A closed loop drying mechanism and a tunnel type mushroom drying system comprising the same

Abstract

The application discloses a closed-loop drying mechanism, which comprises a drying chamber and a drying device arranged on the top of the drying chamber; the drying device comprises an integrated shell, a heat exchanger is arranged in the integrated shell, and an air inlet passage output end of the heat exchanger is connected with an air inlet channel; a condenser, a heater and an air inlet fan are sequentially arranged in the air inlet channel; the drying chamber is provided with an air inlet and an air outlet at two ends respectively, the air inlet channel output end is connected with the air inlet, the air inlet passage input end is connected with an air inlet channel, and a wind valve and a surface cooler are sequentially arranged in the air inlet channel along the air flow direction; the application belongs to the technical field of agricultural product processing mechanical equipment, and has the technical effect that: the external fresh air is pre-dehumidified by the surface cooler, then is subjected to non-contact heat exchange with the high-temperature and high-humidity return air discharged from the drying chamber in the heat exchanger, the sensible heat of the return air is fully recovered to preheat the fresh air, then the condensation heat of the heat pump system is utilized to further heat the air, and the heater is used for fine temperature adjustment when necessary.

Description

Technical Field

[0001] This invention relates to the field of agricultural product processing machinery and equipment, specifically to a closed-loop drying mechanism and a tunnel-type mushroom drying system containing the mechanism. Background Technology

[0002] Mushroom products, such as shiitake, king oyster, and deer antler mushrooms, are highly valued in the market due to their rich content of various amino acids and nutrients. However, their fresh moisture content is generally over 80%, and their delicate tissues make them highly susceptible to spoilage if not handled promptly after harvesting. Therefore, drying is a crucial step in extending their shelf life, enhancing their commercial value, and facilitating storage and transportation. However, drying mushrooms is not a simple dehydration process; it requires a precisely controlled microenvironment, coordinating multiple parameters such as temperature, humidity, and airflow to ensure effective moisture removal while preserving their unique color, intact shape, nutritional components, and flavor to the greatest extent possible. This is a complex heat and mass transfer process, placing stringent demands on the performance of drying equipment.

[0003] Currently, small and medium-sized mushroom processing enterprises generally still rely on traditional hot air drying rooms or simple drying equipment for drying. These devices mostly use direct heating via coal or electricity, using fans to blow hot air over the surface of the material for drying. In practical applications, this type of equipment has revealed several significant drawbacks. First, it has extremely high energy consumption and low heat utilization, with most heat being lost directly during the dehumidification process, resulting in high operating costs. Second, the drying process is poorly controlled, typically only allowing for fixed temperature and time settings, making dynamic adjustments based on the real-time drying status of the material impossible, and even more difficult to precisely control the humidity of the drying medium. This leads to unstable drying quality; the same batch of material often exhibits uneven drying, with some parts becoming over-dry and charred while others remain excessively moist, severely impacting product grade and selling price. Even more problematic is that in the initial drying stage, high-moisture materials encountering high-temperature, dry air are prone to rapid surface evaporation while internal moisture cannot migrate quickly enough, forming a hard outer shell that hinders further internal moisture release, not only prolonging the drying cycle but also potentially causing internal deterioration. Furthermore, traditional equipment lacks efficient active dehumidification methods, relying solely on natural dehumidification through exhaust vents. In humid weather or during the later stages of drying, humidity levels inside the drying chamber are difficult to reduce, resulting in insufficient drying power and a sharp drop in efficiency. Therefore, there is an urgent market need for a high-efficiency drying technology and equipment that can achieve low-temperature energy saving, uniform drying, controllable parameters, and is particularly suitable for the characteristics of fungal materials. Therefore, to address the shortcomings of existing methods, we propose a closed-loop drying mechanism and a tunnel-type mushroom drying system incorporating this mechanism. Summary of the Invention

