Divergence, atmospheric

Vertical air motions affect both weather and the mixing processes of importance to air pollution. Upward vertical motions can be caused by lifting over terrain, lifting over weather fronts, and convergence toward low-pressure centers. Downward vertical motions can be caused by sinking to make up for divergence near high-pressure centers. One must know whether the atmosphere enhances or suppresses these vertical motions to... 

In the cinematic method the airflow in the aperture is understood to be the result of interaction of the air curtain jet and the incident flow. Some of the cinematic methods that were developed did not apply the laws of conservation of the impulse and mechanical energy. These methods did not correspond satisfactorily to test results and were not developed further. In these cases the determination of the jet trajectory does not take into account the effect of the enclosures and the interaction of the jets, and the division of airflows between the room and the outer atmosphere is performed with an arbitrary geometrical construction. The above-mentioned facts lead to divergence of design results and existing test results as to both the release speed and the initial temperature of the air curtain."... 

The gas continues to expand isentropically and the pressure ratio w is related to the flow area by equation 4,47. If the cross-sectional area of the exit to the divergent section is such that >r 1 = (10,000/101.3) = 98.7, the pressure here will be atmospheric and the expansion will be entirely isentropic. The duct area, however, has nearly twice this value, and the flow is over-expanded, atmospheric pressure being reached within the divergent section. In order to satisfy the boundary conditions, a shock wave occurs further along the divergent section across which the pressure increases. The gas then expands isentropically to atmospheric pressure. 

Air passes from a large reservoir at 70°F through an isentropic converging-diverging nozzle into the atmosphere. The area of the throat is 1 cm2, and that of the exit is 2 cm2. What is the reservoir pressure at which the flow in the nozzle just reaches sonic velocity, and what are the mass flow rate and exit Mach number under these conditions ... 

Air flows from a large reservoir where the temperature and pressure are 25°C and 10 atm, through a convergent-divergent nozzle and discharges to the atmosphere. The area of the nozzle s exit is twice that of its throat. Show that under these conditions a shock wave must occur, (y = 1.4.)... 

It should be noted that the gas flow process in the port is not isentropic because mass and heat addihons occur in the port. This implies that there is stagnation pressure loss and so the specific impulse is reduced for nozzleless rockets. When a convergent nozzle is attached to the rear end of port, the static pressure at the port exit, Pj, continues to decrease to the atmospheric pressure and the specific impulse of the nozzleless rocket motor is increased. The expansion process in a divergent nozzle is an isentropic process, as described in Section 1.2. 

Nozzleless rockets are very simplified and low-cost rockets because no nozzles are used. Their specific impulse is lower than that of conventional rockets even when the same mass of propellant is used. Normally, a convergent-divergent nozzle is used to expand the chamber pressure to the atmospheric pressure through an isentropic change, which is the most effective process for converting pressure into propulsive thrust The flow process without a nozzle increases entropy and there is stagnahon pressure loss. 

During a diffusion process, e.g. the migration of an additive from a plastic into the atmosphere, a change in the concentration of the diffusing substance takes place at every location throughout the plastic. The mass flux caused by diffusion is represented by a vector quantity whereas the concentration c and its derivative of time t is a scalar quantity and is connected by the flux with help of the divergence operator. The following example serves to emphasize this relationship. 

The development of the chemistry of the atmosphere was somewhat delayed by the early lack of realisation that there exist various kinds of gases. At first the term air was applied to all gaseous substances, and not until the commencement of the seventeenth century was the difference m the nature of various gases recognised at this time van Helmont, who introduced the term gas, observed the divergence in the properties of gases from different sources, and as an almost immediate result carbon dioxide was accepted as a minor constituent of the atmosphere. 

In the case of TiC, further work on substrates with well characterised bulk and surface compositions is needed to elucidate the diverging results of the literature. Whatever the explanation, it has to be recognized that the wettability of TiC and TiN, and probably of other stable and oxidizable carbides and nitrides such as ZrC, ZrN, HfC and HfN, is very sensitive to the furnace atmosphere. 

The process of dry deposition for gases and particles has three stages which are outlined in Fig. 4. The first one is the transport from the free atmosphere to the laminar boundary layer of air close to the surfaces of objects. The second one is the transport through this layer and in the third the gas or particles must be absorbed and captured or otherwise entrained by the surface. As various species are transported to successive stages in this process the number of individual mechanisms influencing rates of transport increases and rates of transport for different materials diverge. 

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