A thermal mass flow meter is a special type of instrument used for measuring the rate of heat transfer through a material. The device generally utilizes a combination of temperatures and hot elements sensors to measure the static of flowing heat transfer and static processes of a specific fluid.
As long as the specific density and heat of the fluid are known, the sensor will be able to get accurate readings from it. When there’s constant specific heat and density, the device can provide direct readings.
Others will not need pressure temperature compensation in addition to getting accurate reports. Technological progress is now allowing the meters to determine the thermal mass of microscopic objects, and they are often measured in microliters or nanoliters.
What are they Designed to Measure?
The device accurately monitors and measures the small flow of various gasses. Some like the ones on Teledyne Hastings Instruments can have accuracy and fast response times. They are best to apply on gas mass flow where the pressure and temperature tend to fluctuate. Some of the applications are the following:
- Gas leak tests and detection methods
- Gas blending and mixing
- Monitoring of the flue gas where the testers know their composition
- Landfill recoveries
- Natural gas consumption in boiler feeds and burners
- Compressed air distribution and flow
Operation in Theory
These sensors are often applicable to the regulations of gas flows. The operation might involve introducing heat into flowing streams, getting accurate temperatures, or maintaining some probes at a constant temperature. It will also determine the energy required to monitor the temperature in a specific stream constantly.
Some of the components involved in the process are electric heaters and two temperature sensors. Heaters might come from the protruding fluid stream, or they can be attached through an external source.
The direct heat version is where the fixed heating temperature is added. This is done through electric heaters. Most of the process fluid will go through the pipe, and there will be detectors to record the change or rise of the temperature. This is going to be the constant. Check out the post about the thermal mass flow meter when you click here.
The Design of the Tube
The heated-tube meters were created to protect the sensors and the electric heater from the possibility of corrosion. They were also designed to be durable and not be affected by the process’s coating. When the sensors are mounted to the pipes externally, the feature sensing elements might be slow to produce readings, and the relationship between the components can be considered non-linear.
The non-linearity factor might be because the heat was unevenly distributed throughout the pipe. The fluids’ transfer rates might also be different as a result.
This means that the pipe part that’s nearest to the heater will receive the highest temperature. The ones that have a significant distance from the device and the equation that’s going to be used are going to be different.
There are other bypass designs that you might want to check out. These are developed to determine a larger flow rate. The thin-walled capillaries are added to the self-heating detectors, and these devices are the ones already heating the tubes. The ones doing the tests will determine the equation to know the resulting temperature rise. This is a sensor that’s placed to bypass the primary pipe’s restriction, and the size is going to include everything’s full operating range.
If there’s an absence of flow, the heating devices will bypass the tube temperature above 160 degrees Fahrenheit. With this condition, the symmetrical temperature is going to be distributed along the tube’s length.
On the other hand, if there’s an existing flow, the gasses are going to be the ones to carry the molecules down the stream. Most of the temperature change will be shifted according to the direction of the flow. There might also be the presence of a bridge that’s going to connect various terminals in order for the electric signals to be converted in proportion to the significant change in temperature.
The tubes usually have smaller sizes. This makes it possible for them to decrease power consumption and increase the speed at which they take measurements. Since the size is small, the filters will generally be needed to prevent plugging. However, there’s a serious limitation that’s usually attributed to the bypass type, and this is the need for a high-pressure drop for the laminar flow.
Most consider this a cost-effective, easy-to-maintain, and low-accuracy device. The electronic packages that are included might allow for computer recording, chart interfacing, and data collection, but the devices are not as effective as others. Most of the units used in testing gas flow today often have features like the automatic control valve and a controller to enable a complete loop, and this is generally not seen in the bypass type.
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