Answer / subhasish

We need to recall the joule thompson effect.
The Joule-Thomson coeffcient JT is defned as derivative of
the temperature T with respect to the pressure p at
constant enthalpy h.

coeff = (dT/dP) at const h

The curve is an inverted U shaped type and when the slope
i.e. co-eff is +ve then temp of gas increases with increase
in pressure and this is true for LPG also (Boiling point~-
38 degC at 1 atm pressure). It implies, LPG can be
liquefied by increasing pressure as the dew point also
increase. That's why even at room temp, by increasing
pressure LPG can be liquefied.

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