Gravity independent design method for space gas-liquid two-phase heat transport system

Abstract

The present application relates to spacecraft thermal control technology field, especially space gas-liquid two-phase heat transfer system's gravity independence design method. Space gas-liquid two-phase flow heat transfer system is short of effective microgravity environment experimental data support in design, which limits the reliability of space gas-liquid two-phase heat transfer system. The present application proposes a kind of space gas-liquid two-phase heat transfer system's gravity independence design method, using the gravity independence criterion based on dominant force model (including Bond number dominant force model and Froude number dominant force model), according to the heat dissipation requirement of space gas-liquid two-phase heat transfer system, the gravity independence pre-design and analysis is carried out, under the constraint of working medium selection, system / local heat load requirement, the critical diameter of two-phase flow pipe section is determined. Thus, the performance difference between ground simulation test and space application of space gas-liquid two-phase heat transfer system is reduced, to avoid the system design reliability and operation stability problems caused by the difference between heaven and earth.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of spacecraft thermal control technology, in particular to a gravity-independent design method of a space gas-liquid two-phase heat transfer system. BACKGROUND

[0002] Gas-liquid two-phase heat transfer is a high-efficiency enhanced heat transfer technology that utilizes both sensible heat and latent heat of the working medium. It can not only obtain several times of heat transfer performance enhancement of single-phase heat exchange system, but also effectively reduce the mass of the thermal control system. Therefore, it is one of the important technologies in spacecraft thermal control.

[0003] Among the key environmental parameters faced by the two-phase heat transfer system in space applications, gravity is a crucial factor. Due to the large density difference between gas and liquid phases (for example, the density ratio of water and air can be as high as 1000), the presence of gravity will cause strong buoyancy effect, which significantly affects the flow structure in the two-phase flow system, and in turn affects other characteristics of the flow (such as frictional pressure drop, heat transfer performance, and overall stability of the system). Therefore, the gravity effect problem in gas-liquid two-phase flow and heat transfer phenomenon is of great significance to space gas-liquid two-phase heat transfer systems.

[0004] During the whole life cycle of the two-phase flow system in space, it will experience complex gravity environments such as normal gravity (ground), supergravity (acceleration overload), microgravity (free flight in orbit), and partial gravity (such as lunar surface g / 6, Mars surface g / 3). However, due to the limitations of experimental conditions, it is often difficult to achieve effective gravity environment simulation, especially microgravity environment. The existing microgravity environment simulation technologies such as microgravity drop tower, weightless aircraft, and sounding rocket can only obtain microgravity time in the order of seconds to minutes. Obviously, it is difficult to obtain effective microgravity two-phase flow and heat transfer experimental data within such a short time (the residual gravity will affect the accuracy of the measured parameters).

[0005] In addition, the above experiments usually require high experimental costs. This leads to the lack of effective microgravity environment experimental data support for the design of space gas-liquid two-phase flow and heat transfer systems, and only ground normal gravity experimental data can be used for evaluation and prediction, which limits the reliability of space gas-liquid two-phase heat transfer systems.

[0006] In fact, through reasonable structural parameters and system layout design, the gravity effect can be effectively avoided, and the two-phase system flow and heat transfer can achieve gravity-independent effect, which provides a new idea for the design of two-phase flow and heat transfer systems and provides the possibility for ground simulation experiments of space gas-liquid two-phase heat transfer systems. SUMMARY

[0007] The present application is based on the above considerations, proposes a gravity independence design method of space gas-liquid two-phase heat transport system, determines the upper limit value of the internal flow channel size of the two-phase heat transport system two-phase section component, thereby reducing the performance difference of the space gas-liquid two-phase heat transport system in ground simulation test and space application, and further combining the gravity independence layout of the two-phase heat transport system, to avoid the system design reliability and operation stability problems caused by the difference between heaven and earth.

