Efficient heat exchange method of refrigeration and defrosting integrated liquid separation head

Abstract

The invention provides an efficient heat exchange method of a refrigeration and defrosting integrated liquid separation head. In the refrigeration stage, a three-dimensional rotational flow field is generated through a spiral guide plate, a gas-liquid thermal boundary layer is destroyed in combination with a pulsating pressure field, and the heat exchange coefficient is increased to 1500 W / (m < 2 >. K) or above; in the defrosting stage, a reverse heat transfer path is constructed, heat transfer is enhanced through beveled flow deflectors, and the defrosting time is shortened to be within 3.5 minutes. The proportion of hydrophilic and hydrophobic areas on the surface of the liquid separation head is dynamically regulated and controlled through the electrowetting effect, frosting in the refrigeration period is restrained, and defrosting in the frosting period is accelerated. Defrosting waste heat is recycled to preheat a refrigerant, and the COP of the system is increased to 3.5 or above. And based on the differential pressure change rate and infrared thermal imaging data fusion, an LSTM model is adopted to predict the thickness of a frost layer, and accurate defrosting triggering is achieved. The liquid distribution head solves the problems that a traditional liquid distribution head is low in heat transfer efficiency and high in defrosting energy consumption, and is suitable for cold-chain logistics and industrial refrigeration systems.

Description

Technical Field

[0001] The invention relates to the technical field of heat exchange, and in particular to a high-efficiency heat exchange method for a refrigeration and defrosting integrated liquid dispensing head. Background Art

[0002] In the field of heat exchange technology, refrigeration and defrosting are the key links in the operation of many refrigeration equipment. In the actual operation of refrigeration equipment such as refrigerators, air conditioners, cold storage, etc., efficient heat exchange plays a decisive role in equipment performance, energy consumption and operational stability.

[0003] In traditional refrigeration systems, the refrigeration and defrosting functions are often relatively independent, and there are many deficiencies in the heat exchange process. During the refrigeration stage, the flow pattern and heat transfer efficiency of the refrigerant in the liquid distributor head need to be improved. The conventional liquid distributor head design makes the gas-liquid two-phase flow of the refrigerant unevenly distributed, resulting in low phase change heat transfer efficiency of the refrigerant in some flow channels, which in turn affects the overall refrigeration effect. The refrigerant is mostly in a laminar state in the flow channel, and the heat transfer coefficient is low, which limits the cooling capacity and energy efficiency improvement of the refrigeration system.

[0004] During the defrosting stage, the traditional method usually adopts a simple heating defrosting method, which not only takes a long time and consumes a lot of energy, but also is prone to incomplete defrosting. The traditional defrosting heat exchange method lacks an effective reverse heat transfer path design, and the heat transfer efficiency between the defrosting medium and the refrigerant is not high, making it difficult to achieve directional transmission of heat energy, resulting in a large amount of energy waste. In addition, due to the lack of accurate monitoring of the thickness and state of the frost layer, over-defrosting or under-defrosting often occurs. Over-defrosting will waste a lot of energy, while under-defrosting will cause the evaporator performance to decline, affecting the normal operation of the refrigeration equipment.

[0005] In addition, the surface wettability of the traditional dispensing head is fixed and cannot be dynamically adjusted according to the different stages of refrigeration and defrosting. During the refrigeration period, the surface of the dispensing head is prone to frost, and the gradual accumulation of frost will increase thermal resistance and reduce heat exchange efficiency; during the defrosting period, it is difficult to quickly promote the diffusion of the defrosting water film, which prolongs the defrosting time. At the same time, the traditional system has almost zero recycling of defrosting waste heat, resulting in a huge waste of energy and further reducing the energy efficiency of the system.

[0006] With the continuous improvement of people's requirements for the performance of refrigeration equipment and the increasing attention to energy conservation and emission reduction, it is urgent to develop an efficient heat exchange method for an integrated refrigeration and defrosting dispensing head to solve the above-mentioned problems existing in the prior art and improve the comprehensive performance and energy utilization efficiency of refrigeration equipment. Summary of the invention

[0007] In order to solve the above technical problems, the present invention provides a high-efficiency heat exchange method for a refrigeration and defrosting integrated liquid dispensing head.

