A micro-channel aluminum tube integrated forming method for energy-saving refrigeration equipment

Abstract

The present application relates to heat exchange equipment technical field, disclose a kind of microchannel aluminium row pipe integrated forming method for energy-saving refrigeration equipment, comprising: in extrusion die mouth establishes transverse asymmetric steady temperature field, and the plastic metal blank that flows through spontaneously integrally twists after departing from the constraint of die mouth due to the velocity difference in section endogeny, to integrate the parallel microchannel in its interior into spiral flow channel, the temperature unevenness that the present application will avoid in traditional extrusion process is changed into a controllable process element for directly building three-dimensional flow channel structure, so that the movement mode of fluid in heat exchange pipe is changed from laminar flow to composite motion containing secondary flow, so as to change the heat exchange path between pipe wall and main stream area fluid, solve the problem between the two-dimensional stretching characteristics of extrusion forming process and the three-dimensional flow field required by efficient heat exchange.

Description

Technical Field

[0001] This invention relates to a method for integrally forming microchannel aluminum tubes for energy-saving refrigeration equipment, belonging to the technical field of heat exchange equipment. Background Technology

[0002] Currently, heat exchangers made of aluminum alloy microchannel tubes have become a widely used mainstream technology choice due to their compact and efficient characteristics. Their manufacturing process usually relies on mature metal extrusion molding technology, which can mass-produce straight tubes with complex cross-sectional shapes and consistent geometric dimensions along the length direction.

[0003] However, from the perspective of the basic physical laws of fluid heat transfer, when a liquid or gas-liquid two-phase refrigerant flows in a straight microchannel with a smooth inner wall, it is very easy to form a stable laminar boundary layer with extremely low flow velocity close to the tube wall. This boundary layer has extremely high thermal resistance, which is like covering a layer of insulation on the critical path of heat transfer, becoming an obstacle that limits the heat transfer efficiency. In order to overcome the limitation of this boundary layer, existing technologies have made a series of subsequent compensatory attempts, such as etching the inner wall of the channel to increase roughness, adding turbulence-inducing plugs in the channel, or improving the working fluid formula. However, these methods are essentially post-processing or passive adaptation of an already formed straight flow channel. They enhance the disturbance to a certain extent, but also bring new problems such as increased process complexity, increased production costs, and increased refrigerant flow pressure drop. They do not fundamentally change the process path of first manufacturing a straight flow channel with performance limitations and then trying to make up for its deficiencies.

[0004] Analysis reveals that existing technologies are designed and optimized within an inherent technological contradiction: a fundamental mismatch exists between the two-dimensional stretching characteristics of extrusion molding and the three-dimensional turbulent flow field required for efficient heat exchange. Specifically, existing technologies suffer from the following shortcomings: 1. An inherent contradiction between molding methods and performance requirements: metal extrusion naturally and efficiently creates straight flow channels that are detrimental to heat transfer, and all efforts to improve performance are remedial measures under this premise; 2. Non-integrated process and economic constraints: the heat transfer enhancement steps are separated from the pipe extrusion molding process, leading to additional processes, equipment investment, and potential quality control points, increasing overall costs. Therefore, the technical problem to be solved by this invention is how to find a method that can directly and integrally construct a three-dimensional flow channel structure that can fundamentally change the fluid movement mode inside the pipe within the framework of the basic metal extrusion molding process, avoiding the series of problems caused by the separation of molding and enhancement phases in existing technologies. Summary of the Invention

[0005] This invention provides a method for integral molding of microchannel aluminum tubes for energy-saving refrigeration equipment. Its main purpose is to solve the problem that there is a contradiction between the two-dimensional characteristics of the extrusion molding process and the three-dimensional flow field required for efficient heat transfer in the prior art, and that the separation of heat transfer enhancement measures from the tube forming process leads to process complexity and increased cost.

[0006] To achieve the above objectives, this invention provides a method for integral molding of microchannel aluminum tubing for energy-saving refrigeration equipment. The method establishes and maintains a molding process that includes forward drive and closed-loop compensation. The molding process includes: Step a: In the die opening area of ​​the extrusion molding die, a static transverse temperature gradient across the aluminum flow cross section is established and maintained by controlling a heating unit and a cooling unit on two opposite sides of the die opening respectively. Step b: Heat aluminum or aluminum alloy material to a plastic state and let it flow through a die with a transverse temperature gradient. The transverse temperature gradient forms a flow velocity difference on the cross-section of the plastic aluminum material. When the plastic aluminum material leaves the die, the flow velocity difference is converted into a torsional torque acting on the entire aluminum tube, driving the aluminum tube to undergo overall axial torsion without the application of external mechanical torsional force, so that its internal microchannels are integrally formed into a spiral flow channel. Step c: While step b is being executed, the energy input power of the heating unit required to maintain a constant higher temperature region in the transverse temperature field is monitored in real time. Based on the deviation between the real-time monitored energy input power value and a reference power value obtained using standard aluminum material during the calibration phase, a temperature gradient adjustment amount is calculated via a control algorithm. Then, the magnitude of the transverse temperature gradient is automatically adjusted based on this temperature gradient adjustment amount to compensate for the deviation in the pitch of the spiral flow channel caused by the fluctuation of the thermophysical properties between batches of aluminum raw materials.

