Pressure-volume curve

The pressure-volume curve of a proposed centrifugal fan has a different shape. This fan curve must be drawn for the anticipated fan inlet density expected at its location in the system. The point of intersection of these two curves locates the flow rate and pressure rise at which the fan and system operate. This intersection represents a desirable operating combination for fan and system. The system curve intersects the fan curve in the middle of its maximum efficiency range and also at a point where the fan pressure produced varies smoothly but distinctly in a constant trend with flow rate which is desirable for flow control. 

The steep pressure-volume curve permits the axial compressor to oper ate very well in parallel with other axial compressors. The pressures do not have to match precisely to permit load sharing, as the steepness of the curve allows for adjustment without danger of going into surge or taking wild load swings as sometimes happens when attempts are made to opci ate centritiigal compressors in parallel,... 

Fig. 2.17. Fused quartz is known to have an anomalous softening with stress or pressure in both static and shock loading. The time-resolved wave profile measured with a VISAR system shows the typical low pressure ramp followed by a shock at higher pressure. The release to zero pressure is with a shock, in agreement with the shape of the pressure-volume curve (after Setchell [88S01]).

Pressure-volume curve illustration for a turbocharged and direct-injected high-speed heavy-duty four-stroke diesel cycle engine. 

Figure 12-137 illustrates the separate effect of a partially closed outlet damper or vane on a pressure-volume curve. 

The curves should show that the measured value will be different depending on whether the input value is increasing (bottom curve) or decreasing (top curve). Often seen clinically with lung pressure-volume curves. 

More physiologically, it can be shown that work is given by pressure x volume. This enables indices such as work of breathing to be calculated simply by studying the pressure-volume curve. 

To analyse the complete pressure/volume curve simple statistical methods were applied The p/V curves of every single measurement are linear interpolated and then evaluated on a fixed lattice of points at the logarithmic pressure scale. 

For each laboratory and for each sample Bl, Gl, B2, G2, B3, G3 the average pressure/volume curve is calculated. 

It is remarkable that the pressure/volume curves of all samples have similar shapes regardless of sample preparation methods. They can be called a fingerprint of the porous material tested here, i.e. of the cementitious mortar with this composition. 

The preparation methods of 105 °C diying and vacuum pre-treatment yield samples with different residual moisture contents (see Table 1). The pressure/volume curves of dry (Bl Gl) and wet (B2 G2) samples are compared in Fig. 1 and 2. 

The specific pore volume can be determined from nitrogen adsorption measurements if the adsorbent is meso- or microporous. For macroporous adsorbents with pore diameters above 1000 A, the pore volume can be determined by mercury penetration measurements by integrating the pressure volume curve. The total pore volume of meso- and microporous adsorbents can be calculated by assuming that, in the range 0.95 < pjpo < 1, all pores in the adsorbent are filled with condensed gas. The total pore volume is then simply calculated as ... 

A schematic plot of the variation of the pressure with volume, as predicted by the van der Waals equation of state, at various temperatures is given in Fig. 10.2. At temperatures above the critical temperature, the pressure-volume variation is monotonic and qualitatively similar to that of an ideal gas (see dotted-line). At temperatures below tire critical temperature, the pressure-volume curve begins to oscillate, exhibiting a van der Waals" loop (see dashed-line). This behavior is unphysical, but represents tire vapor-liquid transition, and should be replaced by the solid line. The precise location of the solid line is given by the Maxwell construction. 

When the temperature is equal to the critical temperature, the pressure-volume curve exhibits a point with the inflection (concavity) of the curve changes sign. This occurs at the critical point, where we have ... 

Abnormalities in filling are also associated with changes in chamber stiffness that occur in HCM. This stiffness may be the result of myocardial fibrosis, cellular disorganization, or increased myocardial mass. The decreased distensibility leads to an abnormally steep slope of the diastolic pressure-volume curve such that an increase in LV volume results in a disproportionate increase in diastolic pressure. 

HFV has been mentioned as a ventilator option for neonatal RDS (see Table 28-2). The basic concept for its use in ARDS is that the pressure-volume curve in ARDS creates a narrow window of safety... 

This agrees with the description of the graded bar and the equilibrium states we imagined for various portions of that and the approach can clearly be used for the salt-diffusion problem, at the 4 m-wide dike. To treat pressure differences in a parallel manner, one notes that materials become less compressible when compressed the pressure-volume curve for a fixed mass is usually concave away from the origin, as a hyperbola is. Then a profile of graded pressure is like a profile of graded concentration it is intrinsically and unquestionably a nonequilibrium state at every point, but the properties of any small portion can be matched with the properties of an imagined equilibrium state. 

Figure 4. Pressure-volume curve of the interstitial spaces (extrapolated to the human being from data obtained from dogs)...

To measure compliance, the subject is intubated with an esophageal balloon and then told to breathe in or out of a spirometer in 500-ml increments. During breath holding, with the epiglottis open, the alveolar pressure is the same as the pressure at the mouth. Values of volume change and pleural pressure changes measured simultaneously produce a pressure-volume curve similar to that shown in Fig. 13. 

The shape, position, and slope of the static deflation pressure-volume curve is characteristic of certain disease states. Obstructive diseases such as... 

Fic. 13. Pressure-volume curve utilized for measuring lung compliance. Patients with obstructive diseases show a shift of the normal curve upward, whereas in restrictive diseases the curve shifts downward and to the right. 

Expression (7.43) is the pressure relation we shall use in the complete calculations of pressure-volume curves. It will prove useful, however, to use an expression which is less accurate but more directly related to simple potential parameters such as band centres and masses in order to understand the more complete calculations. In the following we shall derive such an expression from canonical band theory. 

FAN PERFORMANCE CURVE - Fan performance curve refers to the constant speed performance curve. This is a graphical presentation of static or total pressure and power input over a range of air volume flow rate at a stated inlet density and fan speed. It may include static and mechanical efficiency curves. The range of air volume flow rate which is covered generally ex tends from shutoff (zero air volume flow rate) to free delivery (zero fan static pressure). The pressure curves are generally referred to as the pressure-volume curves. 

Figure 5 Shape of the pressure-volume curves of the chest wall, lung, and respiratory system. EEV=elastic eqniUhrium volume RV=residual volume.

---