Entrainment in a Free Jet Generated by a Positive Pressure Ventilator

Results of a simple flow model to describe the entrainment into the air cone created by a positive pressure ventilator (PPV) fan are compared to experimental data. Velocity profiles measured in the air cone of a conventional PPV ventilator are used. The entrainment coefficient and the cone angle were determined for the fan investigated. The correspondence between calculated and measured values is discussed and disparities explained. The findings from the tests are turned into practical guidance for the fire brigade and the advantages and limitations of the simplified model are discussed.     

Morphology of TiN thin films grown on SiO2 by reactive high power impulse magnetron sputtering

Thin TiN films were grown on SiO₂ by reactive high power impulse magnetron sputtering (HiPIMS) at a range of temperatures from 45 to 600 °C. The film properties were compared to films grown by conventional dc magnetron sputtering (dcMS) at similar conditions. Structural characterization was carried out using X-ray diffraction and reflection methods. The HiPIMS process produces denser films at lower growth temperature than does dcMS. Furthermore, the surface is much smoother for films grown by the HiPIMS process. The [200] grain size increases monotonically with increased growth temperature, whereas the size of the [111] oriented grains decreases to a minimum for a growth temperature of 400 °C after which it starts to increase with growth temperature. The [200] crystallites are smaller than the [111] crystallites for all growth temperatures. The grain sizes of both orientations are smaller in HiPIMS grown films than in dcMS grown films.     

Measuring incident radiant heat flux using the plate thermometer

This paper shows that the plate thermometer as described in the fire resistance test standards ISO 834-1 and EN 1363-1 can be used for measuring incident radiant flux under ambient conditions as an alternative to water cooled total flux heat metres (HFMs). Measurements with a plate thermometer mounted in the cone calorimeter and exposed to different heat flux levels were analysed as well as simultaneous measurements with total HFMs and plate thermometers in large scale tests. It is shown how the incident radiant flux to a target can be derived from measurements with total HFMs and plate thermometers, respectively, and how well these two methods match. The plate thermometer is therefore deemed to be a practical alternative for measuring thermal conditions including incident radiant heat flux particularly under field conditions. It is, however, recommended that the plate thermometer should be modified when used under ambient conditions to reduce errors.     

An engineering tool to calculate heat release rates of multiple objects in underground structures

Simple theoretical calculations of the overall heat release rate (HRR) of multiple objects have been carried out. The results were compared to fire experiments in a model tunnel using wood cribs placed at equal distances from each other. Three different methods are presented which are based on physical relations for fire spread between the wood cribs. The first method uses a critical heat flux as ignition criteria while the other two methods use an ignition temperature. The method using the critical heat flux as ignition criteria shows very good agreement with the corresponding experimental results used. The two methods using the ignition temperature as ignition criteria did not agree well with the corresponding experimental results. The prerequisites, that the methods should be kept relatively simple to be of practical use and that the burning objects should not necessarily have to be of uniform composition, were fulfilled.     

The maximum temperature of buoyancy-driven smoke flow beneath the ceiling in tunnel fires

In order to detect a fire and provide adequate fire protection to a tunnel structure, the maximum gas temperature beneath the ceiling to which the structure is exposed needs to be estimated. Theoretical analysis of maximum gas temperature beneath a tunnel ceiling based on a plume theory is given. The heat release rate, longitudinal ventilation velocity and tunnel geometry are taken into account. Two series of model-scale experimental tests were also carried out. The results of both analysis and experiments show that the maximum excess gas temperature beneath the ceiling can be divided into two regions. When the dimensionless ventilation velocity is greater than 0.19, the maximum excess gas temperature beneath the tunnel ceiling increases linearly with the heat release rate and decreases linearly with the longitudinal ventilation velocity. When the dimensionless ventilation velocity is less than 0.19, the maximum excess gas temperature beneath the ceiling varies as the two-thirds power of the dimensionless heat release rate, independent of the longitudinal ventilation velocity. In both regions, the maximum excess gas temperature varies as the −5/3 power of the vertical distance between the fire source bottom and tunnel ceiling. The investigation presented here considers only the cases when the continuous flame region is lower than the ceiling height.     

Theoretical and Experimental Study of Critical Velocity for Smoke Control in a Tunnel Cross-Passage

Theoretical analyses and model-scale experiments have been conducted to investigate the critical velocity in a tunnel cross-passage which is defined as the minimum ventilation velocity through the fireproof door to prevent smoke from flowing into a cross-passage. The effect of the fireproof door geometry, heat release rate, ventilation velocity and fire source location were taken into account. The critical velocity in a tunnel cross-passage varies approximately as 3/2 power of the fireproof door height, as one-third power of the heat release rate and as exponential law of the ventilation velocity, almost independent of the fireproof door width. The critical Froude Number mainly ranges from 5 to 10 and consequently as it is not a constant value it is not very suitable to predict the critical velocity in a tunnel cross-passage. A dimensionless correlation that can correlate well with the experimental data was proposed.     

A New Methodology of Design Fires for Train Carriages Based on Exponential Curve Method

Design fires have great influences on the fire safety concepts and safety measures, and are the basis for any assessment and calculation in tunnel fire safety design. A new methodology of design fires for individual train carriages is proposed based on the exponential design fire curve method and state-of-the-art fire research. The three key parameters required for construction of a design fire are the maximum heat release rate, time to maximum heat release rate, and energy content. An overview of the full scale train carriage fire tests is given and the results show that the maximum heat release rate is in a range of 7 MW to 77 MW and the time to reach the maximum heat release rate varies from 7 min to 118 min. The method could be employed to one single train carriage or several carriages, and alternatively one carriage could be divided into several individual sections. To illustrate the use of the methodology, several engineering applications are presented, including design fires for a metro train carriage with a maximum heat release rate of 77 MW, a double-deck railway train carriage with a maximum heat release rate of 60 MW and a tram carriage with a maximum heat release rate of 28 MW. The main objective is to provide practicing engineers with a flexible and reliable methodology to make design fires for individual train carriages in performance-based tunnel fire safety design.