Carnot cycle heat pump

The Carnot cycle is a reversible cycle. Reversing the cycle will also reverse the directions of heat and work interactions. The reversed Carnot heat engine cycles are Carnot refrigeration and heat pump cycles. Therefore, a reversed Carnot vapor heat engine is either a Carnot vapor refrigerator or a Carnot vapor heat pump, depending on the function of the cycle. 

The clockwise direction in C corresponds to the clockwise direction in the Carnot cycle, with heat and work input/output as shown in Fig. 4.2. We can similarly envision a reverse Carnot engine ( heat pump ) C, which is obtained by reversing the directions of heat and work arrows and traversing the Carnot cycle in counterclockwise direction ... 

Carnot Refrigerator and Heat Pump Basic Vapor Refrigeration Cycle Actual Vapor Refrigeration Cycle Basic Vapor Heat Pump Cycle Actual Vapor Heat Pump Cycle Working Fluids for Vapor Refrigeration and Heat Pump Systems Cascade and Multistaged Vapor Refrigerators... 

If the Carnot cycle for a heat engine is carried out in the reverse direction, the result will be either a Carnot heat pump or a Carnot refrigerator. Such a cycle is shown in Fig. 1.5. Using the same graphical explanation that was used in the Carnot heat engine, the heat added from the low-temperature reservoir at Tl is area 1-4-5-6-1 g4i is the amount of heat added to the Carnot cycle from a low-temperature thermal reservoir. 

Referring to Fig. 1.5, the system undergoes a Carnot heat pump or Carnot refrigerator cycle in the following manner ... 

In order to achieve the isothermal heat addition and isothermal heat rejection processes, the Carnot simple vapor cycle must operate inside the vapor dome. The T-S diagram of a Carnot cycle operating inside the vapor dome is shown in Fig. 2.2. Saturated water at state 2 is evaporated isothermally to state 3, where it is saturated vapor. The steam enters a turbine at state 3 and expands isentropically, producing work, until state 4 is reached. The vapor-liquid mixture would then be partially condensed isothermally until state 1 is reached. At state 1, a pump would isentropically compress the vapor-liquid mixture to state 2. 

A steam Carnot cycle operates between 250°C and 100°C. Determine the pump work, turbine work, heat added, quality of steam at the exit of the turbine, quality of steam at the inlet of the pump, and cycle efficiency. 

The simple Rankine cycle is inherently efficient. Heat is added and rejected isothermally and, therefore, the ideal Rankine cycle can achieve a high percentage of Carnot cycle efficiency between the same temperatures. Pressure rise in the cycle is accomplished by pumping a liquid, which is an efficient process requiring small work input. The back-work ratio is large. 

The Carnot cycle is not a practical model for vapor power cycles because of cavitation and corrosion problems. The modified Carnot model for vapor power cycles is the basic Rankine cycle, which consists of two isobaric and two isentropic processes. The basic elements of the basic Rankine cycle are pump, boiler, turbine, and condenser. The Rankine cycle is the most popular heat engine to produce commercial power. The thermal cycle efficiency of the basic Rankine cycle can be improved by adding a superheater, regenerating, and reheater, among other means. 

Does the area enclosed by the Carnot heat pump cycle on a T-s diagram represent the network input for the heat pump ... 

Does the Carnot heat pump cycle involve any internal irreversibilities ... 

Suppose a thermally driven heat pump operates at temperatures Th, Tm, and T1. At the high temperature Th, heat Qh is supplied to the heat pump at temperature Tm, heat is generated by the heat pump and at the temperature T1, heat Qi is extracted from a low temperature source. For a Carnot cycle (reversible process) the following relations hold ... 

With the improved C in hand, we can now envision operating the old Carnot cycle as a heat pump C, then coupling this to C as shown in (4.15), using the heat output qh from heat pump C, to drive the improved heat engine C (i.e., with qh = gj ) ... 

Still another contradiction with experience can be deduced from the assumed existence of any C device that falsifies Carnot s principle. Let us again suppose that the old Carnot cycle is operated as a heat pump C, now coupled to the improved C device through the work (w = w ), as follows ... 