[0008] The efficient heat exchange method of the integrated refrigeration and defrosting dispensing head of the present invention is specifically as follows:

[0009] 1. Swirl flow enhances heat transfer during the refrigeration stage

[0010] Through the internal flow channel design and dynamic control strategy of the liquid dispensing head, the refrigerant flow pattern and phase change heat transfer efficiency are optimized, including:

[0011] Three-dimensional spiral vortex field generation:

[0012] A spiral guide structure is arranged in the liquid separation head, the number of guide plate heads N=2-4, the spiral rise angle is 15°-35°, the thickness of the guide plate decreases from 1.5-2.5mm at the inlet end to 0.8-1.2mm at the outlet end along the flow direction, and the ratio of the guide plate spacing to the inner diameter of the liquid separation head is 0.2-0.4.

[0013] The refrigerant Reynolds number Re=5000-15000 is regulated, and the turbulent mixing efficiency in this range is verified by experiments. Through the upstream high-frequency solenoid valve, the solenoid valve model is: SMC VQZ3320-5G, the duty cycle is 30%-70%, and a pulsating pressure field with a frequency of 5-15Hz and an amplitude of 0.2-0.8MPa is applied. The pressure fluctuation is controlled within ±5% of the set value.

[0014] Phase change heat transfer enhancement:

[0015] V-shaped microgrooves with a depth of 0.1-0.3 mm and a spacing of 0.5-1.0 mm were processed on the surface of the guide plate using a laser etching device (IPG Photonics YLP-20, power 50 W, scanning speed 300 mm / s, argon protection) to enhance turbulent mixing at the gas-liquid interface.

[0016] By real-time monitoring of refrigerant flow and temperature and dynamically adjusting the guide plate inclination angle and pressure field parameters, the heat transfer coefficient can be increased to 2.3-2.8 times that of conventional laminar flow.

[0017] 2. Reverse gradient heat exchange during defrosting stage

[0018] Based on the dual-channel integrated design of the liquid distributor, a reverse heat transfer path between the refrigerant and the defrosting medium is constructed to achieve directional heat transfer and rapid melting of the frost layer:

[0019] Reverse flow channel layout:

[0020] The defrosting head adopts an integrated dual-channel design, with a refrigerant channel diameter D1 = 12mm, a defrost medium channel annular width W = 2.5mm, and a heat transfer angle of 150°-170° between the two channels, maximizing the counter-heat transfer temperature difference.

[0021] 3-5 groups of beveled guide vanes (inclination angle 45°-60°, height 1 / 4-1 / 3 of the flow channel height) are arranged in the defrost medium flow channel. The surface is coated with silicon carbide nano-coating (roughness Ra = 0.8-1.2μm) by PVD magnetron sputtering process (target material purity ≥ 99.9%, sputtering power 200W). The ratio of the guide vane spacing to the flow channel diameter is 0.6-1.0, which increases the Nusselt number Nu by 15%-25%.

[0022] Temperature-flow dual closed-loop control:

[0023] Primary defrost stage: When the evaporator surface temperature difference ΔT≥5℃, start the preheating mode, control the defrost medium temperature to 35-40℃, and the flow rate to 80%-100% of the reference value.

[0024] Enhanced defrosting stage: The thickness of the frost layer is detected by integrating infrared thermal imaging (FLIR T840) and a pressure differential sensor (model: Honeywell26PC). When the frost thickness is ≥ 2mm, it switches to the enhanced mode, raising the medium temperature to 45-55℃ and increasing the flow rate by 30%-50%.

[0025] Exit condition: Defrosting is terminated when the surface temperature uniformity standard deviation σ≤1.5℃ and the flow channel pressure difference recovers to ±5% of the initial value.

[0026] 3. Dynamic regulation of surface wettability

[0027] Based on the electrowetting effect, the hydrophilic and hydrophobic area distribution on the outlet surface of the dispensing head is dynamically switched to inhibit frost and accelerate defrosting:

[0028] Micro-nano composite surface preparation:

[0029] Laser etching technology (power 40-60W, scanning speed 200-400mm / s) is used to process hydrophilic stripes with a width of 100-200μm (contact angle ≤30°) on the substrate surface, and a fluorine-containing hydrophobic coating (contact angle ≥120°, thickness 500nm) is deposited in the non-etched area.

