Best answer: Why must every heat engine have a cold reservoir?

Why must every heat engine have a cold reservoir? Because it is impossible for even a perfect engine to convert heat entirely into mechanical work. Because the cold reservoir keeps the engine from overheating. … Because the cold reservoir increases the power of the engine.

Is it possible to create a heat engine without a cold reservoir?

Clausius: No engine can transfer heat from a cold to a hot reservoir without input of work. Kelvin: No engine can extract heat from a thermal reservoir and convert it entirely to work. Both heat engines and refrigerators may be constructed.

Why do we need a low temperature reservoir in the Carnot cycle?

Heat is absorbed from the low-temperature reservoir, heat is rejected to a high-temperature reservoir, and a work input is required to accomplish all this. The P–V diagram of the reversed Carnot cycle is the same as for the Carnot cycle except that the directions of the processes are reversed.

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What is cold reservoir?

In the case of the automobile engine, the hot reservoir is the burning fuel and the cold reservoir is the environment to which the combustion products are exhausted. The efficiency expression given is a general one, but the maximum efficiency is limited to that of the Carnot cycle.

Why does heat not flow from cold to hot?

Closed 3 years ago. The second law of thermodynamics says that heat cannot spontaneously flow from a colder to a hotter reservoir but only with the expenditure of mechanical energy. This is taken as a postulate or law in thermodynamics.

Why Carnot engine is not possible?

The Carnot cycle can be thought of as the most efficient heat engine cycle allowed by physical laws. … It is not a practical engine cycle because the heat transfer into the engine in the isothermal process is too slow to be of practical value.

Why are Carnot engines not 100 efficient?

In order to achieve 100% efficiency (η=1), Q2 must be equal to 0 which means that all the heat form the source is converted to work. The temperature of sink means a negative temperature on the absolute scale at which the temperature is greater than unity.

Is Carnot engine 100 efficient?

In order to achieve 100% efficiency (η=1), Q2 must be equal to 0 which means that all the heat form the source is converted to work. The temperature of sink means a negative temperature on the absolute scale at which the temperature is greater than unity.

Are heat engines reversible?

13.3 Carnot Power Cycle

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The heat flow through an engine is diminished (i.e., reduced) by its conversion into work. … This cycle is still known as Carnot’s cycle, but because it is defined to be a reversible cycle, no heat engine can ever be made to operate using it.

How can you increase the efficiency of a heat engine?

Therefore, the efficiency of the heat engine can be increased by decreasing the temperature of the cold sink or increasing the temperature of the hot source.

What is a real life example of the second law of thermodynamics?

Examples of the second law of thermodynamics

For example, when a hot object is placed in contact with a cold object, heat flows from the hotter one to the colder one, never spontaneously from colder to hotter. If heat were to leave the colder object and pass to the hotter one, energy could still be conserved.

What are examples of entropy in real life?

examples of entropy in everyday life. Entropy measures how much thermal energy or heat per temperature. Campfire, Ice melting, salt or sugar dissolving, popcorn making, and boiling water are some entropy examples in your kitchen.

Is a Carnot engine possible?

Any engine using the Carnot cycle, which uses only reversible processes (adiabatic and isothermal), is known as a Carnot engine. Any engine that uses the Carnot cycle enjoys the maximum theoretical efficiency. … Carnot cycles without heat loss may be possible at absolute zero, but this has never been seen in nature.

Does heat go to cold or cold to heat?

Heat flows from hot to cold objects. When a hot and a cold body are in thermal contact, they exchange heat energy until they reach thermal equilibrium, with the hot body cooling down and the cold body warming up. This is a natural phenomenon we experience all the time.

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Does heat absorb cold?

Indeed, cold matter, cold objects can absorb heat in that they are warmed by the movement of heat, by radiation (light hits the object and is absorbed, warming the object), or convection (warmer object in contact with colder object and gradually the warm one cools and the cold one warms up until the temperatures are …

What is the rule when it comes to hot and cold air?

In physics, the second law of thermodynamics says that heat flows naturally from an object at a higher temperature to an object at a lower temperature, and heat doesn’t flow in the opposite direction of its own accord.

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