[0004] To address these issues, the present invention provides a closed-loop drying mechanism and a tunnel-type mushroom drying system incorporating the mechanism, thereby resolving the aforementioned problems in the prior art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: According to a first aspect of the present invention, a closed-loop drying mechanism includes a drying chamber and a drying device disposed on top thereof; the drying device includes an integrated shell, inside which a heat exchanger is provided, and the output end of the air inlet passage of the heat exchanger is connected to an air inlet channel. A condenser, a heater, and an intake fan are installed sequentially in the air intake channel; the two ends of the drying chamber are an air inlet and an exhaust outlet, respectively; the output end of the air intake channel is connected to the air inlet; the input end of the air intake passage is connected to the air intake channel; and an air valve and a surface cooler are installed sequentially in the air intake channel along the airflow direction. The inlet of the heat exchanger's exhaust passage is connected to the exhaust port of the drying chamber via an exhaust duct, and the outlet of the exhaust passage is connected to an exhaust channel. An evaporator and an exhaust fan are installed in the exhaust channel. A return air duct is connected between the side wall of the outlet of the exhaust channel and the side wall of the inlet of the air inlet channel. A solenoid valve is installed in the return air duct. The condenser, compressor, liquid receiver, solenoid valve, one-way dryer filter, expansion valve, evaporator, and gas separator are connected in sequence via refrigerant pipelines to form a heat pump dehumidification cycle.

[0006] Furthermore, the drying chamber is equipped with a material support frame consisting of multiple trolleys arranged side by side; each trolley includes a frame and at least two layers of horizontal plates installed within the frame, forming a multi-layer material platform and a through channel for airflow between the horizontal plates and between the horizontal plates and the inner wall of the frame.

[0007] Furthermore, an inlet and an outlet are respectively provided on both sides of the front end of the drying chamber, and sealing doors are installed in both the inlet and the outlet; the movement direction of the trolley is opposite to the flow direction of the drying airflow in the drying chamber.

[0008] Furthermore, it also includes an adaptive feedback control system, which includes a humidity sensor installed on each material platform of each trolley, a programmable logic controller for receiving humidity sensor signals, and an actuator group controlled by the programmable logic controller; the actuator group includes at least the power regulation module of the heater, the speed regulation module of the intake fan, and the trolley moving mechanism.

[0009] Furthermore, the humidity sensor is a non-contact microwave humidity sensor, installed at the center of the bottom of each layer of horizontal plate.

[0010] Furthermore, the programmable logic controller has a pre-stored control parameter lookup table in its internal memory. The lookup table defines the heater power setting value and the intake fan speed setting value under different material humidity, humidity change rate and humidity gradient conditions.

[0011] Furthermore, the programmable logic controller is configured to perform the following steps: periodically acquire the measured values ​​of each humidity sensor on the trolley closest to the air inlet of the drying chamber; calculate the average humidity, humidity change rate, and humidity gradient of the material on the trolley; query the control parameter lookup table according to the calculation results to obtain the corresponding control parameters; and adjust the power of the heater and the speed of the air intake fan according to the control parameters.

[0012] Furthermore, the programmable logic controller is also configured to: predict the remaining drying time based on the average humidity, the target humidity, and the humidity change rate, and control the vehicle moving mechanism to perform a vehicle moving operation when the average humidity reaches the target range and the remaining drying time is less than a safety threshold.

[0013] Furthermore, the actuator assembly also includes at least one of the following: the exhaust fan speed regulation module, the air valve opening regulation module, the solenoid valve opening regulation module, and the compressor frequency regulation module.

[0014] Furthermore, an electrical box is installed on the side wall of the integrated shell to house the electrical control components of the drying equipment.

[0015] A tunnel-type mushroom drying system includes the aforementioned closed-loop drying mechanism.

[0016] Furthermore, the drying chamber houses three of the aforementioned trolleys side by side, forming a continuous three-section counter-current drying tunnel.

