Pool boiling heat exchange enhancing device with steam hood, testing device and method

Abstract

The invention discloses a pool boiling heat exchange enhancing device with a steam hood, a testing device and a method, the pool boiling heat exchange enhancing device comprises a main body frame water cavity, a heat transfer block and a condenser, the main body frame water cavity is partially filled with deionized water, the heat transfer block penetrates through the bottom of the main body frame water cavity, and the upper end of the heat transfer block is located in the deionized water; the condenser is mounted above the water surface of the deionized water, and the steam hood is vertically through, is arranged in the deionized water and is positioned right above the heat transfer block. A solid phase is introduced into an original gas-liquid two-phase heat exchange system, the two processes of bubble separation and rising and liquid backflow are separated, mutual obstruction of bubble separation and liquid backflow in the boiling circulation process is weakened, circulation acceleration of bubble nucleation and separation, liquid backflow and supplementing processes is achieved, and the heat exchange efficiency is improved. The overall boiling efficiency of the pool boiling heat exchange enhancing device is improved, and the heat transfer coefficient and the critical heat flux of the pool boiling heat exchange enhancing device are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of boiling heat transfer enhancement, and relates to a pool boiling heat transfer enhancement device with a steam hood, a testing device and a method. Background Art

[0002] Pool boiling is a passive boiling heat transfer method compared to flow boiling. The cooling liquid on the heat transfer surface undergoes a phase change from liquid to gas phase, thereby achieving efficient heat exchange. The core of this process focuses on the cycle of bubble embryo generation, growth, detachment and liquid reflux replenishment after the onset of nucleation boiling (ONB). As the wall superheat continues to increase, the two-phase heat transfer efficiency (heat flux density) reaches its limit, the heat flux no longer increases, and reaches the critical heat flux (CHF). The heat transfer coefficient (HTC) measures how fast the heat flux rises as the wall superheat increases. Therefore, ONB, CHF, and HTC overall measure the heat transfer efficiency of a structural surface.

[0003] Therefore, how to improve the overall pool boiling efficiency of the system becomes an urgent need.

[0004] Chinese patent document CN101464109A provides a method for preparing a high-efficiency, anti-fouling nano-coated heat transfer surface and a pool boiling device. The heat transfer surface described in this method includes a substrate coated with a nanomaterial coating. Compared to conventional pool boiling devices, the pool boiling device comprising this heat transfer surface exhibits reduced adhesion to dirt, a higher heat transfer coefficient, and a scaling-free operating time that is at least 8-20 times longer.

[0005] However, the pool boiling device has poor insulation effect, severe heat dissipation, and the thermal cycle process mainly relies on natural heat convection. During the boiling cycle, the rising process of bubbles after detachment and the liquid reflux replenishment process hinder each other, and the efficiency of the cycle process is limited. Summary of the Invention

[0006] The purpose of the present invention is to solve the problems mentioned in the background technology and to propose a pool boiling heat exchange enhancement device with a steam hood, a testing device and a method.

[0007] In order to achieve the above technical objectives, the technical solution adopted by the present invention is:

[0008] A pool boiling heat exchange enhancement device with a steam hood includes a main frame water cavity, a heat transfer block and a condenser. The main frame water cavity is partially filled with deionized water, the heat transfer block passes through the bottom of the main frame water cavity, the upper end of the heat transfer block is located in the deionized water, and the lower end is located outside the main frame water cavity. The condenser is installed above the deionized water surface and also includes a steam hood that passes through the upper and lower parts. The steam hood is placed in the deionized water and is located directly above the heat transfer block.

[0009] To optimize the above technical solutions, specific measures taken also include:

[0010] The side of the heat transfer block is covered with a glass fiber insulation layer, which is used to prevent heat from being lost from the side of the heat transfer block.

