Effect of compressibility

The effect of compressibility is important in high mach number machines. Mach number is the ratio of velocity to the acoustic speed of a gas at a given temperature M = Vja. Acoustic speed is defined as the ratio change in pressure of the gas with respect to its density if the entropy is held constant ... 

Effects of Compressible Annular Seals, Proceedings of the 24th Turbomachinery Symposium, Texas A M University, p. 175, 1995. 

In this section incompressible liquid flow is dealt with, and the effect of compressibility is ignored. 

The above is valid for a liquid flow, when the effect of compressibility can be ignored when calculating gas flows with small pressure differences. For instance, in ventilating duct work, air is not compressed, so the density is considered as constant. In HVAC technology a unit of pressure frequently used for convenience is a water column millimeter, 1 mm H.O=10Pa. 

Vj = intake volume including effect of compressibility when applicable... 

FIGURE 9.13 Le Chatelier s principle predicts that, when a reaction at equilibrium is compressed, the number of molecules in the gas phase will tend to decrease. This diagram illustrates the effect of compression and expansion on the dissociation equilibrium ot a diatomic molecule. Note the increase in the relative concentration of diatomic molecules as the system is compressed and the decrease when the system expands. 

EXAMPLE 9.11 Sample Exercise Predicting the effect of compression on an equilibrium... 

Self-Test 9.13B Predict the effect of compression on the equilibrium composition of the reaction C02(g) + H20(1) H2C03(aq). 

We can justify the effect of compression on an equilibrium mixture mathematically by showing that compressing a system will change Q, and the reaction tends to adjust in the direction that restores the value of Q to that of K. 

Suppose we want to discover the effect of compression on the equilibrium in Example 9.1 la. We write the equilibrium constant in its complete form as... 

Experiments were conducted with air through micro-channel A = 319 (friction factor. The relative surface roughness was low k /H = 0.001) and Kn < 0.001, thus the experiments were effectively isolated from the influence of surface roughness and rarefaction. The local friction factor is plotted versus Ma in Fig. 2.25 for air. The experimental A increases about 8% above the theoretical A as Ma increases to 0.35. 

Consider the mass, thermal and momentum balance equations. The key assumption of the present analysis is that the Knudsen number of the flow in the capillary is sufficiently small. This allows one to use the continuum model for each phase. Due to the moderate flow velocity, the effects of compressibility of the phases, as well as mechanical energy, dissipation in the phases are negligible. Assuming that thermal conductivity and viscosity of vapor and liquid are independent of temperature and pressure, we arrive at the following equations ... 

Schematic view of the effect of compressing a fixed quantity of gas into a smaiier voiume at constant T. Decreasing the voiume increases the moiecuiar density, which increases the number of coiiisions per second with the waiis.

The permeation of soil at the root-soil interface by mucilage from the root cap may affect structure, and it may oppose the damaging effects of compression and shearing, but little is known. Another suggested role is that the mucilage assists root-cap cells or acts in concert with them to decrease the friction between the growing root tip and soil (51) or, conversely, that the mucilage acts as a lubricant. 

Fig. 18 Effect of compression pressure on dissolution rate. See the text for an explanation. (From Ref. 17.).

For relatively low pressure drops, the effect of compressibility is negligible, and the general flow equation [Eq. (10-29)] applies. Introducing the conversion factors to give the flow rate in standard cubic feet per hour (scfh) and the density of air at standard conditions (1 atm, 520°R), this equation becomes... 

Figure 6 shows the effects of compression rate on the ji-A curve for the PhDA2-8 thin film at air/water interface. Accompanied with the increase in the compression rate, the hump becomes more significant and the maximum surface pressure of the hump shifts toward the larger surface area. It is to be noted that the region with zero surface pressure appears only with appropriate compression rates of 3 - 7.5 (A2/molecule)/min as in (d), (e), and (f). 

Every gas consists of particles, whether as atoms (such as neon) or as molecules (such as methane). To a relatively good first approximation, any atom can be regarded as a small, incompressible sphere. The reason why we can compress a gas relates to the large separation between the gas particles. The first effect of compressing a gas is to decrease these interparticle distances. 

If kinetic factors due to slow molecular reorganization are important, hysteresis may be observed if a film is alternately compressed and expanded. Figure 13 shows the effect of compressing, expanding, and recompressing a film of optically pure iV-a-methylbenzylstearamide. 

After the tests, Djilali s group used mathematical assumptions and equations to correlate the intensity of the dye in the image with the depth in the gas diffusion layer. With this method they were able to study the effect of compression on diffusion layers and how fhaf affects water transport. Water removal in a flow charmel has also been probed with this technique and it was observed that, with a dry DL slug, formation and flooding in the FF channels followed the appearance and detachment of water droplets from the DL. Even though this is an ex situ technique, it provides important insight into water transport mechanisms with different DLs and locations. 

A. Bazylak, D. Sinton, Z. S. Liu, and N. Djilali. Effect of compression on liquid water transport and microstructure of PEMFC gas diffusion layers. Journal of... 

FIG. 4. The effect of compression pressure on the axial and radial disintegrating pressures of compacts made with AcDiSol (5%) and (A) DiTab or (B) lactose. (Data from Ref 27.)... 

As explained in Section 4.2, the osmotic pressure can be expressed as a product of two independent terms, the derivative of the free energy with respect to the amount of interface a = ( f and a geometrical factor ( f representing the effect of compression (see Eq. (4.1)). Since in solid-stabilized emulsions the interfaces... 

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