Novel compression-injection-absorption thermal coupling type refrigerating system and device

Abstract

The invention discloses a novel compression-injection-absorption thermal coupling type refrigerating system and device, a solution loop between a generator and an absorber is driven by high-temperature waste heat of an outlet of a compressor, and a low-pressure-stage compression function is realized through a solution pump. A compressor is a key component in an electrically-driven compression refrigeration cycle, a two-stage compression refrigeration system is generally adopted in a refrigeration cycle with a lower evaporation temperature in order to reduce the evaporation pressure of a refrigerant and improve the cooling capacity grade, but in the refrigeration cycle, the negative pressure degree of a low-pressure stage is higher, so that the safe and economical operation of the two-stage compression refrigeration system is not facilitated. According to the system and the device, a compression type refrigeration cycle and an absorption type refrigeration cycle are coupled in a cascade serial connection mode through the ejector, and a novel compression-ejection-absorption thermal coupling type refrigeration cycle is constructed; and low-voltage-stage power consumption can be reduced, the operation reliability of low-voltage-stage equipment can be improved, and wide popularization and application prospects are achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of air conditioning heating and ventilation technology, and particularly relates to a compression-ejection-absorption heat coupled refrigeration system and device. BACKGROUND

[0002] According to the form of driving energy, the refrigeration (heat pump) system can be divided into compression type and absorption type. The compression type refrigeration is to improve the pressure of the refrigerant by the compressor to realize the refrigeration cycle. The refrigeration system is composed of a compressor, a condenser (condenser), a refrigeration heat exchanger (evaporator), an expander or a throttling mechanism and some auxiliary equipment. The absorption type refrigeration is to complete the refrigeration cycle by the action of the absorber-generator set, and a binary solution is used as the working medium, in which the low-boiling component is used as the refrigerant, and the high-boiling component is used as the absorbent to complete the working cycle by using the absorption of the refrigerant vapor.

[0003] Unlike the compression type refrigeration system, the absorption type refrigeration technology can be directly driven by low-grade heat energy, and the operating cost is much lower than that of the electric drive system. The absorption type refrigeration system usually uses water-lithium bromide solution, ammonia water solution and other natural working medium as the refrigerant, has the characteristics of environmental friendliness, and has the advantages of safety, noiseless operation, high reliability, etc., but also has the disadvantages of large floor area, high initial investment, high cooling load, low primary energy efficiency, etc. In view of these characteristics, scholars divide the absorption cycle into composite cycles with other non-traditional absorption cycle components, such as "ejection-absorption composite cycle" with ejector, "compression-absorption composite cycle" with compressor, "expansion-absorption composite cycle" with expander, etc. The working principle is to use non-absorption type heat exchange equipment such as ejector, compressor or expander to realize the coupling of energy or mass between cycles, and further expand the utilization range of low-grade energy such as solar energy, geothermal energy or waste heat.

[0004] The compressor is the key component in the electric drive compression refrigeration cycle. In the refrigeration cycle with low evaporation temperature, in order to reduce the evaporation pressure of the refrigerant and improve the cold quantity grade, a two-stage compression refrigeration system is generally used. However, in this refrigeration cycle, the low-pressure stage has a high negative pressure, the size of the low-pressure stage compressor is large, and the mechanical efficiency is low, which is not conducive to the safe and economic operation of the two-stage compression refrigeration system. In view of this problem, the present application innovatively introduces a flash evaporator, a compressor and an ejector into the absorption type refrigeration system by combining the utilization advantages of the composite cycle, couples the compression type refrigeration with the absorption type refrigeration, and proposes a new compression-ejection-absorption heat coupled refrigeration system and device. SUMMARY

[0005] The technical problem to be solved by the present application is: in order to improve the performance of refrigeration cycle and increase the cold quantity grade, the evaporation pressure of refrigerant in the evaporator is generally reduced, but in the refrigeration cycle, the low pressure stage has a high negative pressure degree, the size of the low pressure stage compressor is large, and the mechanical efficiency is low, which is not conducive to the safe and economic operation of the compression refrigeration system. In view of this problem, the present application provides a new compression-ejection-absorption heat coupled refrigeration system and device. The system and device couple the compression refrigeration cycle and the absorption refrigeration cycle in the form of cascade series through the flash evaporator and the ejector, which can not only efficiently utilize the high temperature waste heat of the compressor outlet, but also reduce the power consumption of the low pressure stage, improve the operation reliability of the low pressure stage equipment, and has a wide application prospect.