[0017] The present invention has the following advantages: 1. This closed-loop drying mechanism integrates a plate heat exchanger, a heat pump system (evaporator and condenser), and an auxiliary heater to construct a multi-stage closed-loop air handling process. External fresh air is first pre-dehumidified by a surface cooler, and then undergoes non-contact heat exchange with the high-temperature, high-humidity return air from the drying chamber in the heat exchanger. This fully recovers the sensible heat of the return air to preheat the fresh air. Subsequently, the condensation heat of the heat pump system is used to further heat the air, with the heater used for precise temperature control if necessary. This structure cleverly integrates heat recovery, deep dehumidification, and precise heating, fundamentally changing the inefficient mode of traditional open-loop drying systems where heating-dehumidification-mass heat loss occurs. Waste heat in the exhaust air is reused in the drying process, and the energy efficiency ratio of heat pump dehumidification is significantly improved compared to traditional heating-dehumidification, thus achieving substantial energy savings and consumption reduction at the system level. 2. This closed-loop drying mechanism creates a dynamic counter-current drying environment by introducing a movable trolley array and making its movement direction flow in the opposite direction to the drying airflow. The driest and hottest hot air first contacts the material with the deepest drying degree and lowest moisture content, avoiding over-drying. As the hot air continuously absorbs moisture, its temperature and drying potential energy gradually decrease as it passes through the trolley array. When it reaches the wet material with the highest moisture content that has just entered, its mild conditions are just right for initial drying, effectively preventing surface crusting. This reverse matching of dry material to dry air and wet material to wet air allows the drying potential energy of the hot air to be utilized in a stepped and full manner in space. This not only greatly improves the efficiency of heat energy utilization, but more importantly, it naturally forms a stable temperature and humidity gradient field in the drying chamber, so that the materials in different positions at the same time are in their most suitable drying stage, thereby significantly improving the drying uniformity and overall quality consistency of the entire batch of materials. 3. This closed-loop drying mechanism, by deploying a humidity sensor network on the trolley (i.e., the material about to be dried) at the key location closest to the hot air inlet, and constructing an adaptive feedback control system based on this real-time humidity information, realizes a paradigm shift in the drying process from "process parameter control" to "drying endpoint control." The system uses the real-time humidity of the outlet material as the core feedback signal, and dynamically coordinates heating power, airflow speed, heat pump operating status, and even the timing of trolley relocation by querying a pre-calibrated expert rule table. This not only completely eliminates the reliance on experience for fixed drying time, accurately ensuring that each batch of material reaches the target moisture content and avoiding quality degradation and energy waste caused by over-drying, but also allows for self-adjustment and optimization based on fluctuations in the initial state of the material and environmental conditions. This control system is deeply coupled and synergistically enhanced with the aforementioned counter-current physical structure and closed-loop thermodynamic system, ultimately contributing to a complete solution that is highly efficient, uniform, intelligent, and particularly suitable for the high-quality drying needs of mushrooms. Attached Figure Description

[0018] Figure 1 This is a front view of a closed-loop drying mechanism and a tunnel-type mushroom drying system containing the mechanism proposed in this invention. Figure 2 This is a schematic diagram of the system flow; Figure 3 This is a schematic diagram of the compressor's operating principle. Figure 4 This is a flowchart illustrating the principle. Figure 5 This is a top view of the drying chamber; Figure 6 This is a front view of the drying chamber; Figure 7 This is the front view of the car; Figure 8 This is a schematic diagram of the condenser and compressor.

[0019] In the diagram: 1. Heat exchanger; 2. Heater; 3. Condenser; 4. Intake fan; 5. Expansion valve; 6. One-way dryer filter; 7. Solenoid valve one; 8. Liquid receiver; 9. Compressor; 10. Gas separator; 11. Exhaust fan; 12. Evaporator; 13. Air valve; 14. Electrical box; 15. Surface cooler; 16. Drying chamber; 161. Inlet; 162. Outlet; 163. Sealing door; 17. Cart; 171. Frame; 171, 172. Horizontal plate; Detailed Implementation

[0020] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. 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.

