Microchannel plug flow generator and method of generating

Abstract

The application provides a micro-channel slug flow generating device and a generating method thereof. The device comprises a gas-liquid separator, the gas-liquid separator is provided with a gas phase mixture inlet pipe, the upper part of the gas-liquid separator is communicated with a gas phase pipeline, the lower part of the gas-liquid separator is communicated with a liquid phase channel, the gas phase pipeline and the liquid phase channel are both provided with flow sensing devices, the outlets of the gas phase pipeline and the liquid phase channel are respectively connected with variable diameter pipes, the variable diameter pipes are changed to the size of the micro-channel, and the outlets of the two groups of variable diameter pipes are connected with a gas-liquid mixer. The slug flow generating device and the generating method thereof can control the stability of two-phase flow in the micro-channel and inhibit the complexity of the change of the multi-flow type in the micro-channel.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of micro-channel heat transfer technology, in particular to a micro-channel slug flow generating device and a generating method thereof. BACKGROUND

[0002] The research and application of heat transfer technology plays a vital role in the stable operation of modern high-energy consumption scientific and technological equipment. With the further development of science and technology, the problems of fusion reactor cladding, power batteries, laser and microwave weapons, rocket nozzles and the like have put forward urgent demands for the research of high-efficiency heat transfer technology, and the heat dissipation rate of special electronic equipment has increased from 100W / cm 2 2 in the 1980s to 1000W / cm 2 2 now.

[0003] Compared with conventional heat exchangers, the flow channel of micro-channel heat exchangers is narrower (the traditional view refers to below 1mm or defined by Co number), the heat exchange area in unit volume can be greatly improved, so that the heat exchanger has a more compact structure and occupies a smaller volume. Micro-channel two-phase flow boiling heat transfer coefficient is high, uniform temperature capacity is strong, and pressure drop is small, which is an ideal heat transfer mode under high heat flux, but two-phase flow boiling is prone to unstable oscillation, local flow acceleration and deceleration cause the strengthening and weakening of wall heat transfer, and the device wall temperature also oscillates, which seriously endangers the safety of the equipment. Some researchers have proposed new micro-channel structures or timely discharge of the gas phase generated by boiling, but the effect of flow instability suppression is not obvious. SUMMARY

[0004] The technical problem to be solved by the present application is to provide a micro-channel slug flow generating device and a generating method thereof, to control the stability of two-phase flow in the micro-channel and suppress the complexity of multiple flow pattern changes in the micro-channel.

[0005] To solve the above technical problems, the technical scheme adopted by the present application is: a micro-channel slug flow generating device, comprising a gas-liquid separator, the gas-liquid separator is provided with a gas mixture inlet pipe, the upper part of the gas-liquid separator is in communication with a gas pipeline, and the lower part is in communication with a liquid channel, flow sensing devices are arranged on the gas pipeline and the liquid channel, the outlets of the gas pipeline and the liquid channel are respectively connected with variable diameter pipes, the variable diameter pipes are changed in diameter to the size of the micro-channel, and the outlets of the two groups of variable diameter pipes are connected with a gas-liquid mixer.

[0006] In the preferred scheme, a proportional valve is arranged on the liquid channel, and the proportional valve is controlled by a driver.

[0007] In the preferred scheme, the driver is electrically connected with an amplifier, the two groups of flow sensing devices are electrically connected with a comparator, and the comparator is electrically connected with the amplifier.

[0008] In a preferred embodiment, the upper portion of the gas-liquid separator is provided with a pressure relief valve.

[0009] In a preferred embodiment, the reducer pipe is reduced to a size of less than 1 mm.

[0010] A slug flow generating method using the above-mentioned microchannel slug flow generating device, comprising the following steps:

[0011] Step one, passing the gas phase mixture into the gas-liquid separator, the gas phase pipeline is connected to the upper gas phase space of the gas-liquid separator, and the liquid phase channel is connected to the lower liquid phase space of the gas-liquid separator;

[0012] Step two, measuring the flow rates of the gas phase pipeline and the liquid phase channel by two groups of flow sensing devices respectively, and feeding the signals to the comparator, comparing the flow rate signals and feeding them to the amplifier for signal amplification, and then adjusting the proportional valve through the driver to adjust the mixing ratio of the gas and liquid two phases;

[0013] Step three, the gas phase and the liquid phase are mixed in the gas-liquid mixer after being reduced by the reducer pipe, forming a slug flow.

