-Fundamentals of Fluid Mechanics- Bruce Munson, Donald Young, Theodore Okiishi, Wade Huebsch

Fluids in the News (All Fluids in the News contained here are in the print edition as indicated)

Table of Contents

1. Nanoscale Flows (5th and 6th Edition)

2. Smaller Heat Exchangers (5th and 6th Edition)

3. Listen to the Flow Rate (5th and 6th Edition)

4. New Hi-Tech Fountains (5th and 6th Edition)

5. Deepwater Pipeline (5th and 6th Edition)

F l u i d s i n t h e N e w s

Nanoscale flows The term nanoscale generally refers to objects

with characteristic lengths from atomic dimensions up to a few hun-

dred nanometers (nm). (Recall that .) Nanoscale

fluid mechanics research has recently uncovered many surprising

and useful phenomena. No doubt many more remain to be discov-

ered. For example, in the future researchers envision using

nanoscale tubes to push tiny amounts of water-soluble drugs to ex-

actly where they are needed in the human body. Because of the tiny

diameters involved, the Reynolds numbers for such flows are ex-

tremely small and the flow is definitely laminar. In addition, some

1 nm � 10�9 m

standard properties of everyday flows (for example, the fact that a

fluid sticks to a solid boundary) may not be valid for nanoscale

flows. Also, ultratiny mechanical pumps and valves are difficult to

manufacture and may become clogged by tiny particles such as bio-

logical molecules. As a possible solution to such problems, re-

searchers have investigated the possibility of using a system that

does not rely on mechanical parts. It involves using light-sensitive

molecules attached to the surface of the tubes. By shining light onto

the molecules, the light-responsive molecules attract water and

cause motion of water through the tube. (See Problem 8.10.)

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F l u i d s i n t h e N e w s

Smaller heat exchangers Automobile radiators, air condition-

ers, and refrigerators contain heat exchangers that transfer en-

ergy from (to) the hot (cold) fluid within the heat exchanger

tubes to (from) the colder (hotter) surrounding fluid. These

units can be made smaller and more efficient by increasing the

heat transfer rate across the tubes’ surfaces. If the flow through

the tubes is laminar, the heat transfer rate is relatively small.

Significantly larger heat transfer rates are obtained if the flow

within the tubes is turbulent. Even greater heat transfer rates

can be obtained by the use of turbulence promoters, sometimes

termed “turbulators,” which provide additional turbulent mix-ing motion than would normally occur. Such enhancement

mechanisms include internal fins, spiral wire or ribbon inserts,

and ribs or grooves on the inner surface of the tube. While these

mechanisms can increase the heat transfer rate by 1.5 to 3 times

over that for a bare tube at the same flowrate, they also increase

the pressure drop (and therefore the power) needed to produce

the flow within the tube. Thus, a compromise involving in-

creased heat transfer rate and increased power consumption is

often needed.

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F l u i d s i n t h e N e w s

Listen to the flowrate Sonar systems are designed to listen to

transmitted and reflected sound waves in order to locate sub-

merged objects. They have been used successfully for many years

to detect and track underwater objects such as submarines and

aquatic animals. Recently, sonar techniques have been refined so

that they can be used to determine the flowrate in pipes. These

new flow meters work for turbulent, not laminar, pipe flows be-

cause their operation depends strictly on the existence of turbu-

lent eddies within the flow. The flow meters contain a sonar-based

array that listens to and interprets pressure fields generated by the

turbulent motion in pipes. By listening to the pressure fields asso-

ciated with the movement of the turbulent eddies, the device can

determine the speed at which the eddies travel past an array of sen-

sors. The flowrate is determined by using a calibration procedure

which links the speed of the turbulent structures to the volumetric

flowrate.

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F l u i d s i n t h e N e w s

New hi-tech fountains Ancient Egyptians used fountains in

their palaces for decorative and cooling purposes. Current use of

fountains continues, but with a hi-tech flair. Although the basic

fountain still consists of a typical pipe system (i.e., pump, pipe,

regulating valve, nozzle, filter, and basin), recent use of computer-

controlled devices has led to the design of innovative fountains

with special effects. For example, by using several rows of multi-

ple nozzles, it is possible to program and activate control valves to

produce water jets that resemble symbols, letters, or the time of

day. Other fountains use specially designed nozzles to produce

coherent, laminar streams of water that look like glass rods flying

through the air. By using fast-acting control valves in a synchronized

manner it is possible to produce mesmerizing three-dimensional

patterns of water droplets. The possibilities are nearly limitless.

With the initial artistic design of the fountain established, the ini-

tial engineering design (i.e., the capacity and pressure require-

ments of the nozzles and the size of the pipes and pumps) can be

carried out. It is often necessary to modify the artistic and/or en-

gineering aspects of the design in order to obtain a functional,

pleasing fountain. (See Problem 8.64.)

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F l u i d s i n t h e N e w s

Deepwater pipeline Pipelines used to transport oil and gas are

commonplace. But south of New Orleans, in deep waters of the

Gulf of Mexico, a not-so-common multiple pipe system is being

built. The new so-called Mardi Gras system of pipes is being laid

in water depths of 4300 to 7300 feet. It will transport oil and gas

from five deepwater fields with the interesting names of Holstein,

Mad Dog, Thunder Horse, Atlantis, and Na Kika. The deepwater

pipelines will connect with lines at intermediate water depths to

transport the oil and gas to shallow-water fixed platforms and

shore. The steel pipe used is 28 inches in diameter with a wall

thickness of 1 1�8 in. The thick-walled pipe is needed to with-

stand the large external pressure which is about 3250 psi at a

depth of 7300 ft. The pipe is installed in 240-ft sections from a

vessel the size of a large football stadium. Upon completion, the

deepwater pipeline system will have a total length of more than

450 miles and the capability of transporting more than 1 million

barrels of oil per day and 1.5 billion cubic feet of gas per day.

(See Problem 8.113.)

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