A centrifugal compressor is a type of dynamic compressor, or turbocompressor, with a radial design. Affinity fan laws for centrifugal compressor posted in student. Generation of degraded performance curves using affinity laws. Affinity laws affinity laws are the performance of centrifugal pumps based on change in speed, power, flow, head, impeller diameter. The affinity laws or fan laws, as they are sometimes referred to play an important role in determining centrifugal pump performance when operating conditions change. Care must be taken to correctly read the performance data from pump curves. The only requirement is that the two pumps or fans are dynamically similar, that is the ratios of the fluid forced are the same. The pump capacity, or flow rate, q varies with the ratio of rpm. Moving up a compressor frame size has an efficiency advantage. The affinity law relationships for changing impeller diameter usually work. Centrifugal compressors follow the same affinity laws as that associated with centrifugal fans and pumps. The key component that makes a compressor centrifugal is the centrifugal impeller, figure 0. To approximate the performance of the pump, the affinity laws should be used as follows. For this type of testing it is necessary that models are not only geometrically similar, but are also subjected to similar physical conditions.
The result, which can be regarded as the modified pump affinity laws for. When the fan diameter and the fluid density at the fan suction are constant, the fan laws can be expressed as. Centrifugal pump fundamentals pumps are broadly classified as kinetic or positive displacement. Changes in compressor performance can be determined whenever the speed fluctuates by simply utilizing the affinity laws. Sorokes dresserrand selecting a centrifugal compressor inlet pressure p1 temperature t1. The impeller has a uniform blade length, b, of 2 in. Affinity fan laws for centrifugal compressor student. For the relatively small, highspeed centrifugal compressors in the 200 to 700 kw th capacity range, peak efficiency increases about 2% for each jump in. This implies that speed reduction also reduces the compressors capability of generating pressure increase, or lift. It is often used by designers in sizing and selecting the type of pump or compressor. Another set of the affinity laws deal with changes to the diameter of the impeller.
The affinity laws of centrifugal pumps or fans indicates the influence on volume capacity, head pressure andor power consumption of a pump or fan due to. The affinity laws of a centrifugal pump or fan express the effect on capacity, head and power consumption of a pump or fan due to. Useful to scale from model to prototype useful to understand parameter changes, e. As the flow passes through the centrifugal impeller, the impeller forces the flow to spin faster as it gets further from the rotational axis. Affinity laws the turbo machine affinity laws are common used for pumps and fans to calculate capacity, head and power consumption when changing speed or wheels diameters the affinity laws of a centrifugal pump or fan express the effect on capacity, head and.
Reprinted with permission from cep chemical engineering. Minimum flow point in a centrifugal or axial compressor. As far as i know, this just could be applied when the compressibility factor is. The fan laws of centrifugal pumps or fans, also known as the affinity laws, express the influence of changes in rotational speed, diameter, and density on volumetric flowrate, head or h pressure, and shaft power. Centrifugal pump curves home fluid flow centrifugal pump curves this tool determine centrifugal pump performance for different impellor diameter and speed based on affinity laws. Understand your process, as well as the advantages and disadvantages of each centrifugal compressor configuration, in order to choose the optimal centrifugal compressor for your application. Development of modified affinity law for centrifugal pump to predict the effect of viscosity article pdf available in journal of energy resources technology 1409 april 2018 with 427 reads. Centrifugal pumps are studied and designed based on both mechanical and hydraulic considerations. You may occasionally need to estimate the hydraulic performance of a centrifugal pump at a speed or impeller diameter not shown on the catalog performance curves. If you know the shape of a pump performance curve at a certain speed or with a certain impeller diameter, you can use the affinity laws to predict the. The flow gpm varies proportionally with the change in impeller diameter. With a free discharge fan, the rule power varies with the cube of the speed holds true. Velocitypressure development in a centrifugal compressor.