[0011] A test device for a pool boiling heat exchange enhancement device with a steam hood includes a main frame water cavity, a heat transfer block, a test sample, a heater, a condenser and a detection device. The main frame water cavity is partially filled with deionized water, the heat transfer block passes through the bottom of the main frame water cavity, the test sample is placed on the upper end of the heat transfer block, and the lower end is located outside the main frame water cavity. The heater can heat the heat transfer block and deionized water, and the heat transfer block can transfer heat to the test sample. The test sample is located in the deionized water, and the condenser is installed above the deionized water surface. The detection equipment is used to detect the heat exchange data between the test sample and the deionized water. The device also includes a steam hood that passes through the upper and lower parts, is placed in the deionized water, and is located directly above the test sample.

[0012] The heater includes a deionized water heater, a heat transfer block heater, an AC power supply and a voltage controller. The deionized water heater is installed in the water cavity of the main frame and is used to heat the deionized water. The heat transfer block heater is installed at the lower end of the heat transfer block and is used to heat the heat transfer block. The AC power supply is connected to the voltage controller, and the voltage controller is connected to the deionized water heater and the heat transfer block heater respectively. The voltage controller can control the output power of the AC power supply, thereby controlling the heating efficiency of the deionized water heater and the heat transfer block heater.

[0013] Part of the surface of the heat transfer block within the water cavity of the main frame is covered with a zirconia insulation cover. The test sample contacts the top of the heat transfer block. The zirconia insulation cover has a through hole at the test sample to enable the test sample to contact deionized water. The side of the heat transfer block is covered with a glass fiber insulation layer to prevent heat loss from the side of the heat transfer block.

[0014] The detection equipment includes a thermometer, a computer, a high-speed camera and several temperature sensors. Among them, at least one temperature sensor is placed in deionized water to detect the deionized water temperature. The remaining temperature sensors are connected to the heat transfer block to detect the temperature at different heights of the heat transfer block. The temperature sensor is connected to the thermometer, which is connected to the computer. The thermometer records the temperature data, and the computer filters and processes the temperature data to ultimately obtain the gradient temperature data of the heat transfer block and the deionized water temperature change curve; the high-speed camera is located outside the water cavity of the main frame and is used to observe the dynamic process of bubbles in the water cavity of the main frame during the test. A PTFE ring is set around the temperature sensor connected to the heat transfer block to prevent heat loss from the connection between the heat transfer block and the temperature sensor.

[0015] The inner cavity structure of the steam hood is hyperbolic. By changing the inner cavity curvature, diameter, length structure of the steam hood and the distance between the lower end of the steam hood and the upper surface of the test sample, the bubble separation and liquid reflux during the boiling heat exchange between the test sample and deionized water can be adjusted; the steam hood is fixed on a retractable connector, and the retractable connector is hoisted and fixed to the top of the water cavity of the main frame. The retractable connector can change the distance between the lower end of the steam hood and the upper surface of the test sample by lifting or lowering the steam hood.

[0016] The pool boiling heat transfer enhancement test method with a steam hood uses the test device for the pool boiling heat transfer enhancement device with a steam hood, and specifically includes the following steps:

[0017] S1. Cut, polish and clean the copper sheet, and process the surface texture on the copper sheet to obtain the test sample.

[0018] S2. Place the test sample on top of the heat transfer block and cover it with a zirconia insulation cover. Add deionized water to the water cavity of the main frame. The height of the deionized water should be enough to completely immerse the test sample and the steam cover.

[0019] S3. According to the experimental plan, prepare steam hoods with different inner cavity curvatures, diameters, and lengths. Place the steam hood directly above the test sample and set the distance between the lower end of the steam hood and the upper surface of the test sample.

[0020] S4. Start the voltage controller, the deionized water heater heats the deionized water to 100°C, the heat transfer block heater heats the heat transfer block, the heat transfer block transfers the heat to the test sample, the test sample and the deionized water boil and exchange heat, bubbles separate and rise, and the liquid refluxes inside and outside the steam hood, the temperature sensor collects temperature data, and sends it to the computer via the thermometer. The computer calculates the boiling heat transfer efficiency of the test sample, and selects the steam hood with the best boiling heat transfer efficiency of the test sample as the steam hood of the pool boiling heat exchange enhancement device.

