# Which of the following law of thermodynamics is responsible for heat transfer?

Which of the following law of thermodynamics is responsible for heat transfer?

### Right Answer is: Second law of thermodynamics

#### SOLUTION

According to the first statement of the first law, a closed system undergoing a thermodynamic cycle, the net heat transfer is equal to the total work done. But this does not specify the direction in which the heat and workflows. It also does not give any condition under which these transfers take place.

According to the second statement of the first law, heat energy and mechanical work are mutually convertible. Though the mechanical energy can be fully converted into heat energy, only a part of heat energy is converted into mechanical work.

If you want to heat up a bowl of noodles for lunch, you don’t just let it sit on the table and expect the noodles to cook on their own. Even though the table may have several kilojoules of energy because it has a certain mass and a certain temperature, the quality of the energy isn’t sufficient to cook the noodles. The quality of the energy of the table, room, and bowl of soup is all the same, so no energy can be exchanged between them. If you let a bowl of hot noodles sit on the table, it cools off. Energy flows in a certain direction, just as water naturally flows downhill. In order to provide heating, you need a high-quality source of energy relative to the system receiving the energy. The heat source needs to have a higher temperature than the material receiving the heat.

Unlike the other three laws, the second law of thermodynamics isn’t summed up in a single, simple statement. Instead, the second law is a collection of concepts about the quality of energy for performing a process. The basic idea is that for a typical thermodynamic heat addition process, energy flows from a high-quality High-temperature energy reservoir into the process. Conversely, for a typical heat removal process, energy flows from the process into a low-quality Low-temperature energy reservoir. All thermodynamic cycles that provide work or refrigeration operate between high- and low-temperature reservoirs. The high-temperature reservoir is known as the heat source, and the low-temperature reservoir is known as the heat sink.

When you perform a second law analysis on a system, you evaluate the quality of the energy used in the process as well as how much the quality degrades during the process. When you evaluate the quality of energy, you determine the amount of entropy generated in the process. Processes that generate large quantities of entropy in a process are inefficient. A second law analysis is helpful in looking at thermodynamic cycles and identifying where efficiency improvements are most beneficial.

STATEMENTS OF SECOND LAW OF THERMODYNAMICS

Following are the two common statements of the second law of thermodynamics:

1. Kelvin-Planck statement. The Kelvin-Planck statement of the second law of thermodynamics is as follows:

“it is impossible to construct an engine which, while working in a cycle, produces no effect other than to extract heat from a single thermal reservoir and perform an equivalent work. “

This statement relates to a heat engine and it means that the complete conversion of heat energy into work is impossible. In other words, the *efficiency of a heat engine cannot be 100 percent.

2. Clausius statement. The Clausius statement of the second law of thermodynamics is as follows:

“It is impossible to construct an engine which, while working in a cycle, produces no effect

other than to It answer heat from a low-temperature reservoir to a high-temperature reservoir without the aid of an external agency.”

This statement relates to a heat pump or refrigerator and it means that external work is required to pump heat from a low-temperature reservoir to a high-temperature reservoir. Alternately, it may be stated that the coefficient of performance of a heat pump or a refrigerator is finite.

So this law states that heat is always from high temperature to low temperature. Hence heat transfer is governed by the second law of thermodynamics.

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