[0021] Example 1; Reference Figures 1-8 A closed-loop drying mechanism includes a drying chamber 16, with a drying device mounted on the top of the drying chamber 16. The drying device includes an integrated shell, with an electrical box 14 installed on the side wall of the integrated shell. A heat exchanger 1 is installed inside the integrated shell, and the output end of the air inlet passage of the heat exchanger 1 is connected to an air inlet channel. A condenser 3, a heater 2, and an air intake fan 4 are installed sequentially in the air inlet channel. The two ends of the drying chamber 16 are an air inlet and an exhaust outlet, respectively. The output end of the air inlet channel is connected to the air inlet, and the input end of the air inlet passage is connected to the air intake channel. An air valve 13 and a surface cooler 15 are installed sequentially in the air intake channel along the airflow direction. The heat exchanger 1 has an exhaust passage with an inlet connected to an exhaust duct. The exhaust duct is connected to the exhaust port of the drying chamber 16. The exhaust passage is connected to an exhaust duct. An evaporator 12 and an exhaust fan 11 are installed in the exhaust duct along the airflow direction. A return air pipe is provided between the side wall of the exhaust duct's output end and the side wall of the inlet passage's inlet end. A solenoid valve is installed in the return air pipe. The compressor 9 discharges high-temperature, high-pressure refrigerant vapor, which is cooled by the condenser 3 and transformed into a low-temperature, high-pressure liquid. This liquid then flows through the receiver 8 for gas-liquid separation and storage. The liquid's flow is then controlled by a solenoid valve (soleoid valve 7) in the refrigerant circulation pipeline. After passing through a one-way dryer filter 6 to adsorb impurities and moisture, the liquid enters the expansion valve 5 for throttling and pressure reduction, becoming a two-phase gas-liquid state. It then enters the evaporator 12 for evaporation and heat absorption, transforming into low-temperature, low-pressure refrigerant vapor. This vapor is further separated by the gas separator 10 to ensure that any remaining liquid refrigerant is ultimately drawn into the compressor 9, completing the refrigerant circulation process (i.e., internal circulation). Working principle: The working process includes external circulation and internal circulation; the external circulation is divided into four stages, namely the fresh air treatment stage, the heating stage, the air supply and drying stage, and the return air treatment stage. External fresh air enters through the inlet end of the air intake channel, first flows through the air valve 13 to control the air volume, then passes through the surface cooler 15 for preliminary cooling and dehumidification, and then enters the air intake passage of the heat exchanger 1. In this passage, it exchanges heat with the high temperature and high humidity air in the exhaust passage through a partition, thereby preheating the fresh air, effectively recovering the waste heat of the return air, and reducing the system energy consumption. Preheated fresh air enters condenser 3, and the refrigerant circulates through compressor 9 to release heat in the condenser, achieving secondary heating of the air; when the ambient temperature is low or the required supply air temperature is high, the heater is activated to further heat the air and ensure that the supply air temperature reaches the set requirements. The heated dry air is sent into the drying chamber 16 by the air intake fan 4, where it exchanges heat and moisture with the material (such as mushrooms), removes the moisture from the material, and then becomes low-temperature, high-humidity return air. High-humidity return air enters the exhaust passage of heat exchanger 1 through the return air inlet, where it exchanges heat with the fresh air flow. After the temperature drops, it enters evaporator 12. In evaporator 2, the return air is further cooled and dehumidified. After the moisture is released, part of it is discharged from the system, and the rest enters the intake passage through solenoid valve 1 to participate in the circulation again. Example 2: Basically the same as in Example 1, but further: referring to Figures 1-8A closed-loop drying mechanism and a tunnel-type mushroom drying system containing the mechanism are disclosed. The drying rack for placing materials in the drying chamber 16 is composed of multiple trolleys 17 with casters at the bottom arranged side by side. Each trolley 17 includes a frame 171 and several horizontal plates 172 installed in the frame. Taking two horizontal plates 172 as an example, there are three platforms for drying materials, namely the top of the two horizontal plates 172 and the bottom of the inner wall of the frame. Correspondingly, when the trolleys are connected, three continuous transmission channels with the same width as the trolleys 17 are formed between the bottom of the inner wall of the frame and the bottom of the lower horizontal plate 172, between the top of the lower horizontal plate 172 and the bottom of the upper horizontal plate 172, and between the top of the upper horizontal plate 172 and the top of the inner wall of the frame, which facilitates the uniform flow of air. The front end of the drying chamber 16 is provided