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pawan_ctn
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what is the difference between vapour and gas?
when gas condence it change in liquid...so what difference between gas and vapour?
when gas condence it change in liquid...so what difference between gas and vapour?
pawan_ctn said:what is the difference between vapour and gas?
when gas condence it change in liquid...so what difference between gas and vapour?
Andy Resnick said:A gas is a single well-defined thermodynamic phase, wheras a vapor is a mixture of two phases (generally gas and liquid). A cloud is made of water vapor, the clear sky contains gaseous water. Steam is vaporized water.
klimatos said:All vapors are gases, but not all gases are vapors. Vapors are gases whose mean temperature is below the critical point. In other words, vapor can coexist with their other phases. Water vapor can coexist with liquid water and with ice. In the free atmosphere, it does so all the time.
Jagella said:I thought about your point of vapor coexisting with other phases while gas does not coexist with other phases. I had some trouble coming up with an example of such a gas, though. Oxygen, for instance, can be a liquid at very low temperatures and also a gas can it not? Is there a vaporization curve for oxygen in which liquid oxygen coexists with oxygen as a gas?
I suppose not.
Jagella
Andy Resnick said:A gas is a single well-defined thermodynamic phase, wheras a vapor is a mixture of two phases (generally gas and liquid). A cloud is made of water vapor, the clear sky contains gaseous water. Steam is vaporized water.
Hootenanny said:The term vapour is used to describe the state of a substance when it's gaseous phase is in equilibrium with it's liquid or solid phases, below it's boiling point.
klimatos said:A gas above its critical point does not coexist with its liquid phase because no liquid phase can exist above the critical point.
Jagella said:Isn't that the same case for water vapor? Its vapor does not coexist with its liquid above its critical temperature?
Jagella
renjith_p said:So, is steam a 'vapour of water' or a 'gas of water'?
renjith_p said:So, is steam a 'vapour of water' or a 'gas of water'?
renjith_p said:Let me rephrase...correct me if i am wrong..
1. Wet Steam is a 'vapour of water'.
2. Dry saturated steam (also superheated steam) is a 'gas of water'.
Borek said:Wet steam or dry steam?
klimatos said:I don't know what you mean by either term. I accept the engineering definition of steam to mean water vapor or gaseous water at temperatures above the critical point. You can call it a gas or call it a vapor. You will be correct in either case. There is no meaningful distinction between the two in scientific usage.
Drakkith said:How so? Vapor is defined as a substance in the gas phase at a temperature lower than its critical point. I can easily see where the confusion comes from.
klimatos said:I don't know what you mean by either term.
I don't know what you mean by either term. I accept the engineering definition of steam to mean water vapor or gaseous water at temperatures above the critical point. You can call it a gas or call it a vapor. You will be correct in either case. There is no meaningful distinction between the two in scientific usage.
Andy Resnick said:Steam is vaporized water.
BadBrain said:An engineer working with a steam engine would be very unhappy to find himself working with anything less than pure, gaseous water. That's why steam engines have things like steam strainers to make certain no liquid gets into the steam main, which is called the "dry pipe" for this reason. That's also why steam engines contain superheater tubes, whose purpose is to raise the pressure of the steam well above the boiling point of water (and recapturing what would otherwise have been waste heat from the firebox in the process) to increase its pressure, and, thus, the mechanical potential energy it contains which can then be released as mechanical kinetic energy against the piston head or turbine blades, depending on the type of engine you're powering.
"All aboard!" or "All ashore that's going ashore!", depending on where your engine is mounted.
Mordred said:A solid point, You would have to see a boiler pulse from one drop of water added. On the old steamers we had that hapen on a regular base till they finaly replaced em with diesel engines. One single drop of water would cause the entire boiler pulse, Blow all the safety valves, and melt all rubber and plastic including any wiring in the funnel stack. Not to mention shake up the entire ship. Its something I will never forget.
Andragogue said:Steam can be superheated but still be considered a "dry vapor", if below the critical temperature.
Andragogue said:And some steam turbines are "condensing turbines" and use saturated steam (but we would still guard against liquid slugs.)
Andragogue said:Saturated steam is the steam taken directly off the top of the steam drum. It is at its boiling/condensing temperature at the given pressure. (You might even call it a dewpoint vapor.)
Superheated steam is defined simply as steam heated above its boiling/condensing temperature at a given pressure. To make it, you take the saturated steam and put in through additional tubes in the firebox to add the superheat. The steam's temperature and its enthalpy are both increased.
Andragogue said:You can get useful power out of saturated steam. But you will obviously get more power out of an equal mass of superheated steam due to its higher enthalpy. Studying a steam table makes this apparent.
Andragogue said:However, if you remember the difference between sensible heat (the heat energy that would be extracted through dropping the temperature of superheated steam) and latent heat (the heat energy that would be extracted by condensing saturated steam), in other words, about 0.5 btu/lb-deg F vs. 970 btu/lb at one atmosphere, you get potentially MORE heat energy out of steam if you condense it as you use it. (Of course, the actual amounts vary with system pressure.)
Andragogue said:I've operated both kinds of systems in industrial plants. New power plants operate with supercritical steam; which in this case is superheated steam raised to very high pressure. The benefit, beyond the higher enthalpy of the working fluid, is that as long as supercritical pressure is maintained as the steam expands in the turbine, you need not worry about a phase change (i.e., liquids condensing.)
Andragogue said:As to the comment about calling things by whatever names you want to use, I thought that was the whole point of this exercise... ? It does make a difference, my friend.
Gas and vapour are both forms of matter that exist in a gaseous state. However, there are some key differences between them.
A gas is a substance that exists in a gaseous state at room temperature and atmospheric pressure. It has no definite shape or volume and can expand to fill any container. Vapour, on the other hand, is a gas that is formed when a liquid or solid substance evaporates. It has the same physical properties as a gas, but it is typically denser and easier to condense.
Gas is formed when a substance reaches its boiling point and changes from a liquid to a gas. Vapour, on the other hand, is formed when a substance reaches its vaporization point and changes from a solid or liquid to a gas. Both processes involve the release of energy, which allows the molecules to break free from their bonds and move freely in the gaseous state.
Yes, gas and vapour can be converted into each other through the processes of condensation and evaporation. When a gas is cooled, it can condense into a liquid, and further cooling can cause it to solidify. On the other hand, when a liquid or solid is heated, it can evaporate and form a gas. This conversion between gas and vapour is a continuous cycle in nature.
Gas and vapour behave differently under different conditions. For example, gas is compressible, meaning its volume can be reduced under pressure, while vapour is not. Vapour also tends to be more dense and less mobile than gas. Additionally, gas can exist at a wider range of temperatures and pressures, while vapour is more sensitive to changes in these factors.