Adiabatic quasi

Adiabatic heat storage or accumulation tests are performed to obtain data on temperature-and pressure-time behaviour of a substance at quasi-adiabatic conditions. Where heat dissipation by evaporation is anticipated, the measurements have to be performed in a closed system. If this is not the case the experiment may be carried out in an open system. 

Abstract Acoustic cavitation is the formation and collapse of bubbles in liquid irradiated by intense ultrasound. The speed of the bubble collapse sometimes reaches the sound velocity in the liquid. Accordingly, the bubble collapse becomes a quasi-adiabatic process. The temperature and pressure inside a bubble increase to thousands of Kelvin and thousands of bars, respectively. As a result, water vapor and oxygen, if present, are dissociated inside a bubble and oxidants such as OH, O, and H2O2 are produced, which is called sonochemical reactions. The pulsation of active bubbles is intrinsically nonlinear. In the present review, fundamentals of acoustic cavitation, sonochemistry, and acoustic fields in sonochemical reactors have been discussed. 

Isoperibolic instruments have been developed to estimate enthalpies of reaction and to obtain kinetic data for decomposition by using an isothermal, scanning, or quasi-adiabatic mode with compensation for thermal inertia of the sample vessel. The principles of these measuring techniques are discussed in other sections. 

The Reactive System Screening Tool (RSST), marketed by Fauske and Associates, is a relatively new type of apparatus for process hazard calorimetry [192, 196-198]. The equipment is designed to determine the potential for runaway reactions and to determine the (quasi) adiabatic rates of temperature and pressure rise during a runaway as a function of the process, vessel, and other parameters. 

The test is primarily a screening tool relative to reactivity of substances and reaction mixtures and is highly useful for that purpose. The determined initiation temperature is approximate. The energy calculations based on temperature increase and heat capacities are semi-quantitative because of the quasi-adiabatic mode of the system operation. The method of insulating the test cell results in moderate reproducibility of temperature rise and related pressure rise. Another disadvantage is the relatively small sample quantity with respect to full scale quantities thus, there could be a problem in that the sample may not be truly representative. 

Overadiabatic mode a quasi-adiabatic mode in which the (small) energy leaks to the environment are overcompensated for by input of supplementary energy. 

Quasi-adiabatic a vessel condition that allows for small amounts of heat exchange this condition is typical in testing self-heating by oxidation that is characterized by gas flows (although well-controlled in temperature) into and/or out of the test vessel this condition is typical as well in tests where heat transfer is avoided by active control, that is, the ambient temperature is kept identical to the test vessel temperature, such that an adiabatic condition is approached. 

A correct assessment of the situation would have predicted the explosion. The main error was considering the storage isothermal. In fact, such large vessels, when they are not agitated, behave quasi adiabatically. The correct estimation of the initial heat release rate allows calculation of the temperature increase rate under adiabatic conditions. By taking into account the acceleration of the reaction with increasing temperature, the approximate time of the explosion would have been predictable. This is left as an exercise for the reader (see Worked Example 2.1). 

Hence only about 2% of the reaction energy can be removed by the heat exchange system. Thus, the reactor behaves quasi adiabatic. In other words, the reaction is so fast that the heat exchange system is unable to remove any significant heat. 

The situation is most critical at the entrance of the reactor where the reaction will continue under quasi adiabatic conditions, even if the feed has been stopped. The temperature increase can be limited by adequate construction, such as increase of the heat capacity of the reactor itself. The PFR represents another practicable solution to achieve safe performance of this fast and exothermal reaction at industrial scale. The small volume of 42 liters compared to 900 liters for the CSTR and 5 m3 for the SBR make protecting the reactor against overpressure easy and economical. 

The choice of the saturation gas is critical. When Ar and Kr were sparged in water irradiated at 513 kHz, an enhancement in the production of OH radicals of between 10% and 20%, respectively, was observed, compared with 02-saturated solutions [22]. The higher temperatures achieved with the noble gases upon bubble collapse under quasi-adiabatic conditions account for the observed difference. Because the rate of sonochemical degradation is directly linked to the steady state concentration of OH radicals, the acceleration of those reactions is expected in the presence of such background gases. The use of ozone as saturation gas (in mixtures with 02) provided new reaction pathways in the gas phase inside the bubbles, which also increase the measured reaction rates (see Sect. IV.G.l). 

Of the approximately 12 motion pictures we made of the impact initiation process, all show that the structure of the air bubble is broken down and replaced by a turbulence area. Ignition occurs at the former site of the bubble after an induction period. The compression ratio of the air bubble appears to be the major factor determining probability of initiation by impact. The mechanism for impact initiation of nitroglycerin therefore appears to be a quasi-adiabatic compression of the gas, with heat transfer accelerated by spray formation. Hot spots formed at the former site of the bubble undergo an accelerating exothermic reaction which proceeds to a deflagration. The possibility that liquid explosives under reduced pressure may be sensitized to weak impacts must be considered. 

Dif is a diagonal matrix. Wc have solved the coupled channel ctpiations in Eq. (24) using the quasi-adiabatic log-derivative algorithm of Manolopoulos[29]. 

We have carried out a series of polymerization runs in quasi-adiabatic conditions, as described in Ref. 3, at different concentrations of both initiator and activator, so that not only their absolute amounts but also their relative ratios were widely modified. 

From the data of Table V it is also evident that the maximum polymerization rates in quasi-adiabatic conditions are 10-20 times higher than the initial reactions rates. At increasing concentrations of the active species, the ratio between the two rates regularly decreases. 

There are two different kinds of calorimeter adiabatic (or quasi-adiabatic calorimeters) and non-isothermal, non-adiabatic calorimeters (often referred to as n-n calorimeters). The accuracy of measurements made using such methods will be high if ... 

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