Constant pressure closed cycle

The Joule-Brayton (JB) constant pressure closed cycle is the basis of the cyclic gas turbine power plant, with steady flow of air (or gas) through a compressor, heater, turbine, cooler within a closed circuit (Fig. 1.4). The turbine drives the compressor and a generator delivering the electrical power, heat is supplied at a constant pressure and is also rejected at constant pressure. The temperature-entropy diagram for this cycle is also... 

The working fluid for vapor cycles is alternately condensed and vaporized. When a working fluid remains in the saturation region at constant pressure, its temperature is also constant. Thus, the condensation or evaporation of a fluid in a heat exchanger is a process that closely approximates the isothermal heat-transfer processes of the Carnot cycle. Owing to this fact, vapor cycles closely approximate the behavior of the Carnot cycle. Thus, in general, they tend to perform efficiently. 

The most common internal-combustion engine, because of its use in automobiles, is the Otto engine. Its cycle consists of four strokes, and starts with an intake stroke at essentially constant pressure, during which a piston moving outward draws a fuel/air mixture into a cylinder. This is represented by line 0 - 1 in Fig. 8.8. During the second stroke (line 1 - 3), all valves are closed, and the fuel/air mixture is compressed, approximately adiabatically, along line 1 2. The mixture... 

But, as the external forces reduce to a constant pressure, th admit a potential (Chap. I, Art. 12), so that the work which they perform about a closed cycle is zero. Our hypothesis leads us... 

The plot of this cycle on a temperature-entropy diagram is such that 1 —> 2 is a line of constant entropy (vertical line). 2 -4 3 is a line of constant pressure, 3 -> 4 is another line of constant entropy, and 4 -4 1 closes the cycle with a line of constant temperature. Several different locations for these lines, depending largely on the operation of the boiler, are sjvovvn in Fig. 5.2-2. 

As soon as the piston begins to descend, the pressure falls instantaneously. jWhen the pressure reaches Pj ,et5 the inlet valve opens, still at volume y = 0 for a zero-clearance compressor, point B. Then the gas from the inlet line flows iri at a constant pressure until the piston reaches the bottom of its stroke at (point C). As soon as the piston starts up, the inlet valve closes, and then both valves remain closed while the gas in the cylinder is compressed from its inlet pressure to its outlet pressure. When the gas reaches that pressure, the outlet valve opens P = Poutiet> K)> point D. Then as the piston continues jto rise, the gas is forced out into the outlet line, completing the cycle at poinjt A. 

Rankine cycle A cycle of operations in a heat engine. The Rankine cycle mote closely approximates to the cycle of a teal steam engine that does the Carnot cycle. It therefore predicts a lower ideal thermal efficiency than the Carnot cycle. In the Rankine cycle (see illustration), heat is added at constant pressure Pi, at which water is converted in a boiler to superheated steam the steam expands at constant entropy to a pressure pz in the cylinder heat is rejected at constant pressure pj in a condenser the water so formed is compressed at constant entropy to pressure p, by a feed pump. The cycle was devised by William Rankine (1820-70). 

Hajji, A., and Worek, W.M., Thermodynamics of constant-pressure and constant-volume sorption processes in closed-cycle solid desiccant systems. Chem. Eng. Commun.. 104. 21-40 (1991). 

Another type of safety control is the two-hand control, which requires constant concurrent pressure by the operator to activate the machine. This kind of control requires a part-revolution clutch, brake, and a brake monitor if used on a power press. With this type of device, the operator s hands must be at a safe location (on control buttons) and at a safe distance from the danger area while the machine completes its closing cycle. The advantages of this type of safety control are that the operator s hands are at a predetermined location and that the operator s hands are free to pick up a new part after the first half of a cycle is completed. Some two-hand controls, however, can be rendered unsafe by using an arm on the controls or blocking, thereby permitting one-hand operation. The safety control only protects the operator. 

The steam turbine system is a closed - cycle one. It is used to drive the process reducing steam pressure from high or medium pressure to low or atmospheric pressure. The design pressure of the high or medium pressure turbine can be varied. The power of the high or medium pressure turbine (P, ) is a function of the pressure respectively or of the inlet (Ttur.in) and outlet (Ttur.om) temperatures (a, b and c being constants) ... 

Rankine cycle An ideal reversible thermodynamic cycle used in steam power plants (see Fig. 49) that more closely approximates to the cycle of a real steam engine than the Carnot cycle and converts heat into mechanical work. It involves water being introduced under pressure into a boiler and evaporation taking place, followed by expansion of the vapour without the loss of heat, ending in condensation. The cycle therefore consists of four stages i) steam passes from the boiler to the cylinder at constant pressure ii) the steam expands adiabatically to the condenser pressure iii) heat is given to the condenser at constant temperature iv) condensation is completed and the condensate is remrned to the boiler. In the Rankine cycle, the work done is equivalent to the total heat in the steam at the end of the adiabatic expansion subtracted from the total heat in the steam at the beginning of the expansion. The heat supplied is equal to the sensible heat in the condensed steam subtracted from the total heat. 

Pressure leaf filters are used to separate much the same lands of slurries as are filter presses and are used much more extensively than filter presses for filter-aid filtrations. They should be seriously considered whenever uniformity of production permits long-time operation under essentially constant filtration conditions, when thorough washing with a minimum of hquor is desired, or when vapors or fumes make closed construction desirable. Under such conditions, if the filter medium does not require frequent changing, they may show a considerable advantage in cycle and labor economy over a filter press, which has a lower initial cost, and advantages of economy and flexibility over continuous vacuum filters, which have a higher first cost. 

The transfer process was continued at least 10 times at different surface pressures (20, 10 and 5 mN m->)- The total transferred weight (JEW,) of dry cadmium octadecanoate LB films was plotted against the number of transfer cycle as closed circles in Figure 3. The amount of transferred films was also estimated from the conventional method calculated from a moving area of a barrier in kept the surface pressure constant, and plotted as closed triangles in Figure 3. Straight lines indicate the theoretical mass of Y-type two layers on each side of the QCM. 

After sufficient extraction the dissolved substances have to be separated from the fluid in a following step. Decreasing the pressure at constant temperature reduces the fluid-density, and therefore the solvent-power of the fluid. The extracted substances are collected at the bottom of the separator, as shown in Fig. 6.6-2. To close the solvent cycle, the fluid has to be recompressed to extraction pressure. 

The cryogenic adsorption system was specially developed to measure adsorption isotherms of H2 and D2. This system is equipped with a closed helium cycle two-stage Gifford McMahon refrigerator to operate under cryogenic conditions. The adsorption temperature can be kept constant within 0.03 K at 20 K. Adsorption isotherms are obtained by gas adsorption manometry. This method is based on the measurement of the gas pressure in a calibrated, constant volume, at a known temperature. The dead space volume was calculated from a helium calibration measurement at the temperature of interest. Thermal transpiration effect was calibrated according to the work by Takaishi and Sensui [41]. 

Measured pressure build up versus accumulated amount of fly ash is shown in Fig. 5 a). Calculated fly ash accumulation is based on averaged dust load measured gravimetiically during die respective filtration cycle. Observed pressure loss is close to ideal behavior for surface filtration (i.e. inconqiressible cake formation and constant dust concentration). Calculated specific cake resistance is shown in Fig. 5 b). 

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