CBE 150A – Transport Spring Semester 2014 Flow Measurement and Control

CBE 150A – Transport Spring Semester 2014 Orifice Meter The orifice meter consists of an accurately machined and drilled plate concentrically mounted between two flanges. The position of the pressure taps is somewhat arbitrary.

CBE 150A – Transport Spring Semester 2014 Orifice Meter The orifice meter has several practical advantages when compared to venturi meters. Lower cost Smaller physical size Flexibility to change throat to pipe diameter ratio to measure a larger range of flow rates Disadvantage: Large power consumption in the form of irrecoverable pressure loss

CBE 150A – Transport Spring Semester 2014 Orifice Meter The development of the orifice meter equation is similar to that of the venturi meter and gives: where:  = ratio of orifice diameter to pipe diameter ≈ 0.5 usually S 0 = cross sectional area of orifice V = bulk velocity through the orifice C 0 = orifice coefficient ≈ 0.61 for Re > 30,000 –

CBE 150A – Transport Spring Semester 2014 There is a large pressure drop much of which is not recoverable. This can be a severe limitation when considering use of an orifice meter.

CBE 150A – Transport Spring Semester 2014 Pressure Loss in Orifice Meters

CBE 150A – Transport Spring Semester 2014 ASME Design Standards

CBE 150A – Transport Spring Semester 2014 Rotameters Rotameters fall into the category of flow measurement devices called variable area meters. These devices have nearly constant pressure and depend on changing cross sectional area to indicate flow rate. Rotameters are extremely simple, robust devices that can measure flow rates of both liquids and gasses. Fluid flows up through the tapered tube and suspends a ‘float’ in the column of fluid. The position of the float indicates the flow rate on a marked scale.

CBE 150A – Transport Spring Semester 2014 Rotameters Three types of forces must be accounted for when analyzing rotameter performance: Flow Gravity Buoyancy Flow Buoyancy Gravity For our analysis neglect drag effect

CBE 150A – Transport Spring Semester 2014 Rotameter C R must be determined experimentally. As Q increases the float rides higher.

CBE 150A – Transport Spring Semester 2014 Other Flow Meters

CBE 150A – Transport Spring Semester 2014 Turbine Meter Measure by determining RPM of turbine (3) via sensor (6). Turbine meters are accurate but fragile.

CBE 150A – Transport Spring Semester 2014 Coriolis Meters When fluid is passed through a U-bend, it imposes a force on the tube wall perpendicular to the flow direction (Coriolis force). The deformation of the U-tube is proportional to the flow rate. Coriolis meters are expensive but highly accurate.

CBE 150A – Transport Spring Semester 2014 Pneumatic Control Valves

CBE 150A – Transport Spring Semester 2014 Orifice Meter Example An orifice meter reads a pressure drop of 20 psia, the process pipe is 2 inch Schedule 40 steel pipe and the orifice diameter is ½ inch. What is the flow rate of water in GPM through the line ??? The water temperature is 60 ºF.

CBE 150A – Transport Spring Semester 2014