[0007] Preferably, the establishment and maintenance of a static transverse temperature gradient in step a specifically involves: maintaining a first target temperature on one side of the mold opening and a second target temperature lower than the first target temperature on the opposite side by controlling the heating power of the heating unit and the cooling rate of the cooling unit; and the torsional pitch of the spiral flow channel is controlled by adjusting the temperature difference between the first target temperature and the second target temperature.

[0008] Preferably, the method further includes periodically and symmetrically flipping the spatial direction of the transverse temperature gradient according to a defined time period. This flipping is achieved by alternately switching the temperature control state on both sides of the die opening between heating and cooling, thereby causing the aluminum tube to form multiple segments with alternating twisting directions along its length, thus constituting a conjugate spiral structure.

[0009] Preferably, the system performs periodic and symmetrical flipping according to a predetermined time period. Its control logic is defined as follows: within a control system, based on a control state function... To determine the temperature control mode on both sides of the mold opening, among which ,in, The current time is the time since the aluminum material began to flow steadily out of the die opening. This refers to a positive-zero flip-over cycle duration defined by the process specifications. This is the floor function; when When the calculation result is 0, the first side of the mold opening is in heating mode and the second side is in cooling mode. When the calculation result is 1, the first side of the mold opening is in cooling mode and the second side is in heating mode.

[0010] Preferably, the method further includes, while the extrusion process continues, continuously or in stages modulating the magnitude of the transverse temperature gradient according to a functional relationship calculated from the heat transfer demand along the target heat exchanger, so that a single aluminum tube forms a spiral flow channel with a non-uniform pitch along its length, so that the geometry of different sections of the aluminum tube matches the different phase states of the refrigerant inside the tube when it is used as an evaporator or condenser.

[0011] Preferably, a spiral flow channel with a non-uniform pitch is formed, specifically: for the aluminum tube used as an evaporator, the transverse temperature gradient is controlled to reach its maximum value in the initial stage of the extrusion process to form a spiral flow channel with the smallest pitch, which corresponds to the inlet liquid phase region of the refrigerant; subsequently, the transverse temperature gradient is smoothly reduced in a programmed manner along the extrusion time axis, so that the pitch of the spiral flow channel gradually increases along the length direction of the aluminum tube, which corresponds to the gas-liquid two-phase region and the outlet gas phase region of the refrigerant in sequence.

[0012] Preferably, the method further includes: installing an acoustic vibration sensor on the outside of the extrusion molding die or on a downstream fixed bracket adjacent to it, for real-time acquisition of the accompanying acoustic vibration signal when the aluminum tube undergoes overall axial torsion; performing pattern matching calculation on the spectral characteristics of the real-time acquired acoustic vibration signal with a reference acoustic feature template representing a stable molding process acquired in calibration production to obtain a matching degree value; and determining online whether the molding process of the spiral flow channel is in a stable state based on the matching degree value.

[0013] Preferably, online determination based on the matching degree value further includes: in the start-up stage of extrusion production, when the matching degree value first exceeds a first threshold, the forming process is determined to have entered a stable state, and a signal is generated to instruct the cutting equipment to retain the product from that moment; and in the continuous production stage, when the matching degree value is lower than a second threshold at a certain moment, the forming process is determined to have an abnormality, and an alarm signal is generated, while the product segment corresponding to the abnormal time period is recorded.

[0014] Preferably, the control algorithm in step c is a proportional-integral-derivative (PID) control algorithm; the PID control algorithm uses the deviation between the real-time monitored value and the reference power value as input to calculate the temperature gradient adjustment amount, and applies the temperature gradient adjustment amount to the set values ​​of the heating power of the heating unit and the cooling rate of the cooling unit.

[0015] Preferably, in step a, the temperature on one side of the heating unit is maintained in the range of 470 degrees Celsius to 490 degrees Celsius, and the temperature on the other side of the cooling unit is maintained in the range of 440 degrees Celsius to 460 degrees Celsius; in step b, the aluminum material is a 3000 series aluminum alloy or a 1000 series aluminum alloy; in step c, the monitoring frequency of the energy input power is 1 Hz to 10 Hz.

[0016] Compared with the prior art, the beneficial effects of the present invention are: 1. A horizontal static temperature gradient is established in the extrusion die area. Due to the temperature difference at different positions of the cross section, the aluminum material in the plastic state forms a stable velocity difference when flowing out of the die. After the aluminum material is freed from the geometric constraints of the die, the velocity difference in the cross section is converted into a torsional torque acting on the entire tube, driving the tube to undergo overall axial torsion, so that the originally parallel microchannels inside are integrally formed into a spiral flow channel. This forming process transforms the temperature unevenness that needs to be avoided in the traditional extrusion process into a controllable process element for directly constructing a three-dimensional flow channel structure. This changes the movement mode of the fluid inside the heat exchange tube from laminar flow to a composite movement including secondary flow, changing the heat exchange path between the tube wall and the mainstream fluid.

