An adaptive controllable electric field-enhanced spiral tube flow boiling heat transfer system

Abstract

The present invention discloses an adaptive controllable electric field enhanced spiral tube flow boiling heat transfer system belonging to the field of enhanced heat transfer technology. The spiral tube flow boiling heat transfer system includes a spiral tube heat exchanger, a thin film electrode, a temperature sensitive element, a temperature sensor, a control system, and a high-voltage AC power supply. The spiral tube heat exchanger is provided with a pair of thin film electrodes in the circumferential and axial directions, thereby forming a controllable high-voltage electric field in the spiral tube bundle; the spiral tube heat exchanger with a pair of thin film electrodes designed by the present invention can be coupled with an external electric field regulated by feedback from the control system to realize automatic control of the gas-liquid two-phase state of the flow boiling process in the spiral tube, effectively solving the problems of lack of active regulation of the flow boiling process under dynamic conditions in the spiral tube flow boiling and poor circumferential and axial heat transfer, thereby achieving the purpose of enhanced heat transfer.

Description

Technical Field

[0001] The invention belongs to the technical field of enhanced heat transfer, and in particular relates to an adaptive controllable electric field enhanced spiral tube flow boiling heat transfer system. Background Art

[0002] As a highly efficient phase-change heat transfer method, flow boiling heat transfer plays a vital role in the fields of nuclear energy, aerospace, chemical industry, etc. Compared with straight tube heat exchangers, spiral tube heat exchangers have the advantages of small footprint, high heat transfer efficiency, and good safety. A large number of studies have shown that the centrifugal force and secondary flow effect generated in the spiral tube can enhance the mixing characteristics of the gas-liquid two-phase, break up the fluid boundary layer, and thus significantly improve the heat transfer capacity; in addition, the compact spiral structure makes it possible to miniaturize the heat exchanger of high-power devices. Therefore, in the face of the ever-increasing demand for heat dissipation, spiral tube flow boiling heat transfer may become one of the key technologies to break through the existing heat dissipation bottleneck.

[0003] Flow boiling hazards often occur during flow boiling. While the spiral tube structure increases fluid mixing to a certain extent, when the heat flux density is high, the gas phase accumulates on the spiral tube heat exchanger wall, resulting in localized poor heat transfer. This poor localized heat transfer in the spiral tube can cause local wall temperature spikes, generate significant thermal stress, and reduce the service life of the spiral tube heat exchanger bundle, easily leading to serious accidents such as tube burnout or tube burst. First, when the primary side fluid operating parameters of the spiral tube heat exchanger undergo dynamic changes, the constant secondary side fluid operating conditions will result in poor heat transfer or increased energy consumption, far from meeting the heat dissipation and energy conservation requirements of high-temperature fluids under dynamic conditions. In addition, the spiral structure of the spiral tube can cause circumferential flow unevenness. When the flow rate in the spiral tube is low, buoyancy dominates, and the gas phase tends to be distributed above the tube while the liquid phase is distributed below. When the flow rate in the spiral tube is high, centrifugal force dominates, and the liquid phase is distributed outside the tube while the gas phase is distributed inside the tube. Other operating conditions fall somewhere in between these two conditions. Finally, in spiral tube flow boiling, the steam dryness increases continuously along the axial direction. Spatially uniform enhancement of flow boiling heat transfer clearly cannot achieve precise control. Therefore, it is necessary to combine electric field enhancement technology with a feedback control system to enhance the control of bubble dynamics in both time and space (circumferential and axial) dimensions within the spiral tube heat exchanger, while also achieving adaptive voltage control to further improve the heat transfer performance of the spiral tube heat exchanger.

[0004] Electric field enhancement technology improves two-phase flow through the electric field's electroconvection effects on the fluid and its dynamic effects on bubbles, thereby enhancing boiling heat transfer. A feedback control system actively adjusts the electric field parameters based on changes in parameters within the spiral tube heat exchanger. Therefore, combining electric field enhancement technology with a feedback control system effectively addresses the lack of active regulation and poor circumferential and axial heat transfer during the dynamic boiling process in spiral tube heat exchangers. This is of great significance for improving the heat transfer efficiency of spiral tube heat exchangers. Summary of the Invention

[0005] In order to solve the problems of lack of active adjustment of dynamic working conditions and poor circumferential and axial heat transfer in existing spiral tube heat exchange systems under high heat flux density, the present invention provides an adaptive controllable electric field enhanced spiral tube flow boiling heat transfer system, aiming to further improve the heat transfer efficiency of the spiral tube heat exchanger.

