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Gas Flow Measurements and Controls
Published in Igor Bello, Vacuum and Ultravacuum, 2017
Accordingly, we discern flowmeters from flow controllers, which are coupled with metering valves. In commercial flow controllers, the metering valve is integrated with the flowmeter, which is an elegant way to provide device portability. Both flowmeters and controllers are commercially available. While purchasing, one should be sure of what is needed: to measure or to control gas flow rate. Thermal mass flowmeters and controllers are produced for flow rates ranging from 1.7 × 10−4 to 68 W at 273.15 K (0.1 to 4 × 104sccm). However, this range cannot be covered by a single head device. Flowmeters/flow controllers are made for different flow ranges with heads labeled, for example, as 2, 5, 10, 20, 50, 100, 200, 500, 1000, and 2000 sccm (see products of MKS Instruments), as calibrated for nitrogen. Even heads with a flow rate of 500 sls are available. These numbers denote the upper values of gas flow ranges. However, some producers specify that the real maximal flow rate is 30% higher than the value specified on the flowmeter.
Flow
Published in Anders Andersson, Measurement Technology for Process Automation, 2017
A thermal mass flow meter is often used in ducts and chimneys to measure flow in ventilation systems or smoke going out from a burner. It can be designed in several ways, but a common method is to have two temperature sensors at the tip of the meter probe. One sensor is heated, the other is not. The power required to keep a constant temperature difference is then proportional to mass flow. Another way to do it is to have one sensor exposed to the flow and the other protected. Here, both sensors are heated, and it will take more energy to heat the sensor that is exposed to the flow. Also, in this case the power needed to maintain a constant temperature is proportional to the mass flow rate. This measuring principle has three main advantages: it is relatively good at low flow rates, it is easy to install and the internal design also makes it easier to measure correctly at very small flow rates. Among its disadvantages are that the meter is not very accurate and that there is a need to integrate flow over the pipe area manually as the instrument itself will measure flow velocity in one point only.
Thermal Flowmeters
Published in Jesse Yoder, New-Technology Flowmeters, 2023
Thermal mass flowmeters, on the other hand, directly measure mass flow versus volumetric flow based on heat transfer. Coriolis flowmeters are another technology that produces a direct mass flow measurement, but they are more expensive than thermal mass flowmeters and can be more difficult to install. Most manufacturers of thermal mass flowmeters have models that are highly sensitive to low flow rates. This inherent sensitivity is due to the basic operation of this technology, where one sensor measures the current fluid temperature as a reference and the second sensor is heated and has a constant temperature differential relative to the first sensor at “zero flow.”
Aggregate size effects on the mechanical behaviour and on the gas permeability at damaged state of cement-based materials with and without slag
Published in European Journal of Environmental and Civil Engineering, 2022
Aurélie Fabien, Marta Choinska, Stéphanie Bonnet, Arnaud Pertue, Abdelhafid Khelidj
The device used to test gas permeability is detailed in Figure 7. It includes a permeability cell based on the Cembureau cell (Kollek, 1989; XP P 18-463, 2011). The tests are performed using an inert gas (dry nitrogen, N2). To ensure the uniaxial flow of gas and to prevent parasitic gas leakage, the lateral face of the cylindrical specimens is covered with aluminum wrap. The specimen tested, held in place by a fitted collar is then confined during the tests (0.5 MPa). This confining pressure is quite low, equal for all the specimens (sound and cracked ones) and, for this reason, has a slight impact of the measurements (Choinska & Niknezhad, 2020). The gas is injected at the lower surface of the specimen at pressure Pi, between 0.3 and 0.1 MPa (relative values) while its upper side remains at atmospheric pressure (Patm). To estimate the intrinsic permeability (Klinkenberg, 1941; Picandet et al., 2001), all the tests include some flow measurements at five differential pressures (0.10, 0.15, 0.20, 0.25 and 0.30 MPa, respectively). The injection pressure is maintained until the gas flow stabilizes. The pressure and the flow rates are recorded during the test. Flow rates are measured upstream and downstream of the measurement system using thermal mass flowmeters with different capacities used to convert the mass flow rate into an equivalent volumetric gas flow rate in normalized conditions (P0, T0).
Issues on the Testing of Small Cryogenic Recuperators and Experimental Studies on Perforated Plate Heat Exchangers
Published in Heat Transfer Engineering, 2018
Sukumaramenon Sunil Kumar, Tapas Kumar Nandi
Instrumentation in the test setup is required for the measurement of fluid temperatures and helium mass flow rate. Temperatures are measured by using platinum resistance temperature detectors (PT-100 RTD) (thin film type). The sensors were calibrated with reference to a standard PT-100 RTD (make Lake Shore, USA, model PT-103-14 L). A calibration setup is built for the purpose. Millivolt readings from the sensors during calibration and experimentation are taken by a digital multimeter (make Kiethley Instruments, USA, model 2700 fitted with 20 channel 7700 scanner card). A current source (make Keithley Instruments, model 2400) is used for supplying 1 mA constant DC current to the sensors. Mass flow rate is measured by a thermal mass flow meter (make MKS Instruments, USA, model 247C). One mass flow meter is used in the setup for conducting experiments under balanced flow condition.