Dimenzioniranje Osnovna teorija Enciklopedija o stisnjenem zraku Namestitev zračnega kompresorja Fizika Kako
Ko spoznate osnove fizike, boste morda želeli izvedeti več o razumevanju meritev zračnega kompresorja glede snovi.
Te informacije so zelo uporabne za določanje ustrezne velikosti in moči, ki ju potrebujete za določen način uporabe. V tem članku bomo pojasnili osnove merjenja dela, moči in prostorninskega pretoka.
Mechanical work may be defined as the product of a force and distance over which the force operates on an object. Like heat, work involves energy transferred from one body to another. The difference is that it involves force rather than temperature. An example of this is when gas becomes compressed in a cylinder with a moving piston.
Compression occurs as a result of force moving the piston. Energy, therefore, transfers from the piston to the gas. This energy transfer is work in the thermodynamic sense of the word. The result of work can have many forms, such as changes in the potential, kinetic, or thermal energy.
Mechanical work associated with changes in the volume of a gas mixture is one of the most important processes in engineering thermodynamics.
Power is work performed per unit of time. It is a measure of how quickly work becomes completed.
For example, power or energy flow to a compressor's drive shaft is numerically similar to system heat emissions, plus heat applied to compressed gas.
Compressor flow rates are typically measured using a mass flow meter. Intuitively, it is easier to make sense of a flow rate for a gas in terms of a volume than a mass. A perceived disadvantage to this could be that it is then necessary to specify the inlet conditions of the gas, since the volume will change with changing inlet conditions. However, for a compressor the outlet mass flow rate will depend on the inlet conditions as well, meaning it is always needed to specify the inlet conditions in which a flow rate was achieved.
The volumetric flow rate of a system is a measure of the volume of fluid flowing per unit of time. It may be calculated as the product of the cross-sectional area of the flow and the average flow velocity. The SI unit for volume rate of flow is m3/s.
However, when buying a compressor you will typically find the capacity of the compressor, expressed in liters/second (l/s). This is the FAD or free air delivery of the compressor.
What is free air delivery? Free air means air under inlet conditions of the compressor, so at ambient temperature and pressure. Delivery implies that only the air coming out of the outlet of the compressor is considered. This differs from the air entering at the inlet, since some air can leak out of the compressor between the in- and outlet. The flow rate of a compressor is normally measured with a mass flow meter at the outlet. This means only the delivered air is measured. It is then converted to « free air » using the inlet conditions.
FAD is meant to be used for comparison between different compressors or to match the capacity of a compressor with the consumption of tools. Unless stated otherwise, the FAD of a compressor or tool –which you can find on their spec sheets- has been measured while maintaining reference inlet conditions (being 20°C, 1 bar and 0% RH). The air mass that fits into the swept volume of a compressor element will vary with the air density and thus change the amount of flow effectively obtained at the outlet side of a compressor. The density depends on the temperature and pressure of the air. This is why the measured outlet mass flow is divided by the inlet air density. The effect of density is canceled out this way.
However, there are secondary effects from temperature and pressure. Amongst others, the size of gaps between parts will change depending on temperature, causing more or less leakage. A change in pressure at the inlet will also cause over- or undercompression which will change the resulting outlet flow rate. For this reason it is important to compare compressors at the same conditions, generally (but not necessarily) being the reference conditions defined in the ISO1217:2009 standard. In other sectors or regions different reference conditions can be used.
Another often used flow rate is the Normal flow rate (Nl/s), where the reference is at 0°C, 1 atm and 0% RH.
The relation between the two volume rates of flow is qFAD = qN × TFAD / TN × PN / PFAD
(note that the simplified formula above does not account for humidity).
Where:
qFAD = Free Air Delivery (FAD) in L/s (actual flow rate at outlet conditions)
qN = Normal flow rate in Nl/s (flow rate at standard conditions)
TFAD = Standard inlet temperature (20°C / 68°F)
TN = Normal reference temperature (0°C / 32°F)
PN = Normal reference pressure (1.013 bar(a) / 101.3 kPa)
PFAD = Standard inlet pressure (1.00 bar(a) / 100 kPa)
Engineers and industrial buyers rely on qN for benchmarking, while qFAD is crucial for actual system design and operation.
Ko spoznate osnove fizike tukaj, boste morda želeli izvedeti več o fizikalnih enotah, ki se uporabljajo za merjenje različnih vidikov snovi. To je lahko zelo koristno pri delu s stisnjenim zrakom. V tem članku bomo pojasnili osnove merjenja dela, moči in prostorninskega pretoka.
The SER is a measure for efficiency, expressed as the amount of energy that is required to deliver 1 liter FAD at a certain pressure. This gives a value in Joules/liter (J/l). For example, a machine consuming 35kW to deliver 100L/s has a SER of 350J/l.
Specificiranje sistema za stisnjen zrak s pretokom in tlakom in ne z močjo (kW ali HP) je najboljši način, da uskladite delovanje sistema s svojimi potrebami. Dimenzioniranje kompresorja bi se moralo bolj natančno ujemati z vašimi poslovnimi zahtevami kot zgolj z izbiranjem po nazivni moči.
Preberite več o tem.
V tem članku je uporabljenih veliko tehničnih izrazov v zvezi z mehanskim delom, močjo in pretokom. Razumevanje teh informacij je pomembno, da boste lahko izbrali pravo opremo, ki ustreza vašemu načinu uporabe. Če kupite predimenzionirano ali poddimenzionirano opremo, obstaja tveganje neučinkovitosti.
Pomembno je, da razmislite o tem, koliko sile boste potrebovali, da premaknete predmet in opravite dano delo v danem časovnem okviru. Kot je navedeno zgoraj, se to izraža s pretokom in tlakom. Poleg litrov na sekundo (l/s) se pretok meri v kubičnih čevljih na minuto (cfm) ali kubičnih metrih na uro (m3/h). Vse te meritve se nanašajo na hitrost.
Tlak se izraža v zgoraj omenjenih barih ali funtih na kvadratni palec (psi). Če morate premikati težke predmete, potrebujete višji tlak. Ugotovite tudi, ali potrebujete celodnevno oskrbo z zrakom in ali obstajajo različne zahteve za vaše načine uporabe. Te informacije so uporabne, ko določate velikost in izbirate med pogonom s stalno ali spremenljivo hitrostjo (VSD).
4 avgust, 2022
Za razumevanje delovanja stisnjenega zraka lahko veliko pripomorejo osnove fizike. Opredelili bomo različne fizikalne enote za merjenje tlaka, temperature in toplotne zmogljivosti. Izvedite več.
5 maj, 2023
Za razumevanje delovanja stisnjenega zraka je koristno poznati osnove fizike, ki vključujejo štiri agregatna stanja snovi.
21 april, 2022
Za boljše razumevanje fizike termodinamike zračnih kompresorjev in pridobivanja toplote so v tem članku predstavljena glavna načela in dva plinska zakona.