[0021] In step S2, the test sample is 2 mm thick, and there is a pit with a depth of 1 mm and a diameter of 20 mm on the top of the heat transfer block. The test sample is embedded in the pit, and thermal grease is applied between the test sample and the heat transfer block to make the two fit tightly. There is a circular hole with a thickness of 1 mm and a diameter of 20 mm on the top of the zirconia insulation cover. After covering, the top of the zirconia insulation cover is flush with the test sample.

[0022] The specific test steps of step S4 are:

[0023] 1) Turn on the voltage controller to start heating the deionized water heater. Adjust the voltage to 200V. Heat the deionized water to 100°C. Then lower the voltage and observe the deionized water temperature. If the temperature fluctuates within 0.5°C within 2 minutes, it is considered to have reached a stable state.

[0024] 2) Turn on the condenser to realize the water condensation circulation inside the water cavity of the main frame.

[0025] 3) Turn on the voltage controller to start heating the heat transfer block heater, set the initial voltage to 33V, and observe the temperature at different heights of the heat transfer block. When the temperature reaches a stable state, record the temperature data. Then set the next voltage parameter, and cyclically record the temperature data at different heights of the heat transfer block until the heat transfer block temperature data rises sharply at a certain voltage parameter, which is considered to have reached the critical heat flux. During this process, the test sample maintains boiling heat exchange with deionized water, and bubbles rise and liquid reflux cycles occur inside and outside the steam hood. The temperature sensor collects temperature data, which is sent to the computer via a thermometer. The computer calculates the boiling heat transfer efficiency of the test sample.

[0026] 4) Turn off the voltage controller and wait for the deionized water temperature to drop to room temperature. The experiment is over.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. The present invention effectively improves the boiling heat transfer efficiency of the pool boiling heat exchange device by providing a hyperbolic steam hood. The steam hood is equivalent to introducing a solid phase into the original gas-liquid two-phase heat exchange system, guiding the bubbles to rise from the steam hood, while the liquid flows back from the outside and inside of the steam hood, separating the two processes of bubble detachment and liquid reflux, and reducing the mutual obstruction between bubble detachment and liquid reflux during the boiling cycle, thereby achieving cyclic acceleration of the entire process of bubble nucleation, detachment, liquid reflux, and replenishment, thereby improving the overall boiling efficiency of the pool boiling heat exchange enhancement device and improving the heat transfer coefficient (HTC) and critical heat flux (CHF) of the pool boiling heat exchange enhancement device.

[0029] 2. The present invention wraps a glass fiber insulation layer outside the heat transfer block, which reduces heat loss, increases energy utilization, and is green and energy-saving.

[0030] 3. The present invention further provides a testing device and a testing method for a pool boiling heat exchange enhancement device. The testing device is provided with test samples, heaters and other equipment. Pool boiling tests are carried out by setting the structural parameters of the hyperbolic steam hood. Finally, feedback optimization is performed to obtain the steam hood structural parameters with the best pool boiling enhancement effect, and the steam hood of the pool boiling heat exchange enhancement device is designed based on the structural parameters. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Schematic diagram of the structure of the pool boiling heat exchange enhancement device with a steam hood according to the present invention;

[0032] Figure 2 2. It is a schematic structural diagram of a test device for a pool boiling heat exchange enhancement device with a steam hood according to the present invention;

[0033] Figure 3 It is a schematic diagram of the structure of the steam hood;

[0034] Figure 4 Graph showing heat flux and heat transfer coefficient of the pool boiling heat exchange enhancement device obtained from testing in the embodiment.

[0035] The accompanying drawings are marked as: main frame water chamber 1, heat transfer block 2, test sample 3, deionized water heater 4, heat transfer block heater 5, PTFE ring 6, glass fiber insulation layer 7, zirconia insulation cover 8, condenser 9, temperature sensor 10, thermometer 11, computer 12, AC power supply 13, voltage controller 14, high-speed camera 15, steam hood 16. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solutions and advantages of this application more clearly understood, the present application is described and illustrated below in conjunction with the accompanying drawings and examples. It should be understood that the specific embodiments described herein are merely used to explain this application and are not intended to limit this application. Based on the embodiments provided in this application, all other embodiments obtained by those of ordinary skill in the art without making any creative efforts are within the scope of protection of this application.

