An ejector-enhanced double-condenser heat pump drying system and control method for material drying

Abstract

The present invention discloses an ejector-assisted dual-condenser heat pump drying system and control method for material drying. The system comprises an air circulation loop and a refrigerant circulation loop. In the air circulation loop, wet air at the drying oven outlet is cooled and dehumidified by an evaporator, then passes through low-pressure and high-pressure condensers in sequence, heated to high-temperature dry air, enters the drying oven for heat and moisture exchange, dries the material, and simultaneously becomes wet air for recirculation. The refrigerant circulation loop comprises a variable-frequency compressor, a high-pressure condenser, an ejector, a low-pressure condenser, two electronic expansion valves, a flash evaporator, a subcooler, an evaporator, and temperature and pressure sensors. The present invention introduces an ejector to recover expansion work, reducing irreversible losses in the throttling process and improving the efficiency of the heat pump drying system. The flash evaporator and subcooler increase the subcooling of the refrigerant before the evaporator, improving the dehumidification capacity of the evaporator. The heat recovery effect of the subcooler prevents liquid from being sucked into the compressor, thereby enhancing system stability.

Description

Technical Field

[0001] The present invention belongs to the field of heat pump drying technology and dehumidification technology, and particularly relates to an ejector-enhanced double-condenser heat pump drying system for material drying and a control method thereof, which are used in an air source heat pump device. Background Art

[0002] Drying technology is involved in all areas of the national economy, but it is a highly energy-intensive application technology, accounting for approximately 12% of the total national energy consumption. Currently, commonly used drying technologies include hot air drying, microwave drying, infrared drying, vacuum freeze drying, and heat pump drying. Heat pump drying technology, a key component of my country's industrial and agricultural product processing sectors, has become a highly sought-after material drying method due to its high efficiency, energy conservation, low pollution, high moisture extraction rate, low investment cost, and high drying quality. It holds great promise for development and application.

[0003] In order to optimize the performance of heat pump drying systems to respond to the rapid development of the heat pump drying market, improve system energy efficiency, and enhance system stability, researchers have conducted many experiments and improvements over the past decade. Among them, compressor frequency conversion technology has received attention and application. However, current heat pump drying technology still faces certain technical limitations. The most common heat pump drying systems on the market today have problems such as slow drying rate and low drying temperature. Because only a throttling expansion mechanism is used to throttle the refrigerant, the pressure difference before and after throttling is large, resulting in increased irreversible losses in the refrigerant cycle process and low system efficiency. In particular, when the drying temperature requirement is high, the efficiency of the heat pump drying system is significantly reduced. Secondly, there is the problem of liquid in the suction pipe of the compressor, which is prone to wet compression and liquid hammer, all of which are not conducive to the stable operation of the compressor. Therefore, the development of high-efficiency and energy-saving heat pump drying devices is an important task in the drying field and an important development direction of heat pump drying technology. Summary of the Invention

[0004] To address the problems and shortcomings of the aforementioned prior art, the present invention provides an ejector-enhanced dual-condenser heat pump drying system and control method for material drying. The system incorporates an ejector to recover expansion work, reducing the irreversible losses associated with the throttling process in a throttling expansion mechanism, significantly improving the efficiency of the heat pump drying system. The flash evaporator and subcooler increase the subcooling of the refrigerant before the dehumidification evaporator, enhancing the evaporator's cooling and dehumidification capabilities. The subcooler's heat recovery prevents liquid carryover from the variable-frequency compressor, enhancing system stability. Furthermore, through two condensation processes, high-pressure and low-pressure condensation, the average condensation temperature is lowered, improving system energy efficiency. The dry cold air first exchanges heat with the low-pressure condenser. After a primary temperature increase, it enters the high-pressure condenser for a secondary temperature increase. The stepwise temperature increase of the air side by the high- and low-pressure condensers reduces the average heat exchange temperature difference between the air and the refrigerant, thereby reducing irreversible losses in the condensation heat exchange process and comprehensively improving system efficiency. In addition, the refrigerant flow in the refrigeration system is controlled by detecting the refrigerant state at the outlet of the low-pressure condenser and the refrigerant state at the suction port of the variable frequency compressor.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] An ejector-enhanced double-condenser heat pump drying system for material drying includes an air circulation loop and a refrigerant circulation loop, wherein the refrigerant circulation loop is equipped with a variable frequency compressor 101, which has a variable speed function. The speed of the variable frequency compressor 101 is controlled by changing the motor frequency, thereby adjusting the mass flow rate of the refrigerant in the refrigeration circulation loop; the variable frequency compressor 101 has an air intake and an exhaust port, and the exhaust port of the variable frequency compressor 101 is connected to the inlet of the high-pressure condenser 102. The air is compressed by the variable frequency compressor 101 to increase the temperature and pressure. The high-temperature refrigerant vapor after the condensation enters the high-pressure condenser 102, where the refrigerant exchanges heat with the dry air, causing the refrigerant to be partially condensed; the gas-liquid two-phase refrigerant at the outlet of the high-pressure condenser 102 enters the nozzle inlet of the ejector 103 as a primary flow, and the outlet of the ejector 103 is connected to the inlet of the low-pressure condenser 104. The two-phase refrigerant is completely condensed in the low-pressure condenser 104, and the saturated liquid refrigerant at the outlet of the low-pressure condenser 104 enters the first electronic expansion valve 105. After the isenthalpic throttling process, the two-phase refrigerant is discharged from the first electronic expansion valve 105. The saturated gas phase refrigerant enters the inlet of the flash evaporator 106 at the outlet, where the saturated gas phase refrigerant is injected into the secondary flow inlet of the ejector 103 as a secondary fluid, and the saturated liquid phase refrigerant enters the hot end inlet of the subcooler 107. The cooled refrigerant enters the inlet of the second electronic expansion valve 108 and undergoes an isenthalpic throttling process. The outlet of the second electronic expansion valve 108 is connected to the inlet of the dehumidification evaporator 109. The gas-liquid two-phase refrigerant exchanges heat with the high-humidity air from the drying box in the dehumidification evaporator 109 and evaporates completely after absorbing heat. The saturated gas phase refrigerant at the outlet of the dehumidification evaporator 109 enters The cold end inlet of the subcooler 107 enters the air inlet of the variable frequency compressor 101 after heat recovery, completing the refrigerant circulation of the refrigerant circulation loop; in the air circulation loop, the high-humidity humid air passing through the drying box first passes through the dehumidification evaporator 109, and the temperature and humidity are reduced to form dry cold air. The dry cold air exchanges heat with the refrigerant through the low-pressure condenser 104 for the first temperature increase, and then passes through the high-pressure condenser 102 for heat exchange with the refrigerant for the second temperature increase, forming high-temperature dry air that enters the drying box inlet, completing the air circulation of the air circulation loop.

