If you consider the current cap-tube scenario, you should consider the 5lb/hr rate for the 250btu/h application.

5 lbs an hour works out to be about .083lbs/minute.

I would figure the volume of the gas at the evaporating temperature, and then determine the refrigerant velocity within proposed "channels", or "tubing circuits".

We're only moving about 1.3 oz of refrigerant a minute. Heck, it's almost a moderate leak!