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65-406: Depending on the application, an injector can also take the form of an eductor-jet pump , a water eductor or an aspirator . An ejector operates on similar principles to create a vacuum feed connection for braking systems etc. The motive fluid may be a liquid, steam or any other gas. The entrained suction fluid may be a gas, a liquid, a slurry, or a dust-laden gas stream. The steam injector

130-450: A colder to a warmer place, so their function is the opposite of a heat engine. The work energy ( W in ) that is applied to them is converted into heat, and the sum of this energy and the heat energy that is taken up from the cold reservoir ( Q C ) is equal to the magnitude of the total heat energy given off to the hot reservoir (| Q H |) Their efficiency is measured by a coefficient of performance (COP). Heat pumps are measured by

195-416: A divergent "delivery cone" which slows the jet, converting kinetic energy back into static pressure energy above the pressure of the boiler enabling its feed through a non-return valve. Most of the heat energy in the condensed steam is returned to the boiler, increasing the thermal efficiency of the process. Injectors are therefore typically over 98% energy-efficient overall; they are also simple compared to

260-522: A fundamental limit on the thermal efficiency of all heat engines. Even an ideal, frictionless engine can't convert anywhere near 100% of its input heat into work. The limiting factors are the temperature at which the heat enters the engine, T H {\displaystyle T_{\rm {H}}\,} , and the temperature of the environment into which the engine exhausts its waste heat, T C {\displaystyle T_{\rm {C}}\,} , measured in an absolute scale, such as

325-407: A given amount W m {\displaystyle W_{m}} (in kg/h) of motive fluid. Other key properties of an injector include the fluid inlet pressure requirements i.e. whether it is lifting or non-lifting. In a non-lifting injector, positive inlet fluid pressure is needed e.g. the cold water input is fed by gravity. The steam-cone minimal orifice diameter is kept larger than

390-420: A large ejector for releasing the brakes when stationary and a small ejector for maintaining the vacuum against leaks. The exhaust from the ejectors is invariably directed to the smokebox, by which means it assists the blower in draughting the fire. The small ejector is sometimes replaced by a reciprocating pump driven from the crosshead because this is more economical of steam and is only required to operate when

455-400: A non-ideal process, so 0 ≤ η t h < 1 {\displaystyle 0\leq \eta _{\rm {th}}<1} When expressed as a percentage, the thermal efficiency must be between 0% and 100%. Efficiency must be less than 100% because there are inefficiencies such as friction and heat loss that convert the energy into alternative forms. For example,

520-417: A nozzle. In general, compressible flows through a diverging duct increases velocity as a gas expands. The two sketches at the bottom of figure 15 are both diverging, but the bottom one is slightly curved, and produced the highest velocity flow parallel to the axis. The area of a duct is proportional to the square of the diameter, and the curvature allows the steam to expand more linearly as it passes through

585-497: A primary booster, a secondary high-vacuum (HV) ejector, and a tertiary low-vacuum (LV) ejector. As per the two-stage system, initially the LV ejector is operated to pull vacuum down from the starting pressure to an intermediate pressure. Once this pressure is reached, the HV ejector is then operated in conjunction with the LV ejector to pull vacuum to the lower intermediate pressure. Finally the booster

650-408: A real-world value may be used as a figure of merit for the device. For engines where a fuel is burned, there are two types of thermal efficiency: indicated thermal efficiency and brake thermal efficiency. This form of efficiency is only appropriate when comparing similar types or similar devices. For other systems, the specifics of the calculations of efficiency vary, but the non-dimensional input

715-410: A steam jet to convert the pressure energy of the steam to velocity energy, reducing its pressure to below that of the atmosphere, which enables it to entrain a fluid (e.g., water). After passing through the convergent "combining cone", the mixed fluid is fully condensed, releasing the latent heat of evaporation of the steam which imparts extra velocity to the water. The condensate mixture then enters