with an inlet 161 and an outlet 162 on both sides, and a sealing door 163 is installed in both the inlet 161 and the outlet 162. The key point is that the movement direction of the trolley 17 is opposite to the flow direction of the airflow, which constitutes a reverse flow relationship. Working principle: This embodiment achieves a highly efficient combination of dynamic countercurrent drying and step-by-step continuous production. For example: only three carts 17 can be placed side-by-side in the drying chamber 16; the inlet 161 is located on the left, and the outlet 162 is located on the right, with the drying airflow blowing from right to left; a drying timer is set, with a preset drying time of h; when the three carts 17 are placed side-by-side in the drying chamber 16, the material in the rightmost cart 17 (closest to the hot air inlet) has been dried for 3 hours and is in the later stages of drying; the material in the middle cart 17 has been dried for 2 hours and is in the later stages of drying. Mid-term; the material in the leftmost trolley 17 has been dried for 1 hour and is in the early stage of drying; when the timer expires, open the outlet 161 to take out the rightmost trolley 17 that has been dried, and close the outlet 162; then open the inlet 161 and move the remaining two trolleys 17 in the room one position to the right. At this time, the original middle trolley 17 is moved to the rightmost position, and the original leftmost trolley 17 is moved to the middle position. Then, push a new trolley 17 with wet material from the inlet 161 into the leftmost empty position. Finally, close the inlet 161 and reset the timer, and repeat the above process. This structure ingeniously achieves the counter-current flow of the drying medium (hot air) and the object to be dried (material). The driest and hottest hot air first contacts the driest material (the rightmost trolley), avoiding over-drying. As the hot air continuously absorbs moisture and decreases in temperature as it passes through the array of trolleys 17, when it reaches the wettest material (the newly arrived trolley on the far left), its temperature and humidity are just right to meet the initial drying needs, preventing surface crusting caused by high-temperature rapid drying. This counter-current matching principle allows the drying potential energy (the drying capacity of the air) to be utilized in a stepped and full manner, greatly improving the thermal energy utilization efficiency and drying uniformity. The closed-loop system provides a stable, controllable, and precisely adjustable drying airflow for the drying chamber 16, which is a prerequisite for the efficient and reliable operation of the countercurrent drying process. Conversely, the temperature and humidity gradient distribution naturally formed in the drying chamber 16 by the countercurrent structure ensures that the return air discharged from the exhaust port has a high and stable heat energy and moisture content. Example 3: Similar to Example 2, the above solution suffers from the problem that the drying time setting relies on experience and cannot determine the material drying endpoint in real time. Furthermore, a closed-loop drying mechanism and a tunnel-type mushroom drying system containing this mechanism also include an adaptive feedback control system. The hardware components of this system include: Sensor network: A non-contact microwave humidity sensor is installed at the center of each material platform (below the cross plate 172 and at the top of the inner wall of the frame 171) of each trolley 17; the sensor is connected to the junction box on the side wall of the trolley 17 through a waterproof wire, and then communicates with the controller through a slip ring or wireless transmission module. Actuator group: including solid-state relay power adjustment module of heater 2, frequency converter driver of intake fan 4 (model example: VFD022M21A), frequency converter driver of exhaust fan 11, drive module of solenoid valve 1 (proportional adjustment type), electric actuator of air valve 13, and frequency converter controller of compressor 9. Control Unit: One programmable logic controller (PLC, model example: Siemens S7-1200), equipped with digital input modules (for receiving door 163 switch signals and emergency stop signals), digital output modules (for controlling door 163 electromagnetic lock and vehicle moving mechanism relays), analog input modules (for receiving 4-20mA humidity signals), and analog output modules (for outputting 0-10V control signals to the frequency converter and power adjustment module). Human-machine interface: Touch screen (model example: Weintek MT8102iE), used for parameter setting, status display and manual operation; The system uses the real-time average humidity value of the humidity sensor on the trolley 17, which is closest to the drying gas inlet of the drying chamber 16 (i.e., the rightmost side), as the core feedback signal for the entire drying process. The programmable logic controller (PLC) has a lookup table pre-stored in its internal memory, based on preset rules. This lookup table, obtained through experimental calibration, specifies the optimal parameters for heater 2 power, intake fan 4 speed, and exhaust fan 11 speed under different material humidity, humidity change rate, and environmental conditions. Its workflow is as follows: S1. Operators set the target