[0006] The technical problem to be solved by the present application can be solved by the following technical scheme: a new compression-ejection-absorption heat coupled refrigeration system, which comprises a solution loop, a compression refrigeration cycle and an absorption refrigeration cycle. The absorption refrigeration cycle is composed of an absorber, a refrigerant pump, a solution pump, a heat exchanger and a generator, and the solution flows in series. In the compression refrigeration cycle, the gaseous working medium after the compressor drives the refrigerant working medium generated by the ejector through the generator to directly drive the solution loop between the generator and the absorber, and the heat acts as the driving heat source of the absorption refrigeration cycle. In the absorption refrigeration cycle, the liquid phase refrigerant is reduced to a negative pressure state, and the condensation-generator heat coupling and the solution pump are used to realize the pressure rise of the refrigerant. The compression refrigeration cycle and the absorption refrigeration cycle are coupled in the form of cascade series by using the ejector to realize the coupling of heat and quality between the compression refrigeration cycle and the absorption refrigeration cycle.

[0007] Further, the refrigerant and the absorbent in the solution loop realize the compression and pressure rise of the refrigerant through the four processes of dilution, pressure rise, concentration and throttling.

[0008] Further, the evaporator and the refrigerant pump in the absorption refrigeration cycle constitute a recirculating spray loop, the liquid refrigerant not evaporated at the bottom of the evaporator is sucked out by the refrigerant pump and sprayed on the surface of the heat exchange pipe of the evaporator through the liquid distributor, the liquid refrigerant absorbs the waste heat in the cooling water to form low pressure saturated gaseous working medium which is sent into the absorber to be sprayed and absorbed with the concentrated solution, and the liquid working medium not evaporated is continuously driven by the refrigerant pump to realize liquid circulation.

[0009] Further, the compression refrigeration cycle is composed of a compressor, an ejector, a generator, a low temperature condenser and a flash evaporator; the gaseous working medium in the flash evaporator is pressurized by the compressor to become high temperature and high pressure working medium, and the refrigerant working medium generated by the ejector through the generator improves the thermal energy grade of the working medium at the outlet of the generator to heat the generator of the absorption refrigeration cycle.

[0010] Furthermore, the driving working fluid of the ejector is a high-temperature and high-pressure superheated working fluid output from the compressor, and the ejector working fluid is a saturated gaseous working fluid. During the operation of the ejector, heat and mass transfer in the phase change zone are avoided, thereby improving the reliability of the ejector operation.

[0011] Furthermore, a buffer chamber is set at the generator outlet to store the refrigerant after it absorbs heat and separates into a saturated gaseous working fluid. A water seal device is set between the buffer chamber and the liquid phase water chamber of the flash evaporator to allow the liquid refrigerant at the bottom of the buffer chamber to flow back into the flash evaporator and recover the refrigerant working fluid.

[0012] Furthermore, the refrigerant that releases heat from the generator is subcooled by the low-temperature condenser, which reduces the enthalpy of the refrigerant at the inlet of the flash evaporator and increases the heat absorbed by the refrigerant in the flash evaporator.

