uo Weng

Comparison study on qualitative and quantitative risk assessment methods for urban natural gas pipeline network

In this paper, a qualitative and a quantitative risk assessment methods for urban natural gas pipeline network are proposed. The qualitative method is comprised of an index system, which includes a causation index, an inherent risk index, a consequence index and their corresponding weights. The quantitative method consists of a probability assessment, a consequences analysis and a risk evaluation. The outcome of the qualitative method is a qualitative risk value, and for quantitative method the outcomes are individual risk and social risk. In comparison with previous research, the qualitative method proposed in this paper is particularly suitable for urban natural gas pipeline network, and the quantitative method takes different consequences of accidents into consideration, such as toxic gas diffusion, jet flame, fire ball combustion and UVCE. Two sample urban natural gas pipeline networks are used to demonstrate these two methods. It is indicated that both of the two methods can be applied to practical application, and the choice of the methods depends on the actual basic data of the gas pipelines and the precision requirements of risk assessment.

STUDY ON FLAME HEIGHT OF MERGED FLAME FROM MULTIPLE FIRE SOURCES

A series of experiments to study merged flame from multiple fire sources was carried out. The porous 15-cm2 burner was used as a unit burner and propane was employed as a fuel. Many burners with various heat release rates were placed in a square configuration with various separation distances. Flame height was measured using video images and temperature distribution with height was measured using thermocouples. The numerical results from the Fire Dynamics Simulator (FDS) of the National Institute of Standards and Technology was compared with the experimental data, and the comparison results show that FDS correctly simulates the merged flame from multiple fire sources. In addition, an empirical model to estimate the merged flame height was developed considering the effect of separation distance. The validity of this model was confirmed from the comparison with the simulation results, and excellent agreement is found between the calculated merged flame height from the model and the numerical ones. To study the detailed structure of merged flame, 3 × 3 fire source configuration was taken as an example to quantitatively show oxygen mass fraction profiles and velocity fields, which were also given to indicate the formation mechanism of the merged flame.

Critical condition of backdraft in compartment fires: a reduced-scale experimental study

Abstract Backdraft is a special fire phenomenon in a limited-ventilation building. It can develop from fires of either ordinary combustibles or ignitable liquids that become oxygen starved yet continue to generate a fuel-rich environment. If abundant fresh air is abruptly supplied by opening a door or breaking a window, the hot gas in this vitiated building will rapidly combust and a fire ball and a blast wave will take place. Backdraft has the characteristics of abrupt occurrence and powerful destruction, which may cause the death of people in situ and the collapse of the building. In this paper, the results of a reduced-scale experimental test series are presented. This reduced-scale compartment (length×width×height with 1.2 m × 0.6 m × 0.6 m) was fitted with one opening (width×height with 0.2 m × 0.6 m in the middle of the end wall). The experimental results show that the key parameter determining the occurrence of backdraft is the mass fraction of unburned fuel (i.e. unburned methane in this study). When the mass fraction of unburned fuel in compartment exceeds a critical value, i.e. 9.8% backdraft will take place.

Numerical Simulation of the Effects of Blood Perfusion, Water Diffusion, and Vaporization on the Skin Temperature and Burn Injuries

Skin burn induced by thermal radiation or heat source is one of the common but severe, injuries in firefighting and some industry work exposed to intensive radiation. In this article, a multi-layer skin model on heat and mass transfer is presented article to investigate the effects of blood perfusion, water diffusion, and vaporization on tissue temperature and skin burn after removing the heat source. The numerical results of the model are in good agreement with previous experimental results. A parametric study is carried out to investigate the effects of skin geometrical and thermal parameters, and initial tissue temperature on skin temperature distribution and burn injuries after the removal of the heat source. The results show two-sided effects on tissue temperature, i.e., heat loss due to water vaporization and water diffusion can cool the epidermis; however, blood perfusion and water diffusion heat the subcutaneous tissue incurring skin damage. It is found that the epidermis and dermis thickness, the dermal and subcutaneous tissue thermal conductivity, and the subcutaneous tissue heat capacity have significant impact on tissue temperature and burn injuries, while the epidermis thermal conductivity, the epidermis and dermis heat capacity, the blooding perfusion rate, and the water diffusivity have little influence.

Experimental study of back-draft in a compartment with openings of different geometries

Abstract This paper presents the results of reduced-scale experimental tests to study back-draft in a reduced-scale compartment (1.2 m × 0.6 m × 0.6 m), fitted with six different geometries for the opening on one end-wall and with two geometries for the opening in the ceiling. The experimental variables included the flow rate, the time during which the fuel was burned, and the geometries of the inlet. The quantities recorded before the back-draft included temperature and the concentrations of oxygen, carbon dioxide, and carbon monoxide. To quantify the effect of back-draft, the gas velocities in the inlet and also the pressures in the compartment were measured. The effects of different inlet geometries on the occurrence of back-draft are discussed. This study shows that the mass fraction of total hydrocarbons (i.e, the un-burned methane in this study), whose critical value varies with the geometry of the inlet, is a key parameter determining the occurrence of back-draft.