[0037] Obviously, the drawings described below are merely examples or embodiments of the present application. Those skilled in the art can, without inventive effort, apply the present application to other similar scenarios based on these drawings. Furthermore, it is also understood that, although the effort involved in such a development process may be complex and lengthy, for those skilled in the art related to the content disclosed in this application, changes in design, manufacturing, or production based on the technical content disclosed in this application are merely conventional technical means and should not be construed as an insufficiency of the content disclosed in this application.

[0038] References to "embodiments" in this application mean that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it refer to independent or alternative embodiments that are mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described in this application may be combined with other embodiments unless there is a conflict.

[0039] Unless otherwise defined, the technical or scientific terms used in this application should have the ordinary meaning understood by a person of ordinary skill in the technical field to which this application belongs. The words "a", "an", "a", "the" and the like used in this application do not indicate a limit on quantity and may indicate the singular or plural. The terms "include", "comprise", "have" and any variations thereof used in this application are intended to cover non-exclusive inclusions; for example, a process, method, system, product or device that includes a series of steps or units (units) is not limited to the listed steps or units, but may also include steps or units that are not listed, or may also include other steps or units that are inherent to these processes, methods, products or devices. The words "connect", "connected", "coupled" and the like used in this application are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. The words "multiple" / "several" used in this application refer to two or more. "And / or" describes the association relationship between associated objects, indicating that three relationships can exist. For example, "A and / or B" can mean: A exists alone, A and B exist at the same time, or B exists alone. The character " / " generally indicates that the objects before and after are in an "or" relationship. The terms "first", "second", "third", etc. involved in this application are only used to distinguish similar objects and do not represent a specific order for the objects.

[0040] The pool boiling heat exchange enhancement device with a steam hood of the present invention is as follows Figure 1 As shown, it includes a main frame water cavity 1, a heat transfer block 2, a glass fiber insulation layer 7, a condenser 9 and a steam hood 16. The main frame water cavity 1 is partially filled with deionized water, and the heat transfer block 2 passes through the bottom of the main frame water cavity 1. The upper end of the heat transfer block 2 is located in the deionized water, and the lower end is located outside the main frame water cavity 1. The condenser 9 is installed above the deionized water surface. The steam hood 16 is fixed on a connecting piece, and the connecting piece is hoisted and fixed to the top of the inner cavity of the main frame water cavity 1. The steam hood 16 is connected from top to bottom, and the steam hood 16 is placed in the deionized water and is located directly above the heat transfer block 2. The inner cavity structure of the steam hood 16 is hyperbolic. The glass fiber insulation layer 7 covers the glass fiber insulation layer 7 to prevent heat from being lost from the side of the heat transfer block 2.

[0041] The principle of the pool boiling heat exchange enhancement device of the present invention is to introduce a solid phase into the original gas-liquid two-phase heat exchange system by setting a steam hood 16, thereby accelerating the cycle of bubble separation and liquid reflux during the boiling process, thereby improving the overall boiling efficiency and increasing the heat transfer coefficient (HTC) and critical heat flux (CHF) of the hot surface of the pool boiling heat exchange enhancement device.

[0042] The test device of the pool boiling heat transfer enhancement device with steam cover of the present invention is as follows: Figure 2As shown, the main structure includes a main frame water cavity 1, a heat transfer block 2, a test sample 3, a deionized water heater 4, a heat transfer block heater 5, a PTFE ferrule 6, a glass fiber insulation layer 7, a zirconia insulation cover 8, a condenser 9, a temperature sensor 10, a thermometer 11, a computer 12, an AC power supply 13, a voltage controller 14, a high-speed camera 15, and a steam hood 16. The difference from the pool boiling heat transfer enhancement device is that the test device adds a test sample 3, a deionized water heater 4, a heat transfer block heater 5, a PTFE ferrule 6, a zirconia insulation cover 8, a temperature sensor 10, a thermometer 11, a computer 12, an AC power supply 13, a voltage controller 14, a high-speed camera 15, and a retractable connector for hoisting the steam hood 16 on the basis of the pool boiling heat transfer enhancement device.