[0013] On the other hand, the present invention also provides a novel compression-ejection-absorption thermal coupling refrigeration device, which includes an evaporator, an absorber, a refrigerant pump, a solution pump, a heat exchanger, a generator, a buffer chamber, an ejector, a low-temperature condenser, a flash evaporator, and a compressor. The dilute solution flowing out from the bottom of the absorber is pressurized by a solution pump, heated by a heat exchanger, and then sent to the generator. It is concentrated into a concentrated solution and collected at the bottom of the generator. The low-boiling-point refrigerant in the dilute solution absorbs heat and separates into saturated gaseous working fluid refrigerant vapor, which is stored in a buffer chamber. After being cooled by a heat exchanger, the concentrated solution is directly sprayed onto the heat exchange tube bundle of the absorber. The concentrated solution absorbs the refrigerant vapor generated by the evaporator and is diluted into a dilute solution. The heat released during the dilution process is carried away by cooling water. The gaseous working fluid in the flash evaporator is heated and pressurized by the high-pressure stage compressor and then used as the driving gas source for the ejector to inject the refrigerant vapor in the buffer chamber. After being pressurized and heated, it becomes the driving heat source for the generator. After being initially cooled in the generator, it is sent to the low-temperature condenser to be condensed into liquid refrigerant. The liquid refrigerant enters the flash evaporator as a two-phase gas-liquid mixture through the high-pressure throttling valve to achieve gas-liquid separation and complete the working fluid cycle of compression refrigeration. After the liquid working fluid in the flash evaporator enters the evaporator, it is pressurized by the refrigerant pump and then sprayed onto the surface of the heat exchange tubes by the liquid distributor. The liquid refrigerant absorbs the low-temperature heat of the cooling water to form a low-pressure saturated gaseous working fluid, which is sent into the absorber and sprayed with the concentrated solution for absorption. The temperature of the cooling water is reduced and used for air conditioning refrigeration, realizing an absorption refrigeration cycle.

[0014] The beneficial effects of this invention are: (1) The compression function of the low-pressure stage is realized by the solution pump, which can effectively solve the problems of large size and low mechanical efficiency of the low-pressure stage negative pressure compressor and improve the reliability of system operation; (2) The compression heat of the compression refrigeration cycle drives the solution loop between the generator and the absorber, and the compression heat is efficiently utilized in the cycle through internal thermal coupling; (3) The high-temperature and high-pressure superheated working fluid at the compressor outlet is used to entrain the medium-temperature and medium-pressure saturated gaseous working fluid in the buffer chamber. The working fluid is then mixed with medium-high temperature and medium-high pressure superheated working fluid through pressure matching as the driving heat source of the generator, thereby improving the heat energy utilization rate of the latent heat of vaporization of the saturated gaseous working fluid at the generator outlet. (4) By utilizing the gas-liquid separation principle of flash evaporator, the compressor inlet is a gaseous working fluid with high dryness and the enthalpy value of liquid working fluid at the evaporator inlet is effectively reduced, thereby improving the operating reliability of the compressor and increasing the heat absorption of refrigerant in the evaporator. Attached Figure Description

[0015] Figure 1 This is a process flow diagram of the novel compression-ejection-absorption thermal coupling refrigeration system of the present invention; In the diagram: 1. Evaporator, 2. Absorber, 3. Refrigerant pump, 4. Solution pump, 5. Heat exchanger, 6. Generator, 7. Buffer chamber, 8. Ejector, 9. Low-temperature condenser, 10. Flash evaporator, 11. Compressor, 12. High-pressure throttle valve, 13. Low-pressure throttle valve, 14. Water seal throttle valve, 15. Water seal device, 16. Concentrated solution throttle valve. Detailed Implementation

[0016] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. The present invention is more suitable for use in double-effect and multi-effect absorption refrigeration cycles. In order to illustrate the principle of the patent, the present invention only uses the simplest single-effect system as an embodiment. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] like Figure 1 As shown, this invention can be widely applied in urban residential areas with limited waste heat resources, reducing the heat island effect caused by summer cooling, improving refrigeration cycle performance, and increasing cooling capacity. This invention mainly consists of a solution loop and two refrigerant cycles, namely a bottom cycle and a top cycle. The top and bottom cycles are mainly coupled by a flash evaporator 10 and an ejector 8 to achieve dual energy and mass coupling between the cycles.

[0018] The solution circuit consists of absorber 2, refrigerant pump 3, solution pump 4, heat exchanger 5, generator 6, and concentrated solution throttling valve 16. The solution flows in series. The diluted solution accumulates at the bottom of absorber 2. After being pressurized by solution pump 4, it is preheated by heat exchanger 5 and then sprayed onto the tube bank in generator 6. The low-boiling-point refrigerant in the dilute solution absorbs heat and separates into saturated gaseous working fluid. After passing through the filter membrane between generator 6 and buffer chamber 7, it is stored in buffer chamber 7. The dilute solution is concentrated into concentrated solution and collects at the bottom of generator 6. After being cooled by heat exchanger 5, the concentrated solution is throttled and depressurized and then sprayed onto the condenser tube bank of absorber 2 to absorb low-pressure saturated vapor and dilute into dilute solution. Refrigerant pump 3 is a recirculation pump for the liquid phase in evaporator. In order to improve the heat absorption intensity of refrigerant in evaporator, the refrigerant pump lifts the liquid phase condensed at the bottom of evaporator to the top and sprays it onto the evaporator spray pipe. In the solution circuit, the refrigerant and absorbent achieve refrigerant compression and pressure increase through four processes: dilution, pressurization, concentration, and throttling.