[0007] In the ejector 103, the partially condensed gas-liquid two-phase mixed refrigerant from the high-pressure condenser 102 serves as the primary fluid of the ejector 103, and its pressure is higher than the secondary fluid from the gas phase outlet of the flash evaporator 106, that is, the pressure of the ejected fluid, and the high-pressure condenser 102 realizes partial condensation of the exhaust gas of the variable frequency compressor 101, so its outlet refrigerant is a gas-liquid two-phase flow with a higher enthalpy value, which improves the ability of the ejector 103 to recover expansion work; the gas phase outlet in the flash evaporator 106 is saturated gas-phase refrigerant, which is ejected by the gas-liquid two-phase refrigerant and enters the mixing section of the ejector 103 for isobaric mixing, and enters the low-pressure condenser 104 after being decelerated and pressurized in the diffuser section of the ejector 103.

[0008] The superheated refrigerant vapor discharged from the variable frequency compressor 101 is condensed in a cascade manner in the high-pressure condenser 102 and the low-pressure condenser 104. The refrigerant at the outlet of the high-pressure condenser 102 is in a gas-liquid two-phase state, and the refrigerant at the outlet of the low-pressure condenser 104 is in a saturated liquid phase. An ejector 103 is added between the high-pressure and low-pressure condensers to effectively recover the expansion work, and through the two condensation processes of high-pressure condensation and low-pressure condensation, the average condensation temperature is reduced, thereby improving the energy efficiency of the system. The dry cold air first exchanges heat with the low-pressure condenser 104, and after being heated once, it enters the high-pressure condenser 102 for a second heating. The setting of step-by-step heating of the air side through the high-pressure and low-pressure condensers reduces the average heat exchange temperature difference between the air and the refrigerant, thereby reducing the irreversible loss of the condensation heat exchange process and comprehensively improving the system efficiency.

[0009] The gas-liquid two-phase refrigerant from the first electronic expansion valve 105 enters the flash evaporator 106, wherein the gas-phase refrigerant provides the secondary fluid of the ejector 103, and the liquid-phase refrigerant is supercooled in the subcooler 107 and throttled by the second electronic expansion valve 108 before entering the dehumidification evaporator 109. The flash evaporator 106 effectively reduces the refrigerant inlet temperature before the second electronic expansion valve 108, so that the dryness of the refrigerant passing through the second electronic expansion valve 108 is reduced, thereby increasing the unit cooling capacity of the refrigerant, and the subcooler 107 provides a subcooling effect. The unit cooling capacity is further increased, and the cooling and dehumidification capacity of the dehumidification evaporator 109 is improved. Due to the existence of supercooling, the refrigerant maintains a stable state before entering the second electronic expansion valve 108, thereby enhancing the stability of the system. At the same time, after the heat exchange at the cold end of the subcooler 107, the refrigerant entering the inlet of the variable frequency compressor 101 obtains superheat. The heat recovery effect of the subcooler 107 is utilized to avoid the variable frequency compressor 101 from inhaling liquid, thereby protecting the variable frequency compressor 101 and further improving the stability of the system.

