The FCO96 series of Laminar Flow Elements (LFE’s) is a family of primary flow devices for the measurement of low volume air and gas flows from 0.1 ml/min to 40000 litres/min. The FCO96 LFE’s provide the ability to measure accurately and repeatably the low flows encountered in sampling systems, injectors and respiration applications.

Flow measurements are often made by orifice plate, venturi or nozzle, where the differential pressure generated is related to flow through a square law. The FCO96 Laminar Flow Elements have a linear relationship between differential pressure and flow which allows a much higher turndown to be achieved. Laminar flow conditions are achieved below a Reynolds number of 2000.

The FCO96 Laminar Flow Elements generate a low differential pressure, offering little restriction to flow. A typical value at full flow rate is 10 mmH20 (98 Pa). Suitable measuring instruments are the Furness Controls range of micromanometers and transmitters.

Theory

Laminar flow conditions are present in a gas when the Reynolds number is below the critical figure of 2000. Above this figure the condition of fluid is considered to be turbulent. Below this figure the pressure difference over a given length is linear with flow rate.

Furness Controls’ FCO96 Laminar Flow Orifices are designed around a Reynolds number of 500, putting them well within the laminar flow range. Each device is engineered to provide flow expansion/reduction chambers at the inlet/outlet, so that the flow is linear to differential pressure at the measuring points.