[0017] 2. By periodically alternating the spatial positions of the high-temperature and low-temperature zones on both sides of the die, the thermal load borne by the die tends to be symmetrical over any sufficiently long timescale, thereby suppressing die creep and precision loss caused by long-term unidirectional thermal stress. At the same time, the periodic alternation of this temperature field causes the extruded aluminum tube to form a section with alternating torsional directions along its length. When the fluid in the tube flows through the node where the torsional direction reverses, the established secondary flow vortex core is destroyed and reorganized, triggering local flow field disturbance, thus realizing a further disturbance of the boundary layer based on a single spiral flow channel.

[0018] 3. The energy input or output power used to maintain the die temperature field is used as a signal to sense changes in the thermophysical properties of the raw material. When the power value deviates from the reference, the system automatically adjusts the temperature gradient setting to compensate for the torsional pitch fluctuations that may be caused by batch-to-batch differences in raw materials. This constitutes a closed-loop control aimed at stabilizing the product geometry. This method uses the inherent energy flow information in the process for self-calibration, avoiding the impact of material property changes on product consistency and improving the stability of continuous production. While the extrusion process continues, the magnitude of the temperature gradient is continuously or in stages modulated according to a preset functional relationship, so that a single aluminum tube forms a spiral flow channel with a non-uniform pitch along its length. In this way, the geometry of different sections of the tube can match the different phase states of the refrigerant and the heat exchange requirements at the corresponding positions when used as an evaporator or condenser in actual heat exchange applications. This solidifies a flow-optimized design in the tube structure itself, avoiding the problem of adapting to different fluid states with a uniform structure. Attached Figure Description

[0019] Figure 1 This is a timing diagram of the signal flow and control logic of the online diagnostic method based on acoustic features of the present invention; Figure 2 This is a control effect curve of the closed-loop compensation procedure of the present invention when suppressing disturbances; Figure 3 This is a schematic diagram of the overall process flow and online diagnostic steps of the integral molding method of the present invention. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be described in detail below with reference to the accompanying drawings. However, those skilled in the art will understand that the specific embodiments described below are for illustrative purposes and should not be construed as limiting the scope of protection of the present invention.

[0021] This invention provides a method for integrally molding microchannel aluminum tubes for energy-saving refrigeration equipment. The method uses a molding procedure that includes forward drive and closed-loop compensation to integrally construct a microchannel aluminum tube with a built-in spiral flow channel during the tube extrusion molding stage. The molding procedure mainly includes an integral molding step of spiral flow channel based on thermal torsion, a spiral pitch closed-loop compensation step based on heat dissipation characteristics, and, depending on the application requirements, can also selectively configure a conjugate spiral structure molding step based on dynamic thermal balance, a functional gradient pitch modulation step based on friction heat transfer requirements, or an online diagnostic step of the molding process based on acoustic characteristics.

[0022] In the extrusion process of heat exchange equipment, when a liquid or gas-liquid two-phase refrigerant flows within a smooth, straight microchannel, the heat transfer efficiency is limited due to the presence of a laminar boundary layer. To address this issue, a static transverse temperature gradient spanning the aluminum flow cross-section is established and maintained in the die region of the extrusion die by controlling a heating unit and a cooling unit on opposite sides of the die. Specifically, the initial conditions for this step are: using a microchannel aluminum tube extrusion die, targeting 3000 series or 1000 series aluminum alloys in a plastic state; a heating unit consisting of ceramic heating rods integrated into the outer wall of one side of the die; and a cooling unit consisting of circulating cooling channels processed into the outer wall of the opposite side. Furthermore, a quantified process procedure is used to establish the transverse temperature gradient, i.e., by controlling the heating power of the heating unit and the cooling rate of the cooling unit, a static transverse temperature gradient is maintained on one side of the die. A first target temperature is set, and a second target temperature, lower than the first target temperature, is maintained on the opposite side. To ensure the effectiveness and process stability of this temperature gradient, the first target temperature is set between 470°C and 490°C, while the second target temperature is set between 440°C and 460°C. It should be noted that the torsional pitch of the spiral flow channel is controlled by adjusting the temperature difference between the first and second target temperatures. The larger the temperature difference, the smaller the pitch. Thus, when the ductile aluminum flows through the die with the transverse temperature gradient, the temperature difference at different locations on the cross section causes a difference in the viscosity of the aluminum, which in turn forms a stable flow velocity difference. After the aluminum leaves the geometric constraint of the die, the flow velocity difference within the cross section is converted into a torsional torque acting on the entire tube, driving the tube to undergo an overall axial torsion without the application of external mechanical torsional force, so that the originally parallel microchannels inside are integrally formed into a spiral flow channel.

