what is the difference between adiabatic process & Joule-Thomson effect ?

Question

In thermodynamics the throtlling process is called Joule-Thomson effect

Answer 1

In thermodynamics, an adiabatic process is a process in which no heat is transferred to or from working fluid. The term "adiabatic" literally means an absence of heat transfer; for example, an adiabatic boundary is a boundary that is impermeable to heat transfer and the system is said to be adiabatically (or thermally) insulated. An insulated wall approximates an adiabatic boundary. Another example is the adiabatic flame temperature, which is the temperature that would be achieved by a flame in the absence of heat loss to the surroundings. An adiabatic process which is also reversible is called an isentropic process
In physics, the Joule-Thomson effect, or Joule-Kelvin effect, is a process in which the temperature of a real gas is either decreased or increased by letting the gas expand freely at constant enthalpy (which means that no heat is transferred to or from the gas, and no external work is extracted).

Answer 2

Let's start with the following assumptions: You have a defined amount of gas in an insulated chamber of variable volume. The temperature of the gas increases as the volume decreases. The inverse is also true. Diesel engines work by compressing the fuel until it gets so hot, it explodes spontaneously, using this principal... volume down/temp up.

An adiabatic process denotes a 100% insulated system. Any process or reaction which occurs without the direct transfer of heat in or out of the system is considerred adiabatic. Deisel engines compress deisel fuel until it gets so hot is spontaneously explodes/oxidizes, causing thrust. Theoretically, deisel combustion is an adiabatic process, but if this was true, deisels would not need radiators... some heat is lost after combustion to the metal in the engine.

A regular gasoline engine is not adiabatic. True, the gasoline vapors are compressed by the upstroke, but a spark provides the activation energy for combustion.

Joule-Thomson effect basically describes the mechanism by which this occurs. Allowing gas to expand increases the volume and the room each molecule has to move... increasing potential energy and decreasing kinetic energy (temperature.) The inverse is true also as stated above.

In summary, Joule-Thomson explaines what happens when gas is compressed (temp goes up) and calling something an "adiabatic process" describes what happens to the energy (stays within the system) after the kinetic energy is increased or decreased.

Answer 3

Joules Thompson Effect

Answer 4

I have to take issue with Daktari and Ant regarding the operation of diesel engines.

Diesel engines do use heat caused by compression to cause the fuel to ignite. But it is AIR that is compressed to a high temperature, not fuel (or a fuel-air mixture). When the piston is near top dead center, the diesel fuel is INJECTED into the hot air, and it burns as it mixes with the air. If a fuel-air mixture were compressed, it would be extremely difficult to control the timing of the combustion.

Diesel engines do have glow plugs (at least some engines do). But this is for the purpose of initiating combustion when the engine is cold. The glow plugs are not used once the engine is warm. Compressing the air heats it just as much in a cold engine as in a hot engine, BUT the cold cylinder walls absorb some of the heat when the engine is cold, and the injected fuel would not burn spontaneously if there were no glow plugs.

Answer 5

I just had to correct daktari's theory on diesel engines, they do not compress the fuel till it explodes, diesel burns at a much higher temperature than gasoline, and it has less vapor, I knew soldiers in the Army who were Fuel Specialists, they said in training the instructor threw a lit cigarette in a 1000 gallon tank of diesel, and it didn't ignite. How diesels work is they have to compress the fuel at a much higher rate, which is why all diesels have fuel injection, which you were correct on, but they use glow plugs to ignite the air/fuel mixture, and where a gas engine can't run past 13.5:1, that's the highest compression I ever knew, diesels commonly run at at least 20:1 or higher. Compression relates to the distance from top dead center of the piston to the top of the combustion chamber, which is one unit, to the piston at bottom dead center, and to divide the previous into the latter.

Answer 6

In your mind one is younger than the other

Answer 7

yas