Experimental study of thermophysical properties of coal gangue at initial stage of spontaneous combustion.

The specific heat capacity (Cp), thermal conductivity (λ), and thermal diffusion coefficient (D) of coal gangue (CG) are the main factors that affect the self-ignition potential for heat transferring from burning center to the ground surface. In this paper, the thermophysical properties of CG were investigated by transient plane source method. The correlations and sensitivity analysis were performed to characterize the degree of influence of the thermophysical parameters (Cp, λ, and D) dependence on temperature. The mean values of Cp, λ, and D for CG were at a range of 0.73-0.89 J g-1 K-1, 0.44-0.76 W m-1 K-1, and 0.26-0.43 mm2 s-1, respectively. Compared with coal, CG were located in the low area (Sc < 2) with higher value of λ and D, but lower value of Cp. Results also showed that 70 °C was a critical point for CG at which some kinds of mutation took place in thermophysical properties. The comparison between the experimental data and the correlation outputs exhibited consistency.

Experimental research on explosion suppression affected by ultrafine water mist containing different additives.

The suppression effects of pure ultrafine water mist and 5% mass fraction alkali metal (NaCl, Na2CO3, KHCO3, KCl and K2CO3) solutions ultrafine water mist on methane explosion were conducted under five mist concentrations in a sealed visual vessel. Mist diameters of different additive solutions were measured by a phase doppler particle analyzer. Pressure data and dynamic flame pictures were recorded respectively by a high-frequency pressure sensor and a high-speed camera. Results indicate that alkali metal compound can enhance the suppression effect of ultrafine water mist and it was related to the additive type. The suppression order of alkali metal compound for methane explosion was K2CO3>KCl > KHCO3>Na2CO3>NaCl. Meanwhile, additive radicals can obviously affect explosion intensity and it mainly reflected in the reduction of explosion pressure under different mist conditions (K+>Na+, Cl- >HCO3-). The pressure generated from combustion wave accelerating propagation underwent two accelerating rises and was affected by additive type and mist amount. The effect of additive type on explosion intensity (maximum explosion overpressure (ΔPmax), two peak values of pressure rising rate) was similar with flame propagation velocity and were decreased evidently with increasing mist concentration. The enhancement in explosion suppression was due to the combination of improved physical and chemical effects.

Effect of fire engulfment on thermal response of LPG tanks.

A model has been developed to predict the thermal response of liquefied-pressure gases (LPG) tanks under fire, and three-dimensional numerical simulations were carried out on a horizontal LPG tank which was 60% filled. Comparison between numerical predictions and published experimental data shows close agreement. The attention is focused on the influence of different fire conditions (different fire scenarios, various engulfing degrees and flame temperatures) on thermal response of LPG tanks. Potential hazard probabilities under different fire conditions were discussed by analyzing the maximum wall temperature and media energy after the internal pressure rose to the same value. It is found that the less severe fire scenario and lower engulfing case may lead to a greater probability of burst hazard because of the higher maximum wall temperature and media energy before the pressure relief valve (PRV) opens.