Temperature gradient in the gas

As shown in Fig. 5.25, the temperature gradient in the gas phase at Tq = 243 K and p = 3 MPa reaches a maximum at the burning surface, decreases with distance from the burning surface, and becomes zero at a distance of about 1.1 mm. When the initial temperature, Tq, is increased from 243 K to 343 K, the temperature gradient is increased and becomes zero at about 0.7 mm from the burning surface. 

The heat flux transferred back from the gas phase to the burning surface is dependent on the temperature gradient in the gas phase, which is inversely proportional to the thickness of the reaction zone in the gas phase. Since the reaction in the gas phase is complete at the upper end of the bluish flame, the heat flux defined by Am conforms to the proportionality relationship Am l/6g p0- . The observed pressure dependence of the burning rate, is caused by the pressure depend-... 

Fig. 7.28 Temperature gradients in the gas phase just above the burning surfaces of non-catalyzed and 0.5% LiF-catalyzed AP composite propellants.

The boron particles are thermally inert in the solid phase beneath the burning surface of the pyrolant The oxidation of the boron particles occurs just above the burning surface. This implies that the temperature gradient in the gas phase, (j), increases and hence the burning rate is increased accordingly. 

Substitution of H for H requires the assumption of uniform (though not constant) conditions throughout the tank. This requires the absence of any pressure or temperature gradients in the gas in the tank. 

From Equation 22, the temperature gradient in the gas phase at the droplet surface is ... 

In this chapter, we consider Brownian diffusion, sedimentation, migration in an electric Reid, and thermophoresis. The last term refers to particle movement produced by a temperature gradient in the gas. We consider also the London-van der Waals forces that are important when a particle approaches a surface. The analysis is limited to particle transport in stationary —that is. nonllowing— gases. I ransporl in flow systems is discussed in the chapters which follow. 

The force fields of most interest i n particle transport are gravitational, electrical, and thermal. with the last field produced by temperature gradients in the gas. If a balance exists locally in the gas between the force field and the drag on the particle, the two can be equated to give... 

A u ell-insulated. 0.7-nr gas cylinder containing natural gas which can be considered to be pure methane) at 70 biir and. 100 K is exhausted until the pressure drops to 3.5 bar. This process occurs fast enough that tliere is no heat transfer between the cylinder walls and the gas. but not so rapidly as to produce large velocity or temperature gradients in the gas within the cylinder. Compute the number of moles of gas withdrawn and the final temperature of the gas in the cylinder if... 

The temperature gradient in the gas film just outside a catalyst pellet is steeper than the internal gradient at the surface, because the solid conductivity is generally several times greater than the thermal conductivity of the... 

If the surface of the solid material is isolated from the oxygen by a gaseous layer, the oxygen molecules can reach the surface only by diffusion. Molecules of a combustible gas are intermixed with oxygen also by diffusion. Molecular diffusion in a motionless medium is a spontaneous process caused by the heat-motion of the molecules. It is impelled by the concentration and/or temperature gradients in the gas mixture the diffusion acts in a direction such as to diminish the gradients. The rate of diffusion is inversely proportional to the square root of molecular mass. 

Figure 12 shows the temperature gradient in the gas ullage space at different times during the run. This plot clearly shows a temperature stratification which was maintained during the entire run. All other runs showed a similar stable stratification pattern. 

Neglecting any temperature gradients in the gas and also neglecting any term greater than 0(e), we can write the Burnett momentum equation as... 

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