[0014] In a preferred embodiment, in step two, the formation of the slug flow is realized by adjusting the amplification factor of the amplifier, the flow sensing device is a vortex flow sensor, and the amplification factor of the amplifier is derived as follows:

[0015] In the vortex flow sensor, the gas-liquid flow rate u and the vortex frequency f have the following relationship:

[0016] St = fD / u (1)

[0017] Where St is a dimensionless number, approximately a constant; D is the width of the vortex generator, and f is the vortex frequency;

[0018] In the microchannel, as the void fraction α gradually increases, the flow pattern gradually transitions from bubbly flow to slug flow, and when the void fraction α continues to increase, the flow pattern will transition from slug flow to annular flow. The transition condition from bubbly flow to slug flow is expressed as:

[0019]

[0020] Where J l is the liquid phase reduced velocity, J g is the gas phase reduced velocity, μ l is the liquid phase viscosity, and μ g is the gas phase viscosity; the transition condition from slug flow to annular flow is expressed as

[0021]

[0022] Where α critThe critical value of the void fraction is usually 0.15;

[0023] Therefore, when the liquid phase conversion speed takes the average value of the upper and lower limits of the slug flow, the slug flow can be realized, that is,

[0024] J l =(J l '+J l ") / 2(4);

[0025] It is also known that the conversion relationship between the conversion speed and the flow rate u is

[0026]

[0027]

[0028] Wherein, A1 is the cross-sectional area of the vortex street flow sensor connecting pipe, A micro The cross-sectional area of the microchannel after the mixer;

[0029] The formula (2), formula (3), formula (5) and formula (6) are brought into formula (4), and further processing can obtain

[0030]

[0031] The ratio of the gas-liquid flow rate obtained in the comparator can be obtained by the vortex frequency

[0032]

[0033] Comparing formula (7) and formula (8) can obtain the amplification ratio of the amplifier for realizing the slug flow pattern, which is

[0034]

[0035] The amplifier only needs to satisfy the amplification ratio in formula (9) to generate the slug flow.

[0036] The microchannel slug flow generating device and the generating method provided by the application have the following beneficial effects:

[0037] 1. The instability of two-phase flow is effectively suppressed. The gas-liquid two-phase flow pattern in the microchannel is complex, the flow oscillation and temperature oscillation are violent, and after the device, the stable slug flow pattern is formed, and the oscillation can be effectively controlled.

[0038] 2. Precise adjustment of gas-liquid ratio. The feedback adjustment of the gas-liquid passage can realize the precise control of the gas-liquid flow.

[0039] 3. No need to obtain quantitative and accurate flow information. The comparator, the amplifier and the driver only process the difference signal of the gas-liquid flow, and no accurate value is required.

[0040] 4. Given the significant challenges in implementing measurement and control within microchannels, this device first introduces the gas-liquid mixture into a conventional pipeline, separates and adjusts it, and then introduces it into the microchannel, greatly reducing the difficulty of measurement and control. Attached Figure Description

[0041] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0042] Figure 1 This is a schematic diagram of the overall structure of the present invention;

[0043] In the diagram: 1. Gas phase mixture inlet pipe, 2. Gas-liquid separator, 3. Gas phase pipeline, 4. Liquid phase channel, 5. Flow sensor, 6. Reducer, 7. Gas-liquid mixer, 8. Proportional valve, 9. Driver, 10. Amplifier, 11. Comparator, 12. Pressure relief valve. Detailed Implementation

[0044] like Figure 1 As shown, a microchannel slug flow generating device includes a gas-liquid separator 2. The gas-liquid separator 2 can be of various forms, such as baffle type, vortex type, and gravity type. The gas-liquid volume separation rate should be higher than 99% to ensure the accuracy of subsequent gas-liquid flow rate measurement. It has a heating coil inside, which can heat and boil to generate a gas phase when the gas phase volume is insufficient or the pressure is too low.

[0045] The gas-liquid separator 2 is equipped with a gas phase mixture inlet pipe 1. The upper part of the gas-liquid separator 2 is connected to the gas phase pipeline 3, and the lower part is connected to the liquid phase channel 4. Both the gas phase pipeline 3 and the liquid phase channel 4 are equipped with flow sensing devices 5. There can be two or more flow sensing devices 5. Their function is to measure the gas phase and liquid phase flow. They can be various forms such as vortex flow meters, mass flow meters or electromagnetic flow meters. Their purpose is to generate a signal that has a monotonic function relationship with the flow rate.

[0046] The outlets of the gas phase pipe 3 and the liquid phase channel 4 are respectively connected to the reducer 6. The reducer 6 reduces its diameter to the size of the microchannel. The diameter of the reducer 6 to the size of the microchannel is less than 1 mm. The outlets of the two sets of reducers 6 are connected to the gas-liquid mixer 7. The gas-liquid mixer 7 can be a Y-type or T-type microchannel connector.

