Air volume flow rate

Exhauster and Motor Air movers for LVHV systems are not conventional fans. The low static pressures needed to operate LVHV systems can be generated by multiple-stage centrifugal (turbine-type) exhausters. These utilize high-precision rotating blades that can be damaged by dust. Consequently, it is always necessary to have an air cleaner in an LVHV dust control system to protect the fan. The low static pressures also require air volume flow rates to be corrected to standard conditions for exhauster selection. 

Variable Air Volume Fume Cupboards This type of cupboard incorporates a variable air volume (VAV) controller that regulates the amount of air exhausted from the cupboard such that the face velocity remains essentially constant irrespective of the sash position. A sensor detects either the sash position, the pressure differential l>etween the fume cupboard interior and the room, or the vekxity at some point in the cupboard. This information is used to control either the exhaust fan speed or the position of a control damper. The supply air volume flow rate into the laboratory or workspace should also be regulated. It should be remembered that with the sash in the closed position the amount of air to dilute contaminants in both the fume cupboard and the laboratory is reduced and that there could, for example, be difficulty in reducing contaminant levels below the lower exphasive level. 

The vane anemometer s physical dimensions are often quite large (compared with other local velocity measurement instruments). It does not strictly measure a local velocity at all, but rather provides a spatially integrated mean value. This is an advantage in many cases where the air volume flow rate has to be predicted using local velocities and an integration principle. 

The air volume flow rate plays a major role in planning, commissioning, and running industrial ventilation systems, in the planning phase of a system, the supply, exhaust flows, and total flow rates are specified. When the system is built and running, the contractor and/or the client measures the airflows to determine if they agree with the specification. In such a situation, it is of interest to... 

The tracer is injected into the duct at a constant rate and mixed with the flowing air. The concentration of the air-tracer mixture is measured further downstream. Assuming perfect mixing and that the air entering the test section has a zero concentration, the air volume flow rate can be calculated based on the mass balance of the tracer... 

Air change coefficient The ratio of air volume flow rate and the volume of the space. 

Air volume flow rate q, ) The volume of air or gas moved per unit of time. 

FAN PERFORMANCE CURVE - Fan performance curve refers to the constant speed performance curve. This is a graphical presentation of static or total pressure and power input over a range of air volume flow rate at a stated inlet density and fan speed. It may include static and mechanical efficiency curves. The range of air volume flow rate which is covered generally ex tends from shutoff (zero air volume flow rate) to free delivery (zero fan static pressure). The pressure curves are generally referred to as the pressure-volume curves. 

Air volume flow rates in various places in the system. 

The model begins with a known value of air volume flow rate, solids volume flow rate (from solids mass flow rate and settled bulk density) and strand velocity. From this is it a matter of continuity and simple geometry to calculate the strand cross-sectional area and hence the surface area of strand in contact with the air, as well as the velocity of the air in the clear bore above the strand. 

The results of a specific case study are shown in Fig. 26-49. This depicts the change in inbreathing volume flow rate as a function of time. The middle curve describes the case when the tank is filled with dry air that is, no condensation occurs. When the air is saturated with water vapor at 55°C (131°F) and condensation occurs, the top curve is obtainea. The bottom line represents the volume flow rate brought about by thermal contraction alone, not including the amount condensed. Because of the heat of condensation released, this fraction is less than the volume flow rate without condensation, but this effect is more than compensated for by the additional volume flow rate due to condensation. 

Hence, Sensible heat = Air-mass flow rate (q , kg s ) x Specific heat capacity of humid air at constant volume (c ), which is 1.012 kj kg K. ... 

When calculating for heater and cooler batteries, it is the mass flow rate q that is required, not the volume flow rate q as used above. This is determined by using the appropriate specific volume or density of the air at the actual design temperature and moisture content. 

For a high-production furnace the fume volume flow rate after air dilution to 130 °C will be considerably higher than for secondary fume control by enclosure. A separate primary fume capture system would be used for this case. 

In displacement ventilation systems air is supplied to the room at low velocity, with a volume flow rate near the floor, and is extracted near the ceiling. The temperature of the supplied air is slightly lower than that of the room. Air is heated by the objects in the room, e.g., computer terminals and photocopying machines, and it rises due to buoyancy. 

In thermal models, the ventilation airflow rates normally arc input parameters, to be defined by the user or to be calculated by the program on the basis of a nominal air exchange or flow rate) and some control parameters (demand-controlled ventilation, variable air volume flow ventilation systems), in airflow models, on the other hand, room air temperatures must be defined in the input (see Fig. 11.49). 

Vo volume flow rate of air into system, corrected to a standard temperature (2(PC),... 

Generally, the absolute magnitude of Q is not as important as the ratio leak rate to the total flow rate Qieaf/QtotJ. The leakage rate given by Equation (5.4) is the volume flow rate at the temperature and pressure of the leakage flow, and must be corrected to standard conditions for comparison with reactant feed rates. The total required flow rate of fuel or air to the stack is proportional to the stack current, which increases with the electrochemically active area and is inversely proportional to the cell area specific resistance (R"). 

The significant effect of increased combustion rate is an indication that the volume flow rate of the underfire air through the fuel bed has the greatest effect on the particulate emissions. 

Gas adsorption into the liquid falling down a wetted wall column is of considerable interest. The flow of liquid down the surface of such a tube is essentially laminar if Re < 1200, where Re is defined as iu/vl, u being the volume flow rate of liquid, I the perimeter of the tube, and v the kinematic viscosity of the solvent. Under these conditions, if there are no surface forces acting, the velocity of the air-water surface of the... 

With respect to ventilation systems, we employ standard design criteria for volume flow rate, negative pressure, and face velocity requirements in contaminated and potentially contaminated areas. In contaminated plant areas, we employ a minimum of 20 air changes per hour, while in clean operating areas we use a minimum of 6 air changes per hour. All entries to the contaminated areas incorporate airlocks to prevent migration into the clean areas. 

FIG. 26-49 Effect of water vapor condensation on volume flow rate of air into tank. (Fullarton, Evripidis, and Schlunder, 1987, by permission of Elsevier Science S.A., Lausanne, Switzerland.)... 

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