[0010] The working method of the ejector-enhanced double-condenser heat pump drying system for material drying is as follows: the high-temperature and high-pressure superheated vapor refrigerant at the exhaust port of the variable frequency compressor 101 enters the high-pressure condenser 102 and exchanges heat with the preheated dry air, so that the high-temperature dry air obtains the drying and dehumidifying capacity; the superheated refrigerant partially condenses after releasing heat to form a gas-liquid two-phase mixed refrigerant with high enthalpy value, and then enters the nozzle inlet of the ejector 103 as a primary fluid, and becomes a low-pressure and high-pressure mixed refrigerant after expanding in the nozzle. The high-speed gas-liquid two-phase mixed refrigerant is isobarically mixed with the saturated gas-phase refrigerant from the gas-phase outlet of the flash evaporator 106 in the mixing section of the ejector 103, and then decelerated and pressurized in the expansion section of the ejector 103 before entering the low-pressure condenser 104 as a gas-liquid two-phase refrigerant to preheat the dry cold air from the dehumidification evaporator 109. In this process, the refrigerant is completely condensed, and the saturated liquid-phase refrigerant enters the first electronic expansion valve 105. After the isenthalpic throttling process, a gas-liquid two-phase refrigerant is formed and enters the flash evaporator 106, where the saturated gas-phase refrigerant is used as the second phase refrigerant. The secondary fluid is injected into the ejector 103, and the saturated liquid refrigerant enters the hot end inlet of the subcooler 107, and is heat-recovered with the saturated gas refrigerant at the outlet of the dehumidification evaporator 109. The refrigerant obtains subcooling in the subcooler 107, enters the second electronic expansion valve 108, and forms a gas-liquid two-phase refrigerant after the isenthalpic throttling process, enters the dehumidification evaporator 109 to absorb heat to form a saturated gas refrigerant, cools and dehumidifies the high-humidity air from the drying box, and then enters the cold end inlet of the subcooler 107, which is the saturated liquid refrigerant from the flash evaporator 106. The refrigerant provides subcooling, obtains superheat itself and then returns to the suction port of the variable frequency compressor 101; by introducing the ejector 103, the expansion work is recovered, and the irreversible loss of the throttling process in the throttling expansion mechanism is reduced, thereby significantly improving the efficiency of the heat pump drying system. The flash evaporator 106 and the subcooler 107 increase the subcooling of the refrigerant before the dehumidification evaporator 109, and improve the cooling and dehumidification capacity of the dehumidification evaporator 109. At the same time, the heat recovery effect of the subcooler 107 avoids liquid in the suction of the variable frequency compressor 101, thereby enhancing the stability of the system.

[0011] The control method of the ejector-enhanced dual-condenser heat pump drying system for material drying is to set a temperature sensor and a pressure sensor at the outlet of the low-pressure condenser 104 to obtain the temperature T of the refrigerant at the outlet of the low-pressure condenser. ro1 , the refrigerant pressure P at the outlet of the low-pressure condenser ro1 ; Set a temperature sensor and a pressure sensor at the suction port of the compressor 101 to obtain the refrigerant temperature T at the suction port of the compressor ric , refrigerant pressure P at the compressor suction port ric ; Set a temperature sensor at the outlet of the drying box to obtain the high humidity air temperature T at the outlet of the drying box aod; Using the refrigerant temperature and pressure at the outlet of the low-pressure condenser 104, it is determined according to the thermophysical property equation of the refrigerant whether the refrigerant here is in a saturated liquid state, so as to regulate the opening of the first electronic expansion valve 105; using the refrigerant temperature and pressure at the air intake of the variable frequency compressor 101, it is determined according to the thermophysical property equation of the refrigerant to regulate the superheat of the refrigerant here, so as to regulate the opening of the second electronic expansion valve 108; the high humidity air temperature coming out of the drying box is used to control the speed of the variable frequency compressor 101; the first electronic expansion valve 105 achieves the purpose of controlling the refrigerant flow rate by detecting the refrigerant temperature and pressure parameters at the outlet of the low-pressure condenser 104, and the second electronic expansion valve 108 achieves the purpose of controlling the refrigerant flow rate by detecting the superheat of the refrigerant at the air intake of the variable frequency compressor 101.

[0012] The control method of the ejector-assisted double-condenser heat pump drying system for material drying is specifically implemented as follows: when the high-humidity air temperature T at the outlet of the drying box is detected aod Lower than the preset temperature T aods When the high humidity air temperature T at the drying box outlet is detected, the variable frequency compressor 101 is controlled to increase the speed; aod Higher than the preset temperature T aods When the refrigerant temperature T at the outlet of the low-pressure condenser is detected, the variable frequency compressor 101 is controlled to reduce the speed; ro1 Lower than the calculated refrigerant pressure P at the outlet of the low-pressure condenser ro1 The saturated liquid refrigerant temperature under the same conditions is the preset temperature value T ro1s When the temperature T of the refrigerant at the outlet of the low-pressure condenser is detected, the opening of the first electronic expansion valve 105 is increased; ro1 Higher than the calculated refrigerant pressure P at the low-pressure condenser outlet ro1 The saturated liquid refrigerant temperature under the same conditions is the preset temperature value T ro1s When the opening of the first electronic expansion valve 105 is reduced; when the superheat ΔT of the refrigerant at the suction port of the compressor 101 is detected and calculated ric Higher than the preset superheat value ΔT rics When the opening of the second electronic expansion valve 108 is increased; when the superheat ΔT of the refrigerant at the suction port of the compressor 101 is detected and calculated ric Lower than the preset superheat value ΔT rics , the opening of the second electronic expansion valve 108 is reduced.

