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This is more a theoretical one... we subcool the liquid after condensation...
Let's say we condense R404A at 45°C and we subcool it further with 15K,..
then density changes as well and does this mean - theoretically - that pressure will drop as well along this subcooling coil assuming no volume change of the subcooling coil?
Is it not a bit of a dynamic system when running. I would think you would have pressure drop due to flow through the pipe as well as from subcooling, but then you also have the vapour/liquid from the upstream keeping it pressurised. If you dont keep it pressurised surely it becomes just saturated liquid.
Pressure and temperature related for saturated liquid. If subcooled liquid flows in liquid line pressure will drop slightly but it still be subcooled. Subcool temperature can be reduced from 15K to 10K but it still be subcooled.
Fundamental answer: The reduction in volume as you cool the liquid will not change the pressure because the liquid is contained but not enclosed: so the condensing pressure is still pushing on it even though its colder than the condensing temperature. As with any fluid, flow causes a pressure difference and the piping and components downstream of the sub-cooler cannot offer too much resistance or there will be a "new saturation state", that is flashing, in the downstream containment.