Rankine refrigeration cycle

Figure 5.2-3 (a) The Rankine refrigeration cycle, (b) The Rankine refrigeration cycle on T-S and P-H diagrams. 

Vapor-Compression Cycles The most widely used refrigeration principle is vapor compression. Isothermal processes are realized through isobaric evaporation and condensation in the tubes. Standard vapor compression refrigeration cycle (counterclockwise Rankine cycle) is marked in Fig. ll-72a) by 1, 2, 3, 4. 

This is like Illustration 3.7-2 except that the Rankine rather than vapor compression refrigeration cycle is used. Only properties of point 2, and path from 1 — 2 changes. 

Refrigeration cycles can also be implemented in microsystems. The vapor compression cycle, which is the inverse of the Rankine cycle micro steam turbine), consists of compressing a gas and... 

Refrigeration systems are important in industrial and home use when temperatures less than the ambient environment are required. Of the several types of refrigeration systems, the most widely used is the vapor-compression refrigeration cycle. It is essentially a Rankine cycle operated in reverse, where heat is absorbed from a cold reservoir and rejected to a hot reservoir. Due to the constraints of the second law, this process can be accomplished only with a concomitant consumption of power. 

The working fluids, such as ammonia and freons, used in refrigerators and heat pumps are more desirable than steam for the very low-temperature Rankine cycles. The reason is that the specific volume of such working fluids at low temperature is much less than that of steam, so the resulting turbine sizes can be much smaller and less expensive. 

Why are working fluids such as ammonia and freons, used in refrigerators and heat pumps, more desirable than steam for the low-temperature Rankine cycles ... 

Refrigeration is used in trucks, truck/trailers, intermodal containers, railcars, and ships. The majority of refrigerated vehicles fall into one of three refrigeration classifications (/) 0 to 4°C, perishable produce (2) —2 to 0°C, fresh meats and (3) —43 to —17° C, frozen foods. Although the basic principles of the Rankine cycle apply to transport refrigeration, it has unique methods for powering the compression process. 

The same holds true for the Rankine cycle refrigerant pump (P2), operating between the solar hot water tank and the pond (swamp). Because the condenser temperature (swamp temperature) is more or less constant, one need not detect the AT and can just look at the boiler (solar water tank temperature—T2) and keep P2 running whenever the temperature T2 is above 60°C (140°F). The temperature controller TC-2, brings P2 to full speed as the T2 temperature reaches, say, 70°C (160°F). 

Although the T- diagram is very useful for thermodynamic analysis, the pressure enthalpy diagram is used much more in refrigeration practice due to the fact that both evaporation and condensation are isobaric processes so that heat exchanged is equal to enthalpy difference = Ah. For the ideal, isentropic compression, the work could be also presented as enthalpy difference AW = Ah. The vapor compression cycle (Rankine) is presented in Fig. 11-73 inp-h coordinates. 

There are two major types of VOCs recovery refrigerated condensation (Stone 1997) and adsorption, followed by refrigeration (Hussey and Gupta 1997, Kent 1999). Although there are several types of condensation systems the most common adopted is a reverse Rankine cycle where a closed-cycle heat pump with a separate working fluid is used to condense VOCs. Adsorption is a process whereby the VOCs in the air stream are captured physically on the surface of a solid such as carbon. Steam or inert gas is... 

Figure 36.48 shows the layout of a heat-pump dehumidifying kiln. Moist air is drawn over the evaporator and condenser consecutively in a Rankine cycle heat pump. Besides these basic elements such as an evaporator, a condenser with its associated compressor, and expansion valve, there is an accumulator that prevents the refrigerant from entering and damaging the compressor and a subcooling heat exchanger to enhance the effectiveness of the heat pump. 

A schematic of the ideal vapor-compression cycle is shown in Figure 3.9. The left-hand side shows the four unit processes in order an evaporator, a compressor, a condenser, and a valve. Each of the four individual processes operates as an open system at steady-state. States 1, 2, 3, and 4 are labeled. The right-hand side identifies each of these states on a Ts diagram. Unlike in the Rankine cycle, the work required for refrigeration is not represented by the area enclosed on the Ts diagram because the expansion through the valve is irreversible. 

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