[0008] The present application provides a gravity independence design method of space gas-liquid two-phase heat transport system, which comprises the following steps:

[0009] S1: Establish a dominant force model in two-phase flow structure and determine the critical value of gravity independence Bond number and the critical value of gas phase apparent Froude number

[0010] The dominant force model is:

[0011]

[0012] ρ L is the liquid phase density, ρ G is the gas phase density, g is the gravity acceleration, σ is the surface tension, U SG is the gas phase apparent flow velocity, D1 and D2 are the gravity independent diameters of the pipeline; Bo cr is the critical value of gravity independence Bond number, Fr SG,cr is the critical value of gas phase apparent Froude number, Bo cr and Fr SG,cr are determined according to the test;

[0013] S2: Based on the gravity independence Bond number dominant force model, determine the first pipeline gravity independent critical diameter D 1,cr of the two-phase flow pipeline component of the working medium at each saturation temperature;

[0014] S3: Based on the gravity independence Froude number dominant force model, determine the minimum gas phase apparent flow velocity U SG,min in the two-phase flow pipeline component under the constraint of gravity independence, and convert it into the minimum mass flow rate of the system;

[0015] S4: Considering the working medium selection, system / local thermal load requirement and system heat exchange component heat dissipation performance constraint condition, determining the constraint relationship between the mass flow rate in the heat exchange component and the thermodynamic equilibrium quality and the pipe diameter, calculating the second pipeline gravity independent critical diameter D 2,cr of the two-phase flow pipeline component;

[0016] S5: According to the system motion working temperature or the system saturation pressure range, determine the upper limit value D of the pipeline gravity independence:

[0017] D≤max(D 1,cr , D 2,cr ).

[0018] Advantageously, the overall layout of the system is designed according to the system configuration requirements, and the relative positions of the main components and the flow direction of the working fluid in the pipeline are determined by following the horizontal flow channel of the two-phase section, the system plane layout, the vertical downward flow of the two-phase flow, and the correction of the gravity pressure drop.

[0019] Advantageously, the first pipe gravity-independent critical diameter D in step S2 is 1,cr :

[0020]

[0021] Advantageously, the minimum gas phase superficial velocity U in step S3 is SG,min :

[0022]

[0023] Convert the minimum gas phase superficial flow rate into the system minimum mass flow rate G g,min :

[0024]

[0025] Where x is the dryness of the two-phase flow.

[0026] Advantageously, in step S4, the constraint relationship between the mass flow rate in the heat exchange component, the thermodynamic equilibrium dryness, and the inner diameter of the pipe is:

[0027] G=4qA / (πxD2hevap)

[0028] Where G is the mass flow rate, q is the heat flux, A is the heating / condensing area, and h is the evap is the latent heat of vaporization of the working fluid;

[0029] The gravity-independent critical diameter D of the second pipe of the two-phase flow pipeline assembly is obtained 2,cr :

[0030]

[0031] Advantageously, the two-phase horizontal flow channel requires that the two-phase flow pipe section should be arranged as horizontally as possible.

[0032] Advantageously, the system plane layout requires that the overall system layout should be kept in the same horizontal plane as much as possible.

[0033] Advantageously, the vertical downward direction of the two-phase flow requires that if the existence of height differences in the two-phase flow pipe sections cannot be avoided, the two-phase flow direction of the corresponding pipe sections should be designed to be vertically downward.

[0034] Advantageously, the repositioning pressure drop correction requires that if the presence of a height difference between system components cannot be avoided, the pipe section with the height difference should be ensured to be in a single-phase flow state, and when compared with space applications, the single-phase static pressure gradient and / or two-phase repositioning pressure drop correction needs to be made to the ground test results.

[0035] Beneficial effects: the gas-liquid two-phase heat transfer system designed based on the method can effectively avoid the influence of gravity effect on the flow and heat transfer in the two-phase region, expand the application scenarios of the gas-liquid two-phase heat transfer system under the premise of ensuring the reliability of the two-phase heat dissipation system design and the stability of the operation.