material moisture content (e.g., 12%) and material type code through the human-machine interface; S2. Data Acquisition: The programmable logic controller reads the measured values ​​of the humidity sensor on each layer of the trolley 17 closest to the dry gas inlet according to the set sampling period (e.g., 5 minutes). S3, Data Preprocessing and State Calculation; S31. Calculate the average humidity: Calculate the arithmetic mean of the measured values ​​from each layer of humidity sensors to obtain the average humidity H of the material at the current exit trolley 17. avg ; S32. Calculate the humidity change rate: Record the average humidity at the current time and the previous sampling time, calculate the difference per unit time, and obtain the humidity change rate R (i.e., drying rate); the calculation method is: R = (H avg (This time)-H avg (Last) / Sampling period; S33. Calculate the humidity gradient: Find the maximum value H_max and the minimum value H_min among the three humidity sensor measurements, and calculate the difference ΔH=H max -H min As an indicator of drying uniformity; S4. Query control parameters: The controller will retrieve the currently calculated (H) parameters. avg The array (R, ΔH) is compared with a pre-stored lookup table; the core logic of the lookup table is as follows: When H_avg is much higher than the target value (e.g., > target value + 10%) and R value is small: the lookup table indicates that the power setting of heater 2 should be increased and the speed of intake fan 4 should be increased; When H_avg approaches the set target value (e.g., within ±5% of the target value): the lookup table indicates that the power setting value of heater 2 should be gradually reduced, and the speed of intake fan 4 should be maintained or reduced; When the ΔH value exceeds the preset threshold (e.g., 5%): the lookup table indicates that the speed of the intake fan 4 should be increased to enhance the airflow homogenization effect; S5, Execute control commands; Based on the query results, the controller sends specific adjustment instructions to each actuator through its output module: S51, Temperature regulation execution: Send a new power setting value to the power controller of heater 2 through the analog output module or communication interface; S52, Wind speed regulation: Adjust the motor speed of intake fan 4 via frequency converter; S53. System Coordinated Adjustment: Based on the overall status, adjust the operating frequency of compressor 9, the opening degree of solenoid valve 1, etc., through switch or analog output; S6. Destination Judgment and Vehicle Relocation Decision; The controller continues to execute steps two to five, while simultaneously determining the destination; the judgment logic is as follows: S61. Predicting Remaining Time: Based on the formula T remain =(H avg -H target ) / R estimates the remaining drying time; S62, Vehicle relocation condition trigger: A vehicle relocation command is generated when both of the following conditions are met simultaneously: H avg Achieve the target range (e.g., 11.5%~12.5%). Predicted T remain Less than the safety threshold (e.g., 10 minutes); S63, Perform vehicle relocation: The controller controls the opening of the sealing gate 163 of the vehicle exit 162 and vehicle entrance 161 through the relay output contact, and triggers the vehicle relocation mechanism (such as a pushing device) to complete the vehicle relocation operation according to the process described in Embodiment 2. S7, State Reset and Loop After the vehicle is moved, the new vehicle moves to the far right position; the controller identifies the humidity sensor on the new vehicle as a new monitoring source, resets the relevant calculation parameters (such as the humidity change rate), and returns to step two to start a new round of control cycle; Control rule labeling and lookup table creation: The lookup table was established through the following experimental calibration procedure, ensuring the effectiveness and reliability of the control: (1) Drying tests were conducted on different types of mushrooms (such as shiitake mushrooms and king oyster mushrooms) under typical environmental conditions; (2) In the experiment, the system recorded different (H) avg Under the conditions of R and ΔH), the combination of parameters such as heater power and fan speed that yields the highest energy efficiency and best drying quality; (3) Combine these parameters with the corresponding state (H) avg A mapping relationship is established between R and ΔH to form discrete data points; (4) Using existing linear interpolation or bilinear interpolation algorithms, the discrete data points are expanded into a continuous lookup table covering the entire state space and stored in the controller memory. Working principle: Based on the countercurrent drying in Example 2, an adaptive feedback control based on the humidity of the outlet material is introduced. Its core principle is to use the real-time average humidity of the rightmost trolley 17 (about to be moved out) as the key state variable of the drying process. By querying the pre-calibrated control rule table, the drying temperature, wind speed and the timing of trolley movement are dynamically adjusted to achieve precise control of the drying endpoint. This method effectively solves the problem of over-drying or under-drying that may be caused by fixed time control.

