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 can be used to calculate volume capacity, head or power consumption when speed and wheel diameters are changed. P 1 p 2 n 1 n 2 3 or d 1 d 2 3 where p is equal to power, n is equal to shaft speed, and d is equal to impeller diameter. Pump affinity laws for a specific centrifugal pump volume capacity. Affinity fan laws for centrifugal compressor posted in student. 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 following three 1tterms are used for the simplified fan law approach. So, in short, the basic fan laws are used to express the relationship between fan performance and power. 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 tdh varies directly with the square of the rpm speed that spins the impeller. Pump curve speed calculator this centrifugal pump curve calculator is meant to quickly calculate the different operating conditions when a centrifugal pump is sped up or slowed down. Process engineers lock onto this law as a means to control the flow of process.
The pump affinity laws are widely used in adjusting pump performance curves from one pump or speed to another. Let us examine the effect of speed andor impeller diameter change on the performance of centrifugal pumps. The affinity laws or fan laws, as they are sometimes referred to play an important role in determining centrifugal pump performance when operating. A sdvosb service disabled veteran owned small business. Fan affinity laws calculator changing wheel diameter replace the default values with the actual values. 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. Hvac equipment and systems fan affinity laws for the.
The first law of fans is a useful tool when working out the volumetric flow rate supplied by a fan under speed. Engineers use a shorthand for estimating the effect of speed rpm on power. 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. N fan speed q flow cfm p pressure static inches of water hp horsepower. These laws can also be applied to fans, hydraulic turbines. To explore this further, consider the basic equation for head, h. The fan laws are a group of useful equations for determining the effects of a change in the speed, the diameter of the fan and the density of air in the system. Pump affinity laws are widely used to predict the pump performance at a different speed or with different impeller diameter provided pump performance curve at a certain speed or impeller diameter is known. Affinity laws and other considerations fan application. Using affinity laws, we can accurately calculate the pressure, flow and required. Pressure or head is proportional to the square of shaft speed.
Pump affinity laws with a sample calculation what is piping. Pump affinity laws are equations of proportionality that indicate how a change in impeller diameter d, or rotative speed n, affects the capacity q, the differential head h, and the required brake horsepower hp of a centrifugal pump. Centrifugal pump fundamentals pumps are broadly classified as. The volume capacity of a centrifugal pump can be expressed like. Often times a fan s speed or impeller diameter will be changed. There is a little more to it than this with air density changes but these basic fan laws can keep a field engineer or technician out of trouble. Worked fan law examples fan laws the empiricalmeans very basic. Another set of the affinity laws deal with changes to the diameter of the impeller. The new york blower company is committed to supporting and supplying necessary equipment to meet the critical demands of the supply chains essential to aid america in this time of need.
Usually, pump performance curves are based on standard electric motor speeds in rpm. Variable airflow applications can also cause noise problems. The flow gpm varies proportionally with the change in impeller diameter. 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. Fan not pulling full amps fan performance 80% of design fan sounded like it was hunting eg in stall initial diagnoses was uneven air on conditions due to transition pieces damper in front of fans disruption air flow on to blades. Q 1 rpm 1 q 2 rpm 2 basically this equation says that if fan rpm increases by 10% then the flowrate q would increase by 10%. If the fan rpm increased by say 25% then the flowrate would increase by 25%. Application of the affinity laws to predict the impact of changes in speed can produce highly accurate results.
The performance of a fan is standardly expressed in terms of three affinity laws stated as under. From the fan affinity laws 7, ventilators operates under a predictable law that the air volume delivered by a ventilator is in the onethird order of its operating. The energy savings are achievable through affinity laws. Fan law 3 there is a little more to it than this with air density changes but these basic fan laws can keep a field engineer or technician out of trouble. They are also used for scaleup purposes when performance parameters exceed that of existing pumps refer to figure 2. System curve b describes a system with a relatively high static head vs. Why can we consider as acceptable the affinity fan laws to evaluate the centrifugal compressor behaviour. Affinity laws are also known as affinity equations. Consult local code requirements or the table below for suggested air changes for proper ventilation. Q1q2 n1n2 where q is the volumetric air flow and n is the shaft speed. Pump curve speed calculator affinity law calculator. This method is referred to as the affinity laws or fan and pump laws. 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 for centrifugal pumps and fans are used to express the influence on volume capacity, head pressure andor power consumption due to. Typical independent variable q usually gpm liquids or cfm gases. Affinity fan and pump laws what is the effect of a changing speed. The affinity law for fans and dynamic pumps, 2692018 duration. In most cases, they work fairly well and can be reliably used in modeling studies. 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. Fan laws the fan laws are derived from a dimensional analysis, using the pitheorem as a formal procedure. Centrifugal fans 7 note that when the flow and pressure laws are combined, the result is a formula that matches the system curve formula p k x cfm2. In general, the affinity laws project the new operating points by moving up and down a system curve.
