Non-Flow Processes: Understanding the differences between gases and liquids

Fluids can be classified into liquids and gases, but did you know that they have different characteristics? Here are two key differences between them:

1. Compressibility: Liquids cannot be compressed, while gases can be compressed easily.
2. Intermolecular forces: Gases have almost no forces between their molecules, which allows them to move freely. In contrast, liquids have stronger forces that bind them together.

These unique characteristics make gases for generating and transmitting work. In some, gases are used in rigid chambers, such as in combustion chambers, Stirling engines, and pneumatic devices. Heat is exchanged, and the volume and pressure can vary in these processes. These types of fluid systems are known as non-flow processes.

Understanding the differences between gases and liquids is important for engineers and scientists who work with fluid systems in order to design more efficient and effective processes. By taking advantage of the unique properties of gases, they can create systems that are more reliable and better suited to their specific needs.

Non-flow processes

In thermodynamics engineering, any processes in which gases do not flow past a boundary are known as non-flow or closed-system processes, in which the gas volume is considered to be fixed. See the illustration below:

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Steady Flow vs. Non-Steady Flow Processes: Understanding Reversible and Non-Reversible Processes

When it comes to processes that involve mass flow, there are two types: steady flow and non-steady flow processes. In steady flow processes, there is a fixed amount of mass that enters and leaves the system. In non-steady flow processes, the amount of mass entering and leaving can vary.

Another important distinction is between reversible and non-reversible processes. Reversible processes are those that can be changed back to their original state without changing the system or its surroundings. In the real world, however, all processes are non-reversible. This means that to return the system to its initial state requires drawing energy or work from its surroundings.

Understanding the differences between steady flow and non-steady flow processes, and and non-reversible processes is essential for engineers and scientists who work with thermodynamic systems. By taking these factors into account, they can design more efficient and effective processes that meet their specific needs.

Characteristics of non-flow processes

Understanding Non-Flow Processes in Thermodynamics

Non-flow processes have several important characteristics that go beyond being closed. In therm, gases can be defined by their thermodynamic state, which is determined by three variables: pressure, temperature, and volume. Non-flow processes allow gases to move from one state to another by changing one or more of these three variables while keeping one constant.

There are four states that occur in non-flow processes: isothermal, adiabatic, constant volume (also known as isochoric or isometric), and constant pressure (also known as isobaric).

In an isothermal process, the temperature remains constant while the pressure and volume change.

In an adiabatic process, there is no heat transfer between the system and the surroundings.

In a constant volume process, the volume remains constant while the pressure and temperature change.

In a constant pressure process, the pressure constant while the volume and temperature change.

Understanding these different states and how they relate to non-flow processes is crucial for engineers and scientists who work with thermodynamic systems. By taking these factors into account, they can design more effective processes that meet their specific needs.

Isothermal processes

An isothermal process is a thermodynamic process that occurs at a constant temperature. The product of both pressure (p) and volume (V) stays the same, and both variables follow the relationship shown in the formula pV = constant. In order to keep the temperature nearly constant, heat needs to be introduced into the reservoir slowly, at the same rate at which its temperature changes inside. Additionally, the gas and the section introducing heat must be at the same temperature, so that heat can be conducted to the gas and temperature can be kept constant. In the example given, the initial volume of the sphere is calculated using the sphere volume formula, and the final pressure is calculated using the isothermal equation.

Adiabatic processes

Adiabatic thermodynamic processes are those in which there is no heat or mass transfer between the system and its surroundings. In non-flow processes, there is no exchange of mass, but adiabatic processes also have no heat transfer between the gas and its surroundings. The first law of thermodynamics dictates that the work done (W) by the gas must come only from its internal energy (U) change. This can be expressed with the equation W = ΔU.

Adiabatic processes can be expressed with the following equation:

pV^(γ) = constant

Here, the exponent γ is a particular constant that is different for each gas. It relates the specific heat capacities of the gas at constant pressure (Cp) and constant volume (Cv) according to the equation γ = Cp/Cv. For an ideal gas, γ is a constant that is independent of temperature and pressure.

