Refrigerant Line Velocity and Oil Return
Line velocity from mass flow, inside diameter, and specific volume, with an oil-return verdict against the riser / horizontal minimum and the ~4000 fpm noise ceiling. Per the ASHRAE Refrigeration Handbook.
Formula and source
V_fpm = (mass_flow_lb_hr * specific_volume_ft3_lb) / area_ft2 / 60, where area = (pi/4)(ID_in/12)^2. Oil return needs a minimum velocity (higher in a suction riser); above ~4000 fpm the line is noisy.
ASHRAE Refrigeration Handbook line-sizing and oil-return guidance, by name.
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