Hi, everyone.

There is a concern about flash gas in dry refrigeration systems.
I ask for your opinion on the situation below.

The refrigeration system is in its simplest form (compressor-condenser-expansion valve-evaporator), and the refrigerant is R507.
Let's assume there is no overcooling.

"case 1:"
The pipe between the condenser and the expansion valve was long, resulting in a total pressure loss of 2 Bar.
The flash gas generated by the pressure loss passes through the orifice of the expansion valve.
As such, the flow rate of liquid passing through the orifice will be reduced and the cooling capacity will be slightly reduced.

But what if this pipe was vertical?
"case 2:"
A total pressure loss of 2 bar occurred due to vertical piping.
The flash gas generated at this time collects in the upper part of the pipe, forms pressure, and pushes the refrigerant liquid level down.
Therefore, the expansion valve only passes the flash gas and no cooling effect can be achieved.

The total pressure loss in both cases is the same,
Horizontal piping reduces capacity slightly, while vertical piping loses refrigerating capacity to zero.

I think "case2" is wrong. But I don't know which part is wrong.
What is the actual flow of refrigerant in the pipe?
Is there a formula to estimate the amount of refrigerant loss in a vertical pipe?

I look forward to your wise reply.
Thanks