Thermodynamics Principles and Systems

The first law of thermodynamics states that energy cannot be created or destroyed, only transformed from one form to another.

The first law of thermodynamics does not explain why certain processes happen in a specific direction.

The second law of thermodynamics explains why processes occur in a specific direction and not in reverse.

A system that converts thermal energy into mechanical work.

A device that transfers heat from a cold reservoir to a hot reservoir, requiring external work.

It's impossible to make a machine that can completely convert heat into work.

It's impossible to transfer heat from a cold reservoir to a hot reservoir without external work.

A theoretical thermodynamic cycle with maximum efficiency.

The ability to do work or produce change. It can exist in different forms such as heat, light, and mechanical energy.

The transfer of energy into a system due to a temperature difference between the system and its surroundings. It's the energy that flows when things are at different temperatures.

The transfer of energy into a system due to an external force acting on the system. It's related to the force and the distance over which the force acts.

A measure of how efficiently a thermal engine converts heat energy into work. It's the ratio of the work done by the engine to the heat absorbed from the hot reservoir.

A device that transfers heat from a cold reservoir to a hot reservoir. It requires work input to achieve this process.

The ratio of the heat absorbed from the cold reservoir to the work done by the refrigerator. It indicates how effectively the refrigerator transfers heat.

The total energy of a system. It's determined by the internal energy (temperature) of the system, the external forces acting on it, and the state of the system.

A state where a system returns to its starting conditions after a series of changes. The internal energy of the system remains constant.

The amount of heat required to raise the temperature of a substance by a specific amount. It reflects how much energy is required to change the temperature of a particular substance.

A heat pump works by extracting heat from a cold reservoir and releasing it to a hot reservoir.

The goal of a refrigerator engine is to maintain a cold temperature inside the refrigerated space. The goal of a heat pump is to maintain a warm temperature in the heated space.

The performance of a heat pump is measured by its efficiency, which is the ratio of heat delivered to the hot reservoir to the work input.

The efficiency of a heat pump is given by the equation 𝜂𝐻𝑃 = 𝑄𝐻/(𝑄𝐻 − 𝑄𝐶), where 𝑄𝐻 is the heat delivered to the hot reservoir and 𝑄𝐶 is the heat extracted from the cold reservoir.

It is impossible for a device operating in a cycle to transfer heat from a cold reservoir to a hot reservoir without any other effects.

The first law of thermodynamics, applied to a cyclic heat pump process, states that the total heat exchange is zero, meaning the heat absorbed from the cold reservoir (QC) equals the heat released to the hot reservoir (QH).

An ideal refrigerator, according to the Clausius statement, is impossible because it would require transferring heat from a cold reservoir to a hot reservoir without any work input, which violates the second law of thermodynamics.

A thermodynamic cycle that represents the idealized working of a diesel engine. It involves adiabatic compression and expansion, as well as isobaric expansion.

The relationship between the heat absorbed (QH) and the heat released (QC) in a reversible Carnot cycle is directly proportional to the ratio of the absolute temperatures of the hot (TH) and cold (TC) reservoirs. This relationship applies regardless of the working substance.

The temperature scale based on the Carnot cycle. It uses the triple point of water (273.16 K) as a reference point and is independent of the working substance.

The ratio of work done by a heat engine to the heat absorbed from the hot reservoir.

The heat absorbed by the engine from the hot reservoir during the isothermal expansion phase of the Carnot cycle.

The heat released by the engine to the cold reservoir during the isothermal compression phase of the Carnot cycle.

A device that converts thermal energy into mechanical work.

The amount of heat exchanged between a system and its surroundings at constant volume.

The maximum efficiency achievable by any heat engine operating between two given temperatures.

A thermodynamic process that occurs without any heat exchange between the system and its surroundings.

A thermodynamic process that occurs at constant temperature.

The mathematical expression representing the total work done by a cycle.

The work done by a system during an adiabatic process.

The efficiency of a heat pump, defined as the ratio of heat delivered to the hot reservoir to the work input.

A thermodynamic process that happens at constant pressure.

The efficiency of a Carnot cycle is solely determined by the temperatures of the hot and cold reservoirs.

Carnot's Theorem states that no heat engine operating between two temperatures can be more efficient than a reversible engine operating between the same temperatures. It also states that all reversible engines operating between the same temperatures have the same efficiency. This sets a theoretical limit on the efficiency of thermal engines.

A reversible cycle is a thermodynamic process where the system and its surroundings can be returned to their initial states without any net change in entropy. This means the process is frictionless, involves only heat transfer between systems at the same temperature (or very small temperature difference), and is quasi-static (slow enough for all states to be in equilibrium).

An irreversible cycle involves processes that cannot be reversed without causing a net increase in entropy. This means some energy is lost as heat due to friction, heat transfer between systems at different temperatures, or non-equilibrium states during the process.

The Otto cycle represents an internal combustion engine. An ideal Otto cycle comprises four stages:

1. Adiabatic compression (a to b): The air-fuel mixture is compressed and heated. No heat is added or removed.
2. Isochoric heat addition (b to c): The compressed mixture is ignited causing the volume to remain constant.
3. Adiabatic expansion (c to d): The hot gasses expand and do work, pushing the piston (power stroke). No heat is added or removed.
4. Isochoric heat rejection (d to a): The burnt gasses are exhausted, and the cycle repeats.

The efficiency of a thermal engine is a measure of how much mechanical work it can produce from a given amount of heat. It is calculated as the ratio of the work done by the engine to the heat absorbed from the hot reservoir. The maximum efficiency of a thermal engine is determined by the Carnot theorem and is dependent on the hot and cold reservoir temperatures.

While the Otto cycle provides a simplified model of an internal combustion engine, real engines have imperfections that make them irreversible. This leads to less efficient operation compared to a theoretical reversible Otto cycle. Factors contributing to irreversibility include friction, heat loss, and non-equilibrium states. However, the Otto cycle remains a valuable tool for understanding the basic principles of the internal combustion engine.

In a reversible process, the change in entropy of the system and the surroundings is zero. All processes involving friction, heat transfer between systems at different temperatures, or non-equilibrium states are irreversible.

Quasi-static processes are thermodynamic processes that occur slowly enough to allow the system to remain in equilibrium at each step. This means the system can be considered to be in a series of equilibrium states as it changes. This concept is essential for understanding reversible processes, as a reversible process must be quasi-static.