Heating air jets

Buoyant jets when the buoyant force acts in the direction of the jet supply velocity at the origin, i.e., upward-projected heated air jet or downward-projected cooled air jet... 

Helander, L., S. M. Yen, and W. Tripp. 1957. A.SHRAF1 Research Report No. 1601 Outlet characteristics that affect the dowm throw of heated air jets. ASHVE Transactions, vol. 63, p. 255. 

As it is already shown in experiments that the amount of entrained gas is influenced by the spray chamber design [40]. For spray chambers with small cross-sectional areas, the characteristic maximum of the curves in Fig. 19.8 is lower. The most entrained amount of gas near the inlet can be found for free jets. There is no maximum in this case since there is no recirculation movement. In free heated air jets, the entrainment strongly reduces the gas temperatures. 

The air jet textured yam process is based on overfeeding a yam into a turbulent air jet so that the excess length forms into loops that are trapped in the yam stmcture. The air flow is unheated, turbulent, and asymmetrically impinges the yam. The process includes a heat stabilization zone. Key process variables include texturing speed, air pressure, percentage overfeed, filament linear density, air flow, spin finish, and fiber modulus (100). The loops create visual and tactile aesthetics similar to false twist textured and staple spun yams. 

Filament. Eully drawn flat yams and partially oriented (POY) continuous filament yams are available in yam sizes ranging from about 3.3—33.0 tex (30—300 den) with individual filament linear densities of about 0.055 to 0.55 tex per filament (0.5—5 dpf). The fully drawn hard yams are used directly in fabric manufacturing operations, whereas POY yams are primarily used as feedstock for draw texturing. In the draw texturing process, fibers are drawn and bulked by heat-setting twisted yam or by entangling filaments with an air jet. Both textured and hard yams are used in apparel, sleepwear, outerwear, sportswear, draperies and curtains, and automotive upholstery. 

A number of laboratory tests are used to predict chemical stabihty. The amount of existent gum in a gasoline is determined by ASTM D381. This method involves evaporating a sample by a jet of heated air. The residue is weighed, solubles are extracted with / -heptane, and the sample is reweighed. 

A further hazard exists when eompressed air jets are used to elean maehine eomponents in workplaees flying partieles have eaused injury and blindness. Cylinders may fail if over-pressurized or weakened by the applieation of heat. Liquefied gases, e.g. butane or propane, respond more rapidly to heat than the permanent gases sueh as nitrogen or oxygen. Cylinders are normally proteeted by pressure relief valves, fusible plugs or bursting dises. 

Airborne contaminant movement in the building depends upon the type of heat and contaminant sources, which can be classified as (1) buoyant (e.g., heat) sources, (2) nonbuoyant (diffusion) sources, and (d) dynamic sources.- With the first type of sources, contaminants move in the space primarily due to the heat energy as buoyant plumes over the heated surfaces. The second type of sources is characterized by cimtaminant diffusion in the room in all directions due to the concentration gradient in all directions (e.g., in the case of emission from painted surfaces). The emission rare in this case is significantly affected by the intensity of the ambient air turbulence and air velocity, dhe third type of sources is characterized by contaminant movement in the space with an air jet (e.g., linear jet over the tank with a push-pull ventilation), or particle flow (e.g., from a grinding wheel). In some cases, the above factors influencing contaminant distribution in the room are combined. 

Based on theoretical analyses, Koestel, Sheptelev," and Grimitlyn developed equations for velocities and temperatures in vertical heated and chilled air jets. The assumptions used by these authors are similar, and the method used is described in Koestel. The assumptions used in the analysis can be summarized as follows ... 

The only force opposing the downward flow of the heated air or upward flow of the cooled air is a buoyancy force. In their analysis, Helander and Jakowatz also suggested accounting for inertial forces due to the entrainment of room air. However, this suggestion is not in an agreement with a principle of momentum conservation used in most of the existing models for isothermal jets. 

The throw of downward-projected heated linear jets or upward-projected chilled air jets can be calculated as ... 

The discussion of the interaction of air jets supplied at some angle to each other shows that application of the method of superposition of the interacting jets momentums and surplus heat to predict velocity and temperatures in the combined flow results in inaccuracy when two unequal jets are supplied at a right angle. A different approach was undertaken in the studies of interaction of the main stream with vertical directing jets. Ti i... 

Koestel, A. 1955. Paths of horizontally projected heated and chilled air jets. Heating. Piping and Air Conditioning, July, pp. 221-226. 

Frean, D. H., and N. S. Billington. 1955. The ventilating air jets, journal of the Institution of Heating and Ventilating Engineers, December. 

Sadovskaya, N. N. 1950. Studies of air circulation in the. spaces with heating and ventilating by concentrated air jet supply. Ph.D. thesis. VNIIOT VtsSPS, Leningrad. 

Shepelev, L A., and M. D. Tarnopolsky. 1965. Turbulent air jet spreading in the confined space. In Heat-, Gas Supply and Ventilation Proceedings of the Conference. Budivelnik, Kiev. 

Gobza, R, N. 1947. Warm Air Heating with Concentrated Air Jet Supply. Ser. 436, KTIS. Stroizdat, Moscow. 

Each method has its own design criteria, but common to most ol the methods is that air supply is located close to or inside the controlled zone and the exhaust openings are located inside the uncontrolled zone. The location and power of the buoyancy sources in relation to the supply air jets have a remarkable influence on the accumulations of heat, contaminants, and humidity within the room. 

These combinations are possible without too detailed design of the combined jet and exhaust, since the wide jet itself will act as a separator between inside and outside and the consequences of an imbalance of supply and exhaust airflow are small. The relative mixing of outside and inside air into the jet is less than for a thin air jet, which also makes it easier to design fan(s) and ducts. The high velocity needed requires a high airflow rate and, with heating, can be expensive to operate. 

The biomass is fed overbed through multiple feed chutes using air jets to help distribute the fuel over the surface of the bed. Variable-speed screw conveyors are usually used to meter the fuel feed rate and control steam output. Feedstocks such as bark and waste wood are chipped to a top size of 25 mm (1 in) to ensure complete combustion. The bed usually consists of sand around 1 m (3 ft) deep. This serves to retain the fuel in the furnace, extending its in-furnace residence time and increasing combustion efficiency. It also provides a heat sink to help maintain bed temperature during periods of fluctuating fuel moisture content. 

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