Design and Analysis Coaching
CyclePad incorporates an integrated coaching facility to aid the user in designing and analyzing cycles. To provide this help, CyclePad first makes inferences about the role that each device is playing. A role is defined as the function that a particular device is intended to perform. For example, some gas liquefaction plants use turbines rather than throttles to expand the working fluid because a resisted expansion produces a larger drop in temperature than an unresisted expansion. In this case, even though the cycle may make use of the power derived from the expansion, the intended function of the turbine is to cool the working fluid, not to produce power.
You can view the roles that CyclePad has inferred for your cycle by choosing Tools|AnnotationsTools. Left-clicking on the displayed roles will provide an explanation of why CyclePad inferred that role.
CyclePad uses these role inferences to generate advice for improving the analysis of your cycle. To see this advice, choose Tools|Analysis CoachTools , and any advice that CyclePad has will be displayed in the Explanation WindowInvestigating_a_Cycle_via_the_Explanation_System .
The roles that CyclePad assigns to devices are described in component rolesComponent_Roles:
Cooler Cooler A cooler ejects heat energy from the working fluid to the environment. When acting as a heat-ejector, its purpose is to reduce the energy of the working fluid flowing through it. When acting as a heat-provider, its purpose is to provide heat to the environment. A hot-water radiator is actually a cooler operating as a heat-provider. A heat-ejector role is further partitioned into a fluid-cooler, which acts to cool its working fluid, and an intercooler, which is interleaved with compressor stages and is intended to reduce the work required of later stages by cooling the gas that is being compressed. The intercooler role subsumes the fluid-cooler role, yet we make this distinction because intercoolers are constituents of common thermodynamic structural "idioms" that provide valuable functional information. For example, an intercooler is an indication that the attendant rise in the temperature of the working fluid is an undesirable side-effect.
Heater Heater A heater injects heat energy from the environment to the working fluid. When acting as a heat-injector, its purpose is to increase the energy of the working fluid flowing through it. When acting as a heat-absorber its purpose is to cool the environment by absorbing heat from it. The coils in a domestic refrigerator comprise a heater that absorbs heat energy from the food in the refrigerating compartment. A heat-injector role is partitioned into fluid-heater, preheater, and reheater roles. A preheater adds heat to the working fluid upstream of the main heater (which acts as a fluid-heater) and a reheater adds heat between the stages of a turbine. Both are strategies for increasing the efficiency of the system (the second rational-designer goal), and hence are important roles to distinguish.
Reactor A reactor, like a heater, injects heat-energy into the working fluid. Unlike a heater, however, it does not have a heat-path that crosses the system boundary to connect it to a heat-source in the environment. Reactors, therefore, are never heat-absorbers.
Heat-exchangerHeat_Exchanger The representation of heat-exchangers is slightly more involved. From a structural perspective, a heat-exchanger consists of a device with two inlets and two outlets, but from a functional perspective it is more useful to consider it to be a heater and a cooler connected via a heat-conducting path. We therefore represent heat-exchangers as an hx-heater and an hx-cooler connected via a heat-path, although in CyclePad you’ll always see heat-exchangers as a single device, with the cooler indicated by a red-blue pipe and the heater by a blue-red pipe.
Hx-cooler An hx-cooler is a cooler that ejects thermal energy to a heater, to which it is coupled. Hx-coolers take on the same roles as coolers, but additional testing is necessary to ensure that their corresponding heater halves take on appropriate roles. For example, if a hx-cooler is acting as a heat-provider, then its heater half must be acting as a heat-injector. Otherwise the design would fail to achieve any of the design goals; but would instead be arranging to provide heat to a device that in effect throws it away.
Hx-heater An hx-heater is a heater that receives thermal energy from a coupled hx-cooler, but in other respects behaves like a heater. As in the case of the hx-cooler, additional testing is necessary to ensure that its corresponding half is playing an appropriate role.
Turbine Turbine A turbine consists of a series of fan blades arranged along a shaft; high-energy working fluid flowing through the turbine causes the shaft to rotate, converting thermal energy into mechanical energy, or work. The most common role of the turbine is to produce work, but in this process the temperature of the working fluid falls appreciably, and so turbines can also act as fluid coolers. They are used in this capacity most often in gas-liquefaction systems.