Centrifugal compressor wikimili, the best wikipedia reader. Manual purpose to be used for selection, application into the system, power and cooling water estimation. The affinity laws allow engineers to estimate the resulting changes to certain hydraulic parameters caused by the manipulation of a single centrifugal pump variable. Turbo machines affinity laws can be used to calculate volume capacity, head or power consumption in centrifugal pumps with changing speed or wheel diameters. The affinity laws are a set of forumlas that predict the impact of a change in rotational speed or impeller diameter on the head and flow produced by a pump and power demanded by a pump. Experience of performance modeling the singlestage pipeline centrifugal compressor. As far as i know, this just could be applied when the compressibility factor is negligible. The affinity laws are a group of laws and rules that govern your pumps. For gas compression of large volumetric flow, axial centrifugal compressors with inter. Pump affinity laws for centrifugal and positive displacement. Compressor and turbine performance and operation affinity laws for centrifugal impellers calculating effect of speed change calculating effect of impeller changes characteristic curves effect of change on operating and process parameters operational problems surge stonewall range of working efficiency. For a variablespeed centrifugal compressor you can change the power drawn by changing the frequency of the motor and the affinity laws speed vs inlet volume flow rate, speeed vs polytropic head, speed vs gas horse power as applicable to centrifugal pumps can be applied but with limitations compared to centrifugal pumps. Q1 q2 n1n2 x d1d2 h1 h2 n1n22 x d1d22 p1 p2 n1n23 x d1d23 npsh31 npsh32 n1n22 per standard nomenclature, q is flow rate, h is head, p is power, and npsh3 is net positive suction head for a 3 percent head drop.
Affinity laws when investigating flow phenomena, cost factors often favour the use of models which are geometrically similar to the original, fullsized equipment see similarity conditions. The red colourmark represents the operating point of the. Integrally geared or single shaft, our compressors are among the most efficient in the industry. This means that 10 percent impeller reduction is 10 percent flow reduction. Pdf development of modified affinity law for centrifugal pump to. The affinity laws are useful as they allow prediction of the head discharge characteristic of a pump or fan from a known characteristic measured at a different speed or impeller diameter. If the speed should remain a constant, the affinity laws state. Basic pump parameters and the affinity laws pdh online. Compressor efficiency increases with impeller size both due to reynolds number effect and reduced relative surface roughness.
The affinity laws formulas the affinity laws describe how changes in rpm n affect gpm, head, and hp in centrifugal pumps. Affinity laws can be used to calculate volume capacity, head or power consumption when speed and wheel diameters are changed. D, in electrical submersible pumps manual second edition, 2018. Pdf the purpose of this research is to investigate the flow behavior inside a. The key difference between such compressors and pumps is that the compressor working fluid is a gas compressible and the pump working fluid is liquid incompressible. Pump engineering calculations of brake horsepower, power, kilowatts, motor, motors, voltage drop, circular mills, transformers, turns ratio, ohms law, dc power. Why can we consider as acceptable the affinity fan laws to evaluate the centrifugal compressor behaviour.
Aug 14, 2014 the affinity laws below are well known and used daily by pump people. Klm technology group, 2011 after entering a centrifugal compressor, the gas is accelerated outwards by rotating impellers and then deaccelerated in the diffusers before finally leaving through the discharge nozzle. Unfortunately, we are missing several other key pieces of information if we wish to apply the centrifugal compressor to another application. Power input assuming identical pump efficiencies flow coefficient. If flow is reduced below this point, cyclic variation and even reversal of gas flow and discharge pressure.
Centrifugal compressor surge, modeling and identification for. This means that a centrifugal compressors operational range through speed variation is limited. This, combined with minimal system effects, make these fans excellent candidates for. The affinity laws for centrifugal pumps and fans are used to express the influence on volume capacity, head pressure andor power consumption due to. Unlike displacement compressors that work at a constant flow, dynamic compressors work at a constant pressure and the performance is affected by external conditions such as changes in inlet temperatures. The following model laws thus apply to two geometrically similar centrifugal pumps operating under physically similar conditions. The performance of centrifugal pumps is related to a parameter called. Affinity laws the affinity laws are derived from a dimensionless analysis of three important parameters that describe pump performance. To explore this further, consider the basic equation for head, h. Now we will various curves and point so check in the centrifugal compressor performance curve. Short discussion about prediction of centrifugal compressor performance running with freon assisted. Jun 14, 2014 affinity fan laws for centrifugal compressor posted in student. Centrifugal compressors are also similar to centrifugal pumps of the style shown in the adjacent figures.
