Aerodynamic Performance of Centrifugal Compressors (Lesson six)

GUIDE VANE EFFECT ON PERFORMANCE CURVES

As the alpha angle change in the opposite direction or favor with respect to the direction of rotation, the compressor performance curves shifts to areas of greater or lesser flow respectively, as shown in figure

EXIT GUIDE VANE

In some compressors Exit Guide Vanes are placed after the last stage of compression to redirect the gas into the volute and to minimize the expansion given to sudden rise in the outlet manifold.

VOLUTES

the function of the intake manifold is to accelerate the fluid coming from the inlet flange to the drive, no energy transfer in the collector, the temperature remains constant, while total and static pressure decrease due to lost.

Aerodynamic Performance on Centrifugal Compressor (lesson five)

RETURN GUIDE VANE

The operational principle is similar to the one of Inlet Guides Vane. The previous part of the vane should be curves owing to the fact that they receive the gas from the previous compression stage in tangential direction, the angle usually fluctuates between 45 degrees where it starts the Stonewall and 75 degrees where it begins Surge. The way and behavior of the back part of these vanes are similar to Inlet Guide Vanes them.

Aerodynamic Performance of Centrifugal Compressors LESSON (FOUR)

INLET GUIDE VANE
Receive the flow of the volute of entrance and it take radial towards the center until the entrance of the first impeller. They are three types of vanes according to the way of his final part. It you can observe a transversal cut in the figure of each one of these front teeth or vanes. From the volute, the gas comes with an almost null speed for dimensions of the volutes, the gas takeover the radial direction to the entrance of vane, them but to the exit of these direction depends on the way of the same. Can be radial as in the type 2, the meaning held out against the rotation if is of the type 3 or in meaning of rotation if is of the type 1.
We can observe the effect of the Guide Vanes in the graph, in function to the speed triangle to the entrance. A Guide vane is represented in the intermediate graph with zero exit angle. W1 represents the relative speed, U1 represents the tangential speed, C1 is the absolute speed of the gas and Beta 1is angle of vane. For being straight does not be tangential component of CU1, using the Theorem of Euler, the head will be U2 multiply C1. On the other hand if the vane this crooked one in connection with the rotation meaning (type 1), will have his tangential component, defined by the angle Alpha which consequently the absolute speed will be lower, reducing Head and flow. Converse Case happens in the vanes (type three), where the Head and the flow are increased.

Aerodynamic Performance of Centrifugal Compressors (Lesson Three)

Stator

It is the fixed part in a centrifugal compressor and along with each impeller they form the compression stages. This made up of a diffuser, an elbow of return, return guides vane. Diffuser, gathers the flow of gas that leaves the impeller without energy transfer, the radial diffuser is a stationary component waters under the impeller, whose main function is the one when coming out to reduce the high speed of the gas flow of the impeller, with a minimum of lost, to turn to the maximum possible the pitot pressure into additional static pressure. In the diffuser, energy is not given to the fluid; the Diffuser without vanes, the radial component of the speed of the fluid is reduced based on the increase of areas, where as the tangential component of the speed is reduced based on the differential of the diameter of the impeller and the one of the diffuser to maintain constant the angular momentum. Usually the value of the width of the channel is 0,9 to 0,75 of the width of the end of the impeller, Return guides vanes give the correct angle of entrance to the gas towards the following impeller. Inlet guides vanes are those in charge of gets appropriate direction to inlet gas flow of the scroll of entrance with a very low speed towards the first impeller.

Radial bearings

They’re of the tilted type and segmented (tilted-pad) with the purpose of to prevent oil wheel at any speed of operation, the material of the shoe is of steel with a bimetallic surface (generally babbit), are self-aligning axial as much radial, distributing uniformly the load on the cushion, the bearings can be removed without removing the rotor from casing.
Axial bearings

They are of the tilted type and segmented (tilted-pad) of double action and support the axial loads in both directions, sometimes the balance piston does not manage to compensate the axial forces reason why these bearings act. The material of the shoe is of steel with a surface of babbit and is fixed firmly to the porthole bearings.
Magnetic bearings
A variant that this taking great height at worldwide is the use of the magnetic bearings in replacement of before mentioned. Its advantage is that physical contact between the axis and the bearings does not exist

Aerodynamic Performance of Centrifugal Compressors (Lesson Two)

Casing types
Horizontal disassembles, which have the advantage to allow carrying out medium repair to the aerodynamic component interns in fast and simple form. Due to case this game in two halves the internal flights through these unions will appear to high pressures, reason for which the rank of application for these compressors is up to 300 PSIA approximately.
Vertical disassembles, it consists of a smelting cylinder as unique central piece and two covers where to the bearings and seals are supported. The stators are a subgroup that is inserted in the cylinder casing, it has the advantage to support high pressures and allows to the maintenance men repair of the bearings and seals; the disadvantage is in the necessity of complete disarmament to be able to carry out medium repair to the aerodynamic components.