Compressor Compressor A compressor is very similar to a turbine, but instead of allowing the working fluid flowing through it to expand, mechanical energy applied to its shaft causes the working fluid to be compressed. Compressors can only operate on gaseous working fluids, because condensation causes significant erosion of their fan blades. Compressors are among the least functionally ambiguous components, most often acting as pressure-increasers. There are circumstances, however, in which the attendant increase in thermal energy is the desired effect, and hence they can also act as fluid-heaters.
Pump Pump A pump, like a compressor, generally acts as a pressure-increaser, although it can only operate on liquids. If the working fluid is a mixture of liquid and gas (i.e., in the saturated phase) then the pump will cavitate, which is likely to cause mechanical failure. For this reason, pumps can also act as flash-preventers; by increasing the pressure of the working fluid, they prevent it from flashing into a saturated vapor mixture. This is often necessary when preheaters are used to improve the efficiency of the cycle, and is an example of the third rational-designer goal, preserving the integrity of the system.
Throttle Throttle A throttle, like a turbine, causes the working fluid to expand, but unlike a turbine a throttle generates no work. Throttles have two roles, saturator and pressure-decreaser. A saturator (which subsumes pressure-decreaser) is intended to cause the working fluid to change from either a gas or a liquid to a saturated mixture. A domestic refrigerator uses a throttle to cause the refrigerant that has been cooled in the coils on the back or bottom of the refrigerator to partially vaporize. This vaporization takes place in the cooling coils of the refrigerator, and, because vaporization requires heat, the refrigerant literally sucks the heat out of the contents of the refrigerator. Throttles are also used to step down the pressure of a working fluid to allow it to mix with another, lower-pressure stream. This is a common throttling application in heat-engines, where steam bled from the turbine and used to preheat the working fluid flowing to the boiler must be fed back into the system at a lower pressure.
Mixer Mixer Mixers are among the most flexible of components. They may act as simple flow-joins, as open heat-exchangers, jet-ejectors, or, when coupled with a splitter, as the inlet half of a steam-drum. A flow-join simply joins two flows, and is subsumed by the other three roles. An open heat-exchanger acts to increase the heat of one stream by mixing it with a hotter stream. This direct-contact mixing is more thermodynamically efficient, although it requires the streams to be at the same pressure, which may require more pumps in the system. Direct-contact heat-exchange is also used to deaerate the working fluid in power-plants, as oxygen dissolved in the working fluid can cause corrosion. A jet-ejector uses a high-velocity stream of working fluid to entrain and compress another stream of working fluid, in effect acting as a pump. Whereas pumps receive an input of mechanical energy, jet-ejectors utilize thermal energy. This can be more efficient when there is a source of heat that would otherwise go to waste, and so industrial plants often take advantage of process heat to generate electricity in so-called cogeneration systems. A steam-drum acts as a reservoir of steam, typically to be fed into a turbine series. A saturated mixture is typically fed into a steam drum, and separated into gas, which is fed to the turbines, and liquid, which is recirculated. Saturated mixtures that are more than 7% liquid can do great damage to turbine blades, as the liquid forms into droplets that impinge at high velocities on the turbine blades, so steam drums are often used to provide a pure gas stream to the turbines. They are most common in nuclear plants, which tend to operate at lower temperatures than fossil-fueled plants. Steam drums also act as a buffer against changing loads on the system.
Splitter Splitter Splitters, like mixers, can play several different roles. They may act as simple flow-forks, as steam-drum outlets, as flash-chambers, or as bleed-valves. A flow-fork splits a flow into two flows, and is subsumed by the other three roles. The function of a steam drum is described above, in the chapter on mixers. A flash-chamber is a container in which the working fluid, having just undergone a decrease in pressure, either by flowing through a turbine or through a throttle (which would be acting as a saturator), suddenly changes phase to a saturated mixture. The liquid part of the flow is then separated from the gas part. Flash-chambers are most commonly used in gas liquefaction plants, in which a cooled and compressed working fluid is allowed to precipitate in the flash-chamber. Occasionally industrial refrigerators or air-conditioners will make use of a flash-chamber, and in some nuclear plants the steam flowing into the final turbine stage first passes through a flash chamber to remove the liquid that would otherwise damage the turbine blades. Bleed valves are flow-forks between the stages of a turbine that are intended to bleed off a portion of the working fluid, typically for use in preheating the working-fluid flowing to the boiler. Although bleed-valves are tantamount to flow-forks, they tend to be used in recurring design "idioms" and so we have found distinguishing this role to be quite useful in inferring the role of other components connected to them.
SourceSource A source simply supplies a working fluid, and hence plays only this one role.
SinkSink A sink simply receives a working fluid, and hence plays only this one role.
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