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780-487: A supply of live steam if no exhaust steam was available. Injectors can be troublesome under certain running conditions, such as when vibration causes the combined steam and water jet to "knock off". Originally the injector had to be restarted by careful manipulation of the steam and water controls, and the distraction caused by a malfunctioning injector was largely responsible for the 1913 Ais Gill rail accident . Later injectors were designed to automatically restart on sensing

845-658: A temperature of T H = 816 ∘ C = 1500 ∘ F = 1089 K {\displaystyle T_{\rm {H}}=816^{\circ }{\text{C}}=1500^{\circ }{\text{F}}=1089{\text{K}}} and the ambient temperature is T C = 21 ∘ C = 70 ∘ F = 294 K {\displaystyle T_{\rm {C}}=21^{\circ }{\text{C}}=70^{\circ }{\text{F}}=294{\text{K}}} , then its maximum possible efficiency is: It can be seen that since T C {\displaystyle T_{\rm {C}}}

910-413: A thermal efficiency close to 100%. When comparing heating units, such as a highly efficient electric resistance heater to an 80% efficient natural gas-fuelled furnace, an economic analysis is needed to determine the most cost-effective choice. The heating value of a fuel is the amount of heat released during an exothermic reaction (e.g., combustion ) and is a characteristic of each substance. It

975-414: A two-stage system consists of a primary high-vacuum (HV) ejector and a secondary low-vacuum (LV) ejector. Initially the LV ejector is operated to pull vacuum down from the starting pressure to an intermediate pressure. Once this pressure is reached, the HV ejector is then operated in conjunction with the LV ejector to finally pull vacuum to the required pressure. In operation a three-stage system consists of

1040-479: A typical gasoline automobile engine operates at around 25% efficiency, and a large coal-fuelled electrical generating plant peaks at about 46%. However, advances in Formula 1 motorsport regulations have pushed teams to develop highly efficient power units which peak around 45–50% thermal efficiency. The largest diesel engine in the world peaks at 51.7%. In a combined cycle plant, thermal efficiencies approach 60%. Such

1105-439: A valve to prevent air being sucked in at the overflow. Efficiency was further improved by the development of a multi-stage injector which is powered not by live steam from the boiler but by exhaust steam from the cylinders, thereby making use of the residual energy in the exhaust steam which would otherwise go to waste. However, an exhaust injector also cannot work when the locomotive is stationary; later exhaust injectors could use

1170-413: Is 90% efficient', but a more detailed measure of seasonal energy effectiveness is the annual fuel use efficiency (AFUE). The role of a heat exchanger is to transfer heat between two mediums, so the performance of the heat exchanger is closely related to energy or thermal efficiency. A counter flow heat exchanger is the most efficient type of heat exchanger in transferring heat energy from one circuit to

1235-407: Is a common device used for delivering water to steam boilers, especially in steam locomotives. It is a typical application of the injector principle used to deliver cold water to a boiler against its own pressure, using its own live or exhaust steam, replacing any mechanical pump . When first developed, its operation was intriguing because it seemed paradoxical, almost like perpetual motion , but it

1300-472: Is an active area of research. Due to the other causes detailed below, practical engines have efficiencies far below the Carnot limit. For example, the average automobile engine is less than 35% efficient. Carnot's theorem applies to thermodynamic cycles, where thermal energy is converted to mechanical work. Devices that convert a fuel's chemical energy directly into electrical work, such as fuel cells , can exceed

1365-453: Is an overall theoretical limit to the efficiency of any heat engine due to temperature, called the Carnot efficiency. Second, specific types of engines have lower limits on their efficiency due to the inherent irreversibility of the engine cycle they use. Thirdly, the nonideal behavior of real engines, such as mechanical friction and losses in the combustion process causes further efficiency losses. The second law of thermodynamics puts

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1430-516: Is defined as ratio of the injector's outlet pressure P 2 {\displaystyle P_{2}} to the inlet pressure of the suction fluid P 1 {\displaystyle P_{1}} . The entrainment ratio of the injector, W s / W m {\displaystyle W_{s}/W_{m}} , is defined as the amount W s {\displaystyle W_{s}} (in kg/h) of suction fluid that can be entrained and compressed by

