Compressors kinetic

Volume 1 explains that pumps ean be classified as either positive-displacement or kinetie. The same is true for compressors. In a positive displacement compressor the gas is transported from low pressure to high pressure in a device that reduces its volume and thus inereases its pressure. The most common type of positive displacement eompressors are reeiprocating and rotary (serew or vane) just as was the ease for pumps. Kinetic compressors impart a veloeity head to the gas, which is then converted to a pressure head in accordance with Bernoulli s Law as the gas is slowed down to the velocity in the discharge line. Just as was the case with pumps, centrifugal compressors are the only form of kinetic compressor commonly used. 

The impeller (wheel) of the centrifugal compressor imparts kinetic energy to the gas by increasing the gas velocity through the rotation of the impeller. A static pressure rise in the impeller comes from part of this energy, and the balance is converted to velocity head, which in turn converts to additional pressure rise in the compressor wheel assembly. (See Figures 12-43, 12-44B, 12-461, and 12-47.)... 

An inventor claims to have devised a CO. compressor that requires no shaft work. The device operates at steady state by transferring heat from a feed stream of 2 lb,/s of CO. at 150 psia and 100°F. The CO is compressed to a final pressure of 500 psia and a temperature of 40°F. Kinetic and potential energy effects are negligible. A cold source at -140°F drives the device at a heat transfer rate of 60 Btu/sec. Check the validity of the inventor s claim. 

Figure 3-83). As in the centrifugal compressor, the kinetic energy of the high-velocity flow exiting each rotor stage is converted to pressure energy in the follow-on stator...

The rapid kinetics of Reaction 1, the high volumetric hydrogen storage densities, and the wide range of hydrogen decomposition pressures of the AB5 hydrides initiated proposals to use them as chemical compressors, cryogenic... 

The gas enters the compressor s rotor through the large wheel shown in Fig. 28.2. The purpose of this wheel is to increase the velocity or kinetic energy of the gas. After the high-velocity gas escapes from the vanes in the wheel, the gas enters the stationary elements fixed to the inner wall of the compressor case. This is called the stator. Inside the stator the velocity or kinetic energy of the gas is converted to polytropic feet of head, or potential energy. 

An alternative that is less resource-intensive than the flow loop is the flow wheel apparatus (Bakkeng and Fredriksen, 1994 Lippmann et al., 1994) shown in Figure 6.4b. The wheel (torus) is nominally a 2-5 in. (5.1-12.7 cm) pipe, 2 m in diameter that rotates at 0.3-5.0 m/s while filled with gas and less than 50 vol% liquid. Conceptually, the wheel is spun past the gas and liquid rather than the reverse. Therefore, the flow wheel apparatus does not require circulating devices such as pumps or compressors. Hydrate formation is deduced visually, or by a sharp increase in torque required to turn the wheel. Urdahl et al. (1995) and Lund et al. (1996) report good field transferability from results obtained with this apparatus. Pilot flow loops and flow wheels have been also used to simulate shut-in/start-up conditions (12 h stagnant period) and to test kinetic inhibitors (e.g., Palermo and Goodwin, 2000 Rasch et al., 2002). 

Finally in the diffusa- section 5 the pressure is recovered from the kinetic motion of the gas through some kind of shock wave - the fact which is well known in gas dynamics. Certainly the pressure recovers not up to the initial inlet value. The pressure losses (typically 20 - 30% at present) depend on the desired temperature in the working section 3 (as desired temperature is lower the gas movement is faster and pressure recovering is more difficult). This section acts like a compressor in TET. 

Equation 2.7 relates to Figure 2.1. Give an analogous equation for when the turbine is replaced by a compressor. Then simplify the expression obtained by assuming that the compressor operates adiabatically, without changes in the kinetic and potential energy of the gas flow. 

Hydrogen at a temperature of 20°C and an absolute pressure of 1380 kPa enters a compressor where the absolute pressure is increased to 4140 kPa. If the mechanical efficiency of the compressor is 55 percent on the basis of an isothermal and reversible operation, calculate the pounds of hydrogen that can be handled per minute when the power supplied to the pump is 224 kW. Kinetic-energy effects can be neglected. 

To obtain an equation for calculating the work of conpression, first apply Bernoulli s equation, Equation 5.1, across the compressor. The first term, the kinetic energy term, is small compared to the other terms in the balance. The second term is the change in potential energy, and it is also small. The last two terms are the work done by the system and the friction loss. First, we consider frictionless flow. Thus, the compressor work. 

This obvious relationship is used in Table 5.11 to obtain mass-fraction averages of thermodynamic properties of steam-condensate mixtures. The macroscopic energy balance, is used to obtain the steam flow rate. Like compressors, the kinetic and potential energy terms are not significant, and the expansion is assumed to be adiabatic. 

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