[0043] The test sample 3 is placed on the upper end of the heat transfer block 2, and the zirconia insulation cover 8 covers the heat transfer block 2 and the test sample 3. The zirconia insulation cover 8 has a circular through hole at the top of the test sample 3, so that the test sample 3 can come into contact with deionized water. The deionized water heater 4 is installed in the water cavity 1 of the main frame for heating the deionized water. The heat transfer block heater 5 is installed at the lower end of the heat transfer block 2 for heating the heat transfer block 2. The AC power supply 13 is connected to the voltage controller 14, and the voltage controller 14 is respectively connected to the deionized water heater 4 and the heat transfer block heater 5. The voltage controller 14 can control the output power of the AC power supply 13, thereby controlling the heating efficiency of the deionized water heater 4 and the heat transfer block heater 5.

[0044] There are four temperature sensors 10: three mounted on the heat transfer block 2 and one in the deionized water. The three temperature measurement points on the heat transfer block 2 are designated T1-T3 from bottom to top, while the temperature measurement point in the deionized water is designated T4. A thermometer 11 records temperature data, which is filtered and processed by a computer 12 to ultimately generate the gradient temperature data for the heat transfer block 2 and a deionized water temperature curve. A high-speed camera 15 is located outside the main frame water cavity 1 and is used to observe the dynamics of bubbles within the cavity during testing. A PTFE collar 6 surrounds the temperature sensor 10 connected to the heat transfer block 2 to prevent heat loss from the connection between the heat transfer block 2 and the temperature sensor 10.

[0045] The inner cavity structure of the steam hood 16 is hyperbolic. The inner cavity curvature, diameter, length structure of the steam hood 16 and the distance between the lower end of the steam hood 16 and the upper surface of the test sample 3 can be adjusted. In order to change the distance between the steam hood 16 and the upper surface of the test sample 3, the steam hood 16 is fixed on a retractable connector, and the retractable connector is hoisted and fixed on the top of the inner cavity of the main frame water cavity 1. The retractable connector can change the distance between the lower end of the steam hood 16 and the upper surface of the test sample 3 by lifting or lowering the steam hood 16.

[0046] The test method of the pool boiling heat exchange enhancement device of the present invention is further described below with reference to specific embodiments:

[0047] The sample used in the embodiment is commercially available T2 copper with a density of 8.9 g / cm 3 , thermal conductivity is 390W / (m·K), melting point is 1083 degrees Celsius, it has excellent physical properties and is widely used in electrical, electronic and heat conduction fields.

[0048] Example 1

[0049] In this embodiment, T2 copper is used, the steam hood 16 is not used, no surface texture is added, and a smooth surface is used to carry out the boiling test.

[0050] The preparation steps are as follows:

[0051] 1. Use wire EDM to cut T2 copper sheet into round blanks with a thickness of 2mm and a diameter of 20mm;

[0052] 2. Rough grinding of the circular blank to remove the ablated surface produced by wire EDM to obtain a smooth surface;

[0053] 3. Clean the round blank, remove the oil and impurities on the surface, and obtain the copper sample;

[0054] 4. Place the copper sample to be tested on top of the heat transfer copper block and cover it with a zirconia insulation cover 8, using deionized water as the cooling liquid;

[0055] 5. Turn on the voltage controller 14 to start heating the deionized water heater 4. The voltage is adjusted to 200V. The deionized water heater 4 heats the deionized water to 100°C. The heat transfer block heater 5 starts heating. The input heat is eventually transferred to the copper sample, achieving boiling heat exchange. Bubbles are separated and ascended inside and outside the steam hood, and the liquid refluxes. Finally, temperature data is obtained and the boiling heat transfer efficiency of the copper specimen is calculated. The calculated smooth surface T2 copper critical heat flux and heat transfer coefficient are as follows: Figure 4 As shown. The critical heat flux is 550kw / m 2 , the maximum heat transfer coefficient is 23kw(m 2 ·k).

