Closed system experiment

An example of plasma copolymerization of gases is the incorporation of N2 in the plasma polymer of styrene. N2 mixed with styrene was consumed in plasma polymerization [12]. In a closed-system experiment, pressure measurement is a very useful tool for investigating plasma polymerization, particularly when the monomer used does not produce gaseous by-products. The pressure changes observed in a closed-system plasma reactor with mixtures of N2 and styrene are shown in... 

For calorimetry, two different ways can be considered for closed systems experiments ... 

Tests have shown that for a given load and path length of wear, the wear rate is about the same for both open and closed systems. However, measurements of the loss in closed systems will often appear higher than the loss in open systems. This probably occurs because most closed systems experience higher loads. 

While, in principle, a tricritical point is one where three phases simultaneously coalesce into one, that is not what would be observed in the laboratory if the temperature of a closed system is increased along a path that passes exactly tlirough a tricritical point. Although such a difficult experiment is yet to be perfomied, it is clear from theory (Kaufman and Griffiths 1982, Pegg et al 1990) and from experiments in the vicinity of tricritical points that below the tricritical temperature only two phases coexist and that the volume of one slirinks precipitously to zero at T. ... 

Adiabatic Reaction Temperature (T ). The concept of adiabatic or theoretical reaction temperature (T j) plays an important role in the design of chemical reactors, gas furnaces, and other process equipment to handle highly exothermic reactions such as combustion. T is defined as the final temperature attained by the reaction mixture at the completion of a chemical reaction carried out under adiabatic conditions in a closed system at constant pressure. Theoretically, this is the maximum temperature achieved by the products when stoichiometric quantities of reactants are completely converted into products in an adiabatic reactor. In general, T is a function of the initial temperature (T) of the reactants and their relative amounts as well as the presence of any nonreactive (inert) materials. T is also dependent on the extent of completion of the reaction. In actual experiments, it is very unlikely that the theoretical maximum values of T can be realized, but the calculated results do provide an idealized basis for comparison of the thermal effects resulting from exothermic reactions. Lower feed temperatures (T), presence of inerts and excess reactants, and incomplete conversion tend to reduce the value of T. The term theoretical or adiabatic flame temperature (T,, ) is preferred over T in dealing exclusively with the combustion of fuels. 

In actual experiments we do not usually observe directly the desorbed amount, but rather the derived read-out quantities, as is the time dependence of the pressure in most cases. In a closed system, this pressure is obviously a monotonously increasing function of time. In a flow or pumped system, the pressure-time dependence can exert a maximum, which is a function of the maximum desorption rate, but need not necessarily occur at the same time due to the effect of the pumping speed S. If there are particles on the surface which require different activation energies Ed for their desorption, several maxima (peaks) appear on the time curve of the recorded quantity reflecting the desorption process (total or partial pressure, weight loss). Thereby, the so-called desorption spectrum arises. It is naturally advantageous to evaluate the required kinetic parameters of the desorption processes from the primarily registered read-out curves, particularly from their maxima which are the best defined points. 

In Chapfer 7.2, J.H. Frank and R.S. Barlow describe the basic characteristics of non-premixed flames wifh an emphasis on fundamenfal phenomena relevant to predictive modeling. They show how the development of predictive models for complex combustion systems can be accelerated by combining closely coupled experiments and numerical simulations. 

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. 

Figure 7. Date profile predicted by the D-A model for a recent uptake scenario. Here, the bone takes up U for 9 ky, at a notional groundwater U concentration of 1 after which the concentration is increased to 100 for a further 1 ky. Because the surfaces experience increased U uptake, the apparent closed system dates increase towards the centre of the bone. [Used by permission of Elsevier Science, from Pike et al. (2002),...

A rational development of models for moisture uptake begins with a description of the experimental procedure used to determine moisture uptake as a function of time. The first step in the experiment is to control the relative humidity to which a sample will be exposed. One technique to control humidity is to use saturated salt solutions. When placed in a closed system and held at a constant temperature, a saturated aqueous salt solution will provide a constant humidity (RH0) within that system. Table 1 lists relative humidities that will be maintained over various saturated salt solutions [14],... 

Fig. 2.2. Example of a polythermal path. Fluid from a hydrothermal experiment is sampled at 300 °C and analyzed at room temperature. To reconstruct the fluid s pH at high temperature, the calculation equilibrates the fluid at 25 °C and then carries it as a closed system to the temperature of the experiment.

Polythermal reaction models (Section 14.1), however, are commonly applied to closed systems, as in studies of groundwater geothermometry (Chapter 23), and interpretations of laboratory experiments. In hydrothermal experiments, for example, researchers sample and analyze fluids from runs conducted at high temperature, but can determine pH only at room temperature (Fig. 2.2). To reconstruct the original pH (e.g., Reed and Spycher, 1984), assuming that gas did not escape from the fluid before it was analyzed, an experimentalist can calculate the equilibrium state at room temperature and follow a polythermal path to estimate the fluid chemistry at high temperature. 

The rate of feed vf (in mol 1 1 s ) of the reactant into the reaction medium is now the critical parameter to adjust for a favourable outcome of a cyclisa-tion experiment. A kinetic treatment of the open system under influxion incurs the same difficulties already discussed for the closed system in Section 2. However, when the higher-order polymerisation terms are relatively unimportant and the overall process is described to a useful approximation by (6), an exact mathematical solution is possible (Galli and Mandolini, 1975). After a relatively short initial time9, the concentration of M reaches a steady value [M]st given by (72), where (3 defined by (73) is a dimensionless parameter... 

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