Velocity boost

While smaller than the sonic boost, the velocity boost is more reliable. Even though the velocity in the diffuser throat in Fig. 16.1 falls well below the speed of sound, the increase in pressure in the diverging portion of the diffuser is only slightly reduced. 

The overall pressure boost of a steam jet is obtained by multiplying the sonic boost effect times the velocity boost effect. The overall boost is called the jet s compression ratio. 

Let s further assume that the pressure drop from the jet discharge, through the condenser discharge, is 10 mm Hg. Then, the jet discharge pressure would be 90 mm Hg. Let s also say that the sonic boost is equal to 3.60. The velocity boost is assumed to be equal to 2.5. The overall compression ratio is then... 

Let s say that a jet is already in its critical-flow mode. It is already benefiting from both the sonic boost and the velocity boost. What, then, will be the effect of a reduction in the jet s discharge pressure on the jet s suction pressure Answer—not very much. If a reduction in discharge pressure is made on a jet, which is not working in its critical mode, there will always be some benefit. 

As the steam and gas leave the diffuser throat, the flow then enters the gradually diverging sides of the diffuser. The velocity of the steam and gas is reduced. The kinetic energy of the flowing stream is partially converted to pressiue as the steam and gas slow down. This increase in pressiue is called the velocity boost, which will multiply the pressiue of the steam and gas by a factor of 2 or 3. 

Third— In the diverging section, the velocity of the steam is used to compress the off-gas, air leaks, and the motive steam, due to the reduction in the velocity of the combined vapor flow (the velocity boost). 

Third— If the inlet temperature at the diverging section of the ejector is 200°F, then the temperature at the discharge of the jet will be about 250°F to 300°F. The ejector has been heated another 50°F to 100°F, due to the heat of compression of the flowing vapor provided by the velocity boost. 

Velocity boost Pressure increase in a steam jet due to the reduction of velocity. 

A neutral kink embedded in a ring with 139 sites initially at rest is given a velocity boost of uk - lOwa, and the time evolution is investigated (Fig. 4.7). Immediately after the boost the velocity of the kink uk drops to uk = 5ua and its geometrical half-width Wd drops from initially Wd = 9.15a to Wd = 5.3a, while the rise of a huge hump behind the soliton takes over the excess kinetic... 

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