[0023] During continuous production, the thermophysical properties of different batches of aluminum raw materials fluctuate, which may affect the consistency of the spiral pitch formed under a fixed temperature difference. Therefore, the system employs the following procedure for compensation: While forming the integrated spiral flow channel, the system monitors in real-time the energy input power of the heating unit required to maintain a constant higher temperature region in the transverse temperature field. This monitoring is performed by a power sensor at a frequency of 1 Hz to 10 Hz. The physical meaning of this energy input power is to compensate for the total heat absorbed and carried away by the flowing aluminum material; therefore, fluctuations in this power reflect changes in the thermophysical properties of the aluminum raw material. To convert this monitored value into operable control commands, an initial calibration procedure is first executed. Before production, a batch of standard aluminum material is used for calibration production, and the energy input power of the heating unit under stable forming conditions is recorded as a reference power value. During formal production, a quantitative process judgment procedure is continuously executed. This procedure uses the deviation between the real-time monitored energy input power value and the reference power value as input, and calculates a temperature gradient adjustment amount through a proportional-integral-derivative control algorithm. As a numerical example, if the reference power value is... Real-time monitoring value Then the deviation The proportional-integral-derivative control algorithm will control the deviation. As input, the temperature gradient adjustment amount is calculated. The temperature gradient adjustment is applied to the set values ​​of the heating power of the heating unit and the cooling rate of the cooling unit, thereby automatically adjusting the magnitude of the lateral temperature gradient. In this way, the pitch deviation of the spiral flow channel caused by the fluctuation of the thermophysical properties between batches of aluminum raw materials is compensated.

[0024] For applications requiring continuous production over extended periods, extrusion dies subjected to asymmetrical thermal loads may experience creep and loss of precision. To balance this thermal load, the system can employ a dynamic thermal balance procedure. This procedure achieves balance by periodically and symmetrically reversing the spatial direction of the lateral temperature gradient according to a defined time period. The control logic for this reversal is defined by a control state function. Determined, its expression is ,in, The current time is the time since the aluminum material began to flow steadily out of the die opening. This refers to a positive zero flip-over cycle duration set by the process specifications. This is the floor function; when When the calculation result is 0, the first side of the mold opening is in heating mode and the second side is in cooling mode, while when... When the calculation result is 1, the first side of the die is in cooling mode and the second side is in heating mode; through the periodic alternation of this temperature field, the extruded aluminum tubes form multiple segments with alternating twisting directions along their length, forming a conjugate spiral structure.

[0025] In specific heat exchange applications, such as when used as an evaporator in a refrigeration system, the refrigerant inside the tube undergoes a continuous change from liquid to a two-phase gas-liquid system and then back to a gas phase. Different phase regions have different requirements for the flow channel geometry. To achieve flow channel matching between the aluminum tube structure and its internal fluid state, the method of this invention further includes continuously or in stages modulating the magnitude of the transverse temperature gradient according to a function pre-calculated based on the flow channel heat transfer requirements of the target heat exchanger while the extrusion process is ongoing. Specifically, for aluminum tubes used as evaporators, the modulation procedure is set such that, in the initial stage of the extrusion process, the transverse temperature gradient is set to its maximum value to form a spiral flow channel with the smallest pitch. This section corresponds to the liquid phase region at the refrigerant inlet where heat transfer needs to be enhanced. Subsequently, along the extrusion time axis, the transverse temperature gradient is programmed and smoothly reduced, causing the pitch of the spiral flow channel to gradually increase along the length of the aluminum tube, corresponding sequentially to the two-phase gas-liquid region of the refrigerant and the outlet gas phase region where the flow pressure drop needs to be reduced. In this way, a single aluminum tube forms a spiral flow channel with a non-uniform pitch along its length.

[0026] Considering that the self-organizing forming process of the spiral flow channel occurs in a high-temperature and enclosed region, its stable state is difficult to determine through direct observation. To address this online diagnostic issue, the method also includes an online monitoring procedure based on acoustic vibration signals. The initial condition of this procedure is to install an acoustic vibration sensor on the outside of the extrusion die or on its adjacent downstream fixed support to collect the acoustic vibration signals accompanying the overall axial torsion of the aluminum tube in real time. To establish a judgment benchmark, a calibration process is first executed, i.e., in a calibration production run, vibration signals representing the stable forming process are collected, and their spectral characteristics are processed into a reference acoustic feature template. In formal production, a... The quantification process judgment procedure is continuously executed. This procedure performs pattern matching calculations on the spectral characteristics of the acoustic vibration signals collected in real time with a reference acoustic feature template to obtain a matching degree value. Based on this matching degree value, the system can determine online whether the forming process is in a stable state. Specifically, in the start-up stage of extrusion production, when the matching degree value first exceeds a first threshold determined in the calibration stage, the forming process is determined to have entered a stable state, and a signal is generated to instruct the cutting equipment to retain the product from that moment. In the continuous production stage, when the matching degree value falls below a second threshold also determined in the calibration stage at a certain moment, the forming process is determined to have an abnormality, and an alarm signal is generated.