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. The affinity laws or fan laws, as they are sometimes. The pump speed, head, and flow relationships are expressed by the affinity laws. This means that 10 percent impeller reduction is 10 percent flow reduction. The fan is the commonest of all aerodynamic devices, being employed in as diverse situations as living rooms, factories and jet engines. Centrifugal pump fundamentals pumps are broadly classified as kinetic or positive displacement. Fan types fans are described in three types and several subtypes. The affinity laws are a set of rules to describe the interconnected relationships between speed, flow, power, and pressure seen with fans, turbines, and similar devices.
Leave a comment if you would like to discuss the affinity laws or variable frequency drives. However, the affinity law calculations require using a point on the curve. The centrifugal pump affinity laws, sometimes known as the laws of similarity, describe how changes in rpm affect the gpm, head, and hp in the united states, electricity is at 60 cycles per second hertz. The correct formula for using the affinity laws when there is a. The affinity laws below are well known and used daily by pump people. They are most useful for determining the impact of extrapolating from a known fan performance to a desired performance. Affinity laws, fan curve, fan laws, fans, fan speed, pump curve, pump laws, pumps. When a fan operates in an unchanging system, the fan laws tell us that the airflow varies proportionally to fan rpm, static. Affinity laws are a set of equations or laws governing the operation.
Breeze industrial pedestal fan of diameter 450 mm, chord length. If the speed should remain a constant, the affinity laws state. Fan affinity laws affinity laws can be used to calculate volume capacity, head or power consumption when speed and wheel diameters are changed modulate centrifugal pump capacity adapting pump capacity to variable process demand npsh net positive suction head an introduction to pumps net positive suction head npsh. Using fluid dynamics 1 to estimate the performance of a fan is surprisingly tricky however. 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. Often times a fans speed or impeller diameter will be changed.
As simple as trying to find a motor to spin a fan sounds, the engineer that has to do this needs to know and use the affinity laws for air and hydraulic flow. Centrifugal pump affinity laws are set of mathematical equations correlating the flow rate, head, brake horse power, speed and impeller diameter of the pump. Centrifugal pump affinity laws calculation chemical. The cause for this is the higher volume ratio of the heavy gas. Using the affinity laws, it is possible to determine approximate curves to estimate the centrifugal pumps new best efficiency point. First if the impeller diameter is held constant and the speed of the fan is changed. The affinity laws, also known as pump laws, for pumps are used to express the relationship between variables involved in pump performance such as head, flow rate, shaft speed and power. 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. Pdf evaluating the approximation of the affinity laws. A common mistake is to use a fan that is too small or too large for the application, so that it cannot be run at its most efficient point. First if the impeller diameter is held constant and the speed of the fan is changed, then flow rate varies directly with the speed. These rules are critical for heating and cooling installers, who must select products. For example, lets say that a direct drive fan moves 15,000 cfm at 2.
If the diameter does not change the fans must be geometrically similar. The calculator is generic and can be used with all common units as long as the use is consistent. Dear mates, two question in regards to affinity laws, dimensionless numbers and behaviour prediction in centrifugal compressors. Next n, page down, enter, space bar, left mouse click previous p, page up or backspace end show esc. The affinity laws do not apply to points that belong to system curve b. Pump efficiency is considered as a constant and variation in speed and impeller diameter is analyzed for the variation in above said parameters. When a pump or fan system, or its operation, is not simply over. If the fan is a centrifugal fan, then the change in performance of the fan can be predicted quickly through the affinity laws. As is discussed in the section about the cube rule, that law can be applied to project energy consumption for a fan or pumping system. Louvers to supply makeup air determining cfm after the model is known, the cfm must be determined.
258 1545 38 340 1067 389 936 329 1059 1019 1615 1585 185 418 171 377 534 1386 323 1043 200 1428 1314 18 349 1291 972 263 1378 129 893