Designing Smart Solutions for Gas Flow Devices with Multiphysics Simulation
As India moves toward a reduced dependence on fossil fuels, more urban homes are expected to be supplied with piped natural gas instead of fuels like coal or wood, which emit more greenhouse gases. To optimize various designs for domestic gas meters, researchers at Raychem RPG turned to multiphysics simulation.
By Aditi Karandikar
June 2021
The Principles Behind Gas Meters
A gas meter (Figure 1) is a specialized flowmeter used in residential, commercial, and industrial buildings to measure the amount of fuel gases, such as CNG or LPG, delivered through a pipeline. Gases are highly compressible, which makes them more difficult to measure than liquids because of their sensitivity to changes in temperature and pressure. Gas meters measure a defined volume, regardless of the pressurized quantity or quality of the gas flowing through the meter. Accordingly, adjustments need to be made in temperature, pressure, and heating values to accurately measure the actual amount of gas moving through the meter.
Several different designs of gas meters are common, depending on the volumetric flow rate of gas to be measured, the range of flows anticipated, the type of gas being measured, and other factors. Some of the major types of gas meters include diaphragm meters, rotary displacement meters, turbine meters, ultrasonic flowmeters, and Coriolis meters.
Raychem RPG is one of the leading providers of domestic gas meters in India, accounting for almost 80% of the market share. At the Raychem Innovation Centre (RIC) in Gujarat, India, researchers developed four new designs for gas flowmeters, which were conceptualized, optimized, and validated using multiphysics simulation software.
Design Challenges for Gas Flowmeters
All of the gas meters currently available in India have their own limitations. For example, in diaphragm meters, leakage from moving parts and the diaphragm can cause measurement errors. Rotary displacement meters and turbine meters, on the other hand, have close to 35 components, increasing the probability of mechanical failure and fatigue. Further, the enclosure size for any gas meter is fixed, so any new meter design has to fit within the given enclosure size. Therefore, the size of the device is another important criterion for any new gas meter design. All of these different criteria make it a challenge for these devices to be approved during the final quality testing stages. In fact, rejection rates can be very high.
The Raychem team, led by Mr. Ishant Jain, set out to minimize the number of components in gas flowmeters and reduce their rejection rate during the quality testing phase, thereby reducing the total cost of manufacturing for these devices. To do so, the Raychem team performed simulation analyses in the COMSOL Multiphysics® software.
Validating 4 Gas Meter Designs with Simulation
The Raychem team developed four gas meters based on design optimization using TRIZ, a problem-solving methodology, and customer requirements. They started by validating a finite element model of a conventional gas meter design. The team then extended their findings to evaluate the proposed designs.
Diaphragm Meter with Scotch–Yoke Mechanism
The first of the new gas meter designs is a modification of the existing diaphragm system, where the pantograph assembly is replaced with a Scotch–Yoke mechanism to reduce the number of components.
After arriving at their optimized design (Figure 2), the Raychem team was able to eliminate several mechanical components from the original design, in addition to improving the accuracy and sensitivity of the measurement. The number of components in the meter system was significantly reduced, from 35 components of the earlier diaphragm design to 5 or 6 components, thus assuring the mechanical ruggedness and integrity of the system.
Möbius Band Turbine Meter
The next design consists of a Möbius band turbine, where the rotation of the turbine is used to measure the gas flow rate. These gas meters measure the gas volume by determining the velocity of the gas moving through the Möbius strip. The Möbius-band-shaped rotor is placed in the way of the gas flow passing over it, which rotates the shaft. The output of the shaft is transferred to a bevel gear system. The turbine infers the velocity of the gas, which is transmitted mechanically to an electronic or mechanical counter. The Raychem team used the CFD Module and Multibody Dynamics Module, add-on products to COMSOL Multiphysics®, to model the turbulent gas flow (Figure 3) as well as the stresses and torque developed in the turbine.
It is important to note that the Möbius band turbine gas meter performs well when the gas flow rate is high. Since the gas volume is determined by its flow, the efficacy of the device is limited while measuring flow with a low pressure drop. To circumvent this issue, the Raychem team designed another flowmeter based on a well-known principle: Magnets of the same polarity repel each other.
Turbine Meter with Magnet and Ball/Disc Design
In the third meter design, an object, typically a ball or a disc, is arranged inside the pipe in such a way that the magnetic force causes it to float. The object gets lifted with the flow of gas in the pipe, and the gas flow is measured by the height to which a magnetic plate rises. This kind of meter is highly sensitive and can measure even a small pressure drop. The researchers studied the magnetic properties and device performance using the AC/DC Module and CFD Module, add-ons to COMSOL Multiphysics®, and arrived at an optimized design (Figure 4). In this case, the team was able to propose a highly sensitive device that performs well, even for slight variations in gas flow rates.
Turbine Meter with Vanes
The final design is also based on the rotation of a turbine, but a different turbine design is used. Here, the turbine assembly with fixed guide vanes and runner vanes is placed in the main channel as an obstructing element (Figure 5). The energy captured by the rotating turbine is used to energize the thermal sensors, hence making this device a self-energizing system. The guide vanes act as a nozzle, channeling the gas flow toward the runner vanes, which rotate the shaft and bevel gear pair. Gas flow is measured based on the rotation of the bevel gear pair or by measuring the drop in temperature using thermal sensors. The Raychem team used the CFD Module and Multibody Dynamics Module with COMSOL Multiphysics® to finalize the design. The simulation studies enabled the Raychem team to design a smart energy gas meter with only a U-shaped tube and a sensor in the housing, making it very compact and easy to install.
Future Research Plans
Validated simulation results are at the core of Raychem's four new gas meter designs. The Raychem team is confident in the performance of these flowmeters to suit the requirements of domestic and industrial applications. These designs have been shortlisted for production and should soon be available to urban consumers across India, to be installed directly inside the gas meters fitted in their homes.
Acknowledgements
The Raychem team would like to acknowledge Tito Kishan for assisting in TRIZ application and Ganesh Bhoye for design engineering.