[0006] The technical solutions of the present invention are as follows:

[0007] The main equipment of an adaptive controllable electric field-enhanced spiral tube flow boiling heat transfer system includes a spiral tube heat exchanger, a thin film electrode, a temperature sensitive element, a temperature sensor, a control system, and a high-voltage AC power supply. The thin film electrode covers the outer surface of the spiral tube heat exchanger bundle, and a temperature sensor is installed along the radial outer side. The temperature sensor is connected to the control system, which is connected to the high-voltage AC power supply, and the high-voltage AC power supply is connected to the thin film electrode.

[0008] Furthermore, the material used for the heat exchange tube bundle of the spiral tube heat exchanger is Inconel 625 high temperature resistant and corrosion resistant material.

[0009] Furthermore, multiple pairs of thin film electrodes are provided in the circumferential and axial directions of the heat exchange tube bundle of the spiral tube heat exchanger, and are evenly arranged along the circumferential direction. The thin film electrodes are made of copper or other good electrical and thermal conductors.

[0010] Furthermore, the temperature sensitive element of the temperature sensor is covered on the thin film electrode and is radially farther away from the center of the circle than the thin film electrode. The control system is connected to the temperature sensor and the high-voltage AC power supply to display the set temperature, current temperature and current voltage of the measuring point position of the spiral tube heat exchanger.

[0011] Furthermore, negative feedback regulation of the voltage and frequency of the high-voltage AC power supply is achieved through the control system.

[0012] Furthermore, the heat exchange surface of the spiral tube heat exchanger, the surface of the thin film electrode, and the surface of the temperature sensitive element all need to be insulated. The insulating surface is achieved by coating it with a high-temperature resistant insulating coating, and the material of the insulating coating is diamond or aluminum nitride ceramic.

[0013] Compared with the prior art, the present invention has the following advantages:

[0014] 1. This invention incorporates negative feedback control technology into the flow boiling process of a spiral tube heat exchanger, enabling timely and efficient response to changes in operating conditions. This effectively addresses the problem of heat transfer capacity mismatch in the spiral tube heat exchanger following dynamic changes in heat load. This avoids the situation where increased heat load leads to a rapid increase in bubbles on the heat exchange surface, forming an air film and causing a decrease in heat transfer capacity, and where reduced heat load leads to a mismatch in existing control measures and increased energy consumption. This invention achieves intelligent control of the spiral tube heat exchanger, making it more suitable for a variety of complex heat exchange environments.

[0015] 2. This invention incorporates electric field regulation technology into the flow boiling process of a spiral tube heat exchanger. Thin-film electrode pairs are arranged around the circumference of the spiral tube to achieve a high-voltage electric field. By activating and deactivating different electrode pairs and setting different voltage parameters, the bubble dynamics around the circumference of the spiral tube heat exchanger bundle can be precisely controlled, thereby enhancing the overall flow boiling heat transfer in the spiral tube. This invention leverages the characteristics of the spiral tube flow boiling process to achieve localized precision control, resulting in high efficiency and low energy consumption.

[0016] 3. This invention incorporates electric field regulation technology into the flow boiling process of a spiral tube heat exchanger, arranging thin-film electrode pairs axially along the spiral tube to achieve a high-voltage electric field. During the flow boiling heat exchange process, poor axial heat transfer in the spiral tube bundle occurs at different locations under different operating conditions. By setting a non-uniform voltage across the axial thin-film electrodes, precise regulation can be achieved based on the local gas-liquid two-phase flow state within the spiral tube bundle, maximizing the enhancement of the overall flow boiling heat exchange process while minimizing energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Flow chart of the adaptive controllable electric field enhanced spiral tube flow boiling heat transfer system;

[0018] Figure 2 Schematic diagram of the cross section of a single spiral tube bundle of a spiral tube heat exchanger under different working conditions;

[0019] Figure 3 This is a schematic diagram of the axial arrangement of a single spiral tube bundle in a spiral tube heat exchanger;

[0020] 1. Spiral tube heat exchanger, 2. Thin film electrode, 3. Temperature sensitive element, 4. Temperature sensor, 5. Control system, 6. High voltage AC power supply. DETAILED DESCRIPTION

[0021] The present invention provides an adaptive controllable electric field enhanced spiral tube flow boiling heat transfer system, which is further described in detail below with reference to the accompanying drawings. Specific implementation method one:

[0023] Combine Figure 1The present embodiment is described as follows: the adaptive controllable electric field enhanced spiral tube flow boiling heat transfer system under dynamic working conditions of the present embodiment includes a spiral tube heat exchanger 1, a thin film electrode 2, a temperature sensitive element 3, a temperature sensor 4, a control system 5 and a high-voltage AC power supply 6.