Adiabatic processes are often used in engineering applications, such as in the compression and expansion of gases in engines and turbines. They allow for the efficient conversion of energy from one form to another, without the loss of energy to the surroundings through heat transfer.

Constant pressure processes

In a constant pressure or isobaric process, mechanical work is either made on or extracted from the gas. Work changes the volume of the gas while also modifying its temperature, and a change in temperature involves a change in heat ‘Q’. The work done on or by the gas is equal to the pressure ‘P’ multiplied by its volume change ‘ΔV’, which can also be expressed as the difference in volumes Vf-Vi. The first law of thermodynamics tells us how the heat in gas is related to the internal energy of the gas ΔU and the mechanical work done by or on it.

In the example given, a piston with a radius of 10 cm produces a force of 10 N over a gas in a cylinder with a radius equal to the piston. The gas decreases its volume to 90% of its original value, and its heat increases by 15 J. The work done on the gas is calculated by multiplying the pressure by the change in volume. The pressure is calculated using the area of the piston and the force exerted over it. The final volume is calculated using the cylinder volume formula and multiplying it by 0.9. The first law of thermodynamics is then solved for the internal energy, which increased as a consequence of the compression of the piston transmitting energy to the gas.

In statistical thermodynamics, the heat in gas comes from the gas particles colliding with each other and moving rapidly. In the case of gas being compressed, it will heat up, and this heat increase is proportional to the decrease in volume. On the other hand, when a gas expands, it produces work and decreases its volume, which increases the contact area of the gas. The work done also comes at the expense of energy and decreases the heat of the gas. These principles are important in understanding the behavior of gases in various thermodynamic processes.

Constant volume processes

During a constant volume or isochoric process, the gas does not experience a volume change. If heat is injected into the system, it is spent in changing the internal energy of the gas. This is shown using the first law of thermodynamics, where the heat added to the system is equal to the change in internal energy of the gas. In other words, Q = ΔU.

Non-flow processes are thermodynamic processes in which there is no exchange of mass. Non-flow processes can exchange heat or work with their surroundings. There are four types of thermodynamic non-flow processes, i.e., isochoric, isobaric, isothermal, and adiabatic processes. In isochoric processes, the volume does not change, in isobaric processes, the pressure does not change, in isothermal processes, the temperature does not change, and in adiabatic processes, there is no heat exchange.

Understanding these non-flow processes is crucial in various fields as engineering, physics,., in industry, the concept of isobaric processes is important in understanding how engines work, where the pressure inside the cylinder remains constant during the combustion process. Similarly, the of isochoric processes is used in the design of fuel cells, where the volume remains constant during the electrochemical reaction. Overall, understanding these processes is essential in optimizing energy usage and designing efficient systems.

Non-Flow Processes

What are non-flow processes?

A non-flow process is a process in which there is no mass exchange. However, heat and work can be exchanged with the surroundings.

What is the difference between steady-flow and non-flow processes?

In a non-flow process, there is no mass exchange. In a steady-flow process, mass enters and leaves the system at a fixed rate.

What is a non-flow reversible process?

A reversible process is one in which the gas can revert to its initial state (i.e., its initial temperature, volume, and pressure) without altering its surroundings.In these states, the gas does not need extra energy to revert to its initial state.

What is the difference between flowing and non-flowing systems?

In a flowing system, there is an exchange of mass as it enters through a boundary and leaves through another. In a non-flowing process, fluids are inside a vase or semi-rigid body with no inlet or outlet.

What are flow and non-flow processes?

A flow process is a physical process in which a fluid (gas or liquid) can enter and leave through a boundary. The volume in the boundary is known as control volume, and it can exchange mass and energy and be used to produce work.In a non-flow process, the fluids are kept in a semi-rigid or rigid vase. The fluids can only exchange energy or produce work but cannot flow outside the boundaries of the vase. However, the boundaries of the vase can expand or contract.

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