[0027] Example 1: In a task involving the production of high-efficiency evaporators for a variable frequency air conditioning system, the production process needs to meet higher seasonal energy efficiency ratio targets. Simultaneously, the heat transfer characteristics of the novel refrigerant used in the two-phase region place higher demands on the turbulence state of the fluid within the heat exchanger tubes. Traditional methods of increasing heat exchanger volume or fin density, while increasing cost and system operating pressure drop, offer limited performance improvements and cannot meet design requirements. In this application, the production line utilizes the integrated molding method of this invention. In a continuous extrusion production task, a static transverse temperature gradient spanning the aluminum flow cross-section is first established in the extrusion die region, allowing the extruded 3000 series aluminum alloy micro-channels to achieve optimal heat transfer. The integrated molding of the tubing into an aluminum pipe with a built-in spiral flow channel introduces secondary flow into the refrigerant flow path, disturbing the laminar boundary layer near the pipe wall and providing structural conditions for improving the heat transfer efficiency in the two-phase region. During the middle stage of the production process, due to the adjustment of the production plan, the aluminum raw material was changed to a batch provided by another supplier. The alloy grade and mechanical properties of this batch of material met the standards, but the slight difference in its composition caused its thermophysical properties to deviate from the previous batch. This deviation is reflected in the energy input power required to maintain a constant temperature in the high-temperature zone of the die. The real-time monitoring value of this power showed a continuous drift compared to the reference power value obtained in the initial calibration stage.

[0028] At this point, the spiral pitch closed-loop compensation procedure based on heat dissipation characteristics automatically runs. The system does not interrupt production; instead, through its built-in proportional-integral-derivative control algorithm, it converts the monitored energy input power deviation into a real-time adjustment command for the temperature difference on both sides of the die. Specifically, the controller increases the power output of the heating unit and adjusts the cooling rate of the cooling unit accordingly, thereby increasing the transverse temperature gradient by a compensation amount to offset the weakening effect of the speed difference caused by changes in the thermophysical properties of the new batch of aluminum. After this automatic compensation, the spiral pitch of the extruded aluminum tubes is stabilized within the target tolerance range. The entire process achieves adaptive adjustment to raw material fluctuations. This process demonstrates the synergistic effect of the integrated spiral flow channel forming step and the spiral pitch closed-loop compensation step; that is, the former constructs a geometry that enhances heat transfer. The latter provides process stability unaffected by upstream raw material fluctuations, ensuring the precise and consistent production of this geometric structure. Instead of employing secondary processing on already formed straight tubes to enhance disturbance, this method integrates the construction of the three-dimensional flow channel structure within the tube extrusion molding process. It utilizes the temperature inhomogeneity that typically needs to be suppressed in the extrusion process, transforming it into a controllable forming driving force. This solves the process mismatch between the two-dimensional stretching characteristics of metal extrusion and the three-dimensional flow field required for efficient heat exchange. Ultimately, the evaporator assembled with spiral flow channel aluminum tubes produced using this method exhibits an improved overall heat transfer coefficient compared to evaporators using traditional straight microchannel tubes, enabling the entire air conditioning system to meet the preset energy efficiency ratio design target without increasing the heat exchanger size.

[0029] Example 2: To objectively verify the effectiveness of the microchannel aluminum tube prepared by the integral molding method of the present invention in enhancing heat transfer, a comparative experiment was conducted. The purpose of the experiment was to quantitatively compare the heat transfer performance and flow resistance differences between the aluminum tube with spiral flow channels prepared by the method of the present invention (the test group) and the aluminum tube with straight flow channels of the same cross-sectional dimensions manufactured by the conventional method (the control group) under simulated typical refrigeration system evaporator conditions. The experiment was conducted on a standard refrigerant thermophysical property testing platform, which mainly consists of a compressor, condenser, mass flow meter, expansion valve, and a test section for mounting the test tube sample. The data acquisition system equipped on the platform has a temperature sensor with a measurement accuracy of ±0.1. The pressure sensor has a measurement accuracy of ±0.5% of full scale, and the Coriolis mass flow meter has a measurement accuracy of ±0.2% of the reading. Both sets of samples used in the experiment were made of 3000 series aluminum alloy with the same geometry and material grade. The control group sample had parallel linear microchannels manufactured using a standard extrusion process, while the experimental group sample used the method described in this invention, applying a static transverse temperature gradient at the extrusion die to integrally form a spiral flow channel with a uniform pitch. During the experiment, the control and experimental group samples were sequentially installed in the test section, using refrigerant R134a as the working fluid. To simulate typical operating conditions in the gas-liquid two-phase region of the evaporator, the experimental conditions were set to an evaporation temperature of 5... The refrigerant inlet dryness fraction was 0.2 and the outlet dryness fraction was 0.8. Tests were conducted at multiple different mass flow rates. For each operating point, data was continuously collected and averaged after the system had stabilized. The average heat transfer coefficient and pressure drop along the flow path were then calculated.

[0030] The experimental results show that, under all test conditions, the heat transfer performance of the experimental group is better than that of the control group; for example, at a mass flow rate of... At that time, the average heat transfer coefficient of the control group was The average heat transfer coefficient of the experimental group reached The increase was approximately 39.8% when the mass flow rate increased to At that time, the average heat transfer coefficient of the control group was The experimental group was The increase was approximately 50.1%; regarding flow resistance, the pressure drop in the test group increased. At the mass flow rate, its pressure drop was 27.6 kPa, an increase of 24.9% compared to the control group's 22.1 kPa. At a mass flow rate, the pressure drop was 63.5 kPa, an increase of 31.7% compared to the control group's 48.2 kPa. Data analysis indicates that the spiral flow channel structure inside the experimental sample, by superimposing radial secondary flow in the mainstream direction, disturbs and thins the laminar boundary layer near the tube wall, which is the direct reason for the improved heat transfer performance. Experimental data confirm that the microchannel aluminum tube with spiral flow channel integrally manufactured using the method of this invention can achieve improved heat transfer performance compared to traditional straight flow channel tubes, with only a limited increase in flow resistance, providing an effective technical solution for the design and manufacture of heat exchangers for energy-saving refrigeration equipment.

