Enthalpy of vaporization I've been thinking about refrigeration technology and am a bit confused about two common answers. Specifically, the part where the expansion valve releases the pressurized fluid and stuff gets real cold.
One is that refrigeration works by lower pressure = lower temperature. This makes sense to me because if there is lower pressure, I can imagine it as the opposite of higher pressure = higher temperature. Less pressure means particles are freer to move apart and thus eventually boil and lose energy as they travel further away from each other.
The other is the enthalpy of vaporization, which I understand as meaning that some amount of energy is required for a phase change. This also makes sense to me: when the refrigerant enters the low pressure side of the valve, the particles are more free to spread apart, begin to boil, and thus suck up surrounding energy to break apart from each other. Although, it seems a bit more magical than the lower pressure = lower temperature explanation (it seems odd that already hot liquid particles "suck up" more heat).
Could someone please help me understand this better? Thanks!
NOTE: As you can see, I think of this in very layman terms and am currently reading books like Feynman's lectures. My background is engineering, not physics, so I tend to understand things best in a much more physical-visualization, implementation-details kind of way.
 A: Enthalpy (H) is the internal energy (U) of a material PLUS the product of pressure (P) and volume (V).
$H = U + PV$ by definition
When something boils, the gas phase takes up more volume than the liquid phase.  So unless the boiling is in a vacuum, work is being done by expanding against a pressure, such as atmospheric pressure. This represents a change in the PV term of enthalpy.  At a given temperature and pressure (say boiling water at atmospheric pressure), PV is greater for the gas phase than the liquid phase.  
Additionally, intermolecular forces hold molecules of liquids together.  For example, molecules of a particular compound (say fluoromethane) may have a permanent net dipole moment, and the positive end of one molecule is attracted to the negative end of the other.  There are other types of intermolecular forces such as hydrogen bonding and London forces. It takes energy to pull the molecules apart against such forces.  This represents a change in the internal energy (U) term of enthalpy.  At a given temperature and pressure (say boiling water at atmospheric pressure), U is greater for the gas phase than the liquid phase.
In summary, a desired region is cooled because some of its energy is transferred to the refrigerant to increase its enthalpy.  Part of the energy goes to expanding against a pressure (the PV term) and part goes to the increase in internal energy (the U term).  
