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Blower Application Basics: Figure 1: Typical System Resistance Curve - Pressure Drop Vs

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Blower Application Basics Blower Application Basics: Figure 1: Typical System Resistance Curve - Pressure Drop vs. Flow Rate Selecting a blower for a particular 5 application first requires knowledge or an estimate of the application’s operat- ing point: the flow rate required and the 4 resistance to flow that the system, duct- work, filters, obstructions, etc., will im- pose. This system resistance is often 3 referred to as backpressure or head loss. The performance curves shown in this catalog represent each model’s typ- 2 P = CQ 2 ical maximum performance (full speed) Drop Pressure P - pressure Drop at a constant input voltage. The perfor- Q - flow rate C - constant for given system mance curve describes a blower’s abil- 1 ity to deliver flow rate against backpressure - from zero backpressure (“open flow”) to completely blocked flow 0 (“ sealed”). Since all Ametek BLDC 0 1 2 3 Flow Rate blowers have adjustable speed control, any operating point that lies underneath a given performance curve can be reached. With knowledge of the de- Figure 2: System and Blower Curves - Identifying the Operating Point sired operating point, it is then a simple matter to browse the catalog to identify 5 blowers having performance curves that exceed the desired operating point. Other factors should then be consid- 4 ered, which will be discussed hereafter. Blower performance curve 3 System Resistance Curve: A resis- Actual operating point tance to flow is typically characterized by a pressure drop for a given flow rate, Pressure 2 and often follows a 2nd order relation- ship (see Figure 1) (in some cases such as certain filters, the relationship is 1 Desired operating point mo re linear). If the desired operating System curve point is known, then its associated sys- tem curve can be estimated according 0 2 to the relationship P=CQ . Plugging the 0 1 2 3 values for desired operating point into Flow Rate the P (pressure drop) and Q (flow rate) terms yields the constant C. The sys- tem curve can then be overlaid graphi- best served by selecting the blower that Does my application require modu- cally onto a given blower performance delivers the desired performance with lating the speed during operation, or curve. The intersection of the two the least amount of input power. Typi- simply a single speed adjustment made curves is the actual operating point (see cally, the most efficient blower is the at the time of installation? Figure 2). The pressure rise provided one where the system resistance curve What input voltage will I have avail- by the blower matches the pressure in tersects the blower curve at approxi- able for powering the blower? loss imposed by the system resistance. mately the middle, i.e., half the maxi- Are there additional features that I For quick checks, simply place the op- mum flow rate. require such as a tachometer output, erating point on a given blower curve Other questions to consider when dynamic braking, or speed control func- and “eyeball” the system curve through selecting a blower: tions? Is it a problem for the working fluid it. Will a blower of this size fit in my application? to come into contact with electronics? There are likely to be several mod- What are the environmental factors Would I prefer that the blower have els that can achieve the desired perfor- associated with my application? mance, but not all will operate with the an on-board controller or would I prefer to provide an external controller? same efficiency. The blower perfor- Blower Performance vs. Speed mance curves in this catalog include not Do I need a blower with fast dy- namic response? Changes: Since Ametek’s blowers are only pressure vs. flow rate information, speed controllable, the speed can be Is loudness a major factor? but also current and input power vs. reduced to a desired operating point or flow rate. An application is normally This document is for informational purposes only and should not be considered as a binding description of the products or their performance in all applications. The performance data on this page depicts typical performance under controlled laboratory conditions. AMETEK is not responsible for blowers driven beyond factory specified speed, temperature, pressure, flow or without proper alignment. Actual performance will vary depending on the operating environment and application. AMETEK products are not designed for and should not be used in medical life support applications. AMETEK reserves the right to revise its products without notification. The above characteristics represent standard products. For product designed to meet specific applications, contact AMETEK Technical & Industrial Products Sales department. AMETEK TECHNICAL & INDUSTRIAL PRODUCTS F 1 627 Lake Street, Kent OH 44240 PRECISION MOTION CONTROL USA: +1 215-256-6601 - Europe: +44 (0) 845 366 9664 - Asia: +86 21 5763 1258 ____ www.ametektip.com Blower Application Basics increased if a different operating point is H2O. The blower whose performance is Answer: At full speed, the blower will needed in a dynamic system. Blowers shown in Figure 3 has been chosen. deliver about 8.8 cfm in this system, conveniently have very predictable be- What will be the power consumption at whose backpressure is about 7.2 in havior when it comes to changes in 8 cfm, 6 in H 2O? H2O at that flow rate (see Figure 3). speed. Table 1 summarizes these rela- Since this is delivering too much, the tionships. speed must be reduced to achieve the desired operating point. Gage Pressure vs. Absolute Pressure: Table 1: Fan Laws Related to At full speed, Figure 3 shows the blower Before proceeding, it’s important at this Changes in Blower Speed speed to be about 19.8 krpm and the point to note that this tutorial makes refer- power consumption is 18.3 W. Using ence to both “absolute pressure” and N2 “gage pressure.” Gage pressure is simply Q2 = Q 1 the fan laws shown in Table 1 yields: the difference above or below atmo- ( N1 ) spheric (or barometric) pressure. Abso- N2 lute pressure is the sum of atmospheric N2 8 cfm = 8.8 cfm and gage pressures: m2 = m 1 ( ) ( N1 ) 19.8 krpm Pabsolute = P gage + P atm 2 N2 = 18.0 krpm N2 P2 = P 1 Pressure values stated hereafter are (N1 ) gage values unless otherwise stated. 3 So, the power consumption at the re- N2 duced speed is: 2 = 1 Figure 3 with Example 1 demonstrates ( N1 ) how to calculate the power requirement 3 for an operating point that occurs at a Where, N fan rotational speed 18.0 krpm m mass flow rate 2 = 18.3 W reduced speed. Q volume flow rate ( 19.8 krpm ) Example 1: P static pressure (gage) An application calls for air performance blower power demand of 8 cfm (ft 3/min) at a pressure of 6 inch All other variables constant. 2 = 13.7 W Figure 3: Speed Change Calculation Example 12 24 11 22 10 20 9 18 8 16 O) 2 7 14 6 12 5 10 Speed (krpm) Speed Input(W) Power Pressure (in H Pressure 4 8 3 6 blower pressure vs. flow 2 blower input power vs. flow 4 blower speed vs. flow 1 system resistance 2 0 0 0 2 4 6 8 10 12 14 16 18 Flow Rate (cfm) This document is for informational purposes only and should not be considered as a binding description of the products or their performance in all applications. The performance data on this page depicts typical performance under controlled laboratory conditions. AMETEK is not responsible for blowers driven beyond factory specified speed, temperature, pressure, flow or without proper alignment. Actual performance will vary depending on the operating environment and application. AMETEK products are not designed for and should not be used in medical life support applications. AMETEK reserves the right to revise its products without notification. The above characteristics represent standard products. For product designed to meet specific applications, contact AMETEK Technical & Industrial Products Sales department. AMETEK TECHNICAL & INDUSTRIAL PRODUCTS F 2 627 Lake Street, Kent OH 44240 PRECISION MOTION CONTROL USA: +1 215-256-6601 - Europe: +44 (0) 845 366 9664 - Asia: +86 21 5763 1258 ____ www.ametektip.com Blower Application Basics The speed at the desired operating sure, thereby increasing the blower’s point could also have been found by ability to provide flow against backpres- Table 2: Fan Laws Related to using the ratio of pressures: sure, but this is not a common practice. Changes in Fluid Density: 2 Fluid Density: The density of the work- 2 N2 ing fluid has a significant influence on P2 = P 1 6 in H 2O = 7.2 in H 2O ( 1 ) (19.8 krpm ) blower performance, as can be seen in the relationships listed in Table 2. Be- 2 cause fluid density is a variable that is 2 = 1 Note: There is some minor error in this independent of the blower, the density ( 1 ) calculation because there will likely be must be stated as part of any blower some small change in motor efficiency performance specification. In the previ- 2 at the different operating point. This ous example, the density was ignored m2 = m 1 ( 1 ) can usually be neglected for estimating for simplicity. But the performance power requirements. curves for all blowers in this catalog have the statement “normalized to air Where, fluid density Static and Velocity Pressure: The density = .075 lb/ft 3,” or equivalent P static pressure (gage) energy of a fluid can be viewed as hav- statement. So, in the previous exam- power demand ing two types of pressure: static pres- ple, it was assumed that the desired m mass flow rate sure and velocity pressure.
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