Calorimeter, flow, 33-35, 117 Carnot cycle, 141-148, 248-250, 274-276 for power plants, 250 for refrigeration, 275-276 See also Heat engine Heat pump)... 

If the reversed Carnot cycle were coupled to the irreversible machine and driven by it, there would be a net amount of heat <2i Qi > 0 flowing into the reservoir from this coupled machine. There being no net work production, this amount of heat is obtained from the low-temperature reservoir at T2. The coupled machine would be pumping heat from a lower temperature to a higher temperature while producing no other changes in the surroundings. But such a result is impossible by the second law. 

Note that in both the heating and cooling modes, the heat pump in thi.s illustration has a lower coefficient of performance (and therefore lower efficiency) than a reverse Carnot cycle operating between the same temperatures. Finally, it should be mentioned that the thermodynamic properties listed above were obtained from a detailed thennody-naniic properties table for HFC-134a, akin to the steam tables for water in. < ppendix A.Ill values cannot be obtained from Fig. 3.3-4 to this level of accuracy. ffl... 

Two systems ( ) and ("), not necessarily reservoirs, but big systems, can be thermally coupled by a Carnot cycle. This is in practice a heat pump, or if it runs in the reverse direction, a heat engine. In this case, we have S + S" = 0, thus if the systems are big, for one revolution of the Carnot cycle d5 -I- d5" = 0. This constraint does not imply that T = T". Namely, the Carnot engine is an active device that releases or donates energy. In the Carnot engine, the change of entropy S is not directly connected with the change of entropy S", even when the cross balance d5 -F d5" = 0 over a full turn holds. 

Rankine cycle A cycle of operations in a heat engine. The Rankine cycle mote closely approximates to the cycle of a teal steam engine that does the Carnot cycle. It therefore predicts a lower ideal thermal efficiency than the Carnot cycle. In the Rankine cycle (see illustration), heat is added at constant pressure Pi, at which water is converted in a boiler to superheated steam the steam expands at constant entropy to a pressure pz in the cylinder heat is rejected at constant pressure pj in a condenser the water so formed is compressed at constant entropy to pressure p, by a feed pump. The cycle was devised by William Rankine (1820-70). 

The vapor-compression cycle was first used by French engineer Nicolas Leonard Sadi Carnot in 1824. Then in 1832, American inventor Jacob Perkins was the first to demonstrate a compression cooling technology that used ether as a refrigerant. But it was in 1852 that Scottish engineer William Thomson, also known as Lord Kelvin, conceptualized the first heat pump system, dubbed the heat multiplier. ... 

The energy transfers involved in one cycle of a Camot engine are shown sehematieally in Fig. 4.5(a). When the cycle is reversed, as shown in Fig. 4.5(b), the deviee is eaUed a Carnot heat pump. In each cycle of a Carnot heat pump, gh is negative and qc is positive. Since each step of a Carnot engine or Carnot heat pump is a reversible process, neither device is an impossible device. 

We will be able to reach an important conclusion regarding efficiency by considering a Carnot engine operating between the temperatures Tb and Tc, combined with a Carnot heat pump operating between the same two temperatures. The combination is a supersystem, and one cycle of the engine and heat pump is one cycle of the supersystem. We adjust the cycles of the engine and heat pump to produce zero net work for one cycle of the supersystem. 

Reverse reversible Carnot cycle works as a heat pump described in subsection 4.3. In this cycle, comprehended as a thermodynamic, average-value realization, or model of the transfer process in a channel 1C C, wiiich is transferring an (arbitrary) input message x X containing the average information amount H(X), we use these symbols and denotations ... 

A Carnot heat pump is a Carnot heat engine that is driven backwards by another engine. It removes heat from the cool reservoir and exhausts heat into the hot reservoir. Figure 3.3 represents a Carnot heat pump cycle, which is the reverse of the cycle of Figure 3.2. The steps are numbered with a prime ( ) and are numbered in the order in which they occur. Since we are considering the same Carnot engine run backwards,... 

---