The flow coefficient of a device is a relative measure of its efficiency at allowing fluid flow. It describes the relationship between the pressure drop across an orifice, valve or other assembly and the corresponding flow rate.
Mathematically the flow coefficient can be expressed as:
Cv = Flow coefficient or flow capacity rating of valve.
F = Rate of flow (US gallons per minute).
SG = Specific gravity of fluid (Water = 1).
ΔP = Pressure drop across valve (psi).
In more practical terms, the flow coefficient Cv is the volume (in US gallons) of water at 60°F that will flow per minute through a valve with a pressure drop of 1 psi across the valve.
The use of the flow coefficient offers a standard method of comparing valve capacities and sizing valves for specific applications that is widely accepted by industry. The general definition of the flow coefficient can be expanded into equations modeling the flow of liquids, gases and steam as follows:
Coefficient of discharge is the ratio of actual flow rate to theoretical discharge.
For gas flow in a pneumatic system the Cv for the same assembly can be used with a more complex equation. Absolute pressures (psia) must be used for gas rather than simply differential pressure. For air flow at room temperature, when the outlet pressure is less than 1/2 the absolute inlet pressure, the flow becomes quite simple (although it reaches sonic velocity internally). With Cv = 1.0 and 200 psia inlet pressure the flow is 100 standard cubic feet per minute (scfm). The flow is proportional to the absolute inlet pressure so that the flow in scfm would equal the Cv flow coefficient if the inlet pressure were reduced to 2 psia and the outlet were connected to a vacuum with less than 1 psi absolute pressure (1.0 scfm when Cv = 1.0, 2 psia input).
Use the link below for more details: http://en.wikipedia.org/wiki/Flow_coefficient
Flow Coefficient - Cv - Formulas for Liquids, Steam and Gases - Online Calculators
The flow coefficient - Cv - let us compare flow capacities of valves at different sizes, types and manufacturers. The flow coefficient is in general determined experimentally and express the flow capacity in imperial units - GPM (US gallons per minute) of water that a valve will pass for a pressure drop of 1 lb/in2 (psi).
The flow factor - Kv - is also in common use, but express the capacity in SI-units.
The flow coefficient - Cv - required for a specific application can be estimated by using specific formulas for the different fluids or gases. With the estimated Cv value - the correct valve can be selected from the manufacturers catalogues.
Use the link below for more details. http://www.engineeringtoolbox.com/flow-coefficients-d_277.html
Polytetrafluoroethylene (PTFE) is a synthetic fluoropolymer of tetrafluoroethylene that has numerous applications. The best known brand name of PTFE-based formulas is Teflon by DuPont Co., who discovered the compound.
PTFE is a fluorocarbon solid, as it is a high-molecular-weight compound consisting wholly of carbon and fluorine. PTFE is hydrophobic: neither water nor water-containing substances wet PTFE, as fluorocarbons demonstrate mitigated London dispersion forces due to the high electronegativity of fluorine.
PTFE is a thermoplastic polymer, which is a white solid at room temperature, with a density of about 2200 kg/m3. According to DuPont, its melting point is 600 K (327 °C; 620 °F). It maintains high strength, toughness and self-lubrication at low temperatures down to 5 K (−268.15 °C; −450.67 °F), and good flexibility at temperatures above 194 K (−79 °C; −110 °F).
Property Value Density 2200 kg/m3 Melting point 600 K Thermal expansion 135 • 10−6 K−1 Thermal diffusivity 0.124 mm²/s Young's modulus 0.5 GPa Yield strength 23 MPa Bulk resistivity 1016 Ω•m Coefficient of friction 0.05–0.10 Dielectric constant ε=2.1,tan(δ)<5(-4) Dielectric constant (60 Hz) ε=2.1,tan(δ)<2(-4) Dielectric strength (1 MHz) 60 MV/m
|Density||2200 kg/m3 |
|Melting point ||~600 K|
|Thermal expansion ||135 • 10−6 K−1 |
|Thermal diffusivity ||0.124 mm²/s|
|Young's modulus||0.5 GPa|
|~Yield strength ||23 MPa |
|Bulk resistivity ||1016 Ω•m|
|Coefficient of friction ||0.05–0.10 |
|Dielectric constant ||ε=2.1,tan(δ)<5(-4)|
|Dielectric constant || (60 Hz) ε=2.1,tan(δ)<2(-4)|
|Dielectric strength || (1 MHz) 60 MV/m |
The coefficient of friction of plastics is usually measured against polished steel. PTFE's coefficient of friction is 0.05 to 0.10, which is the third-lowest of any known solid material.