[0031] Example 3: This example combines Figures 1 to 3 This document describes a method for integrally molding microchannel aluminum tubing for energy-saving refrigeration equipment, as follows: Figure 1As shown in the diagram, the five interactive units—acoustic vibration sensor, signal processing unit, pattern matching algorithm, control system, and cutting equipment—are arranged sequentially. The entire process is conducted in a continuous loop monitoring. First, the acoustic vibration sensor continuously transmits vibration signals to the signal processing unit. After performing spectrum analysis, the latter sends the spectrum characteristics to the pattern matching algorithm module. This module then returns the calculated matching degree value to the control system. The control system then makes judgments based on this value and the different stages of production. In an alt condition judgment block, if the current stage is the start-up phase and the matching degree is greater than the second threshold, the system determines that the forming process has entered a stable state and sends a signal to the cutting equipment to start retaining products. If the current stage is the production phase and the matching degree is less than the second threshold, the system determines that the process is abnormal and performs two actions: generating an abnormal alarm and recording products during the abnormal time period. Under normal operating conditions, i.e., when the matching degree is within the normal range, normal production continues.

[0032] like Figure 2 As shown in the figure, the horizontal axis represents time (s) and the vertical axis represents the helical pitch (mm). A dashed line in the figure represents the target pitch, which is constant at 25mm, while a solid line represents the dynamic change of the actual pitch. As can be seen from the figure, around 20s, the actual pitch begins to deviate sharply from the target pitch due to disturbance, reaching a peak of nearly 33mm at about 30s. Subsequently, under the action of the closed-loop control system, the actual pitch begins to fall back, and after a brief overshoot and oscillation, it converges and stabilizes near the target pitch of 25mm at about 90s.

[0033] like Figure 3 As shown in the figure, the process begins with feeding aluminum / aluminum alloy plastic billet into an extrusion device. Through two process steps—establishing a transverse temperature gradient and thermo-induced torsion extrusion—a spiral flow channel microchannel aluminum tube is manufactured in an integrated manner. During this forming process, a parallel closed-loop compensation loop is activated. This loop monitors the heating unit power in real time to sense changes in the thermophysical properties of the raw material and compares the monitored value with a reference power value to calculate the deviation between the real-time monitored value and the reference value. This deviation is then fed into a PID algorithm to calculate the adjustment amount. This algorithm calculates the temperature gradient adjustment amount based on the deviation and feeds it back to the transverse temperature gradient establishment step, thus forming a closed-loop production process quality monitoring system aimed at stabilizing the product geometry.

[0034] Example 4: In a specific production preparation scenario, the task is to establish stable mass production capacity for a microchannel aluminum tube with a specific target helical pitch. When using a new batch of 3000 series aluminum alloy raw material, its thermophysical properties deviate from the calibration benchmark. To ensure that the response of the closed-loop compensation system can effectively suppress the deviation and avoid overshoot oscillation, the proportional, integral, and derivative gain parameters of the PID controller need to be set before mass production. Therefore, a systematic calibration process is executed. The initial conditions of this process are: the extrusion equipment is at a stable operating temperature; a standard batch of aluminum material is used; in open-loop control mode (i.e., without enabling closed-loop compensation), a benchmark lateral temperature gradient is set, and the energy input power of the heating unit during the stable extrusion process is recorded and defined as the benchmark power value. Next, in the second stage of the process, a new batch of aluminum alloy raw material to be tested is fed into the extruder while maintaining the aforementioned baseline transverse temperature gradient. At this time, the data acquisition system simultaneously monitors and records two process variables at a frequency of 10 Hz: one is the real-time value of the energy input power of the heating unit. The second is the real-time measurement value of the spiral pitch of the extruded pipe, which is obtained through an online laser measurement device located immediately downstream of the die.

[0035] By analyzing the collected data, the system's response characteristic curve to a step disturbance in the raw material properties can be obtained; specifically, through calculation... and The deviation can quantify the disturbance magnitude of the energy flow caused by changes in raw material, while the corresponding change in the screw pitch reveals the dynamic response characteristics of the system. Based on this set of measured data containing the system's input disturbance and output response, the critical gain of the control loop is calculated using the Ziegler-Nichols tuning method in the field of process control. With critical oscillation period As a numerical deductive example, if the above experiments show that for a specific system, its The value is 1.5. If the value is 50 seconds, then the three key parameters of the PID controller can be calculated, namely the proportional gain. Set as That is, 0.9, integral gain Set as That is, 0.036, the differential gain. Set as That is, 5.625; after writing this set of parameters calculated through the calibration procedure into the controller, the raw material switching test was repeated again. At this time, the closed-loop compensation system was already in an active state; the monitoring results showed that when a new batch of aluminum material entered the die and caused fluctuations in energy input power, the control system adjusted the transverse temperature gradient according to the newly set PID parameters, so that the helical pitch of the final product converged and stabilized within the preset target tolerance range after experiencing a small and brief fluctuation; this procedure transformed a parameter setting process that relied on experience adjustment into an engineering calibration process with data support, clear steps, and reproducible results.