[0013] Compared with the existing single-stage compression heat pump drying system, the present invention proposes an ejector-enhanced double-condenser heat pump drying system and control method for material drying, which introduces an ejector 103 into the refrigerant circulation loop, and uses the ejector 103 to realize the gas-liquid two-phase refrigerant at the outlet of the high-pressure condenser 102 to eject the refrigerant vapor from the gas phase outlet of the flash evaporator 106, converting the working capacity of the high-pressure refrigerant into the ejection and pressure increase of the secondary fluid, reducing the irreversible loss of the system and effectively improving the energy efficiency of the heat pump drying system; the flash evaporator 106 effectively reduces the refrigerant inlet temperature before the second electronic expansion valve 108, so that the refrigerant vapor passing through the second electronic expansion valve 108 is effectively cooled. The dryness of the refrigerant in valve 108 is reduced, which increases the unit cooling capacity of the refrigerant. The subcooler 107 provides a subcooling effect, further increasing the unit cooling capacity and improving the cooling and dehumidification capacity of the dehumidification evaporator 109. Due to the existence of subcooling, the refrigerant remains in a stable state before entering the second electronic expansion valve 108, thereby enhancing the stability of the system. At the same time, after heat exchange at the cold end of the subcooler 107, the refrigerant entering the inlet of the variable frequency compressor 101 obtains superheat. The heat recovery effect of the subcooler 107 is used to avoid the variable frequency compressor 101 from inhaling liquid, thereby protecting the variable frequency compressor 101 and further improving the stability of the system. The solution proposed by the present invention has played a positive role in promoting the overall performance improvement and energy conservation and emission reduction effects of the heat pump drying system, and can bring better economic and environmental benefits. The present invention provides an economical, reliable and efficient innovative solution, laying the foundation for the future widespread application of heat pump drying systems in industry and agricultural product processing industries. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic diagram of the heat pump drying system of the present invention.

[0015] Figure 2 It is a cyclic pressure-enthalpy diagram (ph diagram) of the working process of the heat pump drying system of the present invention. DETAILED DESCRIPTION

[0016] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0017] like Figure 1As shown, the present invention is an ejector-assisted, dual-condenser heat pump drying system for material drying. The system comprises an air circulation loop and a refrigerant circulation loop, wherein the refrigerant circulation loop is equipped with a variable-speed compressor 101. This variable-speed compressor 101 can be controlled by varying the motor frequency, thereby regulating the mass flow rate of the refrigerant within the refrigeration system. Variable-speed compressor 101 has an intake and an exhaust port, the exhaust port of which is connected to the inlet of a high-pressure condenser 102. High-temperature refrigerant vapor, compressed and heated by variable-speed compressor 101, enters the high-pressure condenser 102, where it undergoes heat exchange with dry air, partially condensing the refrigerant. At the outlet of the high-pressure condenser 102, the gas-liquid two-phase refrigerant enters the nozzle inlet of the ejector 103 as a primary flow. The outlet of the ejector 103 is connected to the inlet of the low-pressure condenser 104. The two-phase refrigerant is completely condensed in the low-pressure condenser 104. The saturated liquid refrigerant at the outlet of the low-pressure condenser 104 enters the first electronic expansion valve 105. After the isenthalpic throttling process, the two-phase refrigerant enters the inlet of the flash evaporator 106 from the outlet of the first electronic expansion valve 105. The saturated gas-phase refrigerant is injected into the secondary flow inlet of the ejector 103 as a secondary fluid. The saturated liquid-phase refrigerant enters the hot end inlet of the subcooler 107. The cooled refrigerant enters the inlet of the second electronic expansion valve 108 and undergoes an isenthalpic throttling process. The outlet of the second electronic expansion valve 108 is connected to the dehumidification evaporator 106. The inlet of the dehumidifier 109 is connected, and the gas-liquid two-phase refrigerant exchanges heat with the high-humidity air from the drying box in the dehumidification evaporator 109, and completely evaporates after absorbing heat. The saturated gas-phase refrigerant at the outlet of the dehumidification evaporator 109 enters the cold end inlet of the subcooler 107, and enters the air inlet of the variable frequency compressor 101 after heat recovery, completing the refrigerant cycle of the refrigerant circulation loop; in the air circulation loop, the high-humidity air passing through the drying box first passes through the dehumidification evaporator 109, and the temperature and humidity are reduced to form dry cold air. The dry cold air exchanges heat with the refrigerant through the low-pressure condenser 104 for the first temperature increase, and then passes through the high-pressure condenser 102 for heat exchange with the refrigerant for a second temperature increase to form high-temperature dry air that enters the drying box inlet, completing the air circulation of the air circulation loop.

