Maximum rate of pressure rise

The maximum rate of pressure rise denoted (dP/dt) and expressed in Pa.s is the highest or maximum value of the rate of pressure rise during the explosion of a gas or vapor obtained by varying the amount of combustible in its mixture with air. The rate of pressure rise dP/dt) is the steepest gradient of the pressure-time curve of an explosion of a defined mixture of combustible and air and sometimes inert gas in a closed vessel under defined measuring conditions. The maximum rate of pressure rise depends on the volume and the shape of the vessel and the state of turbulence of the mixture. 

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Minimum ignition energy (mj) Maximum explosion pressure (psi) " Maximum rate of pressure rise. (psi/s) Maximum oxygen concentration to preyent ignition (% by volume)... 

The influence of vessel volume on the maximum rate of pressure rise for a specified gas is characterized by the Cubic Law, i.e., [54] the rate of pressure rise varies for each gas. 

Note Kg values are not constant and vary with te.st conditions. Kg provides means of comparing maximum rates of pressure rise for various gases, but should only be used for deflagration vent sizing if test data comes from test vessels... 

The maximum rates of pressure rise for propane and hydrogen are r and r , respectively, bar/sec in the same vessel. For linear interpolation ... 

Maximum rate of pressure rise, Kg, for gas in question in a specific vessel = z bar/sec. 

Atomised and flake aluminium powders attain maximum explosion pressures of 5.7 and 8.6 bar, respectively, both with maximum rates of pressure rise exceeding 1.36 kbar/s [9],... 

During the vacuum fractional distillation of bulked residues (7.2 t containing 30-40% of the bis(hydroxyethyl) derivative, and up to 900 ppm of iron) at 210-225°C/445-55 mbar in a mild steel still, a runaway decomposition set in and accelerated to explosion. Laboratory work on the material charged showed that exothermic decomposition on the large scale would be expected to set in around 210-230°C, and that the induction time at 215°C of 12-19 h fell to 6-9 h in presence of mild steel. Quantitative work in sealed tubes showed a maximum rate of pressure rise of 45 bar/s, to a maximum developed pressure of 200 bar. The thermally induced decomposition produced primary amine, hydrogen chloride, ethylene, methane, carbon monoxide and carbon dioxide. 

It decomposes explosively at the m.p., 98°C [1], and shows a high rate of pressure increase on exothermic decomposition [2], The heat of decomposition was determined as 1.34 kJ/g by DSC, and Taii24 was determined as 88°C by adiabatic Dewar tests, with an apparent energy of activation of 223 kJ/mol [3], When finely divided, it also shows significant dust explosion hazards, with a maximum explosion pressure of 7.75 bar, and a maximum rate of pressure rise above 680 bar/s [4], Further work on homogeneous decomposition under confinement has been reported [5],... 

The rate of pressure rise is indicative of the flame front propagation rate and thus of the magnitude of the explosion. The pressure rate or slope is computed at the inflection point of the pressure curve, as shown in Figure 6-15. The experiment is repeated at different concentrations. The pressure rate and maximum pressure for each run are plotted versus concentration, as shown in Figure 6-16. The maximum pressure and maximum rate of pressure rise are determined. Typically, the maximum pressure and pressure rates occur somewhere within the range of flammability (but not necessarily at the same concentration). By using this relatively simple set of experiments, the explosive characteristics can be completely established in this example the flammability limits are between 2% and 8%, the maximum pressure is 7.4 bar, and the maximum rate of pressure rise is 360 bar/s. 

Cubic low The correlation of the vessel volume with the maximum rate of pressure rise. (dP/dt)max = constant =... 

Case Maximum temperature (°C) Maximum pressure (bar) Maximum rate of pressure rise (bar/s) Maximum rate of temperature rise (°C/s) Rate of temperature rise at relief pressure (°C/s)... 

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