Adiabatic self-heating

This test can be used to give early detection of the initial exothermicity. It is possible to estimate thermokinetic parameters (e.g., the activation energy and the adiabatic self-heat rate) and to estimate how the initial temperature for self-sustaining reactions will vary with the quantity of material present. 

The Sikarex safety calorimeter system and its application to determine the course of adiabatic self-heating processes, starting temperatures for self-heating reactions, time to explosion, kinetic data, and simulation of real processes, are discussed with examples [1], The Sedex (sensitive detection of exothermic processes) calorimeter uses a special oven to heat a variety of containers with sophisticated control and detection equipment, which permits several samples to be examined simultaneously [2]. The bench-scale heat-flow calorimeter is designed to provide data specifically oriented towards processing safety requirements, and a new computerised design... 

For adiabatic self-heating (obtained for an infinitely reacting mass or a thermally isolated finite mass), y2T = 0, Consequently the heat... 

The focusing action of the adiabatic self-heating will bnng the pressure wavelets to a focus at a distance in front of the surface which is of the order of magnitude of taVcf where Ve is the speed of sound. Unless the final velocity Vb is of the order of magnitude of the speed of sound, the shock will die out. 

Figure 1. The whole self-heating process up to the thennal explosion of2 em of a chemical of the Tl) type charged in the open-cup cell, or confined in the closed cell, in accordance with the self-heating property of the chemical, and subjected to the adiabatic self-heating test started from a Tj.

The above approach, i.e., the heat generation data by the adiabatic self-heating test, or by the adiabatic oxidatively-heating test, and, the heat transfer data by experimental measurements, has been adopted throughout a series of studies described herein in order to calculate the 7 for a chemical of the TD type, including every gas-permeable oxidatively-heating substance, having an arbitrary shape and an arbitrary size, placed in the atmosphere under isothermal conditions. 

It has been ascertained, as to the value of A T, that, when the value of In t is plotted against that of l/T on several values of A T, with reference to a self-heating process, in the early stages, of 2 cm of a certain chemical of the TD type subjected to the adiabatic self-heating test started from a T several straight lines, which are almost parallel with one another, are obtained. 

The differential equations, in which one of the unknown variables, e.g., temperature, enters in a nonlinear manner, i.e., as an exponential function, while its derivative enters in a linear form, are often dealt with in the thermal explosion theory. Such an equation is called quasilinear in mathematics [21]. For instance, we have assumed in Eq. (50) presented in Section 2.5 that the value of dTIdt remains virtually constant while the self-heating process of 2 cm of a chemical of the TD type, subjected to the adiabatic self-heating test, is in the early stages. 

Thirdly, let us assume that the coefficient, a, i.e., EIR K, of Eq. (44) holding for the individual self-heating processes, in the early stages, of 2 cm each of the ten organic liquid peroxides charged each in the open-cup cell and subjected each to the adiabatic self-heating test, takes a mean and constant value of 14,000 K, on comparing the values of a presented Table 8 in Subsection 5.7.1. 

And lastly, let us assume that, at the time when the adiabatic self-heating test was started from a T, of 60 °C for 2 cm of an organic liquid peroxide charged... 

Then, according to the result of the calculation given in Table 2, at the time when the adiabatic self-heating test started from the T,. is interrupted, i.e., at the time when the temperature of the peroxide has increased by 1.25 K from the the rate of increase in temperature of the peroxide will be about 1.346 (= 1.15 X 1.1701) K/h. 

When the rate of increase in temperature of 2 cm of the chemical subjected to the adiabatic self-heating test started from a T, has varied or has accelerated from 1.15 up to 1.346 K/h after the lapse of one hour, we may assume that the rate has remained, in fact, at a mean, and almost constant, value of 1.25 (1.15 + 1.346)/2 K/h during this one hour. 

The linearity, of this order, of the self-heating process or curve, of 2 cm of a chemical of the TD type subjected to the adiabatic self-heating test started from a Ts, recorded for the time, A t, required for the temperature of the chemical to increase by the definite value of AT of. 25 K from the r is exemplified by a digital record of the self-heating process, which is presented in Table 5 in Section 4.7, of 2 cm of 99 % tert-butyl peroxybenzoate (TBPB) charged in the open-cup cell and subjected to the adiabatic self-heating test started from a nominal T, of 76 °C, for the time, At, required for the temperature of TBPB to increase by the definite value of AT of. 25 K from the nominal T. ... 

Both liquid and powdery chemicals of the TD type are, however, the same to the effect that their exothermic decomposition reactions are accompanied with no phase transition. Therefore, when charged in the open-cup cell, or confined in the closed cell, in accordance with the self-heating property of the chemical, and subjected to the adiabatic self-heating test started from a r, 2 cm each of a liquid chemical, or a powdery chemical, of the TD type continues to self-heat over the at a very slow, but virtually constant, rate depending on the value of Ts in accordance with the Arrhenius equation, after its having been warmed up to the Ts. 

In the last analysis, self-heating chemicals are classified into the two large groups, the TD and the AC type, but in fact they are subdivided into the following four groups in all, in accordance with the difference in the selfheating process which, when subjected to the adiabatic self-heating test started from a T, 2 cm each of them each show, or, in accordance with the difference in the characteristic temperature, i.e., the Tc or the SADT, to express each individual thermal instability, as presented in Table 3. 

Group in. Powdery chemicals to each of which neither of the two equations of the thermal explosion theory can be applied to calculate the Tc. When confined in the closed cell and subjected to the adiabatic self-heating test started from a 7 2 cm of a powdery chemical of this group warms slowly up to the 7j, but the temperature remains near the F, until the chemical has finished melting. Once, however, the chemical finishes melting in the course of time, an apparently sudden quasi-autocatalytic reaction of the resultant liquefied chemical starts [25]. 

Chapter 4 An adiabatic self-heating process recorder 4.1 Introduction... 

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