Refrigerant Line Size for Oil Return
The inverse of the line-velocity tile: the largest line inside diameter that still meets the oil-return minimum velocity, d = 12 sqrt(4 m sv / (pi 60 V)). 600 lb/hr at 0.5 ft^3/lb needs a suction riser no larger than ~0.78 in ID to hold 1500 fpm. Manufacturer line-sizing tables govern.
Formula and source
area_ft2 = (mass_flow_lb_hr * specific_volume_ft3_lb) / (60 * target_velocity_fpm); line ID_in = 12 * sqrt(4 * area / pi). The inverse of the line-velocity relation, solved for the diameter that meets the oil-return minimum velocity.
ASHRAE Refrigeration Handbook line-sizing and oil-return guidance, by name.
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