Owner: Openticle URL:http://openticle.com Join Date: Tue, 11 Dec 2007 07:55:25 -0600 Rating:0 Site Description: Open Article : Free science and engineering article online Site statistics:Click here
Centrifugal Compressors 2008-03-08 17:15:54 Centrifugal Compressors
The centrifugal compressor, originally built to handle only large volumes of low pressure gas and air (maximum of 40 psig), has been developed to enable it to move large volumes of gas with discharge pressures up to 3,500 psig. However, centrifugal compressors are now most frequently used for medium volume and medium pressure air [...]
Rotary Lobe-type Compressor 2008-03-08 17:12:43 The rotary lobe-type, illustrated in Figure 4, features two mating lobe-type rotors mounted in a case. The lobes are gear driven at close clearance, but without metal-to-metal contact. The suction to the unit is located where the cavity made by the lobes is largest. As the lobes rotate, the cavity size is reduced, causing compression [...] Read more:Compressor
, Rotary
Rotary Compressors 2008-03-08 17:09:18 Rotary Compressors
The rotary compressor is adaptable to direct drive by induction motors or multicylinder gasoline or diesel engines. The units are compact, relatively inexpensive, and require a minimum of operating attention and maintenance. They occupy a fraction of the space and weight of a reciprocating machine of equivalent capacity. Rotary compressor units are classified into [...] Read more:Rotary
Single-Acting Air Compressor 2008-03-08 17:07:33 A section of a typical reciprocating single-stage, single-acting compressor cylinder is shown in Figure 2. Inlet and discharge valves are located in the clearance space and connected through ports in the cylinder head to the inlet and discharge connections.
During the suction stroke the compressor piston starts its downward stroke and the air under pressure in [...] Read more:Compressor
, Acting
Air Compressor : Reciprocating Compressors 2008-03-08 17:04:58 Introduction
Air compressors of various designs are used widely throughout DOE facilities in numerous applications. Compressed air has numerous uses throughout a facility including the operation of equipment and portable tools. Three types of designs include reciprocating, rotary, and centrifugal air compressors.
Reciprocating Compressor
s
The reciprocating air compressor, illustrated in Figure 1, is the most common design employed [...]
Solenoid Actuated Valves 2008-03-08 17:00:44 Solenoid Actuated Valves
Solenoid actuated valves provide for automatic open-close valve positioning as illustrated in Figure 35. Most solenoid actuated valves also have a manual override that permits manual positioning of the valve for as long as the override is manually positioned. Solenoids position the valve by attracting a magnetic slug attached to the valve stem. [...]
Hydraulic Actuators 2008-03-08 16:47:56 Hydraulic Actuators
Hydraulic actuators provide for semi-automatic or automatic positioning of the valve, similar to the pneumatic actuators. These actuators use a piston to convert a signal pressure into valve stem motion. Hydraulic fluid is fed to either side of the piston while the other side is drained or bled. Water or oil is used as [...] Read more:Hydraulic
Pneumatic Actuators 2008-03-08 16:46:01 Pneumatic Actuators
Pneumatic actuators as illustrated in Figure 34 provide for automatic or semi-automatic valve operation. These actuators translate an air signal into valve stem motion by air pressure acting on a diaphragm or piston connected to the stem. Pneumatic actuators are used in throttle valves for open-close positioning where fast action is required. When air [...]
Electric Motor Actuators 2008-03-08 16:43:56 Electric Motor
Actuators
Electric motors permit manual, semi-automatic, and automatic operation of the valve. Motors are used mostly for open-close functions, although they are adaptable to positioning the valve to any point opening as illustrated in Figure 33. The motor is usually a, reversible, high speed type connected through a gear train to reduce the motor [...] Read more:Electric
Valve Actuators 2008-03-08 16:41:38 Introduction
Valve
actuators are selected based upon a number of factors including torque necessary to operate the valve and the need for automatic actuation. Types of actuators include manual handwheel, manual lever, electrical motor, pneumatic, solenoid, hydraulic piston, and self-actuated. All actuators except manual handwheel and lever are adaptable to automatic actuation.