[0030] Dynamic Wettability Switching:

[0031] Cooling stage: Apply 0-10V voltage (power supply model: Keysight B2900A) to activate the hydrophobic area to account for ≥70% to inhibit the condensation droplets from agglomerating and forming frost.

[0032] Defrosting stage: increase the voltage to 30-50V (change rate ≤ 5V / s), so that the hydrophilic area accounts for ≥ 60%, the contact angle is reduced to ≤ 20°, and the diffusion of the defrosting water film is accelerated.

[0033] Electrowetting control response time ≤100ms, energy consumption density ≤3W / m 2, control accuracy ±3%.

[0034] 4. Energy coupling management

[0035] Optimize system energy efficiency through waste heat recovery and thermal storage technology:

[0036] Defrosting waste heat recovery:

[0037] A plate heat exchanger (model: SWEP B8T) is used to recover the heat of defrost drainage (temperature drops from 40-45°C to 25-30°C), preheat the air entering the evaporator, and reduce the refrigerant subcooling by 3-5°C.

[0038] The paraffin / expanded graphite composite phase change material (phase change temperature 38°C, heat storage density ≥180kJ / kg) is used to store 30%-40% of the defrosting waste heat.

[0039] Thermal storage release control:

[0040] When the temperature difference between the inlet and outlet of the dispensing head ΔT is less than 2°C, the heat storage material is triggered to release heat, so that the initial temperature of the evaporator is increased by 8-12°C, shortening the system startup time.

[0041] 5. Intelligent defrosting decision

[0042] Fusion of multi-sensor data and prediction algorithms to achieve precise defrost control:

[0043] Frost status detection:

[0044] The infrared thermal imager monitors the surface temperature distribution (resolution 0.05°C) and calculates the temperature gradient and frost growth rate.

[0045] The differential pressure sensor establishes a pressure difference-frost thickness mapping model, and the ultrasonic rangefinder (model: SICK UM30) measures the absolute thickness of the frost layer in real time (sampling frequency ≥ 10 Hz).

[0046] LSTM prediction model:

[0047] Input parameters: temperature, humidity, pressure difference, flow, voltage, and frost thickness time series data (historical data storage time ≥ 30 days, the data set contains 10,000 sets of operating data).

[0048] Model architecture: 2 hidden layers (64 nodes per layer), input parameter normalization method is Min-Max standardization, cross-validation accuracy ≥ 92%.

[0049] Control logic: When the predicted frosting rate is ≥0.2mm / min (error ≤±0.1mm / min), adjust the defrost medium temperature and flow set value 10-15 minutes in advance (control error ≤±1.5℃).

[0050] Compared with the prior art, the present invention has the following beneficial effects:

[0051] This method achieves the following core performance indicators through the above-mentioned collaborative control strategy (test standard: GB / T 7725-2004, testing agency: China Electric Power Research Institute):

[0052] Heat transfer efficiency: heat transfer coefficient ≥1500W / (m 2 K), 63%-70% higher than traditional methods;

[0053] Defrosting speed: Defrosting time ≤ 3.5 minutes, energy consumption reduced by 42%;

[0054] System energy efficiency: COP ≥ 3.5 (ISO 13253:2017), an improvement of 22%-25%;

[0055] Operation stability: frost layer regeneration cycle ≥ 4 hours, the number of invalid defrosting times is reduced by 43%. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 It is a flow chart of the technical solution of the present invention; DETAILED DESCRIPTION

[0057] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0058] like Figure 1 As shown,

[0059] Example 1: Structure and control process of integrated refrigeration and defrosting dispensing head

[0060] 1. The structure of the dispensing head

[0061] Main material: 6061-T6 aluminum alloy, the inner surface is anodized (thickness 20μm), and the outer surface is sprayed with a polyurethane insulation layer (thermal conductivity ≤ 0.03W / (m·K)).

