Centrifugal compressors use a vaned rotating disk or impeller in a shaped housing to force the gas to the rim of the impeller, increasing the velocity of the gas. A diffuser (divergent duct) section converts the velocity energy to pressure energy. They are primarily used for continuous, stationary service in industries such as oil refineries, chemical and petrochemical plants and natural gas processing plants. Their application can be from 100 hp (75 kW) to thousands of horsepower. With multiple staging, they can achieve extremely high output pressures greater than 10,000 psi (69 MPa).
Many large snow-making operations (like a ski resort) use this type of compressor. They are also used in internal combustion engines as superchargers and turbochargers. Centrifugal compressors are used in small gas turbine engines or as the final compression stage of medium-sized gas turbines.
Diagonal or mixed-flow compressors are similar to centrifugal compressors, but have a radial and axial velocity component at the exit from the rotor. The diffuser is often used to turn diagonal flow to the axial direction. The diagonal compressor has a lower diameter diffuser than the equivalent centrifugal compressor.
Axial-flow compressors use a series of fan-like rotating rotor blades to progressively compress the gasflow. Stationary stator vanes, located downstream of each rotor, redirect the flow onto the next set of rotor blades. The area of the gas passage diminishes through the compressor to maintain a roughly constant axial Mach number. Axial-flow compressors are normally used in high flow applications, such as medium to large gas turbine engines. They are almost always multi-staged. Beyond about 4:1 design pressure ratio, variable geometry is often used to improve operation.
Reciprocating compressors use pistons driven by a crankshaft. They can be either stationary or portable, can be single or multi-staged, and can be driven by electric motors or internal combustion engines. Small reciprocating compressors from 5 to 30 horsepower (hp) are commonly seen in automotive applications and are typically for intermittent duty. Larger reciprocating compressors up to 1000 hp are still commonly found in large industrial applications, but their numbers are declining as they are replaced by various other types of compressors. Discharge pressures can range from low pressure to very high pressure (>5000 psi or 35 MPa). In certain applications, such as air compression, multi-stage double-acting compressors are said to be the most efficient compressors available, and are typically larger, noisier, and more costly than comparable rotary units.
Rotary screw compressors use two meshed rotating positive-displacement helical screws to force the gas into a smaller space. These are usually used for continuous operation in commercial and industrial applications and may be either stationary or portable. Their application can be from 3 hp (2.24 kW) to over 500 hp (375 kW) and from low pressure to very high pressure (>1200 psi or 8.3 MPa). They are commonly seen with roadside repair crews powering air-tools. This type is also used for many automobile engine superchargers because it is easily matched to the induction capacity of a piston engine.
A scroll compressor, also known as scroll pump and scroll vacuum pump, uses two interleaved spiral-like vanes to pump or compress fluids such as liquids and gases. The vane geometry may be involute, archimedean spiral, or hybrid curves. They operate more smoothly, quietly, and reliably than other types of compressors.
Often, one of the scrolls is fixed, while the other orbits eccentrically without rotating, thereby trapping and pumping or compressing pockets of fluid between the scrolls.
A diaphragm compressor (also known as a membrane compressor) is a variant of the conventional reciprocating compressor. The compression of gas occurs by the movement of a flexible membrane, instead of an intake element. The back and forth movement of the membrane is driven by a rod and a crankshaft mechanism. Only the membrane and the compressor box come in touch with the gas being compressed.
Diaphragm compressors are used for hydrogen and compressed natural gas (CNG) as well as in a number of other applications.
Air compressors sold to and used by the general public are often attached on top of a tank for holding the pressurized air. Oil-lubricated and oil-free compressors are available. Oil-free compressors are desirable because without a properly designed separator, oil can make its way into the air stream. For some purposes, for example as a diving air compressor, even a little oil in the air stream may be unacceptable.
Charles's law says "when a gas is compressed, temperature is raised". There are three possible relationships between temperature and pressure in a volume of gas undergoing compression:
Since compression generates heat, the compressed gas is to be cooled between stages making the compression less adiabatic and more isothermal. The inter-stage coolers cause condensation meaning water separators with drain valves are present. The compressor flywheel may drive a cooling fan.
For instance in a typical diving compressor, the air is compressed in three stages. If each stage has a compression ratio of 7 to 1, the compressor can output 343 times atmospheric pressure (7 x 7 x 7 = 343 Atmospheres).
Gas compressors are used in various applications where either higher pressures or lower volumes of gas are needed:
Cash
In bookkeeping and finance, "cash" can also refer to checks, money orders, cashier's checks, bank drafts, or traveler's checks. In all these forms, the term indicates the most liquid form of assets, which have a fixed value and can be easily converted to currency: "ready money". For example, wages or salaries paid as "cash" (as opposed to, e.g., stock options) would in most countries normally be paid with checks or direct bank deposits, which are trivially convertible to currency.
Hemer
Hemer is a city in North Rhine-Westphalia, Germany. About 35,000 people live there.
Heating
Heating is making something warm. It could mean:
HVACR "R" stand for Refrigeration
Heating devices, or systems:
Heat engine
In engineering and thermodynamics, a heat engine converts heat energy to mechanical work by using the temperature difference between a hot "source" and a cold "sink". Heat is transferred from the source, through the "working body" of the engine, to the "sink", and in this process some of the heat changes into work by using the qualities of the gas or liquid inside the engine.
There are many kinds of heat engines. Each has a thermodynamic cycle. Heat engines are often named after the thermodynamic cycle they use, like the Carnot cycle. They often pick up everyday names, such as gasoline/petrol, turbine, or steam engines.
Internal combustion engines generate heat inside the engine itself. Other heat engines may absorb heat from an external source. Heat engines can be open to the air or sealed and closed off to the outside (This is called an Open or Closed cycle).
When scientists study heat engines they come up with ideas for engines that cannot actually be built . These are called ideal engines or cycles. Real heat engines are often confused with the ideal engines or cycles they attempt to mimic.
Typically when describing the physical device the term 'engine' is used. When describing the ideal the term 'cycle' is used.
One could say that the thermodynamic cycle is an ideal case of the mechanical engine. One could equally say that the model does not quite perfectly match the mechanical engine. However, much benefit is gained from the simplified models, and ideal cases they may represent.
In general terms, the larger the difference in temperature between the hot source and the cold sink, the more efficient the cycle or engine. On Earth, the cold side of any heat engine is limited to the air temperature of the place where the engine is.