Manual, Fixed, and Hammer Actuators [...]
The Atom 2008-04-11 22:14:04 The Atom
Elements are the basic building blocks of all matter. The atom is the smallest particle to which an element can be reduced while still keeping the properties of that element. An atom consists of a positively charged nucleus surrounded by negatively charged electrons, so that the atom as a whole is electrically neutral. The [...]
Electrostatic Field 2008-04-18 05:10:20 Electrostatic Field
A special force is acting between the charged objects discussed above. Forces of this type are the result of an electrostatic field that exists around each charged particle or object. This electrostatic field, and the force it creates, can be illustrated with lines called “lines of force” as shown in Figure 4.
Charged objects repel [...]
Electrostatic Forces 2008-04-18 04:58:11 Electrostatic Forces
One of the mysteries of the atom is that the electron and the nucleus attract each other. This attraction is called electrostatic force, the force that holds the electron in orbit. This force may be illustrated with lines as shown in Figure 3.
Without this electrostatic force, the electron, which is traveling at high speed, [...]
Units of Electrical Measurement 2008-04-19 04:53:43 System Internationale (SI) Metric System
Electrical units of measurement are based on the International (metric) System, also known as the SI System. Units of electrical measurement include the following:
Ampere
Volt
Ohm
Siemens
Watt
Henry
Farad
Appendix A provides more information concerning the metric system, metric prefixes, and powers of 10 that are used in electrical measuring units.
Voltage
Voltage, electromotive force (emf), or potential difference, [...] Read more:Measurement
Electrical Terminology 2008-04-18 23:16:28 Conductors
Conductors are materials with electrons that are loosely bound to their atoms, or materials that permit free motion of a large number of electrons. Atoms with only one valence electron, such as copper, silver, and gold, are examples of good conductors. Most metals are good conductors.
Insulators
Insulators, or nonconductors, are materials with electrons that are tightly [...]
Free Electrons 2008-04-18 21:55:37 Free Electrons
Electrons are in rapid motion around the nucleus. While the electrostatic force is trying to pull the nucleus and the electron together, the electron is in motion and trying to pull away. These two effects balance, keeping the electron in orbit. The electrons in an atom exist in different energy levels. The energy level [...]
Potential Difference 2008-04-18 21:53:26 Potential Difference
Potential difference is the term used to describe how large the electrostatic force is between two charged objects. If a charged body is placed between two objects with a potential difference, the charged body will try to move in one direction, depending upon the polarity of the object. If an electron is placed between [...] Read more:Potential
Ohm’s Law 2008-04-28 03:56:45 Ohm’s Law
In 1827, George Simon Ohm discovered that there was a definite relationship between voltage, current, and resistance in an electrical circuit. Ohm’s Law defines this relationship and can be stated in three ways.
1. Applied voltage equals circuit current times the circuit resistance. Equation (1-2) is a mathematical respresentation of this concept.
