Description
Thermal mass flow controllers the most common type in flow chemistry laboratories operate on the principle of heat transfer: a small fraction of the gas flow passes through a heated capillary sensor tube, and the temperature differential between upstream and downstream sensors is proportional to the mass flow rate (since thermal conductivity and heat capacity of the gas determine the relationship). A proportional control valve in the main flow path modulates the gas flow to maintain the setpoint mass flow. The control range of a typical MFC is 2% to 100% of full-scale flow, with an accuracy of ±1% of full scale and repeatability of ±0.5%.
For high-flow gas delivery at pilot and production scale, thermal bypass or Coriolis MFCs are used. Coriolis MFCs measure the Coriolis force on a vibrating tube through which the fluid passes — providing true mass flow measurement independent of gas composition, temperature, or pressure. Multi-gas MFCs can be programmed for different calibration curves covering common process gases (H₂, N₂, CO₂, CO, O₂, Cl₂, HCl, SO₂, NH₃, CH₄) and calculate the actual delivered mass flow from a stored calibration database. Safety features include built-in leak test, automatic valve closure on overpressure, and electropolished internal surfaces for corrosive gas service (HCl, Cl₂, F₂).
Key Features
- Enables reactions above solvent boiling point — superheated flow chemistry
- PEEK and Hastelloy wetted parts for full chemical compatibility
- Dome-loaded designs allow variable setpoint 0–350 bar in real time
- Maintains constant upstream pressure independent of flow rate change
- Electronic BPRs support pressure ramping for reaction optimisation
- Safe, controlled system depressurisation on flow stop
- Two-phase BPR designs handle gas–liquid streams without sticking
- Inline pressure sensor feedback for closed-loop pressure control
Technical Specifications
| Measurement Principle | Thermal bypass capillary or Coriolis vibrating tube |
| Full-Scale Flow Range | 0–0.5 sccm (micro) to 0–5000 slm (production) |
| Accuracy | ±1.0% of full scale (thermal); ±0.1% (Coriolis) |
| Repeatability | ±0.5% of setpoint |
| Control Range | 2–100% of full-scale flow |
| Response Time | <2 seconds to 98% of setpoint (standard); <0.5 s (fast MFC) |
| Wetted Materials | SS 316L, Hastelloy C-276, PTFE (for corrosive gases) |
| Gas Compatibility | H₂, N₂, O₂, CO, CO₂, Cl₂, HCl, NH₃, SO₂, inert gases |
| Process Connection | Swagelok face seal, VCR, compression fitting |
| Communication | RS232, RS485, Modbus, DeviceNet, EtherCAT, analogue 0–5V / 4–20 mA |
Industrial Applications
- H₂ delivery for continuous catalytic hydrogenation in tubular or loop reactors
- O₂ / air metering for aerobic oxidation reactions
- CO delivery for carbonylation and hydroformylation synthesis routes
- CO₂ metering for continuous supercritical CO₂ reactions or carboxylation
- HCl gas metering for continuous hydrochlorination reactions
- Ozone metering for ozonolysis continuous flow sequences
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