Vane control

Fig. 7. Control of fan performance with inlet vane control. SoHd lines marked A and N show normal performance without vanes (vanes wide open). As vanes are progressively closed, static and power curves are modified as indicated by dashed lines. Intersection ( - ) of the system resistance curve with these reduced pressure curves at points B, C, D, and E shows how imparting more spin to the inlet air reduces flow. Projecting points A to E vertically downward to the corresponding power curve locates fan power points A through E7 Power savings achieved over throttling control can be estimated by projecting points B through E vertically downward to the A power curve and comparing the value with that from the proper reduced power curve. To...

Results of studies to determine the effect of stator vane control on acceleration are shown in Figures 4-67 and 4-68. The first control step shown in Figure 4-67 is to have the stator vanes normally on flow control with a 2 sec lag in the flow control. On reaching trip, the stator vanes drive to the wide open position after a 1 sec lag. The vanes move at design speed. 

Figure 4-81. Axial compressor antisurge and guide vane control.

Figure 6-7. Pressure-volume chart for an axial-flow compressor with partial stator vane control. (Courtesy ofA-C Compressor Corporatiori ...

Vane control Fan inlet vanes alter fan perform.ance by controlling the swirl. 

Figure 12-135A. Power savings comparison between inlet vane control and outlet dampers. (Used by permission The Howden Fan Company.)...

When suction dampers or guide vane controls are used instead of variable-speed controls, reciprocal gain compensation is recommended due to the... 

Plot the power-input curve AFED for inlet-vane control on the forced-draft fan or inlet-louvre control on induced-draft fans. The data for plotting this curve can be obtained from the fan manufacturer. 

Inlet vane controls should be inspected for linkage or bearing looseness, and adjusted or replaced before they cause more trouble. The minimum air flow should be reset to 10% of maximum to proteet recuperators and any other air-cooled devices. 

Inlet vane controls on blowers and fans should be checked for looseness of linkages and bearings, and corrected or replaced before they cause more trouble. Make sure that inlet screens, filters, and silencers are in place, tight, and cleaned. Do not use any flammable cleaning compound. 

Figure 19-10 Performance curve of vapor compression evaporator with inlet guide vane control.

Speed control for the compressor of an evaporation system with linear characteristics is shown in Figure 19-11. Inlet guide vane control permits greater capacity turndown end allowence for evaporator fouling before the surge condition is reeched. 

The hood pressure control system functions as follows When the pressure in the hood rises, which may occur for example as a result of a decrease in the exit gas flow or an increase in the cooling air flow, the controller increases the volume of air delivered by the exhaust air fan. It does this by adjustment of a damper or an inlet vane control unit or by varying the fan drive motor speed. Conversely, when the pressure in the hood goes down, the air delivery rate of this fan is reduced by the control system. Thus, with the aid of the hood pressure controller, the exhaust air fan performs the function of a pressure relief valve. 

As the air pressure to be developed by the fans varies greatly with the specific load of the cooler, fans having not too flat a characteristic curve (pressure-volume curve) should be chosen. Simple damper control is uneconomical it is preferable to use inlet vane control. 

An inlet vane control system (Fig. 29) comprises a static guide-vane unit which is installed in front of the fan s impeller and whose radial vanes can be swivelled by means of a control device so as to vary the inlet air flow conditions. These vanes deflect the inflowing air in the direction of rotation or in the opposite direction. As a result of this preliminary guidance, the entry losses are substantially less than those associated with ordinary damper control. 

The conditions for fans with inlet vane control which are, respectively, well adapted and unfavourably adapted to the operating requirements are indicated in Figs. 31 and 32. In these diagrams the static pressure of the fan has been plotted against the volume flow for various guide-vane settings. The dot-dash lines indicate the efficiency of the fan. 

On variable-air-volume (VAV) systems, install variable-frequency drives (VFDs) to control supply fan and return fan speed as a function of system pressure set-point in place of inlet-vane control. This is applicable for airfoil or backward-curve fans, not forward-curve fans, which have relatively efficient unloading with inlet-vane control. 

Install VFDs on forced-draft fans and induced-draft fans to control fan speed in lieu of damper or vane control. 

A number of strategies have been developed on how to control the bubble diameter by controlling the airflow rate for internal cooling. Variable speed motors and variable vanes are both used, with the variable vane being the lower cost option. There are pros and cons to the two major methods. If a variable vane controls the flow rate on the supply side of the air, the choking of the air on the supply side causes a pressure drop and the air becomes heated, providing less effective heat transfer. If the vane... 

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