Dynamic loss

The mechanical efficiency of a fan is the ratio of the horsepower output to the horsepower input at the fan shaft. The input horsepower to drive the fan consists of the air horsepower, the energy losses in the fan, fluid dynamic losses, shock losses, leakage, disk friction, and bearing losses (all as horsepower), The fan oudet velocity pressure loss has been included in the fluid dynamic losses. 

The 1,120 psi of this pressure drop is a dynamic loss due to the change in velocity, and 505 psi is a frictional loss due to the fitting. 

The flow loss in a system varies as (velocity) or (flow rate), so the total loss imposed by a system on a pump can be shown to vary with flow rate in the way shown in Figure 32.38(a). Figures 32.38(b) and 32.38(c) illustrate how system curves vary with the proportions of static and dynamic losses. 

The simplest flow control is by valving (Figure 32.41). Either opening or closing a valve in the line changes the dynamic loss. The valve could be pressure controlled, a method much used in boiler feed systems because it... 

The dynamic loss due to friction in the pipe, the miscellaneous losses, and the pressure loss through equipment. 

The static pressure difference will be independent of the fluid flow-rate. The dynamic loss will increase as the flow-rate is increased. It will be roughly proportional to the flow-rate squared, see equation 5.3. The system curve, or operating line, is a plot of the total pressure head versus the liquid flow-rate. The operating point of a centrifugal pump can be found by plotting the system curve on the pump s characteristic curve, see Example 5.3. 

Dynamic mechanical testers apply a small sinusoidal stress or strain to a small sample of the polymer to be examined and measure resonant frequency and damping versus temperature and forced frequency. Instrument software computes dynamic storage modulus (G ), dynamic loss modulus (G") and tan delta or damping factor. Measurements over a wide range of frequency and temperature provide a fingerprint of the polymer with sensitivity highly superior to DSC. 

Figure 5. The variation of the dynamic loss modulus (G") with oscillation frequency at 25 C for UHMWPE pseudo-gel (4% w/w) first run 0 second run A, third run , fourth run.

Figure 9. The variation of the dynamic loss modulus (G") of UHMWPE...

Fig. 15 Effect of different kinds of nanofiller on the dynamic loss tangent of CR vulcanizates with temperature...

The most straightforward way to measure the effect of low temperatures on recovery is by means of a compression set or tension set test. Tests in compression are favoured and a method has been standardised internationally. The procedure is essentially the same as set measurements at normal or elevated temperatures and has been discussed in Chapter 10, Section 3.1. As the recovery of the rubber becomes more sluggish with reduction of temperature the dynamic loss tangent becomes larger and the resilience lower (see Chapter 9), and these parameters are sensitive measures of the effects of low temperatures. Procedures have not been standardized, but rebound resilience tests are inherently simple and quite commonly carried out as a function of temperature. It is found that resilience becomes a minimum when the rubber is in its most leathery state and rises again as the rubber becomes hard and brittle. 

Dynamic loss process occurs at lower temperature. 

A schematic of the system is illustrated in Figure 1. For dynamic frequency sweeps (refer to Figure 2), the polymer is strained sinusoidally and the stress is measured as a function of the frequency. The strain amplitude is kept small enough to evoke only a linear response. The advantage of this test is that it separates the moduli into an elastic one, the dynamic storage modulus (G ) and into a viscous one, the dynamic loss modulus (G"). From these measurements one can determine fundamental properties such as ... 

In conclusion, it is unambiguous from the solid-state NMR investigations that phenyl ring motions are involved in the mechanical ft transition of BPA-PC. Additional support for this statement comes from the fact that the position and shape of the mechanical dynamic loss, G", can be well simulated by using the activation parameters and the Williams-Watts exponent deduced from the analysis of the phenyl ring motions [34], as shown in Fig. 53. 

The dynamic losses can only be estimated by first sizing the pipe diameter of the line between the absorption column and the bleaching column. This is performed using recommended liquid velocities (Ref. P1, p. 163) in conjunction with the known volumetric flowrate. The area calculated can be translated into a standard pipe diameter. The dynamic losses are then estimated by two methods. The first employs Genereaux s formula (Ref. P1, p. 160) ... 

Net positive suction head (kPa) 850.0 848.0 Control valve (% dynamic loss) 68. 0... 

Figure 9. Contour plot (70) of dynamic loss compliance as a function of frequency and temperature for poly(styrene-b-butadiene-styrene).

Fig. 6. Strain sweeps for the dynamic loss (shear) modulus G" of styrene-butadiene rubber samples filled with various carbon blacks (from [81])...

For esterified wood, the change in dynamic loss (G") as a function of temperature with the change in the number of carbons of introduced side chains (n) is shown in Fig. 1. Five dispersions are found for n 3. They are attributed to the main chain motion of lignin (a ), the restricted main... 

Figure 1 The effect of the length of side chains on dynamic loss (G"). n, Number of carbon atoms in introduced side chains. (From Ref. 16.)...

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