[0047] The gas-liquid two-phase mixture enters from the inlet end of the gas-liquid separator 2 and is separated into a gas phase and a liquid phase. The gas phase and the liquid phase flow through the gas-liquid passage, respectively, through the flow sensing device 5 and the reducer 6, and then re-merge in the gas-liquid mixer 7 to form a stable slug flow.

[0048] Preferably, a proportional valve 8 is provided on the liquid phase channel 4, and the proportional valve 8 is controlled by a driver 9. The proportional valve 8 can also be a throttle valve or other valve.

[0049] The driver 9 is electrically connected with the amplifier 10, and the two groups of flow sensing devices 5 are electrically connected with the comparator 11, and the comparator 11 is electrically connected with the amplifier 10.

[0050] To ensure that the ratio of gas and liquid can be suitable for the generation of slug flow, the comparator 11, the amplifier 10 and the driver 9 jointly constitute a flow regulating servo mechanism to automatically control the ratio of gas and liquid.

[0051] Preferably, the upper portion of the gas-liquid separator 2 is provided with a pressure relief valve 12. The inlet of the pressure relief valve 12 is connected with the gas phase space of the gas-liquid separator 2, and the pressure relief valve 12 is opened when the pressure is higher than a specified value to release the gas phase and maintain the pressure in the gas-liquid separator 2 stable.

[0052] The working process of the overall device is that the gas-liquid mixture discharged from the microchannel is separated by the gas-liquid separator 2, the flow information is obtained through the flow sensing devices 5 on the respective passages, and the flow signal is promoted to act on the proportional valve 8 after passing through the comparator 11, the amplifier 10 and the driver 9, thereby changing the flow of the gas phase and the liquid phase. The variable diameter pipe 6 shrinks the regulated number of gas-liquid in the conventional pipeline into the microchannel, and then converges into stable slug flow in the gas-liquid mixer 7.

[0053] A slug flow generation method of a microchannel slug flow generation device, comprising the following steps:

[0054] Step one, the gas phase mixture is introduced into the gas-liquid separator 2, the gas phase pipeline 3 is connected with the gas phase space at the upper portion of the gas-liquid separator 2, and the liquid phase passage 4 is connected with the liquid phase space at the lower portion of the gas-liquid separator 2.

[0055] Step two, the flow rates on the gas phase pipeline 3 and the liquid phase passage 4 are measured through the two groups of flow sensing devices 5 respectively, and the signals are fed back to the comparator 11, the comparator 11 compares the flow rate signals and feeds back to the amplifier 10 for signal amplification, and then the proportional valve 8 is adjusted through the driver 9 to adjust the mixing ratio of the gas and liquid two phases.

[0056] The formation of slug flow is realized by adjusting the amplification factor of the amplifier 10, and the flow sensing device 5 is a vortex flow sensor, and the amplification factor of the amplifier 10 is derived as follows:

[0057] In the vortex flow sensor, the gas-liquid flow rate u and the vortex frequency f have the following relationship:

[0058] St=fD / u (1)

[0059] Wherein, St is a dimensionless number, which is approximately a constant; D is the width of the vortex generator, and f is the vortex frequency;

[0060] In the micro-channel, with the gradual increase of the bubble fraction α, the flow pattern gradually transits from bubbly flow to slug flow, and when the bubble fraction α continues to increase, the flow pattern will transit from slug flow to annular flow, the transition condition of bubbly flow to slug flow is expressed as:

[0061]

[0062] wherein, J l is the liquid phase reduced velocity, J g is the gas phase reduced velocity, μ l is the liquid phase viscosity, μ g is the gas phase viscosity; the transition condition of slug flow to annular flow is expressed as

[0063]

[0064] wherein, α crit is the critical value of the bubble fraction, usually taken as 0.15;

[0065] Therefore, when the liquid phase reduced velocity takes the average value of the upper and lower limits of the slug flow, the slug flow can be realized, that is

[0066] J l =(J l '+J l ") / 2(4);

[0067] It is also known that the conversion relationship between the reduced velocity and the flow velocity u is

[0068]

[0069]

[0070] wherein, A1 is the cross-sectional area of the vortex street flow sensor connecting pipe, A micro is the cross-sectional area of the micro-channel after the mixer;

[0071] The formula (2), formula (3), formula (5) and formula (6) are brought into formula (4), and further processing can obtain

[0072]

[0073] The ratio of the gas-liquid flow velocity obtained in the comparator can be obtained by the vortex frequency

[0074]

[0075] Comparing formula (7) and formula (8) can obtain the amplification ratio of the amplifier for realizing the slug flow pattern, which is

[0076]

[0077] Only the amplification ratio in equation (9) needs to be satisfied in the amplifier to generate the slug flow.

[0078] Step three, after the gas phase and liquid phase are changed in diameter by the variable diameter pipe 6, the gas and liquid are mixed in the gas-liquid mixer 7 to form the slug flow.

