Pulse aerodynamics

This technique has been extended by inclusion of a pulsed ionization laser to vaporize the particles after their size has been determined by aerodynamic time of flight. This causes the particle to vaporize and the resulting fragments are partly ionized. Positive ions are accelerated into the flight tube of a mass spectrometer where their chemical composition is determined [141]... 

For particle sizing, many varieties of cascade imp-actors perform well, although care must be taken to avoid errors introduced by sampling (such as collection in sampling lines). The laser/Doppler-type particle-size device can be used to measure aerodynamic size and low concentrations with a rapid readout. In a system described by Cook, a powerful pulsed laser using temporal analysis of back-scattered light can be used to measure the spatial distribution of particles. 

The cathode is continuously rotated by means of an external motor in order to allow constant ablation conditions for all pulses and a homogeneous consumption of the rod. Higher deposition rates can be obtained by substituting the simple cylindrical nozzle with a more complex one (called focuser) as described in Reference 28. Exploiting inertial aerodynamic effects [28,29], the focuser reduces the angular semiaperture of the beam from 12° to less than 1° concentrating the cluster on the center of the beam. 

Kudra, T., Zbicinski, I., and Benali, M. 2003. Pulse combustion drying aerodynamics, heat transfer and drying kinetics. 

The aerodynamic valves have a specially designed inlet (e.g., a profiled orifice in the inlet pipe, contoured diffuser, or a shrouding duct) in which the fluid flow characteristics act as a physical barrier (fluid diode) to the backflow of combustion products. Such pulse combustors are termed the valveless combustors. Example of valveless pulse combustor is shown in Figure 23.4 (Putnam et al., 1986). 

Kudra, T., Benali, M., and Zbicinski, L, Pulse eombustion drying Aerodynamics, heat transfer, and drying kinetics. Drying Technology, 2003, 21(4), 629-655. 

Based on the manner in which fuel and air charge the combustion chamber, pulse combustors are divided into two general categories those with mechanical valves and those with aerodynamic valves (also called valveless combustors). Mechanical valves can be further divided into three types flapper valves, reed valves, and rotary valves. 

Aerodynamic valves employ the fluid mechanical properties of specially designed inlets to act as a physical barrier to the backflow of combustion products out of the combustor through the inlet section. The main advantage of aerodynamic conflgurations is lack of valves and moving parts so the risk of mechanical breakdown or failure is eliminated. This is a key consideration for heavy-duty pulse combustion burners where the inlet section undergoes severe operating conditions. 

An alternative design of a pulse combustor is a so-called valveless combustor in which the mechanical valves are replaced with an aerodynamic diode in the form of a profiled orifice in the inlet pipe, contoured diffuser, or a shrouding duct [28] (Figure 20.15). Similarly to the combustor with mechanical valves, the high-temperature gases from a combustion chamber start to flow just after a... 

A number of laboratories have developed TOF mass spectrometers for the analysis of aerosol particles and aerosolized bacterial spores. In these instruments, aerosol particles are brought from the atmosphere directly into the vacuum region by means of an aerodynamic lens, skimmers, and differentially pumped regions. They are then ionized directly in flight by a pulsed laser beam. While most of these studies have involved laser desorption, the addition of matrix coatings to aerosol particles in flight has been reported in a MALDI bioaerosol mass spectrometer. 

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