Refrigeration effect evaporators

Basic Refrigeration Methods Three basic methods of refrigeration (mentioned above) use similar processes for obtaining refrigeration effect evaporation in the evaporator, condensation in the condenser where heat is rejected to the environment, and expansion in a flow restrictor. The main difference is in the way compression is being done (Fig. 11-71) using mechanical work (in compressor), thermal energy (for absorption and desorption), or pressure difference (in ejector). 

Refrigerating capacity is the product of mass flow rate of refrigerant m and refrigerating effect R which is (for isobaric evaporation) R = hevaporator outlet evaporator mJef Powei P required foi the coiTipressiou, necessary for the motor selection, is the product of mass flow rate m and work of compression W. The latter is, for the isentropic compression, W = hjisehatge suction- Both of thoso chai acteristics could be calculated for the ideal (without losses) and for the ac tual compressor. ideaUy, the mass flow rate is equal to the product of the compressor displacement per unit time and the gas density p m = p. 

F Saturated Evaporating, 75°F Suction Superheat (Not Included in Refrigeration Effect), 100°F Saturated Condensing ... 

Refrigerating Effect. This is the heat absorbed in the evaporator per lb of refrigerant. It is determined by the difference in enthalpy of a lb of refrigerant vapor leaving the evaporator and that of a lb of liquid just upstream (ahead) of the expansion valve at the evaporator. From Figure 11-48A,... 

For the convenience of users, the refrigerating effect of compressors is usually tabulated (Table 4.1) or given in graphical form (Figure 4.19), and is shown as the net cooling capacity based on the evaporating and condensing temperatures or pressures. Such published data will include absorbed power and indicate any limitations of the application. 

Evaporator. In this H/Ex, metered refrigerant liquid (dilute lithium bromide) from the condenser is sprayed over the evaporator tubes and vaporizes under the vacuum in the evaporator, creating a refrigerating effect. (The vacuum is created by the hygroscopic action of the lithium bromide with water in the absorber). Chilled water is on the other side of the H/Ex, and is cooled from 54°F to 44°F (12.2°C to 6.7°C). 

Consider the vapor-compression refrigeration cycle of Fig. 9.1ft with Freon-12 as refrigerant the evaporation temperature is 10(°F), show the effect of condensation temperature on the coeffi of performance by making calculations for condensation temperatures of 60, 80, and 100(°F). 

Make a thermodynamic analysis of the refrigeration cycle described in one of the parts Prob. 9.3. Assume that the refrigeration effect maintains a heat reservoir at a temperature 9(°F) above the evaporation temperature and that T0 is 9(°F) below the condensation temperature. 

Refrigerating capacity Q, is the product of mass flow rate of refrigerant m and refrigerating effect R which is (for isobaric evaporation)... 

The suction vapor coming from the evaporator could be used to subcool the liquid from the condenser. Graphic interpretation in T-s diagram for such a process is shown in Fig. 11-76. The result of the use of suction line heat exchanger is to increase the refrigeration effect AQ and to increase the work by AW The change in COP is then ... 

The hydrochloric acid and the unreacted nitric add are dissolved in the liquid phase. Obviously both nitric add and hydrochloric acid are soluble in the solvent, but distribution coeffidents differ suffidently for the hydrochloric acid to be removed in a countercurrent liquid extraction system by water. The extraction is carried out in the mixer-setder extraction system vessels. The remaining nitric acid and solvent are recycled through a refrigeration unit to the first reactor. The water is stripped from the solvent, which is also recycled. The low concentration hydrochloric acid is evaporated in a multiple effect evaporator to a concentration of 22%. This acid is use.d in another plant to produce phosphoric acid by a hydrochloric add attack. The latter process is described in Chapter 11. 

---