Wavelet-based image denoising in (digital) particle image velocimetry

Mallat algorithm, which analyzes the evolution of the wavelet transform maxima across scales based on wavelet transform, is applied in image denoising in particle image velocimetry (PIV) in this paper. An improved interrogation method for PIV images based on cross-correlation with discrete window offset, which makes use of a translation of the second interrogation window and rebuilds it considering rotation and shear is also presented. The displacement extracted from PIV images is predicted and corrected by means of an iterative procedure. In addition, the displacement vectors are validated at each intermediate of the iteration process. The method of image denoising in PIV based on wavelet transform is compared with averaging filter, Wiener filter and median filter by interrogation of synthetic and real PIV images and the results are discussed.

Quantitative assessment of the relationship between radiant heat exposure and protective performance of multilayer thermal protective clothing during dry and wet conditions

The beneficial effect of clothing on a person is important to the criteria for people exposure to radiant heat flux from fires. The thermal protective performance of multilayer thermal protective clothing exposed to low heat fluxes during dry and wet conditions was studied using two designed bench-scale test apparatus. The protective clothing with four fabric layers (outer shell, moisture barrier, thermal linear and inner layer) was exposed to six levels of thermal radiation (1, 2, 3, 5, 7 and 10kW/m(2)). Two kinds of the moisture barrier (PTFE and GoreTex) with different vapor permeability were compared. The outside and inside surface temperatures of each fabric layer were measured. The fitting analysis was used to quantitatively assess the relationship between the temperature of each layer during thermal exposure and the level of external heat flux. It is indicated that there is a linear correlation between the temperature of each layer and the radiant level. Therefore, a predicted equation is developed to calculate the thermal insulation of the multilayer clothing from the external heat flux. It can also provide some useful information on the beneficial effects of clothing for the exposure criteria of radiant heat flux from fire.

Experimental Study on the Mitigation of Backdraft in Compartment Fires with Water Mist

In this paper, the results of a reduced-scale experimental test series using water mist to mitigate backdraft in compartment fires are presented. This reduced-scale compartment (1.2 m 0.6 m 0.6 m)was fitted with a variety of end opening geometries: middle-slot, upside-slot, downside-slot, door, window and vertical middle-slot, and ceiling opening geometries: slot and window. Water mist was generated by a downward-directed pressure nozzle that was operated at pressure of 0.2 MPa. Experimental variables included fuel flow rate, burn time, water mist injection time and mass, and opening geometries. Histories recorded prior to backdraft included upper layer temperatures, lower layer temperatures, and species concentration for oxygen, carbon dioxide and carbon monoxide. Data collected to quantify the backdraft included opening gas flow velocities and compartment pressures. The experimental results show that water mist is an effective mitigating tactic that is able to suppress backdraft in compartment fires primarily by means of diluting the gas in the compartment and reducing total hydrocarbons mass fraction, rather than by a thermal mechanism of cooling. KEY WORDS: backdraft, compartment fire, water mist.

Review on modeling heat transfer and thermoregulatory responses in human body.

Several mathematical models of human thermoregulation have been developed, contributing to a deep understanding of thermal responses in different thermal conditions and applications. In these models, the human body is represented by two interacting systems of thermoregulation: the controlling active system and the controlled passive system. This paper reviews the recent research of human thermoregulation models. The accuracy and scope of the thermal models are improved, for the consideration of individual differences, integration to clothing models, exposure to cold and hot conditions, and the changes of physiological responses for the elders. The experimental validated methods for human subjects and manikin are compared. The coupled method is provided for the manikin, controlled by the thermal model as an active system. Computational Fluid Dynamics (CFD) is also used along with the manikin or/and the thermal model, to evaluate the thermal responses of human body in various applications, such as evaluation of thermal comfort to increase the energy efficiency, prediction of tolerance limits and thermal acceptability exposed to hostile environments, indoor air quality assessment in the car and aerospace industry, and design protective equipment to improve function of the human activities.

Experimental and numerical study of physiological responses in hot environments

This paper proposed a multi-node human thermal model to predict human thermal responses in hot environments. The model was extended based on the Tanabes work by considering the effects of high temperature on heat production, blood flow rate, and heat exchange coefficients. Five healthy men dressed in shorts were exposed in thermal neutral (29 °C) and high temperature (45 °C) environments. The rectal temperatures and skin temperatures of seven human body segments were continuously measured during the experiment. Validation of this model was conducted with experimental data. The results showed that the current model could accurately predict the skin and core temperatures in terms of the tendency and absolute values. In the human body segments expect calf and trunk, the temperature differences between the experimental data and the predicted results in high temperature environment were smaller than those in the thermally neutral environment conditions. The extended model was proved to be capable of predicting accurately human physiological responses in hot environments.