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Technical Details

Useful information on Fan Engineering.

ACFM : Actual Cubic Foot per Minute of air moved by fan.

Axial flow fan : Fan in which air/gas moves parallel to fan axis.

Beam Pass Frequency : Number of times per revolution that one fan blade passes over beam. This shows how structure interact with fan blade. Unit : cycles/sec (Hz)

Break Horsepower(HP) : This is the tower required for fan to perform desired/ designed work.

Blade Natural Frequency : Frequency at which blade freely vibrates. Unit: Cycles/Sec(Hz)

Blade Pass Frequency : Number of times per revolution that a fan tip passes a point on fan cylinder. This shows how fan cylinder interact with fan blade. Unit : cycles/se(Hz).

Chord : Straight line distance between leading and training edge.

Leading edge : Thicker portion of airfoil. This is a first part of blade to meet air.

Trailing edge : Thinner part of the airfoil opposite to leading edge.

Net free area : This is net area at fan plane minus area of HUb/Seal disc.

Static pressure : Sum of all the system resistance against which fan brake HP. Normally up to 60 %.

Static efficiency : This is a efficiency based on static pressure and fan brake HP. Normally upto 60%.

Tip clearance : Distance between blade tip and cylinder. Normally it is 0.005 * diameter of fan.

Velocity Pressure : Loss caused by work done to collect all the air in to the fan's inlet. Unit : Inches of water column.

Total Pressure : Static pressure + velocity pressure.

Total Efficiency : This is a fan efficiency based on total pressure and fan brake HP.

WR2 : Moment of Inertia of fan.

Units / Conversions.

Air flow : 2118.64 * m3/sec = ft3/min (CFM)

Volume : 35.314 * m3 = ft3

Density : standard density : 0.075lb/ft3 , 16.018463 * lb/ft3 = kg/m3

Length : 25.4 * inch = mm , 3.281 * m = ft , 1000mm = micron.

Temperature : (oC * 1.8) + 32 = oF , (oF - 32) / 1.8 = oC

Power : 0.746 * HP = KW

Basic Equation.

pressure (TP) : Static Pressure (SP) - Velocity Pressure (VP)

Fan BHP : (TP * ACFM) / (6356 * Efficiency Total)

Actual Velocity Pressure :

(V/4005)2 * (ρ2/ρ1)

where, ρ1 : Std. Air density : 0.075 lb/ft3 , ρ2 : Density at the fan, V : Velocity (ft/min) : (ACFM (ft3/min) / NFA (ft3))

Maximum tip speed : 12000 ft/min.

Tip speed = r * ω

Where ω = Radial velocity of fan . Unit : Radian/min, ω = 2* π * N (N = Fan RPM).

When velocity recovery stack used

VR : (Vp fan - Vp exit) * recovery efficiency

Recovery efficiency is usually 0.6 to 0.8

Fan Laws :

# CFM = fn(RPM) 1.
Airflow varies in direct proportion to RPM.

#SP or TP = fn(RPM) 2.
Pressure capability varies with the square of a change in RPM.

# HP = fn(RPM) 3.
Power required varies with the cube of a change in RPM.

Tests of cooling tower.

a) THERMAL TEST : Thermal test on cooling tower can be carried as per CTI ATC-105. This test is carried out to prove cooling tower performance as per contractual agreement between cooling tower user and supplier. Also this test can be carried out in case of cooling tower up- gradation to check present status of cooling tower compare to its design values.

b) FAN TEST : In case of cooling tower up-gradation fan test can be carried out in order to check fan performance. This test gives the idea whether fine adjustment with existing fan can solve the purpose OR need to replace with higher efficiency fan.

c) DRIFT TEST : In case of sea water cooling tower drift loss is very critical, since it can make damages to surroundings. So to calculate, design and to test drift loss is very critical in case of sea water cooling tower. This test can be carried out as per CTIATC - 140. In case of normal water cooling tower drift test is necessary depending on tower location and application.

Nirvana Technologies
B-501, Om Sarvoday CHS, Rawalpada,
Dahisar(E), Mumbai-400068, India
Tel: +91 22 28970207 / 65813793
Fax: +91 22 28970207

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