[0056] Example 2

[0057] In this embodiment, a T2 copper circular specimen with a diameter of 20 mm is used, the surface of which is a smooth surface without texture processing. A steam hood is used, and the distance h between the steam hood and the upper surface of the specimen is 2 mm; the maximum diameter of the steam hood is 30 mm, and the minimum diameter is 20 mm; the height is 50 mm, and the structure is hyperbolic.

[0058] The preparation steps are as follows:

[0059] 1. Use wire EDM to cut T2 copper sheet into round blanks with a thickness of 2mm and a diameter of 20mm;

[0060] 2. Rough grinding of the circular blank to remove the ablated surface produced by wire EDM to obtain a smooth surface;

[0061] 3. Clean the round blank, remove the oil and impurities on the surface, and obtain the copper sample;

[0062] 4. Use laser processing and CNC micro-milling to process surface texture on the surface of the copper specimen, and finally obtain the copper sample to be tested;

[0063] 5. Place the copper sample to be tested on top of the heat transfer copper block and cover it with a zirconia insulation cover 8, using deionized water as the cooling liquid;

[0064] 6. Place the steam hood 16 directly above the copper sample according to the set gap;

[0065] 7. Turn on voltage controller 14 to start heating deionized water heater 4. Adjust the voltage to 200V and heat the deionized water to 100°C. Heater 5 also begins heating. The input heat is ultimately transferred to the copper specimen, achieving boiling heat transfer. Bubbles rise and liquid reflux circulates inside and outside the steam hood, ultimately obtaining temperature data and calculating the boiling heat transfer efficiency of the copper specimen.

[0066] The calculated critical heat flux and heat transfer coefficient of T2 copper on the steam hood surface are as follows: Figure 4 As shown. The critical heat flux is 667kw / m 2 , the maximum heat transfer coefficient is 29kw(m 2 ·k).

[0067] Comparative Example 1:

[0068] In this embodiment, a T2 copper circular specimen with a diameter of 20 mm is used, the surface of which is a smooth surface without texture processing. A steam hood is used, and the distance h between the steam hood and the upper surface of the specimen is 2 mm; the maximum diameter of the steam hood is 30 mm, and the minimum diameter is 20 mm; the structure is hyperbolic.

[0069] The preparation steps are as follows:

[0070] 1. Use wire EDM to cut T2 copper sheet into round blanks with a thickness of 2mm and a diameter of 20mm;

[0071] 2. Rough grinding of the circular blank to remove the ablated surface produced by wire EDM to obtain a smooth surface;

[0072] 3. Clean the round blank, remove the oil and impurities on the surface, and obtain the copper sample;

[0073] 4. Place the copper sample to be tested on top of the heat transfer copper block and cover it with a zirconia insulation cover 8, using deionized water as the cooling circulating liquid;

[0074] 5. Place the steam hood 16 of a certain structural size directly above the copper sample according to the set gap;

[0075] 6. Turn on voltage controller 14 to start heating deionized water heater 4. Adjust the voltage to 200V and heat the deionized water to 100°C. Heater 5 also begins heating. The input heat is ultimately transferred to the copper specimen, achieving boiling heat transfer. Bubbles rise and liquid reflux circulates inside and outside the steam hood, ultimately obtaining temperature data and calculating the boiling heat transfer efficiency of the copper specimen.

[0076] Research results show that, compared to traditional pool boiling without a steam hood, adding a steam hood management structure increases the critical heat flux by 21% and the heat transfer coefficient by 26%. By introducing a solid phase into the vapor and liquid phases, the vapor-liquid circulation pattern is changed, separating the bubble detachment and ascent process from the liquid reflux replenishment process, thereby accelerating the overall nucleation boiling process and the boiling heat transfer effect.

[0077] The above embodiments are preferred implementations of the present invention, but the implementation of the present invention is not limited to the embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A pool boiling heat exchange enhancement device with a steam hood, comprising a main frame water cavity (1), a heat transfer block (2) and a condenser (9), wherein the main frame water cavity (1) is partially filled with deionized water, the heat transfer block (2) passes through the bottom of the main frame water cavity (1), the upper end of the heat transfer block (2) is located in the deionized water, and the lower end is located outside the main frame water cavity (1), and the condenser (9) is installed above the deionized water surface, and is characterized by: It also includes a steam cover (16), which is connected from top to bottom. The steam cover (16) is placed in deionized water and is located directly above the heat transfer block (2).

