Company Profile

Ultra Low Flow Meter: Microfluidic Miniature Sensors for Chemical Injection

Quick Answer

For chemical injection flows below 2 litres per hour, standard flow meters often miss the reading completely. Silver Instruments supplies microfluidic thermal mass and Coriolis sensor arrays that resolve 0.005 mL/min in dosing lines. These miniature meters come with PTFE or 316L wetted parts, 4-20 mA HART output, and ATEX Zone 1 certification for methanol, catalyst, and odorant injection skids.

Why Standard Flow Meters Fail on Chemical Injection Lines

Chemical injection in oil and gas, water treatment, and pharmaceutical processes often operates at 0.1 to 10 litres per hour. At those rates, the pipe size is small—DN4, DN6, or 1/8-inch tubing. A full-bore electromagnetic flow meter simply cannot generate a stable signal. The electrode noise floor buries the flow signal. Vortex meters have a minimum Reynolds number limit and will drop out below 0.5 m/s velocity. Even small oval gear meters struggle because the fluid viscosity changes with temperature, and the gears can stick when dosing solvents with poor lubricity.

Our customers in Southeast Asia and the Middle East have shown us the same problem many times. A methanol injection skid at a gas well in East Kalimantan was reading zero flow on the panel, but the sight glass showed movement. The installed turbine meter had a cut-off at 1.5 L/h. The actual injection rate needed was 0.3 L/h. When flow meters under-read, the operator increases pump stroke, over-injects expensive chemicals, and still has no custody or compliance data.

The Physics of Microfluidic Flow Sensing

Below a certain channel diameter, flow becomes laminar and dominated by viscosity, not inertia. This is the regime where microfluidic sensors work well. Silver Instruments offers two core technologies for ultra low flow chemical injection.

Thermal microfluidic sensors use a heated element and two temperature sensors on a micro-machined chip. The flow carries heat downstream. The temperature difference is directly proportional to mass flow, not volume. This means you do not need pressure and temperature compensation when dosing fluids whose thermal properties are known. We pre-load the thermal constants for methanol, isopropyl alcohol, corrosion inhibitors, and H₂S scavengers. The sensor chip sits in a flow-through cell with an internal diameter of 0.5 mm. At 0.01 L/h, the response time is under 200 milliseconds. The turndown can reach 100:1, from 0.005 L/h up to 0.5 L/h on the same sensor.

Coriolis microfluidic sensors use a vibrating tube with an internal volume as low as 0.02 mL. The tube is driven at resonance. Flow passing through the tube generates a phase shift between inlet and outlet sensor coils. That phase shift gives direct mass flow. The resonance frequency gives density, so you can detect if the wrong chemical has been loaded into the tank. A chemical plant in Vietnam uses this feature to prevent catalyst poisoning. If the density deviates by more than 0.005 g/mL from the setpoint, the system triggers an alarm before the batch is ruined. The Coriolis miniature sensor measures mass flow from 0.05 g/min up to 100 g/min with an accuracy of ±0.2% of rate. It works on fluids from 0.5 cP to over 100 cP.

Sensor Materials and Chemical Compatibility

The wetted path in ultra low flow meters must handle aggressive chemicals continuously. We see applications with 37% HCl, sodium hypochlorite at 12% active chlorine, organic solvents, and aromatic odorants. For these, the microfluidic sensor body is available in 316L stainless steel, Hastelloy C-276, or solid PTFE with no metal contact. The PTFE version uses a fully encapsulated thermal chip behind a thin fluoropolymer membrane. There are no O-rings in the flow path. This design avoids the swelling and cracking we have seen on Chinese low-cost sensors after three months in service with