Partial condenser, definition

A column having a completely defined single feed, an overhead product, a bottoms product, a condenser, a reboiler, and a fixed column pressure has three degrees of freedom if the number of trays is variable (Section 5.2). The column model depicted in Figure 5.3 meets these definitions and is used here to describe the method. Note that the condenser in this model is a partial condenser, so that the distillate is a saturated vapor. With three degrees of freedom, the column requires three specifications to define its operation. Let the condenser duty, q the distillate composition, 7, and the bottoms composition, Xg, be specified. 

This method also considers the stage temperatures as the independent variables. The algorithm is applied to a single-feed, two-product column with a partial condenser and reboiler. As in the original Thiele-Geddes method, the problem definition is such that the feed component flow rates, are known and fixed. The column pressure profile is also fixed, as well as its configuration, which defines the number of stages and feed location. In addition, one product rate (the distillate) and one internal flow (such as the reflux rate, Lj) are specified. The solution method, outlined below, is described in detail by Holland (1975). 

Since h = h, both points are located underneath the phase envelope, indicating that partial condensation already has occurred in the cold heat exchanger. At point 5, an actual enthalpy of 99.9 kJ/kg corresponds to a temperature of 119 K. Thus, for an ideal heat exchanger at the cold end of the cycle, the maximum temperature for Ty is also 119 K. From the definition for the effectiveness of the heat exchanger, we can now determine hj, the actual enthalpy at point 7, and the corresponding temperature... 

Consider the case of an existing column such as the one shown in Fig. 2-3. Suppose that the specifications are taken to be (1) the total number of stages and the location of the feed plate, (2) the complete definition of the feed (the total-flow rate, composition, and thermal condition), (3) the reflux rate, (4) the distillate rate, (5) the column pressure, and (6) the type of condenser (total or partial). On the basis of this set of specifications, it is desired to find the resulting compositions of the distillate and bottom products. 

For condensation of methylene chloride in water, in cocurrent downflow 4-in. and 6-in. diam columns packed with i-in. Intalox saddles, the volumetric transfer coefficients reported (HlOa) were less than half those obtained with the sieve-plate column. The difference may be due partially to the different definition of the temperature driving-force applied for these two columns. (The log-mean AT was used for the packed bed, and a 2-in. transfer height was assumed.) The volumetric heat transfer coefficients increased with the 0.4-0.6 power of the liquid rate from 65,000 to 150,000 Btu/hr/ft /°F with the liquid rate increasing from 1 to 4 x 10" Ib/hr/ft. Contrary to the sieve-plate and spray-column studies, no effects of the vapor flow rate (from 1100 to 2500 Ib/hr/ft ) on the heat-transfer coefficient were noted in the packed bed study. 

The nuclear resonant inelastic and quasi-elastic scattering method has distinct features favorable for studies concerning the microscopic dynamics (i.e., lattice vibration, diffusion, and molecular rotation) of materials. One advantageous feature is the ability to measure the element-specific dynamics of condensed matter. For example, in solids the partial phonon density of states can be measured. Furthermore, measurements under exotic conditions -such as high pressure, small samples, and thin films - are possible because of the high brilliance of synchrotron radiation. (For the definition of brilliance, see O Sect. 50.3.4.5 of Chap. 50, Vol. 5, on Particle Accelerators. ) This method is applicable not only to solids but also to liquids and gases, and there is no limitation concerning the sample temperature. 

It is, of course, entirely permissible to regard the temperature as being held constant during the variations considered in the above equation. In a two-phase system of C components there are C degrees of freedom, and an arbitrary choice can be made of the temperature, together with the 0—1 mole fractions required to fix the composition of the condensed phase. When this has been done the total pressure and the partial pressures have definite values, and the relationship between the changes in these quantities, as the composition is varied at constant temperaiure is given by the above equation. 

The enthalpy effect might be positive (endothermic solution/mixture) or negative (exothermic solution/mixture) depending on the ratio tijns, i.e., the concentration of the total system. Unfortunately, in some of the older literature, the definition of the sign of the so-called (integral) heat of solution is reversed, compared to the enthalpy, occasionally causing some confusion. In principle, the enthalpy effect depends also on pressure. However, in the case of condensed systems this pressure dependence is relatively small. All values in this handbook usually refer to normal pressiue. Hoa and Hog are the molar enthalpies of pure solvent A and pure copolymer B and and Hg the partial molar enthalpies of solvent and copolymer in the solution/mixture. 

---