Fan pressure

The pressure-volume curve of a proposed centrifugal fan has a different shape. This fan curve must be drawn for the anticipated fan inlet density expected at its location in the system. The point of intersection of these two curves locates the flow rate and pressure rise at which the fan and system operate. This intersection represents a desirable operating combination for fan and system. The system curve intersects the fan curve in the middle of its maximum efficiency range and also at a point where the fan pressure produced varies smoothly but distinctly in a constant trend with flow rate which is desirable for flow control. 

Poor performance can result from fan inlet eccentric or spinning dow, and discharge ductwork that does not permit development of hiU fan pressure. Sometimes inlet restrictions starve a fan and limit performance. To obtain rated performance, the air must enter the fan uniformly over the inlet area without rotation or unusual turbulence. This allows all portions of the fan wheel to do equal work. If more air is distributed to one side of the wheel, such as with an elbow on the inlet, the work performed by the lightiy loaded portions of the wheel is reduced and capacity is decreased by 5—10%. The use of an inlet box duct on a fan can reduce capacity by as much as 25% unless there are turning vanes in the duct. Use of the vanes reduces the capacity loss to around 5%. 

The relative pressure drop, AP, expression is based on the Fanning pressure-drop equation ... 

Firebox Overpressure - The firebox of a forced-draft furnace and boiler is designed to withstand the overpressure that can be generated by the fans with dampers in their closed position. This needs to be specially checked when both forced and induced-draft fans are provided to discharge combustion products through heat recovery facilities, since higher than normal fan pressures may be used to overcome pressure drop. In the case of high-pressure process furnaces, a tube rupture could also be the cause of firebox overpressure. 

LOl>A TK inj c1ion presEure ment hydroxide meni fan pressure menl spray... 

ASTM E779-87. 1987 Standard Method for Determining Air Leakage Rate by Fan Pressurization.. American Society for Testing and Materials, Philadelphia. 

Hence, the fan pressure must not exceed the standard air density of 1.2 kg m" x25 kJ kg" , giving 30 kPa, with the pressure ratio not exceeding 1.30, taking the atmospheric pressure as 100 kPa. 

Description Code Work per unit mass, m kg- Maxirmtm fan pressure, kPa Class... 

External fan pressure difference The difference between the total gauge pressure at the outlet of an air handling unit and the total gauge pressure at the inlet. 

The portion of the fan pressure necessary to overcome friction in the flowing system of gas/air is termed static pres-sure. ... 

For these fans, pressure is produced by the change in velocity passing through the impeller wheel. No pressure is produced by centrifugal force. (See Figures 12-118Candl2-119D and Tables 12-11, 12-12A, and 12-12B). 

Figure 12-137. Effect of partiaiiy ciosed outiet vanes or dampers on fan pressure-voiume curve. (Used by permission Tobin, J. F. Power Engineering, p. 82, Sept. 1954. PennWeii Pubiishing Company/Power Engineering Magazine. Aii rights reserved.)...

Static Pre Two Ideot ssure for ical Fans — 2pf, Result < Stotic % snt Fan Pressure / ft Pfv / ... 

An approximate total system resistance can be estimated from the design average duct loss and the maximum duct length, adding the major fittings. However, this may lead to errors outside the fan power and it is safer to calculate each item and tabulate as shown in Table 27.1 for the system shown in Figure 27.8. Only the longest branch need be taken for fan pressure. 

Increase ID fan pressure drop and provide better mixing of the air and fuel. A better burner can be used if sufficient pressure drop is available. 

The heart of this drying system is a rotary-valved pulse combustor. Referring to Fig. 7.81, combustion air (1) is pumped at low pressure into the pulse combustor s outer shell and flows through an unidirectional air valve (2) into a tuned combustion chamber [ Helmholtz Resonator (3)] where fuel (4) is added. The air valve closes. The fuel-air mixture is ignited by a pilot (5) and explodes, creating hot air which is pressurized to approx. 0.2 bar above combustion air fan pressure. The hot gas exits the chamber through a pipe (6) towards the atomizer area (7). Just above the atomizer, quench air (8) is blended in to achieve the desired process temperature. The orifice releases the liquid... 

When gas pressure produced in upward ventilated roadways, its direction is the same as fan pressure, which is positive for the fan when gas pressure produced in downward ventilation roadways, its direction is opposite to fan pressure, which is negative for the fan. 

Side branch b is considered as object of investigation, and by branch b, the ventilation network can be divided into two parts the left part and the right part Branch a is the roadway with a large amount of gas influx because of outburst, C branch can be divided into BF and FA, where FA is atmospheric branch h, represents gas pressure in branch a and A, fan pressure in the left R- synthesized windage of branch a R synthesized windage of left part represents air quantity of the left part, gj the right R and gj represents windage and air quantity of side branch b respectively. 

Gas turbines can operate in a stand-alone basis or associated with waste heat recovery boilers. There are also several types of auxiliary equipment as fans, pressure reducers and pumps. 

VALUE OF a, CONVERSION FACTOR IN THE FANNING PRESSURE DROP EQUATION... 

Curve 1 is for a fan designed to handle 10,000 cfm in a duct system whose calculated system resistance is determined to be 1" water (gauge). This fan will operate at the point where the fan pressure (SP) curve intersects the system resistance curve (TSH). This intersection point is called the Point of Rating. The fan will operate at this point provided the fan s speed remains constant and the system s resistance does not change. The system-resistance curve illustrates that the resistance varies as the square of the volumetric flow rate (dim). The BHP of the fan required for this application is 2 hp. 

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