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Thermal mass flow meters, also known as thermal dispersion or immersible mass flow meters, comprise a family of instruments for the measurement of the total mass flow rate of a fluid, primarily gases, flowing through closed conduits. A second type is the capillary-tube type of thermal mass flow meter. Many mass flow controllers (MFC) which combine a mass flow meter, electronics and a valve are based on this design. Furthermore, a thermal mass flow meter can be built by measuring temperature differential across a silicon-based MEMS chip.
Both types measure fluid mass flow rate by means of the heat convected from a heated surface to the flowing fluid. In the case of the thermal dispersion, or immersible, type of flow meter, the heat is transferred to the boundary layer of the fluid flowing over the heated surface. In the case of the capillary-tube type, the heat is transferred to the bulk of the fluid flowing through a small heated capillary tube. The principles of operation of the two types are both thermal in nature, but are so substantially different that two separate standards are required. Additionally, their applications are much different. Thermal dispersion flow meters are commonly used for general industrial gas flow applications in pipes and ducts, whereas capillary types are primarily used for smaller flows of clean gases or liquids in tubes. This type is most widely used for thermal mass flow meters in industry. Nevertheless, the capillary type is not the subject of this discussion.
The operation of thermal dispersion mass flow meters is attributed to L.V. King who, in 1914, published his famous King's Law revealing how a heated wire immersed in a fluid flow measures the mass velocity at a point in the flow. King called his instrument a "hot-wire anemometer". However, it was not until the 1960s and 1970s that industrial-grade thermal dispersion mass flow meters finally emerged.
The primary reason thermal mass flow meters are popular in industrial applications is the way they are designed and built. They feature no moving parts, nearly unobstructed straight through flow path, require no temperature or pressure corrections and retain accuracy over a wide range of flow rates. Straight pipe runs can be reduced by using dual-plate flow conditioning elements and installation is very simple with minimal pipe intrusions.
However, in many applications, the thermal properties of the fluid can be dependent upon fluid composition. In such applications, varying composition of the fluid during actual operation can affect the thermal flow measurement. Therefore, it is important for the thermal flow meter supplier to know the composition of the fluid so that the proper calibration factor can be used to determine the flow rate accurately. Suppliers can provide appropriate calibration information for other gas mixtures, however the accuracy of the thermal flow meter is dependent on the actual gas mixture being the same as the gas mixture used for calibration purposes. In other words, the accuracy of a thermal flow meter calibrated for a given gas mixture will be degraded if the actual flowing gas has a different composition. [1]
Pressure measurement is the measurement of an applied force by a fluid on a surface. Pressure is typically measured in units of force per unit of surface area. Many techniques have been developed for the measurement of pressure and vacuum. Instruments used to measure and display pressure mechanically are called pressure gauges,vacuum gauges or compound gauges. The widely used Bourdon gauge is a mechanical device, which both measures and indicates and is probably the best known type of gauge.
A viscometer is an instrument used to measure the viscosity of a fluid. For liquids with viscosities which vary with flow conditions, an instrument called a rheometer is used. Thus, a rheometer can be considered as a special type of viscometer. Viscometers can measure only constant viscosity, that is, viscosity that does not change with flow conditions.
A calorimeter is an object used for calorimetry, or the process of measuring the heat of chemical reactions or physical changes as well as heat capacity. Differential scanning calorimeters, isothermal micro calorimeters, titration calorimeters and accelerated rate calorimeters are among the most common types. A simple calorimeter just consists of a thermometer attached to a metal container full of water suspended above a combustion chamber. It is one of the measurement devices used in the study of thermodynamics, chemistry, and biochemistry.
Spray drying is a method of forming a dry powder from a liquid or slurry by rapidly drying with a hot gas. This is the preferred method of drying of many thermally-sensitive materials such as foods and pharmaceuticals, or materials which may require extremely consistent, fine particle size. Air is the heated drying medium; however, if the liquid is a flammable solvent such as ethanol or the product is oxygen-sensitive then nitrogen is used.
A heat exchanger is a system used to transfer heat between a source and a working fluid. Heat exchangers are used in both cooling and heating processes. The fluids may be separated by a solid wall to prevent mixing or they may be in direct contact. They are widely used in space heating, refrigeration, air conditioning, power stations, chemical plants, petrochemical plants, petroleum refineries, natural-gas processing, and sewage treatment. The classic example of a heat exchanger is found in an internal combustion engine in which a circulating fluid known as engine coolant flows through radiator coils and air flows past the coils, which cools the coolant and heats the incoming air. Another example is the heat sink, which is a passive heat exchanger that transfers the heat generated by an electronic or a mechanical device to a fluid medium, often air or a liquid coolant.
Flow measurement is the quantification of bulk fluid movement. Flow can be measured using devices called flowmeters in various ways. The common types of flowmeters with industrial applications are listed below:
A heat pipe is a heat-transfer device that employs phase transition to transfer heat between two solid interfaces.
