Naikong Fong

Pedestrian movement occurs in evolutionary patterns the effect of which is to facilitate the access of people into and out of living spaces (areas, volumes). In this paper, we rely on the philosophy of Constructal design as applied physics, in order to uncover two fundamental features of evolutionary design for pedestrian evacuation from rectangular areas (e.g., lecture halls with seated occupants). First, the paper shows analytically that the aspect ratio of the floor area can be selected such that the total evacuation time is minimal. Second, the shape of the floor area of each aisle can be tapered such that the total evacuation time is decreased further. These two architectural features are confirmed by means of extensive and systematic numerical simulations of pedestrian evacuation, by using two numerical packages (Simulex and FDS + Evac).

Computational Fluid Dynamics (CFD) has been widely used to evaluate the effects of fire on people and buildings by predicting temperature, radiation heat flux, smoke visibility and combustion products. In this paper, CFD was used to study plume temperature, radiation heat flux, visibility and carbon monoxide concentration in a building fire. The CFD software Fire Dynamics Simulator (FDS) developed by the National Institute of Standards and Technology of USA is generally adopted to model the various fire scenarios in buildings. For FDS modeling, the type of fuel is considered an important input parameter which has a significant effect on the simulation results of different types of combustibles, hence the fire hazard evaluation. In the combustion model of FDS, the fuel and oxygen are burnt to give fire products such as carbon dioxide, water, carbon monoxide and soot. Fuels including propane, wood, polyurethane and polyvinyl-chloride were used in the simulation. By using the same fire size and fuel bed for different combustibles under study, a peak fire size of 3 MW was adopted. Simulations were then carried out with different fuel and respective reaction parameters of these combustibles. Simulation results, the output quantities of plume temperature, visibility, carbon monoxide concentration and radiation heat flux for different scenarios obtained were analyzed and evaluated. It was observed that there were reasonable differences in the results from the fuel packages of different combustibles. These differences were evaluated and their significance was discussed.

Here we show that the configuration of an inhabited area controls the time required by all the pedestrians to vacate the space. From the minimization of the global evacuation time emerges the optimal configuration of the area. This is a fundamental principle for designing living spaces with efficient evacuation quality, and it is demonstrated here with several simple building blocks that can be used as components of more complex living structures: single walkway, corner, and T-shaped walkway. We show analytically and numerically that the ratio of the widths of the stem and branches of the T-shaped walkway has an optimal value that facilitates the evacuation of all the inhabitants. This result is fundamental, and is the crowd-dynamics equivalent of the Hess-Murray rule for the ratio of diameters in bifurcated ducts with fluid flow.

A comparison study on using air-cooled and water-cooled conventional and oil-free chillers in hospitals in Hong Kong is reported. The study commenced with a comprehensive literature review to reaffirm the effectiveness of recommended precaution measures for containing the risk of Legionnaires’ disease (LD) associated with using cooling towers. Numerical performance models for oil-free chillers established for use in the study are presented. Based on recorded cooling demands of two existing hospitals, the life-cycle energy consumption and cost of system options involving different combinations of heat rejection method and chiller type were evaluated, compared and discussed. The results show that water-cooled air-conditioning systems with conventional chillers and cooling towers are still more energy efficient than air-cooled systems with oil-free chillers. Water-cooled oil-free chillers may become an economically viable choice when their price is lowered in future. Pilot installation is recommendable, as it would allow the reliability and maintainability of the new oil-free chillers to be ascertained. Practical applications: Findings of the literature review reaffirmed the effectiveness of measures recommended in contemporary guidelines for LD prevention, which would ease the mind of owners, designers and operation and maintenance personnel in regard of using cooling towers in hospitals. The numerical models for oil-free chillers presented in the paper are useful for evaluation of the energy consumption of this new type of chiller and for comparison with other types of chillers. The study approach described in the paper, including the energy consumption prediction and life-cycle cost evaluation methods, provides a useful framework for similar studies.

With a self-similar parameter b(A_t) = H_i/λ_i, where A_t is the Atwood number, H_i and λ_i are the amplitude and wavelength of bubble (i = 1) and spike (i = 2) respectively, we derive analytically the solutions to the buoyancy—drag equation recently proposed for dynamical evolution of Rayleigh—Taylor and Richtmyer—Meshkov mixing zone. Numerical solutions are obtained with a simple form of b(A_t) = 1/(1 + A_t) and comparisons with recent LEM (linear electric motor) experiments are made, and an agreement is found with properly chosen initial conditions.

Railway is the key transport means in China including the Mainland, Taiwan, and Hong Kong. Consequent to so many big arson and accidental fires in the public transport systems including trains and buses, fire safety in passenger trains is a concern. Numerical simulations with Computational Fluid Dynamics on identified fire scenarios with typical train compartments in China will be reported in this paper. The heat release rate of the first ignited item was taken as the input parameter. The mass lost rate of fuel vapor of other combustibles was estimated to predict the resultant heat release rates by the combustion models in the software. Results on air flow, velocity vectors, temperature distribution, smoke layer height, and smoke spread patterns inside the train compartment were analyzed. The results are useful for working out appropriate fire safety measures for train vehicles and determining the design fire for subway stations and railway tunnels.