2. Current is [...]
Methods of Producing Voltage/Electricity : Thermionic Emission 2008-05-16 03:23:13 Thermionic Emission
A thermionic energy converter is a device consisting of two electrodes placed near one another in a vacuum. One electrode is normally called the cathode, or emitter, and the other is called the anode, or plate. Ordinarily, electrons in the cathode are prevented from escaping from the surface by a potential-energy barrier. When an [...] Read more:Methods
, Voltage
Methods of Producing Voltage/Electricity : Photoelectric Effect 2008-05-15 22:50:02 Photoelectric Effect
Light is a form of energy and is considered by many scientists to consist of small particles of energy called photons. When the photons in a light beam strike the surface of a material, they release their energy and transfer it to the atomic electrons of the material. This energy transfer may dislodge electrons [...] Read more:Methods
, Voltage
Methods of Producing Voltage/Electricity : Thermoelectricity 2008-05-15 22:45:59 Thermoelectricity
Some materials readily give up their electrons and others readily accept electrons. For example, when two dissimilar metals like copper and zinc are joined together, a transfer of electrons can take place. Electrons will leave the copper atoms and enter the zinc atoms. The zinc gets a surplus of electrons and becomes negatively charged. The [...] Read more:Methods
, Voltage
Methods of Producing Voltage/Electricity : Piezoelectric Effect 2008-05-15 22:41:34 Piezoelectric Effect
By applying pressure to certain crystals (such as quartz or Rochelle salts) or certain ceramics (like barium titanate), electrons can be driven out of orbit in the direction of the force. Electrons leave one side of the material and accumulate on the other side, building up positive and negative charges on opposite sides, as [...] Read more:Methods
, Voltage
Methods of Producing Voltage/Electricity : Magnetic Induction 2008-05-15 22:33:21 Magnetic Induction
A generator is a machine that converts mechanical energy into electrical energy by using the principle of magnetic induction. Magnetic induction is used to produce a voltage by rotating coils of wire through a stationary magnetic field, as shown in Figure 13, or by rotating a magnetic field through stationary coils of wire. This [...] Read more:Methods
, Voltage
Methods of Producing Voltage/Electricity : Static Electricity 2008-05-15 22:30:04 Static Electricity
Atoms with the proper number of electrons in orbit around them are in a neutral state, or have a “zero charge.” A body of matter consisting of these atoms will neither attract nor repel other matter that is in its vicinity. If electrons are removed from the atoms in this body of matter, as [...] Read more:Methods
, Voltage
Methods of Producing Voltage/Electricity : Electrochemistry 2008-05-15 22:26:29 Electrochemistry
Chemicals can be combined with certain metals to cause a chemical reaction that will transfer electrons to produce electrical energy. This process works on the electrochemistry principle. One example of this principle is the voltaic chemical cell, shown in Figure 11. A chemical reaction produces and maintains opposite charges on two dissimilar metals that serve [...] Read more:Methods
, Voltage
Inductance and Capacitance 2008-05-15 22:21:47 Inductance
Inductance is defined as the ability of a coil to store energy, induce a voltage in itself, and oppose changes in current flowing through it. The symbol used to indicate inductance in electrical formulas and equations is a capital L. The units of measurement are called henries. The unit henry is abbreviated by using the [...]
Power 2008-05-15 22:15:26 Power
Electricity is generally used to do some sort of work, such as turning a motor or generating heat. Specifically, power is the rate at which work is done, or the rate at which heat is generated. The unit commonly used to specify electric power is the watt. In equations, you will find power abbreviated with [...]
Conductance 2008-05-15 22:11:08 Conductance
The word “reciprocal” is sometimes used to mean “the opposite of.” The opposite, or reciprocal, of resistance is called conductance. As described above, resistance is the opposition to current flow. Since resistance and conductance are opposites, conductance can be defined as the ability to conduct current. For example, if a wire has a high conductance, [...]
Magnetism 2008-05-18 09:37:01 Magnetism is a result of electrons spinning on their own axis around the nucleus (Figure 18).
In magnetic materials, the atoms have certain areas called domains. These domains are aligned such that their electrons tend to spin in the same direction (Figure 19).
The alignment of these domains results in the formation of magnetic poles at each [...] Read more:Magnetism
Magnetic Flux 2008-05-21 09:39:53 Magnetic Flux
The group of magnetic field lines emitted outward from the north pole of a magnet is called magnetic flux. The symbol for magnetic flux is Φ (phi). The SI unit of magnetic flux is the weber (Wb). One weber is equal to 1 x 10 8 magnetic field lines.
Example: If a magnetic flux (Φ) [...]
Recommend Site To A Friend