[0018] like Figure 2The figure shows a pressure-enthalpy diagram (also known as a pH diagram) illustrating the operating process of the ejector-enhanced dual-condenser heat pump drying system for material drying according to the present invention. The heat pump system shown in the figure operates as follows: The refrigerant circulation loop operates as follows: High-temperature, high-pressure, superheated vapor refrigerant (state point 2) at the exhaust port of variable-frequency compressor 101 enters high-pressure condenser 102, where it exchanges heat with preheated dry air, imparting drying and dehumidification capabilities to the high-temperature dry air. The superheated refrigerant forms a gas-liquid two-phase mixed refrigerant (state point 3) after releasing heat and partially condensing. The enthalpy value is relatively high, so it enters the nozzle inlet of the ejector 103 as a primary fluid, and becomes a low-pressure and high-speed gas-liquid two-phase mixed refrigerant after expanding in the nozzle. It is isobarically mixed with the saturated gas-phase refrigerant from the gas phase outlet of the flash evaporator 106 in the mixing section of the ejector 103, and then enters the low-pressure condenser 104 as a gas-liquid two-phase refrigerant (state point 4) after deceleration and pressure increase in the expansion section of the ejector 103 to preheat the dry cold air from the dehumidification evaporator 109. In this process, the refrigerant is completely condensed, and the saturated liquid-phase refrigerant enters the first electronic expansion valve 105 (state point 5). After the isenthalpic throttling process, it forms a gas-liquid two-phase refrigerant (state point 6) and enters the flash evaporator 106. The gas-phase refrigerant (state point 6v) is injected into the ejector 103 as a secondary fluid, and the saturated liquid-phase refrigerant (state point 6l) enters the hot end inlet of the subcooler 107, and is reheated with the saturated gas-phase refrigerant (state point 9) at the outlet of the dehumidification evaporator 109. The refrigerant obtains subcooling (state point 7) in the subcooler 107, enters the second electronic expansion valve 108, and forms a gas-liquid two-phase refrigerant (state point 8) after an isenthalpic throttling process, enters the dehumidification evaporator 109 to absorb heat to form a saturated gas-phase refrigerant (state point 9), cools and dehumidifies the high-humidity air from the drying box, and then enters the cold end inlet of the subcooler 107 to provide subcooling for the saturated liquid-phase refrigerant from the flash evaporator 106. After obtaining superheat itself, it returns to the suction port of the variable frequency compressor 101 (state point 1). The present invention realizes the recovery of expansion work by introducing the ejector 103, reduces the irreversible loss of the throttling process in the throttling expansion mechanism, and thus significantly improves the efficiency of the heat pump drying system. The flash evaporator 106 and the subcooler 107 increase the subcooling degree of the refrigerant before the dehumidification evaporator 109, and improves the cooling and dehumidification capacity of the dehumidification evaporator 109. At the same time, the heat recovery effect of the subcooler 107 avoids the variable frequency compressor 101 from sucking liquid into the air, thereby enhancing the stability of the system.

[0019] like Figure 1 As shown, the control method of the ejector-enhanced dual-condenser heat pump drying system for material drying of the present invention is as follows: a temperature sensor and a pressure sensor are set at the outlet of the low-pressure condenser 104 to obtain the temperature T of the refrigerant at the outlet of the low-pressure condenser. ro1 , the refrigerant pressure P at the outlet of the low-pressure condenser ro1; Set a temperature sensor and a pressure sensor at the suction port of the compressor 101 to obtain the refrigerant temperature T at the suction port of the compressor ric , refrigerant pressure P at the compressor suction port ric ; Set a temperature sensor at the outlet of the drying box to obtain the high humidity air temperature T at the outlet of the drying box aod ; Using the temperature and pressure of the refrigerant at the outlet of the low-pressure condenser 104, it is determined according to the thermophysical property equation of the refrigerant whether the refrigerant here is in a saturated liquid state, so as to regulate the opening of the first electronic expansion valve 105; using the temperature and pressure of the refrigerant at the air intake of the compressor 101, it is determined according to the thermophysical property equation of the refrigerant to regulate the opening of the second electronic expansion valve 108; the high humidity air temperature coming out of the drying box is used to control the speed of the variable frequency compressor 101; the first electronic expansion valve 105 achieves the purpose of controlling the refrigerant flow rate by detecting the refrigerant temperature and pressure parameters at the outlet of the low-pressure condenser 104, and the second electronic expansion valve 108 achieves the purpose of controlling the refrigerant flow rate by detecting the superheat of the refrigerant at the air intake of the variable frequency compressor 101.