1495-432: Is fixed by the environment, the only way for a designer to increase the Carnot efficiency of an engine is to increase T H {\displaystyle T_{\rm {H}}} , the temperature at which the heat is added to the engine. The efficiency of ordinary heat engines also generally increases with operating temperature , and advanced structural materials that allow engines to operate at higher temperatures

1560-535: Is measured in units of energy per unit of the substance, usually mass , such as: kJ/kg, J / mol . The heating value for fuels is expressed as the HHV, LHV, or GHV to distinguish treatment of the heat of phase changes: Which definition of heating value is being used significantly affects any quoted efficiency. Not stating whether an efficiency is HHV or LHV renders such numbers very misleading. Heat pumps , refrigerators and air conditioners use work to move heat from

1625-452: Is operated (in conjunction with the HV & LV ejectors) to pull vacuum to the required pressure. Injectors or ejectors are made of carbon steel , stainless steel , brass , titanium , PTFE , carbon , and other materials. Water eductor A water eductor or water dredge is an eductor-jet pump -based tool used by underwater archaeologists to remove sediments from an underwater archaeological site. Airlifts may be used for

1690-410: Is required for excess steam or water to discharge, especially during starting. If the injector cannot initially overcome boiler pressure, the overflow allows the injector to continue to draw water and steam. There is at least one check valve (called a "clack valve" in locomotives because of the distinctive noise it makes) between the exit of the injector and the boiler to prevent back flow, and usually

1755-445: Is split, with the greater part of the flow leaving the system, while a portion of the flow is returned to the jet pump installed below ground in the well. This recirculated part of the pumped fluid is used to power the jet. At the jet pump, the high-energy, low-mass returned flow drives more fluid from the well, becoming a low-energy, high-mass flow which is then piped to the inlet of the main pump. Shallow well pumps are those in which

1820-430: Is still the same: Efficiency = Output energy / input energy. Heat engines transform thermal energy , or heat, Q in into mechanical energy , or work , W out . They cannot do this task perfectly, so some of the input heat energy is not converted into work, but is dissipated as waste heat Q out < 0 into the surroundings: The thermal efficiency of a heat engine is the percentage of heat energy that

1885-613: Is transformed into work . Thermal efficiency is defined as The efficiency of even the best heat engines is low; usually below 50% and often far below. So the energy lost to the environment by heat engines is a major waste of energy resources. Since a large fraction of the fuels produced worldwide go to powering heat engines, perhaps up to half of the useful energy produced worldwide is wasted in engine inefficiency, although modern cogeneration , combined cycle and energy recycling schemes are beginning to use this heat for other purposes. This inefficiency can be attributed to three causes. There

1950-639: The Carnot theorem . In general, energy conversion efficiency is the ratio between the useful output of a device and the input, in energy terms. For thermal efficiency, the input, Q i n {\displaystyle Q_{\rm {in}}} , to the device is heat , or the heat-content of a fuel that is consumed. The desired output is mechanical work , W o u t {\displaystyle W_{\rm {out}}} , or heat, Q o u t {\displaystyle Q_{\rm {out}}} , or possibly both. Because

2015-537: The Kelvin or Rankine scale. From Carnot's theorem , for any engine working between these two temperatures: This limiting value is called the Carnot cycle efficiency because it is the efficiency of an unattainable, ideal, reversible engine cycle called the Carnot cycle . No device converting heat into mechanical energy, regardless of its construction, can exceed this efficiency. Examples of T H {\displaystyle T_{\rm {H}}\,} are

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2080-447: The ideal gas law . Real engines have many departures from ideal behavior that waste energy, reducing actual efficiencies below the theoretical values given above. Examples are: These factors may be accounted when analyzing thermodynamic cycles, however discussion of how to do so is outside the scope of this article. For a device that converts energy from another form into thermal energy (such as an electric heater, boiler, or furnace),