Gas chromatography (GC) is a common type of chromatography used in analytical chemistry for separating and analyzing compounds that can be vaporized without decomposition. Typical uses of GC include testing the purity of a particular substance, or separating the different components of a mixture. In preparative chromatography, GC can be used to prepare pure compounds from a mixture.
A rotameter is a device that measures the volumetric flow rate of fluid in a closed tube.
A gas meter is a specialized flow meter, used to measure the volume of fuel gases such as natural gas and liquefied petroleum gas. Gas meters are used at residential, commercial, and industrial buildings that consume fuel gas supplied by a gas utility. Gases are more difficult to measure than liquids, because measured volumes are highly affected by temperature and pressure. Gas meters measure a defined volume, regardless of the pressurized quantity or quality of the gas flowing through the meter. Temperature, pressure, and heating value compensation must be made to measure actual amount and value of gas moving through a meter.
A mass flow meter, also known as an inertial flow meter, is a device that measures mass flow rate of a fluid traveling through a tube. The mass flow rate is the mass of the fluid traveling past a fixed point per unit time.
Moisture analysis covers a variety of methods for measuring the moisture content in solids, liquids, or gases. For example, moisture is a common specification in commercial food production. There are many applications where trace moisture measurements are necessary for manufacturing and process quality assurance. Trace moisture in solids must be known in processes involving plastics, pharmaceuticals and heat treatment. Fields that require moisture measurement in gasses or liquids include hydrocarbon processing, pure semiconductor gases, bulk pure or mixed gases, dielectric gases such as those in transformers and power plants, and natural gas pipeline transport. Moisture content measurements can be reported in multiple units, such as: parts per million, pounds of water per million standard cubic feet of gas, mass of water vapor per unit volume or mass of water vapor per unit mass of dry gas.
Thermospray is a soft ionization source by which a solvent flow of liquid sample passes through a very thin heated column to become a spray of fine liquid droplets. As a form of atmospheric pressure ionization in mass spectrometry these droplets are then ionized via a low-current discharge electrode to create a solvent ion plasma. A repeller then directs these charged particles through the skimmer and acceleration region to introduce the aerosolized sample to a mass spectrometer. It is particularly useful in liquid chromatography-mass spectrometry (LC-MS).
The term separator in oilfield terminology designates a pressure vessel used for separating well fluids produced from oil and gas wells into gaseous and liquid components. A separator for petroleum production is a large vessel designed to separate production fluids into their constituent components of oil, gas and water. A separating vessel may be referred to in the following ways: Oil and gas separator, Separator, Stage separator, Trap, Knockout vessel, Flash chamber, Expansion separator or expansion vessel, Scrubber, Filter. These separating vessels are normally used on a producing lease or platform near the wellhead, manifold, or tank battery to separate fluids produced from oil and gas wells into oil and gas or liquid and gas. An oil and gas separator generally includes the following essential components and features:
A positive displacement meter is a type of flow meter that requires fluid to mechanically displace components in the meter in order for flow measurement. Positive displacement (PD) flow meters measure the volumetric flow rate of a moving fluid or gas by dividing the media into fixed, metered volumes. A basic analogy would be holding a bucket below a tap, filling it to a set level, then quickly replacing it with another bucket and timing the rate at which the buckets are filled. With appropriate pressure and temperature compensation, the mass flow rate can be accurately determined.
Custody Transfer in the oil and gas industry refers to the transactions involving transporting physical substance from one operator to another. This includes the transferring of raw and refined petroleum between tanks and railway tank cars; onto ships, and other transactions. Custody transfer in fluid measurement is defined as a metering point (location) where the fluid is being measured for sale from one party to another. During custody transfer, accuracy is of great importance to both the company delivering the material and the eventual recipient, when transferring a material.
A measuring instrument is a device to measure a physical quantity. In the physical sciences, quality assurance, and engineering, measurement is the activity of obtaining and comparing physical quantities of real-world objects and events. Established standard objects and events are used as units, and the process of measurement gives a number relating the item under study and the referenced unit of measurement. Measuring instruments, and formal test methods which define the instrument's use, are the means by which these relations of numbers are obtained. All measuring instruments are subject to varying degrees of instrument error and measurement uncertainty. These instruments may range from simple objects such as rulers and stopwatches to electron microscopes and particle accelerators. Virtual instrumentation is widely used in the development of modern measuring instruments.
Fluid Components International (FCI), headquartered in San Marcos, California, is a manufacturer of thermal dispersion flow and level measurement instrumentation. FCI has two divisions, one serving customers with measurement needs in industrial process and plant applications and an aerospace division, which produces level, temperature, flow and pressure sensors for aircraft manufacturers. FCI was a pioneer in developing thermal dispersion technology and holds numerous design and technology patents for its application in flow and level measurement.
Flow conditioning ensures that the “real world” environment closely resembles the “laboratory” environment for proper performance of inferential flowmeters like orifice, turbine, coriolis, ultrasonic etc.
Gas blending is the process of mixing gases for a specific purpose where the composition of the resulting mixture is specified and controlled. A wide range of applications include scientific and industrial processes, food production and storage and breathing gases.