Nozzle heating

The spectrometer is fitted with a skimmed c.w. supersonic molecular beam source. Many chiral species of interest are of low volatility, so a heated nozzle-reservoir assembly is used to generate, in a small chamber behind a 70-pm pinhole, a sample vapor pressure that is then seeded in a He carrier gas as it expands through the nozzle [103], Further details of this apparatus are given elsewhere [36, 102, 104],... 

Both a pneumatic heated nozzle system [487] and an ultrasonic nozzle/vacuum system [699] have been described for removing the troublesome solvent in order to simplify IR analysis. The former system (LC Transform ) has been commercialised [700], and allows full use of the mid-IR spectral range by providing analyte films free from solvent interference. The evaporative... 

The mass spectrometer is also incompatible with the HPLC system, but for a different reason. The ordinary mass spectrometer operates under very low pressure (a high vacuum see Chapter 10), and thus the liquid detection path must rapidly convert from a very high pressure and large liquid volume to a very low pressure and a gaseous state. Several approaches to this problem have been used, but probably the most popular is the thermospray (TS) technique. In this technique, the column effluent is converted to a fine mist (spray) as it passes through a small-diameter heated nozzle. The analyte molecules, which must be thermally stable, are preionized with the presence of a dissolved salt. A portion of the spray is introduced into the mass spectrometer. The analyte and mobile phase must be polar if the TS technique is used because the mobile phase must dissolve the required salt and the components must interact with the analyte molecule. See Workplace Scene 13.5. 

The general principle of application of this newer type of adhesive is as described earlier, melting taking place in a closed tank at 170°C and the material being pumped through heated lines to a heated nozzle for transfer to the substrate. The difference is in the design of the nozzle, which may either give a fine spray of tiny droplets of adhesive or fine threads of the molten material,... 

Molecules which are capable of undergoing conversion to an i.somer of similar thermodynamic stability via a low activation barrier (>10 kJ mol ) may be quenched in a matrix which has the composition of the vapor prior to deposition. The distribution of isomers in a matrix can be influenced by changing the temperature of a heated nozzle. By analyzing the intensities of relevant infrared absorptions, the molar ratio between two conformers can be determined as a function of the gas temperature. On this basis, the enthalpy difference between the two forms can be obtained by a van t Hoff plot. On the basis of matrix studies for the conversion of the s-cis to the s-gauche form of methyl vinyl ether, a value of AH = 6.62 kJ mol was found (Gunde et al., 1985). 

Hot-melt adhesives, which belong to thermoplastics (Section 3.3.1), are liquefied by heat supply, for example, in electrically heated nozzles of the application device, and then applied to the adherends. Since the hot-melt cools down very quickly the adherends have to be affixed immediately. The open assembly time of these adhesives, that is, the period of time between the application of the adhesive and the fixing of the adherends, is very short and must not be exceeded. The open assembly time strongly depends on the heat conductivity properties of the adherends the faster they dissipate the heat from the melt, the shorter is the open assembly time. Hot-melt adhesives are available in the form of blocks, rods, films, granulate or even in the form of powder. 

Rapid expansion of supercritical solutions. RESS (Figure 8.2) consists of saturating an SCF with the substrate(s), then depressurizing this solution through a heated nozzle into a low-pressure chamber in order to cause an extremely rapid nucleation of the substrate(s) in the form of very small particles - or fibers, or films when the jet is directed against a surface - that are collected from the gaseous stream ]. 

Various waxes, fatty alcohols, fats and fatty adds are also used as coating (carrier) material. In these cases, the active agent is dispersed in the molten carrier (using an emulsifier, if necessary) and the dispersion atomized through heated nozzles into a cooling chamber where the carrier sohdifies to form the coating. 

The spray-dryer is equipped with a heated nozzle (or centrifugal atomizer) to spray the liquid. The main supports for food products are vegetable fat and stearine (MP 45°C-122°C) monoglycerides and diglycerides (MP 45°C-67°C) and vegetable hydrogenated oils (MP 32°C-42°C). The final products can be used in bakery, in soups. Other supports, solid at working temperature, may be chosen as a function of domain of utilization, viscosity, and crystallization properties. 

As presented in Figure 24.5, a supercritical fluid saturated with the substrates is expanded through a heated nozzle into a low-pressure chamber in order to cause an extremely rapid nucleation of the substrates in a micronized form. 

The anticipation of the future improvement of the resolution of such technologies has, nevertheless, maintained the research momentum in this direction. Similarly, another rapid prototyping technique, fused deposition modeling, has been used to fabricate 3-D scaffolds (119). This technique is suitable for processiug thermoplastic polymers. A heated nozzle is utilized to extrude pol5uner... 

Fused deposition modeling (FDM) is a technology where the melt extrasion method is used to deposit filaments of thermal plastics according to a specific pattern. Similar to 3DP, the layout for FDM consists of a printhead able to move along X and Y directions above a build platform. The polymer is extraded through the heated nozzle and laid down as filaments according to the CAD design. The build platform is then lowered and another layer can be built, until the scaffold is completed. ... 

Type of heating. Nozzles have external or internal heating, or both types at once. There are also heat-conducting nozzles. These are short nozzles made of a copper alloy warmed by the heat from the HR manifold. 

---