High heating rates

The gas turbine is the best suited prime mover when the needs at hand such as capital cost, time from planning to completion, maintenance costs, and fuel costs are considered. The gas turbine has the lowest maintenance and capital cost of any major prime mover. It also has the fastest completion time to full operation of any other plant. Its disadvantage was its high heat rate but this has been addressed and the new turbines are among the most efficient types of prime movers. The combination of plant cycles further increases the efficiencies to the low 60s. 

Current use of statistical thermodynamics implies that the adsorption system can be effectively separated into the gas phase and the adsorbed phase, which means that the partition function of motions normal to the surface can be represented with sufficient accuracy by that of oscillators confined to the surface. This becomes less valid, the shorter is the mean adsorption time of adatoms, i.e. the higher is the desorption temperature. Thus, near the end of the desorption experiment, especially with high heating rates, another treatment of equilibria should be used, dealing with the whole system as a single phase, the adsorbent being a boundary. This is the approach of the gas-surface virial expansion of adsorption isotherms (51, 53) or of some more general treatment of this kind. 

In TGA studies on the decomposition of iodine-doped polyacetylene, at high heating rates (30°C/min), decomposition becomes explosive at the m.p. of iodine, 113°C. This was attributed to exothermic reaction of liquid iodine with polyacety-lene. 

For this method, the first derivative of the temperature has to be determined from process measurements with amplified noise filtered out. Since the "safe" temperature need not be specified, the independence and selectivity of this method is greater than with the temperature criterion alone. Another advantage is that a potentially unsafe condition can be identified in its early development stage. However, a number of frequently used, but low hazard thermal processes are characterized by fairly high heating rates, making the use of the first derivative ineffective. 

Heating up of the sample to the selected temperature with a high heating rate (e.g. 100 °C/min). 

Under extraordinary conditions, that is, high heating rates 10000 °C/s, so-called catastrophic fragmentation occurs (pathway 13) resulting in low molecular products,... 

R.A. Beyer, Molecular Beam Sampling Mass Spectrometry of High Heating Rate Pyrolysis. Description of Data Acquisition System and Pyrolysis of HMX in a Polyurethane Binder ,... 

This instrument was designed to yield information intermediate between the ARC and the DSC. A sample of 0.2-0.5 g is loaded into a tube-like container and placed into the device (larger sample sizes may be used at slower scan rates). A thermocouple is connected to the outside of the tube and the cell is fitted with a pressure transducer. A similar, empty cell in the same oven with thermocouple serves as a thermal reference. The oven is heated at a slow, linear rate (0.5 to 1 °C/min), and the pressure and differential thermal data are collected. The data are presented in a fashion similar to DSC - Heat Rate (mW) vs. Temperature (°C). The thermal data are enthalpically calibrated by means of a series of standards (cahbration at high heat rates may be non-linear). Detection of thermal events approaches the sensitivity of the ARC. 

Problems in the direct determination of cadmium in soil extracts by graphite furnace atomic absorption spectrometry are overcome by the use of a low atomisation temperature of 1200 °C (mini-furnace or high heating rate of > 2000 °C/s), the addition of molybdenum, hydrogen peroxide and nitric acid as a matrix modifier, and accurate optimisation of the instrumental parameters. 

Worsoe-Schmidt, P.M., Heat Transfer and Friction for Laminar Flow of Helium and Carbon Dioxide in a Circular Tube at High Heating Rate , Int. J. Heat-Mass Transfer, Vol. 9, pp. 1291-1295,1966. 

---