Rotating anemometer

Gas velocihes can also be measured with anemometers (rotating vane, hot wire, etc.), from visual observations such as the velocity of smoke puffs, or from mass balance data (knowing the fuel consumption rate, air/ fuel ratio, and stack diameter). 

Vane-type anemometers rotate with an angular velocity that is proportional to the wind speed. The three-cup anemometer is insensitive to wind direction. The tail of the impeller design (Figure 3.49) always points the impellers into the wind and therefore can detect both wind speed and wind direction. The response speed of an anemometer is expressed in terms of the length of... 

Gup and Vane Anemometers. A number of flow meter designs use a rotating element kept in motion by the kinetic energy of the flowing stream such that the speed is a measure of fluid velocity. In general, these meters, if used to measure wind velocity, are called anemometers if used for open-channel Hquids, current meters and if used for closed pipes, turbine flow meters. 

Cup anemometers have shaped cups mounted on the spokes of a wheel. The cups, under the action of the fluid forces, spin in a horizontal plane about a vertical shaft mounted in bearings. Vane or propeller types use a multibladed rotor, the axis of which is parallel to the flow direction as the rotating member. Both designs are commonly used for wind speed measurement or similar appHcations such as the velocity in ventilation ducts. Because of inertia, anemometers are most accurate under steady conditions. Velocity fluctuations cause readings that are too high. 

Current Meters. Various vane designs have been adapted for open-channel flow measurement. The rotating element is partially immersed and rotates rather like a water wheel. Operation is similar to that of vane anemometers. 

The vane anemometer is an old invention. It can be likened to a small wind turbine with 4-10 rotating blades and a handle, as in Fig. 12.20. Earlier constructions were fully mechanical, where the spindle rotation was transmitted to a pointer through a series of gears. In modern vane anemometers, an electrical sensor records the spindle rotation and the signal is processed, giving the velocity on a digital display. Such an instrument usually is able to integrate the mean velocity over a time interval. 

The measurement range of a vane anemometer is typically between 0.3 and 30 m s E It may start rotating with slightly lower velocities, but due to the characteristic curve having a small nonlinear part in the low-speed end, the useful range is narrower. The actual precision depends on the quality of the instrument however, the inaccuracy may vary between 1% and 5% of the scale. The larger the vane, the higher the accuracy. 

Rotating anemometer An instrument used to measure gas flow that depends on the rotation of vanes mounted on a spindle. 

Wind speed is measured by a anemometer. Wind blows at different speeds at different times. Wind speed near the earth s surface is measured by the anemometer. Anemometer consists of cups that are hollow hemispheres. The cups face the same direction irrespective of the wind speed. They catch the wind on their open sides. The cups rotate and the number of rotations are marked on a scale. 

Current meter and rotating anemometer. These two, which are the same in principle, determine the velocity as a function of the speed at which a series of cups or vanes rotate about an axis either parallel to or normal to the flow. The instrument used in water is called a current meter, and when designed for use in air it is called an anemometer. As the force exerted depends on the density of the fluid as well as on its velocity, the anemometer must be so made as to operate with less friction than the current meter. 

Cup anemometer three conical cups on a freely rotating vertical shaft. 

Anemometry is a general term to represent the measurement of wind speed— anemos is the Greek word for wind. The earliest anemometer for meteorology is credited to Alberti in 1450. Hooke reinvented the device, which relied on cups or disks mounted on a pole that would rotate by the force of wind. Modern instruments to measure wind speed rely on laser Doppler shift, ultrasonic waves, propellers, and hot wire anemometers. The hot wire anemometer is commonly used for fluid flow measurements and in particular for research applications that require a detailed analysis of velocity in localized areas or for conditions... 

Inferential meters include instruments in which the volumetric flow rate is inferred by the movement of a turbine, propeller, or impeller. The fluid impinging on a blade causes it to rotate at an angular velocity that is proportional to the flow rate. The early anemometers made with plates and cups are examples. These types of meters are becoming less and less common due to the need to calibrate and compensate for effects like viscosity. According to Crabtree (2009), the Coriolis and ultrasonic meters are replacing the turbine meters in most industrial applications. 

Current meters are hydrodynamic instruments with rotating vanes or buckets. The speed of their rotation is proportional to the flow velocity. The forerunners of current meters were the paddle wheels developed in the early 18 century. These were applied by Francesco Domenico Michelotti (1710-1777) in 1767, or by Pierre-Louis Du Buat (1734-1809) in 1786. There are two principal types of current meters, namely the screw and the cup types. The first was conceived by the famous British engineer Robert Hooke in 1783 to measure wind velocity with four vanes similar to a windmill. This type was developed by Reinhard Woltman (1757-1837) in 1790, Andre Baumgarten (1808-1859), Albert Ott (1847-1895), Alphonse Fteley (1837-1903) and Haskell, among many others. The other type meter has several cups on spokes rotating around an axis oriented transverse to the current. These anemometers were first applied around 1850 to measure wind velocities, and then were developed by Theodore Gunville Ellis (1829-1883), or William G. Price (1853-1928) to record flow velocity in rivers. 

The instantaneous pressure and velocity distributions along the resonance tube are monitored by piezoelectric transducers and hot-wire thermal anemometer that are connected to the oscilloscope and photo film recorder. These make possible the tuning of the generator to the acoustic resonance by varying the rotational speed of the crankshaft. Also, there is a provision to attach resonance tubes of various lengths and diameters to obtain required amplitudes of pressure and velocity pulsations. 

Anemometer—A rotating vane, swinging vane, or hot-wire device used to measure air velocity. Anhydrous— A substance in which no water is present in the form of a hydrate or water of crystallization. 

Air velocities can be measmed by a variety of instruments but vane anemometers and heated head (hot wire or thermistor) air meters are the most common. Vane anemometers Figure 3.6.7) have a rotating windmill type head coupled to a meter and are most suitable for use in open... 

Figure 12.5. The S shaped rotor (a) direction of rotation and translation when falling, b) source of rotation due to anemometer action, (c) plan view of anemometer for measuring wind velocity, and d) source of rotation due to lift forces acting toward convex sides of rotor oriented parallel to the velocity vector.

Anemometer A rotating vane, swinging vane, or hot-wire device used to measure air velocity. 

The gas and liquid velocities at key points are measured by hot film anemometers. The locations of the hot film probes are rotated in several similar experiments to get fiill information on velocity distributions. The amount of entrained droplet flow and droplet sizes are measured by several isokinetic sampling probes. The Thermal-hydraulic and Reactor Safe Laboratory has recently developed the isokinetic sampling probe to measure the droplet entraimnent rate and droplet size distribution. For droplet size distribution, the droplets are collected into a oil bath and the CDC pictures of the suspensions are obtained. Using digital image processing system... 

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