2145-401: The thermal efficiency ( η t h {\displaystyle \eta _{\rm {th}}} ) is a dimensionless performance measure of a device that uses thermal energy , such as an internal combustion engine , steam turbine , steam engine , boiler , furnace , refrigerator , ACs etc. For a heat engine , thermal efficiency is the ratio of the net work output to

2210-499: The COP can be greater than 1 (100%). Therefore, heat pumps can be a more efficient way of heating than simply converting the input work into heat, as in an electric heater or furnace. Since they are heat engines, these devices are also limited by Carnot's theorem . The limiting value of the Carnot 'efficiency' for these processes, with the equality theoretically achievable only with an ideal 'reversible' cycle, is: The same device used between

2275-439: The Carnot efficiency. The Carnot cycle is reversible and thus represents the upper limit on efficiency of an engine cycle. Practical engine cycles are irreversible and thus have inherently lower efficiency than the Carnot efficiency when operated between the same temperatures T H {\displaystyle T_{\rm {H}}} and T C {\displaystyle T_{\rm {C}}} . One of

2340-584: The achieved COP to the Carnot COP, which can not exceed 100%. The 'thermal efficiency' is sometimes called the energy efficiency . In the United States, in everyday usage the SEER is the more common measure of energy efficiency for cooling devices, as well as for heat pumps when in their heating mode. For energy-conversion heating devices their peak steady-state thermal efficiency is often stated, e.g., 'this furnace

2405-406: The collapse in vacuum from the steam jet, for example with a spring-loaded delivery cone. Another common problem occurs when the incoming water is too warm and is less effective at condensing the steam in the combining cone. That can also occur if the metal body of the injector is too hot, e.g. from prolonged use. The internal parts of an injector are subject to erosive wear, particularly damage at

2470-468: The combining cone minimal diameter. The non-lifting Nathan 4000 injector used on the Southern Pacific 4294 could push 12,000 US gallons (45,000 L) per hour at 250 psi (17 bar). The lifting injector can operate with negative inlet fluid pressure i.e. fluid lying below the level of the injector. It differs from the non-lifting type mainly in the relative dimensions of the nozzles. An overflow

2535-483: The duct. An ideal gas cools during adiabatic expansion (without adding heat), releasing less energy than the same gas would during isothermal expansion (constant temperature). Expansion of steam follows an intermediate thermodynamic process called the Rankine cycle . Steam does more work than an ideal gas, because steam remains hot during expansion. The extra heat comes from enthalpy of vaporization , as some of

2600-415: The efficiency with which they give off heat to the hot reservoir, COP heating ; refrigerators and air conditioners by the efficiency with which they take up heat from the cold space, COP cooling : The reason the term "coefficient of performance" is used instead of "efficiency" is that, since these devices are moving heat, not creating it, the amount of heat they move can be greater than the input work, so

2665-470: The factors determining efficiency is how heat is added to the working fluid in the cycle, and how it is removed. The Carnot cycle achieves maximum efficiency because all the heat is added to the working fluid at the maximum temperature T H {\displaystyle T_{\rm {H}}} , and removed at the minimum temperature T C {\displaystyle T_{\rm {C}}} . In contrast, in an internal combustion engine,

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2730-479: The flue gases from the boiler which are then ejected via the chimney. The effect is to increase the draught on the fire to a degree proportional to the rate of steam consumption, so that as more steam is used, more heat is generated from the fire and steam production is also increased. The effect was first noted by Richard Trevithick and subsequently developed empirically by the early locomotive engineers; Stephenson's Rocket made use of it, and this constitutes much of

2795-491: The fuel, but is generally close to the air value of 1.4. This standard value is usually used in the engine cycle equations below, and when this approximation is made the cycle is called an air-standard cycle . One should not confuse thermal efficiency with other efficiencies that are used when discussing engines. The above efficiency formulas are based on simple idealized mathematical models of engines, with no friction and working fluids that obey simple thermodynamic rules called