[0036] The features, functions, and advantages that have been discussed can be implemented independently in various examples, or can be combined in other examples. Other details, relating to the examples, can be appreciated upon reviewing the following description and the accompanying figures. BRIEF DESCRIPTION OF DRAWINGS

[0037] The illustrative examples and preferred modes of use, other objects, and its description will be best understood by reference to the following detailed description in conjunction with the accompanying drawings, in which:

[0038] Figure 1 Flow chart for the pipe diameter design method of the two-phase heat transfer system of the present application;

[0039] Figure 2 Flow chart for the layout design method of the two-phase heat transfer system of the present application. DETAILED DESCRIPTION

[0040] The disclosed examples will be described with reference to the drawings in which are shown a few (but not all) examples by way of illustration. Indeed, there can be many different examples that are not specifically described in detail herein. These examples should not be construed as limiting the scope of the disclosure but rather as being illustrative thereof. The examples described herein are intended to achieve the objects of the present disclosure and to provide the following advantages:

[0041] The space gas-liquid two-phase heat transfer system (and its ground simulation test system) is mainly composed of an evaporator, a condenser, a liquid reservoir, a driving pump, a filter, a pipeline and the like. Among them, the inner pipeline of the evaporator and the condenser, and the transmission pipeline between the evaporator and the condenser will appear gas-liquid two-phase flow phenomenon. In this embodiment, the commonly used ammonia working medium is taken as an example to illustrate the gravity-independent design method of the two-phase heat transfer system.

[0042] In combination Figure 1The embodiment of the method for designing the gravity-independent pipe diameter of a space two-phase heat transport system is described. The gravity-independent criterion based on the dominant force model (including the Bond number dominant force model and the Froude number dominant force model) is adopted. The gravity-independent pre-design and analysis are performed according to the heat dissipation requirement of the space gas-liquid two-phase heat transport system. Under the constraints of the working medium selection, system / local heat load requirement, etc., the critical diameter of the gravity-independent two-phase flow pipe section is determined. Specifically, the embodiment includes the following steps:

[0043] S1: establishing the dominant force model in the two-phase flow structure and determining the critical value of the gravity-independent Bond number and the critical value of the gas phase apparent Froude number

[0044] The dominant force model is as follows:

[0045]

[0046] wherein ρ L is the liquid phase density, ρ G is the gas phase density, g is the gravitational acceleration, σ is the surface tension, U SG is the gas phase apparent flow velocity, and D1 and D2 are the gravity-independent diameters of the pipe;

[0047] In the embodiment, the critical value of the gravity-independent Bond number Bo cr = 1.5 and the critical value of the gas phase apparent Froude number Fr SG,cr = 2.2 are determined according to the theoretical analysis and test, and the gravity-independent Bond number and the gas phase apparent Froude number are expressed as follows:

[0048]

[0049] S2: determining the first pipe gravity-independent critical diameter D 1,cr of the two-phase flow pipe component of the ammonia working medium at each saturation temperature based on the gravity-independent Bond number dominant force model, wherein the first pipe gravity-independent critical diameter D 1,cr of the two-phase flow pipe component is derived from formula (2) as follows:

[0050]

[0051] Table 1: the first gravity-independent critical diameter of the two-phase flow pipe component of the ammonia working medium at each saturation temperature

[0052]

[0053]

[0054] As shown in Table 1, based on the thermophysical properties of the ammonia two-phase heat transfer system at various saturation temperatures, the internal flow channel dimensions of the pipes in the evaporator and condenser, as well as the transmission pipe between the evaporator and condenser, are designed according to Equation (3). This provides the relationship between the gravity-independent critical diameter D1,cr of the first pipe of the ammonia two-phase flow piping assembly and the saturation temperature. For example, at a saturation temperature of 300K, the gravity-independent critical diameter D1,cr of the first pipe, determined based on the Bond number-dominant force model, is 2.5 mm. Therefore, when the ammonia two-phase heat transfer system operates at a saturation temperature of 300K, the gravity-independent dimensions of the internal flow channels in the evaporator and condenser, as well as the transmission pipe between the evaporator and condenser, should be no greater than 2.5 mm.

