Ideal compression

Figure 24.22 A simple (ideal) compression refrigeration cycle.

In this example we describe the calculation of the minimum work for ideal compressible adiabatic flow using two different optimization techniques, (a) analytical, and (b) numerical. Most real flows lie somewhere between adiabatic and isothermal flow. For adiabatic flow, the case examined here, you cannot establish a priori the relationship between pressure and density of the gas because the temperature is unknown as a function of pressure or density, hence the relation between pressure and... 

Professor Nicolas L. S. Carnot, in the late nineteenth century, realized that the area inside the plot of pressure vs. volume represented the work needed to compress gas in a reciprocating compressor. In other words, the change of pressure, multiplied by the change in volume, is equal to the work done by the piston on the gas. Professor Carnot called this PV (pressure vs. volume) work. He then used calculus to sum up the area inside the lines shown in Fig. 29.2. The total area is now called ideal compression work. 

The Carnot cycle plot represents ideal compression work. But we in the process industry have to worry about actual compression work, and the loss of compression efficiency caused by these three problems. 

The solid line is the indicator-card plot. The dotted line is the Carnot or ideal compression work cycle which I have drawn myself. The piston position, shown on the horizontal axis, is proportional to the volume of gas inside the cylinder. 

Note that the final actual steam temperature is 73.7°F (40.9°C) higher than that (650°F or 343.3°C) for the ideal compression. 

All calculations were carried out at T = 313.15 K. The vapor-liquid equilibrium (VLB) data for the ternary mixture and the corresponding binaries were taken from [32]. The excess volume data for the ternary mixture A,A-dimethylformamide-methanol-water and binary mixtures A, A-dimethylformamide-methanol and methanol-water were taken from [33], and the excess volume data for the binary mixture A,A-dimethylformamide-water from [34]. There are no isothermal compressibility data for the ternary mixture, but the contribution of compressibility to the binary KBls is almost negligible far from the critical point [6]. For this reason, the compressibilities in binary and ternary mixtures were taken to be equal to the ideal compressibilities, and were calculated from the isothermal compressibilities of the pure components as follows ... 

The ideal compression (in isothermal conditions) work can be calculated according to the following equation ... 

In computer simulation the (ideal) compression work in adiabatic operation is calculated usually as the variation in enthalpy of the gas mixture between initial state, 7j and final state P2, T2 (see also eq. 5.20) ... 

From the view of a higher order transition, the first-order transition is obtained, when the lambda region is ideally compressed in such a manner so that the lambda shape approaches a Dirac delta function. Since the thermodynamic data are obtained ultimately by experimental measurement, one can be never sure, whether there is really a first-order transition or a lambda transition in a small region that cannot be differentiated by the experimental precision. 

Taking into account the given pecularities one may suggest a two phase model for description of irreversible development of cavitation zone which occurs experimentally. The SW spreading over real liquid is calculated as an approximation of ideal compressed liquid due to the low initial concentration of gaseous phase. When in the RW the pressure of cavitation threshold Pj, [1] is achieved its instantaneous relaxation occurs up to the magnitude (the pressure of saturation vapor). 

Because of the problems assodated with the currently available bandages for the treatment of venous leg ulcers as discussed under the heading 6.7, it is vital to research and develop an alternative bandaging regimen that meets aU the requirements of an ideal compression system. 

In comparison to tbe melting length of the ideal compression screw, the melting length of the Barr screw is ... 

If typical values are used for cpb and cpf, the melting length of the Dray and Lawrence screw will about 10 to 20% longer than the ideal compression screw. The melting performance of the Dray and Lawrence screw is thus about the same as the Barr screw and slightly better than the Maillefer screw. A patent on this barrier screw... 

Janelli, M. P., S. Magazu, G. Maisano, D. Majolino, and P. Migliardo. 1994. Non-ideal compressibility in poly(ethylene oxide)-water solutions... 

This surplus, which is also called overflow, flows into the remaining cavity between the force and female mold. The mold is equipped with a very small gap in the area of the shut-off (maximum 0.05 mm) to avoid unnecessary flash. This ensures the ideal compression of the molded part and creates a clear separation between the actual preform and the excess molding compound. Figure 1.84 shows several different designs. 

Ideal compression work Compression work discoimting friction, leakage, and other mechanical losses. 

---