Throttling process is an isoenthalpic process.$$U+PV=constant.$$ during throttling process does the gas do work at the cost of internal energy such that its temperature decreases? Then what is the difference between adiabatic and throttling process? Can we use throttling process to cool an ideal gas?
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An adiabatic throttling process is irreversible, and the internal energy of the gas in such a process typically does not significantly decrease. Any expansion cooling effect of the gas is compensated by irreversible viscous frictional dissipation (heat generation) within the throttling plug or valve. So, for an ideal gas, there is no change in internal energy and no change in temperature. For real gases, there is a very small effect resulting from non-ideal gas behavior.
answered Mar 6, 2016 at 3:02
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$\begingroup$ Can you explain how does cooling effect take place for real gases? $\endgroup$– nayana vMar 6, 2016 at 13:24
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$\begingroup$ In the case of a real gas, enthalpy is a function of both temperature and pressure (unlike an ideal gas, where the enthalpy is only a function of temperature). So, in order for the enthalpy to remain constant in throttling, the temperature must change to accommodate the effect of the pressure change on enthalpy. In this Joule-Thompson operation, the gas temperature can either decrease or increase, depending on the conditions. $\endgroup$ Mar 6, 2016 at 14:14