[0055] Clearly, if the diameter of the two-phase flow pipe section within the ammonia two-phase heat transfer system is less than the minimum value of the first pipe's gravity-independent critical diameter D1,cr, as determined in Table 1, the system meets the gravity-independence requirement. However, from a system design perspective, appropriate evaporator and condenser selection can ensure that their internal flow channel dimensions meet the aforementioned requirements.

[0056] S3: Based on the gravity-independent Froude number-dominant force model, determine the minimum gas phase superficial velocity in the two-phase flow pipeline component under the gravity-independent constraint, that is:

[0057]

[0058] In order to facilitate the design and parameter selection, the minimum gas phase apparent flow rate is converted into the minimum mass flow rate of the system, which can be expressed as:

[0059]

[0060] Where G is the mass flow rate and x is the dryness of the two-phase flow.

[0061] The above formula shows that as the pipe diameter increases or the dryness of the two-phase region decreases, the mass flow rate required to ensure the gravity independence of the two-phase flow and heat transfer in the pipe becomes higher. See Table 2 for the gravity-independent minimum mass flow rate under different pipe diameters and dryness conditions in the ammonia two-phase heat transfer system of this embodiment.

[0062] Table 2 Gravity-independent minimum mass flow rate of ammonia two-phase heat transfer system under different pipe diameters and dryness conditions

[0063]

[0064] S4: Considering the working fluid selection, system / local heat load requirements, and based on the heat dissipation performance constraints of the system heat exchange components, determine the constraint relationship between the mass flow rate in the heat exchange component, the thermodynamic equilibrium dryness, and the inner diameter of the pipe, as shown in formula (6):

[0065] G = 4qA / (πxD 2 h evap ) (6)

[0066] where G is the mass flow rate, q is the heat flux, A is the heating (condensing) area, h evap is the latent heat of vaporization of the working fluid, and x is the quality of the two-phase flow.

[0067] The above equations can be directly applied to the non-phase-change two-phase flow pipe section (constant quality); for the flow boiling pipe section, the quality is calculated using the outlet parameters; for the flow condensing pipe section, the quality is calculated using the inlet parameters.

[0068] The second pipe gravity-independent critical diameter D 2,cr of the two-phase flow pipe assembly can be obtained from equations (5) and (6):

[0069]

[0070] In the design and analysis of the gravity-independent ammonia two-phase heat transfer system, the heat transfer amount (or heat flux and heat transfer area) of the system, i.e., the heat transfer amount of the evaporator and the condenser, needs to be determined. The current system design evaporator heat transfer amount is 70W (heat flux 700W / m 2 , heat transfer area 0.1m 2 ), and the condenser heat transfer amount is 90W (heat flux 160W / m 2 , heat transfer area 0.5m 2 ). The gravity-independent size of the flow passage in the evaporator and the condenser of the ammonia two-phase heat transfer system can be calculated and obtained under different saturation temperature conditions. Referring to Table 3, the relationship between the second pipe gravity-independent critical diameter D 2,cr of the ammonia two-phase flow pipe assembly and the saturation temperature is given. For example, under the condition of a saturation temperature of 300K, the second pipe gravity-independent critical diameter D2,cr of the evaporator and the condenser is determined to be 1.91 and 2.12mm, respectively.

[0071] Table 3 Second gravity-independent critical diameter of ammonia two-phase flow pipe assembly at different saturation temperatures

[0072]

[0073] S5: Compare the first pipe, the second gravity-independent critical diameter, and determine the upper limit value of the pipe gravity independence, as shown in equation (8):

[0074] D≤max(D 1,cr , D 2,cr ) (8)

[0075] According to formula (8), the upper limit of the gravity-independent pipe diameter of the ammonia working medium two-phase heat transfer system evaporator and condenser and the transmission pipe between the evaporator and the condenser at different saturation temperatures can be determined, as shown in Table 4.