[0079] In this embodiment, the inner diameter of the vortex street sensor connecting pipe is 4 mm, and the inner diameter of the micro channel is 1 mm. The relevant data of the slug flow test are shown in Table 1.

[0080] Table 1 Slug flow data

[0081]

[0082]

[0083] From Table 1, for the gas phase with an initial speed of 0.1 m / s and the liquid phase with an initial speed of 0.2 m / s, stable slug flow structure can be realized by adjusting the amplification ratio of the amplifier to 5.9, at which time the liquid phase reduced speed in the micro channel of the generated slug flow is 4.65 m, and the gas phase reduced speed is 1.6 m. In this table, the speed range is 0.1-0.5 m / s, the amplifier amplification ratio increases from 0.98 to 14.7, which is completely within the adjustable range of the amplifier, and the results in this table also illustrate the feasibility of slug flow generation.

Claims

1. A microchannel slug flow generation device, characterized in that, Includes a gas-liquid separator (2), which is provided with a gas phase mixture inlet pipe (1). The upper part of the gas-liquid separator (2) is connected to the gas phase pipe (3), and the lower part is connected to the liquid phase channel (4). Both the gas phase pipe (3) and the liquid phase channel (4) are provided with flow sensing devices (5). The outlets of the gas phase pipe (3) and the liquid phase channel (4) are respectively connected to the reducer pipe (6). The reducer pipe (6) is reduced to the size of the microchannel. The outlets of the two sets of reducer pipes (6) are connected to the gas-liquid mixer (7). The liquid phase channel (4) is provided with a proportional valve (8), which is controlled by a driver (9). The driver (9) is electrically connected to an amplifier (10), and two sets of flow sensing devices (5) are electrically connected to a comparator (11). The comparator (11) is electrically connected to the amplifier (10). The formation of a slug flow is achieved by adjusting the amplification factor of the amplifier (10). The flow sensing device (5) is a vortex flow sensor. The derivation process of the amplification factor of the amplifier (10) is as follows: Within the vortex flow sensor, the gas-liquid flow rate u With vortex frequency f The following relationship exists: （1）； in, St It is a dimensionless number, approximately a constant; D The width of the vortex generator. f The vortex shear frequency; Within the microchannel, as the cavitation fraction... α As the flow rate gradually increases, the flow pattern gradually transitions from bubbly flow to slug flow. When the cavitation fraction continues to increase... α The flow pattern will transition from slug flow to annular flow. The conditions for the transition from bubbly flow to slug flow are stated as follows: （2）； in, For liquid phase reduced velocity, For gas phase reduced velocity, For liquid phase viscosity, The viscosity is the gas phase viscosity; the transition condition from slug flow to annular flow is described as follows: （3）； in, This represents the critical value for the void fraction. Therefore, when the liquid phase reduced velocity is taken as the average of the upper and lower bounds of slug flow, slug flow can definitely be achieved, that is: （4）； It is also known that the converted velocity and flow rate u The conversion relationship is as follows: （5）； （6）； in, This refers to the cross-sectional area of ​​the vortex flow sensor connector. The cross-sectional area of ​​the microchannel after passing through the mixer; Substituting equations (2), (3), (5), and (6) into equation (4), further processing yields: （7）； The ratio of gas-liquid flow velocities obtained within the comparator can be derived from the vortex shedding frequency: （8）； By comparing equations (7) and (8), the amplification ratio of the amplifier that realizes the sponge flow pattern can be obtained as follows: （9）； A slug flow can be generated simply by satisfying the amplification ratio in equation (9) within the amplifier.

2. The microchannel slug flow generating device according to claim 1, characterized in that, The gas-liquid separator (2) is equipped with a pressure relief valve (12) on its upper part.

3. A method for generating slug flow using the microchannel slug flow generating device according to claim 1, characterized in that, Includes the following steps: Step 1: Pass the gas phase mixture into the gas-liquid separator (2). The gas phase pipe (3) is connected to the gas phase space at the top of the gas-liquid separator (2), and the liquid phase channel (4) is connected to the liquid phase space at the bottom of the gas-liquid separator (2). Step 2: The flow rate on the gas phase pipeline (3) and the liquid phase channel (4) is measured by two sets of flow sensing devices (5) respectively, and the signal is fed back to the comparator (11). The comparator (11) compares the flow rate signal and feeds it back to the amplifier (10) for signal amplification. Then, the proportional valve (8) is adjusted by the driver (9) to adjust the mixing ratio of the gas and liquid phases. Step 3: After the gas phase and liquid phase are reduced in diameter by the reducing pipe (6), the gas and liquid are mixed in the gas-liquid mixer (7) to form a slug flow.

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