2. The pool boiling heat exchange enhancement device with a steam hood according to claim 1, characterized in that: The side of the heat transfer block (2) is covered with a glass fiber insulation layer (7), and the glass fiber insulation layer (7) is used to prevent heat from being lost from the side of the heat transfer block (2).

3. A test device for a pool boiling heat exchange enhancement device with a steam hood, comprising a main frame water cavity (1), a heat transfer block (2), a test sample (3), a heater, a condenser (9) and a detection device, wherein the main frame water cavity (1) is partially filled with deionized water, the heat transfer block (2) passes through the bottom of the main frame water cavity (1), the test sample (3) is placed on the upper end of the heat transfer block (2), and the lower end is located outside the main frame water cavity (1), the heater can heat the heat transfer block (2) and the deionized water, the heat transfer block (2) can transfer heat to the test sample (3), the test sample (3) is located in the deionized water, the condenser (9) is installed above the deionized water surface, and the detection device is used to detect heat exchange data between the test sample (3) and the deionized water, and is characterized in that: The device further comprises a steam cover (16), which is connected from top to bottom. The steam cover (16) is placed in deionized water and is located directly above the test sample (3).

4. The test device for the pool boiling heat exchange enhancement device with a steam hood according to claim 3, characterized in that: The heater comprises a deionized water heater (4), a heat transfer block heater (5), an AC power supply (13) and a voltage controller (14). The deionized water heater (4) is installed in the water cavity (1) of the main frame and is used to heat the deionized water. The heat transfer block heater (5) is installed at the lower end of the heat transfer block (2) and is used to heat the heat transfer block (2). The AC power supply (13) is connected to the voltage controller (14). The voltage controller (14) is respectively connected to the deionized water heater (4) and the heat transfer block heater (5). The voltage controller (14) can control the output power of the AC power supply (13), thereby controlling the heating efficiency of the deionized water heater (4) and the heat transfer block heater (5).

5. The testing device for the pool boiling heat exchange enhancement device with a steam hood according to claim 4, characterized in that: Part of the surface of the heat transfer block (2) within the water cavity (1) of the main frame is covered with a zirconia insulation cover (8), the test sample (3) is in contact with the top of the heat transfer block (2), and the zirconia insulation cover (8) is provided with a through hole at the test sample (3) so that the test sample (3) can be in contact with deionized water. The side of the heat transfer block (2) is covered with a glass fiber insulation layer (7), and the glass fiber insulation layer (7) is used to prevent heat from being lost from the side of the heat transfer block (2).

6. The testing device for the pool boiling heat exchange enhancement device with a steam hood according to claim 5, characterized in that: The detection device includes a thermometer (11), a computer (12), a high-speed camera (15) and a plurality of temperature sensors (10), wherein at least one temperature sensor (10) is placed in deionized water for detecting the temperature of the deionized water, and the remaining temperature sensors (10) are connected to the heat transfer block (2) for detecting the temperature at different heights of the heat transfer block (2). The temperature sensor (10) is connected to the thermometer (11), the thermometer (11) is connected to the computer (12), the thermometer (11) records the temperature data, and the computer (12) filtering and processing the temperature data, and finally obtaining the gradient temperature data of the heat transfer block (2) and the deionized water temperature change curve; the high-speed camera (15) is located outside the main frame water cavity (1), and the high-speed camera (15) is used to observe the dynamic process of bubbles in the main frame water cavity (1) during the test process; a PTFE ring (6) is arranged around the temperature sensor (10) connected to the heat transfer block (2), and the PTFE ring (6) is used to prevent heat from being lost from the connection between the heat transfer block (2) and the temperature sensor (10).