[0019] The bottom circulation is primarily an absorption refrigerant loop, consisting of a flash evaporator 10, a low-pressure throttling valve 13, an evaporator 1, an absorber 2, a solution pump 4, a heat exchanger 5, a generator 6, and a buffer chamber 7. The liquid refrigerant separated from the gas in the flash evaporator 10 is throttled and depressurized to a negative pressure state by the low-pressure throttling valve 13 (the evaporator and absorber are evacuated to a high vacuum state by a vacuum pump or other vacuum equipment to create the necessary conditions for the boiling of the low-temperature refrigerant), and then enters the evaporator 1 to absorb residual heat from the cooling water, thereby producing low-temperature chilled water. To improve the low-vacuum heat absorption capacity of the evaporator 1, a recirculation spray circuit is set up. The refrigerant pump 3 draws out the unevaporated liquid refrigerant from the bottom of the evaporator 1 and sprays it onto the surface of the heat exchange tubes of the evaporator 1 through a distributor. After absorbing residual heat from the cooling water, the liquid refrigerant forms a low-pressure saturated gaseous working fluid, which is sent to the absorber 2 for spray absorption with the concentrated solution. The unevaporated liquid working fluid continues to circulate under the drive of the refrigerant pump 3. The solution loop is the absorbent loop of the absorption cycle. The bottom loop and the solution loop together form a medium-pressure absorption refrigeration cycle system, which enables the low-temperature refrigerant to be safely and efficiently raised from a negative pressure state to a medium-pressure and medium-temperature state.

[0020] The top cycle consists of a flash evaporator 10, a compressor 11, an ejector 8, a generator 6, a cryogenic condenser 9, and a high-pressure throttling valve 12. The gaseous working fluid separated in the flash evaporator 10 is pressurized by the compressor 11 to a high temperature and high pressure. This high temperature working fluid then passes through the ejector 8 and rolls over the saturated gaseous refrigerant stored in the buffer chamber 7, increasing the thermal energy grade of the working fluid at the generator 6 outlet. The mixed medium-high temperature working fluid then heats the generator 6 in the bottom cycle, allowing the heat from the top cycle to act as the driving heat source for the bottom cycle. This efficient utilization of heat through thermal coupling within the cycle improves the refrigeration system's cycle performance. The refrigerant released heat by the generator 6 is subcooled by the cryogenic condenser 9, reducing the enthalpy of the refrigerant at the inlet of the flash evaporator 10 and increasing the heat absorbed by the refrigerant within the flash evaporator.

[0021] To improve the refrigerant recovery rate, a buffer chamber 7 is installed at the outlet of generator 6. A water seal device 15 is installed between the buffer chamber 7 and the liquid phase water chamber of flash evaporator 10, so that the liquid refrigerant at the bottom of the buffer chamber 7 can be effectively returned to flash evaporator 10.

[0022] The working principle and process of this invention are as follows: The basic principle of the novel compression-ejection-absorption thermally coupled refrigeration system and device proposed in this invention is as follows: A flash evaporator 10 is added between the condenser 9 and the evaporator 1. Through the gas-liquid separation effect of the flash evaporator 10, the refrigeration cycle structure is separated into a top cycle with a gaseous working fluid and a bottom cycle with a liquid working fluid. The bottom cycle is a typical absorption refrigeration cycle. To improve the quality of refrigeration capacity, the refrigerant in the evaporator 1 is in a high vacuum state, and the negative pressure refrigerant is pressurized through an absorption solution loop. The top cycle is a typical compression refrigeration cycle. To better utilize the high-temperature waste heat at the outlet of the compressor 11, the working fluid at the outlet of the compressor 11 is used to heat the generator of the bottom cycle. Through condensation-generation coupling, the heat of the top cycle acts as the driving heat source for the bottom cycle, and the heat is efficiently utilized through thermal coupling in the cycle. In addition, an ejector 8 is introduced between the top and bottom circulation loops to organically overlap the two circulation structures, thereby achieving coupling between the heat and mass of the compression and absorption cycles. The high-temperature and high-pressure working fluid at the outlet of the compressor 11 is used to eject the saturated gaseous working fluid at the outlet of the generator 6, which improves the heat energy grade of the working fluid at the outlet of the generator 6 and increases the circulation performance of the refrigeration system by more than 20%. Furthermore, the working fluid in the ejector 8 can effectively avoid heat and mass transfer in the phase change zone, thereby improving the reliability of the system operation.