The instability is characterized by large limit cycle oscillations in compressor. In the case where flow passes through a straight pipe to enter a centrifugal compressor the flow is straight, uniform and has no vorticity, ie swirling motion, so the swirl angle. Large or small, we design our centrifugal compressors for economical and efficient operation. The reduction in speed results in a power consumption decrease. Dear mates, two question in regards to affinity laws, dimensionless numbers and behaviour prediction in centrifugal compressors.
The pump speed, head, and flow relationships are expressed by the affinity laws. If the compressor flow, head and efficiency characteristics are known at a given speed, then merely applying the affinity laws at an alternate speed will produce a new curve representing the compressor performance at that speed. The cause for this is the higher volume ratio of the heavy gas. The affinity laws of centrifugal pumps or fans indicates the influence on volume capacity, head pressure andor power consumption of a. This is identical to an axial compressor with the exception that the gases can reach higher velocities and energy levels through the impellers.
Jan 17, 2020 the key component that makes a compressor centrifugal is the centrifugal impeller, figure 0. Dynamic simulation of a centrifugal compressor system. Centrifugal pump affinity laws provide a method to determine a new pump operating point when a performance curve that indicates performance with different impeller diameters or operating speeds is not available. Fundamentals of fluid mechanics chapter 12 pumps and turbines. How to read a centrifugal compressor performance curve. Affinity laws the turbo machine affinity laws are common used for pumps and fans to calculate capacity, head and power consumption when changing speed or wheels diameters the affinity laws of a centrifugal pump or fan express the effect on capacity, head and power consumption of a pump or fan due to. The analysis is based on the reduced impeller being geometrically similar and operated at dynamically similar conditions or equal. Types and performance of pumps and compressors eolss. They are designed for long life, low maintenance and continuous service in dirty and corrosive applications such as petrochemical plants, refineries, natural gas processing, coal gasification and power stations. Using the affinity laws, it is possible to determine approximate curves to estimate the centrifugal pumps new best efficiency point. Pdf development of modified affinity law for centrifugal. If the compressor flow, head and efficiency characteristics are known at a given speed, then merely applying the affinity laws at an alternate.
Fan laws, the use and limits in predicting centrifugal compressor off design performance 93 is operated on a light gas and then operated on a heavy gas, the curve will be steeper for the light gas. These laws are mathematical expressions that define changes in pump brake horsepower bhp, head and capacity when a change is made to pump speed, impeller diameter, or both. In these rotary implements, the affinity laws apply both to centrifugal and axial flows. This manual does not for designing centrifugal compressor and those parts. Important aspects of centrifugal compressor testing part 2. The design of the diffuser generates a circular gas motion preventing. Elliott has been manufacturing single stage centrifugal compressors for over 90 years. The affinity laws for pumpsfans are used in hydraulics, hydronics andor hvac to express the. They are also used for scaleup purposes when performance parameters exceed that of existing pumps refer to figure 2.
A detailed view is shown in figure 5 of the centrifugal compres sor section of figure 4 and can be used as a reference for selection of centrifugal compressor units. How to use affinity laws to calculate a new best efficiency point. Affinity laws for two homologous states a and b, we can use variables to develop ratios similarity rules, affinity laws, scaling laws. The affinity laws below are well known and used daily by pump people. Sep 25, 2012 for a variablespeed centrifugal compressor you can change the power drawn by changing the frequency of the motor and the affinity laws speed vs inlet volume flow rate, speeed vs polytropic head, speed vs gas horse power as applicable to centrifugal pumps can be applied but with limitations compared to centrifugal pumps. If less airflow is needed, the fan is able to reduce its speed.
1086 1177 753 650 711 1198 292 1381 463 52 1564 696 411 23 386 686 1210 38 1027 1110 285 1397 1291 1546 1246 664 671 898 911 769 1581 100 1140 615 1555 644 1202 1423 1176 74 465 1403 646 1213 570