help!thermosyphon oil cooling

Now I am designing a propane thermosyphon oil cooling,but I don't know how to caculate the liquid line Diameter from the receiver tho the heat exchanger.According with the IR hand book.the pressure gradient for this pipe are 22.6pa/m for R22.What's the means of pressure gradient?and how to caculate the Diameter by the pressure gradient.

Condition for selecting of line diameter:
22.6Pa x Total Lenght < r.g.H
Total Lenght = Reale Length of pipe + aquivalent length of valves + fittings
r = kg/m2
g = 9.81
H= Level difference btw. Liquid level of thermosyphone receiver and oil cooler
22.6Pa for R22, you choice other value for Propane.

Condition for selecting of line diameter:
22.6Pa x Total Lenght < r.g.H
Total Lenght = Reale Length of pipe + aquivalent length of valves + fittings
r = kg/m3
g = 9.81 m/s2
H= Level difference btw. Liquid level of thermosyphone receiver and oil cooler
22.6Pa for R22, you choice other value for Propane.