[0036] Example 5: When deploying a production line for high-volume, long-cycle continuous production of microchannel aluminum tubes, the following pre-calibration procedure was performed to ensure the dimensional stability of the extrusion die under long-term asymmetric thermal load and to establish a judgment benchmark for the online quality diagnostic system. In this procedure, the production line first adopts dynamic thermal balance control logic for production. Specifically, the control system operates based on the control state function. With a 300-second flip cycle duration The transverse temperature gradient on both sides of the mold opening is periodically and symmetrically flipped. In this way, the cumulative heat load on both sides of the mold in any complete 600-second cycle is symmetrical, thereby suppressing mold creep and precision loss that may be caused by long-term unidirectional thermal stress.

[0037] After the production line reaches thermal equilibrium and operates stably for one hour, the calibration program of the online diagnostic system for the molding process based on acoustic characteristics is initiated. During this period, acoustic vibration sensors installed on the outside of the extrusion die continuously collect acoustic vibration signals associated with the stable molding process. The signal processing unit performs continuous spectrum analysis on the collected signals and averages all spectrum data within one hour over time to calculate the average power spectral density and its standard deviation at each frequency point, thereby generating a reference acoustic feature template that includes the statistical fluctuation range. Subsequently, two key thresholds for process judgment are set based on this template. The first threshold for judging that the process has stabilized in the start-up phase is set at a matching degree of 98% between the real-time spectrum characteristics and the template, which corresponds to the real-time signal falling within the confidence interval of the template's statistical distribution. The second threshold for judging process anomalies in the continuous production phase is set at a matching degree of less than 90%, which corresponds to a significant level of deviation of the real-time signal from the template's statistical distribution. This procedure provides a quantitative basis for the long-term stability of the die and online monitoring of product quality for subsequent mass production.

[0038] Example 6: In a scenario where a non-uniform pitch microchannel aluminum tube is being developed for a specific evaporator, the design requires the spiral pitch of the tube to vary precisely along its length to match the heat exchange needs of different areas. The core of this engineering task lies in translating the spatial geometric requirements into precise control of the transverse temperature gradient over time during the extrusion process. Therefore, before formal production, a standardized offline calibration procedure must be executed to establish a quantitative relationship model between process parameters and product geometry. This calibration procedure is performed on a process testing extrusion platform equipped with a high-precision infrared thermal imager and a laser displacement sensor. The first step of the procedure is a systematic parameter scan. Using the same 3000 series aluminum alloy as the target product, the testers conduct a series of short-time extrusion tests at a fixed extrusion speed. In each test, the transverse temperature gradient on both sides of the die is measured. It is set to a constant value, which ranges from 10. Begin with 5 The increment will gradually increase to 50. In each After the spiral pitch of the extruded tube stabilizes at the set point, record the current value. The precise value and the stable helical pitch measured online by laser measuring equipment. The values, thus obtaining a set of ( , Corresponding relationship dataset.

[0039] Based on the dataset obtained from the scanning experiment using this parameter, a model describing the helical pitch was established through polynomial regression fitting. With lateral temperature gradient The mathematical model of the functional relationship between them is in the form of: Once this mathematical model is obtained, it can be applied to the generation of production control programs for specific products. First, the design scheme along the pipe length... Distribution of helical pitch requirements Through a known stable extrusion speed Converted to along the extrusion time Distributed helical pitch target curve ,in Then, by solving the inverse function of the previously calibrated mathematical model. The target curve of the helical pitch Ultimately, this translates into the time-varying lateral temperature gradient setpoint curve required by the controller. ; this By loading the curve into the process controller of the production equipment, microchannel aluminum tubes with a preset non-uniform pitch can be extruded in continuous production. This procedure transforms a process that relies on trial and error to determine process parameters into a control program generation process based on model prediction.

[0040] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention.

[0041] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for integrally molding microchannel aluminum tubing for energy-saving refrigeration equipment, characterized in that, The method establishes and maintains a molding procedure that includes positive drive and closed-loop compensation. The molding procedure includes: Step a: In the die opening area of ​​the extrusion molding die, a static transverse temperature gradient across the aluminum flow cross section is established and maintained by controlling a heating unit and a cooling unit on two opposite sides of the die opening respectively. Step b: Heat aluminum or aluminum alloy material to a plastic state and let it flow through a die with a transverse temperature gradient. The transverse temperature gradient forms a flow velocity difference on the cross-section of the plastic aluminum material. When the plastic aluminum material leaves the die, the flow velocity difference is converted into a torsional torque acting on the entire aluminum tube, driving the aluminum tube to undergo overall axial torsion without the application of external mechanical torsional force, so that its internal microchannels are integrally formed into a spiral flow channel. Step c: While step b is being executed, the energy input power of the heating unit required to maintain a constant higher temperature region in the transverse temperature field is monitored in real time. Based on the deviation between the real-time monitored energy input power value and a reference power value obtained using standard aluminum material during the calibration phase, a temperature gradient adjustment amount is calculated via a control algorithm. Then, the magnitude of the transverse temperature gradient is automatically adjusted based on this temperature gradient adjustment amount to compensate for the deviation in the pitch of the spiral flow channel caused by the fluctuation of the thermophysical properties between batches of aluminum raw materials.