[0024] When the heat flux density of the high-temperature fluid flowing in through the primary-side fluid inlet increases or the mass flow rate of the cooling fluid flowing in through the secondary-side fluid inlet decreases, the control system 5 receives a temperature rise signal from the temperature sensitive element 3 of the temperature sensor 4. The control system 5 starts and increases the voltage of the high-voltage AC power supply 6 through a negative feedback regulation strategy. The high-voltage AC power supply 6 forms a high-voltage electric field in the heat exchange tube bundle of the spiral tube heat exchanger 1 through the thin film electrode 2, thereby causing the air film covering the heat exchange wall surface in the cooling fluid flowing in through the secondary-side fluid inlet to collapse, thereby enhancing the heat exchange effect and gradually decreasing the local wall temperature. When the heat flux density of the high-temperature fluid flowing in through the primary-side fluid inlet decreases, the temperature sensitive element 3 of the temperature sensor 4 detects a decrease in the local wall temperature, and the control system 5 reduces the voltage through a negative feedback regulation strategy. Specific implementation method two:

[0026] Combine Figure 1 、 Figure 2 The present embodiment is described as follows: the circumferentially adaptive controllable electric field enhanced spiral tube flow boiling heat transfer system of the present embodiment includes a spiral tube heat exchanger 1, a thin film electrode 2, a temperature sensitive element 3, a temperature sensor 4, a control system 5 and a high-voltage AC power supply 6.

[0027] like Figure 1 、 Figure 2 As shown, multiple pairs of thin film electrodes 2 are evenly arranged on the heat exchange wall surface of a single spiral tube bundle in a spiral tube heat exchanger 1. Temperature sensors 3 are attached to the radially outer sides of the thin film electrodes 2. External leads from each pair of thin film electrodes 2 are connected to a high-voltage AC power supply 6, creating a high-voltage electric field within the heat exchange tube bundle of the spiral tube heat exchanger 1.

[0028] Due to the combined effects of buoyancy and centrifugal force, there are three situations in which the gas-liquid two-phase distribution state in the heat exchange tube bundle of the spiral tube heat exchanger 1 exists, namely Figure 2 (a) (b) (c) When the buoyancy plays a dominant role, the gas-liquid two-phase distribution state is as follows Figure 2 As shown in (a), at this time, the bubbles generated on the heat exchange wall surface at ③① are very likely to form an air film, thereby reducing the heat transfer coefficient and increasing the local wall temperature. The temperature sensitive element 3 of the circumferential temperature sensor 4 detects different degrees of temperature rise, and transmits different temperature rise signals to the control system 5. The control system 5 issues different voltage increase instructions to control the high-voltage AC power supply 6 to increase the voltage, thereby forming electric fields of different intensities at different circumferential angles, and accurately controlling the local flow boiling heat exchange. When the gas-liquid two-phase distribution state is Figure 2Under the working conditions shown in (b) and (c), the feedback regulation strategy is similar, and the voltage of the thin film electrode 2 at different circumferential angles depends on the degree of poor local heat transfer on the heat exchange wall. Specific implementation method three:

[0030] Combine Figure 1 、 Figure 3 The present embodiment is described as follows: the axial direction adaptive controllable electric field enhanced spiral tube flow boiling heat transfer system of the present embodiment includes a spiral tube heat exchanger 1, a thin film electrode 2, a temperature sensitive element 3, a temperature sensor 4, a control system 5 and a high-voltage AC power supply 6.

[0031] Figure 3 The diagram is a schematic diagram of the axial arrangement of a single spiral tube bundle in a spiral tube heat exchanger. The circumferential arrangement of the thin film electrode 2 at each position is as follows: Figure 1 The partially enlarged image on the right is shown. Under different operating conditions, the location of poor axial heat transfer in the spiral tube bundle of the heat exchanger 1 is different. When the temperature sensor 4 sensitive element 3 at different axial positions detects a rise in wall temperature caused by local poor heat transfer, the temperature sensor 4 feeds back the signal to the control system 5. The control system 5 executes the control strategy to adjust the high-voltage AC power supply 6 to control the voltage of the thin film electrode 2 to different values. By arranging different thin film electrodes 2 in the axial direction, the system can flexibly start and stop the corresponding thin film electrodes 2 and adjust different voltages, further alleviating the poor heat transfer along the axial direction during the spiral tube flow boiling process, thereby enhancing the overall heat transfer effect of the spiral tube heat exchanger.