[0020] The control method of the ejector-enhanced double-condenser heat pump drying system for material drying described above is specifically implemented as follows: when the high-humidity air temperature T at the outlet of the drying box is detected aod Lower than the preset temperature T aods When the high humidity air temperature T at the drying box outlet is detected, the variable frequency compressor 101 is controlled to increase the speed; aod Higher than the preset temperature T aods When the refrigerant temperature T at the outlet of the low-pressure condenser is detected, the variable frequency compressor 101 is controlled to reduce the speed; ro1 Lower than the calculated refrigerant pressure P at the outlet of the low-pressure condenser ro1 The saturated liquid refrigerant temperature under the same conditions is the preset temperature value T ro1s When the temperature T of the refrigerant at the outlet of the low-pressure condenser is detected, the opening of the first electronic expansion valve 105 is increased; ro1 Higher than the calculated refrigerant pressure P at the low-pressure condenser outlet ro1 The saturated liquid refrigerant temperature under the same conditions is the preset temperature value T ro1s When the opening of the first electronic expansion valve 105 is reduced; when the superheat ΔT of the refrigerant at the suction port of the compressor 101 is detected and calculated ric Higher than the preset superheat value ΔT rics When the opening of the second electronic expansion valve 108 is increased; when the superheat ΔT of the refrigerant at the suction port of the compressor 101 is detected and calculated ric Lower than the preset superheat value ΔT rics, the opening of the second electronic expansion valve 108 is reduced.

[0021] Compared with the conventional single-stage compression heat pump drying system, the novel heat pump drying system of the present invention realizes the recovery of the expansion work of the traditional throttling mechanism by introducing the ejector 103, reduces the irreversible loss of the throttling process in the throttling expansion mechanism, and thus significantly improves the efficiency of the heat pump drying system. The flash evaporator 106 and the subcooler 107 increase the subcooling degree of the refrigerant before the dehumidification evaporator 109, improve the unit mass cooling capacity of the refrigerant, and improve the cooling and dehumidification capacity of the dehumidification evaporator 109. At the same time, the heat recovery effect of the subcooler 107 avoids the compressor 101 from inhaling liquid, thereby enhancing the stability of the system. The superheated refrigerant vapor discharged from the compressor 101 is condensed in the high-pressure condenser 102 and the low-pressure condenser 104 in stages. Through high-pressure condensation and low-pressure condensation, the average condensation temperature is reduced, and the irreversible loss of the condensation heat exchange process is reduced, thereby comprehensively improving the efficiency of the system. The high-humidity air temperature at the outlet of the drying box is used to control the speed of the variable frequency compressor 101; the refrigerant temperature and pressure at the outlet of the low-pressure condenser 104 are used, and the thermophysical property equation of the refrigerant is used to calculate whether the refrigerant is in a saturated liquid state, so as to regulate the opening of the first electronic expansion valve 105; the refrigerant temperature and pressure at the suction port of the variable frequency compressor 101 are used, and the superheat of the refrigerant here is calculated according to the thermophysical property equation of the refrigerant, so as to regulate the opening of the second electronic expansion valve 108; the first electronic expansion valve 105 achieves the purpose of controlling the refrigerant flow by detecting the refrigerant temperature and pressure parameters at the outlet of the low-pressure condenser 104, and the second electronic expansion valve 108 achieves the purpose of controlling the refrigerant flow by detecting the superheat of the refrigerant at the suction port of the variable frequency compressor 101.

Claims

1. An ejector-enhanced double-condenser heat pump drying system for material drying, characterized by: The system comprises an air circulation loop and a refrigerant circulation loop, wherein the refrigerant circulation loop is equipped with a variable frequency compressor (101), the variable frequency compressor (101) has a variable speed function, and the speed of the variable frequency compressor (101) is controlled by changing the motor frequency, thereby adjusting the mass flow rate of the refrigerant in the refrigeration circulation loop; the variable frequency compressor (101) has an air intake port and an exhaust port, and the exhaust port of the variable frequency compressor (101) is connected to the inlet of the high-pressure condenser (102). After being compressed by the variable frequency compressor (101), the high-temperature refrigerant vapor with the temperature and pressure increased enters the high-pressure condenser (102). 2), wherein the refrigerant exchanges heat with the dry air, causing the refrigerant to be partially condensed; the gas-liquid two-phase refrigerant at the outlet of the high-pressure condenser (102) enters the nozzle inlet of the ejector (103) as a primary flow, the outlet of the ejector (103) is connected to the inlet of the low-pressure condenser (104), the two-phase refrigerant is completely condensed in the low-pressure condenser (104), the saturated liquid refrigerant at the outlet of the low-pressure condenser (104) enters the first electronic expansion valve (105), and after the isenthalpic throttling process, the two-phase refrigerant enters the flash evaporator (105) from the outlet of the first electronic expansion valve (105). 06) inlet, wherein the saturated gas phase refrigerant is injected as a secondary fluid to the secondary flow inlet of the ejector (103), the saturated liquid phase refrigerant enters the hot end inlet of the subcooler (107), and the cooled refrigerant enters the inlet of the second electronic expansion valve (108) to perform an isenthalpic throttling process. The outlet of the second electronic expansion valve (108) is connected to the inlet of the dehumidification evaporator (109), and the gas-liquid two-phase refrigerant exchanges heat with the high-humidity air from the drying box in the dehumidification evaporator (109), and completely evaporates after absorbing heat. The saturated gas phase refrigerant at the outlet of the dehumidification evaporator (109) enters the subcooler The air passes through the cold end inlet of the refrigerant (107), and after heat recovery, enters the air inlet of the variable frequency compressor (101), completing the refrigerant cycle of the refrigerant circulation loop; in the air circulation loop, the high-humidity air passing through the drying box first passes through the dehumidification evaporator (109), and the temperature and humidity are reduced to form dry cold air. The dry cold air passes through the low-pressure condenser (104) to exchange heat with the refrigerant for the first temperature increase, and then passes through the high-pressure condenser (102) to exchange heat with the refrigerant for the second temperature increase, forming high-temperature dry air that enters the drying box inlet, completing the air circulation of the air circulation loop.