7. The testing device for the pool boiling heat exchange enhancement device with a steam hood according to claim 6, characterized in that: The inner cavity structure of the steam hood (16) is hyperbolic. By changing the inner cavity curvature, diameter, length structure of the steam hood (16) and the distance between the lower end of the steam hood (16) and the upper surface of the test sample (3), the bubble separation and liquid reflux during the boiling heat exchange between the test sample (3) and deionized water are adjusted. The steam hood (16) is fixed on a telescopic connecting piece, and the telescopic connecting piece is hoisted and fixed on the top of the inner cavity of the main frame water cavity (1). The telescopic connecting piece can change the distance between the lower end of the steam hood (16) and the upper surface of the test sample (3) by lifting or lowering the steam hood (16).

8. Pool boiling heat transfer enhancement test method with steam hood, characterized by: The test device for the pool boiling heat exchange enhancement device with a steam hood according to claim 7 specifically comprises the following steps: S1, cutting, polishing and cleaning the copper sheet, processing the surface texture on the copper sheet to obtain a test sample (3), S2. Place the test sample (3) above the heat transfer block (2) and cover it with a zirconia insulation cover (8). Add deionized water into the main frame water cavity (1). The height of the deionized water is required to be able to completely immerse the test sample (3) and the steam cover (16). S3. According to the experimental plan, a steam hood (16) with different inner cavity curvature, diameter, and length is prepared, the steam hood (16) is placed directly above the test sample (3), and the distance between the lower end of the steam hood (16) and the upper surface of the test sample (3) is set. S4, start the voltage controller (14), the deionized water heater (4) heats the deionized water to 100° C., the heat transfer block heater (5) heats the heat transfer block (2), the heat transfer block (2) transfers the heat to the test sample (3), the test sample (3) and the deionized water perform boiling heat exchange, bubbles separate and rise, and liquid reflux cycles are carried out inside and outside the steam hood (16), the temperature sensor (10) collects temperature data, and sends it to the computer (12) via the thermometer (11), the computer (12) calculates the boiling heat transfer efficiency of the test sample (3), and selects the steam hood (16) with the best boiling heat transfer efficiency of the test sample (3) as the steam hood of the pool boiling heat exchange enhancement device.

9. The pool boiling heat transfer enhancement test method with a steam hood according to claim 8, characterized in that: In step S2, the test sample (3) has a thickness of 2 mm, and the top of the heat transfer block (2) has a pit with a depth of 1 mm and a diameter of 20 mm. The test sample (3) is embedded in the pit, and heat transfer silicone grease is applied between the test sample (3) and the heat transfer block (2) to make the two fit tightly. The top of the zirconia insulation cover (8) has a circular hole with a thickness of 1 mm and a diameter of 20 mm. After covering, the top of the zirconia insulation cover (8) is flush with the test sample (3).

10. The pool boiling heat transfer enhancement test method with a steam hood according to claim 8, wherein: The specific test steps of step S4 are: 1) Turn on the voltage controller (14) to start heating the deionized water heater (4), adjust the voltage to 200V, and heat the deionized water to 100°C. Then lower the voltage and observe the temperature of the deionized water. If the temperature fluctuates within 0.5°C within 2 minutes, it is considered to have reached a stable state; 2) Turn on the condenser (9) to realize the water condensation circulation inside the main frame water cavity (1). 3) Turn on the voltage controller (14) to start heating the heat transfer block heater (5), set the initial voltage to 33V, observe the temperature at different heights of the heat transfer block (2), record the temperature data when the temperature reaches a stable state, set the next voltage parameter, and cyclically record the temperature at different heights of the heat transfer block (2) until the temperature data of the heat transfer block (2) rises sharply under a certain voltage parameter, which is considered to have reached the critical heat flux; during this process, the test sample (3) maintains boiling heat exchange with deionized water, and bubbles are separated and rising, and liquid reflux cycles are carried out inside and outside the steam cover (16). The temperature sensor (10) collects temperature data and sends it to the computer (12) through the thermometer (11). The computer (12) calculates the boiling heat transfer efficiency of the test sample (3); 4) Turn off the voltage controller (14) and wait for the deionized water temperature to drop to room temperature. The experiment ends.

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