[0023] The present invention proposes a novel compression-ejection-absorption heat-coupled refrigeration system and device, the working process of which can be summarized as follows: (1) The solution flows in series, that is, the solution flowing out of the absorber 2 is pressurized by the solution pump 4, heated by the heat exchanger 5 and then sent to the generator 6. The dilute solution is concentrated by high temperature preheating of the compression refrigeration cycle and then the concentrated solution and refrigerant vapor are separated. (2) The concentrated solution is cooled by the heat exchanger 5 and then sprayed directly onto the heat exchange tube bundle of the absorber 2. The concentrated solution absorbs the refrigerant vapor generated by the evaporator 1 and is diluted into a dilute solution. The heat released during the dilution process is carried away by the cooling water. (3) The refrigerant vapor is stored in the buffer chamber 7. After being injected by the ejector 8 to increase the pressure and temperature, it is used as the driving heat source of the generator. After being initially cooled in the generator 6, it is sent to the low-temperature condenser 9 to be condensed into liquid refrigerant. The liquid refrigerant first enters the flash evaporator in two phases (gas and liquid) through the high-pressure throttling valve 12 to achieve gas-liquid separation. (4) After the gaseous working fluid is heated and pressurized by the high-pressure stage compressor 11, it serves as the driving gas source for the ejector 8, which injects the medium-pressure refrigerant vapor in the buffer chamber 7 to complete the top working fluid circulation. (5) After the liquid working fluid enters the evaporator 1, it is pressurized by the refrigerant pump 3 and sprayed onto the surface of the heat exchange tube by the liquid distributor. The liquid refrigerant absorbs the low-temperature heat of the cooling water to form a low-pressure saturated gaseous working fluid, which is sent into the absorber 2 and sprayed with concentrated solution for absorption. At the same time, the cooling water temperature drops to form low-temperature cold water of 5~7℃, which is used for air conditioning refrigeration to achieve the refrigeration cycle target.

[0024] The above embodiments are used to explain and illustrate the present invention, but not to limit the present invention. Any modifications and changes made to the present invention within the spirit and scope of the claims shall fall within the protection scope of the present invention.

Claims

1. A novel compression-ejection-absorption thermally coupled refrigeration system, characterized in that: The system includes a solution circuit, a compression refrigeration cycle, and an absorption refrigeration cycle; The system consists of an absorber, a refrigerant pump, a solution pump, a heat exchanger, and a generator, with the solution flowing in a series flow. In the compression refrigeration cycle, the gaseous working fluid, after passing through the compressor, is directly driven by the refrigerant working fluid generated by the ejector and the generator, which drives the solution circuit between the generator and the absorber. The heat serves as the driving heat source for the absorption refrigeration cycle. In the absorption refrigeration cycle, the liquid refrigerant is depressurized to a negative pressure state, and the refrigerant pressure is increased by condensation-generation thermal coupling and a solution pump. The compression refrigeration cycle and the absorption refrigeration cycle are coupled in a superimposed series configuration using ejectors, thereby achieving coupling between heat and mass in the compression refrigeration cycle and the absorption refrigeration cycle.

2. The novel compression-ejection-absorption thermal coupling refrigeration system according to claim 1, characterized in that: In the solution circuit, the refrigerant and absorbent achieve refrigerant compression and pressure increase through four processes: dilution, pressurization, concentration, and throttling.