2. The ejector-enhanced double-condenser heat pump drying system for material drying according to claim 1, characterized in that: In the ejector (103), the partially condensed gas-liquid two-phase mixed refrigerant from the high-pressure condenser (102) serves as the primary fluid of the ejector (103), and its pressure is higher than the pressure of the secondary fluid from the gas phase outlet of the flash evaporator (106), that is, the pressure of the ejected fluid, and the high-pressure condenser (102) realizes partial condensation of the exhaust gas of the variable frequency compressor (101), so its outlet refrigerant is a gas-liquid two-phase flow with a higher enthalpy value, thereby improving the ability of the ejector (103) to recover expansion work; the gas phase outlet of the flash evaporator (106) is saturated gas phase refrigerant, which is ejected by the gas-liquid two-phase refrigerant and enters the mixing section of the ejector (103) for isobaric mixing, and then enters the low-pressure condenser (104) after being decelerated and pressurized in the expansion section of the ejector (103).

3. The ejector-enhanced double-condenser heat pump drying system for material drying according to claim 1, characterized in that: The superheated refrigerant vapor discharged from the variable frequency compressor (101) is condensed in a high-pressure condenser (102) and a low-pressure condenser (104) in a stepwise manner. The refrigerant at the outlet of the high-pressure condenser (102) is in a gas-liquid two-phase state, and the refrigerant at the outlet of the low-pressure condenser (104) is in a saturated liquid phase. An ejector (103) is added between the high-pressure and low-pressure condensers to effectively recover expansion work, and the average condensation temperature is reduced through the two condensation processes of high-pressure condensation and low-pressure condensation, thereby improving the energy efficiency of the system. The dry cold air first exchanges heat with the low-pressure condenser (104), and after a primary heating, enters the high-pressure condenser (102) for a secondary heating. The setting of the stepwise heating of the air side through the high-pressure and low-pressure condensers reduces the average heat exchange temperature difference between the air and the refrigerant, thereby reducing the irreversible loss of the condensation heat exchange process and comprehensively improving the system efficiency.

4. The ejector-enhanced double-condenser heat pump drying system for material drying according to claim 1, characterized in that: The gas-liquid two-phase refrigerant from the first electronic expansion valve (105) enters the flash evaporator (106), wherein the gas-phase refrigerant provides the secondary fluid of the ejector (103), and the liquid-phase refrigerant is supercooled in the subcooler (107) and throttled by the second electronic expansion valve (108) before entering the dehumidification evaporator (109). The flash evaporator (106) effectively reduces the refrigerant inlet temperature before the second electronic expansion valve (108), so that the dryness of the refrigerant passing through the second electronic expansion valve (108) is reduced, thereby increasing the unit cooling capacity of the refrigerant, and the subcooler (107) provides subcooling. The effect is further increased, the unit cooling capacity is improved, and the cooling and dehumidification capacity of the dehumidification evaporator (109) is improved. Due to the existence of supercooling, the refrigerant maintains a stable state before entering the second electronic expansion valve (108), thereby enhancing the stability of the system. At the same time, after the cold end of the subcooler (107) undergoes heat exchange, the refrigerant entering the inlet of the variable frequency compressor (101) obtains superheating. By utilizing the heat recovery effect of the subcooler (107), the variable frequency compressor (101) is prevented from sucking liquid into the air, thereby protecting the variable frequency compressor (101) and further improving the stability of the system.

