Turbines critical speed

At a given gas sparging rate, interfacial area a is constant at low mixer speeds. When mixer speed is increased above a critical speed a starts increasing and varies linearly with Ai For Rushton turbines this critical speed, as deterrnined in an sodium sulfate system, is given by the following ... 

Expander-compressor shafts are preferably designed to operate below the first lateral critical speed and torsional resonance. A flame-plated band of aluminum alloy or similarly suitable material is generally applied to the shaft in the area sensed by the vibration probes to preclude erroneous electrical runout readings. This technique has been used on hundreds of expanders, steam turbines, and other turbomachines with complete success. Unless integral with the shaft, expander wheels (disks) are often attached to the shaft on a special tapered profile, with dowel-type keys and keyways. The latter design attempts to avoid the stress concentrations occasionally associated with splines and conventional keyways. It also reduces the cost of manufacture. When used, wheels are sometimes secured to the tapered ends of the shaft by a common center stretch rod which is pre-stressed during assembly. This results in a constant preload on each wheel to ensure proper contact between wheels and shaft at the anticipated extremes of temperature and speed. 

Critical speeds of a turbine operating below its first critical should be at least 20% above the operating speed range. The term commonly used for units operating below their first critical is that the unit has a stiff shaft, while units operating above their first critical are said to have a flexible shaft. There are many exciting frequencies that need to be considered in a turbine. Some of the sources that provide excitation in a turbine system are ... 

All turbines are variable-speed drivers and operate near or above one of the rotor s critical speeds. Narrowbands should be established that track each of the critical speeds defined for the turbine s rotor. In most applications, steam turbines operate above the first critical speed and in some cases above the second. A movable narrowband window should be established to track the fundamental (1 x), second (2x), and third (3x) harmonics of actual shaft speed. The best method is to use orders analysis and a tachometer to adjust the window location. 

The problem with this new air blower, was that we could not bring the turbine speed above its critical speed. The critical speed of a turbine is stamped on the manufacturer s nameplate. Turbines are typically run well above their critical speed. If, for some reason, a turbine is run close to its critical speed, it will experience uncontrolled vibrations and self-destruct. 

The turbine began to slow. It slowed to its critical speed, and began to vibrate. Before shutting down the turbine, to avoid damage due to the vibrations, I noted the following ... 

And the turbine speed came back up, well above its critical speed. 

The offending wildlife were removed. The condenser was reassembled. The motive steam was started to the turbine. Both the turbine and the air blower were running well above critical speed. We lined the flow of combustion air up to the combustion chamber. Everything was finally going my way, except for one minor problem. 

So, the turbine slowed down. And what was the only possible speed that it could slow down to Why, the critical speed, of course. The turbine and blower began to vibrate. The bearings were damaged. The turbine s rotor became unbalanced. A rotating element on the air blower touched a stationary component in the blower s case. The stationary component broke off and wrecked the blower. That was the end of K-805. 

By what law of nature was the turbine forced to slow exactly to its critical speed You see, dear reader, life is perverse. And if anything bad can happen, it is going to happen to me. 

The optimum stirrer, from the point of view of energy efficiency, is the one that requires the least power at the critical speed of rotation. In terms of a dimensionless relation, this can be expressed as the condition where Ne Fr3/jj is minimum. For a propeller stirrer with Ne = 0.50 and a turbine stirrer with Ne = 10.0, and with the values of b already given for the two stirrers, the propeller stirrer requires only 20% of the power needed by the turbine stirrer. Mixing Equipment Co, CA, has recently introduced a new impeller design that consists of a pitched blade turbine (three blades). At the tips of the... 

Performance tests are those tests that need to be carried out on combined equipment such as a gas-turbine driven generator or a pump driven by a high-voltage motor. In such cases the dynamic relationship between the various equipments is of interest. For example, rotor vibration, critical speeds, run-up time to full speed, starting up and shutting down sequences, full-load and over-load performances, heat dissipation and cooling medium performance. 

The choice of drive is determined by the type of energy available In a plant and its cost. Turbine steam rate depends on inlet steam pressure and temperature, exhaust conditions, number of turbine stages, and turbine efficiency. With a turbine drive, evaporation rate may be controlled by varying compressor speed, making sure that the turbine and compressor critical speeds do not fall in the range of interest for the system. 

This standard could be adapted to the fuel compressor for the natural gas to be brought up to the injection pressure required for the gas turbine. Covers the minimum requirements for reciprocating compressors and their drivers used in petroleum, chemical, and gas industry services for handling process air or gas with either lubricated or nonlubricated cylinders. Compressors covered by this standard are of moderate-to-low speed and in critical services. The nonlubricated cylinder types of compressors are used for injecting fuel in gas turbines at the high pressure needed. Also covered are related lubricating systems, controls, instrumentation, intercoolers, after-coolers, pulsation suppression devices, and other auxiliary equipment. 

The presence of a gas in the suspension results in an increase of the stirrer speed required to establish the state of complete suspension. The propeller usually requires a higher speed than the turbine. Furthermore, a critical volume gas flow exists above which drastic sedimentation of particles occurs. Hence, homogenisation of the suspension requires an increase of the rotational speed and/or a decrease of the gas flow rate. The hydrodynamics of suspensions with a solid fraction exceeding 0.25-0.3 becomes very complex because such suspensions behave like non-Newtonian liquids. This produces problems in the scale-up of operations. Hydrodynamics, gas hold-up, mass-transfer coefficients, etc. have been widely studied and many correlations can be found in literature (see e.g. Shah, 1991). 

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