2860-497: The ground surface for easy maintenance. The advent of the electrical submersible pump has partly replaced the need for jet type well pumps, except for driven point wells or surface water intakes. In practice, for suction pressure below 100 mbar absolute, more than one ejector is used, usually with condensers between the ejector stages. Condensing of motive steam greatly improves ejector set efficiency; both barometric and shell-and-tube surface condensers are used. In operation

2925-413: The heat input; in the case of a heat pump , thermal efficiency (known as the coefficient of performance or COP) is the ratio of net heat output (for heating), or the net heat removed (for cooling) to the energy input (external work). The efficiency of a heat engine is fractional as the output is always less than the input while the COP of a heat pump is more than 1. These values are further restricted by

2990-467: The injector became widely adopted for steam locomotives as an alternative to mechanical pumps. Strickland Landis Kneass was a civil engineer , experimenter, and author, with many accomplishments involving railroading. Kneass began publishing a mathematical model of the physics of the injector, which he had verified by experimenting with steam. A steam injector has three primary sections: Figure 15 shows four sketches Kneass drew of steam passing through

3055-440: The input heat normally has a real financial cost, a memorable, generic definition of thermal efficiency is η t h ≡ benefit cost . {\displaystyle \eta _{\rm {th}}\equiv {\frac {\text{benefit}}{\text{cost}}}.} From the first law of thermodynamics , the energy output cannot exceed the input, and by the second law of thermodynamics it cannot be equal in

3120-486: The jet assembly is attached directly to the main pump and are limited to a depth of approximately 5-8m to prevent cavitation . Deep well pumps are those in which the jet is located at the bottom of the well. The maximum depth for deep well pumps is determined by the inside diameter of and the velocity through the jet. The major advantage of jet pumps for deep well installations is the ability to situate all mechanical parts (e.g., electric/petrol motor, rotating impellers) at

3185-401: The locomotive smokebox. The sketch on the right shows a cross section through a smokebox, rotated 90 degrees; it can be seen that the same components are present, albeit differently named, as in the generic diagram of an injector at the top of the article. Exhaust steam from the cylinders is directed through a nozzle on the end of the blastpipe, to reduce pressure inside the smokebox by entraining

3250-407: The many moving parts in a feed pump. Fluid feed rate and operating pressure range are the key parameters of an injector, and vacuum pressure and evacuation rate are the key parameters for an ejector. Compression ratio and the entrainment ratio may also be defined: The compression ratio of the injector, P 2 / P 1 {\displaystyle P_{2}/P_{1}} ,

3315-448: The mouth of the dredge. As the water dredge will remove particles held in suspension in the water, provided it is used correctly it will improve visibility in the immediate area of the excavation. Careful use of the water dredge ensures that artifacts can be recorded in context and features and stratigraphy can be studied. Using a water dredge or airlift, the underwater archaeologist has an advantage over terrestrial counterparts, as

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3380-415: The reason for its notably improved performance in comparison with contemporary machines. The use of injectors (or ejectors) in various industrial applications has become quite common due to their relative simplicity and adaptability. For example: Jet pumps are commonly used to extract water from water wells . The main pump, often a centrifugal pump , is powered and installed at ground level. Its discharge

3445-420: The same purpose. It consists of a large bore straight tube to which is attached a hose pipe through which clean water is pumped . The Bernoulli effect from the flow of pumped water causes suction at the mouth of the dredge. Water and sediment are sucked from the excavation site and released from the far end of the tube. The tube can be made of any rigid material such as steel or plastic . The diameter of

3510-400: The same temperatures is more efficient when considered as a heat pump than when considered as a refrigerator since This is because when heating, the work used to run the device is converted to heat and adds to the desired effect, whereas if the desired effect is cooling the heat resulting from the input work is just an unwanted by-product. Sometimes, the term efficiency is used for the ratio of

