Category: Vapour Compression and Vapour Absorption Systems

The comparison of ammonia-water and lithium bromide-water systems are given m Table 19.2   Table 19.2 Comparison of ammonia-water and lithium bromide-water systems Exercises 19.1. The evaporator and condenser temperatures in an NH3 refrigeration system are –10°C and 40°C respectively. Determine per TR basis: (a) mass flow rate; (b) compressor work, (e) condenser heat rejection; (d) C.O.P.; and…

In the LiBr-water system, water is the refrigerant and LiBr the absorber. The lithium bromide solution has a strong affinity for water vapour because of its very low vapour pressure. The lithium bromide-water vapour absorption system is shown in Fig. 19.25. The evaporator and absorber are placed in one shell which operates at the same low…

In the NH3 − H2O vapour absorption system, ammonia is the refrigerant and water is the absorber. An analyser, a rectifier and two heat exchangers are added to the simple vapour absorption system. The complete schematic diagram of ammonia-water absorption system is shown in Fig. 19.24. The functions of various accessories are:

The ideal vapour absorption refrigeration system is shown in Fig. 19.22 Let Qg = heat given to the refrigerant in the generator. Qrc = heat rejected from the condenses to the atmosphere. Qra = heat rejected from the absorber to the atmosphere. Qe = heat absorbed by the refrigerant in the evaporator. Qp = heat added to the refrigerant due to pump work.…

The advantages of vapour absorption system over vapour compression system are listed in Table 19.1.   Table 19.1 Comparison of vapour absorption and vapour compression systems

The schematic diagram of vapour absorption system is shown in Fig. 19.23. It consists of Figure 19.23 Schematic diagram for vapour absorption system 1 Working In the vapour absorption system, the low pressure ammonia vapour leaving the evaporator, enters the absorber where it is absorbed by the cold water in the absorber. The solution of ammonia vapour…

The vapour absorption system uses heat energy instead of mechanical energy in order to change the conditions of the refrigerant required for the operation of the refrigeration cycle. In the vapour absorption system, the compressor is replaced by an absorber, a pump, a generator and a pressure reducing valve. The vapour refrigerant from the evaporator is…

Consider the T-s and p-h diagrams for the vapour compression cycle shown in Fig. 19.20 in which the refrigerant after condensation process 2′−3′, is cooled below the saturation temperature T3′ before throttling process to temperature T3. Such a process is called undercooling or subcooling of the refrigerant. It is generally done along the saturated liquid line. The effect of undercooling is to increase the…

The vapour compression refrigeration cycle with superheated vapour before compression on T-s and p-h diagrams are shown in Fig. 19.18. The evaporation starts at state 4 and continues upto state 1′, when it is dry and saturated. The vapours are now superheated from state 1′ to state 1, where they enter the compressor. Its effect is to increase the COP.…

The discharge (or condenser) pressure pd increases to pd’ due to frictional resistance to flow or refrigerant. The effects of increase in discharge pressure are (Fig. 19.17): Figure 19.17 p-h diagram Thus the COP decreases. The effect of increase in discharge pressure is similar to that of decrease in suction pressure.