[0062] Core components:

[0063] Spiral guide unit: Built-in 3-head spiral guide plate (N=3), spiral angle 25°, inlet thickness 2.0mm, outlet thickness 1.0mm, guide plate spacing to inner diameter ratio 0.3. V-shaped micro grooves (groove depth 0.2mm, spacing 0.8mm) are processed on the guide plate surface.

[0064] Double channel layout: the inner diameter of the refrigerant channel is 12mm, the width of the defrost medium annular channel is 2.5mm, and the heat transfer angle between the two channels is 160°. There are 4 sets of beveled guide vanes (inclination angle 50°, height 3mm) in the defrost channel, and the surface is coated with silicon carbide coating (Ra=1.0μm).

[0065] Electrowetting surface: The outlet surface is laser etched to prepare 200μm wide hydrophilic stripes (contact angle 25°), the non-etched area is sprayed with a fluorine-containing hydrophobic coating (contact angle 130°), and an ITO transparent electrode (square resistance ≤10Ω / □) is integrated.

[0066] 2. Implementation of swirl enhanced heat transfer in the refrigeration stage

[0067] Swirl field generation:

[0068] A 12 Hz, 0.5 MPa pulsating pressure field was applied through a high-frequency solenoid valve (SMC VQZ3320-5G), and the refrigerant flow rate was adjusted to make Re = 10,000 ± 500.

[0069] The inclination angle of the guide plate is dynamically adjusted by a stepper motor (model: Oriental Motor RKⅡ series), and the response time is ≤200ms.

[0070] Phase change heat transfer monitoring:

[0071] A Coriolis mass flow meter (Emerson CMF300) and a PT100 temperature sensor were used to provide real-time data feedback, and the pulsation parameters were adjusted using a PID algorithm (proportional coefficient Kp = 1.2, integral time Ti = 30 s).

[0072] The experimentally measured heat transfer coefficient is 1650W / (m 2 K), 2.5 times higher than traditional laminar flow.

[0073] 3. Implementation of reverse gradient heat exchange during defrosting stage

[0074] Reverse heat transfer control:

[0075] The defrosting medium (40% ethylene glycol solution) is preheated to the set temperature through a plate heat exchanger (SWEP B8T), and the flow rate is regulated by a variable frequency pump (Grundfos MAGNA3).

[0076] Primary defrosting stage: medium temperature 38°C, flow rate 2.5m 3 / h, for 1 minute; when the infrared thermal imager (FLIRT840) detects that the frost layer thickness is ≥ 2mm, switch to the enhanced mode (temperature 50℃, flow rate 3.8m 3 / h).

[0077] Eddy current strengthening verification:

[0078] CFD simulation (ANSYS Fluent) shows that the beveled guide vanes increase the Nusselt number of the defrosting medium by 21.3% and the melting rate reaches 0.8 mm / min.

[0079] 4. Implementation of dynamic control of surface wettability

[0080] Electrowetting control circuit:

[0081] Cooling stage: 5V DC voltage is applied, the hydrophobic area accounts for 75%, and the contact angle is 125°;

[0082] Defrosting stage: switch to 45V voltage (slope 3V / s), the hydrophilic area accounts for 65%, and the contact angle drops to 18°.

[0083] Energy consumption management: Pulse width modulation (PWM) technology is used, and the measured surface energy consumption is 2.7W / m 2 .

[0084] 5. Energy coupling management system

[0085] Waste heat recovery: The defrost wastewater (initial temperature 42°C) exchanges heat with fresh air through a plate heat exchanger, the temperature drops to 28°C, and 8.2kW·h / day of heat is recovered.

[0086] Phase change heat storage: Paraffin / expanded graphite composite phase change material (phase change temperature 38°C, latent heat 190kJ / kg) stores 35% of defrosting waste heat. When the system starts, it releases heat to increase the initial evaporator temperature by 10°C.

[0087] Trigger logic: When the temperature difference between the inlet and outlet of the dispensing head ΔT is less than 2°C, the PLC (Siemens S7-1200) controls the solenoid valve to release the stored heat, and the response delay is ≤5s.

[0088] 6. Intelligent defrosting decision system

[0089] Data Fusion:

[0090] The pressure difference sensor (Honeywell 26PC) has a sampling frequency of 20 Hz, and a pressure difference growth rate dP / dt and frost thickness mapping model (R 2 =0.96).

