Dali tube

Dali tube, which is a modification of the venturi, have even been standard instruments. Several other solutions based on plates, rings, or wing-type obstructions are commercially available. This wide variety of devices is not covered here. For further information, the reader should contact the manufacturers of such instruments. 

Figure 6.19. Pressure distribution using orifice plate, venturi meter, and Dali tube. Pressure falls by 10% from upper pressure tapping to throat in each case...

In view of the complexity of the pipework, it was difficult to prejudge the likely accuracy of the overall prediction. Total flows were measured by Dali tubes situated in the main downcomers to the pumps over a range of thermal powers ranging up to 300 MW. The predictions were within the scatter of the measured points. At full power the comparison was as shown in Table 3. 

Dali Flow Tube - The advantage is this type of flowmeter is that it has a permanent head loss of only 5 % of the measured pressure differential. This is the lowest pressure drop of all orifice meter designs. Flow ratios as high as 1 10 (e.g., 1.0 to 10 kg/s) can be measured within + 2% of actual flow. Dali flow mbes are available in different materials and diameters up to 1500 mm. 

O. Miner. The Dali flow tube. Instrument Engineer, April 1957, pp. 45-49. 

Figure 4.2 The micro-Flow Tube Reaetor/Mass Spectrometer instrument. 1 — heated gas inlet/vacuum feedthrough, 2 — hot zone of flow tube, 3 — multiion source block, 4 — ion guide, 5 — quadrupole mass spectrometer, 6 — ion guides, 7 — reaction cell, 8 — quadrupole mass spectrometer, 9 — daly detector... 

As with mass analyzers, many types of mass detectors equipped with an electron multiplier are available. Most common mass detectors are the chan-neltron, Daly detector, electron multiplier tubes, and the Faraday cup. All generate a current when charged analytes generated in the source and separated in the analyzer impinge on them. This current is recorded as a function of the masses selected by the electrical-field settings. 

J Scott, P Kirke, A Molloy, L Daly, D Weir. The role of folate in the prevention of neural-tube defects. Proc Nutr Soc 53 631-636, 1994. 

The flow sensors most commonly employed in the industrial practice are those that measure the pressure gradient developed across a flow constriction. Then, using the well-known (from fluid mechanics) equation of Bernoulli, we can compute the flow rate. Such devices can be used for both gases and liquids. The orifice plate (Figure 13.5a), venturi tube (Figure 13.5b), and Dali flow tube are typical examples of sensors based on the foregoing principle. The first is more popular due to its simplicity and low cost. The last two are more expensive but also more accurate. 

Other Types of Detection Systems Scintillation-type transducers consist of a crystalline phosphor dispersed on a thin aluminum sheet that is mounted on the window of a photomultiplier tube. When ions (or electrons produced when the ions strike a cathode) impinge on the phosphor, they produce flashes of light that are detected by the photomultiplier. A specialized version of this type of device is the Daly detector, which consists of an aluminized cathode in the shape of a knoh (the Daly knob) held at a very large negatKc voltage opposite a. scintillation transducer,. Analyte ions collide with the cathode producing secondary electrons that are then attracted to the sur-... 

The Daly detector uses a photomultiplier rather than an electron multiplier. Ions leaving the analyzer are directed onto a conversion dynode, and the ejected electrons are accelerated onto a plate coated with a fast-acting scintillant. Each electron releases a photon from the scintillant. The photons then enter a photomultiplier tube and impact on a photocathode, producing electrons (photoelectric effect) and initiating an electron cascade (Pigure 2.40). The output from the photomultiplier is further amplified electronically, similarly to the output of dynode type electron multipliers. The level of amplification is similar to that of electron multipliers. Photomultiplier tubes last longer than electron multipliers, but the scintillant-coated plates require replacement every few years. 

Figure 11.3 Pitot static and other tubes for velocity measurement. Source Reprinted from Daly BB, Woods Practical Guide to Fan Engineering, Woods of Colchester, 3rd ed., 230, 1992. By kind permission of Flakt Woods Ltd 2004.

Figure 11.5 Location of velocity measurements in ducts, a. Log linear rule for posifions of fraverse points for a Pitot survey on three different diameters of a circular ducf b. Log Tchebycheff Rule for position of measuring points and traverse lines for Pifof survey of a recfangular ducf. Note Minimum ratio of ducf diameter to Pitot static tube diameter is 32 BS 1042 Part 2.1. Source Reprinted from Daly BB, Woods Practical Guide to Fan Engineering, Woods of Colchester, 3rd ed., 231, 1992. By kind permission of Flakt Woods Ltd 2004.

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