Plume expansion

Leisner, A. Rohlfing, A. Berkenkamp, S. Rohling, U. Dreisewerd, K. HUlenkamp, F. IR-MALDI With the Matrix Glycerol Examination of the Plume Expansion Dynamics for Lasers of Different Pulse Duration. 36. DGMS Jahrestagung 2003, Poster. 

Ablation state of target - the deeper the ablation crater in the target is, the more the direction of plume expansion swings around the target normal - use of new and large-area targets. 

Later Mayle, 1970 [400] continued their research by performing measurements of velocity and pressure within the fire whirl. He found that the behavior of the plume was governed by dimensionless plume Froude, Rossby, second Damkohler Mixing Coefficient and Reaction Rate numbers. For plumes with a Rossby number less than one the plume is found to have a rapid rate of plume expansion with height. This phenomenon is sometimes called vortex breakdown , and it is a hydraulic jump like phenomena caused by the movement of surface waves up the surface of the fire plume that are greater than the speed of the fluid velocity. Unfortunately, even improved entrainment rate type models do not predict these phenomena very well. 

The plume development in MD simulations can only be followed up to a few nanoseconds after the pulse, which is not enough to compare the data with various experimental techniques (such as MALDI, TOF-MS, shadowgra-phy, interferometry, or for PLD). The long-term plume expansion is then modeled by the direct simulation Monte Carlo method, which was recently applied to systems relevant to MALDI [112]. 

These similarities are once again a consequence of the plume expansion. During the expansion, collisions become less frequent and the rates of ion-molecule reactions decrease. Because matrix is normally in considerable excess, the last reactions of any ion wUl nearly always be with matrix neutrals. This is fortunate for understanding MALDI spectra, because simple bimolecular matrix-analyte reactions are the limiting reactions. Quantitative understanding of complex processes in dynamic cluster or dense plume environments is not necessary, at least to a good first approximation. 

Plume expansion into a high vacuum 10" bar), maintained in a high conductance system, is sufficiently rapid that the initial plume species information can be retained and representative sampling with MBMS can be achieved [5]. In addition to plume species identities and abundances, MBMS analysis also provides beam time-of-flight information, yielding velocity distributions and gas temperatures. Such data form the basis of gasdynamic models of plume formation and dissipation [3,4] and are essential for future development of film growth models. 

The size and influence of eddies on the vertical expansion of continuous plumes have been related to vertical temperature structure (3). Three ap-... 

Fig. 19-4. Vertical expansion of continuous plumes related to vertical temperature structure, The dashed lines correspond to the dry adiabatic lapse rate for reference.

For these large tr values, eddy reflection has occurred repeatedly both at the ground and at the mixing height, so that the vertical expanse of the plume has been uniformly mixed through the mixing height, i.e., 1/L. 

Buoyancy-induced dispersion, which is caused near the source due to the rapid expansion of the plume during the rapid rise of the thermally buoyant plume after its release from the point of discharge, should also be included for buoyant releases (15). The effective vertical dispersion cr is found from... 

The diameter of the receptor hood is also a critical design variable. The diameter of the heated plume, dp, can be determined geometrically if it assumed that the included angle of expansion is 18°. Alternatively, ACGIH° and Goodfellow give the following equation for the plume diameter ... 

Because the Raj and Emmons (1975) expression for tv cannot be applied in a straightforward manner, the expression given here differs from that recommended by Raj and Emmons (1975). It should be emphasized that w, which represents the inverse of the volumetric expansion due to combustion in the plume, is highly... 

The desorption of ions and neutrals into the vacuum upon irradiation of a laser pulse onto a surface proceeds as a jet-like supersonic expansion. [38] a small, but initially hot and very rapidly expanding plume is generated. [49] As the expansion is adiabatic, the process is accompanied by fast cooling of the plume. [38]... 

Fig. 11.12. Electrospray from a nanoESI capillary. The jet emitted from the Taylor cone is clearly visible and separate from the region of rapid expansion into a plume of microdroplets. By courtesy of New Objective, Woburn, MA.

Fig. 12.11 shows the structure of a rocket plume generated downstream of a rocket nozzle. The plume consists of a primary flame and a secondary flame.Fil The primary flame is generated by the exhaust combustion gas from the rocket motor without any effect of the ambient atmosphere. The primary flame is composed of oblique shock waves and expansion waves as a result of interaction with the ambient pressure. The structure is dependent on the expansion ratio of the nozzle, as described in Appendix C. Therefore, no diffusional mixing with ambient air occurs in the primary flame. The secondary flame is generated by mixing of the exhaust gas from the nozzle with the ambient air. The dimensions of the secondary flame are dependent not only on the combustion gas expelled from the exhaust nozzle, but also on the expansion ratio of the nozzle. A nitropolymer propellant composed of nc(0-466), ng(0-369), dep(0104), ec(0 029), and pbst(0.032) is used as a reference propellant to determine the effect of plume suppression. The burning rate characteristics of the propellants are shown in Fig. 6-31. Since the nitropolymer propellant is fuel-rich, the exhaust gas forms a combustible gaseous mixture with the ambient air. This gaseous mixture is ignited and afterburning occurs somewhat downstream of the nozzle exit. The major combustion products in the combustion chamber are CO, Hj, CO2, N2, and HjO. The fuel components are CO and H2, the mole fractions of which at the nozzle throat are co(0.47) and iH2(0.24).

Fig. 12.17 shows a typical set of afterburning flame photographs obtained when a nitropolymer propellant without a plume suppressant is burned in a combustion chamber and the combustion products are expelled through an exhaust nozzle into the ambient air. The physical shape of the luminous flame is altered significantly by variation of the expansion ratio of the nozzle. The temperature of the combustion products at the nozzle exit decreases and the flow velocity at the nozzle exit increases with increasing e at constant chamber pressure. 

Fig. 12.17 Flame photographs of rocket plumes, showing that the dimensions of the secondary flame decrease as the nozzle expansion area ratio is increased.

Fig. 12.13 shows the extent of the secondary flame zone as a function of the concentration of KNO3 at a chamber pressure of 4 MPa and with Dt = 5.0 mm with nozzle area expansion ratios of e = 6.3 and 11.7. No clear difference is seen for the different values of 8. It is evident that the zone shrinks with increasing concentration of KNO3 and thus also with increasing mass fraction of potassium atoms contained within the propellant Fig. 12.14 shows the extent of the secondary flame zone as a function of the concentration of K2SO4 at a chamber pressure of 4 MPa with D, = 5.0 mm and e = 1. Like KNO3, K2SO4 is seen to be effective as a plume sup-... 

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