What is an isobaric process? How do condensers work isobarically?

Isobaric process vs Isothermal process

An isothermal process is a thermodynamic process in which the temperature remains constant throughout the process. For an ideal gas undergoing an isothermal process, the change in internal energy (ΔU) is zero because the internal energy of an ideal gas is directly proportional to its temperature. To explain this point a little more, it may be noted that while real gases have both KE and PE, an ideal gas has only kinetic energy in the absence of intermolecular interactions. Thus, an ideal gas follows the equation:

Average KE = ? Kb T [ Kb is Boltzmann constant and T is Kelvin]

This equation does not apply to real gases since the internal energy of real gases is the sum of PE and KE.

?Coming back, in an isothermal process, the heat transferred (Q) is equal to the work done (W) on the gas. Mathematically, this can be expressed as Q = W. On the other hand, an isobaric process is a thermodynamic process in which the pressure is held constant. This is typically achieved by allowing heat exchange with the surroundings, such as in the case of a boiler. A boiler is a typical example of an isobaric process.

In an isobaric process, the heat transferred (Q) is equal to the change in internal energy (ΔU) plus the work done (W) by the gas. This can be expressed as Q = ΔU + W, where ΔU represents the change in internal energy and W is the work done. It is important to note that in an isobaric process, at constant pressure, the heat transfer is represented not only by the change in internal energy but also by the work done, and this combination is known as enthalpy transfer (H). This is expressed as Q = ΔH, where H represents enthalpy.

In summary, Q = delta W in the case of an isothermal process while for an isobaric process, Q = delta H

To summarize, in an isothermal process, where there is a constant temperature, only work is transferred, and the change in internal energy is zero. In contrast, in an isobaric process, where pressure is held constant, there is a transfer of both internal energy and work, represented as enthalpy transfer. It's essential to understand the distinctions between these processes and their respective equations to analyze and comprehend the behavior of thermodynamic systems accurately.

How do condensers work isobarically?

A condenser is a crucial component in many heat transfer systems, particularly in refrigeration and power generation. It functions by converting vapor or gas into a liquid state. The condenser operates isobarically, meaning it maintains a constant pressure during the process. When the vapor enters the condenser, it contains latent heat, which must be removed to allow the vapor to condense. This occurs at the saturation temperature while the pressure remains constant. As the vapor condenses into liquid, it undergoes compression work, as the gas molecules are compressed into a denser liquid state. The compression work generates heat which gets added to circulating water.

Throughout this transformation, the vapor transfers its internal energy to the circulating water in the heat exchanger. Thus the energy transfer involves both internal energy and the performance of work, in a manner akin to an isobaric process. Consequently, the condenser is not a constant temperature process, as it involves the interplay of both internal energy transfer and work transfer.

Examples

Isothermal constant temperature process

Let us consider a glass of water sitting on a table. The air blowing over the water's surface brings heat and causes water to evaporate slowly. Every drop of water that evaporates carries a latent heat of vaporization 2257 KJ / kg. But still temperature remains constant. Boiling of water at 100 degc At 100 degc hot water absorbs heat slowly to break its intermolecular bonds to expand and become steam, dU = 0

Isobaric constant pressure process

Steam making

Let us see how a boiler makes steam. A boiler is an isobaric process where the pressure is held constant despite water expanding into steam by consuming a part of the system's energy. Since the pressure is held constant it keeps compensating energy consumption in the expansion work. Therefore, the steam temperature remains constant.

Another example

Power plant condenser

The vapor enters the condenser held at constant pressure. The coolant cools the gas at constant pressure which reduces the kinetic energy of gas molecules. There is a compression effect but still temperature of condensation remains constant corresponding to saturation temperature at the pressure in the condenser

In summary, the condenser plays a vital role in heat transfer processes, particularly in converting vapor into liquid form. It operates isobarically, maintaining constant pressure as the vapor undergoes compression work and transfers its internal energy to the circulating water through a heat exchanger. These factors collectively illustrate that the condenser involves both internal energy transfer and work, thereby distinguishing it from a constant temperature process.