[0091] The infrared thermal imager scans the surface temperature field every 30 seconds and calculates the temperature non-uniformity (standard deviation σ).

[0092] LSTM prediction model:

[0093] Input parameters: ambient temperature and humidity, evaporation temperature, and frost thickness time series data (time window 60 minutes).

[0094] Model training: Using the TensorFlow framework, the training set accuracy is 93.5%, and the predicted frosting rate error is ±0.08mm / min.

[0095] Control output: When the predicted frost thickness is 1.8 mm, adjust the defrost parameters 12 minutes in advance.

[0096] Example 2: Performance Verification Experiment

[0097] Test conditions

[0098] Environmental conditions: dry bulb temperature 7°C / wet bulb temperature 6°C (GB / T 7725-2004);

[0099] Refrigerant: R410A, charge amount 1.2kg;

[0100] Test equipment: Agilent 34970A data logger, FLIR T840 thermal imager.

[0101] The test results are shown in the following table:

[0102]

[0103] Technology expansion plan

[0104] Multi-objective optimization design:

[0105] The NSGA-II algorithm was used to perform multi-parameter optimization on the guide plate helix angle and microgroove size, which increased the heat transfer to pressure drop ratio (j / f factor) by 18%.

[0106] Self-cleaning function extension:

[0107] Integration of TiO on electrowetting surfaces 2 Photocatalytic coating (thickness 500nm), achieves surface sterilization and organic matter decomposition under UV LED irradiation.

[0108] Digital Twin Operation and Maintenance:

[0109] A three-dimensional simulation model of the dispensing head is built based on Digital Twin technology to map the operating status in real time and predict the remaining life (error ≤ 5%).

[0110] The present invention significantly improves heat exchange efficiency and reduces energy consumption through the collaboration of structural innovation and intelligent control, and can be widely used in cold chain logistics, data center cooling and other fields.

[0111] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. An efficient heat exchange method for a refrigeration and defrosting integrated liquid dispensing head, characterized in that: The synergistic effect of refrigeration and defrosting can be achieved through the following steps: (a) Swirl-enhanced heat transfer in the refrigeration stage: A three-dimensional spiral swirling flow field is generated in the liquid separation head to regulate the momentum distribution and phase change heat transfer efficiency of the refrigerant gas-liquid two-phase flow; (b) Reverse gradient heat exchange during defrosting: A reverse heat transfer path between the refrigerant and the defrosting medium is established through the built-in double-channel structure of the liquid distributor, thereby achieving directional transmission of defrosting heat energy; (c) Dynamic regulation of surface wettability: Dynamically adjust the proportion of hydrophilic and hydrophobic areas on the outlet surface of the dispensing head according to the operation stage to inhibit frost formation during the refrigeration period and accelerate thaw during the defrosting period; (d) Energy coupling management: Recover the defrosting waste heat and feed it back to the dispensing head inlet for pre-temperature adjustment, reducing the refrigerant subcooling and defrosting energy consumption; (e) Intelligent defrost decision: Based on the fusion analysis of the internal pressure difference change rate of the dispensing head and the surface temperature distribution data, the frosting state is dynamically judged and the defrost operation is triggered. At the same time, the frost layer growth trend is predicted to adjust the defrost parameters in advance.

2. The high-efficiency heat exchange method of the integrated refrigeration and defrosting dispensing head according to claim 1, characterized in that: The method for generating the three-dimensional spiral vortex field in step (a) comprises: By adjusting the geometric parameters of the flow guide structure in the liquid separation head, the refrigerant generates a swirl trajectory with a spiral angle of 15°-35°; Maintain the refrigerant Reynolds number Re = 5000-15000, and the turbulence intensity ≥ 8%; A pulsating pressure field with a frequency of 5-15 Hz and an amplitude of 0.2-0.8 MPa is applied to destroy the thermal boundary layer of the gas-liquid interface.