Claims

1. A closed-loop drying mechanism, characterized in that, It includes a drying chamber and a drying device located on top of it; the drying device includes an integrated shell with a heat exchanger inside, and the air inlet passage of the heat exchanger is connected to an air inlet channel at its output end. A condenser, a heater, and an intake fan are installed sequentially in the air intake channel; the two ends of the drying chamber are an air inlet and an exhaust outlet, respectively; the output end of the air intake channel is connected to the air inlet; the input end of the air intake passage is connected to the air intake channel; and an air valve and a surface cooler are installed sequentially in the air intake channel along the airflow direction. The inlet of the heat exchanger's exhaust passage is connected to the exhaust port of the drying chamber via an exhaust duct, and the outlet of the exhaust passage is connected to an exhaust channel. An evaporator and an exhaust fan are installed in the exhaust channel. A return air duct is connected between the side wall of the outlet of the exhaust channel and the side wall of the inlet of the air inlet channel. A solenoid valve is installed in the return air duct. The condenser, compressor, liquid receiver, solenoid valve, one-way dryer filter, expansion valve, evaporator, and gas separator are connected in sequence via refrigerant pipelines to form a heat pump dehumidification cycle.

2. The closed-loop drying mechanism according to claim 1, characterized in that, The drying chamber is equipped with a material support frame consisting of multiple trolleys arranged side by side; each trolley includes a frame and at least two layers of horizontal plates installed within the frame, forming a multi-layer material platform and a through channel for airflow between the horizontal plates and between the horizontal plates and the inner wall of the frame.

3. The closed-loop drying mechanism according to claim 2, characterized in that, The front end of the drying chamber has an inlet and an outlet on both sides, and both the inlet and outlet are equipped with sealing doors; the trolley moves in the opposite direction to the airflow direction in the drying chamber.

4. A closed-loop drying mechanism according to claim 3, characterized in that, It also includes an adaptive feedback control system, which includes a humidity sensor installed on each material platform of each trolley, a programmable logic controller for receiving humidity sensor signals, and an actuator group controlled by the programmable logic controller; the actuator group includes at least the power regulation module of the heater, the speed regulation module of the intake fan, and the trolley moving mechanism.

5. A closed-loop drying mechanism according to claim 4, characterized in that, The humidity sensor is a non-contact microwave humidity sensor, installed at the center of the bottom of each layer of horizontal plate.

6. A closed-loop drying mechanism according to claim 4, characterized in that, The programmable logic controller has a pre-stored control parameter lookup table in its internal memory. The lookup table defines the heater power setting value and the intake fan speed setting value under different material humidity, humidity change rate and humidity gradient conditions.

7. A closed-loop drying mechanism according to claim 6, characterized in that, The programmable logic controller is configured to perform the following steps: periodically collect the measured values ​​of each humidity sensor on the trolley closest to the air inlet of the drying chamber; calculate the average humidity, humidity change rate, and humidity gradient of the material on the trolley; query the control parameter lookup table according to the calculation results to obtain the corresponding control parameters; and adjust the power of the heater and the speed of the air intake fan according to the control parameters.

8. A closed-loop drying mechanism according to claim 7, characterized in that, The programmable logic controller is further configured to: predict the remaining drying time based on the average humidity, the target humidity, and the humidity change rate, and control the vehicle moving mechanism to perform a vehicle moving operation when the average humidity reaches the target range and the remaining drying time is less than a safety threshold.

9. A closed-loop drying mechanism according to claim 4, characterized in that, The actuator group further includes at least one of the following: the exhaust fan speed regulation module, the air valve opening regulation module, the solenoid valve opening regulation module, and the compressor frequency regulation module.

10. A closed-loop drying mechanism according to claim 1, characterized in that, An electrical box is installed on the side wall of the integrated shell to house the electrical control components of the drying equipment.

11. A tunnel-type mushroom drying system, characterized in that, It includes a closed-loop drying mechanism as described in any one of claims 1-10.

12. A tunnel-type mushroom drying system according to claim 11, characterized in that, The drying chamber houses three of the aforementioned trolleys side by side, forming a continuous three-section counter-current drying tunnel.

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