Converting from Flow Velocity to Volumetric Flow Rates
It is convenient when comparing results for columns of different sizes to express flow as flow velocity (cm/h). However, flow is usually measured in volumetric flow rate (mL/min). To convert between flow velocity and volumetric flow rate use one of the formulae below.
From flow velocity (cm/h) to volumetric flow rate (mL/min)
| Volumetric flow rate (mL/min) = | Flow velocity (cm/h) 60 |
× column cross sectional area (cm2) |
| Volumetric flow rate (mL/min) = | Y 60 |
× | π × d2 4 |
where
Y = flow velocity in cm/h
d = column inner diameter in cm
Example:
What is the volumetric flow rate in an XK 16/70 column (i.d. 1.6 cm) when the flow velocity is 150 cm/h?
Y = flow velocity = 150 cm/h
d = inner diameter of the column = 1.6 cm
| Volumetric flow rate (mL/min) = | 150 × π × 1.6 × 1.6 60 × 4 |
= 5.03 mL/min |
From volumetric flow rate (mL/min) to flow velocity (cm/h)
| flow velocity (cm/h) = | Volumetric flow rate (mL/min) × 60 column cross sectional area (cm2) |
| flow velocity (cm/h) = | = Z × 60 × | 4 π × d2 |
where
Z = volumetric flow rate in mL/min
d = column inner diameter in cm
Example:
What is the linear flow in a Tricorn 5/50 column (i.d. 0.5 cm) when the volumetric flow rate is 1 mL/min?
Z = volumetric flow rate = 1 mL/min
d = column inner diameter = 0.5 cm
| flow velocity = | 1 × 60 × | 4 π × 0.5 × 0.5 |
= 305.6 cm/h |
From volumetric flow rate (mL/min) to using a syringe
1 mL/min = approximately 30 drops/min on a HiTrap 1 mL column
5 mL/min = approximately 120 drops/min on a HiTrap 5 mL column
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