Pulsation losses

The no-load test is a very informative method to determine the no-load current, core and pulsation losses, friction and windage losses, magnetizing current and the no-load power factor. The test also reveals mechanical imbalance, if any, performance of the bearings, vibration and noise level of the motor. 

Is it then a good idea to make the discharge-valve springs weaker Weaker springs cut down on pulsation losses, but also increase valve... 

I could repeat the same story for the intake or suction valves. Leakage of the intake valves would appear as peaks on the compression portion of the cycle. Pulsation losses for the intake valves would appear as peaks on the indicator card during the suction or intake portion of the cycle. 

The pulsation control elements can have several forms, such as plain volume bottles, volume bottles with baffles, bottles and orifices, and proprietary acoustical filters. See Figure 3-26 for an example of a compressor with a set of attached volume bottles. Regardless of which device or element is selected, a pressure loss evaluation must be made before the selection is finalized because each of these devices causes a pressure drop. 

In reciprocators hf is calculated at peak instantaneous flow, including maximum loss through a dirty filter, and an additional head loss to allow for pulsation acceleration is used ... 

The direction of gas flow through the pellet bed could be important. A pulsating high speed flow of exhaust gases can cause rapid attrition of catalysts, especially if the converter has empty spaces due to catalyst loss or shrinkage, which would promote the internal circulation of catalysts in the converter. The design of a sideflow or an upflow bed must include provisions to avoid empty spaces. A downflow design would minimize these attrition losses. 

A further effect during evolution up the AGB is mass loss through stellar winds, at an increasing rate as the star increases in luminosity and radius and becomes unstable to pulsations which drive a super-wind in the case of intermediate-mass stars. For stars with an initial mass below some limit, which may be of order 6 M , the wind evaporates the hydrogen-rich envelope before the CO core has reached the Chandrasekhar limiting mass (see Section 5.4.3), the increase in luminosity ceases and the star contracts at constant luminosity, eventually becoming a white dwarf (Figs. 5.15, 5.19). A computed relation between initial stellar mass and the final white-dwarf mass is shown in Fig. 5.21. 

The uppermost part of the Hertzsprung-Russell diagram is of particular interest since the stars in that area are apparently close to their limit of existence, which is shown by their stochastic variability, pulsations, large rate of mass loss and occasional episodic mass loss. The curve above which no stars appear to exist is called the Humphreys-Davidson limit (Humphreys and Davidson 1979 De Jager, 1980) cf. Figure 2. Stars close to that limit exhibit many of the properties listed above. In that area one also finds the Luminous Blue Variables, which are stars that erratically expell a large amount of mass. At some distance from the star the gas condenses into dust particles and thus the star becomes reddened. Sometimes the expelled gas is optically... 

Many of the red stars are pulsating and/or show irregular or semiregular variations of brightness and radial velocity. For the Mira stars the mechanism of pulsation-(shock-)driven mass loss has been proposed (Wood and Cahn, 1977 Hill and Willson, 1979), but it appears difficult to make quantitative predictions. 

The concept of stochastic pulsations offers also a natural mechanism to explain episodical mass loss as due to occasionally occurring exceptionally large or rapidly moving pulsation elements. In forwarding this suggestion we realize that its proof should still be given. 

The very accurate spectroscopy by the solid state detectors have led to the discovery of the line profile variations in Be stars on a time scale of several hours to day. Such variations are considered due to nonradial pulsations(NRPs)(see Baade 1987), of which nature is correlated with Be emission activity. Mass-ejection driven by NRPs like radial pulsation was suspected by Willson(1986). But the quasi-periodicity of mass-loss cannot be explained naturally by this mechanism. 

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