[0076] Table 4 Gravity-independent design embodiments of the ammonia working medium two-phase heat transfer system

[0077]

[0078] For a two-phase heat transfer system with a large operating temperature range, the minimum value of the second pipe gravity-independent critical diameter in the system operating temperature range is obtained as the upper limit of the gravity-independent two-phase pipe diameter of the system according to the system operating temperature (or system saturation pressure) range. The ammonia working medium two-phase heat transfer system operates at a temperature range of 240-360 K, and the minimum value of the second pipe gravity-independent critical diameter in the temperature range is taken. The upper limit of the second pipe gravity-independent diameter of the ammonia working medium two-phase heat transfer system evaporator and condenser is 1.69 mm and 1.87 mm, respectively. To ensure the gravity independence of the transmission pipe between the evaporator and the condenser, the upper limit of the pipe diameter should be set to the minimum value of the gravity-independent pipe diameters of the evaporator and the condenser, which is 1.69 mm.

[0079] In combination Figure 2 In further embodiments shown in FIG. 8, the gravity-independent layout design method of the space two-phase heat transfer system is described. The relative positions of the main components and the flow direction of the working medium in the pipe are determined according to the system configuration requirements and considering the two-phase flow horizontal channel, plane layout, two-phase flow vertically downward, and gravity pressure drop correction factors during the design process. Specifically, the following contents are included:

[0080] Horizontal channel design: The two-phase flow pipe section should be arranged as horizontally as possible to avoid the difference between the sky system and the ground system caused by the gravity pressure drop of the two-phase flow, that is, the evaporator, the condenser, and the transmission pipe between the evaporator and the condenser should be arranged in a horizontal manner.

[0081] Plane layout design: In order to avoid the possible influence of the gravity pressure difference between different components on the system performance, the overall layout of the system should be arranged as horizontally as possible, that is, there should be no height difference between the evaporator, the condenser, and the transmission pipe between the evaporator and the condenser, and they should be arranged on the same horizontal plane.

[0082] Two-phase flow vertically downward design: If the height difference of the two-phase flow pipe section cannot be avoided, the two-phase flow direction of the corresponding pipe section should be designed as vertically downward, that is, when the height difference of the transmission pipe between the evaporator and the condenser cannot be avoided, the two-phase transmission pipe between the evaporator and the condenser should be designed as vertically downward.

[0083] If the height difference between system components cannot be avoided, the pipe sections with height difference, especially upward flow pipe sections, should be kept in single phase flow as much as possible. Compared with space applications, the ground test results need to be corrected for single phase static pressure gradient and / or two phase hydrostatic pressure drop, i.e. when there is a height difference between the evaporator and the condenser and / or between the transfer pipe between the evaporator and the condenser, the single phase static pressure gradient and / or the two phase hydrostatic pressure drop should be considered in the system resistance calculation.

[0084] The above description is only the preferred specific implementation of the present application, but the protection scope of the present application is not limited to this. Any skilled person in the art can make equivalent replacements or changes according to the technical solution and the inventive concept of the present application within the technical range disclosed by the present application, which should be covered in the protection scope of the present application.

[0085] Descriptions of different advantageous arrangements have been shown for purposes of illustration and description, but are not intended to be exclusive or limited to the examples disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art. Additionally, different advantageous examples can provide different advantages as compared to other advantageous examples. The chosen and described examples are chosen and described in order to best explain the principles of the examples and practical applications, and to enable others skilled in the art to best understand the disclosure for various examples with various modifications as are suited to the particular use contemplated.

