Affinity laws changes in diameter changes in speed d diameter, in or mm q flow, gpm or m3h h head, ft or m p power, hp or kw q flow, gpm or m3h h head, ft or m p power, hp or kw n speed, rpm bernoullis equation v z g gravitational constant l energy losses p s suction pressure p d discharge pressure v s suction velocity d discharge velocity w work by the pump. Aug, 2014 to the affinity laws and beyond the affinity laws below are well known and used daily by pump people. Turbo machines affinity laws can be used to calculate volume capacity, head or power consumption in centrifugal pumps with changing speed or wheel diameters. Jul 16, 2012 the pump affinity laws can be used to predict the performance of a centrifugal pump as two variables change, the pump shaft rotational speed and the pump impeller diameter. The affinity laws provide accurate performance information for changes in rotational speed and can exceed 95% accuracy for most impeller trims that are 10% or smaller. The laws will help you extrapolate and predict pump performance at different velocities. Centrifugal pump fundamentals pumps are broadly classified as. 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. Affinity laws the affinity laws are derived from a dimensionless analysis of three important parameters that describe pump performance. That means the affinity laws can only be applied to a fixed system, which is an.
They cannot be used, by themselves, to estimate power savings. The affinity laws are applied to a specific point on a performance curve. Basic pump parameters and the affinity laws a pdh online. In general, the affinity laws project the new operating point s by moving up and down a system curve. Affinity law for multistage pumps ione mechanical 19 feb 10 06. They are useful particularly for the modification of existing pumps to meet a new service. Mar 04, 2016 the affinity laws the affinity laws state that 1 flow will change directly when there is a change in speed or diameter, 2 heads will change as the square of a change in speed or diameter, and 3 hp will change as the cube of a change in speed or diameter.
It is also required that the two impellers speed or diameter are running at the same efficiency. The affinity laws state changes in the speed or diameter change capacity by direct proportion. The new speed is estimated and a calculation is made to determine if the new speed will meet the desired condition point. The affinity laws for pumpsfans are used in hydraulics, hydronics andor hvac to express the relationship between variables involved in pump or fan performance such as. There are occasions when you might want to permanently change the amount of fluid youre pumping, or change the discharge head of a centrifugal pump. Graphs may be produced using the software graph facility, in which case the resulting graph with multiple plots must be printed. Using the affinity laws, it is possible to determine approximate curves to estimate the centrifugal pumps new best efficiency point. Evaluating the approximation of the affinity laws and improving the estimate of the 1. Sep 20, 2012 with costs related to solidstate electronics coming down over the years, utilizing vfds for centrifugal pumps and fans gives large power savings for a relatively small change in speed according to the affinity laws and thus has become very attractive. As formulae, affinity laws are expressed as follows in table 1.
Nov 23, 2016 affinity laws are useful when an existing pump must be modified ti give a higher or lower head or different capacity the affinity laws are valid only under conditions of constant efficiency. For this type of testing it is necessary that models are not only geometrically similar, but are also subjected to similar physical conditions. The affinity laws allow engineers to estimate the resulting changes to certain hydraulic parameters caused by the manipulation of a single centrifugal pump variable. They are also useful to modify your pumps for new and different required duties. 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.
Q flow rate h head y specific energy n rotational speed if pq. Estimation of the efficiency for variable speed pumps in. The affinity laws for centrifugal pumps state that the hq curves at various rotational speeds can be derived from the following relationship as conventionally represented. The mathematical relationships that exist between flow rate, head, power and speed and based on a known pump performance are referred to as the affinity laws. Affinity law comes in many form as a manifestation of interactions between power, flow rate, shaft speed, frequency and pressure head in centrifugal loads. Aug 14, 2014 the affinity laws below are well known and used daily by pump people. The course content is in a pdf file 467 kb basic pump parameters and the affinity laws. If you know the shape of a pump performance curve at a certain speed. The following websites offer excellent additional information on pumps and hydraulic systems. Centrifugal pump affinity laws calculation chemical. I have also included the spreadsheets that i used to generate the pump curve illustrations. Using the affinity laws, it is possible to determine approximate curves to estimate the centrifugal pump s new best efficiency point. Note that there are two sets of affinity laws affinity laws for a specific centrifugal pump to approximate head, capacity. Alps assumes you in a stable operating condition, i.