2. The method for integral molding of microchannel aluminum tubing for energy-saving refrigeration equipment according to claim 1, characterized in that, In step a, establishing and maintaining a static transverse temperature gradient specifically involves: maintaining a first target temperature on one side of the mold opening and a second target temperature lower than the first target temperature on the opposite side by controlling the heating power of the heating unit and the cooling rate of the cooling unit; and controlling the torsional pitch of the spiral flow channel by adjusting the temperature difference between the first target temperature and the second target temperature.

3. The method for integral molding of microchannel aluminum tubing for energy-saving refrigeration equipment according to claim 1, characterized in that, The method also includes periodically and symmetrically flipping the spatial direction of the transverse temperature gradient according to a certain time period. This flipping is achieved by alternately switching the temperature control state on both sides of the die opening between heating and cooling, so that the aluminum tube forms multiple segments with alternating twisting directions along its length, forming a conjugate spiral structure.

4. The method for integral molding of microchannel aluminum tubing for energy-saving refrigeration equipment according to claim 3, characterized in that, The system performs periodic, symmetrical flipping according to a predetermined time period. Its control logic is defined as follows: Within a control system, based on a control state function... To determine the temperature control mode on both sides of the mold opening, among which ,in, The current time is the time since the aluminum material began to flow steadily out of the die opening. This refers to a positive-zero flip-over cycle duration defined by the process specifications. This is the floor function; when When the calculation result is 0, the first side of the mold opening is in heating mode and the second side is in cooling mode. When the calculation result is 1, the first side of the mold opening is in cooling mode and the second side is in heating mode.

5. The method for integral molding of microchannel aluminum tubing for energy-saving refrigeration equipment according to claim 1, characterized in that, The method also includes continuously or in stages modulating the magnitude of the transverse temperature gradient according to a function relationship calculated from the heat exchange demand along the target heat exchanger while the extrusion process continues, so that a single aluminum tube forms a spiral flow channel with a non-uniform pitch along its length, so that the geometry of different sections of the aluminum tube matches the different phase states of the refrigerant inside the tube when it is used as an evaporator or condenser.

6. The method for integral molding of microchannel aluminum tubing for energy-saving refrigeration equipment according to claim 5, characterized in that, To form a spiral flow channel with a non-uniform pitch, specifically: for aluminum pipes used as evaporators, the transverse temperature gradient is controlled to reach its maximum value in the initial stage of the extrusion process to form a spiral flow channel with the smallest pitch, which corresponds to the inlet liquid phase region of the refrigerant; subsequently, the transverse temperature gradient is smoothly reduced in a programmed manner along the extrusion time axis, so that the pitch of the spiral flow channel gradually increases along the length direction of the aluminum pipe.

7. The method for integral molding of microchannel aluminum tubing for energy-saving refrigeration equipment according to claim 1, characterized in that, The method also includes: installing an acoustic vibration sensor on the outside of the extrusion molding die or on its adjacent downstream fixed support to collect the accompanying acoustic vibration signal in real time when the aluminum tube undergoes overall axial torsion; performing pattern matching calculation on the spectral characteristics of the real-time collected acoustic vibration signal with a reference acoustic feature template representing a stable molding process collected in calibration production to obtain a matching degree value; and determining online whether the molding process of the spiral flow channel is in a stable state based on the matching degree value.

8. The method for integral molding of microchannel aluminum tubing for energy-saving refrigeration equipment according to claim 7, characterized in that, The online determination based on the matching degree value further includes: in the start-up stage of extrusion production, when the matching degree value exceeds a first threshold for the first time, the forming process is determined to have entered a stable state, and a signal is generated to instruct the cutting equipment to retain the product from that moment; and in the continuous production stage, when the matching degree value is lower than a second threshold at a certain moment, the forming process is determined to have an abnormality, an alarm signal is generated, and the product segment corresponding to the abnormal time period is recorded.

9. The method for integral molding of microchannel aluminum tubing for energy-saving refrigeration equipment according to claim 1, characterized in that, In step c, the control algorithm is a proportional-integral-derivative (PID) control algorithm. This PID control algorithm takes the deviation between the real-time monitored value and the reference power value as input, calculates the temperature gradient adjustment amount, and applies the temperature gradient adjustment amount to the set values ​​of the heating power of the heating unit and the cooling rate of the cooling unit.

10. The method for integral molding of microchannel aluminum tubing for energy-saving refrigeration equipment according to claim 1, characterized in that, In step a, the temperature on one side of the heating unit is maintained in the range of 470 degrees Celsius to 490 degrees Celsius, and the temperature on the other side of the cooling unit is maintained in the range of 440 degrees Celsius to 460 degrees Celsius; in step b, the aluminum material is 3000 series aluminum alloy or 1000 series aluminum alloy. In step c, the monitoring frequency of the energy input power is 1 Hz to 10 Hz.

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