Claims

1. A gravity-independent design method for a space gas-liquid two-phase heat transfer system, characterized in that: The method comprises the following steps: S1: Establish a model of the dominant forces in the two-phase flow structure and determine the critical values ​​of the gravity-independent Bond number and the gas phase apparent Froude number The dominant force model is: ρ L is the liquid density, ρ G is the gas phase density, g is the acceleration due to gravity, σ is the surface tension, U SG is the superficial velocity of the gas phase, D1 and D2 are the gravity-independent diameters of the pipe; Bo cr is the critical value of gravity-independent Bond number, Fr SG,cr is the critical value of the gas phase apparent Froude number, Bo cr With Fr SG,cr Determined by experiment; S2: Based on the gravity-independent Bond number dominant force model, determine the gravity-independent critical diameter D of the first pipe of the two-phase flow pipeline assembly of the working fluid at each saturation temperature. 1,cr ; S3: Based on the gravity-independent Froude number-dominant force model, determine the minimum gas phase superficial velocity U in the two-phase flow pipeline component under the gravity-independent constraint SG,min , and converted into the minimum mass flow rate of the system; S4: Considering the working fluid selection, system / local heat load requirements, and the heat dissipation performance constraints of the system heat exchange components, determine the constraint relationship between the mass flow rate in the heat exchange component and the thermodynamic equilibrium dryness and the inner diameter of the pipe, and calculate the gravity-independent critical diameter D of the second pipe of the two-phase flow pipeline assembly. 2,cr ; S5: Determine the upper limit value D of the pipeline gravity-independent force based on the system's operating temperature or system saturation pressure range: D≤max(D 1,cr ,D 2,cr )。 2. The gravity-independent design method for a space gas-liquid two-phase heat transfer system according to claim 1, characterized in that: The overall layout of the system is designed according to the system configuration requirements. The relative positions of the main components and the flow direction of the working fluid in the pipeline are determined by following the horizontal flow channel of the two-phase section, the system plane layout, the vertical downward flow of the two-phase flow, and the correction of the gravity pressure drop.

3. The gravity-independent design method for a space gas-liquid two-phase heat transfer system according to claim 1 or 2, characterized in that: The gravity-independent critical diameter D of the first pipeline in step S2 1,cr :

4. The gravity-independent design method for a space gas-liquid two-phase heat transfer system according to claim 1 or 2, characterized in that: The minimum gas phase superficial velocity U in step S3 SG,min : Convert the minimum gas phase superficial flow rate into the system minimum mass flow rate G g,min : Where x is the dryness of the two-phase flow.

5. The gravity-independent design method for a space gas-liquid two-phase heat transfer system according to claim 4, characterized in that: The constraint relationship between the mass flow rate in the heat exchange component, the thermodynamic equilibrium dryness, and the inner diameter of the pipe in step S4 is: G=4qA / (πxD 2 h evap ) Where G is the mass flow rate, q is the heat flux, A is the heating / condensing area, and h is the evap is the latent heat of vaporization of the working fluid; The gravity-independent critical diameter D of the second pipe of the two-phase flow pipeline assembly is obtained 2,cr :

6. The gravity-independent design method for a space gas-liquid two-phase heat transfer system according to claim 2, characterized in that: The two-phase horizontal flow channel requires that the two-phase flow pipe section should be arranged as horizontally as possible.

7. The gravity-independent design method for a space gas-liquid two-phase heat transfer system according to claim 6, characterized in that: The system plane layout requires that the overall layout of the system should be kept in the same horizontal plane as much as possible.

8. The gravity-independent design method for a space gas-liquid two-phase heat transfer system according to claim 7, characterized in that: The requirement for two-phase flow to be vertically downward is that if the height difference of the two-phase flow pipe section cannot be avoided, the two-phase flow direction of the corresponding pipe section should be designed to be vertically downward.

9. The gravity-independent design method for a space gas-liquid two-phase heat transfer system according to claim 8, characterized in that: If the height difference between system components cannot be avoided, the pipe section with height difference should try to ensure single-phase flow state, and when compared with space application, single-phase static pressure gradient and / or two-phase weight pressure drop correction should be performed on the ground test results.

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