That means the affinity laws can only be applied to a fixed system, which is an important constraint to recognize if you are going to use them. The affinity laws for pumps that relate power, head, and flow are only useful for drawing new pump curves at various rpms. If a more detailed analysis is required, you should graphically analyze the pump and systems curves. Nov 24, 2016 centrifugal pump affinity laws are set of mathematical equations correlating the flow rate, head, brake horse power, speed and impeller diameter of the pump. In short, the affinity laws can come to the rescue of an enterprising engineer. Typical independent variable q usually gpm liquids or cfm gases. Affinity laws changes in diameter changes in speed d diameter, in or mm q flow, gpm or m3h h head, ft or m p power, hp or kw q flow, gpm or m3h h head, ft or m p power, hp or kw n speed, rpm bernoullis equation v z g gravitational constant l energy losses p s suction pressure p d discharge pressure v s suction. The affinity laws describe how changes in rpm n affect gpm, head, and hp in centrifugal pumps. How the affinity laws affect pump rerates turbomachinery. Centrifugal pump affinity laws calculation chemical engineering. The affinity laws are derived from a dimensionless analysis of three important parameters that describe pump performance.
How to use affinity laws to calculate a new best efficiency point. Turbo machines affinity laws can be used to calculate volume capacity, head or power consumption in centrifugal pumps with changing speed or wheel. 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. Being able to predict these affects allows the rotating equipment engineer to examine the effects before implementing the changes. Pdf evaluating the approximation of the affinity laws and. 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.
Pump efficiency is considered as a constant and variation in speed and impeller diameter is analyzed for the variation in above said parameters. There is a set of affinity laws for changes in viscosity, but unlike changes in speed the change in viscosity does not give you a direct change in capacity, npsh required, or horsepower. The affinity law calculators calculate the head, flow and bhp of a centrifugal pump. Because most pumps are directly coupled to a standard. The analysis is based on the reduced impeller being geometrically similar and operated at dynamically similar conditions or equal. You can quickly determine the effect of changes in either pump speed or impeller diameter on pump performance. Pump affinity laws for centrifugal pumps kinkubi solution.
Law 1 means that as rpm is reduced, flow gpm is reduced in a linear relationship. Affinity law for multistage pumps pump engineering engtips. 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. 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. Pdf centrifugal pump head prediction using affinity laws. Centrifugal pump fundamentals pumps are broadly classified as kinetic or positive displacement. To approximate the performance of the pump, the affinity laws should be used as follows. 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. Pump performance curves and similarity laws pump performance results are typically obtained from an experimental test of the given pump and are presented graphically for each performance parameter.
The speed in rpm, head, capacity, and power draw must be known for that point. Processing industry, pump affinity laws are incorporated in excel file and uploaded. Centrifugal pump affinity laws are set of mathematical equations. Affinity laws are applied in centrifugal loads such as pump, compressor, fan, hydraulic system and the like. Pdf on jan 1, 2018, abhay patil and others published centrifugal pump head prediction using affinity laws modified for viscosity find. Centrifugal pump results on the same graph plot total head h t against flow rate q for each setting. The affinity laws answer these and other similar questions. Apr 28, 2017 the equations relating rotodynamic pump performance parameters of flow, head and power absorbed, to speed are known as affinity laws. The performance of a centrifugal pump is affected by a change in speed or impeller diameter.
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 affinity laws govern the performance of your pumps. In this example, calculate the effect of a change of speed or impeller diameter on flow rate, head, power and npsh. Pump efficiency is considered as a constant and variation in speed and. Pump affinity laws the pump affinity laws predict the affects of changing the speed of a centrifugal or rotary pump on flow rate, head and power. Affinity laws for centrifugal pumps as applicable to variable. The affinity laws give a good approximation of how pump performance curves. 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% head drop. As pump efficiencies are more or less dependent on friction conditions, they are subject to other. Power input assuming identical pump efficiencies flow coefficient. Affinity laws 2 affinity laws 1 pump formulas psig pump eff. It is also required that the two impellers speed or diameter are running at. For example, if rpm drops to 70% of the original, gpm drops to 70% of the original. Most pumps need minimum flow protection to protect them against shutoff.
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