3575-410: The spoil is removed without effort and without needing to be transported across other parts of the archaeological site. Where there is a possibility of small artifacts being missed because of poor visibility, a trap may be used at the outlet so that the lifted sediment can be filtered. Water eductors are also used by marine treasure hunters to suck sediments for filtering for buried artifacts. Using

3640-407: The steam condenses back into dropplets of water intermixed with steam. At the end of the nozzle, the steam has very high velocity, but at less than atmospheric pressure, drawing in cold water which becomes entrained in the stream, where the steam condenses into droplets of water in a converging duct. The delivery tube is a diverging duct where the force of deceleration increases pressure, allowing

3705-466: The stream of water to enter the boiler. The injector consists of a body filled with a secondary fluid, into which a motive fluid is injected. The motive fluid induces the secondary fluid to move. Injectors exist in many variations, and can have several stages, each repeating the same basic operating principle, to increase their overall effect. It uses the Venturi effect of a converging-diverging nozzle on

3770-425: The temperature of hot steam entering the turbine of a steam power plant , or the temperature at which the fuel burns in an internal combustion engine . T C {\displaystyle T_{\rm {C}}} is usually the ambient temperature where the engine is located, or the temperature of a lake or river into which the waste heat is discharged. For example, if an automobile engine burns gasoline at

3835-418: The temperature of the fuel-air mixture in the cylinder is nowhere near its peak temperature as the fuel starts to burn, and only reaches the peak temperature as all the fuel is consumed, so the average temperature at which heat is added is lower, reducing efficiency. An important parameter in the efficiency of combustion engines is the specific heat ratio of the air-fuel mixture, γ . This varies somewhat with

3900-408: The thermal efficiency is where the Q {\displaystyle Q} quantities are heat-equivalent values. So, for a boiler that produces 210 kW (or 700,000 BTU/h) output for each 300 kW (or 1,000,000 BTU/h) heat-equivalent input, its thermal efficiency is 210/300 = 0.70, or 70%. This means that 30% of the energy is lost to the environment. An electric resistance heater has

3965-642: The throat of the delivery cone which may be due to cavitation . An additional use for the injector technology is in vacuum ejectors in continuous train braking systems , which were made compulsory in the UK by the Regulation of Railways Act 1889 . A vacuum ejector uses steam pressure to draw air out of the vacuum pipe and reservoirs of continuous train brake. Steam locomotives, with a ready source of steam, found ejector technology ideal with its rugged simplicity and lack of moving parts. A steam locomotive usually has two ejectors:

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4030-420: The train is moving. Vacuum brakes have been superseded by air brakes in modern trains, which allow the use of smaller brake cylinders and/or higher braking force due to the greater difference from atmospheric pressure. An empirical application of the principle was in widespread use on steam locomotives before its formal development as the injector, in the form of the arrangement of the blastpipe and chimney in

4095-477: The tube depends on the power available from the pump and whether delicate work is required. In the hands of a trained archaeologist, the water dredge performs the same function as a wheelbarrow on land. It is used to carry away sediments, not to dig holes. The archaeologist dislodges the material using a trowel, brush or by making a fanning motion with the hand to cause a current to dislodge sediment. The archaeologist can also place overburden material directly into

4160-457: The water dredge to directly suck sediments means that archaeological information on context and stratigraphy is not recorded. An eductor can also form part of a wet scrubber system which are designed to remove soluble gases and particulate by inducing a gas flow using high pressure liquid focused into a venturi throat. Additionally, eductor scrubbers can be used for direct-contact condensation. Thermal efficiency In thermodynamics ,

4225-549: Was later explained using thermodynamics . Other types of injector may use other pressurised motive fluids such as air. The injector was invented by Henri Giffard in early 1850s and patented in France in 1858, for use on steam locomotives . It was patented in the United Kingdom by Sharp, Stewart and Company of Glasgow . After some initial scepticism resulting from the unfamiliar and superficially paradoxical mode of operation,

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