3. The high-efficiency heat exchange method of the integrated refrigeration and defrosting dispensing head according to claim 2, characterized in that: The geometric parameter control of the flow guiding structure includes: The number of spiral guide plates is N = 2-4, and the thickness of the guide plates decreases along the flow direction, with the thickness at the inlet end being 1.5-2.5 mm and the thickness at the outlet end being 0.8-1.2 mm; The ratio of the guide plate spacing to the inner diameter of the liquid dispensing head is 0.2-0.4; V-shaped micro grooves are arranged on the surface of the guide plate, with a groove depth of 0.1-0.3 mm and a groove spacing of 0.5-1.0 mm.

4. The high-efficiency heat exchange method of the integrated refrigeration and defrosting dispensing head according to claim 1, characterized in that: The method for constructing the reverse heat transfer path in step (b) comprises: The defrost medium flow channel and the refrigerant flow channel are arranged in a concentric sleeve type, and the heat transfer angle between the two flow channels is 150°-170°; A vortex enhancement unit is set in the defrosting medium flow channel to increase the Nusselt number Nu by 15%-25%; The defrost medium temperature is dynamically adjusted according to the thickness of the frost layer: when the frost thickness is ≤1mm, the medium temperature is 35-40℃, and when the frost thickness is greater than 1mm, the temperature rises to 45-55℃.

5. The high-efficiency heat exchange method of the integrated refrigeration and defrosting dispensing head according to claim 4, characterized in that: The implementation of the eddy current enhancement unit includes: Arrange 3-5 groups of oblique guide vanes in the defrosting medium flow channel, with an inclination angle of 45°-60° and a height of 1 / 4-1 / 3 of the flow channel height; The surface of the guide vane is coated with silicon carbide nano-coating, with a roughness of Ra = 0.8-1.2μm; The ratio of the guide vane spacing to the flow channel diameter is 0.6-1.

0.

6. The high-efficiency heat exchange method of the integrated refrigeration and defrosting dispensing head according to claim 1, characterized in that: The dynamic regulation of surface wettability in step (c) is achieved by the following method: Prepare a micron-scale hydrophilic-hydrophobic alternating array on the outlet surface of the dispensing head, with the contact angle of the hydrophilic area ≤30° and the contact angle of the hydrophobic area ≥120°; Cooling stage: through the electrowetting effect, the hydrophobic area accounts for ≥ 70%, inhibiting the condensation droplets from coalescing and forming frost; Defrosting stage: switch to the hydrophilic area with a proportion of ≥ 60% to promote rapid diffusion of the defrosting water film.

7. A high-efficiency heat exchange method for a refrigeration and defrosting integrated dispensing head according to claim 6, characterized in that: The control parameters of the electrowetting effect include: Applied voltage 0-50V, voltage change rate ≤5V / s; The effective area ratio of the hydrophilic zone is linearly related to the voltage value, with a control accuracy of ±3%; Response time ≤100ms, energy density ≤3W / m 2 .

8. The high-efficiency heat exchange method of the integrated refrigeration and defrosting dispensing head according to claim 1, characterized in that: The implementation method of energy coupling management in step (d) includes: The defrost drainage heat is recovered by the plate heat exchanger, and the subcooling degree of the refrigerant at the inlet of the liquid distributor is reduced by 3-5℃; Phase change heat storage material is used to store 30%-40% of defrosting waste heat for preheating at the initial start of the system; A temperature difference feedback mechanism between the inlet and outlet of the dispensing head is established to trigger the release of stored heat when ΔT is less than 2°C.

9. The high-efficiency heat exchange method of the integrated refrigeration and defrosting dispensing head according to claim 1, characterized in that: Step (e) Intelligent defrosting decision: The frosting state is determined based on the internal pressure difference change rate of the dispensing head and the fusion of infrared thermal imaging data; When the pressure difference growth rate is ≥15% / h and the surface temperature unevenness is ≥5℃, start defrosting; Use LSTM neural network to predict frosting trends and adjust defrost parameters 10-15 minutes in advance.

10. A high-efficiency heat exchange method for a refrigeration and defrosting integrated dispensing head according to any one of claims 1 to 9, characterized in that: The conditions for achieving performance optimization indicators include: Heat transfer coefficient ≥1500W / (m 2 K); Defrosting time ≤ 3.5 minutes; System COP ≥ 3.5, COP refers to energy efficiency ratio; Frost layer regeneration cycle ≥ 4 hours.

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