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8.7 Chapter Summary and Study Guide 447<br />

Inlet<br />

Outlet<br />

Slider valves<br />

driven by<br />

diaphragm<br />

Back case<br />

Back<br />

diaphragm<br />

Front case<br />

Front<br />

diaphragm<br />

(a)<br />

(b)<br />

(c)<br />

(d)<br />

F I G U R E 8.49 Bellows-type flow meter. (Courtesy of BTR—Rockwell<br />

Gas Products). (a) Back case emptying, back diaphragm filling. (b) Front diaphragm<br />

filling, front case emptying. (c) Back case filling, back diaphragm emptying. (d) Front<br />

diaphragm emptying, front case filling.<br />

The nutating disk<br />

meter has only one<br />

moving part; the<br />

bellows meter has a<br />

complex set of<br />

moving parts.<br />

of the center sphere, normal to the disk, completes one circle. The volume of <strong>fluid</strong> that has passed<br />

through the meter can be obtained by counting the number of revolutions completed.<br />

Another quantity-measuring device that is used for gas flow measurements is the bellows meter<br />

as shown in Fig. 8.49. It contains a set of bellows that alternately fill and empty as a result of the<br />

pressure of the gas and the motion of a set of inlet and outlet valves. The common household natural<br />

gas meter is of this type. For each cycle [1a2 through 1d2] a known volume of gas passes through<br />

the meter.<br />

The nutating disk meter 1water meter2 is an example of extreme simplicity—one cleverly designed<br />

moving part. The bellows meter 1gas meter2, on the other hand, is relatively complex—it contains many<br />

moving, interconnected parts. This difference is dictated by the application involved. One measures a<br />

common, safe-to-handle, relatively high-pressure liquid, whereas the other measures a relatively dangerous,<br />

low-pressure gas. Each device does its intended job very well.<br />

There are numerous devices used to measure <strong>fluid</strong> flow, only a few of which have been discussed<br />

here. The reader is encouraged to review the literature to gain familiarity with other useful,<br />

clever devices 1Refs. 25, 262.<br />

8.7 Chapter Summary and Study Guide<br />

This chapter discussed the flow of a viscous <strong>fluid</strong> in a pipe. General characteristics of laminar, turbulent,<br />

fully developed, and entrance flows are considered. Poiseuille’s equation is obtained to<br />

describe the relationship among the various parameters for fully developed laminar flow.

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