5. The operating method of the ejector-enhanced double-condenser heat pump drying system for material drying according to any one of claims 1 to 4, characterized in that: The working process of the refrigerant circulation loop is as follows: the high-temperature and high-pressure superheated vapor refrigerant at the exhaust port of the variable frequency compressor (101) enters the high-pressure condenser (102) and exchanges heat with the preheated dry air, so that the high-temperature dry air obtains the drying and dehumidifying capacity; the superheated refrigerant partially condenses after releasing heat to form a gas-liquid two-phase mixed refrigerant with a high enthalpy value, and then enters the nozzle inlet of the ejector (103) as a primary fluid, expands in the nozzle, and becomes a low-pressure and high-speed gas-liquid two-phase mixed refrigerant, which is combined with the saturated gas phase refrigerant from the gas phase outlet of the flash evaporator (106). The refrigerant is mixed at equal pressure in the mixing section of the ejector (103), and then decelerated and pressurized in the expansion section of the ejector (103) before entering the low-pressure condenser (104) as a gas-liquid two-phase refrigerant to preheat the dry cold air from the dehumidification evaporator (109). In this process, the refrigerant is completely condensed, and the saturated liquid refrigerant enters the first electronic expansion valve (105). After the isenthalpic throttling process, the gas-liquid two-phase refrigerant is formed and enters the flash evaporator (106), where the saturated gas-phase refrigerant is injected into the ejector (103) as a secondary fluid, and the saturated liquid phase refrigerant is produced. The refrigerant enters the hot end inlet of the subcooler (107) and reheats with the saturated gas phase refrigerant at the outlet of the dehumidification evaporator (109). The refrigerant obtains subcooling in the subcooler (107) and enters the second electronic expansion valve (108). After the isenthalpic throttling process, it forms a gas-liquid two-phase refrigerant. It enters the dehumidification evaporator (109) to absorb heat to form a saturated gas phase refrigerant, cools and dehumidifies the high humidity air from the drying box, and then enters the cold end inlet of the subcooler (107) to provide subcooling for the saturated liquid phase refrigerant from the flash evaporator (106). After obtaining the superheat, the refrigerant is returned to the air intake of the variable frequency compressor (101); by introducing the ejector (103), the expansion work is recovered, and the irreversible loss of the throttling process in the throttling expansion mechanism is reduced, thereby significantly improving the efficiency of the heat pump drying system; the flash evaporator (106) and the subcooler (107) increase the subcooling degree of the refrigerant before the dehumidification evaporator (109), and improve the cooling and dehumidification capacity of the dehumidification evaporator (109); at the same time, the heat recovery effect of the subcooler (107) avoids the variable frequency compressor (101) from carrying liquid in the air intake, thereby enhancing the stability of the system.

6. The control method of the ejector-enhanced double-condenser heat pump drying system for material drying according to any one of claims 1 to 4, characterized in that: A temperature sensor and a pressure sensor are set at the outlet of the low-pressure condenser (104) to obtain the temperature T of the refrigerant at the outlet of the low-pressure condenser. ro1 , the refrigerant pressure P at the outlet of the low-pressure condenser ro1 ; Set a temperature sensor and a pressure sensor at the air intake of the compressor (101) to obtain the refrigerant temperature T at the air intake of the compressor ric , refrigerant pressure P at the compressor suction port ric ; Set a temperature sensor at the outlet of the drying box to obtain the high humidity air temperature T at the outlet of the drying box aod The invention relates to a method for controlling the opening of the first electronic expansion valve (105) by using the refrigerant temperature and pressure at the outlet of the low-pressure condenser (104) and calculating whether the refrigerant therein is in a saturated liquid state according to the thermophysical property equation of the refrigerant; and controlling the opening of the second electronic expansion valve (108) by using the refrigerant temperature and pressure at the air intake of the variable frequency compressor (101) and calculating the superheat of the refrigerant therein according to the thermophysical property equation of the refrigerant; and controlling the rotation speed of the variable frequency compressor (101) by using the high humidity air temperature coming out of the drying box; and controlling the refrigerant flow rate by detecting the refrigerant temperature and pressure parameters at the outlet of the low-pressure condenser (104). The second electronic expansion valve (108) controls the refrigerant flow rate by detecting the superheat of the refrigerant at the air intake of the variable frequency compressor (101).

7. The control method of the ejector-enhanced double-condenser heat pump drying system for material drying according to claim 6, characterized in that: The specific implementation is as follows: When the high humidity air temperature T at the outlet of the drying box is detected aod Lower than the preset temperature T aods When the high humidity air temperature T at the drying box outlet is detected, the variable frequency compressor (101) is controlled to increase the speed; aod Higher than the preset temperature T aods When the refrigerant temperature T at the outlet of the low-pressure condenser is detected, the variable frequency compressor (101) is controlled to reduce the speed; ro1 Lower than the calculated refrigerant pressure P at the outlet of the low-pressure condenser ro1 The saturated liquid refrigerant temperature under the same conditions is the preset temperature value T ro1s When the temperature T of the refrigerant at the outlet of the low-pressure condenser is detected, the opening of the first electronic expansion valve (105) is increased; ro1 Higher than the calculated refrigerant pressure P at the low-pressure condenser outlet ro1 The saturated liquid refrigerant temperature under the same conditions is the preset temperature value T ro1s When the opening of the first electronic expansion valve (105) is reduced; when the superheat ΔT of the refrigerant at the suction port of the compressor (101) is detected and calculated ric Higher than the preset superheat value ΔT rics When the opening of the second electronic expansion valve (108) is increased; when the superheat ΔT of the refrigerant at the suction port of the compressor (101) is detected and calculated ric Lower than the preset superheat value ΔT rics When the opening of the second electronic expansion valve (108) is reduced.

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