Specifically, what is the mechanism which leads to pressure drops in expansion valves?
THERMOSTATIC EXPANSION VALVE A temperature-regulated valve that controls the amount of restriction to refrigerant flow between the receiver/drier and evaporator. Like the Fixed Orifice Tube, the Expansion Valve is the boundary between the High and Low sides of the refrigerant system. Unlike the Fixed Orifice, the Expansion Valve can regulate the flow of liquid refrigerant to the evaporator to either increase or decrease evaporator cooling based on the temperature of the refrigerant tube at the evaporator outlet. In vapour compression ref. cycle,The condensed liquid refrigerant, in the thermodynamic state known as a saturated liquid, is next routed through an expansion valve where it undergoes an abrupt reduction in pressure. That pressure reduction results in the adiabatic flash evaporation of a part of the liquid refrigerant. The auto-refrigeration effect of the adiabatic flash evaporation lowers the temperature of the liquid and vapor refrigerant mixture to where it is colder than the temperature of the enclosed space to be refrigerated.
I would wager that those losses, or pressure drops, are due to entrance and exit losses through the valve. Calculate the losses yourself. The mechanism is simply friction and geometry. Perhaps the losses are not what some agency says they are. Physical tests can be used should such phenomena govern costly criteria and baselines.
