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Jaime Andrs Mondragn Galeano42111038Facultad de Ingeniera elctrica

__________________________________________________________________A perpetual-motion machine problem forTeaching fluid mechanics andThermodynamics

In university it is extremely important that students acquire knowledge based on

basic fundamentals of science, but not only a process to acquire and retain

knowledge but to develop them for understanding many problems of everyday life

in relation to basic principles branch of science in general. I care because with q

this article with which I am developing this essay , refers to its interest electricalengineering students mainly to studying subjects like fluid mechanics and

thermodynamics , which involve issues of great importance as are Archimedes law

, hydrostatic and buoyancy force .

It is interesting as a method of teaching can influence student interest as recorded

in the article, it is very important how to develop a problem in any area of

engineering which highlight some steps to my account , which are in principle ,

stating the problem , take the problem based on ideal systems and laws which help

us make a good reference of the problem , once we have an ideal system and

likewise a reference point , still impose the restrictions imposed by the samesystem for the solution of the problem and the development does not involve some

complexity that may arise , and have a notion of quantities such as work forces,

pressures , volumes etc. . Or at least that is how it presents the problem of

perpetual motion machine.

Problem perpetual motion machine

Fig. 1 shows the class handout, entitled The Buoyancy Engine. The problem ispresented in the form of a thought experiment. An inventor has proposed abuoyancy engine that comprises a series of air-fi lled barrels, connected in a

continuous loop. In air, the barrels are in static equilibrium. Then water is added onone side of the engine, such that the barrels on that side are submerged, while thebarrels on the other side remain in air. In this configuration, there is an imbalancebetween the upward buoyancy force on the submerged barrels and the downwardgravitational force on the non-submerged barrels. The students are asked whetherthe loop of barrels would turn clockwise, as suggested by the inventor, and,whether or not this invention would produce useful power.


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Then cover this problem is necessary to advance knowledge of the analysis of the

hydrostatic pressure on flat and curved surfaces and the calculation of buoyancy

forces, including the Archimedes principle .

Although the system really a perpetual motion machine does not exist and it is

impossible to work (despite the existence of a hydrostatic force on each barrel as it

enters the water tank. This hydrostatic force provides a counter-torque), the

important to emphasize the development of the paper is the explanation of why it is

not possible from mathematical modelamientos and principles. Discuss two simplesolution methods: a method of strength and energy method. From the perspective

of teaching introductory fluid mechanics, the force method is most appropriate.

Students can easily follow the calculation of the net hydrostatic and buoyancy

forces as it is directly related to recent conference material. Energy method is more

appropriate when the teaching of thermodynamics, since it involves calculating the

work done by the pressure in a movement limit.


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Force method (open body)

In the development of this problem have restrictions, such as:

The weight of the barrel is not considered since it is negligible for the system.

The sum of the buoyant force FB to a number of kegs must be greater than the

hydrostatic force FH.

Upon completion of the analysis is really not possible to operate the system and

that the hydrostatic force is greater than the buoyancy force, so does not work but

even with this imbalance of power in the system can take advantage of energy anti

extracted as useful system time since the hydrostatic force is much greater,

additionally must add that no system is perfect in real life as there are present inthe same lost, either by friction or heating, but still without contradict the law of

conservation of energy.


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Energy Method

In the energy method is shown that the work required to drive each barrel

massless through the wall against the hydrostatic pressure is exactly equal to the

work done by the buoyant force rises as the barrel to the free surface.

To simplify the analysis, a "barrel" thick rectangular W, length L and depth T is

considered, as shown in Fig. April. The resulting hydrostatic pressure on the faceof the cylinder is P = AH, where H is the depth of the centroid of the face surface

with respect to the barrel free.

One can see that, in the ideal situation, the job entry (equation 8) and work output

(equation 11) for each barrel are exactly alike. However, in the real world, it would

be impossible to reach equilibrium.


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The branch of engineering covers a lot of general knowledge, so as students we

should not underestimate the knowledge that can be acquired because in this

physical world all basic law relates to all engineering careers to the naked eye but

cant be observe or recognize, pointed to the example of the hysteresis

phenomenon that takes place in different areas as it simply explains the

phenomenon of saturation and loss in a system, the only change from engineering

to another are the amounts but the phenomenon is the same.

References

[1] D. Naylor. A perpetual-motion machine problem for teaching fluid mechanics

and thermodynamics. International Journal of Mechanical Engineering

Education 37(3), pp. 187-196. 2009. Available:

http://search.proquest.com/docview/741389779?accountid=41919.

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