Rotor

It’s made up of the impellers and a supported central axis on the bearings in their ends, conforms the movable part of a Centrifugal Compressor.

Types of Rotors

Two types of rotors exist: Solids, are those that are made up of a central axis and the impellers fixed to this through pins, the most common technique is to warm up the impellers, taking advantage of the thermal expansion, introduce the central axis placing a pin and to wait to that the set cools off. Modular, they are made up of two shafts, a central axis and the impellers; the components are connected this yes through stretching of the central axis and nut. The shafts and impellers have holes for center the pieces and pins to transmit the torsor momentum between the components. Because the rigidity is proportional to the fourth potency of the effective diameter, in the modular rotors it increases the critical velocity, which is a rotodynamics advantage.

Aerodynamic Performance of Centrifugal Compressors LESSON (ONE)

Basics
The centrifugal compressors are machines of dynamic flow, through which the gas flows mainly in radial form. The energy necessary to increase the pressure of the gas is transmitted for the blades or trowels of the impellers during its rotation. The physical principle at issue is based on the conversion of the kinetic energy given by the impelling equipment in movement in static energy of the gas, that is to say, from speed to pressure.
The basic components of a compressor are: Casing, The Stator, The Rotor, The Bearings, The Seals Interstage, and The Seal System to isolate the product in compression of the environment surrounds that it and The Lubrication System.

Centrifugal Compressors Types
Axial Centrifugal Compressors are those through which gas flows mainly in radial form, that is to say, in parallel line of the rotor shaft a typical example is the compressor of the Gas Producer of a Gas Turbine, these are characterized by handles great gas volumes but to low pressures. In radial compressors, gas in compression it flows mainly in perpendicular direction of the rotor shaft, are characterized to handle great gas pressures. A variant exists that is the mixture of both types in a same axis (to see drawings).

The options but known to exert movement on a centrifugal compressor are:
.Gas Turbine
.Turbine a vapor
.Electric Motor
.EolicTurbine
.Reciprocante Motor

Aerodynamic Performance of Centrifugal Compressors Course

Content
Basic concepts on Compressors ……….. Pseudocritical press and Temp
Compressor types ………………… ………. Reduced press and Temp
Compressor components ………………… Compresibilidad Factor
…Casing …………………………………… ….. Law of gas mixture
…Rotor Gas …………………………………… chromatographies
…Estator Dew point …………………………Partial Condensation
…Guide vanes ………………………………… Partial component of a gas mixture
…Return vanes ………………………………. Gas saturated with water vapor
…Bearings ………………………………….…. Density y Volume specific
…Volutes ………………………………………. Masic Flow Vol., Vol. standard y Normal
.…Impeller…………………………………… Energy general equation
…Types ………………………………………… Enthalpy
…Parts …………………………………………. Head (H)
Seal ……………………………………………….…. Isentropic
…Wet ……………………………………………. … Politropic
…Sec ……………………………………………..…. Real
Velocity Triangle …………………………… Pressure ratio
…Effect of the curvature of the blades .….Effect of type of gas
Compressor losses……………………… … Efficiency
…Skin Friction………………………………… ... Isentropic
…Diffusion ………………………………………… Politropic
…Curvature …………………………………… …Relationship
…Incidence ………………………………….. Temperature ratio T2/T1
…Disk Friction ……………………………… Aerodynamic Power
…Submit expansion ………………… ….. Power Brake or on Shaft
Boundary layer ………………………….. .. Dimensional maps
Surge ……………………………………… .. ……. Flow vs. H, Flow vs. P2/P1, Caudal vs. Hisen
Stonewall ………………………………… .……. Flow vs. P2, Flow vs. P1, Constant Power lines
Transitory Stall y Full develop …… ….… Constant Velocity lines.
Flow & Surge Margin & Turndown … …... Constant Efficiency lines.
Antisurge Control Systems …………. Adimensional maps
Vibration Theory …………………………. Parameters that affect the performance
Axis movements …………… ……………..……. Effect of inlet Temperature
Internal recirculation …………………..………. Effect of inlet pressure
Gases Theory ………………………… ..…….….. Effect of gas type Ts. G. & K)
…Molecular Weight …………………. .….…….. Effect of compressibility factor
…Specific gravity ……………………. …… …… Effect of speed of rotation
…Molar Fraction …………………… ….……….. Effect of mass flow (M)
…State equation ……………………… ………… Effect of Mach Number
…Mechanical heat equivalent ……….… …... Effect of Reynolds Number
…Specific head ………………………….… … Effect of specific speed (NS)
…Isentropic & Politropic Exponent ……Hpoli