3. The novel compression-ejection-absorption thermal coupling refrigeration system according to claim 1, characterized in that: In an absorption refrigeration cycle, the evaporator and refrigerant pump form a recirculation spray circuit. The refrigerant pump draws out the unevaporated liquid refrigerant from the bottom of the evaporator and sprays it onto the surface of the heat exchange tubes of the evaporator through a liquid distributor. After absorbing the residual heat from the cooling water, the liquid refrigerant forms a low-pressure saturated gaseous working fluid, which is sent into the absorber and sprayed with the concentrated solution for absorption. The unevaporated liquid working fluid continues to be driven by the refrigerant pump to achieve liquid circulation.

4. The novel compression-ejection-absorption thermal coupling refrigeration system according to claim 1, characterized in that: The compression refrigeration cycle consists of a compressor, an ejector, a generator, a cryogenic condenser, and a flash evaporator. The gaseous working fluid in the flash evaporator is pressurized by the compressor into a high-temperature and high-pressure working fluid, which is then passed through the ejector to generate the refrigerant working fluid from the generator, thereby increasing the heat energy grade of the working fluid at the generator outlet and heating the generator of the absorption refrigeration cycle.

5. A novel compression-ejection-absorption thermal coupling refrigeration system according to claim 1, characterized in that: The driving working fluid of the ejector is a high-temperature and high-pressure superheated working fluid output from the compressor, and the ejector working fluid is a saturated gaseous working fluid. During the operation of the ejector, heat and mass transfer in the phase change zone are avoided, which improves the reliability of the ejector operation.

6. A novel compression-ejection-absorption thermal coupling refrigeration system according to claim 1, characterized in that: A buffer chamber is set at the generator outlet to store the refrigerant. After the refrigerant absorbs heat, it separates into a saturated gaseous working fluid. A water seal device is set between the buffer chamber and the liquid phase water chamber of the flash evaporator to allow the liquid refrigerant at the bottom of the buffer chamber to flow back into the flash evaporator and recover the refrigerant working fluid.

7. A novel compression-ejection-absorption thermal coupling refrigeration system according to claim 1, characterized in that: The refrigerant that releases heat in the generator is subcooled by the low-temperature condenser, which reduces the enthalpy of the refrigerant at the inlet of the flash evaporator and increases the heat absorbed by the refrigerant in the flash evaporator.

8. A novel compression-ejection-absorption thermal coupling refrigeration device, characterized in that: The device includes an evaporator (1), an absorber (2), a refrigerant pump (3), a solution pump (4), a heat exchanger (5), a generator (6), a buffer chamber (7), an ejector (8), a low-temperature condenser (9), a flash evaporator (10), and a compressor (11). The dilute solution flowing out from the bottom of the absorber (2) is pressurized by the solution pump (4), heated by the heat exchanger (5), and then sent to the generator (6) to be concentrated into a concentrated solution that is collected at the bottom of the generator (6). The low-boiling-point refrigerant in the dilute solution absorbs heat and separates into saturated gaseous working fluid refrigerant vapor, which is stored in the buffer chamber (7). After being cooled by the heat exchanger (5), the concentrated solution is directly sprayed onto the heat exchange tube bundle of the absorber (2). The concentrated solution absorbs the refrigerant vapor generated by the evaporator (1) and is diluted into a dilute solution. The heat released during the dilution process is carried away by the cooling water. The gaseous working fluid in the flash evaporator (10) is heated and pressurized by the high-pressure stage compressor (11) and used as the driving gas source of the ejector (8). It ejects the refrigerant vapor in the buffer chamber (7), and after being pressurized and heated, it is used as the driving heat source of the generator (6). After being initially cooled in the generator (6), it is sent to the low-temperature condenser (9) to be condensed into liquid refrigerant. The liquid refrigerant enters the flash evaporator (10) in two phases (gas and liquid) through the high-pressure throttling valve to achieve gas-liquid separation and complete the working fluid cycle of compression refrigeration. After the liquid working fluid in the flash evaporator (10) enters the evaporator (1), it is pressurized by the refrigerant pump (3) and sprayed onto the surface of the heat exchange tube by the liquid distributor. The liquid refrigerant absorbs the low-temperature heat of the cooling water to form a low-pressure saturated gaseous working fluid, which is sent into the absorber (2) and sprayed with concentrated solution for absorption. The temperature of the cooling water is reduced and used for air conditioning refrigeration to realize the absorption refrigeration cycle.

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