Radiative Heating Laser Pyrolysers

Laser pyrolysers are practically the only type of radiative heating pyrolyser with certain applicability. Attempts were made in the past to use a strong light/heat source and 

The theory of thermal aspects of laser desorption has been developed for a substrate surface subjected to pulsed laser irradiation, assuming that the laser intensity has a Gaussian distribution [21], The given surface is covered with the organic layer, which does not absorb the laser energy. However, the heat flux in the substrate that absorbs the energy heats the sample to the same temperature as the substrate. For this case, the laser intensity flux /(r,t) is given by 

The expression of p(t) depends on the laser construction, and it is difficult to determine an analytical function for p(t). However, it is possible to consider a model where p(t) has a Gaussian expression and then the integral P(t) can be calculated. Taking the pulse 

For a cw laser, powers between 0.5 to 5 W with exposures varying from 1 s up to 5 min. were utilized for pyrolysis. The surface of the area exposed to the laser was also varied from 20 pm to 400 pml The second apparatus uses a pulsed laser (pulse energy of about 1 joule) and an alignment laser to focus the beam on the sample. 

Besides the formation of some unusual products due to secondary reactions, there are several other problems regarding the use of lasers as an energy source for pyrolysis. A first problem is related to the absorption of the radiative energy into the sample. 

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The nature and distribution of pyrolysis products from a particular sample critically depend largely on the pyrolysis temperature and the specific set of pyrolysis conditions (i.e. temperature rise time, sample size, pyrolyser geometry). Laser pyrolysers are practically the only type of radiative heating pyrolyser with certain applicability. A laser pyrolyser consists of five components (i) laser (ii) fibre optics (Hi) probe for sample introduction (iv) pyrolyser body, containing the pyrolysis chamber and (v) heater of the pyrolysis chamber with dedicated control unit. The laser beam can be focused onto a small spot of a sample to deliver the radiative energy. This provides a special way to pyrolyse only a small portion of a sample. Only the sample itself is... 

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