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# Combustion Air Fan Curves

7 replies to this topic
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### #1 chetanhm2

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Posted 24 October 2018 - 06:49 AM

Dear Sir,

I have Natural Gas Fired heater for molten salt unit in Urea plant. For this plant, there is combustion air fan which gives air for combustion with natural gas as a fuel. For this fan, vendor performance curves are availbale in form as flow vs static pressure. But in UniSim Design, compressor module takes it as head vs flow. How to convert this ? Request your help.

### #2 Bobby Strain

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Posted 24 October 2018 - 10:41 AM

Use the compressor equations to convert.

Bobby

### #3 shan

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Posted 24 October 2018 - 01:43 PM

Pressure 1 psi = Head 27.68 inch water (39.2 F)

### #4 Art Montemayor

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Posted 24 October 2018 - 05:57 PM

Head is another expression for pressure.  As Shan points out, it is equal to 27.68 inch water  at 39.2 oF.  It is used in the Bernoulli equation and is a standard measurement in the pump industry.  UniSim Design probably uses it because it pertains to a centrifugal compressor simulation - as Bobby Strain implys.

Through the years, Canadian Jacques Chaurette has been one of my favorite writers regarding pumps and their design and operation.  Read the attached document he has written on head pressure and how it plays a role in pump design.  This may help you identify what it is meant to mean.

### #5 chetanhm2

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Posted 28 October 2018 - 08:16 AM

Respected Sir,

I want to know whether this formula applies for pumps(liquid)  and compressors (gases) both?

Especially for a fan, pressure ratio will be very less say 1.15 times suction pressure. So how to convert static pressure into polytropic head in metre. Also let me know why static pressure is measured for afan in a vendor shop instead of head for a fan?

Best Regards,

Chetan Chavan

### #6 Bobby Strain

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Posted 28 October 2018 - 08:57 AM

You should use your simulator to answer your query. Specify the inlet and discharge pressures and the flow. Then look at the calculated values.

Bobby

### #7 chetanhm2

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Posted 02 November 2018 - 01:48 PM

Dear Sir,

If i specify suction and discharge pressures, then i will get only one point.

### #8 breizh

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Posted 03 November 2018 - 02:43 AM

Hi Chetan and others ,

https://www.nyb.com/...tters/EL-03.pdf