in the range of $0.5\le W/H\le 1.5$ (the “(semi-) axi-symmetrical flame type”) first increases, reaching a maximum value and then decreases with height. However, for the opening with a relative larger aspect ratio ($W/H=2$) (“wall flame type”), the flame width decreases monotonously with height. The maximum flame width and its corresponding vertical position for “(semi-) axi-symmetrical flame type” are found to be well correlated by characteristic length scale ${\ell }_1$ [=${(A\sqrt{H})}^{2/5}$] non-dimensionally after normalized by the flame height. Meanwhile, the maximum flame depth for all conditions is found to be well correlated by characteristic length scale ${\ell }_2$ [=${(A{H}^2)}^{1/4}$] non-dimensionally after normalized by the flame height.     

Effects of temperature on the shear strength of saturated sand

The effect of temperature on the shearing response of saturated, dense sand was investigated using a series of temperature-controlled, isotropically-consolidated, hollow cylinder triaxial compression tests, where specimens were heated in drained conditions followed by shearing in undrained conditions. As expected, the deviatoric stress at the peak state (i.e., the undrained shear strength) was observed to increase with increasing initial mean effective stress. However, it was observed to decrease linearly with increasing temperature. The effects of temperature on the deviatoric stress at the peak state were attributed to a linear increase in the magnitude of negative shear-induced pore water pressure at the peak state with temperature. The relationship between the undrained shear strength and the pore water pressure with changes in temperature was represented well by linear equations. When the shear strength was interpreted in terms of the critical state, no obvious changes in the critical state line in the $p^{\prime }-q$ plane were observed, and the critical state friction angle was unaffected by temperature. During drained heating, the dense sand specimens were observed to expand volumetrically, causing the normal consolidation line in the $e-{\left(p^{\prime }/p_{\text{a}}\right)}^{0.5}$ plane to shift upward with increasing temperature without a change in the slope. The negative pore water pressure during undrained shearing caused the state paths of the dense sand specimens to move to the right. As the magnitude of negative pore water pressure increased with increasing temperature, no obvious effects on the critical state line in the $e-{\left(p^{\prime }/p_{\text{a}}\right)}^{0.5}$ plane were observed.