When we talk about equilibrium or quasi-equilibrium in thermodynamics, we are talking about a system - a system being in equilibrium or quasi-equilibrium. As for the piston you referred to, it typically appears as part of a piston-cylinder enclosure, which contains some gas that you can add heat to or remove heat from. In this case, the gas is the SYSTEM. The piston and the cylinder are the surroundings of the system (the gas). Assuming no leakage between the piston and the cylinder, the gas is a closed system, which can be involved in doing boundary work or receiving boundary work (and possibly heat addition or removal), as the piston moves. In most engineering applications, the gas (the system) can be considered in quasi-equilibrium. If the system is in quasi-equilibrium when it undergoes a process, that process is also called quasi-equilibrium or quasi-static process.
Thank you for uploading the video, I at least understood a little more about this concept. One question, consider the gases in a combustion engine cylinder is the system, then the expansion of the gases is quasi equilibrium because the expansion is infinitesimally small compared to how fast the piston is moving ? I mean the expansion can be neglected---> causes no change to the system.
For all practical purposes, we consider the gas system to be under quasi equilibrium if the expansion or compression is slow comparing to the speed of sound in the gas. When the system is expanding or being compressed, strictly speaking it is not in equilibrium. However, if the system's boundary (such as the inside surface of the piston) moves much slower than the speed of sound, the deviation of the system from equilibrium is very small, and the system is in quasi equilibrium.
@@bing9u0 Thanks for your response. I thought I understand this but now I feel like I dont, this concept is so confusing. Back to the expansion of the combustion gas inside the cylinder, how is the system still remained in equilibrium when there is chemical reactions occurs throughout the process? This is what I learned: A Quasiequalibrium process is, first of all, a thermodynamic equilibrium ( satisfy all these: thermal equilibrium, mechanical equilibrium and chemical equalibrium). I would guess that the system satisfy the first two( thermal and mechanical equilibrium), but why chemical equilibrium? Isn't the gas combustion is chemical reactions?
@@Kay-dx8vm In the context of a typical thermodynamics course offered to Mechanical Engineering students, the chemical reactions in an internal combustion engine are not considered in detail. Instead, the reactions, which lead to the release of chemical energy, are modeled as a heat addition process. Further, the "heat addition" process is typically modeled as either an instantaneous (and hence isochoric) process for the Otto cycle or a constant-pressure process for the Diesel cycle.
So a piston attached to a rotating camshaft, that moves by heating the gas contained up, is not in quasi-equilibrium?
When we talk about equilibrium or quasi-equilibrium in thermodynamics, we are talking about a system - a system being in equilibrium or quasi-equilibrium. As for the piston you referred to, it typically appears as part of a piston-cylinder enclosure, which contains some gas that you can add heat to or remove heat from. In this case, the gas is the SYSTEM. The piston and the cylinder are the surroundings of the system (the gas). Assuming no leakage between the piston and the cylinder, the gas is a closed system, which can be involved in doing boundary work or receiving boundary work (and possibly heat addition or removal), as the piston moves. In most engineering applications, the gas (the system) can be considered in quasi-equilibrium.
If the system is in quasi-equilibrium when it undergoes a process, that process is also called quasi-equilibrium or quasi-static process.
Thank you for uploading the video, I at least understood a little more about this concept. One question, consider the gases in a combustion engine cylinder is the system, then the expansion of the gases is quasi equilibrium because the expansion is infinitesimally small compared to how fast the piston is moving ? I mean the expansion can be neglected---> causes no change to the system.
For all practical purposes, we consider the gas system to be under quasi equilibrium if the expansion or compression is slow comparing to the speed of sound in the gas. When the system is expanding or being compressed, strictly speaking it is not in equilibrium. However, if the system's boundary (such as the inside surface of the piston) moves much slower than the speed of sound, the deviation of the system from equilibrium is very small, and the system is in quasi equilibrium.
@@bing9u0 Thanks for your response. I thought I understand this but now I feel like I dont, this concept is so confusing. Back to the expansion of the combustion gas inside the cylinder, how is the system still remained in equilibrium when there is chemical reactions occurs throughout the process? This is what I learned: A Quasiequalibrium process is, first of all, a thermodynamic equilibrium ( satisfy all these: thermal equilibrium, mechanical equilibrium and chemical equalibrium). I would guess that the system satisfy the first two( thermal and mechanical equilibrium), but why chemical equilibrium? Isn't the gas combustion is chemical reactions?
@@Kay-dx8vm In the context of a typical thermodynamics course offered to Mechanical Engineering students, the chemical reactions in an internal combustion engine are not considered in detail. Instead, the reactions, which lead to the release of chemical energy, are modeled as a heat addition process. Further, the "heat addition" process is typically modeled as either an instantaneous (and hence isochoric) process for the Otto cycle or a constant-pressure process for the Diesel cycle.
@@bing9u0 I see, that makes sense. Thank you so much for your help
very fainted voice almost unable to understand
Voice is not clear😣
Grateful for cc now because I have hearing difficulty. 🦻🏻