Thermodynamics question....?

Question

Can a machinary get 100% efficiency? I need help for my homework. Thanks.

Answer 1

No. That would violate several laws of Physics.
Electrical Superconducters are about as close as you can come.
All devices will have to lose a little bit of energy to heat or friction losses. Some devices will lose a little bit of energy in the form of light.
So, even though the loss of energy in a system would be miniscule and almost unmeasurable, it would still be a loss and therefore never be 100% effiecient.

Answer 2

A machine can never be 100% efficient. In this context I am refering to a machine that uses heat to produce work (a heat engine). Examples of such machinery include all engines - steam, turbine, gas, diesel, etc. The most efficient way to run such a machine is to ensure that every part of the "cycle" is done reversibly.

The limit on the efficiency possible is a perfect engine that runs on what is called the Carnot cycle. This is the best that any machine could theoretically do (based on the laws of thermodynamics).

To clarify what I said above here is a quote from wikipedia:
"The Carnot cycle is a special type of thermodynamic cycle. It is special because it is the most efficient cycle possible for converting a given amount of thermal energy into work or, conversely, for using a given amount of work for refrigeration purposes."

Read more about this cycle at http://en.wikipedia.org/wiki/Carnot_cycle

To cut a long story short, the carnot efficiency (maximum effeciency possible) from a heat engine is:
efficiency = 1 - T(cold)/T(hot) where T is in kelvin.

Therefore for example, it T cold is 0 deg C, and T hot is 273 deg C then the maximum efficiency is 0.5 (or 50%). Remember - this is for an ideal (perfect engine). A real engine would have an efficiency lower than this - so this would be a maximum target for a real engine.

What this tells us is the hotter the engine is inside and the colder the outside is the more efficient the engine becomes. There will always be unusable waste heat produced.

Here is another quote from wikipedia:
"No engine operating between two heat reservoirs can be more efficient than a Carnot engine operating between the same reservoirs. A corollary to Carnot's theorem states that: All reversible engines operating between the same heat reservoirs are equally efficient.

In other words, maximum efficiency is achieved if and only if no new entropy is created in the cycle. Otherwise, since entropy is a state function, the required dumping of heat into the environment to dispose of excess entropy leads to a reduction in efficiency."

So even a perfectly ideal engine would not have an efficiency of 100% (no friction, perfect insulation, etc....)


PS:
I notice one of the answers given was a quote directly from:
http://www.pickens.k12.sc.us/phsteachers/edmunds/Thermodynam%20WS.htm ("Energy: the ability to do work. There are two types of energy: kinetic and potential. Kinetic is energy of movement (thermal and light) while potential is energy of position or stored energy ( chemical). Energy is transformed (not cycled) from one form to another. The study of these transformations is called thermodynamics......."

Answer 3

Yes, machine/Engine working on Carnot cycle will function on 100% Efficiency. Any isentroic process ,in which there is no change in entropy.is 100% efficient, and this is called reverisble process.But this is Ideal.
.

Answer 4

Energy: the ability to do work. There are two types of energy: kinetic and potential. Kinetic is energy of movement (thermal and light) while potential is energy of position or stored energy ( chemical).
Energy is transformed (not cycled) from one form to another. The study of these transformations is called thermodynamics.

Laws of Thermodynamics: First law states that energy of the universe is constant. It may change from one form to another but cannot be created or destroyed. This is sometimes called the Law of conservation of energy.
The second law states that every process increases the entropy (S) of the universe. Entropy is the quantitive measure of disorder of a system. If we look at any organism as a system that needs and uses energy, we can see what would happen if the energy supply was cut off. The system would fail due to lack of the necessary energy to meet its needs. This type of system is considered a closed system. No new energy can enter, while the available energy is changed into useless heat, causing the system to fail.

Heat is a useless form of energy unless it is used to maintain temperature of a system, but it must move from a warm area to a cool one. The earth and its organisms are not closed systems. They are considered open, due to the fact that they can replenish their energy when needed. The sun and food are their means of replacement. If for some reason the energy supply stops they will become a closed system and fail. All open systems will eventually fail due to the process of energy turning into useless heat. The universe will eventually die due to a lack of useful energy and an abundance of heat. The universe is a closed system.
Chemical Energy: is stored in the bonds of the chemical they are holding together. Covalent bonds contain the most energy,while hydrogen bond much less. During a chemical reaction 2 thing must occur,

1). energy must be absorbed to break the bonds of the reactants. 2). Energy is released when new bond are formed. This is called bond energy.

CH4 + 2O2 --------------> CO2 + 2H2O

Each C-H bond contains 99 kcal / mole of stored energy. Since methane contains 4 of them its total bond energy is 396 kcal / mole. The double bonded oxygen contains 118 kcal / mole and there are 2, giving us 236 kcal / mole. Since these bonds must be broken the total energy absorbed is 633 kcal / mole.
On the products side( new molecules being formed), each C = O bond contains 174 kcal /mole since there are 2 each carbon dioxide contains 348 kcal / mole of energy. The O-H bond contains 111 kcal / mole, and there are 4 of them giving us a total of 444 kcal / mole. The total amount of energy released is 792 kcal / mole. 160 kcal / mole is the net energy released or the heat we feel from the reaction. This is the heat of the reaction or delta-H = - 160 kcal / mole. this refers to the stored energy being released. Always subtract the product answer from the reactant answer. If a reaction has a negative delta H, it is said to be exothermic.
Enthalpy : The total potential energy of a molecule. Enthalpy relates to the amount of heat energy released from a chemical reaction. In an exothermic reaction the enthalpy of the products is less than the reactants, hence you feel the heat. In an endothermic reaction the reverse is true, since the products have more enthalpy than the reactants. This occurs at the expense of its surroundings.

Spontaneous Reactions: is a reaction that will occur without any outside help. Specifically it can occur without the introduction of external energy. A nonspontaneous reaction cannot occur on its own. it will only happen if external energy is added.

Free Energy: The quantity that combines total energy ( enthalpy ) and entropy is free energy. Free energy is represented by the letter (G). Spontaneous reactions occur when the free energy of the system decreases. During nonspontaneous reactions the free energy of the system increases.

Based on free energy movement in a system the terms exergonic and endergonic are used to determine the direction of this free energy. An exergonic reaction will release energy from the reaction, while an endergonic reaction will absorb free energy from its surroundings.
In order for an endergonic reaction to go to completion it needs an outside source of energy. In the cell this energy source comes from the chemical compound ATP. ATP helps the cell carry on 3 main types of work. Mechanical ( cell movement), chemical ( anabolism ), and transport ( pumping materials into and out of the cell ). ATP ( adenosine triphosphate) is constructed of a molecule of adenine attached to a molecule of ribose sugar which is attached to 3 phosphates.

Answer 5

No machine can work at 100% efficiency except a Perpetual motion machine which exisits only in theory.

Answer 6

No. Max is about 30%. I'm too lazy to look up why it is max. Make that your homework.

Answer 7

no .only ideal machines can.but it is difficult to build such a machine without loss of any form of energy

Answer 8

in the real world, no, only ideal machines can

Answer 9

If its an ideal m/c .. then yes.!
\

Assume lossless conditions...

Answer 10

My guess is that you don't work at Exxon.