[0032] Example

[0033] Combine Figure 1-Figure 3 To illustrate this implementation:

[0034] In this embodiment, high-temperature fluid and cooling fluid enter through the primary and secondary fluid inlets, respectively. When the heat flux density of the primary high-temperature fluid increases or the mass flow rate of the secondary cooling fluid decreases, the temperature sensor detects localized poor heat transfer on the heat exchange wall, leading to a rise in wall temperature. Upon receiving this signal, the control system gradually increases the high-voltage AC power supply, causing the wall temperature to gradually decrease. When the heat flux density of the primary fluid decreases or the mass flow rate of the secondary cooling fluid increases, the system follows the same feedback control strategy, gradually decreasing the high-voltage AC power supply.

[0035] Similarly, in the spatial dimension, when the heat flux density of the high-temperature fluid on the primary side increases or the mass flow rate of the cooling fluid on the secondary side decreases, the circumferential and axial gas-liquid two-phase distribution states of the spiral heat exchanger bundle vary under different operating conditions. Temperature-sensitive elements at different thin-film electrodes at circumferential and axial positions detect varying degrees of local wall temperature increases and transmit signals to the control system. Based on the magnitude of the temperature rise at different circumferential and axial positions, the control system adjusts multiple pairs of thin-film electrodes to different voltage values, forming electric fields of varying intensities at different circumferential angles and axial lengths of the spiral tube. Under negative feedback control, the local wall temperature gradually returns to normal, thereby achieving precise regulation of the flow and boiling process throughout the spiral heat exchanger bundle.

Claims

1. An adaptive controllable electric field enhanced spiral tube flow boiling heat transfer system, characterized in that: The core equipment of the spiral tube flow boiling heat transfer system includes a spiral tube heat exchanger (1), a thin film electrode (2), a temperature sensitive element (3), a temperature sensor (4), a control system (5) and a high-voltage AC power supply (6). The spiral tube heat exchanger (1) is provided with multiple pairs of thin film electrodes (2) in the circumferential and axial directions of the heat exchange tube bundle. The temperature sensitive element (3) of the temperature sensor (4) is arranged on the radially outer side of the thin film electrode (2) on the wall of the spiral tube heat exchanger. The control system (5) is a negative feedback control system. The thin film electrode (2) is connected to the high-voltage AC power supply (6).

2. The adaptive controllable electric field enhanced spiral tube flow boiling heat transfer system according to claim 1, characterized in that: The thin film electrode (2) is a good conductor of electricity and heat. The heat exchange wall surface of the spiral tube heat exchanger (1), the surface of the thin film electrode (2), and the surface of the temperature sensitive element (3) all need to be insulated.

3. The adaptive controllable electric field enhanced spiral tube flow boiling heat transfer system according to claim 1, characterized in that: When the system is operating normally, the heat flux density of the high-temperature fluid on the primary side of the spiral tube heat exchanger (1) should be higher than 80 KW / m 2 , less than 700 KW / m 2 .

4. The adaptive controllable electric field enhanced spiral tube flow boiling heat transfer system according to claim 3, characterized in that: When the system is operating normally, the mass flow rate of the cooling fluid on the secondary side of the spiral tube heat exchanger (1) is higher than 120 kg / (m 2 ·s), less than 350 kg / (m 2 ·s), and the operating pressure is less than 4 MPa.

5. The adaptive controllable electric field enhanced spiral tube flow boiling heat transfer system according to claim 3, characterized in that: The outer surface of the spiral tube bundle of the spiral tube heat exchanger (1) is plated with multiple pairs of thin film electrodes (2) on the heat exchange wall surface by physical vapor deposition, and each pair of thin film electrodes (2) forms a controllable high-voltage electric field.

6. The adaptive controllable electric field enhanced spiral tube flow boiling heat transfer system according to claim 3, characterized in that: The thin film electrodes (2) are evenly arranged in the circumferential direction.

7. The adaptive controllable electric field enhanced spiral tube flow boiling heat transfer system according to claim 1, characterized in that: The temperature sensitive element (3) is attached to the thin film electrode (2).

8. The adaptive controllable electric field enhanced spiral tube flow boiling heat transfer system according to claim 1, characterized in that: The temperature sensor (4) is connected to the control system (5), and the high-voltage AC power supply (6) is controlled by the control system (5).

9. The adaptive controllable electric field enhanced spiral tube flow boiling heat transfer system according to claim 8, characterized in that: When the temperature exceeds 25% of the stable operating temperature, the control system (5) automatically turns on.

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