However, because of the propensity to creep, Machining PTFE to the tight tolerance and holding the long-term performance of such seals are extreme difficult.
Applications and uses:
The major application of PTFE, consuming about 50% of production, is for wiring in aerospace and computer applications (e.g. hookup wire, coaxial cables). This application exploits the fact that PTFE has excellent dielectric properties. This is especially true at high radio frequencies, making it suitable for use as an insulator in cables and connector assemblies and as a material for printed circuit boards used at microwave frequencies. Combined with its high melting temperature, this makes it the material of choice as a high-performance substitute for the weaker and lower-melting-point polyethylene commonly used in low-cost applications.
Another major application is in fuel and hydraulic lines, due to PTFE's low resistance against flowing liquids. Colder temperatures at high altitudes cause these fluids to flow more slowly. Coating the lines's interior surfaces with low-resistance PTFE helps to compensate by allowing the liquids to move more easily.
In industrial applications, owing to its low friction, PTFE is used for applications where sliding action of parts is needed: plain bearings, gears, slide plates, etc. In these applications, it performs significantly better than nylon and acetal; it is comparable to ultra-high-molecular-weight polyethylene (UHMWPE). Although UHMWPE is more resistant to wear than PTFE, for these applications, versions of PTFE with mineral oil or molybdenum disulfide embedded as additional lubricants in its matrix are being manufactured. Its extremely high bulk resistivity makes it an ideal material for fabricating long-life electrets, useful devices that are the electrostatic analogues of magnets.
See following link for more details: http://en.wikipedia.org/wiki/Polytetrafluoroethylene
Polychlorotrifluoroethene (PCTFE or PTFCE) is a thermoplastic chlorofluoropolymer with the molecular formula (CF2CClF)n, where n is the number of monomer units in the polymer molecule. It is similar to polytetrafluoroethene (PTFE), except that it is a homopolymer of the monomer chlorotrifluoroethene (CTFE) instead of tetrafluoroethene. It has the lowest water vapor transmission rate of any plastic.
PCTFE has high tensile strength and good thermal characteristics. It is nonflammable and the heat resistance is up to 175°C. It has a low coefficient of thermal expansion. The glass transition temperature (Tg) is around 45°C.
PCTFE has the lowest limiting oxygen index (LOI). It has good chemical resistance. It also exhibits properties like zero-moisture absorption and non wetting.
It does not absorb visible light. When subjected to high energy radiations, like PTFE, it undergoes degradation. It can be used as a transparent film.
PCTFE is resistant to the attack by most chemicals and oxidizing agents; a property which is exhibited due to the presence of high fluorine content. However, it swells slightly in halocarbon compounds, ethers, esters and aromatic solvents. PCTFE is resistant to oxidation because it does not have any hydrogen atoms.
PCTFE offers the unique combination of physical and mechanical properties, excellent electrical properties. PCTFE also has extremely low outgassing, making it well suited for use in medical, chemical, aerospace and many other applications.
• Excellent Chemical Resistance
• Wide Temperature Range: -400°F to +400°F.
• Extremely Low Outgassing
• Near Zero Moisture Absorption
• Unique Combination of Physical and Mechanical Properties
• Note: Kel-F® is a registered tradename of 3M Company. In 1996, 3M discontinued manufacturing of Kel-F & today, all PCTFE resin is manufactured by Daikin under the tradename of Neoflon ® or by Allied Signal under the tradename of Aclon ®. Kel-F is still the most commonly used tradename used to describe PCTFE.
Use the link below for more details http://en.wikipedia.org/wiki/PCTFE
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