Rotameters principle

Flow measurements using nonintrusive or low mechanical ac tion principles are desired, such as magnetic, vortex-shedding, or Coriolis-type flowmeters. Orifice plates are easy to use and reliable but have a limited range and may not be suitable for streams which are not totally clean. Rotameters with glass tubes should not be used. 

Other flowmeters are in common use which operate on principles differing from head flowmeters. Mechanical flowmeters have primary elements which contain moving parts. These flowmeters include rotameters, positive displacement meters and velocity meters. Electromagne-... 

Other sensors which are described in Volume 1 (Sections 6.3.7-6.3.9) are the variable area meter, the notch or weir, the hot wire anemometer, the electromagnetic flowmeter and the positive displacement meter. Some of these flowmeters are relatively less suitable for producing signals which can be transmitted to the control room for display (e.g. weir, rotameter) and others are used in more specialist or limited applications (e.g. magnetic flowmeter, hot wire anemometer). The major characteristics of different types of flow sensor are summarised in Table 6.1. Brief descriptions follow of the principles underlying the more important types of flowmeter not described in Volume 1. In many instances such flow sensors are taking the place of those more traditional meters which rely upon pressure drop measurement. This is for reasons of versatility, energy conservation and convenience. 

However, also this calorimetric principle is not without weaknesses. Equ.(4-226) shows that the exact knowledge of the coolant mass flow is pivotal to the overall accuracy of the measurement. Today s commercially available calorimeters are equipped with pumps for the coolant like those known in type from thermostats. They are not able to provide a frilly constant mass flow rate, especially not if the experiment lasts several hours. Furthermore, the preinstalled mass flow meters usually are rotameters of quite a simple type. 

The principle of the falling ball viscometer is similar to that of the rotameter (discussed in Chapter 5)—instead of suspending a bob in the flowing gas, the sphere moves at a constant velocity and the fluid is immobile. As with the rotameter, the gravitational force on the sphere, VsPsg, acts downward and the... 

Orifice meters are not used in gas-solids flows also because of the erosion that will occur in time, giving unreliable or no results at all. Such utilization of orifices, turbine meters, venturis, and rotameters can still be used for gas flow metering and indeed they are employed. In addition, the sonic orifice principle or the Laval meter has been used with considerable success by many people for gas flow. These meters operate on the principle of having a sonic velocity at an orifice and as such, the upstream is not subject to the downstream pressure perturbations in the system. 

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