Semi adiabatic

It is evident from the method of proof that a range of semi-adiabatic cases in which (dTldt r) = 6 -h.H)rICp will also yield unique equilibria it is only necessary that B be independent of r. 

Any chemical reaction is accompanied by an energy conversion, in the most cases heat production, and normally this heat is proportional to the amount of substance converted. It can therefore be a measure of its amount. In an insulated adiabatic system of defined heat capacity (calorimeter), the heat produced leads to a proportional temperature rise, and even in open semi-adiabatic systems proportional temperature changes are observed, however, these systems must be calibrated for substance determinations. Very sensitive devices for the measurement of temperature changes are thermistors, which are semiconductor resistances with high temperature coefficients, eg, 3-4% °C . ... 

Adiabatic calorimeters include here, all at once, the Ideal adiabatic and the Semi-adiabatic The same general meaning for the term adiabatic was kept to define the adiabatic family in sections 4.2. and 4.3. 

Adiabatic measurements and kinetic parameters. The experimental temperature measured in a semi adiabatic box and the adiabatic temperature rise, obtained from a paste with w/c=0,45, is shown in the Fig. 1. Once the adiabatic temperature is known the global heat transfer coefficient (U) can be determinate with a good correlation coefficient (Fig. 2). 

Semi-adiabatic calculations have also been carried out (Clary and Connor (211) for H+F2(v=0. j=0) at Etr 0.106 eV (see Table II). The calculation using the VA approximation for reactants, and the S approximation for the product vibrations, gives a vibrational distribution that agrees closely with the full VADW calculation. However, agreement is poor when the is used for reactants and the VA for products (211. This interesting result Is probably related to the position of the barrier on the potential surface. An accurate description of the reaction dynamics is particularly important around the barrier region, and for H+F2. the barrier is located early in the entrance valley. 

For an ideal adiabatic case, the radiation-induced temperature rise of the absorber of the calorimeter is a linear function of time during irradiation at constant dose rate. The temperature rise of a semi-adiabatic calorimeter during irradiation as a function of time is shown in O Fig. 49.5. 

Temperature rise of a semi-adiabatic caiorimeter before, during, and after irradiation... 

A common design of semi-adiabatic calorimeters contains thin or thick disc-shape absorbers used mainly in monodirectional beams both for low-energy (McDonald et al. 1972) and for higher-energy electron beams (Bewley 1969). Water calorimeters of the same shape were designed by Brynjolfsson et al. (1963) and Fielden and Holm (1970). 

Semi-adiabatic calorimeters have been designed for dosimetry at high-energy electron accelerators (1-10 MeV) both for calibration and for routine process control (Humphreys and McLaughlin 1989 Miller and Kovacs 1985 Burns and Morris 1988) and also for low energies between 100 keV and 500 keV (Janovsky and Miller 1987). The disc-shape absorber is either water or graphite containing thermistors for temperature measurement placed in the center of the absorber. The absorber is placed in polystyrene foam insulation. 

Isothermal calorimeters measure thermal power (heat production rate), while (semi)adiabatic calorimeters measure temperature (change). It is possible to calculate one of these from the other, but to do so we need to take the derivative (to go from semiadiabatic to isothermal) or integrate (to go from isothermal to semiadiabatic) and in both cases we need the heat capacity of the sample. The thermal power signal from an isothermal calorimeter shows more details than the temperature signal from an adiabatic calorimeter as the former directly assesses the rate of the process, while an adiabatic calorimeter measures the integral of the rate. Isothermal calorimetry is thus a more generally useful analytical method than semiadiabatic calorimetry. 

Figure 2.4 An example of how (a) temperature, (b) thermal power and (c) heat develop over time in an Isothermal, a semiadiabatic and an adiabatic calorimeter. Note that paste or mortar is generally used in isothermal calorimetry, while mortar or concrete is used in (semi)adiabatic calorimetry.

Calorimetric techniques have been used for 100 years in the cement field. Today the heat-of-solution method is being phased out, while isothermal and (semi)adiabatic calorimetry will continue to be used both for heat of... 

EN 196-9 (2010). Method of testing cement - Part 8 Heat of hydration - Semi-adiabatic method. 

Wadso, L. (2003). An experimental comparison between isothermal calorimetry, semi-adiabatic calorimetry and solution calorimetry for the study of cement hydration . Nordtest Report TR 522, available at http //www.nordtest.info/index. php/technical-reports/category/building/2.html. 

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